Sex-related Responses In Growth And Defense Of Populus To Elevated Temperature

Climate warming has become one of the hot issues in the world,which usually affect the growth and development of species,interspecific relationship,and then affect the community composition and structure and function of ecosystem.Meanwhile,global warming will directly lead to the enhancement of surface evapotranspiration,resulting in increasingly serious drought.Previous studies on the responses of woody species with global warming are based on monoecious species,while much less attention has been paid in dioecious trees.Due to the differential reproductive cost between two sexes in dioecious plants,which may generate significant gender differences between the growth and defense with the change of environmental resources.Currently,how dioecious species respond to environment mainly focus on abiotic environmental changes,while the studies on how such plants respond to biotic stresses（especially herbivorous insects）in the context of climate warming are less.In this text,Populus cathayana and P.yunnanensis,widely distributed species in China,were been employed to investigate the sexual response in growth and defence with global warming and（or）drought by the heating device of infrared heating tube to simulate warming and the caterpillar of Spodoptera litura（a generalist）in control experiments.The aims were to study the defensive and adaptive law of the males and females against insect under the drought and elevated temperature and the relationship between these defensive response mechanisms and plant growth,which plays an important role in the deep understanding of the growth and reproduction of dioecious plants as well as the adaptation of defensive mechanisms to climate warming.At the same time,the results can provide theoretical basis and scientific reference for poplar population maintenance as well as poplar plantation construction under the future warming climate context.Here are some findings as follows in our study:1.We studied the growth（including morphological traits,biomass,photosynthetic capacity）and defense capacity of male and female P.cathayana under the control treatment（CK;natural temperature with natural moisture content with natural precipitation）,and under the changed soil moisture by elevated temperature（+4℃）treatments（T-W;no watering（natural precipitation）;T+W;by supplemental water to natural soil moisture content）.We also compared the differences to against herbivory between male and female poplar under changed soil moisture.The results showed:the plant growth,photosynthetic rate and defense performance had gender d ifferences when soil moisture content changed under warming.Compared with male s,the total leaf area,leaf biomass,total biomass,root biomass,root-shoot ratio and root branching intensity of females were significantly higher,while the average root dia meter and leaf carbon（C）content were significantly lower.Compared with the control,the net photosynthetic rate（Pn）of males and females decreased in T-W treatment,and Pn,intercellular CO₂concentration（Ci）,stomatal conductance（gs）,transpiration rate（E）of males and females decreased more than that of females,but the instantaneous water use efficiency（WUEi）and carbon isotope composition(δ¹³C)of male and female plants increased significantly,and WUEi of female plants increased significantly and the increased more than males,but the difference of female and male plants was not significant.Compared with males,females had higher leaf nitrogen（N）content and lower C/N ratio（C/N）.T+W treatment significantly reduced WUEi and female plants,b ut increased leaf N content.On the other hand,warming treatment increased the feeding area of male and female leaves by S.litura,and the difference of feeding area between male and female leaves was significantly increased in T-W treatment,and the area of female leaves was significantly larger than that of male leaves.However,there was no significant difference between male and female leaves in feeding area.The dry weight of the caterpillar of S.litura was significantly higher than that of the control and the T+W treatments,but there was no difference in the dry weight of the caterpillar between the two treatments.Compared with the control,T+W treatment significantly increased the activities of phenylalanine ammonia-lyase（PAL）and polyphenol oxidase（PPO）of the leaves of males and females,and the female plants had higher PAL activity than the males;while T-W treatment significantly decreased the PAL activity,total phenol and tannin contents of the female leaves,but significantly increased the PPO activity of the male leaves.The activities of PPO,total phenols and tannins in leaves of females were significantly lower than those of males.2.We also investigated the morphological,physiological and biochemical responses to altered water conditions both in female and male P.yunnanensis,to 1)compare the performance of P.yunnanensis on growth（morphology,gas exchange and nutrient）and defense（e.g.,leaf contents of phenol,tannin and flavonoid）between well-watered（control）and drought;2)compare the sex-related differences in defense traits of P.yunnanensis upon drought treatment;3)evaluate sex-related difference in defoliation-induced tree survival to water availability.We found that compared to well-watered condition,drought inhibited growth and photosynthetic processes in females more than in males.We also found that leaf defensive performance（S.litura caterpillar damage and chemical defense）in females was lower than in males under drought condition.Moreover,higher mortality rate in females found than in males under drought after all leaves defoliated.Thus,due to different reproduction cost of females and males,the differences of certain traits between sexes were magnified under drought.