Morpho-physiological and biochemical responses of four ornamental herbaceous species to water stress

Understanding of water-deficit responses of plants can lead to better establishment and management of water-conserving landscapes. Due to the importance of landscape plants and the need for water relations of field-grown herbaceous species, this study investigated morphological and biochemical responses of Malva sylvestris, Althea rosea, Callistephus chinensis and Rudbeckia hirta under water stress. The main plots were the four plant species and the subplots were irrigation levels of 25%, 50%, 75%, and 100% reference evapotranspiration (ET0). The results indicated that 75% ET0 irrigation treatment had no effect on the relative water content of Althea rosea and R. hirta. Althea rosea and R. hirta had the highest deficit-irrigation tolerance index for root length and root density in 25% ET0. Only A. rosea, exhibited no oxidative stress as reduced chlorophyll content under 75% ET0–50% ET0, and also under 50% ET0–25% ET0. Only in R. hirta, the ratio of chlorophyll a/b was linearly increased. Water stress had no effect on total soluble carbohydrates in C. chinensis, R. hirta and M. sylvestris. Moving from 75 to 25% ET0, R. hirta showed the lowest electrolyte leakage which was followed by A. rosea. Althea rosea and R. hirta displayed a drought-avoidance mechanism.