多尺度典型果树蒸腾耗水实验研究及尺度转换

The accurate measurement or estimation of transpiration procedure and rate for the fruit trees is the basis for the water use efficiency improvement and water scientific management. This project intends to measure the transpiration rate at the leaf, single plant and orchard scaling level for the pear trees using the infrared gas analyzer technique, stem sap flow method and continues atmospheric vapor δ18O data, respectively. Field experiments will be conducted at the Xuehua pear orchard in Zhao xian county, Hebei Province. As the core method, a hydrogen and oxygen isotopes in situ measurement system based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) will be used to obtain the continuous atmospheric vapor δ18O data. Other measurements will be made with the eddy covariance technique, cryogenic vacuum distillation and stable isotope ratio mass spectrometry. The combined method for the TDLAS and eddy covariance technique is the key to obtain the continuous transpiration rate for the stand-scale level. Stem sap flow using the thermal dissipation probe (TDP) will be used to measure the transpiration rate for the whole tree at the same time and frequency. The biological indicates such as the sapwood area, leaf potential and so on will be monitor, simultaneously. On the field experimental basis, we can obtain the transpiration rate at the three different spatial levels and then we would like to preliminarily expound the procedure of the transpiration and the diurnal and seasonal regular pattern for the transpiration rate at the three different spatial scales. Meanwhile, the isotope characters for the evapotranspiration δ18O, plant transpiration δ18O and the soil evaporation δ18O will be used to analyze the procedure of water consumption and control mechanism. Finaly, the comparison will be performed for the transpiration rate at different levels and then the key biological parameters will be ascertained which can be used to do the scale transforming among the three spatial scales. All these results will provide the basal theory for the water management and precise irrigation in a fruit orchard.

果树群体蒸腾耗水过程的准确测定和估算是提高果园群体水分利用效率，加强果园水分精准科学管理的重要依据。本项目拟以河北赵县雪花梨园成龄梨树为研究对象，以红外气体分析技术和热扩散茎流连续观测技术为基础，以大气水汽δ18O的原位连续观测系统与通量廓线技术结合为核心手段，开展同步不同空间尺度的观测。初步阐明果园生态系统枝叶、单木和林分三种空间尺度的蒸腾耗水过程及其季节变异特征，重点关注果园生态系统蒸散δ18O、植物蒸腾δ18O以及土壤蒸发δ18O的过程特征及其控制机制；与涡度相关技术结合，实现林分尺度果树蒸腾耗水的过程连续分析；进而进行枝叶-单木-林分三个不同空间尺度蒸腾的综合对比，量化不同尺度植物蒸腾的强度和相对变化及其受环境与生物因素影响的方式与程度，结合同步观测的生物、环境要素，确定关键的尺度转换参量，建立三种不同空间尺度间的转换技术，为果园水分的精准科学管理和实施科学的栽培技术措施提供理论依

华北地区淡水资源匮乏是影响农业可持续发展的重要因素。果树的蒸腾研究是实现农业水管理的理论依据。本项目以华北典型梨园为研究对象，通过利用红外分析技术、热扩散茎流技术、同位素方法和涡度相关技术，研究了从叶片、单株到林分的蒸腾耗水的变化情况。研究结果表明：梨树不同方位单叶的蒸腾有些差异，南部和北部叶片、东部和西部叶片具有相似的蒸腾变化趋势，而东部和南部的叶片变化相对稳定；利用茎流计测定的单株的蒸腾量，多年年平均为458.0mm，利用涡度相关技术测定的全年蒸散量高达798.5mm，蒸腾占蒸散的比例为57.34%。同时，蒸腾在季节变化上呈单峰的趋势，即从3、4月份开始增加，最大值出现在7月份，然后又下降到10月底结束。氢氧同位素在不同月份的变化来看，3月份出现明显的同位素富集现象，δ18O的平均值为-18.65，δD的平均值为-126.12，这说明这段时间土壤蒸发较为强烈植物蒸腾较弱，使同位素出现了富集现象。4、5月份随着梨树叶片的生长，同位素富集现象较弱，说明蒸腾较为强烈。氢氧同位素从日尺度变化来看，水汽重同位素特征随时间推移富集明显，而在不同时段又因外部气象因子影响具有不同特征，午夜蒸发和蒸腾水汽同位素组成特征相似，清晨由于叶片凝结水仍然较多的缘故蒸腾水汽比蒸发水汽轻，午间因为作物根系吸水不发生同位素分馏，蒸腾水汽比蒸发水汽重，符合同位素分馏特性，δ18O的变化特征和δD一致。确定了影响蒸腾的主要因素为大气蒸散力，然后为土壤含水量，生物学因素。在生物学因素中心材面积和叶面积指数是确定蒸腾关键因素，而叶面积指数是蒸腾空间转换的关键参数，其可以利用儒略日进行拟合。尺度转换中，通过分析从单株到林分尺度的蒸腾变化关系，可以利用测定的地面净辐射、潜热进行蒸腾量的估算，确定了可以利用叶面积指数的生物参数作为主要因子进行转换。