Physiological And Ecological Responses Of Sexual-specific Populus Deltoides Seedlings To Drought Stress

With the continuous change of global climate,drought problem is increasingly serious.Dioecious plants are important parts of terrestrial ecosystems,showing gender differences in response to different environmental stresses.The aim of the present study was to detect the sex-specific responses to drought（30%soil water content）in one-year-old male and female seedlings of Populus deltoides.Changes in morphology characteristics such as plant height,root morphological characteristics and biomass accumulation,as well as leaf water parameters,chlorophyll fluorescence parameters,gas exchange parameters,mitochondrial alternative oxidase activity,non-structural carbon and stoichiometric analysis,and other physiological and biochemical indicators of seedlings were determined.The different impacts of drought stress on male and female seedlings were compared.The physiological mechanisms of the sexual difference response to drought could provide important reference for the resistance of dioecious plants to unfavorable environments.The main findings are as follows:（1）Under drought stress,the growth of males was significantly better than that of females,with the higher growth rate of plant height and biomass accumulation in the underground parts.Compared to female plants,the total root length and root surface area of male plants were significantly increased,and the root volume,number of root tips,and number of crossings were increased（p<0.05）.Under drought stress,the excess carbon consumption of root system was reduced in male plants,while root volume and the total surface area were increased,which ensures the contact area with the soil enlarged.The deep root system has more lateral root branches,which could better utilize and absorb the water in the deep layer of the soil and improve males’drought resistance.Male plants have better resistance and adaptive mechanisms to drought stress environment.（2）The net photosynthetic rate P_n of females under drought stress was significantly reduced mainly due to the influence of non-stomatal factors,that is,the reduced activity of RUBP carboxylase（Rubisco）.The significant decrease in P_n of males was the results of the combined effect of stomatal and non-stomatal factors.Compared with female plants,the conservative water use strategy promoted the drought resistance in males.The F_v/F_m of females decreased significantly.Although the original photochemical efficiency of PSⅡdecreased with the decrease of soil water content,the damage suffered by PSⅡdue to drought stress was reversible.The Y_（II）of the male plants was higher than that of the females.The damage to the PSⅡreaction center and the inhibition of photosynthesis of males were lower than those of females.Male plants form a certain protective mechanism in response to drought stress,which can better improve the protective ability of photosynthetic apparatus.The AOX enzyme activity of male poplars was higher than that of females.By adjusting the alternate pathways,the excess energy in the chloroplast was eliminated,PSⅡand electron transfer efficiency were optimized,and the photosynthetic electron transfer was maintained at a high level,thereby reducing the stress on the photosystem.（3）Compared with female plants,under drought stress,the male plants of Populus deltoides have higher C assimilation efficiency,stronger C accumulation and nutrient enrichment ability in the roots,and stronger drought resistance ability.Although the total amount of carbon assimilation decreased under drought stress,the soluble carbohydrate content of the females significantly increased,which increased the cell osmotic potential and reduced the damage of drought stress to plants.（4）After 30 days of rewater treatment following drought stress,The net photosynthetic rate,the growth rate of plant height and ground diameter of male and female plants were significantly lower than those of the control group,which indicated that drought stress limited the growth of male and female seedlings of Populus deltoides.Even after rewatering,the plants could not recover from drought stress in a short time.The results showed that the growth of male and female seedlings was inhibited under drought stress,and the female seedlings were more affected.Male plants improve their resistance to drought stress by adjusting nutrient allocation,changing root morphology,optimizing water use strategies,and increasing adaptation mechanisms.