Search

Habitat heterogeneity is one of the important drivers of biodiversity, but the underlying mechanisms are still vague. Increasing habitat heterogeneity often coincides with greater habitat space and/or greater food availability for organisms, but it is unclear whether and how these components are related to habitat selection. Downed dead wood (i.e., dead wood laying on the ground) is an important but understudied component of dead plant matter that creates spatial habitat heterogeneity for soil fauna on the ground. To unravel the role of dead wood for providing niche dimensionality for soil fauna via variance in resource use, we sampled Collembola communities from moss growing on bark and from bark on the logs of two tree species (pedunculate oak and Norway spruce) and from soil next to the logs. We assessed habitat selection of Collembola species combining abundance data with trophic position data using stable isotope ratios (i.e., δ13C and δ15N). Based on the Bray-Curtis dissimilarity, Collembola community composition differed significantly among the three habitats (i.e., moss, bark and soil). Collembola community-weighted mean δ13C and δ15N values also differed among the three habitats (average δ13C values of moss: −25.94‰, bark: −25.30‰, soil: −25.60‰; average δ15N values of moss: −4.80‰, bark: −3.83‰, soil: −5.11‰), partly reflecting isotopic differences of the habitats themselves (δ13C of moss: −29.83‰, bark: −28.26‰, soil: −29.04‰; δ15N of moss: −7.59‰, bark: −4.18‰, soil: −7.84‰). These findings indicate that Collembola depend on food sources derived from the habitats they inhabit at least at the community level. Collembola community-weighted variance of both δ13C and δ15N values ranked as bark > moss > soil. Species-level data suggested that the bark community included both bark-specific food specialists as well as species which likely use bark only as a temporary habitat based on their morphological traits supporting high mobility. These findings together indicate that the trophic niche variation of the Collembola community is larger in bark than in soil. Our results stress the importance of downed dead wood as a source of habitat heterogeneity, which in turn promotes soil animal diversity, likely via heterogeneity in food sources. Furthermore, the presence of dead wood on the ground could have consequences for organic matter processing by the soil animal community through sustaining a larger trophic niche variation even at a small spatial scale. • Deadwood provides multiple habitats and food sources for diverse animal communities. • Springtail communities differ between deadwood bark, moss on bark and adjacent soil. • Trophic niche variation (variance in δ13C and δ15N) is ranked as bark > moss > soil. • Deadwood microhabitat heterogeneity promotes the soil animals' functional diversity. [ABSTRACT FROM AUTHOR]

Facilitation between species is thought to be a key mechanism in community assembly and diversity, as certain species create microhabitats for others. A profound characteristic of forest ecosystems is a large amount of dead wood which is colonised by a vast array of invertebrate species. Bark beetles (Scolytinae) feed and breed on dying or dead trees, puncturing holes into the bark and engraving inner bark and outer wood with their galleries. These holes and galleries might facilitate other invertebrates by providing access to the inner bark for shelter, feeding and reproduction. We tested this hypothesised facilitative interaction during the early decomposition phase of coarse woody debris of spruce ( Picea abies L. Karst.) incubated in two environmentally contrasting forest sites in the ‘common garden’ experiment LOGLIFE. We sampled invertebrates in 25 cm diameter logs at different degrees of colonisation by bark beetles. Our results indicated that (1) bark beetles facilitated the entrance into spruce logs of other invertebrates with body width that matched the size of bark-beetle holes, and (2) the abundance of invertebrates was often positively related to the proportional surface area of inner bark consumed by bark beetles, but more so in the nutrient-rich site than in the nutrient poor site. This study provides the first quantitative test of facilitation between invertebrate clades in dead wood communities. Including facilitative interaction in community assembly studies may change some predictions about relationships between tree functional traits and invertebrate diversity and will lead to a more accurate and comprehensive understanding of dead wood communities. [ABSTRACT FROM AUTHOR]

Woody plants are important components of dryland ecosystems. Our understanding of wood decomposition in drylands, an important component of biogeochemical cycling, is poor compared to that in mesic ecosystems. To uncovering the complex interactive effects of the different key drivers, we studied the effects of precipitation, position (aboveground and belowground), wood size and litter quality of plant species (four to five local species and one widespread woody species) on woody litter decomposition rates along a precipitation gradient from 37 to 369 mm, spanning five dryland sites. Wood dry matter content (DMC) was a critical negative predictor of wood decomposition in water-limited ecosystems. Thicker woody litter had lower decomposition rates (k values) directly because of smaller relative surface exposure, and indirectly through higher wood DMC or lower bark mass ratio (bark mass divided by wood mass for a given branch length). Mean annual precipitation (MAP) increased the k values both directly, and indirectly by decreasing the wood DMC and increasing the bark mass ratio due to species turnover. The k values of buried woody litter were mostly two to three times higher than litter on the soil surface, but not different at the extremely arid site. A steeper slope of the relationship between overall woody litter quality (particularly wood DMC) or annual precipitation and k values was observed belowground than aboveground, as related to the higher moisture belowground than aboveground. These findings highlight the complex interactions among climate (precipitation), litter position, size and quality on wood decomposition in drylands, thereby helping to improve our mechanistic understanding of dryland woody litter decomposition. We conclude that wood decomposition at the regional and local scales will influence biogeochemical cycling in drylands under future climate change through both direct effects of moisture and indirect effects of litter quality characteristics. • Precipitation drives dryland wood decomposition directly and indirectly via wood litter quality. • Precipitation has a stronger effect on wood decomposition belowground than aboveground. • The wood quality effect on decomposition is stronger belowground than aboveground. • Carbon models should include interactions of climate, litter traits and locations. [ABSTRACT FROM AUTHOR]

