Plant size, leaf economics, and their diversity are strong controls of tundra carbon cycling

By Konsta Happonen et al.

Abstract

The functional composition and diversity of plant communities are globally applicable predictors of ecosystem functioning. Yet, it is unclear how traits influence carbon cycling. This is an important question in the tundra where vegetation shifts are occurring across the entire biome, and where soil organic carbon stocks are large and vulnerable to environmental change. To study how traits affect carbon cycling in the tundra, we built a model that explained carbon cycling (above-ground and soil organic carbon stocks, and photosynthetic and respiratory fluxes) with abiotic conditions (air temperature and soil moisture), plant community functional composition (plant size described with average plant height, and leaf economics with leaf dry matter content and specific leaf area), and functional diversity (weighted standard deviations of the traits). The explanatory power of the models was relatively high, but a large part of variation in soil organic carbon stocks remained unexplained. 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 photosynthesis, ecosystem respiration, and soil organic carbon stocks. 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. Synthesis: 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. The importance of functional diversity highlights a potentially important mechanism controlling the vast carbon pools that should be better recognized. More research on root traits and decomposer communities is needed to understand the below-ground mechanisms regulating carbon cycling in the tundra.

This article appeared on the BioRxiv website at https://www.biorxiv.org/content/10.1101/865899v3