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Summary 1.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. 2.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.3. 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 belowground 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.

Predicting climate change impact on ecosystem structure and services is one of the most important challenges in ecology. Until now, plant species response to climate change has been described at the level of fixed plant functional types, an approach limited by its inflexibility as there is much interspecific functional variation within plant functional types. Considering a plant species as a set of functional traits greatly increases our possibilities for analysis of ecosystem functioning and carbon and nutrient fluxes associated therewith. Moreover, recently assembled large-scale databases hold comprehensive per-species data on plant functional traits, allowing a detailed functional description of many plant communities on Earth. Here, we show that plant functional traits can be used as predictors of vegetation response to climate warming, accounting in our test ecosystem (the species-rich alpine belt of Caucasus mountains, Russia) for 59% of variability in the per-species abundance relation to temperature. In this mountain belt, traits that promote conservative leaf water economy (higher leaf mass per area, thicker leaves) and large investments in belowground reserves to support next year's shoot buds (root carbon content) were the best predictors of the species increase in abundance along with temperature increase. This finding demonstrates that plant functional traits constitute a highly useful concept for forecasting changes in plant communities, and their associated ecosystem services, in response to climate change.alpine plant community | root traits | plant traits | seed mass | specific leaf area C limate change is affecting the structure and composition of vegetation worldwide. Increasing temperatures are considered to be a key driver of recent tundra greening (1, 2) and upward migration of vascular plant species in mountains (3-6). Predicting climate change impact on ecosystem structure and services is one of the most important challenges in ecology (7). Previous studies of plant response to warming used concepts of growth form or functional type as predictors of plant response to warming and demonstrated that evergreen and deciduous (dwarf) shrubs and rushes increase their abundance in response to experimental warming in cold biomes (1, 8). However, the categorization of plants into fixed functional types has been criticized for being imprecise and too coarse for accurate prediction of plant response to climate change (9).Considering a plant species as a set of functional traits instead of an entity belonging to a fixed functional type greatly increases our possibilities for analysis of ecosystem functioning (10), enabling generalization of our knowledge on plant functioning at ecosystem, landscape, or regional scale. When linked to directional changes in the abundance of plant species, variation in traits involved in plant effects on biogeochemical cycling can be applied in estimates of changes in ecosystem carbon and nutrient turnover (9). This provides a powerful tool in environmental assessment an...

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 À3 ) of watersaturated and oven-dried patches, evaporation rate (g Á m À2 Á s À1 ) 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 climateinduced shifts in species abundance, and feedbacks of such species shifts on permafrost insulation and carbon sequestration functions.