| 1. |
- Hasselquist, Eliza Maher, et al.
(author)
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Changes in nitrogen cycling in riparian zones along a chronosequence of restored streams in northern Sweden
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Other publication (other academic/artistic)abstract
- Understanding how stream restoration affects nitrogen (N) cycling in riparian zones is crucial for setting realistic performance criteria for restored streams. Most streams in northern Sweden were channelized for timber floating, and many streams have now been restored. Channelization disconnected streams from the riparian zone, and reduced the flooding that creates anoxic conditions necessary for many N-cycling reactions. We used a space-for-time substitution consisting of stream reaches restored 2 to 25 years ago, unrestored channelized and natural reference reaches to determine how N-cycling in riparian zones changes with time after restoration. Using stable isotopes of N (δ15N), we found that restoration caused more enriched foliar and root δ15N in recently restored sites, suggesting more gaseous losses of N in younger sites. This enrichment in foliar and root δ15N decreased over the 25-year chronosequence suggesting that the N-cycle becomes tighter and loses less N as it ages. Although the [N] in foliage, roots, and soils did not change over time, understory biomass decreased over time, suggesting that more N was available to plants in younger compared to older sites. Changes in the mechanism of N acquisition (i.e., mycorrhizal colonization, as shown by Δδ15N), plant species richness, and cover of deciduous trees (carbon source), were the most important factors explaining variation in δ15N along with time after restoration. It is clear that the restoration of these streams causes a large and rapid change in nitrogen processing in the riparian zone and this alteration persists for at least 25 years.
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| 2. |
- Hasselquist, Eliza Maher, et al.
(author)
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Management of non-native annual plants to support recovery of an endangered perennial forb, Ambrosia pumila
- 2013
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In: Restoration Ecology. - 1061-2971 .- 1526-100X. ; 21:2, s. 224-231
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Journal article (peer-reviewed)abstract
- Invasive non-native plants pose a ubiquitous threat to native plant communities and have been blamed for the decline of many endangered species. Endangered species legislation provides legal instruments for protection, but identifying a general method for protecting endangered species by managing non-natives is confounded by multiple factors. We compared non-native management methods aimed at increasing populations of an endangered forb, Ambrosia pumila, and associated native plants. We compared the effects of a grass-specific herbicide (Fusilade II), hand-pulling, and mowing in two degraded coastal sage scrub sites in southern California, U.S.A. At both sites, hand-pulling had the greatest effect on non-native cover, and correspondingly resulted in the greatest increase in A. pumila stems. Fusilade II application also led to an increase in A. pumila, but was not as effective in controlling non-native plants as hand-pulling and its effect varied with the dominant non-native species. Mowing was not effective at promoting A. pumila, and its effect on non-native cover seemed to be related to rainfall patterns. Although some methods increased A. pumila, none of our treatments simultaneously increased cover of other native plants. Hand-pulling, the most effective treatment, is labor intensive and thus only feasible at small spatial scales. At larger scales, managers should take an experimental approach to identifying the most appropriate method because this can vary depending on the specific management objective (endangered species or whole native community), the dominant non-natives, yearly variation in weather, and the timing of treatment application.
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| 3. |
- Hasselquist, Eliza Maher, et al.
(author)
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Recovery of nitrogen cycling in riparian zones after stream restoration using delta N-15 along a 25-year chronosequence in northern Sweden
- 2017
-
In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 410:1-2, s. 423-436
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Journal article (peer-reviewed)abstract
- Swedish boreal streams were modified to transport timber by pushing boulders to stream sides, creating levees that disconnected streams from riparian areas. Many streams have since been restored and our goal was to understand how this affects riparian nitrogen (N) cycling. We compared the natural abundance of delta N-15 isotopes in foliage and roots of Filipendula ulmaria plus soils and litter along streams restored 2-25 years ago. We measured sources of N, potential immobilization of N, namely plant diversity and biomass, and the amount and sources of carbon (C) to determine if these were important for describing riparian N cycling. The delta N-15 of F. ulmaria foliage changed dramatically just after restoration compared to the channelized, disconnected state and then converged over the next 25 years with the steady-state reference. The disturbance and reconnection of the stream with the riparian zone during restoration created a short-term pulse of N availability and gaseous losses of N as a result of enhanced microbial processing of N. With increasing time since restoration, N availability appears to have decreased, and N sources changed to those derived from mycorrhizae, amino acids, or the humus layer, or there was enhanced N-use efficiency by older, more diverse plant communities.
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| 4. |
- Kozii, Nataliia, et al.
(author)
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Partitioning growing season water balance within a forested boreal catchment using sap flux, eddy covariance, and a process-based model
- 2020
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In: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 24, s. 2999-3014
-
Journal article (peer-reviewed)abstract
- Although it is well known that evapotranspiration (ET) represents an important water flux at local to global scales, few studies have quantified the magnitude and relative importance of ET and its individual flux components in high-latitude forests. In this study, we combined empirical sapflux, throughfall, and eddy-covariance measurements with estimates from a process-based model to partition the water balance in a northern boreal forested catchment. This study was conducted within the Krycklan catchment, which has a rich history of hydrological measurements, thereby providing us with the unique opportunity to compare the absolute and relative magnitudes of ET and its flux components to other water balance components. During the growing season, ET represented ca. 85 % of the incoming precipitation. Both empirical results and model estimates suggested that tree transpiration (T) and evaporation of intercepted water from the tree canopy (I-C) represented 43 % and 31 % of ET, respectively, and together were equal to ca. 70 % of incoming precipitation during the growing season. Understory evapotranspiration (ETu) was less important than T and I-C during most of the study period, except for late autumn, when ETu was the largest ET flux component. Overall, our study high-lights the importance of trees in regulating the water cycle of boreal catchments, implying that forest management impacts on stand structure as well as climate change effects on tree growth are likely to have large cascading effects on the way water moves through these forested landscapes.
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| 5. |
- Laudon, Hjalmar, et al.
(author)
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Northern landscapes in transition : Evidence, approach and ways forward using the Krycklan Catchment Study
- 2021
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In: Hydrological Processes. - : John Wiley & Sons. - 0885-6087 .- 1099-1085. ; 35:4
-
Journal article (peer-reviewed)abstract
- Improving our ability to detect changes in terrestrial and aquatic systems is a grand challenge in the environmental sciences. In a world experiencing increasingly rapid rates of climate change and ecosystem transformation, our ability to understand and predict how, when, where, and why changes occur is essential for adapting and mitigating human behaviours. In this context, long-term field research infrastructures have a fundamentally important role to play. For northern boreal landscapes, the Krycklan Catchment Study (KCS) has supported monitoring and research aimed at revealing these changes since it was initiated in 1980. Early studies focused on forest regeneration and microclimatic conditions, nutrient balances and forest hydrology, which included monitoring climate variables, water balance components, and stream water chemistry. The research infrastructure has expanded over the years to encompass a 6790 ha catchment, which currently includes 11 gauged streams, ca. 1000 soil lysimeters, 150 groundwater wells, >500 permanent forest inventory plots, and a 150 m tall tower (a combined ecosystem-atmosphere station of the ICOS, Integrated Carbon Observation System) for measurements of atmospheric gas concentrations and biosphere-atmosphere exchanges of carbon, water, and energy. In addition, the KCS has also been the focus of numerous high resolution multi-spectral LiDAR measurements and large scale experiments. This large collection of equipment and data generation supports a range of disciplinary studies, but more importantly fosters multi-, trans-, and interdisciplinary research opportunities. The KCS attracts a broad collection of scientists, including biogeochemists, ecologists, foresters, geologists, hydrologists, limnologists, soil scientists, and social scientists, all of whom bring their knowledge and experience to the site. The combination of long-term monitoring, shorter-term research projects, and large-scale experiments, including manipulations of climate and various forest management practices, has contributed much to our understanding of boreal landscape functioning, while also supporting the development of models and guidelines for research, policy, and management.
