黄土高原山地苹果林蒸散分割、水分利用特征及生产力模拟

Abstract：Construction of apple forest in the slope land is a successful case of the Sloping Land Conversion Program, the improvement of soil and water conservation measures, and the development of modern agro-forestry. Also planting apple trees is an upcoming trend of sustainable development of modern agro-forestry in the dry-land of the Loess Plateau. However, the largest area of regrown economic forest with high density will lead to some uncertain ecological issues such as dried soil layer due to soil water depletion if there is no understanding of its water consumption and supply. So it is necessary to study the characteristics of water consumption by transpiration and eco-hydrological effects of apple forests. For this project, the methods will be used including the stable isotopes and eddy correlation techniques combined with simulation of Shuttleworth-Wallace model for evapotranpiration and WinEPIC model for water productivity in the Ansai and Mizhi agricultural-ecology experimental research stations. The purposes are to know the function and the process of evaporation and transpiration of apple trees in the regional water cycle by the partition of soil-evaporation/plant-transpiration, simulate the water productivity and the sustainable utilization ability of apple forest lands, reveal the processes of soil desiccation, elucidate the inter-relationship between water productivity and dried soil layers, and determine the reasonable planting density and yields of apple forest with the local precipitation. It is believed that the study will provide some theoretical basis for the rational distribution of apple forest in the slope lands, the optimal utilization of soil water and the sustainable management of economic forest ecosystem in the Loess Plateau.

摘要：山地苹果林的建设是黄土高原实施退耕还林、深化水土保持和发展现代农林业的成功案例，也是未来旱地农林业可持续发展的重要方向；但大面积、高密度发展人工经济林会造成土壤水分过度消耗并形成土壤干层等影响果业健康发展的生态问题，因此急需深入开展苹果林蒸腾耗水规律和生态水文效应的研究。本项目利用稳定性同位素技术、涡度相关技术和模型模拟等手段，通过对土壤蒸发和林分蒸腾的有效分割，重点研究苹果林地蒸发和蒸腾对蒸散总量的贡献比例及其在水分循环中的功能与规律，利用WinEPIC模型模拟黄土高原苹果林地水分生产力和土壤水分持续利用能力，揭示苹果林地土壤干化发生过程，明确土壤干层与水分生产力之间的动态变化机制，确定与当地降水条件相适应的苹果林地合理栽植密度和产量，实现减轻林地土壤干化危害的科学目标，为黄土高原有限水资源条件下山地苹果发展的合理布局、产业的可持续发展以及林地水分的优化利用提供科学依据。

围绕黄土高原山地苹果林土壤水分过度消耗、并形成土壤干层等影响果业健康发展的生态问题，开展苹果林蒸腾耗水规律和生态水文效应的研究。（1）从全局、单株耗水对土壤水分的影响角度，研究了山地苹果林的土壤水分动态特征和土壤干燥化状况。6年生山地苹果园土壤已经出现干化现象，且在90~300 cm存在明显的低湿层，土壤体积含水量常年处在12%以下，土壤水分测定点的最佳位置是距树干105cm。（2）通过热扩散茎流计（TDP）等测定苹果林地水分平衡中果树蒸腾量、土壤蒸发量等组分，量化评估了土壤蒸发及植被蒸腾的强度和变化规律，有效分割了苹果林地的蒸腾和蒸发，揭示苹果林地蒸发和蒸腾对蒸散总量的贡献比例及其在水分循环中的功能与规律。山地苹果林蒸腾、蒸发、冠层截留对蒸散的贡献率分别为 58.9%、26.8%、14.3%。（3）针对山地苹果林水分研究中忽视果树根系集中分布对水分利用产生的影响的问题，研究出了山地果园集雨-壤中防渗技术。自然降水利用率提高了24.5%。（4）针对传统表层滴灌灌溉水蒸发散失快、效率低的突出问题，研究集成了山地苹果林根部注灌技术。根部注灌比传统表层滴灌水分利用率提高23.0%，灌溉水利用率提高19.6%。（5）通过WinEPIC模型模拟黄土高原苹果林地水分生产力和土壤水分持续利用能力，揭示苹果林地土壤干化发生过程，明确土壤干层与水分生产力之间的动态变化机制，确定与当地降水条件相适应的苹果林地合理栽植密度和产量，并利用偏最小二乘回归模型界定气象、施肥等因子对苹果产量、水分生产力的影响程度。陕北黄土区成龄苹果林年均蒸散量为511.2mm，影响苹果林产量的最大因子是降水量，其标准化回归系数分别为0.274，深层土壤干层出现时间分别为8年。以上研究结果可为黄土高原有限水资源条件下山地苹果发展的合理布局、减轻土壤干化危害、实现苹果林地水分的优化利用以及产业的可持续发展提供重要科学依据。