Arbuscular mycorrhizal fungus-mediated interspecific nutritional competition of a pasture legume and grass under drought-stress

It is widely claimed that common mycorrhizal networks (CMN) play significant roles in facilitated transfer of nutrients between plants. This experiment investigated the role of a common mycorrhizal network with a C₃ legume and a C₄ grass under drought-stressed conditions, and assessed whether there was an interaction between water and plant species on rhizosphere bacterial DNA community profile. Shoot biomass of Trifolium subterraneum increased by almost 150% when grown in close proximity to Panicum clandestinum when the only possible connection between their roots was via a common mycorrhizal network. Inter-species competition between T. subterraneum and P. clandestinum was observed in low-nutrient soil. The soil bacterial communities in rhizospheres of both T. subterraneum and P. clandestinum were similar. Drought-stress increased the relative abundance of Firmicutes and Actinobacteria and decreased the relative abundance of Proteobacteria, especially when plants were likely connected by a CMN. Drought-stress decreased the abundance of N-cycling genes under P. clandestinum but not under T. subterraneum. The competitiveness of T. subterraneum when grown adjacent to P. clandestinum corresponded with enhanced P acquisition and depletion of soil P under P. clandestinum for both water treatments at different times. Thus, T. subterraneum may have been more competitive due to enhanced direct P acquisition from soil under P. clandestinum rather than by direct P transfer from P. clandestinum to T. subterraneum via a common mycorrhizal network.