Influence Of Grazing On Community Characteristic And Reproduction Traits Of Plant Population

This study was carried out at Bai Yin Xi Le Farm within Inner Mongolia Xi Lin River Basin and Xi La Mo Lun Farm within Si Zi Wang County, Inner Mongolia in 2003-2004 to inspect the effects of the vegetative propagation and sexual reproduction on vegetative characteristics under the grazing pressure, explore the relationship between the plant reproductive adaptability and stability in community, and open out the theory between vegetation succession and degeneration in grazing condition, in order to estimate the potential of continuable utilization in grassland, and provide some scientific basis for grassland management. The experimental materials were based on the small stoloniferous shrub of Artemisia frigida and Potentilla acaulis, the length of rhizome between two interconnected adjacent ramets of Leymus chinesis, Agropyron michnoi and Carex duriucula, and the perennial bunchy grasses Stipa grandis, Stipa briveflora, Cleistogenes squarrosa in the communities of steppe and desert grassland. The results shown that:1. Bai Yin Xi Li steppe were degenerate under grazing condition, and the dominant plant species with rhizome and perennial bunchy grasses were replaced as Potentilla acaulis, compared with steppe, the plant species were more scanty in desert grassland.2. There are different reproductive characteristics and adaptive strategy in different live form plant species, the plants both rhizome and small stoloniferous shrub were titled as "guerilla colone type" which reproducing with vegetative, the perennial bunchy grasses were titled as "phalanx density type", which provided with both vegetative propagation and sexual reproduction.3. The sexual reproduction of Artemisia frigida were counteracted at grazing pressure, especially under heavy grazing condition, but there were an anomalous change with the changing of grazing pressure in Artemisia frigida reproduction characteristics, for example, the differentiation proportion of reproductive branch, inflorescence number per reproductive branch, seed yields, seed maturity degree, and so on. There were a significant change with changing of grazing density in two typed grassland in distances and quantities of adventitious root in Artemisia frigida community, but reproductive branch increased with increasing of grazing pressure in steppe, and on the contrary in desert grassland. The densities and seed yields of Potentilla acaulis increased with increasing of grazing pressure.4. The reproductive characteristics of grasses were different in different plant species under grazing pressure, and there were different adaptive ways in the plant with rhizome and stoloniferous shrub under different grazing conditions. There were no significant difference in distance of both sprout branch, but there was a significant increase in nodal point of sprout branch.But the length of rhizome between two interconnected adjacent ramets of Leymus chinesis became significantly shorten under grazing than that without grazing; however, that length and the number of nodes between two interconnected adjacent ramets did not differ significantly among the different grazing pressure, but with an increasing variance on the intensified grazing pressure.5. The perennial bunchy grasses of Stipa grandis, Stipa grandis, Achnatherum sibiricum, Koeleria cristata significantly reduced their height, bunch size and mean bunch aboveground biomass in the grazing plots with a certain grazing pressure. The grazing caused bunches be minished in size and population productivity be reduced. Because of the different tolerance and adaptive capability to the grazing among different grass species, the numbers of bunches in the community and the numbers of tillers of individual bunches after grazing showed the different dynamitic pattern among them. The production of tillers of the bunch grass species had been observed to have a significant compensatory effect on the grazing defoliation for the given grazing pressure.6. There was a co-existed both the vegetative propagation and sexual reproduction in Stipa briveflora community. Grazing showed an expressive influence on the vegetative reproduction of Stipa breviflore, and the heavy grazing caused the seed yields to be reduced. Tiller and root growing of Cleistogenes songorica were better in moderate grazing than heavy and no grazing, and the orders of distributing resource were root, stem and leaf in Cleistogenes songorica under different grazing pressures.