Drought‐induced leaf senescence and regreening upon rewatering associated with chlorophyll metabolism in Kentucky bluegrass

Abstract Drought stress is a major factor limiting the quality and persistence of cool‐season turfgrass species by accelerating leaf senescence and reducing overall vigor. This study was conducted to examine physiological responses associated with drought‐induced leaf senescence and post‐drought regreening in Kentucky bluegrass ( Poa pratensis L.), with particular emphasis on chlorophyll metabolism. Plants of two cultivars, Baron and Bewitched, were grown under controlled environmental conditions and subjected to well‐watered control and drought stress treatments, with post‐drought rewatering. Physiological parameters such as turf quality, relative water content, chlorophyll fluorescence, and chlorophyll content were evaluated throughout drought and recovery. In addition, the activities of a chlorophyll degradation enzyme, pheophytinase (PPH), and a chlorophyll synthesis enzyme, porphobilinogen deaminase (PBGD), were measured in response to drought and rewatering to observe the effect of drought on chlorophyll metabolism and to determine which pathway plays a more important role. Drought stress caused leaf dehydration, chlorophyll loss, reduced photochemical efficiency, and lower turf quality in both cultivars, although these parameters recovered following rewatering. PPH activity increased significantly during prolonged drought stress, whereas PBGD activity did not change significantly under drought. During post‐drought recovery, PBGD activity increased, while PPH activity declined to non‐stress levels. The decline in chlorophyll during drought‐induced leaf senescence may be associated with enhanced chlorophyll degradation enzyme activity, whereas the regreening observed during rewatering is likely related to the resumption of chlorophyll synthesis. These findings provide insight into the physiological mechanisms controlling drought‐induced senescence and post‐stress recovery in turfgrass and may be useful for the development of drought‐tolerant cultivars.