# Direct and Indirect Effects of Floral Defoliation on Photochemical and Non‐Photochemical Chlorophyll Fluorescence Dynamics of a Semiarid Bunchgrass

## TL;DR

This study explores how clipping florets in crested wheatgrass affects photosynthesis and energy dissipation in remaining parts of the plant.

## Contribution

The study reveals an integrated photosynthetic response in crested wheatgrass following floral defoliation.

## Key findings

- Clipping basal florets increased regulated non-photochemical photoprotection without reducing PSII quantum yield.
- Distal florets showed higher PSII quantum yield and reduced unregulated energy dissipation after clipping.
- Crested wheatgrass compensates for tissue loss through an integrated reproductive photosynthetic system.

## Abstract

Photosynthetic florets support reproductive development and energetic seed provisioning of semi‐arid bunchgrasses whose population dynamics rely mainly on sexually produced propagules. Photosynthetic gas exchange studies including crested wheatgrass (
Agropyron cristatum
) have found compensatory increases in seed‐head photosynthesis following floral defoliation are accompanied by reduced light‐adapted PSII quantum yield (ϕ
PSII). We undertook a field experiment to ascertain if altered ϕ
PSII and optimal PSII quantum yield (F
v/F
m) were concurrent with higher quantum yield of regulated (ϕ
NPQ) or unregulated (ϕ
NO) non‐photochemical PSII absorbed energy dissipation. We quantified these responses in directly affected basal florets, and in unclipped distal florets to establish indirect responses to tissue loss. Clipping basal florets reduced F
v/F
m and increased ϕ
NPQ, indicating effective engagement of regulated non‐photochemical photoprotection, but did not reduce ϕ
PSII compared to unclipped controls. Florets distal to clipped basal florets had higher ϕ
PSII but not F
v/F
m, with concurrently lower ϕ
NO compared to those distal to unclipped controls, possibly due to improved electron transport due to carbon supplementation from damaged basal florets to developing distal propagules. These results demonstrate crested wheatgrass possesses a remarkably integrated reproductive photosynthetic apparatus, facilitating its ability to consistently produce viable seed cohorts under conditions that limit native bunchgrasses reproductive success.

After herbivory, crested wheatgrass florets must scrub excess absorbed light as heat via regulated physiological processes or less effective unregulated means. We found clipped florets heightened physiological control while undamaged florets reduced unregulated dissipation of excess light energy.