Abstract

GARCIA, Silvina; PEZZANI, Fabiana; LEZAMA, Felipe  and  PARUELO, José M.. Grazing components differentially affect mycorrhizas in Paspalum ditatatum Poir. Ecol. austral [online]. 2019, vol.29, n.2, pp.164-173. ISSN 1667-782X.

Grazing by large herbivores represents an important disturbance in natural grasslands, affecting its structure and function. Arbuscular mycorrhizas (AM) are cosmopolitan interactions in these ecosystems, particularly in grasses, main constituent of this ecosystem. Mycorrhizas show contradictory responses to grazing (AM colonization has been positively, negatively and not affected by grazing). We hypothesized that each grazing component (selective defoliation, trampling and urine deposition) would differentially affect mycorrhizal colonization, and this could explain the high variability in AM responses. Our objective was to assess the effect of trampling, selective defoliation and nitrogen (N) addition on AM colonization of one of the most important grasses in Río de la Plata grasslands: Paspalum dilatatum. Grazing components were simulated in a manipulative experiment where we evaluated their individual and combined effects on total AM colonization and the occurrence of different fungal structures (arbuscules, coils and vesicles). No grazing component affected total AM colonization and arbuscules, while other fungi structures were affected by different treatments. Coil colonization (one of the nutrient interchange structures between the symbionts) was positively affected by selective defoliation and it was negatively affected by N addition; these structures were also affected by the combined effect between selectivity x trampling and by trampling x N addition. Vesicle colonization was negatively affected by trampling, maybe because of mechanical damage to roots and to extraradical mycelium caused by this disturb. The study of the individual grazing components showed that each one caused different effects on mycorrhizal interaction and their relative influence could affect the overall grazing effect on this interaction.

Keywords : arbuscular mycorrhiza; selective defoliation; urine deposition; trampling.

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