Understanding what drives soil fauna species composition through space and time is crucial because we should preserve soil fauna biodiversity and its key role in ecosystem functioning in this era of fast environmental change. As plant leaf litter provides both food and habitat for soil fauna, a focus on litter traits that relate to these two functions will help in understanding soil invertebrate community structure and dynamics comprehensively. To advance this agenda, we propose a conceptual framework to explicitly link the invertebrate community composition to the temporal dynamics of the litter trait space defined by two axes: a food-quality axis related to plant resource economics and chemistry and a habitat-quality axis related to litter particle size and shape. Disentangling of what drives the composition and dynamics of belowground diversity is needed to predict ecosystem-level consequences of environmental change. Incorporating the notion that soil fauna live in 'a house made of food' could bridge the gap between soil fauna diversity and plant community solely based on litter traits as a food source. To assess the dynamic habitat for soil fauna, partly through their own feeding activities, we add temporal aspects into the trait space defined by food- and habitat-related trait axes. Integration of temporal dynamics in trait-based ecology is critical to assess almost all ecological processes accompanied by temporal change in traits of targeted organisms. [ABSTRACT FROM AUTHOR]

Bryophytes cover large territories in cold biomes, where they control soil temperature regime, and therefore permafrost, carbon and nutrient dynamics. The mechanisms of this control remain unclear., We quantified the dependence of soil temperature fluctuations under bryophyte mats on the interplay of bryophyte heat conductance traits, mat thickness, density and moisture regimes., For seventeen predominant bryophytes in six typical subarctic ecosystems, we assessed in situ soil temperature dynamics under bryophyte mats in comparison with bryophyte-removal patches and per-species mat field moisture. In a complimentary laboratory investigation, we studied how per-species bryophyte thermal conductivity and volumetric heat capacity depend on mat density and moisture content. Subsequently, we tested whether heat transfer through bryophyte mats could be modelled as a function of mat thickness, thermal conductivity and volumetric heat capacity, the latter two being determined by mat density and field moisture content., Laboratory assessment revealed that bryophyte thermal conductivity and volumetric heat capacity were independent of mat density, and depended linearly on mat moisture content, but the dependencies were not species-specific. In the field, bryophytes reduced amplitudes of soil temperature fluctuations and freeze-thaw frequency during the growing season, but not mean soil temperature. These effects differed between species and between ecosystems, being strongest in Sphagnum fuscum-dominated dry tundra, but were well explained by bryophyte mat thickness and field moisture content as affecting thermal conductivity and volumetric heat capacity., We suggest that reduction in soil temperature amplitudes is a generic feature in (sub) arctic ecosystems and should be considered as an important mechanism of bryophyte control on carbon and nutrient turnover. Although heat transfer through bryophyte mats differs greatly among species and ecosystems, species differences are fully explained by differences in mat thickness and moisture content and generally comply with physical laws, without deviations due to biological processes. These results imply that in global vegetation models of carbon and nutrient cycling, the heat transfer through bryophyte mats can be modelled without taking into consideration bryophyte species composition, but considering bryophyte mat depth and moisture availability only. This will allow us to enhance modelling precision through an improved representation of the soil temperature regime. [ABSTRACT FROM AUTHOR]

Background:Climate, land-use and disturbance regimes are key drivers of treeline dynamics worldwide, but local and regional spatio-temporal patterns indicate that additional factors play an important role. Some studies suggest that shrub-tree interactions control tree seedling recruitment patterns across the treeline ecotone, but little is known about the generality of this interaction. Aims:We established an experiment in a treeline ecotone in the central Pyrenees to investigate the role of such interactions and other environmental factors on tree seedling growth and survival. It was based on a similar experiment we completed recently in the subarctic Scandes. By comparing local phenomena between both experiments we assessed the generality of the findings across regions with different biogeographic histories and species characteristics. Methods:We followed the survival and growth of transplantedPinus uncinataseedlings during three growing seasons in a multi-factorial design (forest vs. treeline, +/– shrub removal, +/– temperature increase and +/– nutrient addition). Results:There was better seedling growth at the treeline compared to the forest, and the presence of shrubs prevented seedling winter damage and herbivory. Both temperature and nutrient increase enhanced seedling performance. Conclusions:Although some particular details were exclusive to the Pyrenees or to the Scandes, the similarities indicated general patterns and help to interpret the underlying mechanisms of treeline dynamics in both regions. This convergence of responses points to the potential of the development of a robust mechanistically founded predictive framework for scaling up shrub impacts on treeline dynamics to other regions. [ABSTRACT FROM PUBLISHER]

