Long-term straw and plastic film mulching have divergent effects on maize rhizosphere enzyme activity and bacterial community structure

Mulching is widely adopted in arid regions to improve soil environment and crop productivity. However, our understanding of the underlying mechanisms of such improvements from enzyme activity and rhizosphere microbial community structure perspectives remain poor. To fill the gap, soil zymography was coupled with highthroughput sequencing to investigate enzyme activities and bacterial community structure in a 10-year field experiment in a semi-arid region. We examined the effects of two mulching measures (plastic film mulching [FM] and straw mulching [SM], with no mulching as the control [CK]) on the maize rhizosphere extent of beta-glucosidase and leucine aminopeptidase activities and the abundance of the bacterial genes encoding these two enzymes. The enzyme activity in the SM and FM measures was higher compared to the CK measures (P < 0.05). SM had higher influence than FM on beta-glucosidase activity and its rhizosphere extent. This was related to the increase in soil organic carbon (SOC) content and the stable bacterial community structure and interactions under SM. In contrast, leucine aminopeptidase activity was the highest under FM due to the higher soil temperature and moisture content under FM which further intensified nutrient competition among microorganisms or between microorganisms and plants. In addition, Proteobacteria and Acidobacteria were the major contributors to beta-glucosidase activity despite their genes encoding beta-glucosidase not increasing under SM. Conversely, the copy number of genes encoding leucine aminopeptidase and the genes encoded by Proteobacteria (the main contributor) decreased under FM. Therefore, total gene number is not a stable indicator of microbial function (such as enzyme activity) and cannot explain enzyme activity adequately. Overall, this study establishes a connection between rhizosphere enzyme activity and bacterial communities, revealing the mechanisms by which changes in environmental nutrient supply and bacterial community composition under straw mulching and plastic film mulching measures lead to variations in enzyme efficiency.