亚热带樟树树干液流通量变化规律

采用热脉冲技术于2013―2015 年连续测定了樟树的树干液流，并同步监测了环境因子，分析了樟树树干液流日变化和季节变化特征以及对不同环境条件的响应。结果表明：樟树树干液流速率晴天日变化为典型的单峰型曲线，季节变化明显，液流速率峰值夏季＞春季＞秋季＞冬季，峰宽随季节变化存在“窄→宽→窄”的逐步变化过程。樟树存在微弱的夜间液流，且生长季较其他月份活跃。液流启动时间夏季最早，冬季最晚，液流结束（进入夜间低值）时间夏季晚于冬季约1~2 h。上下午液流量比值均＜1，平均值为0.74。同月不同天气条件下，液流速率和液流量均为晴天＞阴天＞雨天。干旱环境下，樟树树干液流峰值下降了约95%，与2014 年相比，同期内液流总量减少了约47.8%，在干旱中液流量与气温、水汽压亏缺呈显著负相关，改变了常年中（没有干旱）液流量与气温和水汽压亏缺呈显著正相关的关系。干旱显著降低了樟树的树干液流量，也反映了樟树对干旱的适应过程。

Sap Flow Characteristics of Cinnamomum Camphora,a Subtropical Evergreen Tree Species

In this study, the heat pulse sap flow sensors were applied to investigate the stem sap flow of Cinnamomum camphora in the central south China from April to October of 2013 and from July to November of 2015. The measurements of microclimatic variables (solar radiation, rainfall, air temperature, relative humidity and wind speed) were also conducted in the two study sites. During the year 2013, a severe drought occurred in July and August. The aims of this study were to analyze the variation of daily sap flow velocity and seasonal characteristics and response of sap flow to different environmental conditions. The results show that daily course of sap velocity exhibited mono-peak patterns during sunny days. Daily peaks of sap velocity were notably different in different seasons, they were ranked as summer > spring > autumn > winter. The width of peak values changed against seasons with a narrow-wide-narrow pattern. Nighttime sap flow was also found for Cinnamomum camphora especially obvious during growing seasons. This was likely associated with an enhanced vapor pressure deficit during night, but more reasons that whether nighttime transpiration or water recharge caused nighttime sap flow need further studies. The starting time of sap flow was the earliest in summer, while the latest in winter. The ending time that sap flow reached very low values in nighttime was 1-2 hours later in summer than in winter.These seasonal differences were consistent with variation of solar radiation, time of sunrise and sunset during different seasons. Sap flow ratio of morning over afternoon also varied over seasons with a mean value of 0.74, but all values were smaller than 1.0. This ratio was higher in summer and autumn than in winter and spring. Under different weather conditions, this study analyzed the responses of daily sap flow to sunny days, cloudy days and rainy days. A significant difference appeared in daily sap velocity and flow rate, showing a sequence as sunny days > cloudy days > rainy days. During the summer drought of 2013, a dramatic decrease in sap flow was accompanied with an increase of temperature and vapor pressure deficit. Daily peak sap velocity declined by ~ 95% and the total flow rate during the drought decreased by ~47.8%, as compared with total flow rate in the same time of 2014. Flow rate showed a significant positive correlation with temperature and vapor pressure deficit under no drought conditions while a significant negative correlation between flow rate and temperature and vapor pressure deficit during the summer drought in 2013. Decreasing sap velocity and flow rate during drought indicated an efficient adjustment of Cinnamomum camphora for saving plant water use.