黄土丘陵区红枣林蒸腾耗水机制及其水分利用策略研究

Since the initiation of the “Grain for Green” project, jujube orchards have been established extensively on the hilly region of the Loess Plateau. However, serious imbalance of water supply and demand appears during jujube growth period because of water shortage and strong water consumption by transpiration. Therefore, deep-layer soil water is prone to be overused and this further results in soil desiccation. Based on regional precipitation and production practices, this project is to investigate transpiration mechanism and soil water uptake strategies of jujube trees by integrating the approaches of field in situ observations of soil water and evapotranspiration, hydrogen and oxygen isotope labeling, lab isotope measurements and theoretical analysis. Primary focuses will be on as follows. Probe the effects of pruning on regulating soil water and transpiration of jujube trees. Reveal behaviors of transpiration of jujube trees and main affecting factors and realize the effective partitioning of soil evaporation and transpiration of jujube trees. Determine water sources of jujube absorption and illustrate water uptake strategies. Based on the above efforts, this project would put forward a suitable mode of pruning technology for jujube trees to reduce effectively excessive transpiration, alleviate soil desiccation caused by overuse of soil water, and finally realize the co-development of production and ecology for jujube trees. This project is expected to provide insights into facilitating sustainable development of the late stage of “Grain for Green” project and increasing farmer’s income and have great potential of applications.

国家退耕还林（草）工程实施以来，黄土丘陵区大面积发展红枣林。但是由于干旱缺水和枣树蒸腾耗水强烈，导致枣树生长的水分供求关系矛盾突出，容易出现以过度消耗深层土壤水分为代价而引起的土壤干燥化。本研究立足于区域降水和生产实际，采用野外土壤水分和蒸散组分连续定位观测、氢氧稳定同位素人工标记、水氢氧稳定同位素室内测定与理论分析相结合方法，对红枣林蒸腾耗水机制及其水分利用策略进行研究。重点探明不同矮化修剪对土壤水分和枣树蒸腾耗水的调控效果，揭示枣树蒸腾耗水规律及主要影响因素，实现土壤蒸发和枣树蒸腾有效分离，明确枣树水分来源，阐明水分利用策略，提出适宜矮化修剪技术模式，有效降低枣树奢侈性蒸腾耗水，缓解土壤水分过度消耗而引起的土壤干燥化，同步实现红枣林生产与生态协同提升。该研究对于保障国家退耕还林（草）工程后期持续健康发展和促进农民增收具有重要借鉴意义和应用前景。

针对国家退耕还林（草）工程实施以来，黄土丘陵区大面积发展红枣林所导致的枣树生长水分供求矛盾突出问题，本项目立足于区域降水和生产实际，采用土壤水分和蒸散组分连续定位观测、氢氧稳定同位素室内测定与理论分析相结合方法，对红枣林蒸腾耗水机制及其水分利用策略进行研究。在红枣林土壤水分时空动态和蒸腾耗水特征方面，采用土壤储水亏缺补偿度等指标对降水-土壤水转化关系进行分析，与裸地相比，不同工程和农艺组合措施可以有效拦蓄降水和抑制蒸发，在不同水平年对土壤储水均有显著补偿效果；根据枣树不同生长阶段（萌芽展叶期、开花坐果期、果实膨大期、成熟落叶期）土壤水分、蒸腾耗水、枣树产量和品质等因素，确定出适宜修剪技术形式，有效降低奢侈性蒸腾耗水；利用土壤水分自动监测装置计算枣树蒸腾耗水，鱼鳞坑措施降雨入渗较清耕增加41.3%-65.0%，枣树蒸腾耗水增加33.5%-40.9%。鱼鳞坑无覆盖措施显著增加土壤无效蒸发量，对枣树蒸腾量无显著影响，而对鱼鳞坑加以覆盖措施后，无效蒸发降低24.0%-42.9%，提出了一种适用于复杂下垫面条件的快速有效估算经济林果蒸散量的方法，建立基于Hydrus-1D的工程措施和农艺措施组合的生态水文过程模型；采用直接对比法、IsoSource、MixSIR和SIAR等模型量化枣树水分来源，发现不同树龄枣树主要利用浅层土壤水分，当浅层土壤水分匮乏时，枣树会增加中层（40～120cm）和深层（120～200cm）土壤水分的吸收比例。根据不同树龄水分利用特征，对其进行水分管理可以有效减少浅层土壤水分的非生产性耗水和枣树自身奢侈性耗水。研究提出黄土丘陵沟壑区旱作枣园“工程措施+农艺措施”蓄水保土技术模式，该研究对于同步实现黄土高原果业生产与生态协同发展具有重要借鉴意义和应用前景。