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

Authors: Hamerlynck, Erik; Ziegenhagen, Lori

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2019
Publication Date: 1/1/2020
Citation: Hamerlynck, E.P., Ziegenhagen, L.L. 2020. Seed head photosynthetic light responses in clipped and unclipped sagebrush steppe bunchgrasses. Journal of Arid Environments. 172. https://doi.org/10.1016/j.jaridenv.2019.104013.
DOI: https://doi.org/10.1016/j.jaridenv.2019.104013

Interpretive Summary: This study showed that crested wheatgrass, an exotic species widely used in sagebrush-steppe restoration efforts because it readily establishes from seed, has seed heads with higher photosynthetic capacity that are also more efficient at capturing light than the native grasses, squirreltail and bluebunch wheatgrass, and that simulated grazing did not affect seed head photosynthetic characteristics. Clipping and shading did reduce reproductive biomass in squirreltail, but not the two wheatgrasses, which may have used carbon from other plant parts to set seed. This study could be useful in selecting native grasses to develop reproductive photosynthetic characters more like crested wheatgrass.

Technical 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.