Drought and heat stress injury to two cool-season turfgrasses in relation to antioxidant metabolism and lipid peroxidation

Drought and high temperature are two major factors limiting the growth of cool-season turfgrasses during summer in many areas. The objective of the study was to examine whether the adverse effects of drought and heat alone or in combination on tall fescue (Festuca arundinacea L.) and Kentucky bluegrass (Poa pratensis L.) involve oxidative stress. Grasses were exposed to drought (withholding irrigation), heat (35 degrees C/30 degrees C), and the combined stresses for 30 d in growth chambers. Turf quality (TQ), leaf relative water content (RWC), and chlorophyll content (Chl) decreased with prolonged drought, heat, and combined stresses for both species, but the severity of decline varied with stress type and duration. Transient increases in superoxide dismutase (SOD), ascorbate peroxidase (AP), and glutathione reductase (GR) activities occurred at 6 or 12 d of drought and the combined stresses in both species; however, the activities of all three enzymes decreased with extended periods of drought and the combined stresses. The SOD activity was not affected by heat stress alone. The activities of AP and GR were reduced after 18 d of heat stress for both species, but reductions were less than under the combined stresses. The catalase (CAT) activity continued to decrease to below the control level, beginning at 12 d for drought-stressed or heat-stressed plants and 6 d for plants exposed to the combined stresses. Lipid peroxidation occurred after 18 d of stresses in both species, as indicated by the increase in malondialdehyde (MDA) content. The results suggested that injuries of drought, heat, or the combined stresses to both tall fescue and Kentucky bluegrass, as manifested by declines in TQ, RWC, and Chl, could be associated with a decrease in antioxidant enzyme activities and an increase in membrane lipid peroxidation.