Long-term straw substitution for chemical fertilizers promotes an increase in phosphorus availability in greenhouse soils by modulating the microbial community structure

Long-term excessive fertilizer application degrades soil quality and disrupts phosphorus (P) cycling and availability in greenhouse agroecosystems. On the basis of a 14-year field experiment, we evaluated the effects of different maize straw substitution ratios for fertilizer nitrogen (N), which were calculated on an equivalent pure N basis, on soil physicochemical properties, inorganic phosphorus fractions, enzyme activities, microbial biomass, and bacterial community structure. Compared with 100% chemical fertilizer input (100CF), partial or complete substitution of mineral fertilizer N with maize straw–derived N (25S, 50S, and 100S, representing 25%, 50%, and 100% replacement, respectively) significantly increased the soil pH, total carbon (TC), total nitrogen, available phosphorus, and phosphorus activation coefficient but decreased the total phosphorus and stable phosphorus fractions (Ca 10 -P and O-P). Notably, 50S strongly promoted Ca 2 -P accumulation. Straw substitution also increased phosphatase activity, microbial biomass carbon and phosphorus, and the microbial C:P ratio, thus increasing phosphorus transformation and release. High-throughput sequencing revealed that straw substitution markedly altered the bacterial community structure, increasing the relative abundance of Acidobacteriota and Actinomycetota while decreasing that of Bacillota. The highest bacterial α-diversity was observed under 25S, whereas the diversity decreased with further increases in substitution rates. Network analysis revealed OTU19 (Pseudomonadota) and OTU127 (Bacillota) as key nodes within microbial co-occurrence networks. Redundancy analysis further indicated that soil pH, TC, and Ca 2 -P were the key environmental factors associated with bacterial community composition. Overall, the partial substitution of chemical fertilizer with maize straw–derived N improved the characteristics of the soil phosphorus fraction, increased phosphorus availability, increased microbial activity, and reshaped the bacterial community structure. These findings provide strong evidence to support the sustainable management of greenhouse agroecosystems. • Long-term trials show straw substitution improves soil nutrients and P availability. • Straw substitution stimulates microbes, enhancing phosphatase activity and P turnover. • Straw substitution improves bacterial diversity, peaking at 25%. • Soil pH, total carbon, and Ca 2 -P are strongly correlated with bacterial community structure.