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Warm-season turfgrasses may be subjected to increasing drought as future urban irrigation regulations become more restrictive. Species differences in water use and transpiration response to drying soil may be exploited in the future to increase survival and maintain green color under drying soil conditions. This study was undertaken to provide background documentation on the sensitivity to soil–water deficit of three warm-season grasses: ‘Argentine’ bahiagrass (Paspalum notatum); ‘Floratam’ St. Augustinegrass (Stenotaphrum secundatum), and ‘Empire’ zoysiagrass (Zoysia japonica). Each of these turfgrasses demonstrated a two-phased linear transpiration response to gradually drying soil as expressed by a normalized ratio between the transpiration rates of drought stressed to well-watered plants (NTR). In this study, well-watered bahiagrass used 30% more water on a daily basis than did well-watered St. Augustinegrass or zoysiagrass. However, under drought, the three grass species transpired the same amount of water during the soil drying period up until NTR to 0.1. Since bahiagrass reached an NTR of 0.1 at 10.3 days versus 12.7 and 13.0 days for St. Augustinegrass and zoysiagrass, respectively, bahiagrass demonstrated a more rapid water loss rate during the drying period. The fraction of transpirable soil water (FTSW) remaining in the soil at the breakpoints for bahiagrass, St. Augustinegrass and zoysiagrass were 0.13, 0.16, and 0.19, respectively, in 2010, but were 0.18, 0.30, and 0.22, respectively, under slightly warmer conditions in 2011. The consistently low FTSW breakpoint for bahiagrass means that compared to the other species, bahiagrass continues to use water at a high rate late into the soil drying cycle before conserving soil water by decreasing stomatal conductance. That is, bahiagrass is likely to be subjected to greater soil–water deficits in lengthy droughts and needs mechanisms to better survive these droughts. The differences in breakpoints by year may be due to a combination of soil factors and temperature differences in the greenhouse. |
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