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Background <p>The forest-steppe ecotone, a critical transition zone sensitive to global change, faces increasing nitrogen deposition. However, the interplay between nitrogen conversion processes and soil enzyme activity remains unclear. We investigated the effects of nitrogen addition on plant nutrient dynamics, microbial functional genes, and enzyme activity in northwest Liaoning, China.</p> Results <p>Nitrogen addition significantly increased leaf nitrogen content in <i>Potentilla tanacetifolia</i> (peak under N40) and <i>Artemisia frigida</i> (peak under N40), while <i>Lespedeza daurica</i> showed a non-linear response (peak under N20). Phosphorus content remained unaffected across species. Soil enzyme activities (urease, nitrate reductase, dehydrogenase) increased with nitrogen input, with protease activity rising proportionally to nitrogen addition rate. Functional genes (<i>nirK</i>, <i>nifH</i>, AOB-<i>amoA</i>) exhibited dynamic responses: <i>nirK</i> abundance peaked under N40, <i>nifH</i> under N10, and AOB-<i>amoA</i> increased with nitrogen input. Structural equation modeling revealed that <i>nirK</i> gene abundance positively influenced enzyme activity (<i>λ</i> = 0.512), while <i>nifH</i> negatively correlated with leaf N/P ratios (<i>λ</i> = −0.606). Soil protease activity directly drove leaf N/P ratios (<i>λ</i> = 0.734).</p> Conclusions <p>Nitrogen addition enhances plant nitrogen uptake and enzyme-driven mineralization, but species-specific responses highlight ecological trade-offs. Soil pH and protease activity are pivotal in mediating nitrogen conversion and plant nutrient stoichiometry. These findings underscore the need to integrate microbial and enzymatic dynamics into nutrient management strategies for ecotones under nitrogen enrichment.</p>

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Nitrogen addition changes the nitrogen conversion process in forest steppe ecotone by increasing enzyme activity

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年4月9日

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  • Baihui Ren,
  • Haoyan Li,
  • Daiyan Li,
  • Meng Meng,
  • Jiahuan Li,
  • Long Bai,
  • Yulong Feng

摘要

Background

The forest-steppe ecotone, a critical transition zone sensitive to global change, faces increasing nitrogen deposition. However, the interplay between nitrogen conversion processes and soil enzyme activity remains unclear. We investigated the effects of nitrogen addition on plant nutrient dynamics, microbial functional genes, and enzyme activity in northwest Liaoning, China.

Results

Nitrogen addition significantly increased leaf nitrogen content in Potentilla tanacetifolia (peak under N40) and Artemisia frigida (peak under N40), while Lespedeza daurica showed a non-linear response (peak under N20). Phosphorus content remained unaffected across species. Soil enzyme activities (urease, nitrate reductase, dehydrogenase) increased with nitrogen input, with protease activity rising proportionally to nitrogen addition rate. Functional genes (nirK, nifH, AOB-amoA) exhibited dynamic responses: nirK abundance peaked under N40, nifH under N10, and AOB-amoA increased with nitrogen input. Structural equation modeling revealed that nirK gene abundance positively influenced enzyme activity (λ = 0.512), while nifH negatively correlated with leaf N/P ratios (λ = −0.606). Soil protease activity directly drove leaf N/P ratios (λ = 0.734).

Conclusions

Nitrogen addition enhances plant nitrogen uptake and enzyme-driven mineralization, but species-specific responses highlight ecological trade-offs. Soil pH and protease activity are pivotal in mediating nitrogen conversion and plant nutrient stoichiometry. These findings underscore the need to integrate microbial and enzymatic dynamics into nutrient management strategies for ecotones under nitrogen enrichment.