三种温带树种树干储存水对蒸腾的贡献

Contribution of stem water storage to daily transpiration of three temperate trees in northeastern China

树干储存水在协调叶片水分和碳平衡、维持树木水分收支平衡中起着重要作用。以无孔材红松(Pinus koraiensis)、散孔材山杨(Populus davidiana)和环孔材蒙古栎(Quercus mongolica)为对象,于2010年8月中旬至9月末(生长季后期)测定其冠基和干基树干液流通量以及树干储存水的日变化过程,量化分析树干储存水对日蒸腾量的贡献及其生物影响因子。结果表明:冠基的液流比干基启动得早,而且两者在一天中存在显著的时滞。树干储存水的日进程总体上可分为:完全释放、以释放为主补充为辅、以补充为主释放为辅、饱和稳定等4个阶段,但每个阶段的持续时间和变化格局随树种而变。红松的树干储存水在一天内表现出两个释放-补充周期,而两种阔叶树种均只经历了一次释放-补充过程。在测定时段内红松、山杨、蒙古栎标准化到平均木(边材体积为0.29 m3)的树干储存水释放量分别为:(3.4±1.5)、(2.4±0.6)和(1.5±0.4)kg.d–1,分别占日蒸腾量的18.9%、17.1%和8.8%。树干储存水释放量与日蒸腾量呈显著的指数函数关系,而与干基的边材面积和树高呈正相关关系。该研究突显了树木大小(树高和边材面积)和材性特征对树干储存水释放量及其对蒸腾量贡献的重要影响。

Aims Stem water storage plays a significant role in maintaining a favorable leaf water and carbon balance and minimizing temporal imbalances between water supply and demand.Few measurements,however,have been made on the daily dynamics of discharge and recharge of stem water storage,especially for Chinese temperate trees.Our objectives were to（1） examine diurnal courses of stem water storage of three temperate trees with different characteristics in Northeast China,i.e.,coniferous needle-leaved Korean pine（Pinus koraiensis）,broadleaved diffuse-porous aspen（Populus davidiana） and ring-porous Mongolian oak（Quercus mongolica）,（2） quantify the contribution of stem water storage to the daily transpiration loss for these trees and（3） explore biotic factors influencing stem water storage.Methods Sapflow was measured simultaneously at the crown base and trunk base with calibrated thermal dissipation probes from mid-August to late-September 2010.The daily stem water storage was calculated by comparing the diurnal patterns of trunk basal and crown basal sapflow for each of three replicated trees per species.Important findings Crown basal sapflow started earlier than trunk basal sapflow in the morning for all trees,and a distinct time lag existed during the daytime.This suggested stem water storage was significant in regulating tree transpiration losses.The diurnal course of stem water storage was divided into four stages,i.e.,full discharge,mainly discharge supplemented with recharge,mainly recharge supplemented with discharge,and saturated steady stages.However,the duration and pattern of each stage varied with species.The pine experienced two periods of discharge and recharge of stem water storage,while the two broad-leaved species experienced only one.The daily amount of water withdrawn from storage and subsequently replaced that was normalized to the mean sapwood volume（0.29 m 3） was（3.4 ± 1.5）,（2.4 ± 0.6） and（1.5 ± 0.4） kg.d –1（mean ± SD） for the pine,aspen,and oak,respectively,accounting for 18.9%,17.1% and 8.8% of the total daily water loss,respectively.Use of stem-stored water exponentially increased with daily water loss,and was positively correlated with the basal sapwood area and tree height.These results emphasize the effects of tree size（i.e.,tree height and sapwood area） and timber properties on stem water storage and its contribution to daily water losses.