Seminar: Qing-Fang Bi

Soil microorganisms are central to biogeochemical processes, shaping ecosystem dynamics and stability in response to global change. Despite the remarkable diversity of microbial life in soil, only a fraction is actively growing at any given time. Learning how soil living microbes use carbon or energy in creative ways, is essential for mechanistic comprehension of biogeochemical cycling. Emerging paradigms suggest that microbial carbon use efficiency (CUE) is a key trait controlling the fate of assimilated carbon, theoretically promoting higher biomass and Soil Organic Carbon (SOC) formation under high CUE. However, its dynamic nature often confounds its effect on SOC, leaving CUE as an ambiguous and poorly understood concept. Resolving this ambiguity requires exploring underlying processes like microbial respiration and growth that directly govern SOC loss and accumulation. In this talk, we aim to understand ecosystem-specific microbial physiological strategies driving SOC cycling using a global CUE database and field observations from the three German Biodiversity Exploratories. First, the global-scale findings suggest microbial physiology significantly differs across biomes, with higher estimated maintenance respiration in alpine/boreal forest and polar tundra, resulting in lower CUE at low growth overtime. Second, the regional-scale observations indicate that the quantity of microbial-derived carbon (necromass) in soil depends more strongly on microbial biomass size and total microbial growth rate than on plant carbon input or CUE. Specifically, belowground microbial diversity and physiological traits drive a higher necromass contribution to SOC in forests (complex resources, K-strategists) than in grasslands (labile C source, high turnover). Overall, we found that microbial growth is a more influential factor than CUE when linking microbial contribution to SOC at both global and regional scales. For effective management of soil carbon stocks, enhancing microbial growth is likely more effective than targeting CUE alone.