Poplar agroforestry systems in eastern China enhance the spatiotemporal stability of soil microbial community structure and metabolism

Agroforestry systems provide soil microorganisms with a rich variety of carbon sources and a relatively stable living environment. However, the effects of agroforestry systems on the metabolic dynamics of soil microorganisms have not been well studied, especially in the subsoil. To assess the vertical and seasonal variations in soil microbial metabolic capacity as a consequence of various planting systems, five typical planting systems, including three poplar agroforestry systems, were investigated. The Biolog EcoPlate method was used to determine the vertical and seasonal variations in soil microbial metabolic capacity. The average well colour development, carbon source utilization ability, and microbial diversity index values were higher throughout the soil profile, and highly stable with seasonal changes in the poplar (Populus x euramericana "Nanlin 895") + wheat (Triticum aestivum L.) + soybean (Glycine max) and poplar + potherb mustard (Brassica juncea var. multiceps) agroforestry systems. Furthermore, the influence of the planting systems and seasonal changes on the metabolic activity of soil microorganisms decreased with an increase in soil depth. Over-stocking chickens in the forest reduced the metabolic activity of soil microorganisms. It was also found that plants influenced soil microbial metabolism through affecting the available carbon source types. Therefore, agroforestry systems improved the metabolic potential of the soil microbial community. Our results demonstrated that soil microbial communities are affected by the planting system and soil depth. The findings enhance our understanding of the functional diversity of soil microorganisms in agroforestry systems.