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| 6. |
- Artaxo, Paulo, et al.
(author)
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Tropical and Boreal Forest – Atmosphere Interactions : A Review
- 2022
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In: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 74:1, s. 24-163
-
Research review (peer-reviewed)abstract
- This review presents how the boreal and the tropical forests affect the atmosphere, its chemical composition, its function, and further how that affects the climate and, in return, the ecosystems through feedback processes. Observations from key tower sites standing out due to their long-term comprehensive observations: The Amazon Tall Tower Observatory in Central Amazonia, the Zotino Tall Tower Observatory in Siberia, and the Station to Measure Ecosystem-Atmosphere Relations at Hyytiäla in Finland. The review is complemented by short-term observations from networks and large experiments.The review discusses atmospheric chemistry observations, aerosol formation and processing, physiochemical aerosol, and cloud condensation nuclei properties and finds surprising similarities and important differences in the two ecosystems. The aerosol concentrations and chemistry are similar, particularly concerning the main chemical components, both dominated by an organic fraction, while the boreal ecosystem has generally higher concentrations of inorganics, due to higher influence of long-range transported air pollution. The emissions of biogenic volatile organic compounds are dominated by isoprene and monoterpene in the tropical and boreal regions, respectively, being the main precursors of the organic aerosol fraction.Observations and modeling studies show that climate change and deforestation affect the ecosystems such that the carbon and hydrological cycles in Amazonia are changing to carbon neutrality and affect precipitation downwind. In Africa, the tropical forests are so far maintaining their carbon sink.It is urgent to better understand the interaction between these major ecosystems, the atmosphere, and climate, which calls for more observation sites, providing long-term data on water, carbon, and other biogeochemical cycles. This is essential in finding a sustainable balance between forest preservation and reforestation versus a potential increase in food production and biofuels, which are critical in maintaining ecosystem services and global climate stability. Reducing global warming and deforestation is vital for tropical forests.
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| 7. |
- Bargues Tobella, Aida, et al.
(author)
-
Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa
- 2017
-
In: Ecohydrology. - : Wiley. - 1936-0584 .- 1936-0592. ; 10
-
Journal article (peer-reviewed)abstract
- Agroforestry parklands, in which annual crops are grown under scattered mature trees, constitute the most prevalent farming system in semiarid West Africa, covering vast areas of land. The most dominant tree species in these systems is Vitellaria paradoxa, an indigenous tree to West Africa. Despite the importance of this tree in the region, no study to our knowledge has examined its sources and patterns of water uptake. In this study, we used oxygen stable isotopes at natural abundance levels to investigate water sources used by V. paradoxa both in the dry and wet season in an agroforestry parkland in Burkina Faso. We found that during the wet season soil moisture was highest near the soil surface (< 10 cm depth), yet during this time V. paradoxa preferentially accessed water from slightly deeper soil depths, obtaining ca. 90% of its water from 10 to 50 cm depth. In contrast, soil moisture in the upper soil layers was significantly lower during the dry season and as a result V. paradoxa shifted to deeper water sources, obtaining ca. 30% of its water from groundwater and ca. 50% from 30 to 600 cm depth. We also found a negative relationship between tree size and the contribution of groundwater during the dry season, whereas during the wet season V. paradoxa predominantly used water near the soil surface regardless of tree size. Knowledge about the sources and patterns of tree water uptake provides crucial information to better understand how trees influence the local water balance.
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| 8. |
- Bargues Tobella, Aida, et al.
(author)
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Trees in African drylands can promote deep soil and groundwater recharge in a future climate with more intense rainfall
- 2020
-
In: Land Degradation and Development. - : Wiley. - 1085-3278 .- 1099-145X. ; 31, s. 81-95
-
Journal article (peer-reviewed)abstract
- Tropical regions are likely to experience more intense rainfall events in the future. Such an increase in rainfall intensities will affect soil and groundwater recharge, with potential consequences for millions of people. However, little is known about the impact of tree cover on soil and groundwater recharge under higher rainfall intensities. Here, we investigated the effect of tree cover and rainfall intensity on soil water drainage in an agroforestry parkland in West Africa. We collected soil water drainage from lysimeters located at 50 and 150 cm depth in both small and large open areas among trees, which represent contrasting degrees of tree cover, and analyzed a subset of water samples for delta O-18 and delta H-2 to gain insights into the mechanisms of water flow within the soil profile. We found that under high rainfall intensities (>20 mm d(-1)), the median daily soil water drainage amount at 150 cm was 13 times higher in the small compared with the large open areas, whereas at 50 cm, there were no significant differences. Low rainfall intensities (<10 mm d(-1)) resulted in little soil water drainage both at 50 and 150 cm depth, regardless of canopy opening size. The isotopic signature of soil water drainage suggested less evaporation and a higher degree of preferential flow in small compared with large open areas. Our results suggest that maintaining or promoting an appropriate tree cover in tropical African drylands may be key to improving deep soil and groundwater recharge under a future climate with more heavy rainfall.
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| 9. |
- Benegas, Laura, et al.
(author)
-
Positive Effects of Scattered Trees on Soil Water Dynamics in a Pasture Landscape in the Tropics
- 2021
-
In: Frontiers in Water. - : Frontiers Media SA. - 2624-9375. ; 3
-
Journal article (peer-reviewed)abstract
- As a result of canopy interception and transpiration, trees are often assumed to have negative effects on the local hydrological budget resulting in reduced soil and groundwater resources. However, it has also been shown that trees can have positive effects through reducing surface run-off and improving soil infiltrability and groundwater recharge, especially in many tropical ecosystems characterized by high rain intensity and degradation-prone soils. In this study, we used isotopic measurements of soil water to better understand the main processes by which trees influence local soil water dynamics within a tropical pasture with scattered tree cover in the Copan River catchment, Honduras. We also determined the stable isotope signature of xylem water in grasses and trees to assess potential competition for water sources during the wet and dry seasons. During the wet season, when soil water availability was not limiting, both grasses and trees primarily utilized soil water near the soil surface (i.e., 0–10 cm). In contrast, during the dry season, we observed niche partitioning for water resources where grasses primarily utilized soil moisture at deeper soil depth (i.e., 90–100 cm) while trees relied heavily on groundwater. Moreover, isotopic data of soil water suggest that trees reduce evaporative water losses from the soil surface, as indicated by the lack of correlation between soil water content and lc-excess (line condition excess) values of surface soil water under trees, and enhance preferential flow as suggested by less negative lc-excess values under trees compared to open areas during the dry season. Taken together, our findings provide further support that trees can have positive effects on the local water balance with implication for landscape management, promoting the inclusion of scattered trees to provide water ecosystem services in silvopastoral systems, adding to other ecosystem services like biodiversity or carbon sequestration.
