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<p>Biological nitrogen fixation (BNF) is a key process that supplies nitrogen (N) to terrestrial ecosystems, yet its capacity to supply N can be suppressed by global change drivers that increase soil N availability. For example, atmospheric N deposition (<i>N</i>+) can directly raise soil N concentrations, whereas decreases in precipitation (<i>Rain</i>−) may indirectly raise soil N concentrations by constraining plant and microbial N uptake. Biotic interactions, including N inputs or N uptake from plant roots and mycorrhizal fungi, can also interact to mediate N availability and BNF responses under these global change factors, though their interactions on BNF remain poorly understood. Here, we show that in a humid subtropical forest, <i>N</i>+ significantly reduced BNF rates by 43% (<i>P</i>=0.03) and nitrogenase gene (<i>nifH</i>) abundance by 57% (<i>P</i> &lt;0.001), whereas <i>Rain</i>− increased BNF rates by 55% without altering <i>nifH</i> abundance (<i>P</i>=0.03). Notably, the combined <i>N</i>+<i>Rain</i>− treatment neutralized the inhibitory effect of <i>N</i>+, producing BNF rates similar to those under ambient conditions. Structural equation modeling revealed that <i>Rain</i>− indirectly enhanced BNF by increasing soil water-extractable organic carbon (WEOC), whereas <i>N</i>+ directly impaired diazotrophic activity, indicating a novel buffering mechanism that balances opposing effects of these global change drivers. Root and mycorrhizal exclusion treatments showed negligible effects on BNF or <i>nifH</i> abundance, and did not interact with <i>N</i>+ or <i>Rain</i>−, indicating that diazotrophic activity is largely independent of plant root and mycorrhizal inputs. Taken together, our findings highlight the nonlinear outcomes of multi-factor global changes: while <i>N</i>+ can suppress diazotrophic functioning, concomitant declines in precipitation may, paradoxically, sustain BNF via a carbon-mediated facilitation in humid subtropical soils. This apparent buffering capacity, related to WEOC dynamics, highlights how changes in precipitation can mitigate disruptions in N cycling caused by N deposition, with implications for incorporating hydroclimatic-carbon-nitrogen relationships into Earth system models.</p>

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Precipitation reduction mitigates the negative impact of nitrogen deposition on soil nitrogen fixation in subtropical Chinese fir plantations

  • 期刊论文

  • 发表日期：

    2026年4月10日

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  • Fengyi Han,
  • Yongxin Lin,
  • Maokui Lyu,
  • Hang-Wei Hu,
  • Xiangyin Ni,
  • Qiufang Zhang,
  • Jinsheng Xie,
  • Ji-Zheng He,
  • Peter M. Homyak

摘要

Biological nitrogen fixation (BNF) is a key process that supplies nitrogen (N) to terrestrial ecosystems, yet its capacity to supply N can be suppressed by global change drivers that increase soil N availability. For example, atmospheric N deposition (N+) can directly raise soil N concentrations, whereas decreases in precipitation (Rain−) may indirectly raise soil N concentrations by constraining plant and microbial N uptake. Biotic interactions, including N inputs or N uptake from plant roots and mycorrhizal fungi, can also interact to mediate N availability and BNF responses under these global change factors, though their interactions on BNF remain poorly understood. Here, we show that in a humid subtropical forest, N+ significantly reduced BNF rates by 43% (P=0.03) and nitrogenase gene (nifH) abundance by 57% (P <0.001), whereas Rain− increased BNF rates by 55% without altering nifH abundance (P=0.03). Notably, the combined N+Rain− treatment neutralized the inhibitory effect of N+, producing BNF rates similar to those under ambient conditions. Structural equation modeling revealed that Rain− indirectly enhanced BNF by increasing soil water-extractable organic carbon (WEOC), whereas N+ directly impaired diazotrophic activity, indicating a novel buffering mechanism that balances opposing effects of these global change drivers. Root and mycorrhizal exclusion treatments showed negligible effects on BNF or nifH abundance, and did not interact with N+ or Rain−, indicating that diazotrophic activity is largely independent of plant root and mycorrhizal inputs. Taken together, our findings highlight the nonlinear outcomes of multi-factor global changes: while N+ can suppress diazotrophic functioning, concomitant declines in precipitation may, paradoxically, sustain BNF via a carbon-mediated facilitation in humid subtropical soils. This apparent buffering capacity, related to WEOC dynamics, highlights how changes in precipitation can mitigate disruptions in N cycling caused by N deposition, with implications for incorporating hydroclimatic-carbon-nitrogen relationships into Earth system models.