天山林区4种主要灌木夏季水分来源差异

Differences in water sources of four main shrubs of Tianshan Mountains in summer

天山林区群落结构相对简单、木本植物种类较少,但天山林区灌木群落中主要木本植物间的水分竞争模式尚不明确,水分利用动态缺乏定量分析。运用稳定同位素技术,对天山林区灌木群落4种主要灌木的茎杆水分及各潜在水源的氢氧稳定同位素组成进行测定,运用IsoSource模型定量分析4种灌木在夏季对各潜在水源的相对利用比例,探讨天山林区灌木群落主要灌木树种水分来源差异及动态变化。结果发现:7月,当浅层土壤含水量充足时,密刺蔷薇、黑果栒子和金丝桃叶绣线菊均大幅度吸收利用浅层土壤水,相对利用比例高于89.3%,异果小檗则相反,即吸收利用各潜在水源(浅层土壤水30.7%、中层土壤水29.4%、深层土壤水25.7%、溪水14.2%,下同);8月,当浅层土壤含水量降低时,密刺蔷薇转移至60—100 cm深层土壤水和溪水,相对利用比例分别为64.8%和27%,黑果栒子和金丝桃叶绣线菊以相似比例吸收利用各潜在水源(33.8%和36.8%、30.9%和29.7%、23.5%和22.3%、11.8%和11.2%),异果小檗则表现出可能吸收利用80—100 cm以下更稳定的深层土壤水;9月,当浅层土壤含水量升高时,4种灌木均大量吸收利用浅层土壤水,相对利用比例高于72.2%。这表明,天山林区灌木群落主要树种可通过可塑性转换水分来源来应对环境水分变异,在时间和空间上有效分割灌丛水源从而减缓对水分资源的竞争压力,从而通过在水分资源利用上的生态位分化促进物种间的共存。

The community structure in the Tianshan Mountains is relatively simple and there are a few woody plant species. However, the water competition pattern among the main woody plants in the shrub community of the Tianshan Mountains is not clear due to lack of the quantitative analysis related to water use dynamics of the shrubs. The hydrogen and oxygen stable isotope composition of xylem water of four main shrubs and their potential water sources in the shrub community in the study area were measured in this paper by using stable isotope technology. In order to explore the differences and dynamics in water sources of main shrub species in shrub community of Tianshan Mountains, the IsoSource model was used to analyze quantitatively the relative contributions of each potential water source used by the four shrubs in summer. The results showed that in July, when 0—20 cm shallow soil water content was sufficient, Rosa spinosissima, Cotoneaster melanocarpus and Spiraea hypericifolia extensively extracted shallow soil water, and the relative utilization ratio was higher than 89.3%. On contrary, Berberis heteropoda absorbed water from all the potential water sources(30.7% of shallow soil water, 29.4% of middle soil water, 25.7% of deep soil water, 14.2% of stream water, the same below);In August, when the water content of the shallow soil decreased, the Rosa spinosissima converted to 60—100 cm deep soil water and stream water, and the relative utilization ratios were 64.8% and 27%, respectively. Cotoneaster melanocarpus and Spiraea hypericifolia extracted water from all the potential water sources in similar proportions(33.8% and 36.8%, 30.9% and 29.7%, 23.5% and 22.3%, 11.8% and 11.2%). Berberis heteropoda relied mainly on the stable deep soil water below 80—100 cm;In September, when the shallow soil water content increased, all of the four shrubs absorbed large amount of shallow soil water, and the relative utilization ratio was higher than 72.2%. This indicates that the main tree species of the shrub community in the Tianshan Mountains could convert the plasticity of the water sources to deal with the environmental water variation, by dividing the water sources in time and space to reduce the pressure of competition on water resources, which would promote the coexistence of species through niche differentiation in water resource utilization.