Photosynthetic photon flux density influences grass responses to extended photoperiod

Abstract

While plant sensitivity to extended photoperiod has been well documented, virtually no attention has been given to the possibility that low-level photosynthetic photon flux density (PPFD) during the extended photoperiod has an influence on the expression of the photoperiodic response. This study was undertaken with four grasses (Pensacola bahiagrass, Paspalum notatum Flugge, Tifton 85 bermudagrass, Cynodon dactylon L., Florakirk bermudagrass, Florona stargrass, Cynodon nlemfuensis Vanderyst var. nlemfuensis) grown under field conditions to examine their photoperiodic responses under a PPFD gradient. Individual lamps were positioned above each experimental plot to impose a PPFD gradient (from 0.1 to 30 μmol m −2 s −1) during the extended photoperiod treatment. The experiment was undertaken during two seasons of short daylengths and plant responses were measured as mass accumulation and height. There was a linear increase in both measured variables with increasing PPFD up to a level where the plant responses were light saturated. Saturating PPFD was generally consistent between mass accumulation and height within a species, but there were substantial differences among grasses. Grasses with the greatest relative increase in mass accumulation under saturating PPFD for the extended photoperiod also were found to require the greatest PPFD for saturation. Overall, these results provided original observations on the quantitative response of plants to PPFD showing that there was a linear increase in response at very low PPFD and a saturating PPFD that varied among the grasses.