放牧强度与季节因子变化对高寒草甸植物群落组成的影响

Effects of grazing intensity on plant community composition in alpine meadow with seasonal changes

放牧是人类对草地最主要的干扰活动,放牧强度不同会对草地植物群落产生差异化的影响。而放牧季节的温度、降水等变化,也是影响植物群落年际内变化的主要驱动因素,与放牧强度共同影响植物群落组成,但二者的共同作用常常被研究者忽视。为明晰草地植物群落在放牧强度和季节变化耦合作用下的组成动态,以青藏高原东北缘高寒草甸为研究区,设置6个放牧强度样地,以植物群落物种丰富度和重要值为基础数据,将季节作为独立因素,应用双因素方差分析、物种累积曲线和RDA排序等方法,分析放牧强度和季节变化下植物群落的组成动态。结果表明:(1)放牧强度和季节对物种丰富度和重要值均有极显著影响(P<0.01);(2)物种丰富度和重要值在不同季节均随放牧强度的增加而显著降低(P<0.01),在不同放牧强度区从返青期到盛草期均显著增高(P<0.05);(3)放牧干扰改变了群落生活型和功能型组成,对一年生植物和杂类草影响最为明显。随放牧强度增加,低矮的莲座型植物增加;随季节变化,丛生型禾本科植物的增长最为显著。最终高寒草甸植物群落在放牧强度和季节变化的共同作用下加剧了物种组成的差异性。

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.