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| 10. |
- Gutierrez Lopez, Jose, et al.
(author)
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How tree species, tree size, and topographical location influenced tree transpiration in northern boreal forests during the historic 2018 drought
- 2021
-
In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27, s. 3066-3078
-
Journal article (peer-reviewed)abstract
- Trees in northern latitude ecosystems are projected to experience increasing drought stress as a result of rising air temperatures and changes in precipitation patterns in northern latitude ecosystems. However, most drought-related studies on high-latitude boreal forests (>50 degrees N) have been conducted in North America, with few studies quantifying the response in European and Eurasian boreal forests. Here, we tested how daily whole-tree transpiration (Q, Liters day(-1)) and Q normalized for mean daytime vapor pressure deficit (Q(DZ), Liters day(-1) kPa(-1)) were affected by the historic 2018 drought in Europe. More specifically, we examined how tree species, size, and topographic position affected drought response in high-latitude mature boreal forest trees. We monitored 30 Pinus sylvestris (pine) and 30 Picea abies (spruce) trees distributed across a topographic gradient in northern Sweden. In general, pine showed a greater Q(DZ) control compared to spruce during periods of severe drought (standardized precipitation-evapotranspiration index: SPEI < -1.5), suggesting that the latter are more sensitive to drought. Overall, Q(DZ) reductions (using non-drought Q(DZ) as reference) were less pronounced in larger trees during severe drought, but there was a species-specific pattern: Q(DZ) reductions were greater in pine trees at high elevations and greater in spruce trees at lower elevations. Despite lower Q(DZ) during severe drought, drought spells were interspersed with small precipitation events and overcast conditions, and Q(DZ) returned to pre-drought conditions relatively quickly. This study highlights unique species-specific responses to drought, which are additionally driven by a codependent interaction among tree size, relative topographic position, and unique regional climate conditions.
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| 11. |
- Hasselquist, Niles, et al.
(author)
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Canopy cover effects on local soil water dynamics in a tropical agroforestry system: Evaporation drives soil water isotopic enrichment
- 2018
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In: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 32, s. 994-1004
-
Journal article (peer-reviewed)abstract
- Despite the widely held assumption that trees negatively affect the local water budget in densely planted tree plantations, we still lack a clear understanding of the underlying processes by which canopy cover influences local soil water dynamics in more open, humid tropical ecosystems. In this study, we propose a new conceptual model that uses a combination of stable isotope and soil moisture measurements throughout the soil profile to assess potential mechanisms by which evaporation (of surface soil water and of canopy-intercepted rainfall) affects the relationship between surface soil water isotopic enrichment (lc-excess) and soil water content. Our conceptual model was derived from soil water data collected under deciduous and evergreen plants in a shade grown coffee agroforestry system in Costa Rica. Reduced soil moisture under shade trees during the drier season, coinciding when these trees were defoliated, was largely the result of increase soil water evaporation as indicated by the positive relationship between soil water content and lc-excess of surface soil water. In contrast, the evergreen coffee shrubs had a higher leaf area index during the drier season, leading to enhanced rainfall interception and a negative relationship between lc-excess and soil water content. During the wet season, there was no clear relationship between soil water content and between lc-excess of surface soil water. Greater surface soil water under coffee during the dry season may, in part, explain greater preferential flow under coffee compared with under trees in conditions of low rainfall intensities. However, with increasing rainfall intensities during the wet season, there was no obvious difference in preferential flow between the two canopy covers. Results from this study indicate that our new conceptual model can be used to help disentangling the relative influence of canopy cover on local soil water isotopic composition and dynamics, yet also stresses the need for additional measurements to better resolve the underlying processes by which canopy structure influences local water dynamics.
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| 12. |
- Hasselquist, Niles
(author)
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Complementary water uptake depth of Quercus petraea and Pinus sylvestris in mixed stands during an extreme drought
- 2019
-
In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 437, s. 93-115
-
Journal article (peer-reviewed)abstract
- AimsThe growing demand from forest managers is to identify silvicultural practices to overcome projected water scarcity during the next decades. One solution is to mix tree species in the same stand, thereby increasing resource partitioning and minimizing competition for limited soil water. This study investigates the mixture approach for Quercus petraea (Matt.) Liebl. and Pinus sylvestris L. during an extreme summer drought event.MethodsDuring the summer drought event in 2016, we analyzed the isotopic signatures of large- and small-tree xylem and soil water throughout the soil profile to assess the depth of water uptake for both tree species. We also measured predawn leaf water potentials (PLWP) to assess water availability for individual tree species.ResultsWhen grown in pure stands, both species primarily utilized soil water near the surface. In contrast, partial niche complementarity for limited water resources between the two species in mixed stands resulted in less water constraint (i.e., less negative PLWP) for oak trees compared to pure stands, especially for small trees.ConclusionsResults from this study show that contrasting water use strategies can change water availability for trees and could help some species, though not all, to cope with the water scarcity predicted in a changing climate.
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| 13. |
- Hasselquist, Niles, et al.
(author)
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Contrasting effects of low and high nitrogen additions on soil CO2 flux components and ectomycorrhizal fungal sporocarp production in a boreal forest
- 2012
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In: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 18, s. 3596-3605
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Journal article (peer-reviewed)abstract
- Nitrogen (N) added through atmospheric deposition or as fertilizer to boreal and temperate forests reduces both soil decomposer activity (heterotrophic respiration) and the activity of roots and mycorrhizal fungi (autotrophic respiration). However, these negative effects have been found in studies that applied relatively high levels of N, whereas the responses to ambient atmospheric N deposition rates are still not clear. Here, we compared an unfertilized control boreal forest with a fertilized forest (100kgNha-1yr-1) and a forest subject to N-deposition rates comparable to those in Central Europe (20kgNha-1yr-1) to investigate the effects of N addition rate on different components of forest floor respiration and the production of ectomycorrhizal fungal sporocarps. Soil collars were used to partition heterotrophic (Rh) and autotrophic (Ra) respiration, which was further separated into respiration by tree roots (Rtr) and mycorrhizal hyphae (Rm). Total forest floor respiration was twice as high in the low N plot compared to the control, whereas there were no differences between the control and high N plot. There were no differences in Rh respiration among plots. The enhanced forest floor respiration in the low N plot was, therefore, the result of increased Ra respiration, with an increase in Rtr respiration, and a doubling of Rm respiration. The latter was corroborated by a slightly greater ectomycorrhizal (EM) fungal sporocarp production in the low N plot as compared to the control plot. In contrast, EM fungal sporocarp production was nearly eliminated, and Rm respiration severely reduced, in the high N plot, which resulted in significantly lower Ra respiration. We thus found a nonlinear response of the Ra components to N addition rate, which calls for further studies of the quantitative relations among N addition rate, plant photosynthesis and carbon allocation, and the function of EM fungi.
