Interaction between legume and arbuscular mycorrhizal fungi identity alters the competitive ability of warm-season grass species in a grassland community

Abstract Arbuscular mycorrhizal fungi (AMF) and N 2 -fixing legumes can alter the community structure of grasses. However, the effect of AMF, N 2 -fixing legumes, and their interaction on the dynamics of prairie grass communities remains unclear. The aim of this study was to clarify the influence of two AMF ( Glomus cubense and Glomus sp.) and two legumes ( Medicago sativa and Dalea purpurea ) on the competitive relationship between three native cool-season ( Elymus canadensis , Elymus trachycaulus ssp. subsecundus , and Elymus lanceolatus ssp. lanceolatus ) and two native warm-season species of grasses ( Schizachyrium scoparium and Bouteloua gracilis ). Results show that AMF and legumes altered the community structure of the grasses. G. cubense favoured the productivity of warm-season B. gracilis when growing with M. sativa . This might be related to a negative impact of G. cubense on the nitrogen-fixing activity of M. sativa and to a lower N-use efficiency of E. canadensis and E. lanceolatus ssp. lanceolatus under competition. This suggested an increased ability of B. gracilis to use the available N resource as affected by more competitive species, whereas Glomus sp. reduced the competitive ability of this grass when associated with M. sativa . The decrease in B. gracilis biomass was thus likely caused by enhancement of P uptake by M. sativa over this grass. Glomus sp. was beneficial to S. scoparium , another warm-season species, in the absence of legumes, and this may be attributed to improved P-use efficiency of this grass under competition with cool season-grasses. In contrast, AMF and legumes were not beneficial for the cool season grasses. G. cubense depressed the growth of E. trachycaulus ssp. subsecundus , and M. sativa decreased nutrient uptake by cool-season native grasses. This study shows that beneficial effect of the arbuscular mycorrhizal symbiosis on the coexistence of warm-season grasses with more competitive cool-season grasses depends on the identity of the AMF symbiont, the presence of legume species, and nitrogen resource availability that was affected by the most competitive species or P-use efficiency of warm season species.