| 11. |
- Sundqvist, Maja K., et al.
(författare)
-
Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra
- 2011
-
Ingår i: Oikos. - Copenhagen : Munksgaard. - 0030-1299 .- 1600-0706. ; 120:1, s. 128-142
-
Tidskriftsartikel (refereegranskat)abstract
- An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above- and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.
|
|
| 12. |
- Wardle, David, et al.
(författare)
-
Above-ground and below-ground responses to long-term nutrient addition across a retrogressive chronosequence
- 2016
-
Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 104:2, s. 545-560
-
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.
|
|
| 13. |
- Asplund, Johan, et al.
(författare)
-
Secondary compounds can reduce the soil micro-arthropod effect on lichen decomposition
- 2013
-
Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 66, s. 10-16
-
Tidskriftsartikel (refereegranskat)abstract
- Phenolic compounds have been shown in several studies to have important 'carryover effects' on litter decomposition, microbial nutrient immobilization and nutrient availability. These effects arise in part because of the adverse effect they have on the feeding activities of litter-feeding invertebrates such as micro-arthropods that drive decomposition processes. However, the interactive effects of phenolic compounds and soil micro-arthropods on litter decomposition are poorly understood. Phenolic compounds can easily be removed by acetone rinsing from living lichens, allowing us to specifically test the role that phenolic compounds (and their removal) have in controlling the effects of micro-arthropods on the decomposition of their litter. We performed a litter-bag experiment aimed at exploring how lichen litter mass loss and nutrient release during decomposition was affected by phenolics (by using acetone rinsed and non-rinsed lichen material) and micro-arthropod activity (by using different mesh sizes to allow or exclude entry by micro-arthropods) for each of six contrasting lichen species (Cladonia rangiferina, Cladonia stellaris, Evernia prunastri, Hypogymnia physodes, Pseudevernia furfuracea and Usnea dasypoga). Both the removal of phenolic compounds and the presence of micro-arthropods accelerated mass and nutrient release overall, but not for either of the two Cladonia species. Removal of phenolics also had an overall positive effect on the effects of arthropods on the loss of P, but not mass and N, from the decomposing lichens. Further, for U. dasypoga, but not the other species, natural levels of phenolic compounds deterred micro-arthropods from accelerating mass loss, and the removal of these compounds enabled micro-arthropods to enhance its decomposition. Our findings that lichen phenolic compounds can sometimes interact with micro-arthropods to influence lichen litter mass loss and nutrient release during decomposition assists our understanding of how lichens and their consumers may impact on organic matter dynamics, biochemical nutrient cycling and other related ecosystem processes. (c) 2013 Elsevier Ltd. All rights reserved.
|
|
| 14. |
- Ibáñez, Theresa Simona, et al.
(författare)
-
Effects of Soil Abiotic and Biotic Factors on Tree Seedling Regeneration Following a Boreal Forest Wildfire
- 2022
-
Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 25, s. 471-487
-
Tidskriftsartikel (refereegranskat)abstract
- Wildfire disturbance is important for tree regeneration in boreal ecosystems. A considerable amount of literature has been published on how wildfires affect boreal forest regeneration. However, we lack understanding about how soil-mediated effects of fire disturbance on seedlings occur via soil abiotic properties versus soil biota. We collected soil from stands with three different severities of burning (high, low and unburned) and conducted two greenhouse experiments to explore how seedlings of tree species (Betula pendula, Pinus sylvestris and Picea abies) performed in live soils and in sterilized soil inoculated by live soil from each of the three burning severities. Seedlings grown in live soil grew best in unburned soil. When sterilized soils were reinoculated with live soil, seedlings of P. abies and P. sylvestris grew better in soil from low burn severity stands than soil from either high severity or unburned stands, demonstrating that fire disturbance may favor post-fire regeneration of conifers in part due to the presence of soil biota that persists when fire severity is low or recovers quickly post-fire. Betula pendula did not respond to soil biota and was instead driven by changes in abiotic soil properties following fire. Our study provides strong evidence that high fire severity creates soil conditions that are adverse for seedling regeneration, but that low burn severity promotes soil biota that stimulates growth and potential regeneration of conifers. It also shows that species-specific responses to abiotic and biotic soil characteristics are altered by variation in fire severity. This has important implications for tree regeneration because it points to the role of plant-soil-microbial feedbacks in promoting successful establishment, and potentially successional trajectories and species dominance in boreal forests in the future as fire regimes become increasingly severe through climate change.
|
|
| 15. |
- Kardol, Paul, et al.
