CONICET | Buscador de Institutos y Recursos Humanos

Defoliation reduces photosynthetic activity resulting in losses of carbon andnutrients. Mycorrhizae can facilitate regrowth by improving plant nutrition. However, postdefoliation recovery of the plants could be influenced by their mycorrhizal responsiveness and soil phosphorus availability. We evaluated mycorrhizae effects on post-defoliation recovery in Agropyron elongatum and Brachiaria brizantha at different phosphorus supplies. Materials and Methods: A manipulative experiment with two forage grass species was designed: A. elongatum low responsiveness, temperate) and B. brizantha (high responsiveness, tropical). For each species, treatments were: inoculation with arbuscular mycorrhizal fungi (non-inoculated and inoculated), soluble P-supply (low: 0,02mM and high: 1mM) and defoliation (non-defoliated and 60% defoliation). After 22 and 34 days post-defoliation, biomass production, number of tillers perplant and relative growth rate (RGR) were assessed. In A. elongatum, at low P/+Inoc. and high P/-Inoc., no differences were found in total biomass between non-defoliated and defoliated plants. In those treatments, relative growth rate(RGR) of defoliated plants was higher than in non-defoliated ones. Consequently, removed biomass was compensated. At high P, mycorrhizae depressed post-defoliation recovery of plants (32% less tillers per plant). In B. brizantha, mycorrhizae had a positive effect in all treatments. In A. elongatum at low P, mycorrhizae favors plants regrowth, while the opposite occurs at high P supply. In B. brizantha, mycorrhizae always promoted plant regrowth. Our results indicate that the relationship between AMF and defoliated grasses varywith the mycorrhizal affinity of the host species and is modulated by phosphorus supply.