Aeration increases soil bacterial diversity and nutrient transformation under mulching-induced hypoxic conditions.

Soil oxygen (O2) deficiency induced by organic mulching is easy to overlook. Aeration has been shown to potentially alleviate soil hypoxia stress. However, the responses of soil bacterial communities to such mulching-induced hypoxic conditions and aeration remain elusive. Therefore, a three-year field experiment, consisting of mulching (T1), mulching with aeration (TA1, poor aeration; TA2, strong aeration), and no-mulching (CK) treatments, was conducted in bamboo (Phyllostachys praecox) plantations. According to our results, the strong aeration treatment (TA2) alleviated soil acidification, increased soil nutrient availability, and significantly increased soil O2 content by 18.44% (P < 0.05) when compared with T1. In addition, TA2 significantly increased soil β-glucosidase, invertase, urease, and acid phosphatase activities compared with CK and T1 (P < 0.05). The alpha diversity indices with TA2 treatment were the highest, indicating that aeration increased the species richness and diversity of bacteria. The changes in bacterial community composition associated with TA2 treatment (i.e., an increase in Firmicutes, Verrucomicrobia, and Faecalibacterium abundance and a decrease in Chloroflexi and Bradyrhizobium abundance) were mainly related to nutrient and O2 content. Mantel Test results suggested that soil O2 content and temperature were the key factors shaping bacterial community composition. Structural equation modeling revealed that soil O2 content had a positive and direct influence on bacterial community diversity. Functional annotation of prokaryotic taxa predicted that TA2 significantly increased the relative abundance of bacterial communities associated with nitrification, nitrogen fixation, and ureolysis. Our results demonstrated that optimal soil aeration conditions (17.60% of O2 content) could enhance the diversity and function of soil bacterial communities. Overall, the findings of this study could serve as a benchmark for alleviating soil hypoxia caused by organic mulches, which is important for increasing the functionality of nutrient cycling bacterial communities in the soil.