Effects of living mulches on the soil nutrient contents, enzyme activities, and bacterial community diversities of apple orchard soils

Living mulches are used widely for soil management in apple orchards on the Loess Plateau of China. However, little information is available on the impact of living mulches on the soil enzyme activities and the soil micro-ecological environment. We compared three commonly used living mulch treatments: living mulch with white clover (Trifolium repens L.), living mulch with crown vetch (Coronilla varia L.), living mulch with perennial ryegrass (Lolium perenne L.) and a no mulch treatment, and analyzed their effects on the soil nutrient contents, enzyme activities, and bacterial community function, structure and diversity. Total organic carbon (TOC) in the soil under the living mulch treatments was 16–44% greater than with no mulch, while total nitrogen (TN) under white clover and crown vetch was 50% greater than with no mulch. TN under perennial ryegrass was not significantly different from the no mulch treatment. The white clover and crown vetch significantly improved the soil invertase, urease, and alkaline phosphatase activity levels, whereas the perennial ryegrass only improved the soil alkaline phosphatase activity. All living mulches significantly increased the soil bacterial carbon metabolic activity and the bacterial community diversity. Principal component analysis (PCA) of the Biolog and terminal restriction fragment length polymorphism (T-RFLP) showed that living mulch significantly altered the soil bacterial community structure and function, and different types of living mulch have various impacts on that. Our results indicate that the living mulch application benefits the development of soil micro-ecology and soil quality, and the long-term influences of living mulch on soil biological status should be considered when selecting the types of living mulch to be used. According to this study, living mulch with crown vetch is recommended in apple orchards on the Loess plateau.