title: Light asymmetry explains the effect of nutrient enrichment on grassland diversity.
abstract: 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.
authors.affiliation: Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem, Givat Ram, Jerusalem, 91904, Israel.
authors.forename: Niv
authors.initials: N
authors.lastname: DeMalach
authors.affiliation: Department of Natural Resources, Institute of Plant Sciences, Agriculture Research Organization, Ministry of Agriculture, Gilat Research Center, Gilat, 85280, Israel.
authors.forename: Eli
authors.initials: E
authors.lastname: Zaady
authors.affiliation: Department of Ecology, Evolution and Behavior, The Hebrew University of Jerusalem, Givat Ram, Jerusalem, 91904, Israel.
authors.forename: Ronen
authors.initials: R
authors.lastname: Kadmon
mesh_terms: D044822:Biodiversity; D018533:Biomass; D065948:Grassland; D008027:Light; D018521:Plant Physiological Phenomena / Q000528:radiation effects*
keywords: Annual plants; biomass; competition; fertilization; forbs; nitrogen; productivity; richness; size asymmetry; species loss