Supraoptimal soil temperatures induced oxidative stress in leaves of creeping bentgrass cultivars differing in heat tolerance

High temperature is a major factor limiting growth of cool-season grasses during summer months. The objective of this study was to determine whether oxidative stress is involved in leaf injury induced by high soil temperatures in two creeping bentgrass (Agrostis palustris Huds.) cultivars, heat-tolerant L-93 and heat-sensitive Penncross. Shoots and roots were exposed to four differential temperature regimes in growth chambers and water baths: (i) 20/20 degrees C (control); (ii) 20/35 degrees C (high soil temperature); (iii) 35/20 degrees C (high air temperature); and (iv) 35/35 degrees C (high shoot/soil temperatures). Turf quality, leaf photochemical efficiency (Fv/Fm), electrolyte leakage (EL), content of a lipid peroxidation product (malondialdehyde, MDA), and activities of the antioxidants superoxide dismutase (SOD) and catalase (CAT) were determined. Turf quality and leaf Fv/Fm ratio decreased, whereas EL and MDA contents increased under high soil temperature alone or in combination with high air temperature regimes in both cultivars, but to a greater extent in Penncross than in L-93. Decreases in turf quality and Fv/Fm ratio and increases in EL and MDA were more pronounced at 20/35 degrees C than at 35/20 degrees C. The activities of SOD and CAT decreased with prolonged periods of high temperatures and to a greater extent for Penncross than for L-93. The reductions in SOD and CAT activities were more severe at 20/35 than at 35/20 degrees C. These results suggest that high soil temperature caused more severe oxidative damage to leaves than high air temperature by limiting antioxidant activities and inducing lipid peroxidation. This oxidative stress was associated with accelerated leaf senescence under high temperature conditions. Maintenance of antioxidant activities and low levels of lipid peroxidation was related to the better tolerance of creeping bentgrass to high soil temperature stress imposed on roots or high air temperature on shoots.