青藏高原高寒草甸生物量动态变化及与环境因子的关系——基于模拟增温实验

以青藏高原高寒草甸为研究区,设置模拟增温实验样地,于2010年开始持续增温,2012和2013年调查植被地上-地下生物量,探讨气候变暖背景下高寒草甸生物量的动态变化及其与环境因子的关系。结果表明:(1)增温处理下地上-地下生物量与根冠比的中值和平均值大于对照,其中地下生物量(变异系数为0.30)的增加幅度大于地上生物量(变异系数为0.27),根冠比的变异系数(0.33)大于地上-地下生物量,这表明增温可导致高寒草甸植被生物量分配出现差异。(2)地上-地下生物量呈极显著的幂指数函数关系(R~2=0.147,P0.001),表现为异速生长,但在增温处理下异速生长出现减缓(R~2=0.102,P0.05)。(3)地上生物量受深层土壤水分和浅层土壤温度影响较大,地下生物量受深层土壤水分和深层土壤温度影响较大;土壤温度对地上-地下生物量的影响强于土壤水分,表现为20 cm深度土壤温度对地上生物量(R=0.582,P0.01)和根冠比(R=-0.238,P0.05)影响较大,60 cm深度土壤温度对地下生物量影响较大(R=0.388,P0.01),100 cm深度土壤水分对地上生物量(R=0.423,P0.01)和地下生物量(R=0.245,P0.05)影响较大,这说明增温导致浅层土壤温度对生物量分配产生影响,使生物量更多分配到地上部分,而冻土融化致使深层土壤水分对生物量产生影响。

Dynamic changes in biomass and its relationship with environmental factors in an alpine meadow on the Qinghai-Tibetan Plateau, based on simulated warming experiments

The Qinghai-Tibetan Plateau (QTP) is considered to be an ideal region in which to study the responses of terrestrial ecosystems to climate warming. Alpine meadows, a common ecosystem on the QTP, are extremely fragile and highly sensitive to increasing temperatures, and, once destroyed, are very unlikely to recover quickly, potentially leading to desertification of the site. It is therefore extremely important that we gain a full understanding of the changes in the floral communities of alpine meadows that will occur in response to climate warming on the QTP. In previous research, we established 20 experimental plots based on a randomized-block design in an alpine meadow on the QTP, which included five replicates of four treatments:control, warming alone, clipping alone, and interaction of warming and clipping. In the present study, we focused on the control and warming-alone plots and surveyed aboveground biomass (AGB), and belowground biomass (BGB) of vegetation in the 2012 and 2013 growing seasons (from May to September) in the two types of plots. The aim of this study was to examine the variations in biomass allocation and the relationship between biomass and environmental factors. The biomass indexes we focused on included AGB, BGB, and root-to-shoot ratio (RSR), with the environmental factors consisting of soil temperature and soil moisture at various depths (10, 20, 40, 60, and 100 cm). We found the followings. (1) The AGB, BGB, and RSR data fitted to normal distributions, where the frequency range of BGB was greater than that of RSR, which was in turn greater than that of AGB. Median and mean values of AGB, BGB, and RSR were all higher in the warming-alone treatment than in the control, where the increased amplitude of BGB with a coefficient of variation of 0.30 was larger than that of AGB (0.27). The coefficient of variation of RSR (0.33) was larger than that of both AGB and BGB in different treatments, illustrating that biomass variation resulted from the considerable difference between the above- and belowground environment. (2) AGB and BGB exhibited a highly significant functional relationship of the power exponent (R²=0.147, P<0.001), behaving as an allometric correlation, but with the allometry slowing in the warming-alone treatment (R²=0.102, P<0.05). (3) AGB was primarily influenced by deep-soil moisture and shallow-soil temperature, whereas BGB was most highly influenced by deep-soil moisture and deep-soil temperature. However, the effect of soil temperature on both AGB and BGB was greater than that of soil moisture. Soil temperature at a depth of 20 cm had a considerable effect on AGB (R=0.582, P<0.01) and RSR (R=-0.238, P<0.05), whereas soil temperature at a depth of 60 cm had a considerable effect on BGB (R=0.388, P<0.01). Soil moisture at a depth of 100 cm had a substantial effect on both AGB (R=0.423, P<0.01) and BGB (R=0.245, P<0.05). Based on these results, we conclude that shallow-soil temperature in warming conditions influences biomass allocation and induces a higher allocation of biomass to aboveground vegetation communities, whereas deep-soil moisture influences biomass production as a result of the thawing of frozen soil by the warming conditions.