Is the positive relationship between species richness and shoot morphological plasticity mediated by ramet density or is there a direct link?
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Little is known about the consequences of phenotypic plasticity in co-existing species for plant community structure. However, it has been proposed that the potential of plants to exhibit plastic responses to light availability could be a key factor determining the capability of individuals to co-exist at small scales. Our previous research demonstrated that morphological plasticity to light was positively related to small-scale species richness in a temperate grassland. However, it remained unclear whether this relationship was solely due to a higher shoot density in plastic assemblages, or whether diversity was directly related to the morphological plasticity of the co-inhabitants. We used two data sets to clarify this relationship: experimentally acquired estimates of plasticity to light availability for 45 herbaceous plant species, and species richness and ramet density data from a 2-year permanent plot study in a semi-natural calcareous grassland. There was little ramet mortality observed in the permanent plot study indicating that the link between plasticity and richness does not operate through reduced mortality in more morphologically plastic assemblages. The local density of ramets explained most of variation in small-scale richness, but there was also a significant direct density-independent effect of mean shoot plasticity on richness, showing that plasticity to light directly enhances the small-scale co-existence of species.
KeywordsGrassland vegetation Herbaceous species Plant density Plasticity Species diversity
We are grateful to all members of the working group for their help with the experiments and two anonymous referees for valuable comments. Special thanks to Anu Lepik and Oliver Parrest for assistance with fieldwork. Jaan Liira helped with the statistical analysis. Two anonymous reviewers and editors provided numerous comments that helped significantly to improve the manuscript. The study was supported by the Estonian Science Foundation (5535, 7576, 9269) and the University of Tartu (IUT 20-31). The experiments comply with the current laws of the Republic of Estonia.
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