Grazing Intensity Affects Communities of Culturable Root-Associated Fungi in a Semiarid Grassland of Northwest China

Intensive grazing by large herbivores is known to result in the degeneration of grassland worldwide. However, little is known about how grazing affects the fungi living in roots, especially those with septate hyphae. We investigated grazing intensity effects on culturable root-associated fungi (c-RAF) of three dominant plant species; Artemisia capillaris, Lespedeza davurica, and Stipa bungeana, in a semiarid grassland of northwest China. Plant roots were sampled from four grazing intensities at four sampling dates. The total colonization rate of c-RAF was not affected by grazing intensity, but the diversity of c-RAF displayed a hump-shaped trend with grazing intensities. Few c-RAF were present in all plant species, with most of them being confined to only one or two plant species. The sixteen most commonly isolated species were selected to investigate their effects on plant growth and health. Three Fusarium species were most pathogenic c-RAF. Three dark-sterile species did not affect growth parameters, regardless of host plants. With A. capillaris, the occurrence of Fusarium spp. was highest in the control plots while with S. bungeana, the occurrence tended to increase as the grazing intensity increased. Two dark-sterile species, including Darksidea alpha, in L. davurica roots increased with grazing intensities; in contrast, D. alpha decreased for S. bungeana with grazing intensities. Our results strongly suggest that in grasslands grazing intensity can lead to changes in the colonization of specific root fungal taxa, and these fungal changes would potentially feed back to plant performance depending on the abundance of host plants.