Soil resources and climate jointly drive variations in microbial biomass carbon and nitrogen in China's forest ecosystems.

Microbial metabolism plays a key role in regulating the biogeochemical cycle of forest ecosystems, but the mechanisms driving microbial growth are not well understood. Here, we synthesized 689 measurements on soil microbial biomass carbon (C_mic) and nitrogen (N_mic) and related parameters from 207 independent studies published during the past 15 years across China's forest ecosystems. Our objectives were to (1) examine patterns in C_mic, N_mic, and microbial quotient (i.e., C_mic /C_soil and N_mic =N_soil rates) by climate zones and management regimes for these forests; and (2) identify the factors driving the variability in the C_mic, N_mic, and microbial quotient. There was a large variability in C_mic (390.2mg kg^-1), N_mic (60.1mg kg^-1), C_mic :N_mic ratio (8.25), C_mic =C_soil rate (1.92%), and N_mic =N_soil rate (3.43%) across China's forests, with coeffcients of variation varying from 61.2 to 95.6%. The natural forests had significantly greater C_mic and N_mic than the planted forests, but had less C_mic :N_mic ratio and C_mic =C_soil rate. Soil resources and climate together explained 24.4-40.7% of these variations. The C_mic :N_mic ratio declined slightly with the C_soil :N_soil ratio, and changed with latitude, mean annual temperature and precipitation, suggesting a plastic homeostasis of microbial carbon-nitrogen stoichiometry. The C_mic =C_soil and N_mic =N_soil rates were responsive to soil resources and climate differently, suggesting that soil microbial assimilation of carbon and nitrogen be regulated by different mechanisms. We conclude that soil resources and climate jointly drive microbial growth and metabolism, and also emphasize the necessity of appropriate procedures for data compilation and standardization in cross-study syntheses. [ABSTRACT FROM AUTHOR]