Shelter for microbes? Quantitative insights into soil microbial communities in shelterbelt agroforestry systems

Shelterbelts are planted at the edges of agricultural fields primarily to reduce wind speeds and thereby protecting soil from wind erosion and improving microclimatic conditions. However, shelterbelts can also enhance other beneficial ecosystem functions, including natural pest control, carbon sequestration, and water regulation. Despite their effectiveness in soil protection, little is known on the impacts of shelterbelts on soil microorganisms. Here, we quantified bacteria, fungi, archaea, and 14 functional genes involved in C, N, and P cycling at ten shelterbelts and their adjacent organically farmed croplands. Soil sampling was conducted within the shelterbelts as well as at five distances from the trees into the croplands at two sampling depths: 0–5 and 0–30 cm topsoil. Overall microbial abundance was greater at 0–5 than at 0–30 cm sampling depth, likely reflecting greater availability of resources in the surface soil. Compared to croplands, shelterbelts promoted the abundance of bacteria and fungi but not archaea, whereas fungi benefited more than bacteria. Furthermore, most functional genes showed greater abundance in the shelterbelts than in the croplands at 0–5 cm. However, the promotion of microorganisms by the shelterbelts did not gradually extend into the adjacent croplands and differences between shelterbelts and sampling positions in the croplands were more frequently detected at 0–5 than at 0–30 cm. Therefore, differences in soil sampling depth may explain discrepancies among agroforestry studies. In summary, our study reveals that shelterbelts promote microorganisms and that even within topsoil, sampling depth matters.