| Genetic diversity is the basis for biological adaptation to the environment,and plays an important role in the phylogenetic evolution of species,community assembly and ecosystem functioning.Phenotypic diversity is the external manifestation of genetic diversity,which is subject to genetic variation and external environment.Changes in landscape patterns caused by human activities are profoundly affecting the phenotype and genetic diversity of species,and comparing the intraspecies variation of genetic,and plant functional traits of the same species in different environment helps to predict the species' fate as well as related ecosystem functions under the changing environment,and also helps to predict the ecological and evolutionary consequences of anthropogenic activities in the ecosystem.The common reed(Phragmites australis)is an important foundational species in wetland ecosystems,its phenotypic and genetic diversity are affected by human factors such as river management and habitat fragmentation.This study investigated 30 natural populations of P.australis in Ningxia Plain along the Yellow River,including 11 populations in the northeast populations along the lower reaches of the Yellow River(NE),11 populations in the south along the upper reaches(S)and 8 population in the northwest along the lower reaches of the Yellow River with serve fragmentation(NW).The geographic location information of the population was recorded.Nine plant functional traits such as height,base diameter and leaf water content of the common reed were measured to analyze the phenotypic diversity of P.australis population.And 2 chloroplast DNA fragments and 11 nuclear microsatellite markers(SSR)were used to analyze the genetic diversity of P.australis population.At the same time,the rhizomes of the common reed were collected to carry out common garden experiments to elucidate the genetic and environmental effects on phenotypic variation in the common reed.The main results and conclusions of this article are listed as follows:(1)Among the three regions in this study,compared with the genetic diversity of P.australis in NE and S regions along the river(NE:Na?11.18,I=3.85,He?0.70;S:Na=11.09,1=3.17,He=0.69),the populations in NW region in fragmented habitats had the lowest number of alleles and genotype diversity(Na=9.73,I=2.77),but its expected heterozygosity was higher(He?0.72).The results of molecular variance analysis(AMOVA)in regions showed that NW maintained the highest genetic differentiation(?PT?0.51)and the most obvious genetic structure,and the genetic differentiation was the lowest in NE(?PT=0.06).The results suggested that the genetic diversity of P.australis may be more sensitive to habitat fragmentation.The fragmented habitat in NW region was dynamically changing because of agricultural activities,and there were three populations in NW region contained only one genotype(clone),which implied that the main reason for the loss of genetic diversity in NW may be a bottleneck effect,rather than subsequent genetic drift and restricted gene flow.(2)AMOVA results showed that the 57.22%of genetic variation of P.australis populations came from within population;the genetic differentiation coefficient of the common reed population between regions ranged from 0.008 to 0.015,indicating that the degree of genetic differentiation between regions was very low.Bayesian clustering and principal coordinate analysis(PCoA)results showed that there was no distinguishable genetic divergence among three regions.The Mantel test and multiple matrix regression test results showed that there was no relationship between pairwise geographic and genetic distances.Above results indicated that P.australis in this study area was more affected by the influence of habitat or river,which supported the inference that the reason for the loss of genetic diversity in NW was not restricted gene flow.The genetic differentiation between relatively upstream and relatively downstream regions(S and NE)was much smaller than that between non-riparian and riparian regions(NW and NE,or NW and S),which indicated the prominent effects of the propagule transport of the river flow or the continuity of riparian habitat on gene flow along the river of P.australis.The high genetic diversity of the common reed in NE also proved that the gene flow between upstream and downstream may be asymmetric due to the direction of river flow.(3)The analysis of chloroplast haplotype showed that haplotype O was the main haplotype of P.australis in the study area.Compared with NW and S,there were fewer haplotypes in NE.The differences in nuclear genetic variation and chloroplast haplotype abundance indicated that the impact of pollen transmission by continuous habitats along rivers may be more important than the rhizome dispersal by water flow for shaping genetic diversity and structure.In long distance continuous habitats,sexual reproduction played a greater role in promoting the genetic connectivity and diversity of common reed.(4)NW harbored the highest level of phenotypic diversity within and among populations.According to Pearson correlation and linear regression analysis,there was no significant correlation between the coefficient of variation of plant functional traits and Shannon's diversity index of genetic variation in 30 P.australis populations.There was no significant correlation between the common reed in common garden and the corresponding population in Ningxia Plain for all plant functional traits except height and leaf length.The results suggested that the height and leaf length of P.australis were greatly affected by genetic variation,while other plant functional traits were greatly affected by the environment.That was to say,phenotypic and genetic response to the habitat fragmentation were different,the level of phenotypic variation was not related to genetic diversity in P.australis natural populations,and genetic effects had a weak effect on plant phenotypes.This study revealed the phenotypic and genetic variation of P.australis populations in different river positions and habitats in Ningxia Plain,and highlighted the significant role of habitat connectivity along riverbanks and habitat fragmentation caused by human activities in wetland plant phenotypic and genetic diversity.And our study can serve as important references and suggestions for conservation and management of wetland ecosystem. |
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