Temperature and Water Stress Effects on Growth of Tropical Grasses

Abstract

Coastal bermudagrass (Cynodon dactylon (L.) Pers.) and Kleingrass “75” (Panicum coloratum L.) were grown under controlled environments to evaluate the effects of high growth temperaturesand water stress on forage growth. Plants were grown under a controlled environment with 14/10 hour day/night temperatures of 30/20,35/25, and 40/3W C; 2 water regimes; and 3 stages or ages of regrowth at harvest. High growth temperatures significantly (KO.05) increased dry matter yield and accelerated tiller number and the maturation rate of the plants. Significant (JYO.05) increases in leaf area, weight per tiller, and plant height were observed as growth temperatures were increased. Reduction of number of tillers per pot due to water stress reduced dry matter yields approximately 380/o. The percent leaf was greater for the water-stressed plants than for the well-watered plants, but the leaf area per plant was less due to reduction of growth and delayed maturation. Dry matter yield of water-stressed plants grown under higher temperatures increased more than corresponding wellwatered plants as a result of increased rate of stem elongation and leaf development. Though water-stressed plants were shorter and had less leaf area than well-watered plants, the relative increase in both height and leaf area at higher temperatures of stressed plants was greater than well-watered plants. Apparently supraoptimal temperature (400 C) does not have a negative effect on yield in the presence or absence of moisture stress. Reduction of digestible dry matter content has been reported for warm-season tropical grasses sampled under conditions of high temperature and water stress (Holt 1975, Pitman et al. 1981, Wilson 1981). Environmental stresses also affect growth rates and yields of grasses. Optimum temperatures for growth of tropical grasses are 30 to 35” C during the day and 25 to 30” C at night (Dirven and Deinum 1977, Ivory and Whiteman 1978). Optimum temperature results in an increased rate of stem elongation and leaf appearance (Dirven and Deinum 1977) and an increase of the number of tillers and of leaves per tiller. An increase in area per leaf and leaf area per plant also contributes to the greater production. Conversely, water stress in tropical grasses reduces yield (Ng et al. 1975, Wilson et al. 1976) slows cell enlargement and stem elongation, and reduces leaf area and the shoot/ root ratio. High temperature can accentuate the rate of water loss, plant water deficits, and water stress. Although mid-summer sampling of warm-season grasses has facilitated evaluation of the combined effects of high temperatures and water stress, the independent effects of high temperature and water stress, and their interaction, remain to be quantified in controlled environments. Henderson and Robinson (1982) reported the effects of growth temperatures on yield of tropical grasses under 2 watering regimes, but the effects on yield components were not reported. In addition, growth temperatures reported to date generally have not exceeded 35’ C in most studies, yet summer daytime temperature extremes in the Southwestern United States commonly exceed 35” C. The objective of this study was to quantify the independent effects of high growth temperature and water stress, and their interaction, on yield and growth components of Coastal bermudagrass and Kleingrass 75.