氢同位素在内蒙古小叶锦鸡儿灌丛水分来源研究中的应用

Application of stable hydrogen isotope in study of water sources for Caragana microphylla bushland in Nei Mongol

小叶锦鸡儿(Caragana microphylla)是我国内蒙古草原广泛分布的优势灌木,目前国内外有关小叶锦鸡儿水分利用来源的定量研究较少。该文运用氢稳定同位素法,分析了内蒙古小叶锦鸡儿木质部水和潜在水源(夏季降雨、冬季降雪和土壤水)的氢稳定同位素比率(δD)的季节变化,发现小叶锦鸡儿在遮雨处理和自然状态下δD季节变化差异不明显,分别为–101.36‰±13.02‰和–101.18‰±12.71‰。在遮雨处理条件下,小叶锦鸡儿主要利用0–20 cm土壤层水分,占其所利用水分的73.30%±16.14%;自然状态下,小叶锦鸡儿对0–20、20–60和60–100 cm不同土壤层土壤的水分利用较为均衡,分别为34.66%±7.83%、32.44%±7.42%和32.90%±4.14%。该结果表明不同生境下灌木与草本的水分竞争可能是小叶锦鸡儿对不同土层水分利用差异的原因。结合两源模型分析了降雨对各土壤层的贡献率,并用Iso Source多源混合模型分析了各土壤层对小叶锦鸡儿用水的贡献率,发现降雨对小叶锦鸡儿的贡献率为42.65%–63.92%。该结果反映了小叶锦鸡儿对夏季降雨和冬季融雪的利用情况。

Aims Caragana microphylla is a dominant shrub widely distributed in the grasslands of Nei Mongol. Its water utilization pattem has an important effect on local plant community composition. However, the water source for C. microphylla remains poorly quantified, which is vital in understanding the adaptation of this specie to arid en- vironment. This study aims to investigate the dynamics of water use in C. microphylla and its response to soil wa- ter fluctuations resulting from precipitation pattern including summer rains and winter snow. Methods Seasonal variations of hydrogen stable isotope ratios （δD） in the xylem of C. rnicrophylla and potential sources of water （summer rains, winter snow and soil water） were analyzed by LGR hydrogen stable isotope trac- er method. The contribution of soil water to C. microphylla was calculated by IsoSource model and the contribu- tion of rainfall to soil water was calculated by a two-source model. Important findings The xylem of C. microphylla （xylem） showed no seasonal differences in ~D, whereas there were significant differences in the water source of plants between two contrasting hydrological environments. In habitats where rainfall was shielded off, C. microphylla mainly used the soil water at depth of 0-20 cm, which accounted for 73.30% ±16.14% of the total water usage; whilst under natural conditions, water uptake by C. mi- crophylla was more or less similar at the depths of 0-20 cm, 20-60 cm and 60-100 cm, accounting for 34.66% ± 7.83%, 32.44% ± 7.42%, 32.90% ± 4.14% of the total water usage, respectively. Competition for water between shrubs and grasses gave a possible explanation for different water utilization pattems of the plants. In addition, rainfall accounted for 42.65%-63.92% of the water sources for C. microphylla. Results in this study demonstratedthat C. microphylla used both summer rains and winter snow, and dynamics of water use in C. microphylla re- flects its adaptation to the water-limiting arid environment.