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| 3. |
- Giesler, Reiner, et al.
(författare)
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Boreal Forests Sequester Large Amounts of Mercury over Millennial Time Scales in the Absence of Wildfire
- 2017
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 51:5, s. 2621-2627
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Tidskriftsartikel (refereegranskat)abstract
- Alterations in fire activity due to climate change and fire suppression may have profound effects on the balance between storage and release of carbon (C) and associated volatile elements. Stored soil mercury (Hg) is known to volatilize due to wildfires and this could substantially affect the land air exchange of Hg; conversely the absence of fires and human disturbance may increase the time period over which Hg is sequestered. Here we show for a wildfire chronosequence spanning over more than 5000 years in boreal forest in northern Sweden that belowground inventories of total Hg are strongly related to soil humus C accumulation (R-2 = 0.94, p < 0.001). Our data clearly show that northern boreal forest soils have a strong sink capacity for Hg, and indicate that the sequestered Hg is bound in soil organic matter pools accumulating over millennia. Our results also suggest that more than half of the Hg stock in the sites with the longest time since fire originates from deposition predating the onset of large-scale anthropogenic emissions. This study emphasizes the importance of boreal forest humus soils for Hg storage and reveals that this pool is likely to persist over millennial time scales in the prolonged absence of fire.
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- Siefert, Andrew, et al.
(författare)
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A global meta-analysis of the relative extent of intraspecific trait variation in plant communities
- 2015
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 18:12, s. 1406-1419
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Forskningsöversikt (refereegranskat)abstract
- Recent studies have shown that accounting for intraspecific trait variation (ITV) may better address major questions in community ecology. However, a general picture of the relative extent of ITV compared to interspecific trait variation in plant communities is still missing. Here, we conducted a meta-analysis of the relative extent of ITV within and among plant communities worldwide, using a data set encompassing 629 communities (plots) and 36 functional traits. Overall, ITV accounted for 25% of the total trait variation within communities and 32% of the total trait variation among communities on average. The relative extent of ITV tended to be greater for whole-plant (e.g. plant height) vs. organ-level traits and for leaf chemical (e.g. leaf N and P concentration) vs. leaf morphological (e.g. leaf area and thickness) traits. The relative amount of ITV decreased with increasing species richness and spatial extent, but did not vary with plant growth form or climate. These results highlight global patterns in the relative importance of ITV in plant communities, providing practical guidelines for when researchers should include ITV in trait-based community and ecosystem studies.
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- Wardle, David, et al.
(författare)
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Above-ground and below-ground responses to long-term nutrient addition across a retrogressive chronosequence
- 2016
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 104:2, s. 545-560
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Tidskriftsartikel (refereegranskat)abstract
- There is much interest in understanding ecosystem responses to local-scale soil fertility variation, which has often been studied using retrogressive chronosequences that span thousands of years and show declining fertility and plant productivity over time. There have been few attempts to experimentally test how plant nutrient limitation changes during retrogression.We studied a well-characterized system of 30 forested lake islands in northern Sweden that collectively represent a 5350-year post-fire retrogressive chronosequence, with fertility and productivity decreasing as time since fire increases. For each island, we set up four plots on understorey vegetation, each subjected to a different fertilizer treatment over 6 years: no additions, nitrogen (N) only, phosphorus (P) only and N + P.We found that both N and P additions reduced feather moss and thus total plant biomass. Meanwhile, the three dominant vascular plant species showed contrasting biomass responses, but similar responses of foliar nutrient concentrations to nutrient additions. Fertilization reduced most microbial groups and altered CO2 fluxes, most likely through feather moss reduction. Against expectations, the majority of interactive effects of N and P were antagonistic.Changes in effects of nutrient additions during retrogression were usually modest.Empetrum hermaphroditum biomass was increasingly promoted by P and N + P addition, while vascular plant N-to-P ratios were increasingly reduced by P addition, indicating increasing plant limitation by nutrients (notably P) during retrogression. Below-ground, positive effects of N addition on soil mineral N increased, while negative effects of N addition on soil fungi decreased during retrogression; no other below-ground effects of fertilization changed along the gradient.Synthesis. Our results show that forest understorey communities on islands of different fire history and thus stages of retrogression show relatively modest differences in how they respond to nutrient addition despite large changes in ecosystem productivity and soil fertility, probably because of high species turnover and adaptation of communities to infertile conditions. While increased nutrient availability (as expected through global change) may have important ecological consequences, these effects are likely, especially below-ground, to be rather similar across ecosystems that differ greatly in nutrient availability and productivity.
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- Kardol, Paul, et al.
(författare)
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Trophic cascades in the bryosphere: the impact of global change factors on top-down control of cyanobacterial N-2-fixation
- 2016
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 19, s. 967-976
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Tidskriftsartikel (refereegranskat)abstract
- Trophic cascades in which predators regulate densities of organisms at lower trophic levels are important drivers of population dynamics, but effects of trophic cascades on ecosystem-level fluxes and processes, and the conditions under which top-down control is important, remain unresolved. We manipulated the structure of a food web in boreal feather mosses and found that moss-inhabiting microfauna exerted top-down control of N-2-fixation by moss-associated cyanobacteria. However, the presence of higher trophic levels alleviated this top-down control, likely through feeding on bacterivorous microfauna. These effects of food-web structure on cyanobacterial N-2-fixation were dependent on global change factors and strongly suppressed under N fertilisation. Our findings illustrate how food web interactions and trophic cascades can regulate N cycling in boreal ecosystems, where carbon uptake is generally strongly N-limited, and shifting trophic control of N cycling under global change is therefore likely to impact ecosystem functioning.
