In this study, the Grainer's thermal dissipation probe method was applied to monitor sap flux density (SFD) of a mangrove species Kandelia obovata over a period of one year (2010-10-2011-10) in Zhangjiangkou Mangrove National Nature Reserve, Fujian, China. The results showed that both season and diameter class exerted significant effects on the SFD of K. obovata trees. In summer, when the diameter at breast height (DBH) reached 8-10 cm, the highest SFD was found at a depth of 2 cm with a value of 38.21 g·m-2·s-1, which was comparable with those for other mangrove tree species and forested wetland tree species. The mean whole tree transpiration (i.e. daily water use) of all stem size classes demonstrated large changes from winter to summer, increased from 0.14 to 0.19 kg·d-1 in small trees (S, DBH=2-4 cm), from 0.94 to 1.45 kg·d-1 in medium trees (M, DBH=4-8 cm) and from 1.96 to 3.43 kg·d-1 in large ones (L, DBH=8-10 cm). The daily transpiration of K. obovata stand was calculated by summing all size classes, which was then summed up for entire year to estimate annual transpiration of entire K. obovata forest, which was about 100.38 mm, less than 6% of local annual precipitation. Key environmental factors all had significant effects (all P<0.001) on the stand transpiration rate (Es) of K. obovata forest, and photosynthetically active radiation (PAR) and vapor pressure deficit (VPD) were the main driving factors, which explained 60%-92% seasonal variation of Es. The PAR and VPD had larger effects on the Es in summer than that in winter. In addition, we observed an obvious time lag phenomenon in the relationship between Es and PAR or VPD, which should be taken into account when explaining seasonal variation of Es in K. obovata forest.
利用Granier热消散式探针法对福建漳江口国家级红树林自然保护区内红树植物秋茄的树干茎流密度(SFD)进行1年(2010年10月至2011年10月)的连续监测.结果表明: 季节和树干径级对秋茄树干茎流密度均有显著影响.在夏季,胸径(DBH)为8～10 cm时秋茄树干最外层2 cm处的SFD达到最大,为38.21 g·m-2·s-1,这与其他红树物种以及湿地乔木物种的茎流密度相当.不同径级(小、中、大径级分别为2～4、4～8、8～10 cm)秋茄每日整树蒸腾量(即水分日利用量)也呈现明显的季节变化,从冬季到夏季的波动值分别为0.14～0.19、0.94～1.45、1.96～3.43 kg·d-1.通过整合各个径级秋茄树的日蒸腾量推算得到秋茄林的日蒸腾量,再全年累加计算得到秋茄林年总蒸腾量为100.38 mm,不到当地年降水量的6%.主要环境因子对秋茄林蒸腾速率(Es)均有极显著影响(P<0.001),其中,光合有效辐射(PAR)和饱和水汽压差(VPD)是Es最主要的驱动因子,解释了Es 60%～92%的季节变异,且夏季秋茄Es 对PAR和VPD的依赖性大于冬季.秋茄Es与环境因子之间存在明显的时滞现象,需要在解释秋茄林Es季节变异时加以考虑.
Keywords: Grainer's thermal dissipation probe method; environmental regulations; mangrove forest; time-lag phenomenon; transpiration.