Red clover intercropping of apple orchards improves soil microbial community functional diversity

Abstract

This study investigated the effects of forage species and sampling depths on microbial community functional diversity in soil collected between rows of apple trees. Apple orchard soils' intercropping of three different forage species, including native wild grasses, red clover (RC), ryegrass, and clean tillage (CT) at varying depths (0–10, 10–20, and 20–30 cm), was analyzed using Biolog Eco-PlateTM. The average well color development (AWCD) in samples subject to ELISA indicated that the carbon metabolic capacities of the microbial community in RC soil were greater than those in the remaining three soil treatments, with no significant (P>0.05) differences among the three depths. Diversity and richness indices of the bulk soil samples (except the RC) declined significantly with depth, while the evenness indices of most soil samples only demonstrated a slight change. The diversity and richness indices of the CT of 0–10-cm soil sample were markedly higher than those of 10–20-cm and 20–30-cm soil samples, especially when compared with the remaining three soil treatments. Principal component (PC) analysis showed that the CT soil at 10–20 and 20–30 cm was oriented in the axis-positive direction of the PC2 axis, but was oriented in the axis-negative direction at 0–10 cm. Therefore, we surmise that there exists an extensive microbial diversity among the soil samples. In summary, our results show that planting RC improved microbial community functional diversity to a greater extent than did the other forage species and CT at all the three measured soil depths, except for CT at a 0–10 cm soil depth.