Photochemical performance of reproductive structures in Great Basin bunchgrasses in response to soil-water availability

Authors: Hamerlynck, Erik; O'Connor, Rory

Submitted to: AoB Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2021
Publication Date: 12/17/2021
Citation: Hamerlynck, E.P., O'Connor, R.C. 2021. Photochemical performance of reproductive structures in Great Basin bunchgrasses in response to soil-water availability. AoB Plants. 14(1). Article plab076. https://doi.org/10.1093/aobpla/plab076.
DOI: https://doi.org/10.1093/aobpla/plab076

Interpretive Summary: Effective restoration requires understanding what features make for a good restoration plant. Seed quality is one of those features in sagebrush steppe bunchgrasses, which are needed to restore the integrity of degraded sagebrush steppe rangelands. Seed production and seed filling in grasses depends on the physiological functioning of two reproductive structures: the seedhead and the flag leaf, but how the performance of these relates to soil water availability is unknown. We measured photochemical functioning under optimal (i.e. dark) and sub-optimal (i.e. ambient light) in watered and unwatered plants of two important sagebrush steppe restoration species, crested wheatgrass and squirreltail wild rye. We found watering improved overall photochemical function in both species, but this improvement was expressed best in the reproductive structure most important to grain filling in that species. We also found the photosynthetic characteristics of individual florets plays a role in seed head photosynthetic performance in addition to the seedhead’s physical structure. We concluded that using this kind of information could be used to develop better bunchgrass cultivars for sagebrush steppe restoration.

Technical Abstract: Active restoration, especially seeding, is necessary in sagebrush steppe rangelands degraded by the spread and dominance of exotic invasive annual grasses, in part due to low, episodic seed production of native perennial bunchgrasses. In contrast, the widespread exotic bunchgrass, crested wheatgrass, readily produces viable seed cohorts. How soil-water availability affects the ecophysiology of the reproductive structures that may underlie these differences are unclear. To address this, we measured pre- and post-anthesis chlorophyll fluorescence parameters of optimal (Fv/Fm) and light-adapted PSII quantum yield (''PSII) and ''PSII-derived electron transport rate (ETR) response to photosynthetic photon flux density (PPFD) in seed heads and flag leaves of watered and unwatered crested wheatgrass and squirreltail wild rye. Watering increased Fv/Fm in the sampled structures of both species, but ''PSII was similar between watering treatments. Pre- to post-anthesis Fv/Fm levels were maintained in crested wheatgrass seed heads but declined in flag leaves, with the opposite pattern apparent in squirreltail. Watering did not affect the ETR–PPFD response, but crested wheatgrass seed heads maintained higher ETR across saturating PPFD than did squirreltail. These findings suggest (i) photochemical efficiency is expressed in structures most closely associated with reproductive effort, and (ii) documented differences in seed head photosynthetic characteristics likely include some degree of allocation to individual floret photosynthetic capacity in addition to structural characteristics. We concluded that these physiological and structural differences may contribute to the differential ability of these species to establish from seed, and may help in effective plant material selection needed to improve restoration and conservation success in sagebrush steppe rangelands.