Soil phosphorus fractions, phosphatase activity, and the abundance of phoC and phoD genes vary with planting density in subtropical Chinese fir plantations

Plants and microorganisms have developed mechanisms to acquire soil phosphorus (P). The present studyoccurred 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 phoDgenes; and (3) to identify the correlations among P fractions, phosphatase activity, and the abundance of phoCand 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.The result of unary linear regression showed that phosphatase activity was positivelycorrelated with the abundance of phoC and phoD genes in 35-year-old plantations and with the abundance ofphoC gene in 5-year-old plantations. In 35-year-old plantations, the phosphatase activity and the abundance ofphoC and phoD genes were positively correlated with NaHCO3-Pi and NaOH-Pi, but significantly negativelycorrelated 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.

植物与微生物已演化出获取土壤磷（P）的适应性机制。本研究以5年生和35年生的酸性土壤杉木人工林为对象，设置5种种植密度（1667、3333、5000、6667、10000株·公顷⁻¹）。本研究旨在：（1）解析土壤磷的无机态（Pi）与有机态（Po）组分，以及活性磷（包括树脂态无机磷AER-Pi、碳酸氢钠提取态无机磷NaHCO₃-Pi与有机磷NaHCO₃-Po）、中度活性磷（包括氢氧化钠提取态无机磷NaOH-Pi、有机磷NaOH-Po以及盐酸提取态无机磷HCl-Pi）与残留磷的含量特征；（2）评估土壤磷酸酶活性及phoC、phoD功能基因的丰度；（3）明确磷组分、磷酸酶活性与phoC、phoD基因丰度之间的相关关系。研究结果表明：在5年生和35年生林分中，土壤总无机磷、AER-Pi与NaHCO₃-Pi含量在低密度（≤3333株·公顷⁻¹）组均高于高密度（≥5000株·公顷⁻¹）组；而NaOH-Po与NaHCO₃-Po仅在35年生林分中呈现相反的变化趋势。一元线性回归分析结果显示，35年生杉木人工林的磷酸酶活性与phoC、phoD基因丰度呈显著正相关，5年生林分的磷酸酶活性仅与phoC基因丰度呈正相关。在35年生林分中，磷酸酶活性及phoC、phoD基因丰度与NaHCO₃-Pi、NaOH-Pi呈显著正相关，而与NaHCO₃-Po、NaOH-Po呈显著负相关。上述研究结果共同表明，酸性土壤中磷的生物有效性、磷组分特征、磷酸酶活性以及phoC、phoD基因丰度均随种植密度发生显著变化，该发现可为亚热带与热带生物地球化学过程研究，以及解析微生物代谢调控磷生物转化的内在机制提供潜在参考。