Changes in the soil bacterial community structure and enzyme activities after intercrop mulch with cover crop for eight years in an orchard

Bacteria are major decomposers of plant residues in soil and play important roles in nutrient cycling. However, in apple orchards, little is known about the responses of soil bacterial communities to intercrop mulch of the cover crop. Thus, two treatments were tested in this study: 1) conventional approach (CT), where no cover crop was planted and natural weeds were controlled every month by a farmer; 2) intercrop-mulch of the cover crop (GC), where the cover crop grew from late March to early July and it was mowed in early July, August, and September, and residues were left on the soil surface as mulch. Intercrop mulch of the cover crop enhanced the total nitrogen (TN), soil organic carbon (SOC), and soil water content (SWC) by approximately 19%, 15%, and 28%, respectively, compared with CT. The activities of β-glucosidase (BG), β-xylosidase (BXYL), and cellobiohydrolase (CBH) were also increased by the intercrop-mulch of the cover crop, where the activities after the GC treatment were 12.3%, 22.0%, and 14.7% higher than CK, respectively. The relative abundances of the phylum Firmicutes, class Clostridia, order Clostridiales, and families Ruminococcaceae and Lachnospiraceae were enhanced greatly by GC. The relative abundances of some genera (relative abundance > 0.05%) in the families Ruminococcaceae and Lachnospiraceae differed significantly under GC and CT (GC > CT, p < 0.05). Some of these genera had positive correlation (p < 0.05) with TN, SOC, BG, BXYL, and CBH. However, PICRUSt and Tax4Fun analyses indicated that the relative abundances of potential genes encoding BG and BXYL were not increased by GC, and the relative abundance of the potential gene encoding CBH was higher in GC according to PICRUSt analysis. We conclude that intercrop mulch with the cover crop can increase the BG, BXYL, CBH activities and the relative abundances of some bacteria which were related to plant biomass degradation.