Metabolic tradeoffs and heterogeneity in microbial responses to temperature determine the fate of litter carbon in a warmer world

Abstract

Climate change has the potential to destabilize the Earth’s massive terrestrial carbon (C) stocks, but the degree to which models project this destabilization to occur depends on the kinds and complexities of microbial processes they simulate. Of particular note is carbon use efficiency (CUE), which determines the fraction of C processed by microbes that is anabolized into microbial biomass rather than being lost to the atmosphere as carbon dioxide. The temperature sensitivity of CUE is often modeled as a homogeneous property of the community, which contrasts with empirical data and has unknown impacts on projected changes to the soil carbon cycle under global warming. We used the DEMENT model – which simulates taxon-level litter decomposition dynamics – to explore the effects of introducing organism-level heterogeneity into the CUE response to temperature for decomposition of leaf litter under 5 °C of warming. We found that allowing CUE temperature response to differ between taxa facilitated increased loss of litter C, unless fungal taxa were specifically restricted to decreasing CUE with temperature. Increased loss of litter C was observed when the growth of a larger microbial biomass pool was fueled by higher community-level average CUE at higher temperature in the heterogeneous microbial community, with effectively lower costs for extracellular enzyme production. Together these results implicate a role for diversity of taxon-level CUE responses in driving the fate of litter C in a warmer world.