Effects of Extended Daylength on Shoot Growth and Carbohydrate Metabolism for Creeping Bentgrass Exposed to Heat Stress

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Heat injury in creeping bentgrass (Agrostis stolonifera var. palustris Huds) has been associated with decreases in carbohydrate availability. Extending light duration may increase carbohydrate availability and thus improve growth of creeping bentgrass under heat stress. The objective of this study was to investigate whether turf performance and carbohydrate status could be improved by extending daily light duration for creeping bentgrass exposed to supraoptimal temperature conditions. `Penncross' plants were initially grown in growth chambers set at a day/night temperature of 20/15 °C and 14-hour photoperiod and then exposed to a day/night temperature of 33/28 °C (heat stress) and three different light durations: 14 (control), 18, and 22 hours (extended light duration) for 30 days. Turf quality and tiller density decreased with the duration of heat stress, as compared to the initial level at 20 °C, regardless of the light duration. However, both parameters increased with extended light duration from 14 to 18 or 22 hours. Extended light duration, particularly to 22 hours, also improved canopy net photosynthetic rate from -1.26 to 0.39 μmol·m-2·s-1 and daily total amount of carbon assimilation from -6.4 to 31.0 mmol·m-2·d-1, but reduced daily total amount of carbon loss or consumption to 50% through dark respiration compared to 14 hours treatment by the end of experiment. In addition, extending light duration from 14 to 22 hours increased water-soluble carbohydrate content in leaves both at the end of light duration and the dark period. These results demonstrated that extending light duration improved turf performance of creeping bentgrass under heat stress, as manifested by the increased tiller density and turf quality. This could be related to the increased carbohydrate production and accumulation. Supplemental lighting could be used to improve performance if creeping bentgrass is suffering from heat stress.