Varied morphological and physiological responses to drought stress among four tea Chrysanthemum cultivars

Drought is a serious stress factor,limiting crop yield and restricting the expansion of production area. Breeding and commercialization of drought-resistant varieties is an important approach to alleviate the negative impact. Tea Chrysanthemum with its multiple health benefit has shown a great potential for the improvement of people's living standards.Current research activities have been centered on cultivation techniques,product processing,and chemical analysis.However,there is only limited information on varietal differences in response to drought stress and its mechanisms. In this study,four tea Chrysanthemum cultivars were used to investigate morphological, physiological, and photosynthetic characteristics of seedlings in pot experiments with varied relative water content( RWC) in the soil( control,RWC at85% —90%; light stress,RWC at 65% —70%; medium stress,RWC at 45% —50%; sever stress,RWC at 25% —30%) in order to unveil varietal differences and possible mechanisms of drought resistance. Multiple indicator variables were analyzed by the method of membership function to evaluate synthetic drought resistance. These variables provide a theoretical basis for the cultivation and breeding of water-saving drought-resistant varieties.Results showed that,following the increased severity of drought stress,the growth of four tea Chrysanthemum cultivars was inhibited as parameters for the leaf increment,leaf area,and biomass were decreased,while the root to shoot ratioincreased to enhance the soil moisture utilization. Following the decrease of leaf relative water content,the content of malonic dialdehyde( MDA) was increased,while the content of praline( Pro) and soluble protein( SPC) was increased to maintain the cell turgor content. The activities of superoxide dismutase( SOD) were enhanced to protect cell membranes from damages. Under the increased levels of drought stress,chlorophyll( Chl) content was significantly increased,and net photosynthetic rate( Pn),transpiration rate( Tr),and stomatal conductance( Gs) were significantly reduced. The intercellular CO2concentration( Ci) initially decreased and then increased,indicating that the reduced photosynthetic rate of plants under drought conditions was related to stomatal and non-stomatal factors. In the meantime,following the increased levels of drought stress,differences in morphology,biochemical and photosynthetic characters among four tea Chrysanthemum cultivars were observed. The leaf relative water content of Ruhe,Huangchulong,and Fanbailu were higher than in Yurenmian. The biomass yield and Pro content were higher and MDA content was lower in Ruhe,and it significantly differed from the rest of varieties. The membership function method was used to calculate the synthetic drought resistance. Ruhe was the most drought resistant,followed by Huangchulong,then Fanbailu,and finally Yurenmian,suggesting that Ruhe should be considered first for water-saving cultivation.