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| 14. |
- Hasselquist, Niles
(author)
-
Contrasting effects of nitrogen addition on soil respiration in two Mediterranean ecosystems
- 2017
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In: Environmental Science and Pollution Research. - : Springer Science and Business Media LLC. - 0944-1344 .- 1614-7499. ; 24, s. 26160-26171
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Journal article (peer-reviewed)abstract
- Increased atmospheric nitrogen (N) deposition is known to alter ecosystem carbon source-sink dynamics through changes in soil CO2 fluxes. However, a limited number of experiments have been conducted to assess the effects of realistic N deposition in the Mediterranean Basin, and none of them have explored the effects of N addition on soil respiration (R-s). To fill this gap, we assessed the effects of N supply on Rs dynamics in the following two Mediterranean sites: Capo Caccia (Italy), where 30 kg ha(-1) year(-1) was supplied for 3 years, and El Regajal (Spain), where plots were treated with 10, 20, or 50 kg N ha(-1) year(-1) for 8 years. Results show a complex, non-linear response of soil respiration (R-s) to N additions with Rs overall increasing at Capo Caccia and decreasing at El Regajal. This suggests that the response of Rs to N addition depends on dose and duration of N supply, and the existence of a threshold above which the N introduced in the ecosystem can affect the ecosystem's functioning. Soil cover and seasonality of precipitations also play a key role in determining the effects of N on Rs as shown by the different responses observed across seasons and in bare soil vs. the soil under canopy of the dominant species. These results show how increasing rates of N addition may influence soil C dynamics in semiarid ecosystems in the Mediterranean Basin and represent a valuable contribution for the understanding and the protection of Mediterranean ecosystems.
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| 15. |
- Hasselquist, Niles, et al.
(author)
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Convergence of soil nitrogen isotopes across global climate gradients
- 2015
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 5
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Journal article (peer-reviewed)abstract
- Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future patterns of primary productivity, carbon sequestration, nutrient fluxes to aquatic systems, and climate forcing. With limited direct measures of soil N cycling at the global scale, syntheses of the N-15 : N-14 ratio of soil organic matter across climate gradients provide key insights into understanding global patterns of N cycling. In synthesizing data from over 6000 soil samples, we show strong global relationships among soil N isotopes, mean annual temperature (MAT), mean annual precipitation (MAP), and the concentrations of organic carbon and clay in soil. In both hot ecosystems and dry ecosystems, soil organic matter was more enriched in N-15 than in corresponding cold ecosystems or wet ecosystems. Below a MAT of 9.8 degrees C, soil delta N-15 was invariant with MAT. At the global scale, soil organic C concentrations also declined with increasing MAT and decreasing MAP. After standardizing for variation among mineral soils in soil C and clay concentrations, soil delta N-15 showed no consistent trends across global climate and latitudinal gradients. Our analyses could place new constraints on interpretations of patterns of ecosystem N cycling and global budgets of gaseous N loss.
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| 16. |
- Hasselquist, Niles, et al.
(author)
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Dosage and duration effects of nitrogen additions on ectomycorrhizal sporocarp production and functioning: an example from two N-limited boreal forests
- 2014
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In: Ecology and Evolution. - : Wiley. - 2045-7758. ; 4, s. 3015-3026
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Journal article (peer-reviewed)abstract
- 1 Although it is well known that nitrogen (N) additions strongly affect ecto-mycorrhizal (EM) fungal community composition, less is known about how different N application rates and duration of N additions affect the functional role EM fungi play in the forest N cycle.2 We measured EM sporocarp abundance and species richness as well as determined the delta N-15 in EM sporocarps and tree foliage in two Pinus sylvestris forests characterized by short-and long-term N addition histories and multiple N addition treatments. After 20 and 39 years of N additions, two of the long-term N addition treatments were terminated, thereby providing a unique opportunity to examine the temporal recovery of EM sporocarps after cessation of high N loading.3 In general, increasing N availability significantly reduced EM sporocarp production, species richness, and the amount of N retained in EM sporocarps. However, these general responses were strongly dependent on the application rate and duration of N additions. The annual addition of 20 kg.N.ha(-1) for the past 6 years resulted in a slight increase in the production and retention of N in EM sporocarps, whereas the addition of 100 kg.N.ha(-1).yr(-1) during the same period nearly eliminated EM sporocarps. In contrast, long-term additions of N at rates of ca. 35 or 70 kg.N.ha(-1).yr(-1) for the past 40 years did not eliminate tree carbon allocation to EM sporocarps, although there was a decrease in the abundance and a shift in the dominant EM sporocarp taxa. Despite no immediate recovery, EM sporocarp abundance and species richness approached those of the control 20 years after terminating N additions in the most heavily fertilized treatment, suggesting a recovery of carbon allocation to EM sporocarps after cessation of high N loading.4 Our results provide evidence for a tight coupling between tree carbon allocation to and N retention in EM sporocarps and moreover highlight the potential use of delta N-15 in EM sporocarps as a relative index of EM fungal sink strength for N. However, nitrogen additions at high dosage rates or over long time periods appear to disrupt this feedback, which could have important ramifications on carbon and nitrogen dynamics in these forested ecosystems.
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| 17. |
- Hasselquist, Niles
(author)
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Ecological interpretations of nitrogen isotope ratios of terrestrial plants and soils
- 2015
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In: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 396, s. 1-26
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Research review (peer-reviewed)abstract
- Knowledge of biological and climatic controls in terrestrial nitrogen (N) cycling within and across ecosystems is central to understanding global patterns of key ecosystem processes. The ratios of N-15:N-14 in plants and soils have been used as indirect indices of N cycling parameters, yet our understanding of controls over N isotope ratios in plants and soils is still developing.In this review, we provide background on the main processes that affect plant and soil N isotope ratios. In a similar manner to partitioning the roles of state factors and interactive controls in determining ecosystem traits, we review N isotopes patterns in plants and soils across a number of proximal factors that influence ecosystem properties as well as mechanisms that affect these patterns. Lastly, some remaining questions that would improve our understanding of N isotopes in terrestrial ecosystems are highlighted.Compared to a decade ago, the global patterns of plant and soil N isotope ratios are more resolved. Additionally, we better understand how plant and soil N isotope ratios are affected by such factors as mycorrhizal fungi, climate, and microbial processing. A comprehensive understanding of the N cycle that ascribes different degrees of isotopic fractionation for each step under different conditions is closer to being realized, but a number of process-level questions still remain.
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| 18. |
- Hasselquist, Niles
(author)
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Fertilization alters nitrogen isotopes and concentrations in ectomycorrhizal fungi and soil in pine forests
- 2019
-
In: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 39, s. 267-275
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Journal article (peer-reviewed)abstract
- To assess how nitrogen (N) availability affected ectomycorrhizal functioning and to test a theoretical model of ectomycorrhizal N-15 partitioning, we measured C/N and delta N-15 in soils and nine fungal taxa in two Swedish N addition experiments. Sporocarp C/N and soil C/N decreased with fertilization, implying that N uptake per unit fungal growth increased. The S horizon was more responsive than the F and H horizons to changes in N addition, with N turnover for these horizons of 24, 57, and 57 y, respectively. Fungal and soil delta N-15 patterns identified fungal N sources, with N acquisition primarily from the S, F, or H horizon for two, five, and two taxa, respectively. With increasing N availability, sporocarp N-15 enrichment increased in five taxa, in agreement with our model of fungal-plant N partitioning. However, it decreased in Lactarius rufus and Russula aeruginea, perhaps indicating shifts towards greater inorganic N uptake in these two taxa. This may relate to the generally lower sensitivity of these taxa to N deposition compared to the Cortinarius and Suillus taxa that fit our model of N-15 partitioning. (C) 2019 Elsevier Ltd and British Mycological Society. All rights reserved.
