Long-term grazing alters soil resource availability and microbial biomass stoichiometry in grassland ecosystems. Exploring the relationship between soil stoichiometric imbalance and microbial carbon use efficiency (CUE) in grazed desert steppe can help understand soil carbon dynamics from a microbial perspective. Based on a long-term grazing platform in Stipa breviflora desert steppe of Inner Mongolia established in 2004, taking heavy, moderate and light grazing intensities, using no grazing as a control, we measured soil available nutrients, microbial biomass and associated enzyme activities for their acquisition, and calculated soil microbial CUE using ecological stoichiometry. The results showed that grazing inhibited soil microbial CUE by 1.0%-10.3%. Soil C:N imbalance was significantly increased by 20.6% in the moderate grazing treatment, while both C:P imbalance and N:P imba-lance were significantly increased by 20.7% and 25.2% in the heavy grazing treatment, indicating that soil microbial communities were more susceptible to N and P limitation. Soil microbial communities maintained their stoichiometric balance by regulating the threshold of elemental stoichiometry ratios and the production of extracellular enzymes. Structural equation modelling (SEM) results indicated that stoichiometric imbalance indirectly affected microbial CUE by altering the threshold of elemental stoichiometry ratios, microbial biomass stoichiometry, and enzyme stoichiometry.
长期放牧改变了草地生态系统的土壤资源可利用性和微生物生物量化学计量。研究放牧荒漠草原土壤化学计量不平衡与微生物碳利用效率(CUE)的关系,有助于从微生物视角理解土壤碳动态。本研究依托2004年建立的内蒙古短花针茅荒漠草原长期放牧实验平台,以围封禁牧为对照,设置重度、中度和轻度放牧处理,测定了土壤有效养分、微生物生物量及其获取的相关酶活性,并利用生态化学计量法对土壤微生物CUE进行计算。结果表明: 与对照相比,放牧抑制了土壤微生物CUE,降幅为1.0%～10.3%;土壤C∶N不平衡在中度放牧处理下显著增加20.6%,C∶P不平衡和N∶P不平衡在重度放牧处理分别显著增加20.7%和25.2%,这表明土壤微生物群落更容易受N、P限制。土壤微生物群落通过调节元素阈值计量比和胞外酶的产生来维持自身化学计量平衡。结构方程模型结果表明,化学计量不平衡通过改变元素阈值计量比、微生物生物量化学计量和酶化学计量间接影响微生物CUE。.
Keywords: extracellular enzymatic activity; grazing intensity; microbial carbon use efficiency; stoichiometric imbalance.