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Microbial mechanisms maintaining soil phosphorus stability in Chinese fir plantations under long-term nitrogen addition
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DOI：10.1016/j.ejsobi.2026.103833.png)
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Abstract
En 中文
Long-term nitrogen (N) deposition may exacerbate phosphorus (P) limitation in forest ecosystems, yet how soil P cycling responds to chronic N input and the underlying microbial mechanisms remain unclear. To address this, we conducted a long-term N addition experiment in a Chinese fir plantation, established in 2004, with four N addition levels (0, 60, 120, and 240 kg N ha−2·yr−1 applied monthly as urea solution). In August 2024, topsoil (0–10 cm mineral layer) samples were collected and analyzed for basic chemical properties, P fractions, microbial biomass, hydrolase activities, and microbial community structure using phospholipid fatty acid analysis and high-throughput sequencing. The results showed that long-term N addition significantly reduced soil pH (by 7.7% under high N) and microbial biomass carbon and nitrogen (by 43.9% and 38.9%, respectively), while markedly increasing nitrate N content (by 277.7%). In contrast, microbial biomass P, all measured P fractions (labile, moderately labile, and occluded), and acid phosphatase activity remained stable. Microbial community analysis revealed that Gram-negative bacteria and arbuscular mycorrhizal fungi were suppressed under higher N inputs. Importantly, a clear functional reorganization was observed within the phosphate-solubilizing community: while phosphate-solubilizing bacterial structure remained stable (dominated by taxa such as Bradyrhizobium), key phosphate-solubilizing fungi, notably Aspergillus and Trichoderma, showed compensatory increases of 138.5%–552.2% and 216.3%–310.4%, respectively. Redundancy analysis indicated that phosphate-solubilizing fungi and bacteria explained 42.2% and 62.7% of the variation in P fractions, with Penicillium, Aspergillus, Paenibacillus, and Rhodoferax identified as key drivers. In conclusion, the stability of soil P cycling under long-term N addition is maintained not through overall microbial community stability, but via microbial functional reorganization, in which compensatory increases in specific phosphate-solubilizing fungi play a critical role. This highlights a mechanism of niche compensation within microbial functional groups, supporting forest ecosystem adaptation to chronic N deposition.
Keywords:
soil phosphorus cycling
long-term nitrogen addition
microbial functional reorganization
phosphate-solubilizing fungi
niche compensation
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