Seaweed Extract-based Biostimulant Impacts on Nitrate Reductase Activity and Root Viability of Ultradwarf Bermudagrass Subjected to Heat and Drought Stress

Bermudagrass is a warm-season turfgrass species widely used for sports fields, home lawns, and golf courses. Ultradwarf bermudagrass has been used for golf course greens, but its quality declines with abiotic stresses. This 2-year study was designed to investigate if foliar applications of seaweed extract-based biostimulant Utilize (R) could improve ultradwarf bermudagrass photosynthetic function, nitrate reductase activity, root growth, and root function while under heat stress and drought stress conditions. Utilize (R) was applied to ultradwarf bermudagrass canopy at 0, 88, 117, 175, and 234 mu L.m(-2). Two weeks after the initial application of Utilize (R), bermudagrass was subjected to heat (40/36 ?, day/night) and drought stress (40-50% evapotranspiration replacement) for up to 42 days. Heat stress and drought stress caused decline of the turf quality. Foliar application of Utilize (R) at 117, 175, and 234 mu L.m(-2) biweekly consistently improved turf quality and leaf color ratings and increased leaf chlorophyll and carotenoid concentrations, net photosynthetic rate, nitrate reductase activity, and root growth and viability. On average, Utilize (R) at 117, 175, and 234 mu L.m(-2) increased turf quality ratings by 9.1%, 12.1%, and 10.6%, respectively, net photosynthetic rates by 32.4%, 45.0%, and 35.0%, respectively, and nitrate reductase activity by 16.7%, 18.8%, and 14.6%, respectively, compared with the control. Utilize (R) at 117, 175, and 234 mu L.m(-2) increased the root biomass, root length, surface area, and root volume compared with the control. Utilize (R) at 88, 117, 175, and 234 mu L.m(-2) in-creased root viability by 46.2%, 73.1%, 88.5%, and 74.4%, respectively, relative to the control. The results of this study suggest that seaweed extract-based biostimulant Utilize (R) improves nitrogen metabolism, photosynthetic function, root growth, and root viability. Foliar application of Utilize (R) at rates between 117 and 175 mu L.m(-2) biweekly can be considered an effective approach to improving ultradwarf bermudagrass performance under heat stress and drought stress environments.