Landmark Issue 19 2021 SINGLE PAGES

ISSUE 19 | 2021 29 TEACHING & LEARNING : RESEARCH A three-year project based in China, leading to the successful completion of a PhD by Maede Faghihinia, revealed some intriguing points about grazing impacts. Impacts of grazing have generally been studied by comparing grazed and non-grazed sites, but here the focus was on the intensity of grazing or livestock stocking rate. The work was carried out in a large scale field experiment in Inner Mongolia which included seven different grazing intensities ranging from 0 to 9 ewes per two-hectare plot. The experiment had been running for 13 years. This timescale is important as it may take several years for ecological changes to become evident. Efforts were focused on mycorrhizal fungi, which are symbiotic fungi forming associations with plant roots. Most plant species (around 90 % ) are mycorrhizal and the symbiosis involves movement of carbon from the plant to the fungus and movement of phosphorus from the fungus to the plant. The fungal partner produces extensive hyphal networks in the soil to take up nutrients and colonises plant roots where the exchange of products occurs. We showed that the density of external mycorrhizal hyphae in the soil was strongly impacted by grazing and that it decreased as grazing intensity increased. This would mean that the capacity for the fungus to obtain nutrients and translocate them to the plant partners would be decreased. The mycorrhizal fungal colonization within roots was however, unaffected, which would mean the ratio of these two fungal components (hyphae in roots vs hyphae in soil) would be modified leading to changes in the functioning of the symbiosis. Furthermore, this decrease in mycorrhizal hyphal density in the soil could have large implications for the potential for the more heavily grazed soils to sequester carbon. Indeed, mycorrhizal fungi are a substantial pathway for carbon movement to soil and they also produce compounds which are slow to decompose thus facilitating carbon build- up in soil. Further data also showed that some of these relationships between grazing intensity and mycorrhizal fungal abundance might be humped shaped, which would imply that there would an optimal level of grazing to maximise benefits to soil biodiversity and carbon sequestration. This has clear implications for two global challenges: biodiversity loss and climate change. Grazing and soil biodiversity Dr Philip Staddon Principal Lecturer in Environment and Sustainability