绿洲农田防护林树干水分传输的方位差异

Azimuthal Variation in Water Transport in Tree Trunks of Shelterbelt Forests of Oasis Farmland

[目的]对栽植于渠道旁的绿洲农田防护林树干向、背渠两侧边材液流速率进行定位观测和比较,明确特殊立地条件下树干边材水分传输的方位差异,为提高利用液流估算树木蒸腾精度提供科学依据。[方法]以乌兰布和沙漠绿洲农田防护林的3种杨树(小美旱杨、新疆杨和北抗杨)为研究对象,采用有8个监测位点的热场变形液流测定技术同步监测和对比树干向渠和背渠2个方位的边材液流速率。[结果]边材液流速率在向渠侧(J_(Q-side))显著高于背渠侧(J_(NQ-side))(P<0.01),且3个树种表现一致。观测期内,小美旱杨、新疆杨和北抗杨的J_(Q-side)为J_(NQ-side)的1.83倍(R^(2)=0.90)、1.40倍(R^(2)=0.71)和3.55倍(R^(2)=0.71),典型晴天的J_(Q-side)日峰值平均值分别可达3.38、2.47和5.35 cm·h^(−1),午间前后,树干向、背渠两侧边材液流速率差异最大。J_(Q-side)和J_(NQ-side)均表现出随边材深度而递减的显著变化,其中向渠侧边材各位点(1.5~7.5 cm)的液流速率均显著高于背渠侧相应位点(P<0.01),该径向变化规律在每个树种不同方位均表现出一致性,可通过负指数函数较好拟合(R^(2)>0.98)。[结论]灌渠引起绿洲农田防护林树干向、背渠两侧边材的水分传输产生显著差异,但并不改变各方位的径向变化格局。

[Objective]This study aims to determine the azimuthal variations of water transport in the sapwoods of the trees under special site conditions,so as to provide a scientific basis for improving the accuracy in estimating tree transpiration by sap flow through observing and comparing the sap flow velocity of sapwoods facing and backing to an irrigation channel in the oasis farmland protection forest trees planted alongside the channel.[Method]Three typical poplar species(Populus×popularis,P.alba var.pyramidalis and P.deltoides cl.Beikang)in the oasis farmland shelterbelt in Ulan Buh Desert were selected as the research objects.The heat field deformation(HFD)method was used to synchronously monitor the sap flow velocity of the trunk that was either face to or back to the irrigation channel in eight measuring sites.[Result]Sap flow velocity of sapwood facing to the irrigation channel(J_(Q-side))was significantly higher than that of sapwood backing to the irrigation channel(J_(NQ-side))in each tree species(P<0.01).J_(Q-side)values of P.×popularis,P.alba var.pyramidalis and P.deltoides cl.Beikang were 1.83(R^(2)=0.90),1.40(R^(2)=0.71)and 3.55(R^(2)=0.71)times of corresponding J_(NQ-side)values,respectively.On sunny days,the average J_(Q-side)peak values of the three tree species were 3.38,2.47,and 5.35 cm·h^(-1),respectively.The differences in sapwood sap flow velocity between the two sides reached the maximum around noon.Both J_(Q-side)and JNQ-side showed a decreasing trend with the increase of sapwood depth,and the sap flow velocity at each point(1.5-7.5 cm)of sapwood facing to the irrigation channel was significantly higher than that of sapwood backing to the irrigation channel(P<0.01).The radial variation pattern of sap flow velocity in different azimuths in each poplar specie was consistent,which could be well fitted by the negative exponential function(R^(2)>0.98).[Conclusion]The irrigation channel causes significant differences in the sapwood water transport between facing side and backing side to the channel,but does not change the radial variation pattern of sap flow of the trees in farmland shelterbelt.