Under pressure: overgrazing decreases mycorrhizal colonization of preferred and unpreferred grasses in the Patagonian steppe

GRIMOLDI, AA; DUDINSZKY, N; CAVAGNARO, RA; GOLLUSCIO, RA; PERO, E

Praga

Congreso; 9th International Conference on Mycorrhiza; 2017

International Mycorrhiza Society

Arbuscular mycorrhizal fungi (AMF) are related to plant community dynamicsand ecosystem functioning. Overgrazing can negatively affect plant performance unbalancing the association with AMF. We studied the effect of sheep grazing pressure on AMF colonization for preferred (Bromus pictus and Poa ligularis) and unpreferred grasses (Pappostipa humilis and Pappostipa speciosa) in the Patagonian steppe. The degree of AMF colonization (hyphae, arbuscules and vesicles) in ungrazed, moderate and intense grazing sites was quantified. Root samples were taken during two contrasting seasons: summer (active plant growth) and autumn (descending plant growth). In ungrazed sites, during the summer, B. pictus showed the highest degree of AMF colonization (59% B. pictus > 29% P. speciosa > 24% P. ligularis > 16% P. humilis). Moreover, in B. pictus, the most preferred species, AMF colonization markedly decreased from ungrazed sites tothose with moderate and intense grazing. In all species, mycorrhizal colonization was reduced by intense grazing conditions. Decrease of AMF colonization by intense grazing was higher in the most preferred species, but also significant for the unpreferred species. Notably, the reduction of AMF colonization in unpreferred species did not match with their greater abundance under intense grazing conditions, revealing AMF colonization as an indicator of system deterioration. Our results suggest that benefits of mycorrhizal symbiosis for mineral nutrition and plant survival are being disrupted by overgrazing as an indicator property for the whole system, eventually revealing an increasing degree of ecosystem degradation.