Abstract: Extreme climate events are increasing in frequency and duration and may directly impact belowground foodwebs and the activities of component soil organisms. The soil invertebrate community, which includes keystone decomposers, might respond to these newly induced soil microclimate conditions by shifts in density, species composition, spatial patterning and/or functional traits. To test if and how short-term extreme climatic conditions alter the structure, the vertical stratification and the community weighted trait means of the springtail (Collembola) community in sub-arctic peatbogs, we experimentally subjected Sphagnum peat cores in a field setting to factorial treatments of elevated temperature and episodically increased moisture content. The large precipitation peaks did not affect the springtail community, but an average soil temperature increase of 4 °C halved its density in the shallower peat layers, mainly caused by the reduced dominance of Folsomia quadrioculata. A hypothesized net downward shift of the surface-dwelling springtail community, however, was not observed. We observed species-specific responses to warming but the overall community composition in subsequent organic layers was not significantly altered. Although the effects of an extreme warming event on density, species composition and vertical stratification pattern seemed subtle, functional trait analysis revealed directional community responses, i.e. an overall increase of soil-dwelling species due to warming, even though warming did not alter layer-specific community weighted trait means. We suggest that subtle changes in moisture conditions, due to increased evapotranspiration, have decreased typically surface-dwelling species relative to soil-dwelling species. The extent to which this directional change in the community is maintained after an extreme event, and its costs for the community''s resilience to multiple sequential extreme events will consequently determine its longer-term effects on the community and on ecosystem functioning. [Copyright &y& Elsevier]

The carbon flux from woody debris, a crucial uncertainty within global carbon-climate models, is simultaneously affected by climate, site environment and species-based variation in wood quality. In the first global analysis attempting to explicitly tease out the wood quality contribution to decomposition, we found support for our hypothesis that, under a common climate, interspecific differences in wood traits affect woody debris decomposition patterns. A meta-analysis of 36 studies from all forested continents revealed that nitrogen, phosphorus, and C : N ratio correlate with decomposition rates of angiosperms. In addition, gymnosperm wood consistently decomposes slower than angiosperm wood within common sites, a pattern that correlates with clear divergence in wood traits between the two groups. New empirical studies are needed to test whether this difference is due to a direct effect of wood trait variation on decomposer activity or an indirect effect of wood traits on decomposition microsite environment. The wood trait–decomposition results point to an important role for changes in the wood traits of dominant tree species as a driver of carbon cycling, with likely feedback to atmospheric CO2 particularly where angiosperm species replace gymnosperms regionally. Truly worldwide upscaling of our results will require further site-based multi-species wood trait and decomposition data, particularly from low-latitude ecosystems. [ABSTRACT FROM AUTHOR]

The plant economics spectrum integrates trade‐offs and covariation in resource economic traits of different plant organs and their consequences for pivotal ecosystem processes, such as decomposition. However, in this concept stems are often considered as one unit ignoring the important functional differences between wood (xylem) and bark. These differences may not only affect the performance of woody plants during their lifetime, but may also have important "afterlife effects." Specifically, bark quality may strongly affect deadwood decomposition of different woody species. We hypothesized that (1) bark quality strongly influences bark decomposability to microbial decomposers, and possibly amplifies the interspecific variation in decomposition by invertebrate consumption, especially termites; and (2) bark decomposition has secondary effects on xylem mass loss by providing access to decomposers including invertebrates such as termites. We tested these hypotheses across 34 subtropical woody species representing five common plant functional types, by conducting an in situ deadwood decomposition experiment over 12‐month in two sites in subtropical evergreen broad‐leaved forest in China. We employed visual examination and surface density measurement to quantify termite consumption to both bark and the underlying xylem, respectively. Using principal component analysis, we synthesized seven bark traits to provide the first empirical evidence for a bark economics spectrum (BES), with high BES values (i.e., bark thickness, nitrogen, phosphorus, and cellulose contents) indicating a resource acquisitive strategy and low BES values (i.e., carbon, lignin, and dry matter contents) indicating a resource conservative strategy. The BES affected interspecific variation in bark mass loss and this relationship was strongly amplified by termites. The BES also explained nearly half of the interspecific variation in termite consumption to xylem, making it an important contributor to deadwood decomposition overall. Moreover, the above across‐species relationships manifested also within plant functional types, highlighting the value of using continuous variation in bark traits rather than categorical plant functional types in carbon cycle modeling. Our findings demonstrate the potent role of the BES in influencing deadwood decomposition including positive invertebrate feedback thereon in warm‐climate forests, with implications for the role of bark quality in carbon cycling in other woody biomes. [ABSTRACT FROM AUTHOR]

