Physiological Responses and Turf Performance of Warm-Season Turfgrass Under Drought.

Water availability for irrigating turf is limited in many areas of the U.S. where mandatory watering restrictions have become commonplace. Understanding the physiological responses and associated turf performances of commonly used warm-season turfgrass species is essential to improve their overall drought resistance and to generate irrigation recommendations for end users. The objectives of the study were: 1) to determine the relationship between physiological responses / turf performance and drying soil indicated by fractional transpirable soil water (FTSW); 2) to compare species and genotypes differences of four warm-season turfgrass species for physiological responses and turf performance under a progressive dry down in the greenhouse; and 3) to associate the above results with the turf performance in field plots under sandy soil. Sixteen genotypes from St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntz] (STA), Zoysia japonica (Steud.) (ZJ), Zoysia matrella (L.) Merr. (ZM), and bermudagrass [Cynodon dactylon (L.) Pers.] (CB) were planted in 120 cm deep acrylic tubes. Photosynthetic rate, transpiration rate, turfgrass quality and leaf firing during dry down were measured. The same 16 genotypes were also planted in field plots, and were evaluated for percent green cover, NDVI, turfgrass quality and leaf firing during naturally occurring drought in May for three weeks. Transpiration of the four turfgrass species declined earlier (FTSW=0.63-0.79) than photosynthesis (FTSW=0.54-0.79) followed by the progression of leaf firing (FTSW=0.40-0.71) and the decline of turfgrass quality (FTSW=0.31-0.61). Genotype UFCD347 CB maintained photosynthesis longer after transpiration declined. ‘Zeon’ ZM delayed leaf firing after both transpiration and photosynthesis declined compared to other ZM entries. Differences of ZM found when grown in acrylic tubes were consistent with the field study. In addition, STA was able to maintain green cover longer (4-16 days) than both zoysiagrass species in two years. No difference was found among STA cultivars in the greenhouse study. But in the field study, ‘Sapphire’ STA was the top performer. ‘Captiva’ STA had poor drought performance and slow recovery in the second year. Turfgrass quality of CB was greater than acceptable throughout the field study and resulted in little variation. Characteristics such as maintaining photosynthesis and delayed leaf firing found in the study warrant further research on elucidating the drought mechanisms of the genotypes demonstrating different physiological responses to drought.