华北山区核桃液流变化特征及对不同时间尺度参考作物蒸散量的响应

核桃是华北山区重要的经济树种,但该地区水资源紧缺,因此研究核桃液流耗水变化及其对气象因子的响应对于加强核桃水分管理、确定水分承载力具有指导意义。2008—2010年连续3个生长季节观测分析了华北山区核桃单株液流变化特征,研究了不同时间尺度(日尺度、月尺度)核桃液流与气象因子、参考作物蒸散量(ET0)的关系,并利用2009—2010年数据建立了拟合方程,在此基础上用拟合方程的估算值与2008年液流实测值进行了对比验证。结果表明:核桃液流具有明显的时间变化特征,最大液流量出现在5、6月份,2008—2010年生长季节(4—9月份)核桃液流量分别为893.23 L、854.88 L和841.77 L,日平均液流量分别为4.96 L、4.75 L和4.68 L。液流年际差异主要是由年降雨量引起。核桃液流与不同时间尺度下气象因子、ET0均有较好的相关性,且随着时间尺度的增加,二者间的相关性变大。利用2009—2010年液流实测值与气象因子、ET0建立的拟合方程,对2008年液流值进行了拟合,并与实测值进行了对比验证,发现不同时间尺度下液流拟合值与实测值均具有较好的一致性。在不能实现对液流进行连续观测的情况下,可以结合当地的气象资料、ET0等因子,利用建立的拟合方程对树木液流进行估算,弥补缺失的数据,具有较高的精确性,可用于指导当地核桃水分管理。

Characteristics of Juglans regia L. sap flow and its response to reference evapotranspiration on different time scales in the rocky mountain of North China

Walnut (Juglans regia L.) is an important economic tree species in rocky mountain of North China, which plays a key role in adjusting agricultural structure and promoting farmers'' economic income. As a kind of hygrophilous tree species, irrigation is the main measure for the walnut water management in the region located in semi-arid zone with limited water resource. So it is necessary to accurately evaluate water consumption of walnut trees during the growing seasons to enhance water use efficiency. The main purpose of this paper is to observe and analyze the individual walnut water consumption and its response to meteorological factors during the growing seasons. Sap flow of walnut trees was measured by thermal dissipation probe (TDP) method and meteorological factors, reference crop evapotranspiration were acquired by automatic weather station and local astronomy data. The study measured, analyzed diurnal and monthly sap flow characteristics of individual trees of Juglans regia L. and the relationship with meteorological factors, reference crop evapotranspiration on daily and monthly time scales in 3 consecutive growing seasons from 2008 to 2010. The fitted equations between sap flow and meteorological factors, reference crop evapotranspiration were established with the observed data from the year of 2009 to 2010. Finally, the simulated values derived from the fitted equation were compared with those measured in 2008. The results followed that diurnal variation of sap flow velocity showed broad-peak curve, which was consistent with that of solar radiation on typical sunny days, and narrow-peak curve was found during rainy days, which was mainly regulated by precipitation and vapor pressure deficit. Sap flow of walnut trees showed obviously seasonal variation, the maximum value occurred in May and June. The total sap flow of walnut during the growing season (April to September) from 2008 to 2010 was 893.23 L, 854.88 L, and 841.77 L, respectively. Average daily sap flow was 4.96 L, 4.75 L, and 4.68 L, respectively. The interannual difference of sap flow was mainly caused by rainfall. Sap flow of walnut trees had good correlationship with meteorological factors, reference crop evapotranspiration on daily and monthly time scales. Moreover, the correlationship on monthly time scale was better than that on daily time scale. The simulated values of walnut sap flow by fitted equation were good agreement with measured values in 2008 on daily and monthly time scales. The fitted equation could be used to evaluate walnut sap flow with the data of meteorological factors and reference crop evapotranspiration in the absence of long time sap flow measurements. The fitted equation was reliable to estimate walnut water consumption, and could be applied to guide the walnut tree water management in the local area.