Deadwood heterogeneity is regarded as a primary causal driver of deadwood-associated soil biodiversity, but the underlying mechanisms remain elusive. This is partly due to the technical difficulties in disentangling and quantifying different components (e.g., deadwood is both habitat and food) of heterogeneity to which soil organisms may have context-dependent responses. Furthermore, non-trophic interactions, e.g., facilitation, also add complexity to deadwood heterogeneity-biodiversity relationships, yet their influences are unaccounted for in most deadwood biodiversity studies. To address these research gaps, we sampled isopod communities from 40 logs of two isotopically distinct tree species, which had been cut and incubated reciprocally for eight years in each of two environmentally contrasting sites (e.g., differences in background isotopic signatures and litter turnover rates). We then assessed the extent to which the variation in the biodiversity of isopod communities is explained by deadwood heterogeneity induced by wood-boring beetles. Stable isotope ratios (i.e., δ13C and δ15N) were employed to examine the response of trophic diversity of isopod communities to the rarely tested food facet of deadwood heterogeneity. We hypothesized the deadwood heterogeneity is boosted by wood-boring beetles and thereby positively affects the abundance, taxonomic diversity and trophic diversity of isopod communities. Our results supported this hypothesis: the abundance and Shannon and Simpson diversity as well as trophic diversity of isopods were positively correlated to wood-boring beetle tunnel densities in both sites and across the two tree species. We observed significant tree species and reciprocal treatment effects on the δ15N values of isopods in one of the two sites. This result suggested that the use of deadwood as food sources versus habitats by isopods is environmentally dependent. This study demonstrates that there is substantial heterogeneity within deadwood that promotes the diversity and trophic diversity of macroinvertebrates. This relationship is mediated by saproxylic beetle facilitation, with implications for the roles of saproxylic beetles and within-deadwood heterogeneity in determining microbial wood decomposition in temperate forests. • Wood beetles facilitate the food and habitat facets of deadwood heterogeneity. • Stable isotopes are useful to quantify the food facet of deadwood heterogeneity. • Wood beetle facilitation increases the trophic diversity of isopods. • Isopods' dependence on deadwood may depend on soil properties. • Fine-scale deadwood heterogeneity greatly benefits soil animals with low mobility. [ABSTRACT FROM AUTHOR]

• We grew seven C 3 annuals at a factorial of CO 2 (160-450-750 ppm) and soil water availability (100-40-20%). • Compared to well-watered conditions the relative effect of drought was the same at all CO 2 conditions. • Across all traits measured, we found mostly additive effects of CO 2 and water. • In drought prone regions, results suggest CO 2 fertilization will not counter the effects of reduced water availability. Carbon dioxide and water are crucial resources for plant growth. With anthropogenic fossil fuel emissions, CO 2 availability is and has been increasing since the last glacial maximum. Simultaneously water availability is expected to decrease and the frequency and severity of drought episodes to increase in large parts of the world. How plants respond to these two changes will help in understanding plants' responses to climate of the future. Here we sought to understand how drought affects plant traits responses to CO 2 and whether there are trade-offs in responsiveness to low and elevated CO 2 and drought. We grew seedlings of seven C 3 annuals at past low (160 μl l−1), ambient (450 μl l−1) and elevated (750 μl l−1) CO 2. At each concentration plants were subjected to well-watered conditions (100% soil water availability, SWA), 40% SWA or 20% SWA. We measured biomass allocation, relative growth rate, tissue N concentration, and gas exchange. Compared to well-watered conditions plant size was an important element in the absolute response to SWA decrease, i.e. the smaller, slow growing species were unaffected by drought at low CO 2. Plants allocated less mass to root tissue at low CO 2 contrasting with increased root mass fraction at lower SWA at ambient CO 2. Across all traits measured, we found mostly additive effects of CO 2 and water. As due to climate change regions become more drought prone these results suggest CO 2 fertilization will not counteract the effects of reduced water availability. [ABSTRACT FROM AUTHOR]

Abstract Sand burial is a common phenomenon in inland semi-arid and arid areas, affecting plant growth and even plant community structure. Precipitation regime, including the variation of precipitation intensity and frequency, also drives community structure and functions in such areas. However, few studies have focused on the combined effect of sand burial and changed precipitation regime on community function, specifically its role in carbon storage. A 2-yr field experiment with factorial treatments of precipitation (control, slight enhancement and strong enhancement) and sand addition (control and 5 cm sand addition) was conducted to test the responses of plant and soil carbon content in a semi-arid typical steppe in N China. Results showed that sand burial had no significant effect on plant carbon density, but significantly changed the allocation of plant carbon from aboveground to belowground; these responses differed among species and life forms in the community. Precipitation enhancement had no significant effects on plant carbon and its allocation, perhaps because effects of precipitation on plants are due more to precipitation frequency than to precipitation intensity per event. Sand burial and precipitation enhancement decreased soil carbon, especially soil organic carbon, and promoted soil carbon to be distributed deeper down the soil profile. These findings will help to understand how sand deposition affects plant and soil carbon storage and their allocation in plant communities under a changing precipitation regime, and more generally, to understand carbon storage dynamics in early-successional sandy ecosystems in the context of global change. Graphical abstract Unlabelled Image Highlights • Sand burial significantly changed the allocation of plant carbon from aboveground to belowground. • Precipitation enhancement had no significant effects on plant carbon and its allocation. • Sand burial and precipitation enhancement promoted soil carbon to be distributed deeper down the soil profile. [ABSTRACT FROM AUTHOR]

