Phosphorus fertilizer input threshold shifts bacterial community structure and soil multifunctionality to maintain dryland wheat production

As an important factor affecting crop yield in agroecosystems, phosphorus (P) fertilizer addition can significantly alter the soil microbial community, functional gene composition, and multifunctionality. However, the major factors that determine wheat grain yield and the changes in wheat yield caused by the P fertilizer input threshold in dryland wheat production have not been adequately characterized. Based on a long-term field experiment (18 years) with five P addition gradients (0, 50, 100, 150, and 200 kg P₂O₅ ha⁻¹ yr⁻¹) in the Loess Plateau of China, amplicon (16 S rRNA) and metagenomic sequencing were used to investigate the effects of long-term P fertilization on soil bacterial communities, rhizosphere microbial functions, soil multifunctionality, and wheat grain yield. Long-term P input significantly affected the compositions and functions of the soil bacterial communities. Conversely, long-term high-P treatment (P200) inhibited soil bacterial diversity and soil P cycling genes but increased carbon (C) cycling genes and soil multifunctionality. Meanwhile, there is a threshold of P fertilizer (71.6−78.1 kg ha⁻¹ yr⁻¹) input for wheat grain yield, beyond which the grain yield of wheat did not significantly increase. In addition, the rhizosphere selection effect significantly increased the complexity of the rhizosphere network and microbial interactions and directed the recruitment of microorganisms and genes with special functions to maintain wheat grain yield. Therefore, this study revealed that the threshold of P fertilizer input can provide a basis for reducing P fertilizer and regulating microorganisms to maintain soil multifunctionality and network complexity in the dryland agriculture system of the Loess Plateau to maintain wheat grain yield.