Multi-symbiotic systems: functional implications of the coexistence of grass-endophyte and legume-rhizobia symbioses

GARCIA PARISI, PABLO ADRIÁN; LATTANZI, FERNANDO ALFREDO; GRIMOLDI, AGUSTÍN ALBERTO; OMACINI, MARINA

OIKOS

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2015

0030-1299

Aboveground belowground relationships between plants and microbial symbionts have important implications on plant community structure and ecosystem functioning. The coexistence of symbionts with different functional roles in co-occurring plants is highly probable in terrestrial ecosystems, and understanding how they affect key processes is currently arousing interest. We performed an outdoor mesocosms experiment to investigate the consequences from the interaction of a provider belowground symbiont of legumes (i.e. nitrogen-fixing bacteria) and a protector aerial fungal symbiont of grasses (i.e.Epichloё endophyte) for N dynamics and aboveground net primary productivity (ANPP). Four plants of the legume Trifolium repens (Trifolium) either inoculated with Rhizobium leguminosarum or not, were grown surrounded by 16 plants of the annual grass Lolium multiflorum (Lolium), with either low or high symbiotic status level with the endophyte Neotyphodiumoccultans. After 5 months, we quantified the number of nodules in Trifolium roots and shoot biomass production per plant species and we estimated the contribution of each nitrogen source (soil vs. atmospheric N) within each plant aboveground tissues with the 15N natural abundance technique. The endophyte increased grass biomass production by 16% and nitrogen absorption from the soil ?the main source for grasses-, and reduced the nodulation of Trifolium plants. Nonetheless, these effects reduced neither N2-fixation ?the main source of nitrogen for legumes? nor Trifolium biomass production, which were both doubled by Rhizobium addition. Thus, thetotal amount of nitrogen in aboveground tissues was greater in high Rhizobium-mesocosms and aboveground productivity increased with both symbionts. These results show that the coexistence of these aboveground and belowground symbioses can generate complementarity effects on N-dynamics and aboveground productivity. Here we show for the first time complementarity effects of the interaction between grass-endophyte symbiosis and legume-rhizobia symbiosis coexisting in a community, with additive implications on the functioning of this multi-symbiotic ecosystem.