The Impact of End of Day Light Quality on Turfgrass Morphology.

The impact of light quantity on turfgrass morphology is well known. However, to date, research on light quality has been limited. Alterations to the quality of photosynthetic active radiation (PAR) occur under vegetative shade due to a decrease in the red light to far-red light ratio (R:FR). This shift in the PAR spectra results in shade avoidance responses that decrease turfgrass quality. Additionally, similar changes in light quality can be observed at dawn and dusk, and changes to light quality at those times can regulate the growth of turfgrasses under shade as well as full sun conditions. End of day (EOD) light responses are phytochrome regulated, and decreased red to far red ratios observed at dusk (or dawn) can decrease plant density and increase vertical growth. The objective of this research was to determine if applications of monochromatic red light applied at the end of the day could decrease shade avoidance responses in creeping bentgrass (Agrostis stolonifera L.). Creeping bentgrass plants were grown under greenhouse conditions in either full sun or under qualitative shade (0.7 R:FR), both with and without EOD red light treatment. We found that 70 µmol m^-2 s^-1 of red light applied for 30 minutes near the end of civil twilight improved creeping bentgrass morphology compared to plants not treated with EOD red light. Under full sun, creeping bentgrass treated with EOD red light exhibited a significant decrease in average leaf length along with a significant increase in turfgrass density. Under qualitative shade, however, there was no significant change in average leaf length, but plants treated with red light did exhibit a significant increase in turfgrass density. These preliminary results demonstrate the impact of EOD light quality on turfgrass morphology. Further, our results show that prescriptive light treatments applied at specific times of the day can improve the morphology of turfgrasses grown under shade or full sun.