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| 19. |
- Hasselquist, Niles
(author)
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First report of the ectomycorrhizal status of boletes on the Northern Yucatan Peninsula, Mexico determined using isotopic methods
- 2011
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In: Mycorrhiza. - : Springer Science and Business Media LLC. - 0940-6360 .- 1432-1890. ; 21, s. 465-471
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Journal article (peer-reviewed)abstract
- Despite their prominent role for tree growth, few studies have examined the occurrence of ectomycorrhizal fungi in lowland, seasonally dry tropical forests (SDTF). Although fruiting bodies of boletes have been observed in a dry tropical forest on the Northern Yucatan Peninsula, Mexico, their occurrence is rare and their mycorrhizal status is uncertain. To determine the trophic status (mycorrhizal vs. saprotrophic) of these boletes, fruiting bodies were collected and isotopically compared to known saprotrophic fungi, foliage, and soil from the same site. Mean delta N-15 and delta C-13 values differed significantly between boletes and saprotrophic fungi, with boletes 8.0% enriched and 2.5% depleted in N-15 and C-13, respectively relative to saprotrophic fungi. Foliage was depleted in C-13 relative to both boletes and saprotrophic fungi. Foliar delta N-15 values, on the other hand, were similar to saprotrophic fungi, yet were considerably lower relative to bolete fruiting bodies. Results from this study provide the first isotopic evidence of ectomycorrhizal fungi in lowland SDTF and emphasize the need for further research to better understand the diversity and ecological importance of ectomycorrhizal fungi in these forested ecosystems.
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| 20. |
- Hasselquist, Niles, et al.
(author)
-
Greater carbon allocation to mycorrhizal fungi reduces tree nitrogen uptake in a boreal forest
- 2016
-
In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97:4, s. 1012-1022
-
Journal article (peer-reviewed)abstract
- The central role that ectomycorrhizal (EM) symbioses play in the structure and function of boreal forests pivots around the common assumption that carbon (C) and nitrogen (N) are exchanged at rates favorable for plant growth. However, this may not always be the case. It has been hypothesized that the benefits mycorrhizal fungi convey to their host plants strongly depends upon the availability of C and N, both of which are rapidly changing as a result of intensified human land use and climate change. Using large-scale shading and N addition treatments, we assessed the independent and interactive effects of changes in C and N supply on the transfer of N in intact EM associations with similar to 15 yr. old Scots pine trees. To assess the dynamics of N transfer in EM symbioses, we added trace amounts of highly enriched (NO3-)-N-15 label to the EM-dominated mor-layer and followed the fate of the N-15 label in tree foliage, fungal chitin on EM root tips, and EM sporocarps. Despite no change in leaf biomass, shading resulted in reduced tree C uptake, ca. 40% lower fungal biomass on EM root tips, and greater N-15 label in tree foliage compared to unshaded control plots, where more N-15 label was found in fungal biomass on EM colonized root tips. Short-term addition of N shifted the incorporation of N-15 label from EM fungi to tree foliage, despite no significant changes in below-ground tree C allocation to EM fungi. Contrary to the common assumption that C and N are exchanged at rates favorable for plant growth, our results show for the first time that under N-limited conditions greater C allocation to EM fungi in the field results in reduced, not increased, N transfer to host trees. Moreover, given the ubiquitous nature of mycorrhizal symbioses, our results stress the need to incorporate mycorrhizal dynamics into process-based ecosystem models to better predict forest C and N cycles in light of global climate change.
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| 21. |
- Hasselquist, Niles, et al.
(author)
-
Seasonality and nitrogen supply modify carbon partitioning in understory vegetation of a boreal coniferous forest
- 2016
-
In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 97:3, s. 671-683
-
Journal article (peer-reviewed)abstract
- Given the strong coupling between the carbon (C) and nitrogen (N) cycles, there is substantial interest in understanding how N availability affects C cycling in terrestrial ecosystems, especially in ecosystems limited by N. However, most studies in temperate and boreal forests have focused on the effects of N addition on tree growth. By comparison, less is known about the effects of N availability on the cycling of C in understory vegetation despite some evidence that dwarf shrubs, mosses, and lichens play an important role in the forest C balance. In this study, we used an in situ 13CO2 pulse-labeling technique to examine the short-term dynamics of C partitioning in understory vegetation in three boreal Pinus sylvestris forest stands exposed to different rates of N addition: a low and high N addition that receive annual additions of NH4NO3 of 20 and 100 kg N/ha, respectively, and this is a typo. It should be an unfertilized control. Labeling was conducted at two distinct periods (early vs. late growing season), which provided a seasonal picture of how N addition affects C dynamics in understory vegetation. In contrast to what has been found in trees, there was no obvious trend in belowground C partitioning in ericaceous plants in response to N additions or seasonality. Increasing N addition led to a greater percentage of 13C being incorporated into ericaceous leaves with a high turnover, whereas high rates of N addition strongly reduced the incorporation of 13C into less degradable moss tissues. Addition of N also resulted in a greater percentage of the 13C label being respired back to the atmosphere and an overall reduction in total understory carbon use efficiency. Taken together, our results suggest a faster cycling of C in understory vegetation with increasing N additions; yet the magnitude of this general response was strongly dependent on the amount of N added and varied seasonally. These results provide some of the first in situ C and N partitioning estimates for plants growing under the complex web of resource limitations in the boreal understory.
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| 22. |
- Hasselquist, Niles, et al.
(author)
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Short-term response of soil respiration to nitrogen fertilization in a subtropical evergreen forest
- 2014
-
In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 76, s. 297-300
-
Journal article (peer-reviewed)abstract
- Little is known about the effects of nitrogen (N) additions on soil respiration (Rs) in tropical and subtropical forests. We therefore conducted an N-fertilization experiment in a subtropical evergreen forest in eastern China to better understand the short-term response of Rs to increased N availability. N additions stimulated Rs compared to control plots, yet the magnitude of the increase depended on the amount of N added, with Rs being greater in the low-N treatment (50 kg N ha(-1) yr(-1)) than the high-N treatment (100 kg N ha(-1) yr(-1)). Differences in Rs among treatments correlated with changes in fine root biomass, suggesting increases in Rs reflect those in autotrophic respiration. Our findings challenge the dogma that N fertilization often reduces soil respiration and highlights the need to better understand the effects of low N additions, so as to reliably predict how projected climate change scenarios may affect the cycling of soil carbon (C) in tropical and subtropical forests. (C) 2014 Published by Elsevier Ltd.
