Soil extracellular enzymes, soil carbon and nitrogen storage under straw return: A data synthesis

Straw return is an important agricultural practice with the potential to impact soil carbon (C) and nitrogen (N) cycling. Extracellular enzyme activity (EEA) is crucial for soil organic matter degradation. However, it remains unclear how soil EEA respond to straw return or whether these responses can predict changes in soil C and N cycling induced by straw return. By synthesizing 135 field studies worldwide, we showed that straw return significantly increased the activities of C-acquisition (C-acq), N-acquisition (N-acq), phosphorus-acquisition (P-acq), and oxidative-decomposition (OX) enzymes by 26.5 %, 20.3 %, 17.8 %, and 9.1 %, respectively. Notably, we found a significant positive relationship between the logarithmic response ratios (lnR) of the activities of OX and C-acq and soil C, suggesting that changes in combined EEA might serve as indicators of soil C storage under straw return. Interestingly, the changes in EEA due to straw return were unrelated to increases in soil total N (TN). Moreover, the positive effects of straw return on the activities of C-acq and P-acq negatively correlated with the amount of straw applied. Some abiotic factors, such as soil pH and soil C:N ratio, influenced the straw return-induced changes in soil C and N. These findings highlight the importance of considering key abiotic factors in understanding the microbial mediation of soil C and N cycling under straw return. Overall, by analyzing the changes in EEAs, we can gain in-depth mechanistic understandings of how soil carbon and nitrogen transform and cycle, which is crucial for elucidating soil C and N dynamics.