Herbivore removal reduces influence of arbuscular mycorrhizal fungi on plant growth and tolerance in an East African savanna
The functional relationship between arbuscular mycorrhizal fungi (AMF) and their hosts is variable on small spatial scales. Here, we hypothesized that herbivore exclusion changes the AMF community and alters the ability of AMF to enhance plant tolerance to grazing. We grew the perennial bunchgrass, Themeda triandra Forssk in inoculum from soils collected in the Kenya Long-term Exclosure Experiment where treatments representing different levels of herbivory have been in place since 1995. We assessed AMF diversity in the field, using terminal restriction fragment length polymorphism and compared fungal diversity among treatments. We conducted clipping experiments in the greenhouse and field and assessed regrowth. Plants inoculated with AMF from areas accessed by wild herbivores and cattle had greater biomass than non-inoculated controls, while plants inoculated with AMF from where large herbivores were excluded did not benefit from AMF in terms of biomass production. However, only the inoculation with AMF from areas with wild herbivores and no cattle had a positive effect on regrowth, relative to clipped plants grown without AMF. Similarly, in the field, regrowth of plants after clipping in areas with only native herbivores was higher than other treatments. Functional differences in AMF were evident despite little difference in AMF species richness or community composition. Our findings suggest that differences in large herbivore communities over nearly two decades has resulted in localized, functional changes in AMF communities. Our results add to the accumulating evidence that mycorrhizae are locally adapted and that functional differences can evolve within small geographical areas.
KeywordsBelow and aboveground interactions Arbuscular mycorrhizal fungi Simulated herbivory Local adaptation Kenya Long-term Exclosure Experiment (KLEE)
We thank, G. Clarke, C. Armstrong, D. Heleba for help in the greenhouse and comments on JBG’s thesis. Special thanks to JBG’s MSc committee, J.M. Harris and J.O. Vigoreaux, for constructive criticism of the analysis and interpretation of the results, and to A. Howard (UVM) and F. Vermeylen (Cornell) for help with the statistical analysis. We thank J. Morton (INVAM, WVU) for his mentorship in the field of AMF and for constructive remarks on this and other AMF projects. Our work was supported by NSF DEB-0519223 to A.K. Brody. Mpala Research Centre and staff provided logistical support. KLEE was carried out under Government of Kenya research clearance permit No. NCST/RCD/12B/012/42. KLEE was built and maintained by grants from the James Smithson Fund of the Smithsonian Institution (to A.P. Smith), The National Geographic Society (Grants 4691-91 and 9106-12), NSF (LTREB DEB 97-07477, 03-16402, 08-16453, 12-56004, and 12-56034) and the African Elephant Program of the US Fish and Wildlife Service (98210-0-G563) (to T.P. Young, C. Riginos, and K.E. Veblen).
Author contribution statement
JBG, RHP and AKB conceived of the ideas, designed and conducted the experiments, and wrote the initial manuscript. OF and ETK provided expertise, laboratory materials and equipment and assistance in the molecular identification of the fungal communities, and helped write the final manuscript. KEV provided expert knowledge of KLEE and helped write the final manuscript.
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