Ecological Adaptation Strategies Of Dominant Species In Inner Mongolia Typical Steppe

The research was conducted at Inner Mongolia Grassland Ecosystem Research Station of Chinese Academy of Sciences (43?26' -44?08' N, 116?04' -117?05' E) . It was studied that clonal morphological plasticity, reproductive strategy and resource allocation patterns of Artemisia frigida and Potentilla acaulis under different grazing intensities (zero grazing, light grazing: 1.33 sheep-hm'2, moderate grazing: 4.00 sheep-hm"2, heavy grazing: 6.67 sheep-hnr2) . Resource allocation patterns of four dominant species (Leymus chinensis, Stipa grandis, Artemisia frigida and Potentilla acaulis) in response to precipitation changes were investigated by simulation experiment.1) Morphological plasticity was one of the important ecological strategies to utilizing heterogeneous resources. Spacer length and branching intensity of Artemisia frigida and Potentilla acaulis responded to grazing intensities significantly. Spacer length of Artemisia frigida was the longest under zero grazing and shortest under moderate grazing while that of Potentilla acaulis was the longest under light grazing and shortest under heavy grazing. Branching intensity of both species increased significantly along the grazing gradient. Difference in morphological plasticity of these two species indicated that they had different ecological strategies to grazing intensities.2) Reproductive strategy was the trade-offs of resource allocation to maintenance, growth and production. It indicated adaptive ability and reproductive potentiality of plant population.Index of reproductive shoots density, tubular flower number and seeds per area of Artemisia frigida were significantly different between grazing treatments. Sexual reproduction allocation was 10.61%, 8.54%, 6.41%, 0.92% respectively from zero grazing to heavy grazing. There were significant differences between zero grazing and moderate grazing, zero grazing and heavy grazing, light and heavy grazing. The results of clipping experiment were identical to that of grazing experiment. Sexual reproduction ability of Artemisia frigida was affected significantlyby grazing intensities. There was significant difference in reproductive shoot density between zero grazing and heavy grazing. The number of inflorenscences per reproductive shoot of Potentilla acaulis increased with the increase of grazing intensities. But there was no significant difference between treatments.Results of clipping experiment showed that regrowth ability of Artemisia frigida under proportional clipping was superior to that under stubble clipping. Biomass allocation patterns of Artemisia frigida were significantly different between treatments, particularly allocation to leaves and flowers. Sexual reproduction allocation decreased with the increase of grazing or clipping intensities, which suggested that reproductive mode of Artemisia frigida changed under heavy grazing. Biomass allocation in priority to regenerative organism and reproductive mode alteration to clonal growth to sustain and propagate population were important ecological strategies to heavy grazing.3) Biomass allocation pattern indicated plant s adaptive strategy. ANOVA results showed significant effects of grazing treatments on population total biomass, above-ground biomass and R/S ratio. Population total biomass in Artemisia frigida decreased while that in Potentilla acaulis decreased firstly and then increased with the increase of grazing intensities The above-ground biomass in Artemisia frigida decreased significantly with the increase of grazing intensities. The reverse trend was true for Potentilla acaulis. Trends in R/S were similar to that in above-ground biomass.Biomass allocation pattern of Artemisia frigida was: roots > leaves >stems. ANOVA results did not show significant effects of treatment on biomass of leaves, roots and their allocation in Artemisia frigida except stem and its allocation. The difference in stem biomass and its allocation was significant between no grazing and light grazing, light and heavy grazing.ANOVA results showe...