Grass-endophyte symbiosis: A neglected aboveground interaction with multiple belowground consequences

Most terrestrial plants form symbiosis with a large variety of microorganisms that can be major determinants of morphological and physiological host traits that, ultimately, affect the structure and function of communities. Epichloae fungal endophytes (Clavicipitaceae) are widespread symbionts of grasses that asymptomatically inhabit aerial host tissues, and confer defense to herbivores and tolerance to multiple stresses. Research on symbionts of plants has focused on soil organisms such as nitrogen-fixing bacteria and mycorrhizal fungi, although recent studies suggest that endophytes of great agronomic interest can also generate major shifts in the belowground subsystem. We conducted a meta-analysis to examine the available knowledge on the effects of endophytes on the soil. Our objective was to provide a synthesis of existing data that, comprehensively and quantitatively, evaluates the different pathways by which the grass-endophyte symbiosis may affect belowground components and processes, and high-lights gaps in knowledge relevant to agroecosystem management. The presence of endophyte was found to reduce root biomass and mycorrhizal colonization of plants. In turn, a significant stimulation of root exudates by endophytes was detected. Effects of endophytes on soil respiration and litter decomposition were not significant. No pattern was found in the response of the soil fauna to endophyte presence. Our review revealed that we still need to improve our understanding about the impact of endophytes on other mutualistic symbionts. The grass-endophyte symbiosis is a promising interaction that, like those involving nitrogen-fixing bacteria and mycorrhizal fungi, may become an important tool for sustainable agriculture. (c) 2011 Elsevier B.V. All rights reserved.