Soil multifunctionality improved by functional bacterial community in a poultry-farming agroforestry ecosystem

Soil quality plays critical roles in supporting the sustainable development of agriculture and forestry. In agroforestry ecosystems, soil multifunctionality refers to soil quality and further affects forest management practices. However, it still remains obscure how soil microbial communities and their functional genes affect soil multifunctionality. This study quantitatively evaluated the soil multifunctionality in a poultry-farming agroforestry ecosystem to reveal its relation to functional bacterial community. At seven years after a three-year experiment of poultry farming, soil samples were collected from poplar plantation (Populus × euramericana 'Neva') across three soil layers (topsoil: 0-30 cm, middle: 30-60 cm, deepsoil: 60-90 cm). Further, soil properties, soil bacterial community composition and structure, bacterial functional genes related to nitrogen and phosphorus cycling were fully examined. The results showed that soil multifunctionality was significantly increased in poultry-farming plantation of poplar, with notable improvements observed in the topsoil and deepsoil. Soil microbial diversity in the poultry farming plots was significantly higher than in the non-poultry farming plots, and diversity indices showed positive correlations with soil multifunctionality. Meanwhile, in the poultry farming plots, bacterial community transitioned from oligotrophic (e.g., Acidobacteria, Chloroflexi) to copiotrophic taxa (e.g., Actinobacteria, Proteobacteria). Additionally, bacterial functional genes related to nitrification (e.g., amoA2) and organic phosphorus mineralization (e.g., CPhy) were significantly enriched in the topsoil. Some specific microbial taxa (e.g., Gaiella) were indicated to play crucial roles in driving soil nitrogen and phosphorus cycling, and soil multifunctionality was significantly regulated by these key functional microbial taxa. The study revealed deeper microbial mechanisms improving soil productivity in a poultry-farming agroforestry ecosystem, proposing a possible countermeasure for sustainable management of the plantation forest.