Ecosystem-dependent microbial respiration and growth strategies with consequences for global soil carbon cycling

The quantitative understanding of microbial physiological roles in microbial-explicit soil organic carbon (SOC) models has been limited by focusing primarily on microbial carbon use efficiency (CUE) in relation to SOC storage. To improve this understanding, it is essential to explore underlying processes such as microbial respiration and growth, which directly impact SOC loss and sequestration. 

Using a global database of CUE measured through ¹⁸O-microbial DNA growth, we found that total microbial respiration and growth rates behave differently across various climate zones and land uses. Respiration and growth rates are the highest in temperate grasslands and boreal forests, while no significant differences are observed for specific rates. Moreover, microbial respiration is found to be more sensitive to environmental constraints than microbial growth, although both are ecosystem-dependent. For example, the contrasting relationships between SOC-CUE and microbial biomas C-CUE in temperate grasslands and tropical forests arise from the interplay of C availability, nitrogen limitation, and microbial growth and respiration dynamics. While temperate grasslands maintain a balance between microbial growth and respiration despite nitrogen limitations, tropical forests experience severe inefficiencies due to higher microbial activity and faster nutrient cycling. These differences underscore the ecosystem-specific nature of microbial respiration, growth, and consequently CUE.