Photosynthetic Rate and Root Growth Responses to Ascophyllum nodosum Extract–based Biostimulant in Creeping Bentgrass under Heat and Drought Stress

Creeping bentgrass ( Agrostis stolonifera ) experiences quality decline during summer in the United States transition zone and warmer regions. Various bioproducts have been used to improve creeping bentgrass performance and to mitigate effects of summer stress in the United States transition zone. This 2-year study was carried out to examine if foliar application of seaweed extract (SWE; Ascophyllum nodosum )-based biostimulant Utilize ® could enhance creeping bentgrass nitrate reductase (NaR) activity, and root viability under heat and drought stress conditions. The Utilize ® was sprayed biweekly on creeping bentgrass foliage at 0, 29, 58, 87, and 116 µL⋅m −2 , with application volume of 815 L⋅ha −2 . Two weeks after first application, plants were exposed to heat (35/25 °C, day/night) and drought stress (40% to 50% evapotranspiration replacement) conditions for 42 days in an environment-controlled growth chamber. In general, the abiotic stress caused turf quality reduction. Foliar application of Utilize ® at 58, 87, and 116 µL⋅m −2 increased turf quality, leaf color ratings, leaf chlorophyll, carotenoid content, and net photosynthetic rate (Pn). Utilize ® at 58, 87, and 116 µL⋅m −2 increased NaR activity by 26.5%, 16.3%, and 16.3%, respectively, when compared with the control. Utilize ® at 58, 87, and 116 µL⋅m −2 increased root biomass, root length, surface area (SA), and root volume when compared with the control. Utilize ® at 58 and 87 µL⋅m −2 improved root viability by 16.3% and 30.9%, respectively, when compared with the control. Our data indicate that the SWE-based biostimulant Utilize ® improves nitrogen (N) metabolism and root viability. Utilize ® treatment at 58 µL⋅m −2 biweekly can be considered an effective approach for improving creeping bentgrass performance during summer stress.