Soil extracellular enzyme activity linkage with soil organic carbon under conservation tillage: A global meta-analysis

Conservation tillage has a profound impact on soil organic carbon (SOC) and extracellular enzyme activity (EEA), thereby influencing the global soil nutrient cycle. However, there is currently a lack of comprehensive understanding regarding the key factors influencing changes in SOC and EEA, as well as their correlations. To address this gap, a meta-analysis was conducted using data from 78 published papers, encompassing 2005 comparisons from around the world. The goal was to quantify the effects of conservation tillage on SOC and EEA while assessing the effect sizes of categorical variables. The meta-analysis results revealed that conservation tillage significantly increased SOC and carbon (C)-, nitrogen (N)-, phosphorus (P)-, and sulfur (S)-related enzyme activities, with effect sizes of 1.34, 1.57, 1.50, 1.06, and 1.81, respectively. Additionally, conservation tillage resulted in a decrease in soil pH compared to conventional tillage. Furthermore, significant correlations were found between changes in SOC and N-, P-, and S-related enzyme activities. However, only β-glucosidase (βG) and β-xylosidase (βX) in C-related enzyme activities were found to be relevant to SOC. Moreover, the results from the structural equation model indicated that several factors directly influenced the EEA of C-, N-, P-, and S-related enzymes. Climatic factors such as latitude and mean annual temperature (MAT), agronomic practices (including fertilization and tillage duration), and soil properties (such as soil depth), were identified as having direct effects on the EEA of the respective enzymes. From a global perspective, conservation tillage was observed to enhance the potential activity of C-related enzymes, while the balanced activity of N-, P-, and S-related enzymes requires greater attention. Additionally, latitude, MAT, fertilization, tillage duration, and soil depth emerged as important aspects requiring careful consideration in the development of management strategies for conservation tillage.