放牧干扰下高寒草甸物种、生活型和功能群多样性与生物量的关系

为明晰放牧强度对高寒草甸物种、生活型以及功能群多样性和生物量的时间累积作用以及对多样性与生物量之间相互关系的影响。选择青藏高原东北缘高寒草甸,在6个放牧强度样地连续4 a(2012—2015)进行物种、生活型、功能群多样性和生物量调查。采用重复测量方差分析和线性回归法分析放牧强度和放牧年份对物种、生活型、功能群多样性以及多样性与生物量之间的相关关系的影响。结果表明:(1)放牧强度和放牧年份均对生物量产生显著影响。随放牧强度增加,生物量显著降低。但随放牧年份延长,不同放牧强度区生物量无一致的变化规律。(2)放牧年份对物种、生活型和功能群丰富度、均匀度和优势度的影响均达到显著水平。但放牧强度和放牧年份只对物种丰富度产生交互作用,放牧强度对物种丰富度的影响具有时间的累积效应。(3)放牧干扰下不同层次多样性,仅物种丰富度与所有多样性指数显著相关,物种丰富度可以作为物种多样性测度的代表性指标。(4)多样性与生物量关系的研究,对丰富度而言,仅低放牧强度样地(Plot2)中物种丰富度随生物量增加而显著降低,其余放牧强度样地的物种、生活型和功能群丰富度均与生物量无关。对均匀度而言,高放牧强度样地(Plot4、Plot5、Plot6)生活型均匀度随生物量的增加而显著降低。对优势度而言,高放牧强度样地生活型优势度随生物量的增加而显著增加。生活型多样性可作为放牧干扰下生物量变化快速预测的有效指标。

Relationship between plant species, life form, functional group diversity, and biomass under grazing disturbance for four years on an alpine meadow

This study was performed to gain an understanding of the time cumulative effects of grazing intensity on the diversity of species, life forms, functional groups, and biomass and their relationships on an alpine meadow. From 2012 to 2015, we conducted a controlled grazing trial with six grazing intensities on an alpine meadow located in the northeastern Qinghai-Tibet Plateau. We investigated the diversity and life form of species, functional group diversity (richness, evenness, and dominance were used as diversity indices), and aboveground biomass in four years. We used repeated measures and linear regression methods to analyze the effect of grazing intensities and grazing years on plant species diversity, life forms, and functional groups, as well as on the relationship between the diversities and biomass. The following results were obtained. (1) Grazing intensity and grazing year had significant effects on biomass, with the biomass significantly decreasing with an increase in grazing intensity. There was irregularity in biomass changes in different grazing intensity plots with progression of the grazing year. (2) There were significant effects of grazing year on abundance, evenness, and dominance in term of the plant species, life forms, and functional groups. However, the grazing intensity and grazing year had an interactive influence on the richness of plant species, and grazing intensity had a time cumulative effect on the richness of plant species. (3) In the plant diversities with different organizational levels under grazing disturbance, only the richness of plant species was significantly correlated with all diversity indices. The richness of plant species can be used as a representative index for measuring plant species diversity. (4) In the study of the relationship between diversity and biomass, the richness of plant species in the lighter grazing intensity plot (Plot 2) was significantly decreased with increasing biomass, whereas the richness of plant species, life forms, and functional groups showed no relationship with biomass in other grazing intensity plots. The evenness of life forms in the high intensity grazing plots (Plots 4, 5, and 6) significantly decreased with an increase in biomass. The dominance of life forms in the high intensity grazing plots (Plots 4, 5, and 6) significantly increased with an increase in biomass. In conclusion, the diversity of life forms can be used as an effective index for rapidly predicting plant biomass under grazing disturbance because this diversity is the most sensitive to biomass variation.