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Longterm effects of grazing on arbuscular mycorrhizal fungi

Heyde, Mieke van der, Bennett, Jonathan A., Pither, Jason, Hart, Miranda
Agriculture, ecosystems & environment 2017 v.243 pp. 27-33
fungal communities, grasslands, grazing, hyphae, mycorrhizal fungi, plant response, soil, spores, symbionts, vesicular arbuscular mycorrhizae
Arbuscular mycorrhizal (AM) fungi are obligate root symbionts and are thought to help plants tolerate grazing. Evidence shows that grazing can stimulate, inhibit, or have no effect on AM fungi. This inconsistency may be due to empirical limitations, specifically: (i) choice of AM fungal response variable, (ii) confounding effects of soil and plant responses to grazing, and (iii) variation in the duration of studies. To test these hypotheses, we compared AM fungi between grazed and ungrazed grassland plots, with grazing exclosures varying in age from 17 to 85 years. Our findings clearly show that grazing does not universally inhibit AM fungi: grazing had no effect on root colonization plots but spore density was higher and soil hyphal length was lower in grazed plots. While soil and plant variables were unrelated to fungal responses, time since grazing cessation was an important factor explaining the difference between grazed and ungrazed AM fungal communities at a site, indicating possible time lags in responses. Understanding of grazing effects on AM fungi can be enhanced by considering multiple fungal responses and increasing the time scale under which they are studied.