A Study Of Phenotypic Plasticity And Genetic Polymorphism Of Leymus Chinensis Populations Under A Long-term Grazing Disturbance Along Northeast China Transect (Nect)

Plants adapt to the heterogeneous resources under the long-term grazing disturbance. This adaptaion is considered a strategie in the course of the co-evolution between plant and herbivore, mainly through the production of phenotypic plasticity to achieve. We uesed the molecular ecology methods combined with traditional methods to investigate the phenotypic plasticity and genetic polymorphism of L. chinensis populations and explain the adaptation mechanisms in the molecular level under grazing disturbance.Three L. chinensis populations with 10 to 30year exclosures were selected for this study along the NECT in 2008, the phenotypic plasticity of architecture and biomass allocation pattern responding to long-term grazing was investigated. At the same time, we used amplified fragment length polymorphism (AFLP) to detect genetic variation among populations. Ous results showed:1. The indexes of leaf morphological plasticity in all populations decreased under long-term grazing, including number of live leaves, leaf length, leaf width, leaf angle, especially the leaf angle. The heights of L. chinensis populations showed significant changes affected by the grazing. The average height of grazed populations in Changling is 8.45 cm, only one-third of ungrazed populations. Long-term grazing also reduced L. chinensis population and rhizome densities. The average biomass per tiller of grazed populations were less than ungrazed ones but the biomass allocation and the ratio of above and below ground biomass had no changes. It was shown that the long-term grazing effects was greater than geographical isolation in 2-factor variance analysis.2. Nine AFLP primer pairs detected a total of 482 bands of which 385 were polymorphic, the percentage of polymorphic loci was 79.87%. Genetic diversity, genetic similarity, genetic distance, gene flow, the UPGMA cluster analysis, AMOVA were analyzed based on the pofile observed in AFLP. The results showed that genetic diversity of L. chinensis populations was affected by long-term grazing disturbance, but this effect was small, mainly caused by environmental heterogeneity after grazing or gene flow. Cluster analysis results divided the 6 populations into three categories according to geographical location, indicating that the effects of geographic isolation on genetic divergence and diversity of L. chinensis populations are greater than the long-term effects of grazing. Further analysis indicated that no significant correlation was observed between the genetic diversity and the changes in phenotypic plasticity in grazed and ungrazed populations.In conclusion L. chinensis populations in NECT offer phenotypic plasticity in the adaptation to long-term grazing. AFLP analysis was applied to a wide range of genetic diversity exists between and within the L. chinensis populations, this diversity is decided by geographical isolation and grazing. The long-term grazing on L. chinensis populations significantly affect changes in the phenotypic plasticity but small to the genetic diversity.