西北干旱荒漠绿洲区葡萄园水热通量特征及其主要影响因素

Characteristics and influencing factors of water and heat fluxes over an vineyard in arid desert oasis region in the Northwest China

关键词:  干旱区, 葡萄, 水热通量, 干旱平流, 通径分析, 影响因素

Key words:  arid area, grape, water and heat fluxes, arid advection, path analysis, influence factors

摘要:

为提高干旱绿洲区农田地表过程的科学认识及改善农业水管理,该研究基于涡度相关技术,运用葡萄园生长季能量平衡观测资料,分析了不同时间尺度的水热通量变化特征,以及干旱平流和冠层导度(G_c)在不同生长阶段上对水热通量的影响,并应用通径分析研究了环境因子对潜热通量(LE)的影响路径和程度。结果表明:(1)日尺度上,LE呈现出不同程度多峰状,其余水热通量总体上呈单峰状。整体上,各生长阶段日间净辐射(R_n)>LE >感热通量(H)>土壤热通量(G)。G相较于R_n呈现出明显的滞后现象。(2)整个生长季上,LE和H分别占白天可利用能量(R_n-G)的86%和14%,表明LE始终是白天葡萄园可利用能量的主要消耗项。干旱平流对白天LE的贡献范围为5%～59%,全生长季平均贡献为28%; G_c对LE的影响在生长季上呈动态变化,且在新梢生长期和落叶期对LE的影响强于中间生长阶段。(3)LE主要受R_n的影响,饱和水汽压差(VPD)和气温(T_a)对LE 的影响程度相近且仅次于R_n。通径分析表明,R_n主要通过直接作用方法影响LE,VPD和T_a主要通过R_n对LE产生间接作用。总之,西北干旱荒漠绿洲葡萄园水热通量存在明显的日和季节变化特征,环境因子对其影响明显,且各自影响程度与路径存在差异。

Abstract:

To improve our understanding of farmland surface process and agricultural water management in arid oasis area, we analyzed the characteristics of water and heat fluxes at different time scales, and the influence of arid advection and canopy conductance(G_c)on water and heat fluxes at different growth stages. In addition, we used path analysis to study the influence path of environmental factors on latent heat flux(LE). In this paper, the water and heat fluxes were measured by eddy-covariance in 2017. The results were as follows:(1)LE showed multiple peaks, while the other fluxes were basically unimodal shapes at the daily scale. On the whole, the values of daily net radiation(R_n)were maximum, followed by LE, sensible heat flux(H)and soil heat flux(G)at each growth stage. The variation of diurnal G showed obvious lagged effect compared to that of R_n.(2)LE and H accounted for 86% and 14%(respectively)of daytime energy during the whole growing stages, indicating that LE was the main energy consumption item. The contribution of arid advection to daytime LE ranged from 5% to 59% with an average value of 28% at whole growing season. The influence of G_c on LE was stronger at the new shoot and leaf-fall stages than that in the middle growing season.(3)LE was mainly affected by R_n, followed by vapor pressure deficit(VPD)and air temperature(T_a), and the influence degrees of VPD and T_a on LE were similar. Furthermore, the path analysis showed that R_n directly affected LE; VPD and T_a mainly affected LE indirectly through R_n. As a whole, the water and heat fluxes in vineyards of arid desert oasis in Northwest China display significant diurnal and seasonal variations, and the influences of environmental factors on these exists great discrepancies in magnitude and path.