Abstract:Grazing is the most important factor of disturbance to rangeland.The grazing intensity has a differential effect on plant community of rangeland.Season is another factor that driving the annual changes in plant communities because it integrates the effect of temperature and rainfall on plants.However,the factor is often neglected by researchers to study the effect of grazing disturbance to rangeland ecosystem.To clarify the effects of grazing intensity with seasonal variation on plant species richness,important value,life type and function group of plants in rangeland.We selected the alpine meadow located in the northeast edge of Tibetan Plateau as the study area,and set up six research plots with different grazing intensity.Based on the data of species richness and the importance of the species on the plant community,and setting the season as an independent factor,the composition changes of the plant community under the dual effects of grazing intensities and seasons were analyzed by two-way ANOVA,species accumulation curve and redundancy analysis.The results showed that grazing intensity and season had significant effects on species richness and importance (P<0.01).Both species richness and important values decreased significantly with the increase of grazing intensity (P<0.01),and both showed the highest values in August with seasonal changes (P<0.05).Further redundancy analysis results showed that with the increase of grazing intensity,rosettes plants increased,and the succession pattern of plant community mainly because of the developing from annual to rosette plants.In conclusion,the composition of plant community on alpine meadow changed significantly under the disturbance of grazing,but the community showed positive adaptation at both the functional group and the life-type level,mainly with the increase of rosette plants.In addition,no matter the grazing intensity,with the change of seasons,the growth of bunch type-grass plants is the most significant.Finally,the species composition of plant community in alpine meadow increases differentiation under the combined action of grazing intensity and seasonal variation.