How does resource addition affect the assembly trajectories of plant communities?

Author Qianna Xu provides further insights for their new research article, which explores the impacts of nitrogen and water levels on plant community composition. Recently published in Journal of Ecology, Volume 107 Issue 5.

This article is part of our latest Special Feature: Is Phylogenetic and Functional Trait Diversity a Driver or a Consequence of Grassland Community Assembly?

A key characteristic of biodiversity is its non-even distribution around the biosphere. The ensuing differences in community composition among different locations is often quantified as beta-diversity. Understanding the mechanisms driving beta-diversity among localities is one of the major goals of community ecology.

A semi-arid steppe in Inner Mongolia, China. (Photo: Jian Song)

Anthropogenic environmental changes are known to affect biodiversity. However, how environmental changes influence beta-diversity dynamics of the impacted communities remains underexplored. In particular, we know virtually nothing about how these changes influence phylogenetic beta-diversity, which accounts for species evolutionary relationships, leaving a knowledge gap that calls for investigation. In our paper, we addressed the question how increased nitrogen (N) deposition and precipitation affect plant taxonomic and phylogenetic beta-diversity with a nine-year field experiment in the temperate semi-arid steppe of Inner Mongolia in China.

Plots established in our experiment. (Photo: Ang Zhang)

We found that taxonomic beta-diversity increased in response to N and water addition. Moreover, N addition also significantly increased phylogenetic beta-diversity. After the differences in local community size were controlled for using null models, the standard effect size of taxonomic beta-diversity (i.e., β-deviation) also increased with N and water addition, suggesting that resource enrichment led to increased taxonomic divergence among communities. However, water addition, but not N enrichment, significantly decreased the standard effect size of phylogenetic β-diversity (i.e., SES.Dpw), suggesting that water addition drove communities to converge towards more similar phylogenetic structure.

Changes in taxonomic β-diversity (a), phylogenetic β-diversity (c), and their respective standardized effect sizes (b, d) among replicate plots within each treatment over time.

Elucidating how anthropogenic environmental changes alter beta-diversity across ecological communities is useful toward a better understanding of why biodiversity is distributed the way it is, and is also essential for making informed decisions on conserving the Earth’s biodiversity in the face of significant environmental changes. Our study shows that changes in N deposition and precipitation can differentially affect taxonomic and phylogenetic beta-diversity among the impacted plant communities. These results suggest that while stochastic processes may cause taxonomic composition in communities to diverge from each other, deterministic processes can still drive convergence in phylogenetic community structure under anthropogenic environmental changes. Next questions to ask are whether our findings can be extended to other ecosystems and whether the effects of environmental changes on beta-diversity would translate into ecosystem functions.

Qianna Xu, Georgia Institute of Technology, USA

Read the full paper: Resource addition drives taxonomic divergence and phylogenetic convergence of plant communities” by Yang et al.

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