Stoichiometry of soil microbial biomass carbon and microbial biomass nitrogen in China's temperate and alpine grasslands

Abstract

Soil microorganisms play a key role in terrestrial ecological processes, especially in soil organic matter (SOM) formation and nutrient recycling. To perform these essential functions, microbes require mineral nutrients and labile C from the soil solution in amounts that roughly follow the Redfield ratio. However, it remains unclear how soil microorganisms maintain their C:N stoichiometry in grassland ecosystems. Here, we explored the patterns of microbial biomass C (MBC) and N (MBN), along with their controlling factors, using published data on alpine and temperate grasslands across northwestern China (from Inner Mongolia to Tibet). We tested the hypothesis that soil microbial biomass is more sensitive to climate factors than to edaphic factors. The results showed that MBC (670.0 mg kg−1), MBN (78.5 mg kg−1), and the ratio of MBC to MBN (10.9:1) in alpine grasslands were greater than in temperate grasslands (MBC = 317.4 mg kg−1, MBN = 59.9 mg kg−1, MBC:MBN = 6.2:1). Soil MBC in temperate grasslands had a stronger relationship with MBN (y = 0.83x - 0.33, r2 = 0.53, p < 0.01) than in alpine grasslands (y = 0.62x + 0.09, r2 = 0.29, p < 0.01). Climate factors were more sensitive than edaphic factors for MBC and MBN in both grasslands, but climate factors explained only 26% of the variation. These findings demonstrate that climate generally affects microbial C:N stoichiometry more strongly than do edaphic factors in alpine and temperate grasslands. However, some biotic factors could be more influential than climatic factors, necessitating further investigation.