Community‐level plant functional strategies explain ecosystem carbon storage across a tropical elevational gradient

Plant functional traits play an important role in shaping plant ecological responses to environmental conditions and influencing ecosystem functioning. However, how whole-plant functional strategies manifest at the community level to influence aboveground and below-ground carbon storage across environmental gradients remains poorly understood. We measured above-ground and below-ground carbon stocks and the variation in whole-plant (above- and below-ground) functional strategies at the community level in twelve ecosystem types across a broad savanna–forest–alpine elevational gradient of climate and land use on Mt. Kilimanjaro, Tanzania. Using Structural Equation Models, we disentangled the direct and land-use-mediated influences of climate on carbon storage from indirect influences mediated by variation in plant functional strategies. We found strong coordination between above- and below-ground functional traits at the whole community level, which corresponded with functional strategies related to two major trade-offs: a slow-conservation to fast resource-acquisition axis represented by a spectrum from high leaf dry matter content to high fine root nitrogen concentration; and a size-related woody to grassy community axis represented by a spectrum spanning high canopy height to high specific root length. The slow-fast and woody-grassy strategy axes were primarily driven by precipitation and land-use intensity, respectively. Both functional strategies mediated the effects of climate on carbon storage. The slow-fast strategy axis was strongly and positively associated with above-ground carbon stocks. Meanwhile, the woody-grassy strategy axis was negatively associated with both above-ground carbon stocks and soil organic carbon stocks. Synthesis. We demonstrate that major plant functional strategies manifest at the community level along elevational gradients. These strategies also explain variation in carbon storage, although above-ground storage is mostly driven by trait effects, and below-ground storage by direct effects of climate. Together, these results underscore the importance of incorporating community functional trait data into future analysis of climate change impacts on carbon storage, which would enhance our ability to predict shifts in ecosystem functioning.