Phenotypic Plasticity And Local Adaptation Of Phragmites Australis In Response To Environmental Changes

With rising sea levels and frequent extreme climates,the erosion of ocean tides makes coastal wetlands face more complicated environmental changes,such as salt stress and rising water levels.In some inland wetlands,increased heat dissipation leads to water shortages and few flooding.The survival and adaptation of wetland plants in coastal wetlands and inland wetlands are affected by environmental factors such as salinity,water level,and neighboring plant species.Phragmites australis is a dominant herb widely distributed in wetlands with high genetic variability,phenotypic plasticity,and ecological adaptability.It usually forms monodominant community and is an important species in the temperate wetland ecosystem.Phenotypic plasticity and local adaptation are important strategies for P.australis to respond to abiotic and biotic stresses in their habitats,and play key determinants in response to environmental changes in the short and long term,which are potentially important for species evolution.Therefore,studying the relative importance of phenotypic plasticity and local adaptation in the process of P.australis ecological adaptation,exploring the response mechanism of P.australis populations to different environmental factors and the intraspecific differences are important for the protection and restoration of wetland ecosystems guiding significance.In this study,we selected the P.australis populations in coastal wetlands Yellow River Delta and inland freshwater such as the Mata Lake Wetland and Panjin Wetland.The common garden experiment were conducted through measuring the total biomass,the distribution of above-ground and underground biomass,plant height,density,base diameter,leaf water potential,relative water content,specific leaf area and photosynthetic rate,transpiration rate and stomatal conductance and other plant functional traits to explore the morphology and physiology of P.australis under the effect of salinity,climate,water level and neighboring plants.The differences in phenotypic plasticity response and fitness of salt marsh and freshwater P.australis populations to heterogeneous habitats were compared,and the epigenetic basis of phenotypic plasticity was explored through DNA demethylation.From the perspective of phenotypic plasticity and local adaptation,the physiological and ecological responses,adaptation strategies and causes of the P.australis population under heterogeneous biological and abiotic factors were revealed.The following experiments were mainly carried out:(1)An experiment was conducted to determine the adaptation strategies of different P.australis populations to salinity and climate.The results show that salinity significantly influenced morphology,biomass,leaf number and ion content,and these traits changes with different climatic conditions.In Panjin and Fanggan gardens,P.australis changed morphology,relative water content,photosynthesis,chlorophyll fluorescence,and ion and element content in leaves and roots.In addition,the biomass,rhizome ratio,stomatal conductance,and leaf ion content of salt marsh populations and freshwater populations had obvious trait plasticity under salt stress.Studies have found that in humid climates,salt tolerance of P.australis was low and ion absorption increased,which may be osmotic adjustment through increased osmotic pressure and the efflux of sodium ions from leaves.P.australis had higher salt tolerance in Panjin low relative air humidity,which may be related to osmotic adjustment and leaf dehydration.Leaf dehydration does not require any energy input,which was also confirmed by higher biomass.At the same time,different genotypes in different populations had great differences in salt tolerance.Under the conditions of wetland salinization in the future,the survival of salt intolerant genotypes may be affected,thereby reducing the genetic diversity of P.australis.All in all,the study found that both salt marsh and freshwater P.australis can survive and grow under the salt condition of 20 g/L.Under higher soil salinity,salt marsh population do not show better characteristics than freshwater population.Both P.australis populations response to soil salinity and climate change through phenotypic plasticity.(2)An experiment was carry out to determine adaptation strategies of different P.australis populations to gradient water level and frequency.The results showed that the P.australis could tolerate stable water levels and fluctuating water levels of different frequencies below 30 cm,due to its developed aeration organization,the growth of adventitious roots,the increase in branch elongation and water use efficiency.Coastal saltmarsh populations were more adaptable to high and low water levels than populations from inland freshwater wetlands.Saltmarsh population could quickly extend plant height and distribute higher biomass to leaves,improving gas capture and carbon assimilation capabilities,contributed to the survive of P.australis in flooded conditions.Compared with saltmarsh populations,freshwater populations had lower biomass,but their rapid physiological adjustment capabilities promoted the adaptation of P.australis to the 30 cm water level.Populations from coastal saltmarsh with variable water levels were more tolerant to high and low water levels than inland freshwater populations,which preferred medium water levels(15 cm).At the same time,highfrequency water level fluctuations had greater negative impact on the growth of P.australis than that of low-frequency fluctuations,and there is no difference in the traits of saltmarsh and freshwater populations in response to fluctuation frequency.This experiment showed that there may be local adaptations related to water level in coastal salt marsh and inland freshwater P.australis populations,and the intraspecific differentiation of P.australis played an important role in ecological adaptation.