Adaptive Strategies Of Clonal Plants Growing In Heterogeneous Environments

Heterogeneity in space and in time is the ubiquitous feature of habitats. Almost all plants complete their life histories in temporally and spatially heterogeneous environments at certain scales. In the evolutionary process,plants may have constituted various adaptive strategies to cope with environmental heterogeneity. In principle,clonal growth contributes markedly to the ability of clonal plants to make use of environmental heterogeneity. In this thesis,the strategies of guerilla-type clonal plants to adapt themselves to heterogeneous environments are addressed using both field and greenhouse experiments.In inland dune habitats like Maowusu sandland in northeastern China,sand burial is a common episode encountered by plants. Due to the unevenness of burial in horizontal space,genet or clonal fragment of clonal plants often incurs partial sand burial. In one greenhouse and two field experiments,effects of clonal integration on survival and growth of the ramets of the stoloniferous herb Potentilla anserina and the rhizomatous grass Psammochloa villosa in response to sand burial were investigated. The results show that clonal integration greatly enhanced the survivorship of the buried ramets of both species. Cost-benefit analysis shows that the ramets of P. anserina which survived sand burial benefited significantly from clonal integration,while their connected unburied ramets did not incur any cost,so that the growth of the whole clonal fragments of P. anserina was enormously enhanced. It is,therefore,concluded that clonal integration is one of the adaptive strategies for clonal plants to manage local stress caused by sand burial in sand dune habitats.Two greenhouse experiments were conducted to study clonal plasticity of the stoloniferous clonal herb Halerpestes ruthenica in response to light intensity,nutrient availability and salinity. Light intensity,nutrient availability and salinity all have significant effects on clonal growth and clonal morphology of H. ruthenica. Deep shade,low nutrient availability and high salinity markedly reduced its growth.Moreover,the degree and pattern of plasticity in biomass,leaf area,number of ramets,stolon length,petiole length and root to shoot ratio in response to salinity demonstrated genotypic variation. Under low nutrient availability,the stolon internode of H. ruthenica elongated while the stolon branching intensity decreased,which are consistent with the foraging model,indicating that H. ruthenica can forage nutrients (i.e.,improve nutrient acquisition) by means of clonal plasticity when growing in spatially heterogeneous environments. It is concluded that clonal plasticity is an alternative means for clonal plants to battle environmental heterogeneity.In another greenhouse experiment,we addressed the responses of three stoloniferous clonal herbs inhabiting different habitats to artificial environments with reciprocal patchiness of light and nutrients. When ramet grown in high light intensity and low nutrient availability was connected to that grown in low light intensity and high nutrient availability,biomass of both ramets grown in high light intensity and low nutrient availability,and in low light intensity and high nutrient availability,as well as whole clonal fragments,was significantly enhanced. Meanwhile,root to shoot ratio of the ramet grown in low light intensity and high nutrient availability significantly increased while that of the ramet grown in high light intensity and low nutrient availability greatly decreased. These results indicate that the three studied clonal herbs demonstrated division of labor induced by reciprocal patchiness of light and nutrients. This environmentally induced division of labor benefits the whole genet greatly,and thus is another adaptive strategies of clonal plants to grow successfully in heterogeneous environments.