Physiological And Ecological Responses Of Different Phragmites Australis Haplotypes To Salt Stress And Spartina Alterniflora Competition

East Asia is a very representative center of diversity of Phragmites austrilis(Cav.)Trin.ex Steud.In China,the P.austrilis population is mainly composed of two P.austrilis populations from different geographical sources(haplotype O and haplotype P).In order to explore the differences in the growth and physiological performance of the two haplotype,this study was based on the Yellow River Delta in Shandong Province.The two haplotypes of P.austrilis were distinguished through preliminary sampling and non-coding chloroplast DNA(cpDNA)detection and applied to greenhouse planting experiments.And in the greenhouse experiment,the two main haplotype(haplotype O,haplotype P)of the local dominant plant populations were exposed to the salt environment(salt water irrigation treatment 0%,1%,2%),the survival situation in the wild that grows and competes with Spartina alterniflora.The results showed that after 100 days of treatment,haplotype O performanced better than the haplotype P in morphology traits,biomass accumulation,asexual reproduction and leaf physiology traits.But with the addition of S.alterniflora,in some indicators,competition factor makes the gap between the two haplotypes smaller.Details as follows:In terms of morphology,the haplotype O obtained a larger plant height and leaf number than the haplotype P.The base diameter of the two haplotypes was not much different,and the relative growth rate was higher for haplotype P.Higher salt stress caused a greater decrease in plant height,while competition caused an increase in the relative growth rate.The results showed that the haplotype O has more advantages in morphology,tends to mature when harvested,and grown rapidly in the early growth period to obtain better light conditions.And the increased in the number of leaves expands the plant's availability for photosynthesis.Combined with the leaf enzyme activity analysis in Chapter 5,it can be concluded that the haplotype P has higher productivity at harvest.Both haplotypes maintain their advantage in the competition by increasing the relative growth rate.In terms of biomass accumulation and distribution strategies,haplotype O showed more biomass accumulation than haplotype P,indicating that it has greater productivity and stronger salt tolerance.However,it is worth noting that the addition of competition has narrowed the gap in biomass accumulation between the two haplotypes,which indirectly indicates that the haplotype P has stronger competitiveness when coexisting with S.alterniflora.The accumulation of biomass decreased under the influence of salt stress,and the distribution made a difference under the influence of competition.Facing the S.alterniflora competition,more stem biomass allocation of haplotype O was related to higher plant height,and more light was obtained through stem elongation,thereby enhancing light assimilation.The higher root biomass allocation of haplotype P indicates that it tends to enhance its competitiveness by increasing the absorption of nutrients and water under competitive pressure.In terms of reproductive characteristics,haplotype O showed stronger asexual reproduction ability than haplotype P.Similarly,the addition of competition also narrowed the gap in asexual reproduction between the two haplotypes.The number of ramets was affected by salt stress mainly in the later stages of growth,indicating that the clonal propagation of the two haplotypes is less affected by salt when the resources are sufficient.In terms of leaf physiological characteristics,haplotype O showed greater ability to maintain chlorophyll and photosynthesis to accumulate carbohydrates,and have higher values of certain physiological characteristics,including photosynthesis,transpiration,water use efficiency and nitrogen content.The haplotype O in this study showed higher physiological characteristics and stronger physiological response than the haplotype P,indicating its stronger growth ability and salt tolerance.In response to S.alterniflora competition,many physiological indicators of haplotype P changed little under the influence of salt stress,and this response is conducive to the stable growth of plants.The growth and reproduction performance of S.alterniflora illustrated the inhibition of the growth of S.alterniflora by the two haplotypes,and reflects the competitive ability of the two haplotypes.The results showed that the haplotype O inhibited S.alterniflora in growth and biomass accumulation,while the haplotype P mainly restricted the reproduction of S.alterniflora.In response to salt stress,the two haplotypes maintained the number of leaves,specific leaf area,leaf nitrogen and phosphorus to ensure the photosynthetic area and the material input required for physiological processes.Under high salt stress,higher chlorophyll content and chlorophyll fluorescence were used to regulate and maintain photosynthetic production capacity.In these key functional traits in response to salt stress,haplotype O outperformed haplotype P for the most part.In response to the competition of S.alterniflora,both haplotypes maintain high morphological growth to ensure resource acquisition and colonization capabilities;and increased the number of leaves and leaf phosphorus content to compensate for the weakening of photosynthesis caused by competition.In this study,the haplotype O showed strong growth ability and tolerance to salt stress.This was consistent with the haplotype distribution observed in the field,that is,the related genotypes of haplotype O mostly occured in the areas with the highest salt impact,and the related genotypes of haplotype P occured in the areas with the lowest salt impact.In the sampling process of this study,the P.austrilis communities that growed together with S.alterniflora under field conditions were all haplotype P.However,in the competition with S.alterniflora,the haplotype P was less affected by competition than the haplotype O,and inhibited the reproduction of S.alterniflora.Salt tolerance and competitiveness may be the key to the population retention of the two haplotypes respectively in the complex and dynamic environment of the Yellow River Delta.