Dominant plant species alter stoichiometric imbalances between soil microbes and their resources in an alpine grassland: Implications for soil microbial respiration

Soil microbes are subject to stoichiometric imbalances, which are the dissimilarities in elemental stoichiometry between microbial biomass and resources. Shifts in dominant plant species co-occur with unparallel changes in the stoichiometry of soil microbial biomass and resources, leading to stoichiometric imbalances. However, how soil microbes deal with stoichiometric imbalances induced by changes in dominant plant species, and what the implications are for soil carbon cycling, remain unknown. Here, we compared the stoichiometric imbalances of five plant patch types with the dominant plant community (Kobresia pygmaea) in a Tibetan alpine grassland to examine how soil microbes respond physiologically to stoichiometric imbalances, thereby affecting soil microbial respiration (SMR). We found that C:N and C:P imbalances varied between plant patches and differed significantly from those in the soil of K. pygmaea. We also found that the regulation of extracellular enzyme production, SMR, potential microbial carbon use efficiency (CUE), net N mineralization, and net ammonification were essential mechanisms for soil microbes to deal with C:N imbalances. Simultaneously, soil microbes dealt with fluctuating C:P imbalances by regulating their net P mineralization and CUE. Further, structural equation modeling revealed that stoichiometric imbalances induced by changes in dominant plant species could indirectly affect SMR by regulating extracellular enzyme stoichiometry and net nutrient mineralization. These results highlight the importance of the stoichiometry of soil microbe/resource interactions in regulating metabolic activities and modifying terrestrial carbon flows in shifting plant communities.