The trade-off between growth rate and yield in microbial communities and the consequences for under-snow soil respiration in a high elevation coniferous forest

Abstract

Soil microbial respiration is a critical component of the global carbon cycle, but it is uncertain how properties of microbes affect this process. Previous studies have noted a thermodynamic trade-off between the rate and efficiency of growth in heterotrophic organisms. Growth rate and yield deter- mine the biomass-specific respiration rate of growing microbial populations, but these traits have not previously been used to scale from microbial commu- nities to ecosystems. Here we report seasonal variation in microbial growth kinetics and temperature responses (Q10) in a coniferous forest soil, relate these properties to cultured and uncultured soil microbes, and model the effects of shifting growth kinetics on soil heterotrophic respiration (Rh). Soil microbial communities from under-snow had higher growth rates and lower growth yields than the summer and fall communities from exposed soils, causing higher biomass-specific respiration rates. Growth rate and yield were strongly negatively correlated. Based on experiments using specific growth inhibitors, bacteria had higher growth rates and lower yields than fungi, overall, suggesting a more important role for bacteria in determining Rh. The dominant bacteria from laboratory-incubated soil differed seasonally: faster- growing, cold-adapted Janthinobacterium species dominated in winter and slower-growing, mesophilic Burkholderia and Variovorax species dominated in summer. Modeled Rh was sensitive to microbial kinetics and Q10: a sixfold lower annual Rh resulted from using kinetic parameters from summer versus winter communities. Under the most realistic scenario using seasonally changing communities, the model estimated Rh at 22.67 mol m -2 year -1 , or 47.0% of