Intercropping increases soil N-targeting enzyme activities: A meta-analysis

Intercropping rationally utilizes land resources and effectively increases soil biodiversity. The enzyme-mediated biological catabolism of soil organic and mineral components is a crucial step in controlling soil carbon and nutrient circulation and fixation in agroecosystems, and those enzymes involved in nitrogen (N) cycling are particularly important. However, when considering different crop combinations, the effects of intercropping on N-targeting enzyme activities remain uncertain. Given such incomplete knowledge of these belowground processes and interactions, we synthesized results for three kinds of N-targeting enzyme activities in response to intercropping based on 117 peer-reviewed papers, in which 454 observations were included. We found that intercropping significantly increased the activity of N-acetyl-glucosaminidase by 26.1%, protease by 10.2%, and urease by 22.2%. Our results suggest that the intercropping effect is mediated by responses of the soil microbes to the diversity of soil nutrients under different crop combinations. Soil N availability and crop competition for nutrients between plant crops mediate patterns of microbial nutrient acquisition strategies and secretion of N-targeting enzymes. Our comprehensive meta-analysis highlights the importance of intercropping for better soil quality and biodiversity and has implications for the role of intercropping in regulating soil carbon dynamics.