北京山区侧柏水分利用策略

Water use strategy of Platycladus orientalis in Beijing mountainous area

侧柏是北京山区分布范围较广的典型针叶树种,揭示其在不同土壤水分条件下的水分利用策略具有重要意义。通过测定分析生长季内侧柏枝条水、土壤水和地下水的δD和δ^(18)O值,并利用多元混合模型(Iso-source软件)计算侧柏对土壤水或地下水的利用比例,再结合叶片水势(ψ)、气孔导度(Gs)、光合速率(Ps)和蒸腾速率(Tr)等生理生态因子同步观测,了解侧柏在生长季内的水分来源及生理生态适应。结果表明:侧柏的水分利用策略随季节波动,其在不同季节对不同土层水分的利用比例存在差异。在旱季,侧柏对表层0—20cm土壤水的平均利用率介于27.6—31.3%,对深层80—100cm土壤水和地下水的利用率分别介于27.0—33.7%和22.0—28.9%之间;进入雨季,侧柏对表层0—20cm土壤水利用比例增大,介于47.2—60.9%,对深层80—100cm土壤水和地下水的利用比例减小,分别介于10.5—16.2%和15.2—19.8%。旱季的侧柏水分亏缺更为严重,其叶片水势峰值比雨季低44.5%;旱季中的侧柏气孔导度在上午10:00达到峰值,但比雨季峰值低51.67%,其光合速率和蒸腾速率峰值也相应的下降了22.3%和37.0%。侧柏能通过降低气孔导度减少水分损失来获得较高的碳同化速率,维持较高的水分利用效率来适应干旱生境,表现出较强的适应能力。

In order to understand water source of the dominant tree species Platycladus orientalis and its eco-physiological adaptation during growing season in Beijing mountainous area, the Platycladus orientalis of water use strategy under different soil moisture conditions during growing season was studied. We employed the Iso-source software and measured the δD and δ18O in branches of trees, soil and groundwater to clarify their water source during growing season, and analysis combined with eco-physiological factors,such as leaf water potential （ψ）, stomatal conductance （GS） and water use efficiency （WUE）. Results show that Platycladus orientalis water use strategy with seasonal fluctuations, the in different seasons of different depths of soil moisture utilization ratio are different. In the dry season, Platycladus orientalis absorbed water in 0-20cm soil layer, the average utilization rate between 27.6-31.3%, at the same time, it utilization of 80-100 cm deep soil water and groundwater are in the range of 27.0%-33.7% and 22.0%-28.9% respectively. In the rainy season, the ratio of Platycladus orientalis absorbed 0-20cm soil water increased range of 47.2%-60.9%, the ratio of absorbed water in 80-100 cm deep soil layer and groundwater is decreased, range of 10.5%-16.2% and 15.2%-19.8% respectively. In dry season, the drought and water shortage of Platycladus orientalis is more serious, leaf water potential 44.5% less than in the rainy season; the peak of Platycladus orientalis stomatal conductance appeared at 10：00 am in the dry season, but 51.67% less than in rainy season, the photosynthetic rate and transpiration rate of peak also corresponding fell 22.3% and 37.0% respectively. Platycladus orientalis can reduce stomatal conductance decrease water loss to obtain higher carbon assimilation rate and maintain higher water use efficiency to adapt the arid condition, showed high adaptability to arid condition.