Are there links between nutrient inputs and the response of microbial carbon use efficiency or soil organic carbon? A meta-analysis

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Microbial carbon (C) use efficiency (CUE) is a comprehensive parameter to measure the accumulation and loss of soil C caused by microbial growth and respiration, which is considered to determine the fate of soil organic C (SOC). Microbial CUE is sensitive to the changes in soil nutrients, such as nitrogen (N) and phosphorus, making it crucial to assess the response of microbial CUE to nutrient inputs caused by climate change and human activities, as well as its contribution to SOC accumulation. Here, we curated a dataset from 58 studies (389 paired observations) to examine the effects of nutrient inputs on global soil microbial CUE and the relationship between microbial CUE and SOC. The meta-analysis showed that nutrient inputs increased soil microbial CUE by 11.5%. The response of microbial CUE to nutrient inputs varied among different treatments (i.e., nutrient form, application rates in N, and experiment duration), ecosystems, and climatic factors. The variable response of microbial CUE to nutrient inputs was mainly affected by the changes of soil N availability and C-, N-related hydrolase activity, showing significant positive and negative relationships, respectively. There was no significant statistic correlation between microbial CUE and SOC under the condition of nutrient inputs. While a significant positive correlation was observed between microbial CUE and SOC under both inorganic and short-term nutrient inputs. The present study sheds light on a comprehensive understanding of microbial CUE in the global range of nutrient inputs, and highlights the need for more studies paying more attention to the role of microbial CUE in SOC sequestration.