青藏高原高寒草甸植被特征与温度、水分因子关系

以广布于青藏高原的高寒草甸为研究对象,进行模拟增温实验,探讨高寒草甸植被特征与温度、水分因子关系,并试图论证高寒草甸植被是否符合生物多样性代谢理论.结果表明:①高寒草甸植被物种多样性的对数与绝对温度的倒数呈显著线性递减关系,空气-地表-浅层土壤(0-20 cm)温度(R2 ＞0.6,P＜0.01)较深层土壤(40-100 cm)温度(R2＜0.5,P＜0.05)对物种多样性影响大；其植被新陈代谢平均活化能为0.998-1.85 eV,高于生物多样性代谢理论预测值0.6-0.7 eV,这是高寒草甸植被对长期低温环境适应进化的结果.②除趋势对应分析和冗余分析显示,温度对植被地上部分影响较大,而土壤水分对全株影响均较大,适当的增温与降水均可极显著促进高寒草甸植被生长.③逐步回归和通径分析显示,40 cm、60 cm深度土壤水分对植被地上部分产生直接影响,20 cm高度空气相对湿度和40 cm深度土壤温度对其产生间接影响；40 cm深度土壤温度和60 cm深度土壤水分对植被地下部分产生直接影响,红外地表温度对其产生间接影响.深层土壤温度和水分对高寒草甸植被具有影响作用,这可能与增温后冻土的融化有关,但其机理尚待进一步研究.

Correlation among vegetation characteristics, temperature and moisture of alpine meadow in the Qinghai-Tibetan Plateau

Climate warming has become a credible fact, owing to the increase of greenhouse gases. It is generally believed that ecosystem responses to elevated temperature are highly sensitive and rapid in high-latitude and high-elevation regions, especially in the Qinghai-Tibetan Plateau (QTP). The QTP has been considered as an ideal region for studying responses of terrestrial ecosystems to global climate changes. Representing a typical QTP vegetation type, alpine meadows are extremely fragile and highly sensitive to climate warming. Once they are destroyed, it is very difficult for these meadows to recover quickly, which results in their degradation or desertification. Therefore, it is extremely important and urgent to investigate the relationship between vegetation characteristics and environmental factors under climate warming in the QTP. We used infrared heaters to control experimental warming. Fifteen experimental warming plots (EWPs) of 2 m × 2 m area and 60 non-experimental plots (NEPs) of 20 cm × 20 cm or 30 cm × 30 cm areas were established in an alpine meadow. EWPs included three treatments: 0 W/m² (control, T0), 130 W/m² (increasing ground temperature by about 1°C, T1), and 150 W/m² (increase of about 3°C, T2). Each type of treatment had five replications. Vegetation height, coverage, above- and belowground biomass were measured in NEPs. In EWPs, vegetation height, coverage, species richness, plus temperature and moisture were investigated after 1 year of warming. Then, detrended correspondence analysis (DCA), redundancy analysis (RDA), stepwise regression analysis, and path analysis were used to find correlations among vegetation characteristics, temperature and moisture. Our results show that log-transformed species richness was significantly linearly correlated with the reciprocal of absolute temperature in the alpine meadow. Air temperature at 20 cm height, ground temperature, and soil temperature in the 0-20 cm layer had greater impacts on species diversity (R²>0.6, P<0.01) than deep soil temperature in the 40-100 cm layer (R²<0.5, P<0.05). Average activation energy of metabolism in alpine meadow vegetation (0.998-1.85 eV) was greater than that of the metabolic theory of biodiversity (0.6-0.7 eV). This indicates that the activation energy of alpine meadow vegetation was high, enabling it to survive such harsh conditions as low temperature, drought, and gales. In DCA ordination, the relationship between vegetation characteristics and environmental factors fit the linear model best. Therefore, RDA ordination was chosen to study correlation among vegetation characteristics, temperature, and moisture. In RDA ordination, temperatures had a greater impact on aboveground vegetation, whereas soil moisture had more influence on above-and belowground vegetation. In a certain range, both elevated temperature and increased soil moisture enhanced vegetation growth most significantly in the meadow. In the stepwise regression and path analyses, soil moisture at 40 cm and 60 cm depths affected aboveground vegetation directly, whereas atmospheric relative humidity at 20 cm height and soil temperature at 40 cm depth affected it indirectly. Belowground vegetation was directly affected by soil temperature at 40 cm and soil moisture at 60 cm, and it was indirectly affected by soil surface temperature. It was also found that deep soil temperature and moisture influenced the growth of alpine meadow vegetation to a degree. We believe that this may be related to the melting of frozen soil caused by warming.