Morphological and physiological responses to drought stress in eleven genotypes of the Juniperus species

Drought is one of the most prevalent and critical environmental stresses affecting a variety of plants, particularly ornamental plants. One of the useful methods to alleviate the effect of drought stress is to screen for and develop drought-tolerant varieties. In this study, a factorial experiment based on the completely randomized design was conducted to investigate the responses of 11 genotypes from different Juniperus species at two irrigation regimes (normal, drought: not irrigated for a four-week period) in terms of growth and biochemical characters. Drought stress had a significant negative impact on the assessed growth characters. The G3 and G8 genotypes had the highest root fresh weight and root dry weight at both normal and water-deficit stress conditions. G3 showed the highest root volume at normal conditions but at the drought stress, the highest root volume belonged to G1 and G8. At drought stress conditions, the leaf fresh weight and dry weight of G9, G8, G6, G4, G3 and G11 were higher than other genotypes. The stem fresh weight of G3 and G11 and the stem dry weight of G11 and G8 manifested higher values than other genotypes when water deficit stress was imposed. Stem diameter decreased in the seedlings at the drought stress, however, G2, G3, G4, G8, G9 and G11 had higher values than others at stress conditions. The relative water content decreased in the plants under stress, however, the reduction in G3, G5 and G6 were smaller than the rest of the genotypes. Among the genotypes, G5 and G3 showed the highest antioxidant activity under water-deficit stress. The genotypes G1, G6, G7 and G8 had also a notable increase in the antioxidant activity at drought stress conditions. Under drought stress, the highest increase in the proline content belonged to G3 followed by G5, G6 and G7 and the G5, G6, G10 and G8 genotypes had the highest amount of soluble sugars. In conclusion, G3 (Juniperus chinensis var. Sargentii) and G8 (Juniperus chinensis ‘Kallayʼs Compact’) showed mainly better performance under drought stress, which can be suggested as candidate drought-tolerant genotypes to be used in breeding programs for the sustainable development of urban landscape in arid and semi-arid areas. Although G5 (Juniperus procumbens ‘Nana’) had low biomass in this experiment, it showed high antioxidant activity, proline and soluble sugars at the drought stress conditions. Therefore, further investigation is needed, especially at more severe drought stress conditions, to elucidate its outstanding response to drought stress in terms of antioxidant activity and proline and soluble sugars content.