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Purpose <p>Soil microbial communities are crucial for ecosystem functioning, particularly in climate-sensitive alpine environments. Nitrogen-fixing microorganisms among them provide essential nitrogen input to these nutrient-limited ecosystems. Alpine treeline ecotones represent critical boundary for understanding microbial responses to environmental gradients, yet the relative importance of elevational versus topographic factors in structuring specialized diazotrophic communities remain unclear.</p> Materials and methods <p>We examined <i>nifH</i>-harboring community dynamics across slope aspects and treeline positions at Mount Sygera, Tibetan Plateau. Twenty-four soil samples from four groups (sunny/shady slopes×above/below treeline) were analyzed via high-throughput sequencing of <i>nifH</i> genes. Diversity patterns were assessed using alpha/beta diversity indices and multivariate analyses. Interaction patterns were revealed by co-occurrence network analysis. Community assembly processes were quantified using iCAMP to determine deterministic versus stochastic contributions. Ecological strategies were classified through niche breadth analysis, with phylogenetic distributions examined for specialists. Environmental drivers were identified through ordination and partitioning analyses.</p> Results and discussion <p>Slope aspect emerged as the stronger driver of community composition than treeline position. <i>NifH</i> gene abundance was highest on shady slopes, and beta diversity analysis demonstrated stronger slope aspect than treeline effects through compositional dissimilarity patterns. Multi-dimensional analyses consistently supported this phenomenon, as environmental filtering by topographic variation shaped distinct interaction patterns, assembly processes, and ecological strategies across slope aspects.</p> Conclusion <p>These findings suggest that slope aspect effects on N-fixing communities may equal or exceed small-scale elevational differences, enriching understanding of topographic versus elevational factors in structuring specialized functional microbial communities in alpine ecosystem.</p>

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Slope aspect dominates over treeline position in structuring nitrogen-fixing microbial communities in Tibetan alpine ecotones

  • 期刊论文

  • 发表日期：

    2026年3月15日

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  • Jing-Ru Hao,
  • Congcong Shen,
  • Yan Li,
  • Yuqiang Sang,
  • Yuan Ge

摘要

Purpose

Soil microbial communities are crucial for ecosystem functioning, particularly in climate-sensitive alpine environments. Nitrogen-fixing microorganisms among them provide essential nitrogen input to these nutrient-limited ecosystems. Alpine treeline ecotones represent critical boundary for understanding microbial responses to environmental gradients, yet the relative importance of elevational versus topographic factors in structuring specialized diazotrophic communities remain unclear.

Materials and methods

We examined nifH-harboring community dynamics across slope aspects and treeline positions at Mount Sygera, Tibetan Plateau. Twenty-four soil samples from four groups (sunny/shady slopes×above/below treeline) were analyzed via high-throughput sequencing of nifH genes. Diversity patterns were assessed using alpha/beta diversity indices and multivariate analyses. Interaction patterns were revealed by co-occurrence network analysis. Community assembly processes were quantified using iCAMP to determine deterministic versus stochastic contributions. Ecological strategies were classified through niche breadth analysis, with phylogenetic distributions examined for specialists. Environmental drivers were identified through ordination and partitioning analyses.

Results and discussion

Slope aspect emerged as the stronger driver of community composition than treeline position. NifH gene abundance was highest on shady slopes, and beta diversity analysis demonstrated stronger slope aspect than treeline effects through compositional dissimilarity patterns. Multi-dimensional analyses consistently supported this phenomenon, as environmental filtering by topographic variation shaped distinct interaction patterns, assembly processes, and ecological strategies across slope aspects.

Conclusion

These findings suggest that slope aspect effects on N-fixing communities may equal or exceed small-scale elevational differences, enriching understanding of topographic versus elevational factors in structuring specialized functional microbial communities in alpine ecosystem.