(författare)
-
Trophic cascades in the bryosphere: the impact of global change factors on top-down control of cyanobacterial N-2-fixation
- 2016
-
Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 19, s. 967-976
-
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.
|
|
| 16. |
|
|
| 17. |
- Wardle, David
(författare)
-
The use of chronosequences in studies of ecological succession and soil development
- 2010
-
Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 98, s. 725-736
-
Forskningsöversikt (refereegranskat)abstract
- P>1. Chronosequences and associated space-for-time substitutions are an important and often necessary tool for studying temporal dynamics of plant communities and soil development across multiple time-scales. However, they are often used inappropriately, leading to false conclusions about ecological patterns and processes, which has prompted recent strong criticism of the approach. Here, we evaluate when chronosequences may or may not be appropriate for studying community and ecosystem development.2. Chronosequences are appropriate to study plant succession at decadal to millennial time-scales when there is evidence that sites of different ages are following the same trajectory. They can also be reliably used to study aspects of soil development that occur between temporally linked sites over time-scales of centuries to millennia, sometimes independently of their application to shorter-term plant and soil biological communities.3. Some characteristics of changing plant and soil biological communities (e.g. species richness, plant cover, vegetation structure, soil organic matter accumulation) are more likely to be related in a predictable and temporally linear manner than are other characteristics (e.g. species composition and abundance) and are therefore more reliably studied using a chronosequence approach.4. Chronosequences are most appropriate for studying communities that are following convergent successional trajectories and have low biodiversity, rapid species turnover and low frequency and severity of disturbance. Chronosequences are least suitable for studying successional trajectories that are divergent, species-rich, highly disturbed or arrested in time because then there are often major difficulties in determining temporal linkages between stages.5. Synthesis. We conclude that, when successional trajectories exceed the life span of investigators and the experimental and observational studies that they perform, temporal change can be successfully explored through the judicious use of chronosequences.
|
|
| 18. |
- Jonsson, Micael, et al.
(författare)
-
Direct and Indirect Drivers of Moss Community Structure, Function, and Associated Microfauna Across a Successional Gradient
- 2015
-
Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 18:1, s. 154-169
-
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.
|
|
| 19. |
- Bay, Guillaume, et al.
(författare)
-
Boreal feather mosses secrete chemical signals to gain nitrogen
- 2013
-
Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 200:1, s. 54-60
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanistic basis of feather moss-cyanobacteria associations, a main driver of nitrogen (N) input into boreal forests, remains unknown. Here, we studied colonization by Nostoc sp. on two feather mosses that form these associations (Pleurozium schreberi and Hylocomium splendens) and two acrocarpous mosses that do not (Dicranum polysetum and Polytrichum commune). We also determined how N availability and moss reproductive stage affects colonization, and measured N transfer from cyanobacteria to mosses. The ability of mosses to induce differentiation of cyanobacterial hormogonia, and of hormogonia to then colonize mosses and re-establish a functional symbiosis was determined through microcosm experiments, microscopy and acetylene reduction assays. Nitrogen transfer between cyanobacteria and Pleurozium schreberi was monitored by secondary ion mass spectrometry (SIMS). All mosses induced hormogonia differentiation but only feather mosses were subsequently colonized. Colonization on Pleurozium schreberi was enhanced during the moss reproductive phase but impaired by elevated N. Transfer of N from cyanobacteria to their host moss was observed. Our results reveal that feather mosses likely secrete species-specific chemo-attractants when N-limited, which guide cyanobacteria towards them and from which they gain N. We conclude that this signalling is regulated by N demands of mosses, and serves as a control of N input into boreal forests.
|
|
| 20. |
- Bokhorst, Stef Frederik, et al.
(författare)
-
Contrasting responses of springtails and mites to elevation and vegetation type in the sub-Arctic
- 2018
-
Ingår i: Pedobiologia. - : Elsevier. - 0031-4056 .- 1873-1511. ; 67, s. 57-64
-
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.
|
|
