基于^18O稳定同位素对银川平原北部4种灌木夏季水分利用特征研究

Characteristics of Water Use of Four Bushes Growing in Northern Areas of Yinchuan Plain in Summer Based on the ^(18)O Stable Isotope Analysis

为了分析银川平原北部4种灌木对不同水源的利用特征,测定了20年生多枝柽柳(Tama-rix ramosissima)、3年生多枝柽柳、3年生宁夏枸杞(Lycium barbarum)和3年生四翅滨藜(Atri-plex canescens)木质部水及不同潜在水源稳定氧同位素组成(δ18 O),应用同位素线性混合模型估算了不同灌木对不同水源的利用率。结果表明:不同深度土壤水δ18 O值存在较大差异,并呈规律性变化。表层(0～5cm)土壤水δ18 O值较井水δ18 O值偏正,说明其受蒸发影响较大。120～140cm土层δ18 O值最正,说明该土层同位素分馏作用最大。140～200cm土壤水受蒸发影响最小,土壤水δ18 O与井水最为接近。3年生多枝柽柳、3年生宁夏枸杞、3年生四翅滨藜的木质部水δ18 O值分别为-8.62‰、-8.64‰和-9.23‰,均比20年生多枝柽柳木质部水δ18 O(-9.40‰)偏正。用Iso-Source软件计算的结果显示20年生多枝柽柳和3年生四翅滨藜对地下水和表层土壤水(0～5cm)的利用程度较高,分别利用11.6%和9.3%的地下水,18.2%和14.6%的表层水。3年生多枝柽柳和3年生宁夏枸杞对40～120cm土层水分利用程度较高,分别为93.8%和92.3%。

In order to understand the utilization of different potential water sources for the four bushes i. e. twenty-year-old Tamarix ramosissirna , three-year-old T. ramosissima, L ycium barbarum, and Atriplex canescens, in Northern areas of Yinchuan Plain, stable 18O isotope compositions （δ^18O） of different potential water sources and xylem water were analyzed to calculate the contribution of different water sources to the growth of different bushes using isotope linear mixing model. The results showed that soil water δ^18O in different depths differed regularly. The soil water δ^18O value in surface soil profile （0-5 cm） was more positive than that of well water, implying the effect of evaporation on δ^18O. The most positive δ^18O value found in the profile 120-140 cm indicated the most intense effect of isotopic discrimination in this soil layer. Similar δ^18O value to well water was recorded in the soil profile from 140 cm to 200 cm suggesting the least effect of evaporation. The xylem water 3180 values of three-year-old T. ramosissima, L. barbarurn and A. canescens, i.e. --8.62‰, -8.64‰ and -9.23‰, respectively, were more positive than that of twenty-year-old T. ramosissirna （-9. 40‰）. According to the calculation result of IsoSource, twenty- year-old T. ramosissima and A. canescens tapped 11.6‰ and 9.3% groundwater, and 18.2‰ and 14.6% surface soil water （0-5 cm）, respectively. Three-year-old T. ramosissima and three-year-old L. barba- rum tapped 93.8% and 92.3% soil water in the profile of 40-120 cm, respectively.