Plant community functional composition and diversity drive fine-scale variability in carbon cycling in the tundra
AbstractThe functional composition and diversity of plant communities are globally applicable predictors of ecosystem functioning. However, exactly how traits influence carbon cycling is yet unclear, as are the implications in a warming world.To study how traits affect carbon cycling in the tundra environment, we built a hierarchical model that included abiotic conditions (summer air and winter soil temperatures, and soil resources), plant community functional composition and diversity (plant size and leaf economics), and carbon cycling (above-ground and soil organic carbon stocks, and photosynthetic and respiratory fluxes). We also simulated warming effects on peak-season ecosystem CO2 budget.Plant size was the strongest predictor of all carbon cycling variables except soil carbon stocks. Communities of larger plants were associated with larger CO2 fluxes and above-ground carbon stocks. Communities with fast leaf economics had higher rates of photosynthesis and soil respiration, but lower above-ground biomass.Diversities on axes of size and leaf economics affected ecosystem functions differently. Leaf economic diversity increased CO2 fluxes and soil organic carbon stocks, while size diversity increased the above-ground carbon stock. The contributions of functional diversity metrics to ecosystem functioning were about as important as average leaf economic traits.Simulations suggested that warmer summer air temperatures increase plant size, while warmer winter soil temperatures increase plant size and accelerate leaf economics. All these changes would enhance CO2 uptake during peak growing season.Synthesis: We show how traits mediate the link between abiotic conditions and carbon cycling. Community composition and diversity on the two axes of the global spectrum of plant form and function have clear and separate effects on ecosystem functioning. Warmer temperatures increase plant size and accelerate leaf economics, which leads to faster net assimilation of carbon during peak growing season. More research on soil carbon stocks is needed.