Effects of a biostimulant on the heat tolerance associated with photosynthetic capacity, membrane thermostability, and polyphenol production of perennial ryegrass

Limited research has been published to determine the impact of amino acid based biostimulants on turfgrass stress physiology and metabolism. Physiological responses of perennial ryegrass (Lolium perenne L.) treated with or without Macro-Sorb Foliar (FOLIAR) and subjected to optimal growing conditions or high air temperature stress (20, 28, and 36 degrees C) were investigated in vivo using three separate growth chamber experiments. Turfgrass photochemical efficiency (Fv/Fm ratio), leaf membrane thermostability, and leaf antioxidant (polyphenol) concentration were measured. Perennial ryegrass treated with 0.64 mL m(-2) FOLIAR and exposed to prolonged high air temperature stress (36 degrees C) exhibited 95% better mean photochemical efficiency and 65% better membrane thermostability than control plants. Leaf polyphenol concentrations were largely unaffected by individual treatments or temperature. No treatment differences were detected for plants maintained in the optimal temperature regime (20 degrees C), and only photochemical efficiency treatment difference were found for plants maintained at 28 degrees C. The results show that exogenous and sequential applications of FOLIAR improved perennial ryegrass metabolic responses in a highly controlled growth chamber environment. It remains difficult to extrapolate data obtained from growth chamber experiments to the field; therefore, caution must be taken when making turfgrass management recommendations.