| Summary: | We used metagenomics to investigate the rhizosphere microbial community assembly and functions associated with different nutrient cycles in Chinese fir at different monoculture times and growth stages. Mantel test results indicated significant positive correlations between soil TP contents and bacterial communities. The concentrations of soil AP also exhibited a significantly positive association with the fungal community. The relative abundance of ko00720 and ko00680 increased from young-old stands to mature stands. It then decreased in over-mature plantations (45 years) and had a recovery in 102-year-old stands. The potential degradation pathway of cellulose had the highest abundance in 26-year-old stands than the other aged plantations. Potential N cycling processes were dominated by assimilatory nitrate reduction to ammonium and dissimilatory nitrate reduction to ammonium pathways. The variation-partitioning analysis revealed that three forms of N contents (NH<sub>4</sub><sup>+</sup>-N, NO<sub>3</sub><sup>−</sup>-N, and DON) comprised 7%, whereas the other soil properties constituted 15.6% variation in the relative abundance of the genes involved in N cycling. Thus, metagenomics elucidates the evolution characteristics of rhizomicrobial composition and their functional changes at different developmental stages of Chinese fir plantations, providing a suitable reference for the potential utilization of carbon and nitrogen properties.
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