Solar radiation mediated photodegradation of leaf litter has been studied substantially as it plays important roles in the cycling of carbon (C) and nutrients in dryland ecosystems. However, the mechanism by which ultraviolet (UV) radiation and its interaction with litter quality and microbial degradation affect dryland litter decomposition is still uncertain. A field experiment was carried out in semiarid Mu Us inland dunes of Inner Mongolia, China to investigate the effects of UV radiation and litter position on leaf litter decomposition of eight contrasting species (three perennial grasses, three shrubs, two annual forbs) representing different litter qualities over a whole year of incubation. The results showed that UV radiation increased mass loss of suspended litters for two perennial grasses and two annual forbs, but had no significant effect on the other four species considered; across species the percentage increase in mass loss ranged from 4.5 to 27.3% with an average of 13.7%. C release from suspended litters in response to UV radiation showed similar patterns with mass loss. Nitrogen (N) release from litters on the soil surface was lower than in suspended position because the former was involved in N immobilization driven by microbial decomposition. There were no net effects of UV radiation on decomposition rates of surface litters possibly due to the positive effects of photochemical process offsetting negative effects on microbes. Multiple linear regressions showed that the C:N ratio of initial leaf litter and leaf dry matter content (LDMC) could predict the rate of litter decomposition, in which litter C:N ratio had stronger influence. The findings, based on multiple species, highlight the importance of photodegradation on litter nitrogen and/or carbon mineralization in drylands as mediated by different abiotic and biotic drivers. [ABSTRACT FROM AUTHOR]

Aims Sand burial and precipitation play important roles in vegetation of inland deserts and desertified areas, and both are under strong influence of climate and land-use change. Sand deposition and precipitation both vary greatly in space and time, and different plant species, with diverse adaptations, occupy different niches along spatial gradients in the combination of sand and water availability dynamics. We hypothesized that species specificity in spatial and temporal niche occupation along such gradients is a mechanism for their co-existence and, thereby, a driver and stabilizer of biodiversity in dry, sandy areas. Location Ordos Plateau, China. Methods We conducted a 2-yr field experiment with factorial treatments of precipitation (control, slight enhancement, strong enhancement) and sand addition (control, medium addition, large addition). Plant cover of the six dominant species was followed over different seasons, as we expected different species to benefit from different treatments in different seasons and years with different weather regimes. Results Sand burial alone significantly affected plant cover of all six dominant species, while precipitation enhancement had no significant effect. Effects of sand burial on plant cover changed overall during the two hydrologically contrasting years. Our key finding was that there were multiple significant two- and three-way interactions between species, sand burial and precipitation enhancement on plant cover, while there were also multiple two- and three-way interactions involving species, sand burial or precipitation treatment with year and/or season. Conclusion Our results supported our hypothesis, i.e. the co-existence of species in a semi-arid sand dune can be explained from the different niches they occupy in terms of seasonal and year-to-year variation in precipitation in combination with sand deposition regime. The interactions of these drivers on plant cover with experimental enhancement of precipitation, mimicking a realistic scenario for this region, suggest that shifts in species composition are to be expected this century. More generally, our findings advance our understanding of what drives species co-existence and thereby biodiversity, now and in the future. [ABSTRACT FROM AUTHOR]

Abstract: In high-latitude ecosystems climate change induced plant community shifts toward dominance of shrubs and trees will potentially have large consequences for soil carbon dynamics. Changes in the litter layer due to an altered quantity and quality of litter input, or by its indirect effect on the microclimate, might affect the decomposer community. To be able to predict the effects of increased litter input on decomposers and consequently on soil carbon dynamics, we studied the contribution of Collembola to carbon processing in a high-latitude peat bog system. Moreover, we assessed the effects of changing litter inputs on their abundance, diversity and diet choice, using a 13C tracer approach. The δ 13C signatures of Collembola in peat moss (Sphagnum fuscum) showed that species differed in their diet. However, when vascular plant litter (Betula pubescens) entered the Sphagnum peat ecosystem, the δ 13C signatures of the Collembola, changed and species-specific differences disappeared. There were no significant changes in Collembola species composition and density after Betula litter addition, but all species showed a strong dietary preference for Betula-associated food sources over Sphagnum; 67% of their diet contained carbon originating from Betula litter. Decomposition patterns corresponded to these findings; mass loss (after 406 days of incubation) of Betula increased from 16.1% to 26.2% when decomposing in combination with Sphagnum, and Sphagnum decomposed even slower in combination with Betula litter (from 4.7% to 1.9%). Our results indicate that the change in litter quality rather than its effects on microclimate is the main way in which vascular litter inputs alter the role of Collembola in carbon turnover. Collembola are plastic in their diet choice, which implies that changes in carbon turnover rates in situations where vegetation shifts occur, might well be due to diet shifts of the present decomposer community rather than by changes in species composition. [Copyright &y& Elsevier]

