| 1. |
- Rappe George, Martin, et al.
(författare)
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Indications that long-term nitrogen loading limits carbon resources for soil microbes
- 2017
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 115, s. 310-321
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Tidskriftsartikel (refereegranskat)abstract
- Microbial communities in the organic horizon (O-horizon) of forest soils play key roles in terrestrial nitrogen (N) cycling, but effects on them of long-term high N loading, by N deposition or experimental addition, are not fully understood. Thus, we investigated N-loading effects on soil microbial biomass N, carbon (C) and phosphorus stoichiometry, hydrolytic and oxidative enzymes, community composition (via phospholipid fatty acids, PLFA) and soil chemistry of the O-horizon in study plots of three well-studied experimental Norway spruce (Picea abies) forests in Sweden and the Czech Republic. These forests span substantial gradients in current N deposition, experimental N addition and nitrate (NO3 −) leaching. Current N deposition ranges from ∼3 kg ha−1 year−1 of N in central Sweden (Stråsan) to ∼15 kg ha−1 year−1 of N in SW Sweden (Skogaby) and Czech Republic (Čertovo). Furthermore, accumulated historical N loading during 1950–2000 (which include experimental N addition performed at Stråsan and Skogaby) ranged ∼200–∼2000 kg ha−1 of N. Across all sites and treatments, current NO3 − leaching ranged from low (∼0.1 kg ha−1 year−1 of N) at Stråsan, to high (∼15 kg ha−1 year−1 of N) at Skogaby and Čertovo. We found significantly lower C/N ratios and greater amounts of extractable inorganic N species in the forest soils’ O-horizons at the high N loading plots. Microbial biomass and basal respiration decreased under experimental N addition treatments and tended to decrease with increased N deposition. Similarly, activities of hydrolytic enzyme activity associated with N acquisition were lower, although differences in activities at specific sites with the highest and intermediate historical N deposition levels failed statistical significance. Conversely, activities of soil hydrolytic enzymes associated with C acquisition were greater in study plots exposed high N loading. PLFA profiles indicated shifts in microbial community composition induced by long-term N load, towards higher and lower relative abundance of Gram-positive and Gram-negative bacteria, respectively (but no changes in fungal relative abundance). Taken together, our results suggest that long-term N loading of N-limited Norway spruce forests aggravates limitation of other resources, likely of C, for soil microbial communities. Although microbial variables in the soil O-horizon differed between plots exposed to low and high current N loading, microbial variables in plots that leached small amounts and large amounts of NO3 − exposed to high N load were similar. © 2017
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| 2. |
- Ahlberg, Erik, et al.
(författare)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 3. |
- Choma, Michal, et al.
(författare)
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Recovery of the ectomycorrhizal community after termination of long-term nitrogen fertilisation of a boreal Norway spruce forest
- 2017
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048 .- 1878-0083. ; 29, s. 116-122
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Elsevier Ltd and British Mycological Society.Ectomycorrhizal fungi (ECM) are a fundamental component of boreal forests promoting tree growth and participating in soil nutrient cycling. Increased nitrogen (N) input is known to largely influence ECM communities but their potential recovery is not well understood. Therefore, we studied the effects of long-term N-fertilisation on ECM communities, and their recovery after termination of N treatment. Fungal ITS sequencing data indicated that N-fertilisation (34 kg N ha-1 y-1) for 46 y decreased the relative abundance of ECM species in the fungal community and suppressed originally dominating medium-distance fringe exploration types adapted to N-limited conditions, while the ECM diversity remained unaffected. In other plots, 23 y after termination of fertilisation at 73 kg N ha-1 y-1 for 23 y, the relative abundance of ECM species shifted closer to, but did not reach, control levels. These observations indicate only slow recovery of ECM community, likely due to a high soil N retention capacity.
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| 4. |
- Gebrehiwot, Solomon Gebreyohannis, et al.
(författare)
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Forest cover change over four decades in the Blue Nile Basin, Ethiopia : comparison of three watersheds
- 2014
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Ingår i: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 14:1, s. 253-266
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Tidskriftsartikel (refereegranskat)abstract
- The objective of this study was to quantify forest cover changes in three watersheds (Gilgel Abbay (1,646 km(2)), Birr (980 km(2)), and Upper-Didesa (1,980 km(2)) of the Blue Nile Basin between 1957 and 2001. Four land cover maps were produced for each watershed for 1957/1958, 1975, 1986, and 2000/2001. Nine different types of land cover were identified, five of which were forest cover classes. Between 1957 and 2001, the total forest cover increased in Gilgel Abbay (from 10 to 22 % cover) and decreased in Birr (from 29 to 22 % cover) as well as in Upper-Didesa (from 89 to 45 % cover). The increase in Gilgel Abbay was primarily due to the expansion of eucalyptus plantations. Natural forest cover decreased in all three watersheds. Wooded grassland decreased by two-thirds, dry/moist mixed forests decreased by half, and riverine forests had disappeared by 1975 in Gilgel Abbay and Birr. Major deforestation had already taken place in the northern watersheds, Gilgel Abbay and Birr, before the 1960s and 1970s, while in the southern watershed, Upper-Didesa, much of the deforestation occurred after 1975. The southern watershed still remained by far the most forested watershed in 2001 despite the strong ongoing deforestation. The changes in forest cover could affect natural resource management, greenhouse gas emissions, water resources, and agricultural production including coffee production. The patterns of change are different in the three watersheds. We therefore recommend further studies of the local conditions and drivers of change as the basis for designing effective policy to halt further loss of natural forest, which offers a wealth of ecosystem services.
