Abstract
Due to its inherent asymmetry, competition for light is thought to cause loss of diversity from eutrophied systems. However, most of the work on this topic in grasslands has been phenomenological and has not measured light directly. We present the results of one of the few mechanistic experiments investigating the outcome of short-term competition using measurements of light interception from monocultures of five perennial grass species grown under fertilized and irrigated conditions. We found that the level of incident light intercepted by each species in monoculture, a direct measure of resource-reduction ability, was an excellent predictor of the relative competitive effect in pairwise mixtures. Competition for light was asymmetric in relation to differences in light intercepting ability. Our results are consistent with the idea that when light is a limiting resource, competition between species for this resource can be asymmetric, contributing to high dominance and low diversity.
Highlights
One of the mostly widely observed results of global change is that in many different types of ecosystems eutrophication leads to diversity loss [1,2,3]
The observed competitive hierarchies averaged over all targetneighbour species combinations were: H. lanatus.A. pratensis..A
Target plant biomass of F. rubra and A. odoratum decreased strongly when they were surrounded by the taller A. pratensis and H. lanatus, in comparison to their biomass when growing surrounded by conspecifics (Fig. 1)
Summary
One of the mostly widely observed results of global change is that in many different types of ecosystems eutrophication leads to diversity loss [1,2,3]. In eutrophied terrestrial plant communities, such as many European grasslands, competition for light is thought to be a mechanism for this diversity loss [4,5,6,7] and the asymmetric nature of this competition can lead to an outcome which supports only low plant diversity [8,9,10]. The best developed mechanistic theory of resource-competition is Tilman’s R* [7,11]. In terrestrial plant communities R* theory has only been applied to belowground resources, soil nitrogen, and almost exclusively at a single site [12,13], namely the well-known nitrogen-limited prairie at Cedar Creek, Minnesota, USA. Studies there support the ability of R* to predict species’ relative abundances and the outcome of competition during secondary succession in old fields [13,14,15,16,17]
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