Conceptual frameworks relating plant traits to ecosystem processes such as organic matter dynamics are progressively moving from a leaf-centred to a whole-plant perspective. Through the use of meta-analysis and global literature data, we quantified the relative roles of litters from above- and below-ground plant organs in ecosystem labile organic matter dynamics., We found that decomposition rates of leaves, fine roots and fine stems were coordinated across species worldwide although less strongly within ecosystems. We also show that fine roots and stems had lower decomposition rates relative to leaves, with large differences between woody and herbaceous species. Further, we estimated that on average below-ground litter represents approximately 33 and 48% of annual litter inputs in grasslands and forests, respectively., These results suggest a major role for below-ground litter as a driver of ecosystem organic matter dynamics. We also suggest that, given that fine stem and fine root litters decompose approximately 1.5 and 2.8 times slower, respectively, than leaf litter derived from the same species, cycling of labile organic matter is likely to be much slower than predicted by data from leaf litter decomposition only., Synthesis. Our results provide evidence that within ecosystems, the relative inputs of above- versus below-ground litter strongly control the overall quality of the litter entering the decomposition system. This in turn determines soil labile organic matter dynamics and associated nutrient release in the ecosystem, which potentially feeds back to the mineral nutrition of plants and therefore plant trait values and plant community composition. [ABSTRACT FROM AUTHOR]

Plant species and functional groups in nitrogen ( N) limited communities may coexist through strong eco-physiological niche differentiation, leading to idiosyncratic responses to multiple nutrition and disturbance regimes. Very little is known about how such responses depend on the availability of N in different chemical forms. Here we hypothesize that idiosyncratic year-to-year responses of plant functional groups to availability and form of nitrogen explain species coexistence in an alpine meadow community after release from grazing. We conducted a 6 year N addition experiment in an alpine meadow on the Tibetan Plateau released from grazing by livestock. The experimental design featured three N forms (ammonium, nitrate, and ammonium nitrate), crossed with three levels of N supply rates (0.375, 1.500 and 7.500 g N m−2 yr−1), with unfertilized treatments without and with light grazing as controls. All treatments showed increasing productivity and decreasing species richness after cessation of grazing and these responses were stronger at higher N rates. Although N forms did not affect aboveground biomas s at community level, different functional groups did show different responses to N chemical form and supply rate and these responses varied from year to year. In support of our hypothesis, these idiosyncratic responses seemed to enable a substantial diversity and biomass of sedges, forbs, and legumes to still coexist with the increasingly productive grasses in the absence of grazing, at least at low and intermediate N availability regimes. This study provides direct field-based evidence in support of the hypothesis that idiosyncratic and annually varying responses to both N quantity and quality may be a key driver of community structure and species coexistence. This finding has important implications for the diversity and functioning of other ecosystems with spatial and temporal variation in available N quantity and quality as related to changing atmospheric N deposition, land-use, and climate-induced soil warming. [ABSTRACT FROM AUTHOR]

Questions: What are the water economy strategies of the dominant subarctic bryophytes in terms of colony and shoot traits? Can colony water retention capacity be predicted from morphological traits of both colonies and separate shoots? Are suites of water retention traits consistently related to bryophyte habitat and phylogenetic position? Location: Abisko Research Station, North Sweden. Methods: We screened 22 abundant subarctic bryophyte species from diverse habitats for water economy traits of shoots and colonies, including desiccation rates, water content at field capacity, volume and density (mg cm−3) of water-saturated and oven-dried patches, evaporation rate (g·m−2·s−1) and cell wall thickness. The relationships between these traits and shoot and colony desiccation rates were analysed with Spearman rank correlations. Subsequent multivariate (cluster followed by PCA) analyses were based on turf density, turf and shoot desiccation rate, cell wall thickness and amount of external and internal water. Results: Individual shoot properties, i.e. leaf cell wall properties, water retention capacity and desiccation rate, did not correspond with colony water retention capacity. Colony desiccation rate depended on density of water-saturated colonies, and was marginally significantly negatively correlated with species individual shoot desiccation rate but not related to any other shoot or colony trait. Multivariate analyses based on traits assumed to determine colony desiccation rate revealed six distinct species groups reflecting habitat choice and phylogenetic relationships. Conclusions: General relationships between shoot and colony traits as determinants of water economy will help to predict and upscale changes in hydrological function of bryophyte-dominated peatlands undergoing climate-induced shifts in species abundance, and feedbacks of such species shifts on permafrost insulation and carbon sequestration functions. [ABSTRACT FROM AUTHOR]

