北方四种城市树木蒸腾耗水的环境响应

2008年6-8月,以大连市劳动公园内雪松、大叶榉、水杉和丝棉木4种树木作为研究对象，采用热扩散探针（TDP）法对其树干边材液流进行了连续动态测定，并同步测定了土壤水分与小气候等环境因子.结果表明：观测季节内，树木所处立地条件下不存在水分胁迫，树木液流与土壤湿度相关性不显著（R²<0.05,P>0.211,n=1296).4种样木白天液流速率与太阳辐射变化存在“时滞”现象，液流速率的相关系数(R²)在0.624～0.773(P=0.00,n=1296)，其影响主要集中在5：00-8：00和18：00-20:00辐射骤变期间（R² >0.700，P<0.05).水汽压亏缺(VPD)是影响样木夜间蒸腾的主要因子(R²>0.660，P<0.05，n=1872)，与全天液流速率的R²值在0.650.～0.823(P=0.00,n=1296)，以VPD建立的统计模型可以解释90%以上全天液流的变化(P=0.00).风速与树木液流呈极显著相关关系，但R²值 小于前两者(R²<0.380,P=0.00,n=1296).此外，树木液流的环境响应存在饱和现象.

Environmental responses of four urban tree species transpiration in northern China

By using thermal dissipation probes (TDP), this paper monitored the sap flow of four tree species ( Cedrus deodara, Zelkova schneideriana, Euonymus bungeanus, and Metasequoia glyptostroboides) at the Laodong Park in Dalian City from June to August 2008, and the soil moisture content and micrometeorological variables were measured simultaneously. Due to the absence of water-stress in the habitat, the sap flow of all sampled trees had no significant correlation with soil moisture content (R~2 < 0. 050, P > 0. 211, n = 1296). The correlation coetticient between solar radiation and sap flow reached 0. 624-0. 773 (P =0. 00, n = 1296) despite the existing hysteresis.Solar radiation had major effect ( R~2 > 0. 700, P < 0. 05 ) during early morning ( 5 : 00-8 : 00 ) and late afternoon (18:00-20:00) when undergoing dramatic changes. As the main factor determining nighttime sap flow (R~2 >0. 660, P <0. 05, n = 1872), vapor pressure deficit (VPD) had a corre-lation coefficient as high as 0. 650-0. 823 ( P = 0. 00, n = 1296 ) with the sap flow in whole-day scale. Meanwhile, the models constructed on the basis of VPD were able to explain 90% of daily sap flow change ( P = 0. 00). The correlation coefficient between sap flow and wind speed was relatively smaller than the previous two (R~2 <0. 380, P =0. 00, n = 1296), though showing significant correlation in affecting sap flow. Observations also deteeted the saturation phenomenon of sap flow to the environmental demands.