Variation of Soil Phosphorus Fractions and the Phosphorus Solubilizing Microbial Communities in Chinese Fir Monoculture Plantations with Different Ages

【Objective】 This article aims to analyze the variation of phosphorus fractions in the soil of Chinese fir plantations with different stand ages, and to explore the internal relationship between the stand age and the species and relative contents of phosphorus solubilizing microbes at different classification levels, so as to provide reference for the effective use of soil phosphorus and sustainable management of plantations. 【Method】 Five Chinese fir plantations of different ages (4-, 15-, 24-, 43- and 100-year-old) were selected in Nanping, Fujian. The modified Hedley phosphorus grading method was used to determine the phosphorus content of different grades in 0-20 cm soil layer. High-throughput sequencing technology was used to determine the phoD gene amplified by PCR to obtain the relative abundance of phosphorus solubilizing microbes at different classification levels. 【Result】 Overall, at the same age of Chinese fir plantations, the phosphorus content of different grades was Residual-P > NaOH-P > NaHCO3-P > H2O-P > HCl-P. The content of H2O-IP increased significantly with the increase of stand age (P3-IP increased and then decreased with the increase of the stand age, reaching the maximum in 43-year-old stands. As the stand age increased, the soil NaOH-P content fluctuated significantly, showing 24 year-old stands > 100-year-old stands > 43-year-old stands > 4-year-old stands > 15-year-old stands. The total amount of organic phosphorus showed an upward trend as a whole, in the order of 100-year-old stands > 24-year-old stands > 43-year-old stands > 15-year-old stands >4-year-old stands. With the increase of stand age, the content of labile phosphorus in the soil of Chinese fir plantation gradually increased. The soil phosphorus activity in young forest, middle-aged forest, and near-mature forest of Chinese fir showed that stable phosphorus > moderately labile phosphorus > labile phosphorus. The phosphorus activity of over-mature forest showed the order of stable phosphorus > labile phosphorus > moderately labile phosphorus. Overall, the abundance of phosphorus solubilizing microbes in the soil of Chinese fir forest showed 43-year-old stands > 100-year-old stands > 24-year-old stands > 15-year-old stands > 4-year-old stands, and the diversity showed 43-year-old stands > 100-year-old stands > 15-year-old stands > 24-year-old stands > 4-year-old stands. OTU Venn diagram and PCoA analysis showed that the structure and diversity of phosphorus solubilizing microbes in 15-year-old stands and 24-year-old stands were similar. The soil of 43-year-old Chinese fir plantation contained the most abundant and unique groups of phosphorus solubilizing microbes. The number of phosphorus solubilizing microbes in 4-year-old stands Chinese fir forest was the least. At the phylum classification level, the content of Proteobacteria in the soil was the highest, followed by Deinococcus-Thermus and Actinobacteria. At the genus classification level, the dominant groups were mainly Bradyrhizobium, Pseudolabrys, Pseudomonas, Deinococcus, etc. Redundancy analysis showed that there was a significantly positive correlation between relative contents of soil NaHCO3-IP and Firmicutes, and a significant negative correlation between NaOH-IP and Actinobacteria, Gemmatimonadetes, etc. HCl-OP was significantly negatively correlated with Acidobacteria, while H2O-OP, and NaHCO3-IP were significantly negatively correlated with Bradyrhizobium. 【Conclusion】 With the increase of stand age, the content of different forms of phosphorus in the soil of Chinese fir plantation varies significantly, and the level of soil labile phosphorus continuously increases. The potential supply capacity of the soil in near-mature and over-mature forests is higher than that of young and middle-aged forests. The changes in soil chemical properties affect soil microbial activity, and the increase in the abundance and diversity of phosphorus solubilizing microbes may increase the availability of soil phosphorus in Chinese fir plantations to a certain extent. © 2022, Editorial Department of Scientia Silvae Sinicae. All right reserved.