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| 5. |
- Gebrehiwot, Solomon Gebreyohannis, et al.
(författare)
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The long-term hydrology of East Africa's water tower : statistical change detection in the watersheds of the Abbay Basin
- 2014
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Ingår i: Regional Environmental Change. - : Springer Science and Business Media LLC. - 1436-3798 .- 1436-378X. ; 14:1, s. 321-331
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Tidskriftsartikel (refereegranskat)abstract
- Forty-five years (1960-2004) of hydrological data from 12 watersheds in the Abbay Basin, Ethiopia, were tested for possible trends over the entire time series and differences in medians (step-wise changes) between three sub-periods. The classification of the sub-periods was based on the major political changes in 1975 and 1991. Variables investigated were rainfall (P), total flow (Q(t)), high flow (Q(h)), low flow (Q(1)), low flow index (LFI) and run-off coefficient (C). Data were checked for outliers, errors and homogeneity. Trend was tested after serial and cross-correlation tests. The data for each variable were serially uncorrelated from 1 to 10 lag years. There were five globally significant trends out of 50 test cases and 36 significant step-wise changes out of 180 tests. The majority of the significant changes were watershed specific. Run-off coefficient was the single variable showing a consistently increasing trend and stood for ca. 25 % of the total significant trends and step-wise changes. Half of these changes occurred after 1991. We concluded that despite the land use policy changes in 1975 and 1991, as well as the long-term soil degradation, the hydrological regime was quite stable over the 45-year period, with the exception of an increase in the run-off coefficient in the latter part of the run-off record in some watersheds.
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| 6. |
- He, Hongxing, 1987, et al.
(författare)
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CoupModel (v6.0): An ecosystem model for coupled phosphorus, nitrogen, and carbon dynamics - Evaluated against empirical data from a climatic and fertility gradient in Sweden
- 2021
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 14, s. 735-761
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Tidskriftsartikel (refereegranskat)abstract
- © Author(s) 2021. This study presents the integration of the phosphorus (P) cycle into CoupModel (v6.0, referred to as Coup-CNP). The extended Coup-CNP, which explicitly considers the symbiosis between soil microbes and plant roots, enables simulations of coupled carbon (C), nitrogen (N), and P dynamics for terrestrial ecosystems. The model was evaluated against observed forest growth and measured leaf C/P, C/N, and N/P ratios in four managed forest regions in Sweden. The four regions form a climatic and fertility gradient from 64°N (northern Sweden) to 56°N (southern Sweden), with mean annual temperature varying from 0.7-7.1 °C and soil C/N and C/P ratios varying between 19.8-31.5 and 425-633, respectively. The growth of the southern forests was found to be P-limited, with harvested biomass representing the largest P losses over the studied rotation period. The simulated P budgets revealed that southern forests are losing P, while northern forests have balanced P budgets. Symbiotic fungi accounted for half of total plant P uptake across all four regions, which highlights the importance of fungal-tree interactions in Swedish forests. The results of a sensitivity analysis demonstrated that optimal forest growth occurs at a soil N/P ratio between 15-20. A soil N/P ratio above 15-20 will result in decreased soil C sequestration and P leaching, along with a significant increase in N leaching. The simulations showed that Coup-CNP could describe shifting from being mostly N-limited to mostly P-limited and vice versa. The potential P-limitation of terrestrial ecosystems highlights the need for biogeochemical ecosystem models to consider the P cycle. We conclude that the inclusion of the P cycle enabled the Coup-CNP to account for various feedback mechanisms that have a significant impact on ecosystem C sequestration and N leaching under climate change and/or elevated N deposition.
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| 7. |
- Shibabaw, Tebkew, et al.