Although direct contributions of soil invertebrates to carbon turnover are modest, they have a disproportionally large indirect impact through their control over the activity of microbial decomposers. Shifts in soil invertebrate species distribution might have a substantial effect on the decomposition process because their functional role depends on the species' vertical position in soils. Gradients in microclimate and substrate quality and structure largely determine the vertical position of soil invertebrates. Because of the possible impact of climate change on soil invertebrate distribution, and consequently on decomposition, it is important to know the relative contributions of microclimate and substrate quality to the vertical distribution patterns of soil invertebrates. We studied this for springtails (Collembola) as a keystone group in cool and cold biomes, by turning peat cores in a subarctic blanket bog upside down, thereby reversing the substrate quality gradient and leaving temperature and moisture gradients intact. Two opposing groups of springtail species could be distinguished with respect to their abundance responses along the vertical gradient: (i) species that remain associated with the stratum they were originally found in ('stayers') and (ii) species that re-establish the original stratification pattern, by remigration either to the top or deeper layers, irrespective of any substrate quality change ('movers'). Within the 'mover' response pattern, the direction of their migration in response to microclimate changes seemed to coincide with their ecomorphological traits. Our results not only demonstrate that springtail species differ in their responses to changes in climate or substrate quality; they also suggest that interspecific faunal trait variation may provide a useful tool to predict animal responses to climatic changes. [ABSTRACT FROM AUTHOR]

Question. Competitive and facilitative interactions among plant species in different abiotic environments potentially link productivity, vegetation structure, species composition and functional diversity. We investigated these interactions among four alpine communities along an environmental productivity gradient in a generally harsh climate. We hypothesised that the importance of competition would be higher in more productive sites. Location. Mt. M. Khatipara (43°27′N, 41°41′E, altitude 2750 m), NW Caucasus, Russia. Communities ranged from low-productivity alpine lichen heath (ALH) and snowbed communities (SBC), to intermediate productivity Festuca grassland (FVG), and high-productivity Geranium-Hedysarum meadow (GHM). Methods. We quantified the relative influence of competition and facilitation on community structure by expressing biomass of target species within each natural community proportionally to biomass of the species in a 'null community' with experimental release from interspecific competition by removing all other species (for 6 years). An overall index of change in community composition due to interspecific interactions was calculated as the sum of absolute or proportional differences of the component species. Results. Species responses to neighbour removal ranged from positive to neutral. There was no evidence of facilitation among the selected dominant species. As expected, competition was generally most important in the most productive alpine community (GHM). The intermediate position for low-productivity communities of stressful environments (ALH, SBC) and the last position of intermediately productive FVG were unexpected. Conclusions. Our results appear to support the Fretwell-Oksanen hypothesis in that competition in communities of intermediate productivity was less intense than in low- or high-productive communities. However, the zero net effect of competition and facilitation in FVG might be the result of abiotic stress due to strong sun exposure and high soil temperatures after neighbour removal. Thus, non-linear relationships between soil fertility, productivity and different abiotic stresses may also determine the balance between competition and facilitation. [ABSTRACT FROM AUTHOR]

Intensively managed grasslands are large sources of the potent greenhouse gas nitrous oxide (N 2 O) and important regulators of methane (CH 4) consumption and production. The predicted increase in flooding frequency and severity due to climate change could increase N 2 O emissions and shift grasslands from a net CH 4 sink to a source. Therefore, effective management strategies are critical for mitigating greenhouse gas emissions from flood-prone grasslands. We tested how repeated flooding affected the N 2 O and CH 4 emissions from 11 different plant communities (Festuca arundinacea, Lolium perenne, Poa trivialis, and Trifolium repens in monoculture, 2- and 4-species mixtures), using intact soil cores from an 18-month old grassland field experiment in a 4-month greenhouse experiment. To elucidate potential underlying mechanisms, we related plant functional traits to cumulative N 2 O and CH 4 emissions. We hypothesized that traits related with fast nitrogen uptake and growth would lower N 2 O and CH 4 emissions in ambient (non-flooded) conditions, and that traits related to tissue toughness would lower N 2 O and CH 4 emissions in flooded conditions. We found that flooding increased cumulative N 2 O emissions by 97 fold and cumulative CH 4 emissions by 1.6 fold on average. Plant community composition mediated the flood-induced increase in N 2 O emissions. In flooded conditions, increasing abundance of the grass F. arundinacea was related with lower N 2 O emissions; whereas increases in abundance of the legume T. repens resulted in higher N 2 O emissions. In non-flooded conditions, N 2 O emissions were not clearly mediated by plant traits related with nitrogen uptake or biomass production. In flooded conditions, plant communities with high root carbon to nitrogen ratio were related with lower cumulative N 2 O emissions, and a lower global warming potential (CO 2 equivalent of N 2 O and CH 4). We conclude that plant functional traits related to slower decomposition and nitrogen mineralization could play a significant role in mitigating N 2 O emissions in flooded grasslands. Unlabelled Image • Flooding increases N 2 O from managed grasslands • Plant community composition explains flood-induced N 2 O • Festuca arundinacea decreased, and Trifolium repens increased, flood-induced N 2 O • Higher root C:N is related to lower flood-induced N 2 O [ABSTRACT FROM AUTHOR]

