Microbial functional groups activate insoluble rhizosphere phosphorus to mitigate P limitation of Chinese fir...

The decline in soil phosphorus (P) reserves and its low solubility pose significant challenges in long-term plantation cultivation. In P-limited subtropical environments, the rhizosphere microbial community and associated genes play a crucial role in driving P cycling and availability during the long-term development of forest plantations. Using the space-for-time substitution method, we investigated rhizosphere P cycling in Chinese fir (Cunninghamia lanceolata) plantations at different growth stages in Fujian Province, southern China. We utilized the modified Hedley fractionation method and metagenomic sequencing for rhizosphere soil samples from stand ages of 6, 26, 45, and 102 years. The results revealed that, with stand development, rhizospheric concentrations of total, stable and moderately labile P decreased significantly, whereas labile P became progressively enriched (P < 0.05). Genes involved in organic P mineralization and P transport were positively correlated with labile P concentrations in the rhizosphere (P < 0.05), whereas P metabolism regulatory genes were negatively correlated with moderately labile P (P < 0.05). Additionally, the dominant P-solubilizing bacteria-Bacteroidetes and Rudaea-exerted significant positive effects on labile P and negative effects on stable P, respectively (P < 0.05). Overall, rhizospheric P reserves were significantly depleted in the Chinese fir plantations during their developmental progression. However, this unsustainable trend in P reserves was mitigated through synergistic interactions between P-solubilizing bacteria and P metabolism genes, which catalyzed the conversion of insoluble P into labile P, while enhancing plant P uptake efficiency. Consequently, we propose science-informed management practices-such as optimizing P fertilization management, inoculating P-solubilizing microbial agents, utilizing organic fertilizers, and introducing native broadleaf species-to sustain functional stability and long-term productivity of subtropical plantation ecosystems.