Forage legume responses to climate change factors

Incorporating forage legumes into grasslands is a recommended climate change mitigation strategy, but accruing desired benefits from legumes is contingent upon their resilience when exposed to climate change factors (CCF). Our objective was to synthesize literature describing responses to CCF of a broad array of forage legume species, including annuals and perennials from both temperate and tropical/subtropical regions. Most‐represented species in the related literature include alfalfa ( Medicago sativa L.), various Trifolium and Lotus species, rhizoma peanut ( Arachis glabrata Benth.), and capitata stylo ( Stylosanthes capitata Vogel). The data indicate that while CCF effects on forage legumes can be generalized, interactions among CCF, species, and site‐specific soil/climate conditions may cause variation from expected responses. In most instances, exposing forage legumes to CO 2 enrichment (eCO 2 ) increased forage accumulation (FA), but elevated temperature (eT) often reduced the magnitude of the positive response to eCO 2 . Photosynthetic acclimation to eCO 2 occurs in non‐N‐fixing plants, but legume nodules are large C sinks and drive sustained increases in legume FA to eCO 2 . Legume N 2 fixation and the proportion of legume N derived from N 2 fixation increase with eCO 2 , but the magnitude of the increases lessens with eT. Legume nutritive value (NV) responses to eCO 2 are less pronounced than FA responses, but decreased herbage N and greater nonstructural carbohydrate concentrations are common. Exposure to eT negatively affects NV unless intervals between defoliation events are shortened. Limited data on reproductive performance show CCF affect flower number, pollen grain morphology and viability, and behavior of pollinators, potentially influencing legume reproductive success.