Effects of various irrigation regimes on water use efficiency and visual quality of some ornamental herbaceous plants in the field

Efficient use of water by selection of appropriate plant species is becoming increasingly important in semi-arid and arid regions to save scarce water resources. In this study, the effects of water deficit irrigation on physiological responses, water-use efficiency (WUE) and visual quality of four herbaceous ornamental species (Malva sylvestris, Althea rosea, Callistephus chinensis and Rudbeckia hirta) were investigated. The experiment was a split-plot treatment based on a randomized complete block design experiment with four irrigation levels (25%, 50%, 75%, and 100% reference evapotranspiration (ET0)) and four replications. Althaea rosea and Rudbeckia hirta showed dehydration avoidance by modifying their leaf shape, decreasing stomatal conductance and increasing Water Use Efficiency (WUEi). The lowest specific leaf area and highest root/shoot ratio were seen in Althaea rosea at 25% and 50% ET0, respectively. Malva sylvestris used a drought escape strategy by early flowering. In terms of landscape aesthetic values, Malva sylvestris performed well with a minimum of 75% ET0. Althaea rosea and Rudbeckia hirta were well-maintained with 25%-50 % ET0 irrigation levels. However, for an acceptable aesthetic landscape appearance, the minimum level of irrigation for Callistephus chinensis was 50% ET0. These results suggest that use of drought-tolerant spices such as Althaea rosea and Rudbeckia hirta can improve irrigation management and conserve aesthetic performance in urban landscapes.