Suaeda salsa is a pioneer species in coastal wetlands of East Asia and recently an ecosystem engineer species, Phragmites australis , has started to enter into S. salsa communities owing to either autogenic or external drivers. The consequences of this phenomenon on the ecosystem functions of coastal wetlands are still unclear, especially for decomposition processes. Here we compared the decomposition rate of S. salsa litter, and associated litter chemistry dynamics, between sites with and without P. australis encroachment. We conducted a litter transplantation experiment to tease apart the effects of litter quality and decomposing environment or decomposer community composition. Our results showed that P. australis encroachment led to higher carbon and phosphorus losses of S. salsa litter, but equal losses of total mass, lignin, hemicellulose and nitrogen. Phragmites australis encroachment might affect decomposition rate indirectly by making S. salsa produce litter with higher lignin concentrations or via increasing the fungal diversity for decomposition. Moreover, P. australis as an ecosystem engineer might also alter the allocation of total phosphorus between the plants and the soils in coastal wetlands. Our findings indicate that P. australis could impact aboveground and belowground carbon and nutrient dynamics in coastal wetlands, and highlight the important consequences that encroaching plant species, especially ecosystem engineers, can have on ecosystem functions and services of coastal wetlands, not only in East Asia but probably also elsewhere in the world. Unlabelled Image • Phragmites australis encroachment affected the soil properties of salt marshes. • Phragmites australis encroachment affected the litter qualities of Suaeda salsa. • Decomposition of S. salsa litter was affected by P. australis encroachment. • Salt-marsh ecosystem functions and services could be altered by such an encroachment. [ABSTRACT FROM AUTHOR]

• Long-term N enrichment caused changes in green leaf and litter N, P and C concentrations. • Plasticity in leaf nutrient concentrations induced little variation in litter decomposition in the six species. • N enrichment induced a reduction in leaf trait diversity and community-level litter decomposition. • N-induced dissimilarity of leaf traits could contribute to a reduction of litter decomposition at community level. Anthropogenic activities introduce nitrogen (N) into terrestrial ecosystems, inducing changes in quantity and quality of plants. However, little is known about how do nitrogen (N)-mediated such changes alter functional diversity of green leaf traits? How does N-mediated changes in leaf quality contribute to the rate of litter decomposition at intra- or inter-species level? How can such N-mediated changes in quantity and quality be scaled up to explain and predict community-level litter decomposition? A common garden litter decomposition was conducted in an alpine meadow on the Tibetan Plateau, where six litter species and litter mixtures from the communities that had experienced eight-year N addition treatment, were subjected to decomposition for 641 days, with three harvests. For litter mixtures, littles were selected randomly from aboveground shoots collected from 0.5 × 0.5 m2 quadrats. We found that N enrichment increased green leaf and litter N concentrations, and caused small and idiosyncratic variations in phosphorus and carbon concentrations. Plasticity in leaf nutrient concentrations induced little variation in litter decomposition in the six species. Meanwhile, N enrichment induced a reduction in leaf trait diversity and community-level litter decomposition. Correspondingly, positive relationship between decomposition rate (k) and leaf trait diversity were observed. N enrichment reduced dissimilarity of leaf traits, which could relate a reduction of litter decomposition at community level. By integrating intra- and interspecific trait variation with the abundances of coexisting species, these findings can help predict ecosystem function with N enrichment. [ABSTRACT FROM AUTHOR]

In arid zones, strong solar radiation has important consequences for ecosystem processes. To better understand carbon and nutrient dynamics, it is important to know the contribution of solar radiation to leaf litter decomposition of different arid-zone species. Here we investigated: (1) whether such contribution varies among plant species at given irradiance regime, (2) whether interspecific variation in such contribution correlates with interspecific variation in the decomposition rate under shade; and (3) whether this correlation can be explained by leaf traits. We conducted a factorial experiment to determine the effects of solar radiation and environmental moisture for the mass loss and the decomposition constant k-values of 13 species litters collected in Northern China. The contribution of solar radiation to leaf litter decomposition varied significantly among species. Solar radiation accelerated decomposition in particular in the species that already decompose quickly under shade. Functional traits, notably specific leaf area, might predict the interspecific variation in that contribution. Our results provide the first empirical evidence for how the effect of solar radiation on decomposition varies among multiple species. Thus, the effect of solar radiation on the carbon flux between biosphere and atmosphere may depend on the species composition of the vegetation. [ABSTRACT FROM AUTHOR]