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| 23. |
- Hasselquist, Niles
(author)
-
Variation of leaf-level gas exchange rates and leaf functional traits of dominant trees across three successional stages in a Southeast Asian tropical forest
- 2021
-
In: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 489
-
Journal article (peer-reviewed)abstract
- Deforestation has created heterogeneous patches of old-growth and secondary forests throughout Southeast Asia, posing challenges for understanding the hydrological and carbon cycles. In addition to changes in species composition, environmental conditions differ across successional stages which in turn can influence forest water use and productivity. Here, we investigated leaf-level area-based photosynthesis (Aarea) and stomatal conductance (gs) of 11 tree species dominating an old-growth (OF; >200 years), an intermediate (IF; -44 years), and a young forest (YF; -4 years) in Thailand during both the wet and dry season. Specifically, we compared Aarea and gs and assessed the sensitivity of gs to vapor pressure deficit (VPD). We also examined relationships between gas exchange parameters and key functional leaf traits, including leaf mass per area (LMA), nitrogen (N), phosphorus (P), and chlorophyll concentration. All three forests showed comparable Aarea and gs in the wet season, whereas significantly lower values were observed in IF during the dry season. All forest stages displayed similar sensitivity of gs to VPD. Among the leaf functional traits considered, LMA, N and P were significantly higher in YF compared to the other two successional stages. Our results suggested that forest succession may not influence gas exchange, rather, canopy development associated with forest stage produced the main effect. Furthermore, the young forest was the most active in resource acquisition with its high LMA and leaf nutrient concentrations, which could result in high photosynthetic rates. However, low soil water availability in YF possibly limit the gas exchange rates thereby making them similar to those in the old-growth forest. These findings highlight the potential effects of canopy characteristics inherent in successional forests on water and carbon exchanges between trees and the atmosphere and their sensitivity to atmospheric drought. These results call for the need for further studies to identify the main factors influencing forest productivity during secondary succession in the tropics, particularly in the Southeast Asian region where such information is lacking.
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| 24. |
- Hasselquist, Niles
(author)
-
Water relations of evergreen and drought-deciduous trees along a seasonally dry tropical forest chronosequence
- 2010
-
In: Oecologia. - : Springer Science and Business Media LLC. - 0029-8549 .- 1432-1939. ; 164, s. 881-890
-
Journal article (peer-reviewed)abstract
- Seasonally dry tropical forests (SDTF) are characterized by pronounced seasonality in rainfall, and as a result trees in these forests must endure seasonal variation in soil water availability. Furthermore, SDTF on the northern Yucatan Peninsula, Mexico, have a legacy of disturbances, thereby creating a patchy mosaic of different seral stages undergoing secondary succession. We examined the water status of six canopy tree species, representing contrasting leaf phenology (evergreen vs. drought-deciduous) at three seral stages along a fire chronosequence in order to better understand strategies that trees use to overcome seasonal water limitations. The early-seral forest was characterized by high soil water evaporation and low soil moisture, and consequently early-seral trees exhibited lower midday bulk leaf water potentials (I(L)) relative to late-seral trees (-1.01 +/- A 0.14 and -0.54 +/- A 0.07 MPa, respectively). Although I(L) did not differ between evergreen and drought-deciduous trees, results from stable isotope analyses indicated different strategies to overcome seasonal water limitations. Differences were especially pronounced in the early-seral stage where evergreen trees had significantly lower xylem water delta(18)O values relative to drought-deciduous trees (-2.6 +/- A 0.5 and 0.3 +/- A 0.6aEuro degrees, respectively), indicating evergreen species used deeper sources of water. In contrast, drought-deciduous trees showed greater enrichment of foliar (18)O (a dagger(18)O(l)) and (13)C, suggesting lower stomatal conductance and greater water-use efficiency. Thus, the rapid development of deep roots appears to be an important strategy enabling evergreen species to overcome seasonal water limitation, whereas, in addition to losing a portion of their leaves, drought-deciduous trees minimize water loss from remaining leaves during the dry season.
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| 25. |
- Högberg, Mona N, et al.
(author)
-
The return of an experimentally N-saturated boreal forest to an N-limited state : observations on the soil microbial community structure, biotic N retention capacity and gross N mineralisation
- 2014
-
In: Plant and Soil. - : Springer Netherlands. - 0032-079X .- 1573-5036. ; 381:1-2, s. 45-60
-
Journal article (peer-reviewed)abstract
- To find out how N-saturated forests can return to an N-limited state, we examined the recovery of biotic N sinks under decreasing N supply. We studied a 40-year-old experiment in Pinus sylvestris forest, with control plots, N0, three N treatments, N1-N3, of which N3 was stopped after 20 years, allowing observation of recovery. In N3, the N concentration in foliage was still slightly elevated, but the N uptake capacity of ectomycorrhizal (ECM) roots in N3 was no longer lower than in N0. Per area the amount of a biomarker for fungi, here mainly attributed ECM, was higher in N3 and N0 than in N1 and N2. Retention of labeled (NH4)-N-15 (+) by the soil was greater in the control (99 %) and N3 (86 %), than in N1 (45 %) and N2 (29 %); we ascribe these differences to biotic retention because cation exchange capacity did not vary. Gross N mineralisation and retention of N correlated, negatively and positively, respectively, with abundance of ECM fungal biomarker. The results suggest a key role for ECM fungi in regulating the N cycle. We propose, in accordance with plant C allocation theory, that recovery is driven by increased tree below-ground C allocation to ECM roots and fungi.
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| 26. |
- Kozii, Nataliia, et al.
(author)
-
Increasing water losses from snow captured in the canopy of boreal forests: A case study using a 30 year data set
- 2017
-
In: Hydrological Processes. - : Wiley. - 0885-6087 .- 1099-1085. ; 31, s. 3558-3567
-
Journal article (peer-reviewed)abstract
- Water losses from snow intercepted by forest canopy can significantly influence the hydrological cycle in seasonally snow-covered regions, yet how snow interception losses (SIL) are influenced by a changing climate are poorly understood. In this study, we used a unique 30 year record (1986-2015) of snow accumulation and snow water equivalent measurements in a mature mixed coniferous (Picea abies and Pinus sylvestris) forest stand and an adjacent open area to assess how changes in weather conditions influence SIL. Given little change in canopy cover during this study, the 20% increase in SIL was likely the result of changes in winter weather conditions. However, there was no significant change in average wintertime precipitation and temperature during the study period. Instead, mean monthly temperature values increased during the early winter months (i.e., November and December), whereas there was a significant decrease in precipitation in March. We also assessed how daily variation in meteorological variables influenced SIL and found that about 50% of the variation in SIL was correlated to the amount of precipitation that occurred when temperatures were lower than -3 degrees C and to the proportion of days with mean daily temperatures higher than +0.4 degrees C. Taken together, this study highlights the importance of understanding the appropriate time scale and thresholds in which weather conditions influence SIL in order to better predict how projected climate change will influence snow accumulation and hydrology in boreal forests in the future.
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| 27. |
- Lussetti, Daniel, et al.
