典型林区水分氢氧稳定同位素在土壤-植物-大气连续体中的分布特征

土壤-植物-大气连续体(SPAC)中水循环是水文学和生态学研究的重要内容,氢氧稳定同位素在不同水体中组成特征的差异可以指示水分循环过程。本研究通过分析成都平原区亚热带常绿阔叶林中降水、土壤水、植物水的同位素组成,探讨SPAC系统中水分的氢氧稳定同位素演化特征,揭示区域水循环不同界面过程。结果表明: 研究区雨季大气降水线方程为: δD=7.13δ¹⁸O+2.35(R²=0.99),土壤蒸发线方程为: δD=6.98δ¹⁸O-0.32(R²=0.92)。在降水→土壤水→植物水的界面水输送过程中,氢氧同位素逐渐富集。浅层土壤(0～35 cm)水δ¹⁸O受降水的直接影响,响应关系明显,中深层土壤(35～100 cm)水则相对稳定。观测期间,植物木质部水同位素比土壤水略微富集,说明水分在植物体内输送过程中可能通过韧皮部或树皮发生轻微蒸发或蒸腾。采用直接相关法初步估计植物对不同土层土壤水的利用情况,樟树主要利用中层土壤水,构树主要利用浅层土壤水,金星蕨因根系分布浅更倾向于利用浅层土壤水和植物截留的降水。与金星蕨相比,樟树和构树的叶片水分蒸发和同位素动力分馏程度更强。

Distribution of hydrogen and oxygen stable isotope of water in soil-plant-atmosphere continuum (SPAC)system of a typical forest area

Water cycle in the soil-plant-atmosphere continuum (SPAC) is an important research topic in hydrology and ecology. The differences in the composition of hydrogen and oxygen stable isotopes in different water bodies can indicate water cycle process. Based on the measurements of isotopic compositions in precipitation, soil water, and plant water, we analyzed water isotope evolution in a SPAC system located in a subtropical evergreen broad-leaved forest in Chengdu Plain. The different interface processes of regional water cycle was revealed. The results showed that the local meteoric water line (LMWL) equation was δD=7.13 δ¹⁸O+2.35 (R²=0.99), and the soil evaporation line (SEL) equation was δD=6.98δ¹⁸O-0.32 (R²=0.92). In the water transportation process of precipitation-soil water-plant water, hydrogen and oxygen isotopes were gradually enriched. The δ¹⁸O in water of the surface soil layer (0-35 cm) was sensitive to precipitation input, as it was directly affected by precipitation. In contrast, the δ¹⁸O in water of the middle and deep layers (35-100 cm) was relatively stable. The isotopes of plant xylem water were slightly more enriched than those of soil water, indicating the possibility of slight evaporation or transpiration through phloem or bark in plant water transportation. The estimation of plant water intake from different soil layers was performed by direct correlation method. Cinnamomum camphora mainly used water from the middle layer, Broussonetia papyrifera mainly used that from the surface layer, and Parathelypteris glanduligera tended to use surface soil water and precipitation intercepted by plants because of the shallow root system. Compared with P. glanduligera, C. camphora and B. papyrifera experienced stronger water evaporation and the isotopes were influenced by more intense dynamic fractionation.