Effects Of Competition Modes On Growth And Physiological Characteristics Of Populus Yunnanensis In Different Light Environments

Populus yunnanensis is a native poplar tree species in China.Previous studies have shown that there are significant differences in the responses of poplars of different genders to environmental stress,competition for nutrients and water also affects the growth and development of poplars of different genders.However,there is a lack of research on the competition of light between different genders,which is not conducive to the understanding of the natural regeneration of poplar and the change of sex ratio under closed field conditions.Therefore,in this study,the male and female seedlings of Populus yunnanensis were selected as experimental objects,and two models of intra-sex competition(same-sex competition)and inter-gender competition(heterosexual competition)were set up under 100% and 55% light conditions,studied the effects of different competition patterns on the morphological growth,biomass accumulation,photoresponse curve,photosynthetic pigments content,total carbon(C),total nitrogen(N)and total phosphorus(P)content and stoichiometric characteristic ratio of male and female seedlings of Populus yunnanensis were studied in different light environment.The purpose of this study was to determine the changes of material accumulation,physiological and biochemical changes of poplar seedlings under different light conditions,understand the effects of competition model on population sex ratio and population structure,to provide theoretical reference for the population variation of Populus yunnanensis and the undergrowth of poplar.Through this experiment,the following results are obtained:(1)Under full illumination,compared with the intra-sex competition,female plant height,basal diameter and leaf area decreased significantly,stem dry weight decreased27.90%,male plant leaf area and aboveground biomass increased significantly under inter-sexual competition.Under shading condition,the plant height and leaf area of male and female poplar increased significantly,but the biomass decreased significantly,especially the underground biomass;Compared with the intra-sex competition,inter-sexual competition decreased the growth and biomass of the two genders,the basal diameter of female plants decreased more,and the dry weight of leaves of male plants decreased more.Under shading condition,the basal diameter and total leaf area of male plant were larger than that of female plant.(2)Under shading condition,the photosynthetic ability of Populus tomentosa decreased significantly,but the light compensation point(LCP)had no significant change.Light saturation point(LSP)decreased,chlorophyll a,chlorophyll b,turnip increased significantly and chlorophyll a / b decreased;the photosynthetic capacity of male plant was significantly lower than that of female plant,and the chlorophyll a/b of female plant in inter-sexual competition was significantly lower than that of female plant,which was beneficial to the capture of light energy.(3)Under the condition of full illumination,compared with the intra-sex competition,the content of total C in stem and leaf of female and male decreased significantly,but the content of total P increased,and the content of total N in all organs of male plant did not change significantly;The increase of C/N in leaves and thick roots of female plants,the decrease in C/P and N/P in leaves,and the increase in C/P in thick roots;The male stem and thick root C/N decreased,the stem C/P and N/P decreased,and the rest of the organ N/P did not change significantly.Under shading condition,compared with the intra-sex competition,the total C content in the thick roots and stems of male plants increased significantly under the condition of inter-sexual competition,but the total C content of organs of female plants did not change significantly;The content of n in leaves and thick roots of male and female plants increased,the content of total N in fine roots of female plants decreased,and that in stems of male plants decreased;The content of total P in the underground parts of both male and female plants decreased significantly,but there was no significant change in the aboveground parts;The ratio of total C/N in stems of male and female plants increased significantly,but the other organs did not change significantly;the percentage of total C/P in the underground organs of female and male was increased,while that of male was increased only in thick root;The leaf and thick roots of female plants increased,while the stem total N/P of male plants decreased significantly,while that of other organs showed no significant difference.(4)Under sufficient light,the contents of sucrose,glucose,fructose and total sugar in male and female plants were decreased in inter-sexual competition compared with the intra-sex competition,and the decrease of male plants was more obvious than that of male plants;the rubisco activity of female plants increased significantly,but the activity of fbpase decreased significantly,while the activity of two enzymes did not change significantly in male plants.Compared with intra-sex competition,the content of sucrose and glucose increased slightly,but fructose content decreased slightly compared with intra-sex competition;the total sugar content of female plant decreased significantly,while that of male plant did not change significantly,and the Rubisco enzyme and FBPase of both sexes did not change significantly.The results showed that shading significantly affected the morphological characteristics,biomass accumulation,photosynthetic enzyme activity and photosynthetic ability of poplar seedlings,which resulted in the decrease of carbon assimilation ability and the decrease of non-structural carbohydrates.In order to adapt to shading environment,poplar seedlings not only adopted the strategies of increasing plant height,reducing basal diameter,increasing leaf area and optimizing biomass distribution,but also increasing photosynthetic pigment and regulating the distribution of C,N and P.Changing the stoichiometric characteristic ratio of each organ and reducing the physiological characteristics were used to improve the adaptability of each organ,such as debase LSP.The competition model obviously affected the adaptability of poplar seedlings to low light environment,the growth and biomass accumulation of male plants was better than that of female plants under sufficient light,and the whole illumination environment was beneficial to the growth and development of male plants.Under shading condition,the superiority of male plant was not obvious compared with that of female plant,and the competitive power between male and female plant was equal.