中文摘要：

旱冬瓜（Alnus nepalensis）是元阳梯田水源区的优势树种之一,其作为一种速生树种被发展为当地居民重要的薪炭林和经济林,树种的生长发育和地理分布受到水分制约,其吸收水分和水分利用的变化将会直接影响森林生态系统的水循环。该研究于2014年5-11月间进行,研究时段内累计降雨1 262 mm,地下水δD值在-71‰～-53‰范围,δ（18）O在-10.6‰～-7.0‰范围,受环境因子的影响很小,基本上保持常年稳定。土壤水是可供树种直接吸收利用的水源,基于氢氧稳定同位素技术,对比元阳梯田水源区旱冬瓜树种茎干水δD和其林地不同深度土壤水δD的同位素组成情况,结合不同深度土壤含水量,定性分析判断旱冬瓜对土壤水的利用,结果表明旱冬瓜旱季利用的土壤水主要分布在40 cm土层附近,而雨季利用的土壤水范围较广,分布在0～60 cm的土层。利用多元线性混合模型Iso Source软件定量分析旱冬瓜对土壤水和地下水的利用,结果表明：旱冬瓜水分来源分布较广,各土层土壤水和地下水均有贡献,雨季旱冬瓜主要利用0～60 cm深土壤水,其中雨后旱冬瓜绝大部分水分来源于0～10 cm的土壤水分,利用比例为66%～73%;其它时间主要利用40～60cm的土壤水,贡献率高达73%;旱季旱冬瓜的绝大部分水分来源于地下水,对地下水的利用比例为18%～68%,同时,40～60 cm的土壤水也是其重要的水源。从不同时间尺度考察旱冬瓜对土壤水和浅层地下水的需求,更加准确地认识元阳梯田水源区不同森林类型优势树种的水分来源,为梯田森林生态系统经营与维护以及梯田的可持续发展提供了理论依据。

英文摘要：

Alnus nepalensis is one of dominant tree species in the water source area of Yuanyang terrace. As a fast-grow-ing tree species, it has been the important firewood forests and economic forests to local residents. Water constrains its vegetation growth and geographic distribution. In SPAC system, forest vegetation as the main body of forest ecological system and dominate the redistribution of water resources, its absorption of moisture and water utilization change will di-rectly affect the water cycle of forest ecosystem. We conducted this study from May to Novernber of 2014, with accumula-tive rainfall 1 262 mm. The groundwater in the study area of δ D values ranged from -71‰ to -53‰,δ18 O values ranged from -10.6‰ to -7.0‰, less affected by environmental factors, basically remained stable; In this paper, A. nepalensis roots absorbed water from all the water sources and transport in the xylem water did not occur isotopic fractionation char-acteristic. We combined with the soil moisture content, the water utilization sources of A. nepalensis mainly came from 40 cm soil layer in dry season and 0-60 cm in rainy season to analyze the A. nepalensis water utilization strategies by com-parison with the δ D values of xylem water and soil water, with hydrogen and oxygen stable isotope techniques. The re-sults of quantify analysis its water sources with multivariate linear mixed model of Isosource software showed that A. ne-palensis had a wide distribution of water source, both the soil water and groundwater had contribution, 0-60 cm soil wa-ter was important water sources in the rainy season, and after raining most of the water source from 0-10 cm soil mois-ture, the proportion was 66%-73%;Other main water source from 40-60 cm soil water, contribution rate was as high as 73%;In the dry season, A. nepalensis utilize groundwater proportion was higher, the proportion was 18%-68%. Water constrained vegetation growth and geographic distribution. In SPAC system, forest vegetation as the main body of forest ecological