Contrasts and commonalities in compensatory reproductive photosynthesis between exotic and native sagebrush steppe perennial bunchgrasses

Authors: Hamerlynck, Erik; O'Connor, Rory

Submitted to: Ecological Society of America Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/6/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Photosynthetic activity by the seed-head itself significantly contributes to seed provisioning in sagebrush steppe perennial bunchgrasses whose population dynamics are reliant on sexual reproduction and establishment from seed. It has been demonstrated that photosynthetic rates increased in experimentally clipped florets compared to unclipped controls in crested wheatgrass (Agropyron cristatum), a widely distributed exotic in North American sagebrush steppe. This compensatory photosynthetic response might co-enhance tolerance to both grazing and drought, as it takes place directly at the point of reproduction. However, it is currently unknown if compensatory reproductive photosynthesis response is common to native semiarid bunchgrasses, or, if present, varies with phenological stage. To address this uncertainty, we experimentally defoliated basal florets in seed-heads of crested wheatgrass and in two native perennial bunchgrasses, bluebunch wheatgrass (Pseudoroegneria spicata) and Great Basin wildrye (Leymus cinereus). We measured direct and indirect net photosynthetic gas exchange (Anet) responses in clipped basal and unclipped distal florets, respectively, and compared these to rates in florets at similar positions on unclipped seed-heads over both pre- and post-anthesis reproductive stages. Crested wheatgrass basal floret Anet was 2.1 to 4.3 times higher than rates in native grasses, regardless of clipping treatment or phenological period. Clipping did not induce increased Anet in any species over the pre-anthesis, while Anet was ca 50% higher in clipped basal florets compared to unclipped controls in all species over the post-anthesis period. Anet in florets distal to clipped basal portions did not differ from those above unclipped controls over the pre-anthesis. However, post-anthesis crested wheatgrass florets distal to clipped florets had Anet (6.2 umol m-2 s-1 +0.42 S.E.) significantly higher than florets above controls (4.5 umol m-2 s-1 +0.22 S.E.; p < 0.05), something not observed in either native grass. The overall higher reproductive photosynthetic rates in crested wheatgrass, and the higher rates of both clipped basal and unaffected florets distal over the post-anthesis grain filling period to these likely contribute to this exotic grass’s demonstrated ability to produce viable seeds under conditions that limit native bunchgrass seed production. Moreover, these results also suggest compensatory reproductive photosynthesis is a common feature in semiarid bunchgrasses, and is likely a mechanism contributing to variation in convergent drought- and grazing-tolerance in semi-arid bunchgrasses.