(author)
-
Soil Carbon Pool and Carbon Fluxes Estimation in 26 Years after Selective Logging Tropical Forest at Sabah, Malaysia
- 2022
-
In: Forests. - : MDPI AG. - 1999-4907. ; 13
-
Journal article (peer-reviewed)abstract
- The soil carbon pool holds an enormous amount of carbon, making it the largest reservoir in the terrestrial ecosystem. However, there is growing concern that unsustainable logging methods damage the soil ecosystem, thus triggering the release of soil carbon into the atmosphere hence contributing to ongoing climate change. This study uses a replicated (n = 4) logging experiment to examine the impact of supervised logging with climber cutting (SLCC) and conventional logging (CL) on basic soil characteristics, litter input to soils, soil carbon pools, and soil respiration in a mixed dipterocarp forest 26 years after logging. This study found that there was no significant difference observed in the soil physicochemical properties and total carbon pools between the logging treatments and the virgin forest. Soil carbon pools dominated the total carbon pools, and the highest mean value was recorded in SLCC (87.95 +/- 13.67 Mg C ha(-1)). Conventional logging had a lower mean value (71.17 +/- 12.09 Mg C ha(-1)) than virgin forest (83.20 +/- 11.97 Mg C ha(-1)). SLCC also shows a higher value of soil respiration rate (161.75 +/- 21.67 mg C m(-2) h(-1)) than CL (140.54 +/- 12.54 mg C m(-2) h(-1)). These findings highlight the importance of accurate quantification of the effect of different logging methods on the forest's carbon pools.
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| 28. |
- Lussetti, Daniel, et al.
(author)
-
Soil physico-chemical properties in a selectively logged forest at Gunung Rara. Forest Reserve, Sabah, Malaysia
- 2023
-
In: Journal of Sustainability Science and Management. - 2672-7226. ; 18, s. 73-86
-
Journal article (peer-reviewed)abstract
- The tropical rainforest has various lists of crucial functions in forest productivity. However, unsustainable logging method has led to the decline of soil fertility in the forest. This study aimed to investigate the impacts of different logging methods on the soil’s physical and chemical properties at Gunung Rara Forest Reserve, Sabah, Malaysia. The logging treatments were supervised logging with climber cutting (SLCC) and conventional logging (CL), and a virgin forest (VF) was used as the control plot. The size for each plot was one hectare and each was replicated into four plots making the total plots 12. Soil sampling was done at four depths (0–10 cm, 10–20 cm, 20–50 cm, and 50–100 cm) for soil analysis and bulk density. The finding shows that the soil properties in the treatment plots were not significantly different from the untreated plot. The soil organic matter, total nitrogen, and total carbon decreased with soil depths. The soil in all study areas was found acidic, ranging from 4.12 to 4.46. The soil textures were clay, sandy clay loam, and sandy loam. The SLCC plot recorded a higher mean of soil organic matter (5.93–7.40%), total phosphorus (0.08–0.09 meq/100 g), and cation exchange capacity (5.69–7.05 meq/100 g) compared to other plots. This study highlights the importance of analysing the impact of different logging methods on the soil’s physicochemical properties
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| 29. |
- Maaroufi, Nadia, et al.
(author)
-
Anthropogenic nitrogen deposition enhances carbon sequestration in boreal soils
- 2015
-
In: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 21:8, s. 3169-3180
-
Journal article (peer-reviewed)abstract
- It is proposed that carbon (C) sequestration in response to reactive nitrogen (N-r) deposition in boreal forests accounts for a large portion of the terrestrial sink for anthropogenic CO2 emissions. While studies have helped clarify the magnitude by which N-r deposition enhances C sequestration by forest vegetation, there remains a paucity of long-term experimental studies evaluating how soil C pools respond. We conducted a long-term experiment, maintained since 1996, consisting of three N addition levels (0, 12.5, and 50kgNha(-1)yr(-1)) in the boreal zone of northern Sweden to understand how atmospheric N-r deposition affects soil C accumulation, soil microbial communities, and soil respiration. We hypothesized that soil C sequestration will increase, and soil microbial biomass and soil respiration will decrease, with disproportionately large changes expected compared to low levels of N addition. Our data showed that the low N addition treatment caused a non-significant increase in the organic horizon C pool of similar to 15% and a significant increase of similar to 30% in response to the high N treatment relative to the control. The relationship between C sequestration and N addition in the organic horizon was linear, with a slope of 10kgCkg(-1)N. We also found a concomitant decrease in total microbial and fungal biomasses and a similar to 11% reduction in soil respiration in response to the high N treatment. Our data complement previous data from the same study system describing aboveground C sequestration, indicating a total ecosystem sequestration rate of 26kgCkg(-1)N. These estimates are far lower than suggested by some previous modeling studies, and thus will help improve and validate current modeling efforts aimed at separating the effect of multiple global change factors on the C balance of the boreal region.
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| 30. |
- Maaroufi, Nadia, et al.
(author)
-
Anthropogenic nitrogen enrichment enhances soil carbon accumulation by impacting saprotrophs rather than ectomycorrhizal fungal activity
- 2019
-
In: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 25:9, s. 2900-2914
-
Journal article (peer-reviewed)abstract
- There is evidence that anthropogenic nitrogen (N) deposition enhances carbon (C) sequestration in boreal forest soils. However, it is unclear how free-living saprotrophs (bacteria and fungi, SAP) and ectomycorrhizal (EM) fungi responses to N addition impact soil C dynamics. Our aim was to investigate how SAP and EM communities are impacted by N enrichment and to estimate whether these changes influence decay of litter and humus. We conducted a long-term experiment in northern Sweden, maintained since 2004, consisting of ambient, low N additions (0, 3, 6, and 12 kg N ha(-1) year(-1)) simulating current N deposition rates in the boreal region, as well as a high N addition (50 kg N ha(-1) year(-1)). Our data showed that long-term N enrichment impeded mass loss of litter, but not of humus, and only in response to the highest N addition treatment. Furthermore, our data showed that EM fungi reduced the mass of N and P in both substrates during the incubation period compared to when only SAP organisms were present. Low N additions had no effect on microbial community structure, while the high N addition decreased fungal and bacterial biomasses and altered EM fungi and SAP community composition. Actinomycetes were the only bacterial SAP to show increased biomass in response to the highest N addition. These results provide a mechanistic understanding of how anthropogenic N enrichment can influence soil C accumulation rates and suggest that current N deposition rates in the boreal region (<= 12 kg N ha(-1) year(-1)) are likely to have a minor impact on the soil microbial community and the decomposition of humus and litter.
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| 31. |
- Maher, Eliza L., et al.
(author)
-
Interactive effects of tree and herb cover on survivorship, physiology, and microclimate of conifer seedlings at the alpine tree-line ecotone
- 2005
-
In: Canadian Journal of Forest Research. - 0045-5067 .- 1208-6037. ; 35:3, s. 567-574
-
Journal article (peer-reviewed)abstract
- Factors affecting the establishment of trees in subalpine meadows are important to population dynamics of trees in the alpine tree- line ecotone ( ATE). Interactive effects of tree and herb cover on conifer seedlings were investigated in the ATE of the Snowy Range, Wyoming, USA. Microclimate, physiology, and survivorship of first-year conifer seedlings of Pinus albicaulis Engelm., Picea engelmannii Parry, and Abies lasiocarpa Hook. were measured in response to manipulations of surrounding herb and tree cover, as well as water availability. Tree and herb cover had nearly additive effects on survivorship and photosynthesis of conifer seedlings, except under alleviated water stress. In P. albicaulis, photosynthesis was greater near compared with away from trees and herbs, and photosynthetic efficiency ( F-v/ F-m) increased under herb cover. Tree cover led to greater nighttime temperatures, soil water contents, and, like herb cover, shade from solar radiation for seedlings. We did not detect any negative responses of conifer seedlings to surrounding vegetation. Furthermore, the effect of surrounding vegetation on conifer establishment appeared dependent on the type of surrounding vegetation, the species of conifer, and microsite stress level. These factors may lead to variation in the way conifer seedlings interact with surrounding vegetation and could explain changes in the relative abundances of tree species during forest succession in ATEs.