(författare)
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The combined impacts of land use change and climate change on soil organic carbon stocks in the Ethiopian highlands
- 2023
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Ingår i: Geoderma Regional. - : Elsevier BV. - 2352-0094. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Land Use Change (LUC), especially deforestation in tropical regions, significantly contributes to global anthropogenic greenhouse gas (GHG) emissions. Here, we address potential combined impacts of LUC and Climate Change (CC) on Soil Organic Carbon (SOC) stocks in the Ethiopian highlands. The soil model Q was employed to predict SOC stocks for various combinations of LUC and CC scenarios until the year 2100. Four reference scenarios (cropland, bushland, natural forest, and Eucalyptus plantations under contemporary climatic conditions) were evaluated against reported measurements of SOC stocks. We studied impacts of six common LUC scenarios, including deforestation and planting Eucalyptus, on SOC stocks under contemporary and future climates. To assess the impact of CC, effects of elevated temperature (mean annual temperature + 2.6 °C) together with three litterfall scenarios (no change in litterfall, a 5% reduction and 22% increase, designated CC0, CCd, and CCi, respectively) were considered to test potential vegetation responses to increases in temperature and atmospheric CO2 concentrations. Most of the tested combinations of LUC and CC led to losses of SOC stocks. Losses were most severe, both relatively and absolutely, in the deforestation scenarios: up to 30% was lost if natural forest was converted to cropland and temperature increased (under the CC0 scenario). Gains in SOC stocks of 4–19% were modelled when sparse vegetation was converted to more dense vegetation like Eucalyptus plantation with substantially increased litterfall (the CCi scenario). Elevated temperature accelerated decomposition rates, leading to circa 8% losses of SOC stocks. We conclude that effects of LUC and CC on SOC stocks are additive and changes in litterfall caused by LUC determine which has the largest impact. Hence, deforestation is the biggest threat to SOC stocks in the Ethiopian highlands, and stocks in sparse vegetation systems like cropland and bushland are more sensitive to CC0 than LUC. We recommend conservation of natural forests and longer rotation periods for Eucalyptus plantations to preserve SOC stocks. Finally, we suggest that use of the Q model is a viable option for national reporting changes in SOC stocks at Tier 3 within the LULUCF sector to the United Nations Framework Convention on Climate Change (UNFCCC) as it is widely applicable and robust, although it only requires input data on a few generally available variables.
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| 8. |
- Gebrehiwot, Solomon, et al.
(författare)
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Hydrological characterization of watersheds in the Blue Nile Basin, Ethiopia
- 2011
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Ingår i: Hydrology and Earth System Sciences. - : Copernicus GmbH. - 1027-5606 .- 1607-7938. ; 15:1, s. 11-20
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Tidskriftsartikel (refereegranskat)abstract
- Thirty-two watersheds (31-4350 km(2)), in the Blue Nile Basin, Ethiopia, were hydrologically characterized with data from a study of water and land resources by the US Department of Interior, Bureau of Reclamation (USBR) published in 1964. The USBR document contains data on flow, topography, geology, soil type, and land use for the period 1959 to 1963. The aim of the study was to identify watershed variables best explaining the variation in the hydrological regime, with a special focus on low flows. Moreover, this study aimed to identify variables that may be susceptible to management policies for developing and securing water resources in dry periods. Principal Component Analysis (PCA) and Partial Least Square (PLS) were used to analyze the relationship between five hydrologic response variables (total flow, high flow, low flow, runoff coefficient, low flow index) and 30 potential explanatory watershed variables. The explanatory watershed variables were classified into three groups: land use, climate and topography as well as geology and soil type. Each of the three groups had almost equal influence on the variation in hydrologic variables (R-2 values ranging from 0.3 to 0.4). Specific variables from within each of the three groups of explanatory variables were better in explaining the variation. Low flow and low flow index were positively correlated to land use types woodland, dense wet forest and savannah grassland, whereas grazing land and bush land were negatively correlated. We concluded that extra care for preserving low flow should be taken on tuffs/basalts which comprise 52% of the Blue Nile Basin. Land use management plans should recognize that woodland, dense wet forest and savannah grassland can promote higher low flows, while grazing land diminishes low flows.
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| 9. |
- Hansson, Linnea, et al.
(författare)
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Soil Compaction Effects on Root-Zone Hydrology and Vegetation in Boreal Forest Clearcuts
- 2019
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Ingår i: Soil Science Society of America Journal. - : Wiley. - 0361-5995 .- 1435-0661. ; 83
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Tidskriftsartikel (refereegranskat)abstract
- Soil compaction is a common consequence of forestry traffic traversing unprotected, moist soils; it decreases porosity and affects hydraulic conductivity even in coarse-textured soils. The aim here was to study root-zone hydrology and vegetation in three microsites (in, between, and beside wheel tracks) 4 to 5 yr after forwarder traffic, on stony and sandy till soils in two clearcuts in northern Sweden. Measurements of soil volumetric water content (VWC), vegetation indicators and one-dimensional hydrological modeling (Hydrus-1D) of wheel tracks and undisturbed soil were conducted. Soil VWC was monitored hourly during 2017 and 2018 in three or four plots along a slope on each site. Soil VWC was also measured once with a portable sensor in 117 plots along two slopes at each site, where the vegetation was recorded and analyzed using Ellenberg indicator indexes. Soil VWC was highest in wheel tracks and lowest between tracks; this was corroborated by the species composition in the wheel tracks (Ellenberg indicator for soil moisture). Bare soil was more frequent in wheel tracks and between tracks than in undisturbed soil. The model simulations indicated that the changed soil hydraulic properties influenced the VWC results in the wheel tracks. However, the differences in average pressure heads in the root zone were small between the microsites and only apparent during dry periods. In the wheel tracks, air-filled porosity was <0.10 m(3) m(-3), indicating insufficient soil aeration during 82% (Site T) and 23% (Site R) of the 2017 growing season. Insufficient aeration could be one explanation for the presence of some still unvegetated areas.
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| 10. |
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