Approach To The Phenotypic Plasticity Of Leymus Chinensis Population Responding To Grazing

Phenotypic plasticity of plants plays a very important role in their coevolution with herbivores. Hierarchical organization of clonal plants offers various levels of phenotypic plasticity in their adaptation to environmental changes including grazing.In the Songnen Plains, the phenotypic plasticity of architecture and biomass allocation pattern responding to herbivores in the rhizomatous herb of Leymus chinensis was investigated with different grazing intensities as no grazing, light grazing, moderate grazing, heavy grazing and overgrazing. The research was conducted over two growth seasons from year 2002 to 2003. The results were shown that:Grazing reduced the standing numbers of live leaves per tiller and the cumulative patterns of leaf births and deaths per tiller. In the same time, new leaves spread all the growth seasons with different grazing intensities. The average leaf angles of plant deceased in different plots with grazing intensified. Both horizontal and vertical spacers in un-grazed plot were elongated longer than those in the grazed plots, while the nodes of rhizome spacer were reverse.The foraging and trampling of herbivores made the tillers of L. chinensis lateral spread, changing the growth form from erect to prostrate. Moderate grazing simulated L. chinensis to produce more tillers, keeping a larger density, while heavily grazing affected the renewal of tiller.Grazing also changed the patterns of biomass accumulation and biomass allocation in L. chinensis. It reduced the biomass per tiller, and biomass in grazed plots were 7.71, 22.76, 11.56 and 6.66% of that in un-grazed plot, while these of shoot biomass were 49.43, 33.38, 8.87 and 3.93%, and these of rhizome biomass were 77.29, 69.58, 30.31 and 9.40%, respectively.The ratio of above and below ground biomass decreased with increase of grazing intensities, which indicated that shoot biomass decreased more quickly than rhizome, and relatively more biomass were allocated to stem in un-grazed plot, while less in grazed plots. Furthermore, much more biomass was allocated to leaves when grazing intensities increased.As a result, the architecture plasticity and biomass allocation of L. chinensis population were investigated at three levels of leaf, clone and population, which supported the idea that the phenotypic plasticity is selected to increase the performance of L. chinensis in habitats with different grazing intensities.