| In view of the lack of woody materials for vegetation restoration and slope greening in the subtropical area,the male and female cutting of native dioecious plant Broussonetia papyrifera were selected as materials.The cuttings were treated for 60days at light,medium and heavy drought respectively,then component properties,biomass structure,photosynthesis,metabolic material content,antioxidant enzyme activity and osmotic material content of the seedlings were measured.Same time,The characteristic parameters of four B.papyrifera young trees populations with significant difference in soil water content caused by topography were measured.The purpose was to analyze the seedlings responses to drought stress,and to study seedlings growth rate,physiological response and survival strategy under different drought stress,and to find out the effects of drought on population density,sex ratio and age structure.Then,study whether the above results will affect population density,population ratio and age structure ultimately.In order to provide the basis for variety selection,cultivation and conservation,development and utilization and resource protection for B.papyrifera.The main results are as follows:?1?There are significant gender differences in the quantity and quality components of root,stem and leaf?P<0.05?.The seedlings by reducing leaf number,leaf length,leaf width,single leaf area and total leaf area,but increasing leaf thickness to deal with drought stress.The leaves number of females was lower than that of males,while the length,width,thickness and area of leaves were higher than males?P<0.05?.Without gender difference the seedlings all reducing height and increasing stem diameter to responded drought stress.The females by increasing root length and reducing root volume,while the males by increasing root length and root volume to deal with drought.There were significant gender differences in leaf and root traits under drought stress.?2?There are significant gender differences in biomass accumulation and allocation strategies of the seedlings?P<0.05?.With drought increase,the total biomass of seedlings were decreased?P<0.05?,but the seedlings adapted to drought stress by increasing the root biomass and reducing the leaf proportion.Drought reduced stem distribution ratio,but there was no difference among drought gradients and between gender.The females total biomass was lower than males?P<0.05?,with leaf distribution ratio decreased more than males,while root distribution decreased less than males.However,the females leaves distribution ratio was higher than males,while the roots ratio was lower than males.?3?The photosynthetic pigment content of seedlings was significantly affected by drought.The contents of Chla,chlb and Chla+b increased first and then decreased with the increase of drought degree?P<0.05?,while the contents of Caro and Chla/b increased continuously?P<0.05?.The seedlings responded to drought stress by changing the content and proportion of photosynthetic pigment.With drought increase,Chla and Chla+b contents of females were more and more than males,while chlb,Caro contents and Chla/b had no gender difference.There was a significant difference in photosynthetic pigment among drought degrees,the difference was Caro>Chla+b>Chla>chlb>Chla/b,but all the females Chla and Chla+b contents were significantly larger than the males.?4?Drought significantly affects photosynthetic pigment?P<0.05?.With the increase of drought degree,photosynthetic rate?Pn?and stomatal conductance?Gs?decreased,transpiration rate?Tr?and intercellular CO2 concentration?Ci?increased first and then decreased.The Pn and Gs values of mild drought were the highest,the Tr and Ci values of moderate drought were the highest,and the photosynthetic parameters of severe drought were inhibited.Under sufficient water,the parameters were lower than that of mild or moderate drought,indicating that B.papyrifera was a drought resistant plant.Photosynthetic pigment is significantly affected by drought?P<0.05?,and the order of effect was Tr>Pn>Ci>Gs,but significant effects by gender was Pn>Gs>Tr>Ci.Severe drought damages the photosynthetic system and reduces the potential Pn.There was no difference in potential Pn between light and moderate drought and CK.The Pn?Gs?Tr and Ci of males were higher than females,but the potential Pn was lower than females.?5?The effect of drought on physiological metabolism had significant gender difference?P<0.05?.With increase of drought,the content of soluble sugar?SS?and the activity of nitrate reductase?NR?increased and decreased successively,the content of sucrose?SU?and starch?ST?decreased gradually,and the content of pyruvate?PA?increased significantly.The content of SU and ST was the highest in mild drought,SS and NR were the highest in moderate drought,and PA was the highest in severe drought.Under drought,the sugar and nitrogen metabolism of females was higher than males.Sugar content and NR activity of males was higher than females,while the PA of males was lower than females.The influence of drought on metabolites was ST>SU>PA>NR>SS,and the influence between gender was ST>PA>NR>SU>SS,and drought had greater effects on metabolites than gender.?6?There was a significant gender difference in the effects of drought on the activities of antioxidant enzymes and the contents of permeable substance?P<0.05?.With the increase of drought degree,the activities of SOD,POD and CAT,and the contents of MDA and SP increased significantly.The activities of 3 enzymes and the contents of MDA and SP in females were higher than males.The SOD and POD activities and MDA content in females responded to drought faster than males.Droughts and genders had a significant effect on the activities of the three enzymes in the order of SOD>POD>CAT.Droughts had more effect on MDA than genders,but less on SP.?7?In natural B.papyrifera population with poor water holding capacity and low water content,the population size and population density of decreased significantly,and the age structure changed from growth type to decline type,and plant height and ground diameter decreased at all ages.The dry habitat reduced the sex ratio,with females mortality was significantly higher than males.Higher population soil water content,more clustered the young trees.With the increase of tree age,the distribution coefficient decreased gradually,from young tree's cluster distribution to adult tree's random or even distribution.In summary,drought had significant effects on the components,biomass structure,photosynthesis,physiological metabolism,antioxidant enzyme activity and osmotic substance content of B.papyrifera seedlings.Gender differences are significant between male and female seedlings.Male and female seedlings can respond to drought by adjusting the root,stem and leaf traits,and by changing the amount and proportion of photosynthetic pigments,and by changing the biomass allocation strategy.Seedlings adjust physiological metabolic rate and activate antioxidant enzymes system to resist drought,and increase the permeability of substances to reduce the damage caused by drought.In this experiment,mild drought is more conducive to the growth of the seedlings than adequate moisture,indicating that B.papyrifera have strong drought resistance.Males showed better morphological and physiological basis than females in terms of root traits,photosynthetic rate,antioxidant enzyme system and osmotic substance content.The gender differences in drought resistance of seedlings have significant effects on population density,population structure,population ratio and spatial distribution.Therefore,when selecting B.papyrifera cultivars,establishing artificial population,formulating cultivation measures and developing products,More attention should be paid to the possible effects of gender differences in drought resistance. |
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