To clarify the effects of environmental factors on transpiration process of apple trees in rain-fed ecosystem, the dynamics of sap flow in apple trees from Loess Plateau area in western Shanxi Province of China were monitored using the thermal diffusion technique. Meanwhile, environmental factors including meteorological elements and soil moisture content were measured. The results showed that both net solar radiation (Rn) and atmospheric vapor deficit (VPD) were closely correlated with sap flow rate (Js), as the main ones among all the measured environmental factors. At both hourly and daily scales, the cumulative variances of the three principal components of the environmental factor were above 86%. The first principal component contained VPD and Rn, and explained the variance of over 52% (at hour scale) and 63% (at daily scale), which could be classified as the evaporation demand index (EDI) and as the key comprehensive environmental varia-bles affecting tree sap flow. The second principal component mainly included soil moisture content (SWC) and other factors, which were referred to the soil water and heat supply index. The third principal component mainly included wind speed and other factors, and could be classified into the hydrothermal dissipation index. At the scale of hourly or daily, the response of Js to EDI showed a significant exponential growth relationship. At the hourly time scale, Js of apple trees could be accurately modelled based on the first principal component EDI (R2=0.72). At the daily scale, Js of apple trees could be better modelled based on potential evapotranspiration (ET0) (R2=0.88). Our results were of great significance for clarifying the responses of water transport in apple tree to environmental factors, estimating water consumption of apple tree based on meteorological factors, as well as directing orchard water management.
为明确环境因子对树木蒸腾过程的驱动机制,以晋西黄土残塬沟壑区的苹果树(红富士)为对象,利用热扩散式液流技术监测生长季苹果树树干液流的动态变化,并同步监测了气象和土壤水分等环境要素的季节动态.结果表明: 在众多环境因子中,太阳净辐射(Rn)、大气水分亏缺(VPD)与液流速率(Js)间的相关性最强.在小时或日尺度,环境因子主成分分析中前3个主成分的累积方差贡献率均在86%以上.其中,第一主成分主要包含VPD、Rn等因子,方差贡献率达52%(小时尺度)和63%(日尺度)以上,可归为蒸发需求因子(EDI),是影响该地区果树树干液流的关键综合环境要素集;第二主成分主要包括土壤含水率(SWC)等因子,归为土壤水热供给因子;第三主成分主要包括风速等因子,归为大气水热散失动力因子.在小时或日尺度上,Js对两种环境因子综合变量(EDI或潜在蒸发散ET0)的响应都呈显著的指数增长关系,在小时尺度上,基于EDI模拟苹果Js的指数模型精度更高(R2=0.72),在日尺度上,基于ET0模拟苹果Js的指数模型模拟精度更高(R2=0.88).研究结果对于明确苹果树水分传输对环境驱动的响应规律,根据气象要素估算苹果树蒸腾耗水量,并指导果园水分管理均具有重要意义.
Keywords: evaporative demand index; net solar radiation; sap flow rate; thermal dissipation method; vapor pressure deficit.