不同树龄小叶锦鸡儿干旱降水过渡时期用水策略研究

在阿古拉生态水文试验区的固定沙丘上选取了两组具有代表性的3、5和9年生小叶锦鸡儿灌丛,采用氧稳定同位素技术,在连续15 d内比较了干旱、两次降水后(15.6、33.1 mm)灌丛内距离基茎3等分点及边缘处土壤水、降水与植株木质部水的δ¹⁸O值,研究了小叶锦鸡儿从干旱到雨后的用水模式变化,同时结合不同位置根系密度和灌丛内不同位置水分动态分析其变化原因。结果表明:小叶锦鸡儿在干旱条件下主要靠减少体内水量损失来维持生存而非利用深层土壤水,可能会将表层凝结水作为用水来源;雨后1 d内3种小叶锦鸡儿植物水δ¹⁸O值均趋向降水,3 d内3、5年生小叶锦鸡儿植物水δ¹⁸O值变化显著,9年生则基本不变;雨后5 d内10~60 cm为3种树龄小叶锦鸡儿的主要吸水层位,0~10 cm土壤水不是稳定的用水来源,3、5年生小叶锦鸡儿灌丛1/3处和边缘处及9年生边缘处水会优先被利用;随树龄增加小叶锦鸡儿的浅根系密度显著增大使其能有效利用降水,但灌丛下深层土壤水补给愈发困难,不利于地区水文平衡。建议人为控制大树龄小叶锦鸡儿的分布密度。

Water use strategy of Caragana microphylla during the transition from drought to rainfall

This study compared the water use strategy in 3, 5 and 9 year old Caragana microphylla communities in the Agula eco-hydrological research area. We compared, soil water, precipitation and xylem water content of C. microphyllas using oxygen stable isotope (δ¹⁸O) technology to examine their water utilization pattern in a period of drought followed by rainfall events (15.6, 33.1 mm) after 15 days. Root density and soil moisture dynamics were measured to help identify response mechanisms. The results show that, in drought, C. microphyllas mainly depended on maintaining internal moisture levels rather than absorbing subsoil water to survive. They may be utilized the condensation water of the surface soil; Within a day of rain, the δ¹⁸O content of xylem water at all ages trended to that present in the rain water. Within three days of rain, the δ¹⁸O of xylem water of 3 and 5 year plants changed remarkably, whereas 9 year plants remained stable. C. microphyllas of all ages mainly utilised soil water at 10 to 60 cm depth in the 5 days after rainfall; 3- and 5-year C. microphylla primarily utilised water from 1/3 point and edge, but the 9 year plants mainly used water from edge. With increasing tree age, the density of shallow roots increased markedly. It is suggested that manual control the distribution density of old C. microphyllas plants would help the hydrological balance in the region.