| The recruitment of seedlings is the key to maintaining population dynamics.The process of seedings is generally influenced by the age of neighbor with same or different,and that the process is often restricted by soil microorganisms,especially pathogenic microorganisms.At present,the research on sapling recruitment is mainly based on monoecious species,few studies based on dioecious plants.In this thesis,the widely distributed economic,ecological and garden plants Populus cathayana was chosen as the research object,I compared the effect of different genders,different ages of neighbor and soil sterilization treatment on male and female P.cathayana sapling through the field replantation experiment and indoor control experiments.The differences in seedling morphology,biomass accumulation and distribution,physiological biochemical and survival rates were analyzed to understand the neighbor relationship of plants at the gender level and to provide scientific basis on population dynamics and the construction of poplar forests.The main findings are as follows:1.Differences of male and female P.cathayana seedlings responding to larger age neighborsIn field experiment,it was found that the survival rate of seedlings under adjacent plants of adult poplars was low(less than 40%)and basically stopped growing through replanting seedlings around adult neighbors experiments;the survival rate increased first then decreased as the distance from the parent tree increased.Moreover,the survival rate of the seedlings with the opposite sex adult poplar was higher than that of the same sex.In addition,female seedlings had a higher survival rate than male seedlings.Based on the control experiment,after planting the seedlings of P.cathayana under the neighboring plants of different ages and sexes,it was found that the female seedlings in each treatment compared with the male plants in morphology(plant height growth,basal diameter growth,total root length,total root surface area),The biomass(leaf biomass,root biomass,total biomass)and photosynthesis(net photosynthetic rate,instantaneous water use efficiency)are the same or better.From the perspective of the sex of neighboring plants,neighboring plants of the same sex of different ages had a significant negative effect on the seedlings,while neighboring plants of the opposite sex of different ages had a negative or neutral effect on the seedlings.From the perspective of sterilization treatment,after sterilization,the neighbor effect,root neighbor effect and plant neighbor effect of female plants under heterosexual neighbors of different ages have changed from a neutral relationship to a negative correlation,while the leaf neighborhood of male plants effect,root neighbor effect,stem neighbor effect,and plant neighbor effect changed from a negative correlation to a neutral or positive relationship.In addition,the neighbor relationship between male and female seedlings of adjacent plants of the different age and the same sex did not differ before and after sterilization but showed a significant negative correlation.2.Differences of male and female P.cathayana seedlings responding to the same age neighborsThe results of planting female and male Populus cathayana seedlings under neighboring plants of the same age showed that female plants had higher biomass accumulation(leaf biomass,total biomass)than male plants.Neighboring plants of the same age and the same sex reduced the root growth(total root length,total root surface area),biomass accumulation(leaf,stem,root biomass),photosynthesis(net photosynthetic rate,instantaneous water use efficiency)and leaf nitrogen.There was no significant difference or increase in content between neighboring plants of the same age and opposite sex compared with a single plant.The neighbor effect analysis showed that the same age and the same sex neighbor plants had a significant negative effect on the P.cathayana plants,while the same age and opposite sex neighbor plants had no negative effect and even promoted the growth of female plants.At the same time,after sterilization,the neighbor relationship between female plants of the same age and opposite sex changed from a positive effect to a neutral relationship,and the neighbor relationship between male plants also changed from a neutral relationship to a negative relationship.However,sterilization had little influence on the relationship between the same age and the same sex neighbor plants.They both showed a significant negative correlation.In summary,the growth of male and female Populus cathayana seedlings was affected by the sex of the neighboring plant.The opposite-sex neighboring plants of P.cathayana were more beneficial to the growth of seedlings than the same-sex neighboring plants,and the direction and intensity of the neighboring effect were affected by the different developmental stages of the neighboring plants with greater neighbor effect when growing with a older neighboring plant.From the perspective of soil sterilization,the responses of P.cathayana seedlings to neighboring plants of the opposite sex were related to soil microorganisms,while the responses to neighboring plants of the same sex were not driven by soil microorganisms.The results give new knowledges on plant neighbor relationships,but also can provide scientific basis for population dynamic of P.cathayana and some potential application value during the construction of poplar plantations. |
