Effect of reduced irradiance on drought resistance of three turfgrasses

Abstract Irrigation management of turfgrass under reduced irradiance can be complicated by interactions between reduced evaporative demand, shade tolerance, and competition for soil water from tree roots. A greenhouse study was conducted to understand how reduced irradiance influences the drought resistance of three turfgrasses. The turfgrasses used in this study were Falcon IV tall fescue [ Schedonorus arundinaceus (Schreb.) Dumort., nom. cons.], OKC1119 (Latitude 36 ® ) hybrid bermudagrass [ Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt Davy], and Meyer Japanese lawngrass ( Zoysia japonica Steud.). Plants were established in 15‐cm diameter lysimeters and subjected to two irradiance levels: shaded (55% nominal shade fabric) and non‐shaded (ambient greenhouse conditions with supplemental lights). Within each irradiance level, plants were subjected to either well‐watered conditions (daily replacement of evapotranspiration) or drought stress (no irrigation). Plants were assessed for leaf relative water content, visual leaf firing, water use rate, and dry root mass. The fraction of transpirable soil water (FTSW) was used to compare the break point where transpiration began to decline due to soil water stress. Transpiration began to decline at 48%–53% of FTSW under the non‐shaded environment. Irradiance intensity had no effect on the transpiration break point for tall fescue or Japanese lawngrass, while the break point was delayed (soil became drier) for hybrid bermudagrass. Results suggest reduced irradiance affects bulk surface resistances to transpiration (e.g., stomatal regulation) of turfgrasses under declining soil water differently for shade‐tolerant species and shade‐sensitive species.