Unraveling Microbial Carbon Use Efficiency in Global Grassland Ecosystems: Integrating Ecoenzymatic Stoichiometry and Microbial Nutrient Limitation

Abstract

Grassland ecosystems serve as vital terrestrial carbon reservoirs , with microbial decomposers playing a pivotal role in soil carbon cycling. However, there is a notable dearth of studies investigating the relationship between microbial carbon use efficiency (CUE) and metabolic constraints within grassland ecosystems. This study aimed to characterize microbial CUE and nutrient limitations in such ecosystems and uncover their driving factors. To bridge this knowledge gap, data from 59 study sites (comprising 298 soil samples), encompassing 80 alpine meadows, 66 desert grasslands, 37 grassland deserts, and 115 typical grasslands, were collected and analyzed. Microbial CUEs were estimated using a biogeochemical equilibrium model, while ecoenzymatic stoichiometry and microbial nutrient limitation were used to evaluate metabolic constraints on microbial growth, investigating the relationship between soil stoichiometric ratios and CUE. The results of the study revealed that the mean CUEs of alpine meadows, desert grasslands, grassland deserts, and typical grassland ecosystems, estimated through modeling approaches, were 0.41, 0.33, 0.28, and 0.42, respectively. All four types of grasslands were significantly carbon-limited, with steppe deserts exhibiting the most pronounced carbon limitation. Correlation analysis indicated that grassland microorganisms exhibited better capacity to absorb and utilize soil nitrogen, while grassland ecosystems were more susceptible to phosphorus limitation. Mean annual temperature emerged as a significant climatic factor influencing CUEs in grassland ecosystems. Moreover, soil pH consistently and significantly positively correlated with CUEs. The integration of stoichiometric and metabolic models offers a quantitative depiction of the functional organization of soil microbial communities, enhancing the representation of CUE in microbial process and ecosystem simulation models. This research elucidates a conceptual framework of microbial CUEs in grassland ecosystems and furnishes theoretical evidence to enhance soil microbial carbon sequestration capacity in response to global change.

Keywords: carbon use efficiency, ecoenzymatic activity, Ecological stoichiometry, Meta-analysis, grassland ecosystems