Plants and microorganisms have developed mechanisms to acquire soil phosphorus (P). The present study occurred in Chinese fir plantations with five planting densities (1667, 3333, 5000, 6667, and 10,000 stems∙ha⁻¹) at age 5 and 35 in acidic soils. We aim to (1) assess the inorganic (Pi) and organic (Po) forms of P and the labile P (including resin-Pi (AER-Pi), NaHCO₃-Pi, and NaHCO₃-Po), moderately labile P (including NaOH-Pi, NaOH-Po, and HCl-Pi), and residual P in soils; (2) to evaluate phosphatase activity and the abundance of phoC and phoD genes; and (3) to identify the correlations among P fractions, phosphatase activity, and the abundance of phoC and phoD genes. The results showed that the total Pi, AER-Pi, and NaHCO₃-Pi were higher in low densities (≦ 3333 stems∙ha⁻¹) than high densities (≧ 5000 stems∙ha⁻¹) at age both 5 and 35, but the NaOH-Po and NaHCO₃-Po were the opposite at age 35 only. Moreover, the NaOH-Pi content was higher in low densities than high densities at age 35 only. The phosphatase activity and the abundance of phoC and phoD genes were higher in high densities than low densities at age 5, whereas the opposite was true for age 35. Therefore, the decrease in planting density was expected to increase soil P bioavailability in acidic soils with the development of plantations from 5 to 35 years. The result of unary linear regression showed that phosphatase activity was positively correlated with the abundance of phoC and phoD genes in 35-year-old plantations and with the abundance of phoC gene in 5-year-old plantations. In 35-year-old plantations, the phosphatase activity and the abundance of phoC and phoD genes were positively correlated with NaHCO₃-Pi and NaOH-Pi, but significantly negatively correlated with NaHCO₃-Po and NaOH-Po. These findings together demonstrate that P bioavailability and fractions, phosphatase activity, and the abundance of phoC and phoD genes varied with planting density in acidic soils, with potential implications for subtropical and tropical biogeochemical processes and for understanding how microbial metabolism regulates P biotransformation.

植物和微生物已开发出获取土壤磷（P）的机制。本研究发生在5岁和35岁的酸性土壤中的五种密度（1667、3333、5000、6667和10,000茎∙ha ^-1）的杉木人工林中。我们旨在（1）评估P和不稳定P（包括树脂-Pi （AER-Pi），NaHCO ₃ -Pi和NaHCO ₃ -Po），中度不稳定P的无机（Pi）和有机（Po）形式（包括NaOH-Pi，NaOH-Po和HCl-Pi）和土壤中的残留P；（2）评估磷酸酶活性以及phoC和phoD基因的丰度；（3）确定P组分，磷酸酶活性以及phoC和phoD丰度之间的相关性基因。结果表明，在5和35岁时，低密度（≤3333个茎∙ha ^-1）的总Pi，AER-Pi和NaHCO ₃ -Pi高于高密度（≥5000个茎∙ha ^-1），但NaOH-Po和NaHCO ₃ -Po仅在35岁时相反。此外，仅在35岁时，低密度的NaOH-Pi含量高于高密度的。磷酸酶活性以及phoC和phoD的丰度在5岁时，高密度基因比低密度基因高，而在35岁时则相反。因此，随着种植园的发展，种植密度从5年提高到35年，种植密度的降低有望提高酸性土壤的土壤P生物利用度。一元线性回归结果表明，磷酸酶活性呈正丰的相关phoC和phoD在35岁的种植园和同丰的基因phoC在5岁的种植基因。在35岁的人工林中，磷酸酶活性以及phoC和phoD基因的丰度与NaHCO ₃正相关。-Pi和NaOH-Pi，但与NaHCO ₃ -Po和NaOH-Po显着负相关。这些发现共同表明，酸性土壤中磷的生物利用度和含量，磷酸酶活性以及phoC和phoD基因的丰度随种植密度而变化，对亚热带和热带生物地球化学过程以及理解微生物代谢如何调节P的生物转化具有潜在的影响。