The combined effects of water deficit and heat stress on physiological characteristics of endangered Nouelia insignis

Abstract

Dry-hot valley is characterized by water deficit and heat stress which often occur simultaneously in the field. Nouelia insignis has become endangered and natural regeneration of the species in the dry-hot valley is limited. Seedlings subjected to each water deficit treatment (achievement by withholding irrigation for 0, 3 and 6 days, respectively) were randomly divided into three groups and transferred to climate chambers set at 25, 40 and 50 °C for 1 h, respectively. Leaf relative water content, photosynthetic activity and maximum quantum yield of photosystem II (Fv/Fm) determined after 1 day of recovery were decreased significantly, but pigment content and catalase (CAT) activity increased significantly under severe water deficit or extreme heat. Soluble sugar content increased significantly under severe water deficit or moderate heat stress. Significant interactive effects between water deficit and heat were found in leaf relative water content, Fv/Fm, non-photochemical quenching coefficient (NPQ), CAT activity and soluble sugar content. Fv/Fm of seedlings treated at combination of 50 °C and water deficit did not recover to the original level after 1 day of recovery. In conclusion, both severe water deficit and heat stress could lead to water loss of leaves and adversely affect plant metabolic activities of N. insignis. Particularly, the effects were aggravated when severe water deficit and extreme heat occurred simultaneously. Water deficit and heat, particularly their combination, might be the key factors which limited natural regeneration of N. insignis in the dry-hot valley.