黄土塬区苹果林蒸腾耗水规律及其尺度效应

The development of apple forest is one of main measures to cope with the reduction of arable lands and farmer’s income in the Loess Plateau. Now the apple tree has become the largest area of regrown economic forest, and its ecological process is closely linked with the water utilization mode of plant which determines the response results of apple forest to the variation of environment water status. Now there is absent of systematic research about eco-hydrological effect of apple forest. The large-area development of apple forest could lead to some uncertain ecological issues if there is no understanding of its water consumption and supply. For this project, there is two main problems that will be solved include the partition of soil-evaporation/plant-transpiration and scale expansion of water consumption of apple forest based on the yearly work accumulation in Changwu agricultural-ecology experimental research station. The methods will be used including the sap flow and eddy correlation techniques combined with monitoring of plant physiological and ecological factors. The objectives are to know the process of water consumption compared with young and mature apple forests, determine the distribution, the characteristics of spatial-temporal variation and impact factors of evapotranspiration composition in the apple forest ecosystem, elucidate the characteristics of water cycle and water balance, and reveal the hydrological effect and threshold value of inter-conversion in the different scales. It is believed that our study will provide some theoretical basis for the optimal utilization of soil water and the sustainable management of apple forest ecosystem in the Loess Plateau.

苹果经济林的发展是黄土区应对耕地大面积减少后百姓收入减少的主要措施，已成为该区面积最大的人工经济林，其生态水文过程与植物对水分的消耗模式息息相关。黄土区人工苹果林的生态水文效应尚缺乏系统研究，在不明确其水分消耗和供给的状况下，推进果树种植可能会导致一系列不可预测的生态问题。本项目针对黄土区土壤蒸发/植被蒸腾如何有效分割和蒸腾耗水的尺度扩展两大问题，以黄土高塬沟壑区的典型代表长武塬国家生态站为研究平台，在已往工作积累的基础上，运用树干液流技术和涡度相关原理，结合植物生理生态监测，将幼林、成林果园对比分析，研究苹果林的蒸腾耗水过程，确定苹果林生态系统蒸散组分的分配、变化特征及影响因子，分析苹果林的耗水规律及其在不同空间和时间尺度上的变化特征，揭示苹果林在不同尺度上的水文效应及相互转换的阈值条件，为黄土区经济林管理和苹果产业的可持续发展及土壤水分优化利用提供理论依据。

本项目以黄土高塬沟壑区的典型代表长武塬国家生态站为研究平台，运用树干液流技术和涡度相关原理，将幼林、成林果园对比分析，研究苹果林的蒸腾耗水过程，确定苹果林生态系统蒸散组分的分配、变化特征及影响因子，分析苹果林的耗水规律及其在不同空间和时间尺度上的变化特征，为黄土区经济林管理和苹果产业的可持续发展及土壤水分优化利用提供理论依据。（1）为明确黄土塬区主要农林用地土壤水分变化特征及其干化现状，利用中子仪于 2014年对长武塬区19龄果园、9龄果园、玉米地及小麦地0-600 cm的土壤水分进行长期监测和分析。结果表明，1）0-600 cm土壤贮水量表现为9龄果园＞玉米地＞小麦地＞19龄果园，除9龄果园与玉米地间差异性不显著（P＞0.05）外，其他农林用地土壤贮水量两两比较均呈显著性差异（P＜0.05）；2）19龄苹果园土壤干化最严重，0-200 cm土壤干化程度呈季节性变化，200-250 cm、250-320 cm土层分别为严重干燥化与强烈干燥化，320-600 cm呈极度干燥化，形成永久性土壤干层；其次为小麦地，0-100 cm产生临时性干层，250-300 cm发生强烈干燥化；玉米地与9龄果园干化程度较轻，只在土壤浅层产生临时性土壤干层。（2）为了明确不同时间尺度下不同林龄苹果林蒸腾量与环境因子的关系，建立蒸腾量与环境因子的关系模型，于2015年选取10 a和20 a苹果林生态系统，用热扩散探针法对苹果树生长季日、月尺度下苹果树干液流速率进行连续监测和分析。结果表明，1）日尺度下，苹果林蒸腾与空气温度和水汽压差均呈现正相关关系；月尺度下，与蒸腾相关的环境因子仍为空气温度和水汽压差；2）20 a苹果林Tr/ET为29.25-67.51%，10 a苹果林Tr/ET为36.44-62.06%，两个树龄的Tr/ET整体表现为先升高后降低的趋势。20 a苹果林Tr/ET在8月达到峰值后急剧下降，而10 a苹果林经过一个缓慢下降的过渡期后，从9月份开始急剧下降。