Seed head photosynthetic light responses in clipped and unclipped sagebrush steppe bunchgrasses

Abstract Low seedling establishment limits the long-term success of sagebrush steppe restoration, and the physiological mechanisms underlying this remain unclear. To address this, we measured the photosynthetic light responses and seed head specific length (mg cm−1) of shaded and unshaded seed heads in clipped and unclipped plants to determine if grazing affects reproductive photosynthesis in sagebrush steppe bunchgrasses. We measured responses in an exotic species, Agropyron cristatum (crested wheatgrass) that readily establishes from seed, and two native grasses, Elymus elymoides (squirreltail wild rye) and Psuedororegnaria spicata (bluebunch wheatgrass), which do not. Defoliation did not affect seed head light saturation responses in any of the grasses. Agropyron cristatum seed heads attained higher light-saturated photosynthesis and higher photosynthetic light use efficiencies than the native grasses, consistent with its ability to produce viable seed crops. Defoliation and shading reduced post-anthesis seed head specific masses only in E. elymoides, suggesting this species reproductive effort relies on carbon fixed by the seed head itself. These findings could help in the selection and development of native plant materials with characteristics similar to the successful exotic grass to improve restoration efforts in degraded sagebrush steppe ecosystems.