In this study, we applied thermal dissipation probe technology to examine sap flow in various directions (east, south, west, and north) and at different depths (0-2, 2-4, 4-6 cm) within the stem of natural Picea mongolica trees in the eastern of Otindag Sandy Land to provide a scientific basis for accurately quantifying water consumption of P. mongolica forests through transpiration and to enhance the understanding of water relations. The results showed that the diurnal variation of sap flow in different directions displayed a unimodal curve, with the sap flow sequence being south>east>west>north. The sap flow at different sapwood depths exhibited an obvious unimodal curve, with a significant decrease as sapwood depth increased. Compared with that calculated from the mean sap flux density in four directions (23.57 kg·d-1), water consumption calculated using the mean value in south-east, east-west, south-west, north-east, north-south, and north-west was overestimated by 10.2%, 5.5%, 14.5%, and underestimated by 12.3%, 8.2%, 9.8%, respectively. The water consumption calculated using the values from the east, south, and west was overestimated by 6.1%, 14.4%, and 15.4%, respectively, and underestimated by 30.7% in the north. In addition, compared with the water consumption calculated from the mean value in three sapwood depths (48.51 kg·d-1), that calculated using sap flux density at sapwood depths of 0-2, 2-4, and 4-6 cm were overestimated by 18.8%, underestimated by 1.7%, and underestimated by 62.9%, respectively. These results indicated that sap flow of P. mongolica had significant azimuthal and radial variations, which considerably influence the estimation of tree water consumption. Installing probes at 0-2 cm simultaneously in both the north and east of the trunk could effectively reduce the estimation error of whole-tree water consumption by 4.2%. This approach enabled the accurate quantification of water consumption of individual P. mongolica trees in sandy areas, thereby improving the precision of transpiration water consumption estimates scaling up from individual level to stand level.
本文利用热扩散技术研究了浑善达克沙地东缘天然沙地云杉树干不同方位(东、南、西、北)和不同深度(0～2、2～4、4～6 cm)的液流动态及其对蒸腾耗水估算的影响,为精准量化沙地云杉天然林蒸腾耗水量和理解树木水分关系提供科学依据。结果表明: 沙地云杉不同方位树干液流日变化呈单峰曲线,呈现出南面>东面>西面>北面;不同边材深度树干液流呈单峰曲线,且随边材深度的增加而降低。与4个方位液流密度平均值计算的耗水量(23.57 kg·d-1)相比,采用东南、东西、西南、东北、南北、西北两个方位平均值计算的耗水量分别高估10.2%、5.5%、14.5%和低估12.3%、8.2%、9.8%;采用东、南、西和北单一方位计算的耗水量分别高估6.1%、14.4%、15.4%和低估30.7%。采用 0～2、2～4和4～6 cm单一边材深度液流密度测算的耗水量较采用3个边材深度平均值测算的耗水量(48.51 kg·d-1)分别高估18.8%、低估1.7%和低估62.9%。沙地云杉树干液流具有明显的周向和径向变化特征,而且显著影响整树耗水量的估算;在树干东北两个方位同时安装0～2 cm探针能够有效降低整树耗水量估算误差(4.2%),准确量化沙地云杉单株耗水量,进而提高单株向林分尺度扩展的蒸腾耗水量的估算精度。.
Keywords: Picea mongolica; azimuthal variation; radial variation; sap flux density; transpiration estimation.