Effect of herbivory on the interaction of grasses and their multiple fungal mutualists in a high altitude trans-Himalayan rangeland
Yadugiri V T
National Centre For Biological Sciences
Yadugiri V T, Sumanta Bagchi, Mahesh Sankaran
Grazing alters plant interactions with mycorrhizae (AMF) and endophytic fungi (EF). Understanding AMF-EF-host interactions is critical for the management of high altitude rangelands such as in the trans-Himalayas, which have supported wild herbivores and livestock for millennia and which are vulnerable to current climate changes. Our discussion focuses on AMF and EF density responses to grazer exclusion and possible mutual inhibition under herbivory pressure.
Root and shoot samples from ~10 individuals each of three common grasses and a sedge were collected from 15 eight-year old herbivory exclosures and adjacent grazed plots in the growing season (July-August 2012), and AMF and EF densities in each plant determined microscopically. Predictions on decreasing AMF and increasing EF (putative herbivore defence mutualists) densities under herbivory, and AMF-EF inhibition of each other under these conditions were tested.
The plant species studied showed different AMF density responses to grazing, with some showing a reduction and others not. Overall EF incidence and densities were both lower under grazing despite their possible role in herbivory defence. Interestingly, in the grazed plots, individual plants with higher densities of AMF supported lower densities of EF, while such a relationship was not seen when grazers were excluded, perhaps due to carbon limitation under grazing.
Species level differences in mutualist densities is potentially due to different plant strategies to handle herbivory while maintaining sufficient mutualists to withstand extreme aridity. AMF and EF densities can influence plant performance, and understanding mutualist responses to grazing will help in more accurate assessment of the potential of these rangelands for the continued sustenance of grazers, especially in the face of climate change.