One of the most ubiquitous patterns in plant ecology is species loss following nutrient enrichment. A common explanation for this universal pattern is an increase in the size asymmetry of light partitioning (the degree to which large plants receive more light per unit biomass than smaller plants), which accelerates the rates of competitive exclusions. This ‘light asymmetry hypothesis’ has been confirmed by mathematical models, but has never been tested in natural communities due to the lack of appropriate methodology for measuring the size asymmetry of light partitioning in natural communities. Here, we use a novel approach for quantifying the asymmetry of light competition which is based on measurements of the vertical distribution of light below the canopy. Using our approach, we demonstrate that an increase in light asymmetry is the main mechanism behind the negative effect of nutrient enrichment on species richness. Our results provide a possible explanation for one of the main sources of contemporary species loss in terrestrial plant communities.
Bibliographical noteFunding Information:
We thank Ronen Ron, Daniel Barkai, Yaakov Knoll and Lior Iluz for field assistance; Christoph Scherber and Micha Mandel for statistical advices; and three anonymous reviewers for comments on previous versions of this manuscript. We also thank Beit Guvrin National Park for their logistic support. The study was supported by the Israel Science Foundation grants no. 454/11 and 447/15, the Hebrew University Advanced School of Environmental Studies, the Ring Foundation, and the Nature and Parks Authority.
© 2016 John Wiley & Sons Ltd/CNRS
- Annual plants
- size asymmetry
- species loss