Adaptive Characteristics Of Different Life Form Steppe Plants To Environmental Change

This dissertation studied on the growth of different life form steppe plants through the analysis of reactions of different life form steppe plants to environmental change, the analysis of growth plasticity and regeneration growth of modules of grass populations, and the analysis of displacement and compensation growth among different life form grass populations.(1) Reactions of different life form steppe plants to environmental change were researched in different spatial scales by dry weight per plant index. The results showed that, in large spatial scale, from large to small the rank of coefficient of variance (cv) of dry weight per plant of life form steppe was that stolon grass > rhizome grass> bunch grass> taproot grass, this proved that stolon grass and rhizome grass were more sensitive to environmental change; In middle spatial scale, the rank from large to small of cv of dry weight per plant of life form steppe was that rhizome grass> stolon grass > bunch grass> taproot grass, the reaction rule in middle spatial scale was similar with the reaction in large scale; In small spatial scale, the rank of cv of dry weight per plant of species was that Melilotoides ruthenica>Artemisia frigida>Stipa grandis>Agropyron michnoi> Cleistogenes squarrosa >Leymus chinensis, this also proved that stolon grass was more sensitive to environmental change than other types, but the reactions of rhizome grass and bunch grass in small spatial scale were some different with the reactions in middle scale and large scale, because the spatial heterogeneity in small spatial scale was not large enough to make the reaction rules of different life form steppe plants clearly.(2) There was a significant growth plasticity of modules of plant populations and biomass under natural grazing gradients. Aboveground weight, underground weight, and biomass of Leymus chinensis, as one rhizome grass, significantly decreased with grazing intensity increased. Biomass of Agropyron michnoi increased with grazing intensity increased, but not significant. Aboveground weight, underground weight, and biomass of Stipa grandis, one bunch grass, decreased obviously with grazing intensity increased, but tiller number increased with grazing intensity increased. With grazing intensity increased, Artemisia frigida, one stolon grass, its shoots density and adventitious roots number increased, but dry weight per shoots and shoots length decreased. This proved that there was a complemental relationship between shoots density and shoots weight.(3) Under different interferential measures, plasticity of modules and biomass variance of different life form steppe plants were similar, but in some aspects, there were some difference.In field artificial grazing measures, the growth was single peak type with grazing intensity, low grazing intensity could improve the growth of rhizome grass, and plant height reduced if artificial grazing intensity increased more. But for bunch grass Stipa grandis, stolon grass Artemisia frigida and taproot grass, the growth restrained by artificial grazing, plant height also decreased with grazing intensity increased.The results of artificial grazing experiment in pots showed that, rhizome internode length of rhizome grass Leymus chinensis did not change obviously. Bunch grass Stipa grandis's tiller number decreased with artificial grazing intensity increased. The rules of modules of artificial grazing experiment in pots was reverse with the rules in natural field grazing gradients. But for stolon grass Artemisia frigida, adventitious roots number increased and shoots length decreased with artificial grazing increased, this was same with the results from field grazing.(4) Growth speeds of regeneration of different life form steppe plants were not same in artificial grazing experiments. Growth speeds of regeneration of rhizome grass increased with artificial grazing intensity increased. Growth speed of regeneration of Leymus chinensis during initial stage was lower than speed during flourishing stage under same grazing intensity. Regeneration growth speed of bunch grass Stipa grandis significantly increased with grazing intensity increased, and growth speed of regeneration during initial stage was higher than speed during flourishing stage. Regeneration growth speed of stolon grass Artemisia frigida decreased with grazing intensity increased, and graze influenced Artemisia frigida's growth speed of regeneration during flourishing stage more than speed during initial stage.(5) The displacement among different life form steppe plants were obvious during community succession (degradation succession and restoration succession).During community degradation succession, hemicryptophytes biomass fluctuant decreased with grazing intensity increased, component percentage of hemicryptophytes in community increased with grazing increased, the percentage of hemicryptophytes was higher than other life form plants in moderate grazing intensity and heavy grazing intensity. Biomass and density of geophyte decreased obviously with grazing intensity increased, component percentage of geophyte decreased with grazing increased. However, biomass and density of chamaephyte increased very significantly with grazing intensity increased, chamaephyte play a more and more important role in community when grazing intensity increased. So, geophyte Leymus chinensis'?, role in community decreased obviously while grazing intensity increased, and displaced with chamaephyte species in heavy grazing intensity, community transformation was mainly reflected by the change of roles of different life form steppe plants in community.During community restoration succession, biomass and density of geophyte increased year by year, and play a more and more important role in community. On the contrary, biomass and density of chamaephyte decreased year by year, play a less and less important role in community, and chamaephyte was displaced by geophyte gradually. The evidences proved that community succession in grazing gradients was similar with that in restoration succession, but the direction was reverse.(6) There were different compensation growth of different life form steppe plants in community degradation succession. Rhizome grass Leymus chinensis population did not have the ability of over-compensatory growth under grazing influence, and the ability of compensatory growth of rhizome grass Agropyron michnoi was equal-compensation, so that rhizome grass were displaced by other populations with grazing intensity increased in degradation succession. There were over-compensation growth of bunch grass Stipa grandis under low and moderate grazing intensity, and there were over-compensation growth of Cleistogenes squarrosa under moderate and heavy grazing intensity. Stolon grass Artemisia frigida had the ability of over-compensatory growth under all grazing gradients, and the ability of over-compensatory growth increased with grazing intensity increased, so that Artemisia frigida displaced rhizome grass Leymus chinensis as constructive species in community, and Leymus chinensis steppe was degraded into Artemisia frigida short bunchgrasses steppe.