Changes of Leaf Membrane Fatty Acid Composition and Saturation Level of Warm-Season Turfgrass during Drought.

Although there is mounting evidence to support the association between drought tolerance and altered unsaturation levels in leaf membrane fatty acids (FA), a relevant study is lacking in zoysiagrass (Zoysia spp.) and St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze.] species. Our objectives are 1) to substantiate that variation exists among species and genotypes for leaf tissue FA composition under well-watered conditions; 2) to associate well-watered leaf FA composition with turf performance under drought; and 3) to determine if modifications in FA content occur during drought stress and if the changes associate with improved drought responses. Nine genotypes of three species were subjected to both controlled dry down and well-watered conditions for 12 days in a greenhouse. They were evaluated for water use, transpiration response, turfgrass quality (TQ), and leaf FA analysis. St. Augustinegrass had a constitutively higher unsaturation level of FA than two zoysiagrass species, owing to its higher linolenic acid and low palmitic acid levels. But the association between constitutively FA composition and drought tolerance has not been established. During dry down, relative FA contents remained stable and no early alteration of unsaturation level was found. Two genotypes UF182 Japanese lawngrass (Z. japonica Steud.) and ‘Zeon’ manilagrass [Z. matrella (L.) Merr.] displayed an increase in unsaturated fatty acids when severe drought stress occurred, which is likely associated with their good drought tolerance. These results support previous evidence suggesting that increased levels of linolenic acid under drought stress to be a defensive mechanism.