(3)We tested the adaptation strategies of P.australis to neighboring plants under salt stress.The results showed that under the salt condition,the stem biomass,leaf biomass,underground biomass,plant height,density and base diameter of P.australis were significantly reduced.Compared with the non-neighborhood plant group,neighboring plants of different functional types had significant effects on the biomass,plant height,density and basal diameter of P.australis,but the effects on specific leaf area and leaf thickness were not significant.When no salt is added,the neighbor effect of the same species of neighboring plants and gramineous neighboring plants with P.australis was negative,which might be due to the overlap of niches,and the application of salt alleviated this negative effect,especially in gramineous plants,the neighbor effect changed from a negative competition effect to a positive promotion effect.This result was consistent with the stress gradient theory.P.australis adjusted phenotypic traits to adapt to the salinity and neighbor plant environment.It showed strong phenotypic plasticity in response to salinity and neighboring plant conditions,especially the plasticity of biomass allocation.Phenotypic plasticity played an important role in responding to different neighborhood environments.(4)To test the role of epigenetics in the effect of different P.australis populations on salinity,DNA methylation experiment was conducted.The results showed that the salinity treatment significantly reduced the biomass,plant height,base diameter,relative elongation rate,net photosynthetic rate and flowering rate,and significantly increased the root-to-shoot ratio of the P.australis.Consistent with the previous results,phenotypic plasticity played an important role in the salt tolerance of salt marshes and freshwater populations.Phenotypes and physiological traits of P.australis from different origins were significantly different.The morphology of P.australis was significantly related to the soil electrical conductivity of the sampling site.The phenotypic differences of P.australis populations from different salt conditions were stable,indicating that the phenotypic plasticity might not be the only strategy for P.australis populations in salt environment,the local adaptation formed by P.australis also promoted their survival in the salt environment.After the DNA demethylation and salt treatment,the basal diameter of the freshwater population increased significantly,while the basal diameter of the salt marsh population decreased significantly.The same change trend was observed in the biomass,flowering rate,and photosynthetic rate of the P.australis,which indicated that the DNA demethylation treatment enhanced the salt tolerance of freshwater populations,but reduces salt tolerance of salt marsh populations.DNA demethylation treatment had a significant impact on the salt tolerance of different P.australis populations,confirming that the change of P.australis phenotype was regulated by DNA methylation.In addition,DNA demethylation had different effects on the salt tolerance of different genotypes of P.australis.Plant phenotypic plasticity wass regulated by DNA methylation,but it was also affected by genetic variation.In summary,P.australis has high phenotypic plasticity and local adaptation.Phenotypic plasticity and local adaptation play an important role in the heterogeneous habitat as an adaptation strategy of P.australis.Salt marsh and freshwater population respond to environmental heterogeneity such as water and salt in coastal wetlands and inland wetlands by adjusting the morphological and physiological characteristics such as biomass allocation,plant height,density and photosynthetic rate.Coastal salt marsh and inland freshwater population can adapt to salt stress and neighboring plant stress through phenotypic plasticity.At the same time,P.australis populations also have certain local adaptability to salinity and water level.The epigenetic variation of P.australis is one of the molecular mechanisms that form the regulation of phenotypic plasticity.The results of this study can provide a theoretical basis for the prediction of the adaptation and distribution of wetland plants under future environmental changes,The results are of great significance for determining the mechanism of intraspecific variation driving the composition of local species and forming a wide range of ecological adaptation.