Physiological response and drought resistance evaluation of Gleditsia sinensis seedlings under drought- rehydration state
Authors: Liu Fuhua , Zhao Yang , Wang Xiurong , Wang Biao , Xiao Feng , He Kequan 
Published: August 2023

Abstract
G. sinensis is an economically and ecologically important tree species with a wide distribution in China. Nearly two thirds of China's landmass is an area of arid or semi-arid regions. G. sinensis seedlings are very susceptible to drought-rehydration-drought cyclic pattern during the growth process, the physiological mechanisms of drought resistance and rehydration of G. sinensis lack of quantitative systematic research, the lack of good drought-resistant family in production practice, and the lack of reasonable evaluation of drought-resistant ability of the method, which seriously impeded the promotion of the selection and breeding of good family lines of G. sinensis and the development of the industry. Therefore, in this study, we conducted simulated natural drought and rewatering experiments on seedlings of 58 G. sinensis families to compare the differences between morphological, photosynthetic and physiological indexes of seedlings of different families with different degrees of drought and rewatering, with the aim of searching for suitable methods of evaluating the drought resistance of G. sinensis seedlings and screening drought-resistant families, elaborating on the differences in the effects of drought stress on G. sinensis, and revealing the mechanisms of G. sinensis growth and physiological response in different periods of drought. The drought resistance index (DRI) was used as the main index, combined with growth, leaf morphology and photosynthetic physiological indexes to comprehensively grade out five different drought tolerance taxa and screen out five representative family lines. The contents of proline (Pro), soluble protein (SP) and malondialdehyde (MDA), and the activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) of the seedlings of the five families in successive droughts increased with the degree of drought, and the highest values basically appeared in the period of severe drought, and then gradually declined after the rehydration. Pro, SP and MDA contents, CAT, POD and SOD activities of the high resistance (HR) family were 1.70, 0.61, 2.24, 3.75, 1.28 and 1.16 times higher than those of the natural control treatments during the severe drought period. Principal component analysis (PCA) revealed MDA and soluble sugars (SS) as the main indicators of response to drought and rehydration in G. sinensis. Increased antioxidant enzyme activity and changes in the content of osmoregulatory substances may be important factors causing drought tolerance mechanisms. The synthesis of growth, leaf morphology and photosynthetic indexes of G. sinensis seedlings under arid environments can be used as a method for its evaluation of drought resistance, and provide a reference for the screening of good drought- resistant family lines. G. sinensis are less drought tolerant in the seedling stage, so drought tolerant family lines should be selected for production applications and adequate moisture should be ensured for the seedlings.