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- Jonsson, Micael, et al.
(författare)
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Direct and Indirect Drivers of Moss Community Structure, Function, and Associated Microfauna Across a Successional Gradient
- 2015
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 18:1, s. 154-169
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Tidskriftsartikel (refereegranskat)abstract
- Relative to vascular plants, little is known about what factors control bryophyte communities or how they respond to successional and environmental changes. Bryophytes are abundant in boreal forests, thus changes in moss community composition and functional traits (for example, moisture and nutrient content; rates of photosynthesis and respiration) may have important consequences for ecosystem processes and microfaunal communities. Through synthesis of previous work and new analyses integrating new and published data from a long-term successional gradient in the boreal forest of northern Sweden, we provide a comprehensive view of the biotic factors (for example, vascular plant productivity, species composition, and diversity) and abiotic factors (for example, soil fertility and light transmission) that impact the moss community. Our results show that different aspects of the moss community (that is, composition, functional traits, moss-driven processes, and associated invertebrate fauna) respond to different sets of environmental variables, and that these are not always the same variables as those that influence the vascular plant community. Measures of moss community composition and functional traits were primarily influenced by vascular plant community composition and productivity. This suggests that successional shifts in abiotic variables, such as soil nutrient levels, indirectly affect the moss community via their influence on vascular plant community characteristics, whereas direct abiotic effects are less important. Among the moss-driven processes, moss litter decomposition and moss productivity were mainly influenced by biotic variables (notably the community characteristics of both vascular plants and mosses), whereas moss functional traits (primarily specific leaf area and tissue nutrient concentrations) also were important in explaining moss di-nitrogen-fixation rates. In contrast, both abiotic and biotic variables were important drivers of moss microfaunal community structure. Taken together, our results show which abiotic and biotic factors impact mosses and their associated organisms, and thus highlight that multiple interacting factors need to be considered to understand how moss communities, associated food webs, and the ecosystem processes they influence will respond to environmental change.
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| 9. |
- Bokhorst, Stef Frederik, et al.
(författare)
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Contrasting responses of springtails and mites to elevation and vegetation type in the sub-Arctic
- 2018
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Ingår i: Pedobiologia. - : Elsevier. - 0031-4056 .- 1873-1511. ; 67, s. 57-64
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is affecting the species composition and functioning of Arctic and sub-Arctic plant and soil communities. Here we studied patterns in soil microarthropod (springtails and mites) communities across a gradient of increasing elevation that spanned 450 m, across which mean temperature declined by approximately 2.5 degrees C, in sub-Arctic Sweden. Across this gradient we characterized microarthropod communities in each of two types of vegetation, i.e., heath and meadow, to determine whether their responses to declining temperature differed with vegetation type. Mite abundance declined with increasing elevation, while springtail abundance showed the opposite response. Springtail communities were dominated by larger species at higher elevation. Mite abundance was unaffected by vegetation type, while springtail abundance was 53% higher in the heath than meadow vegetation across the gradient. Springtails but not mites responded differently to elevation in heath and meadow vegetation; hemi-edaphic species dominated in the heath at higher elevation while epiedaphic species dominated in the meadow. Our results suggest that sub-Arctic mite and springtail communities will likely respond in contrasting ways to changes in vegetation and soil properties resulting from climate warming.
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| 10. |
- De Long, Jonathan, et al.
(författare)
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Contrasting Responses of Soil Microbial and Nematode Communities to Warming and Plant Functional Group Removal Across a Post-fire Boreal Forest Successional Gradient
- 2016
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Ingår i: Ecosystems (New York. Print). - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 19:2, s. 339-355
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Tidskriftsartikel (refereegranskat)abstract
- Global warming is causing increases in surface temperatures and has the potential to influence the structure of soil microbial and faunal communities. However, little is known about how warming interacts with other ecosystem drivers, such as plant functional groups or changes associated with succession, to affect the soil community and thereby alter ecosystem functioning. We investigated how experimental warming and the removal of plant functional groups along a post-fire boreal forest successional gradient impacted soil microbial and nematode communities. Our results showed that warming altered soil microbial communities and favored bacterial-based microbial communities, but these effects were mediated by mosses and shrubs, and often varied with successional stage. Meanwhile, the nematode community was generally unaffected by warming and was positively affected by the presence of mosses and shrubs, with these effects mostly independent of successional stage. These results highlight that different groups of soil organisms may respond dissimilarly to interactions between warming and changes to plant functional groups, with likely consequences for ecosystem functioning that may vary with successional stage. Due to the ubiquitous presence of shrubs and mosses in boreal forests, the effects observed in this study are likely to be significant over a large proportion of the terrestrial land surface. Our results demonstrate that it is crucial to consider interactive effects between warming, plant functional groups, and successional stage when predicting soil community responses to global climate change in forested ecosystems.
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