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| 32. |
- Marshall, John, et al.
(author)
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Isotopic Branchpoints: Linkages and Efficiencies in Carbon and Water Budgets
- 2021
-
In: Journal of Geophysical Research: Biogeosciences. - 2169-8953 .- 2169-8961. ; 126
-
Journal article (peer-reviewed)abstract
- Forests pass water and carbon through while converting portions to streamflow, soil organic matter, wood production, and other ecosystem services. The efficiencies of these transfers are but poorly quantified. New theory and new instruments have made it possible to use stable isotope composition to provide this quantification of efficiencies wherever there is a measurable difference between the branches of a branchpoint. We present a linked conceptual model that relies on isotopes of hydrogen, carbon, and oxygen to describe these branchpoints along the pathway from precipitation to soil and biomass carbon sequestration and illustrate how it can be tested and generalized.Plain Language Summary The way a forest works can be described in terms of carbon and water budgets, which describe the ways that carbon and water flow through the forest. The paths of such flows are frequently branched and the branches are often different in their stable isotope composition. This means that stable isotopes can be used to describe the branching events. We present isotopic methods of quantifying several such events, then link them in a chain that begins with the evaporation of water and ends with biomass production.
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| 33. |
- Metcalfe, Daniel B., et al.
(author)
-
Patchy field sampling biases understanding of climate change impacts across the Arctic
- 2018
-
In: Nature Ecology and Evolution. - : Springer Science and Business Media LLC. - 2397-334X. ; 2:9, s. 1443-1448
-
Journal article (peer-reviewed)abstract
- Effective societal responses to rapid climate change in the Arctic rely on an accurate representation of region-specific ecosystem properties and processes. However, this is limited by the scarcity and patchy distribution of field measurements. Here, we use a comprehensive, geo-referenced database of primary field measurements in 1,840 published studies across the Arctic to identify statistically significant spatial biases in field sampling and study citation across this globally important region. We find that 31% of all study citations are derived from sites located within 50 km of just two research sites: Toolik Lake in the USA and Abisko in Sweden. Furthermore, relatively colder, more rapidly warming and sparsely vegetated sites are under-sampled and under-recognized in terms of citations, particularly among microbiology-related studies. The poorly sampled and cited areas, mainly in the Canadian high-Arctic archipelago and the Arctic coastline of Russia, constitute a large fraction of the Arctic ice-free land area. Our results suggest that the current pattern of sampling and citation may bias the scientific consensuses that underpin attempts to accurately predict and effectively mitigate climate change in the region. Further work is required to increase both the quality and quantity of sampling, and incorporate existing literature from poorly cited areas to generate a more representative picture of Arctic climate change and its environmental impacts.
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| 34. |
- Metcalfe, Daniel, et al.
(author)
-
Effects of nitrogen fertilization on the forest floor carbon balance over the growing season in a boreal pine forest
- 2013
-
In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 8223-8231
-
Journal article (peer-reviewed)abstract
- Boreal forests play a key role in the global carbon cycle and are facing rapid shifts in nitrogen availability with poorly understood consequences for ecosystem function and global climate change. We quantified the effects of increasing nitrogen availability on carbon fluxes from a relatively understudied component of these forests - the forest floor - at three intervals over the summer growing period in a northern Swedish Scots pine stand. Nitrogen addition altered both the uptake and release of carbon dioxide from the forest floor, but the magnitude and direction of this effect depended on the time during the growing season and the amount of nitrogen added. Specifically, nitrogen addition stimulated net forest floor carbon uptake only in the late growing season. We find evidence for species-specific control of forest floor carbon sink strength, as photosynthesis per unit ground area was positively correlated only with the abundance of the vascular plant Vaccinium myrtillus and no others. Comparison of understorey vegetation photosynthesis and respiration from the study site indicates that understorey vegetation photosynthate was mainly supplying respiratory demands for much of the year. Only in the late season with nitrogen addition did understorey vegetation appear to experience a large surplus of carbon in excess of respiratory requirements. Further work, simultaneously comparing all major biomass and respiratory carbon fluxes in forest floor and tree vegetation, is required to resolve the likely impacts of environmental changes on whole-ecosystem carbon sequestration in boreal forests.
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| 35. |
- Pain, Adam, et al.
(author)
-
What Is Secondary about Secondary Tropical Forest? Rethinking Forest Landscapes
- 2020
-
In: Human Ecology. - : Springer Science and Business Media LLC. - 0300-7839 .- 1572-9915. ; 49, s. 239-247
-
Journal article (peer-reviewed)abstract
- Forests have long been locations of contestation between people and state bureaucracies, and among the knowledge frameworks of local users, foresters, ecologists, and conservationists. An essential framing of the debate has been between the categories of primary and secondary forest. In this introduction to a collection of papers that address the questions of what basis, in what sense, and for whom primary forest is 'primary' and secondary forest is 'secondary,' and whether these are useful distinctions, we outline this debate and propose a new conceptual model that departs from the simple binary of primary and secondary forests. Rather, we propose that attention should be given to the nature of the disturbance that may alter forest ecology, the forms of regeneration that follow, and the governance context within which this takes place.
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| 36. |
- Poyatos, R., et al.
(author)
-
Global transpiration data from sap flow measurements: the SAPFLUXNET database
- 2021
-
In: Earth System Science Data. - : Copernicus GmbH. - 1866-3508 .- 1866-3516. ; 13:6, s. 2607-2649
-
Journal article (peer-reviewed)abstract
- Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land-atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The "sapfluxnetr" R package - designed to access, visualize, and process SAPFLUXNET data - is available from CRAN.
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| 37. |
- Skov Nielsen, Cecilie, et al.
(author)
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A Novel Approach for High-Frequency in-situ Quantification of Methane Oxidation in Peatlands
- 2019
-
In: Soil systems. - : MDPI AG. - 2571-8789. ; 3
-
Journal article (peer-reviewed)abstract
- Methane (CH4) oxidation is an important process for regulating CH4 emissions from peatlands as it oxidizes CH4 to carbon dioxide (CO2). Our current knowledge about its temporal dynamics and contribution to ecosystem CO2 fluxes is, however, limited due to methodological constraints. Here, we present the first results from a novel method for quantifying in-situ CH4 oxidation at high temporal resolution. Using an automated chamber system, we measured the isotopic signature of heterotrophic respiration (CO2 emissions from vegetation-free plots) at a boreal mire in northern Sweden. Based on these data we calculated CH4 oxidation rates using a two-source isotope mixing model. During the measurement campaign, 74% of potential CH4 fluxes from vegetation-free plots were oxidized to CO2, and CH4 oxidation contributed 20 +/- 2.5% to heterotrophic respiration corresponding to 10 +/- 0.5% of ecosystem respiration. Furthermore, the contribution of CH4 oxidation to heterotrophic respiration showed a distinct diurnal cycle being negligible during nighttime while contributing up to 35 +/- 3.0% during the daytime. Our results show that CH4 oxidation may represent an important component of the peatland ecosystem respiration and highlight the value of our method for measuring in-situ CH4 oxidation to better understand carbon dynamics in peatlands.
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