Do Large Herbivores Influence Plant Allocation to Above- and Belowground Compartments?
Plants allocate biomass to aboveground (shoot) and belowground (root) structures to capture light and nutrients, respectively. Plant allocation strategies are a key feature of ecosystem structure, and function, as they have broad influence over material and energy flow. Herbivores can exercise strong control over plant allocation, and thereby influence ecosystem structure and function. Theoretical models of plant allocation strategies predict that root:shoot ratio is related to leaf nitrogen (N) concentration; specifically root:shoot ratio declines monotonically over a broad range of N concentrations. Here, I assess whether grazing by large mammalian herbivores alters the inverse relationship between root:shoot ratio and leaf-N concentration. Data from an herbivore exclusion experiment in the arid Trans-Himalayan ecosystem were in general agreement with predictions of theoretical models. Herbivores did not affect the slope of the relationship, rather they lowered the intercept, and this change was independent of their influence over plant community composition. Reduction in root:shoot ratio with increasing leaf-N, and lowering biomass allocation to roots with grazing, are consistent with other studies on how herbivores influence plants.
KeywordsEcosystem structure and function Grazer effects Leaf nitrogen Plant strategies Root:shoot ratio Trans-Himalayan
The dataset used for this analysis was created with funding support from Syracuse University, US National Science Foundation (DDIG DEB-0608287), Rufford Foundation, and Wildlife Conservation Society. I am grateful to M.E. Ritchie, Y.V. Bhatnagar, and C. Mishra for numerous discussions on plant–herbivore interactions. I am also grateful to the Himachal Pradesh Department of Forest Farming and Conservation, and to all the assistants, interns, and volunteers who have worked very hard in helping me in the field. Initial drafts were greatly improved by critiques from anonymous referees and the editors.
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