Mulching practices alter soil microbial functional diversity and benefit to soil quality in orchards on the Loess Plateau

To improve our understanding about the responses of microbial functional diversity to different mulching practices, this study used a metagenomic approach to reveal soil microbial functional specificity under four tillage regimes: conventional tillage (CT), organic mulch practices with ryegrass (Lolium perenne L.) intercropping cover (RE) and cornstalk mulch (CS), and inorganic mulching with black ground fabric (BF) in a 7-year field experiment in an apple orchard of the Loess Plateau in China. Enzyme activity and soil physicochemical properties were measured. A redundancy analysis showed that the RE and CS treatments had positive effects on soil nutrient and enzyme activity compared to that of the BF and CT treatments. The CS and RE treatments increased β-glucosidase, cellobiohydrolase, and β-xylosidase activities. In addition, the CS treatment significantly enhanced the β-N-acetylglucosaminidase and urease activities compared to that under CT treatment. However, the activity of these enzyme was reduced in the BF treatment compared with that of the CT treatment. The results also indicated that the enzymes activities were not completely consistent with the changing trends of the genes encoding these enzymes. In addition, the RE and CS treatments also increased the abundance of genes encoding carbohydrate enzymes. It is interesting that the RE and CS treatments had more pathway genes associated with the carbon cycle, nitrogen cycle, and amino acid metabolism compared with the BF treatment. Remarkably, RE and CS treatments effectively increased the abundance of carbon fixation gene cbbL compared to CT treatment. In summary, organic mulching practices increased the soil microbiological functional diversity related to the carbon and nitrogen cycle, while inorganic mulching practice reduced them. This study enhanced our understanding of how mulching practices may alter soil microbial functional diversity and benefit soil quality.