中间锦鸡儿(Caragana intermedia)是一种优良的防风固沙灌木。有关其蒸腾作用的测定研究多是通过对单叶或小枝蒸腾速率的测定值推算整株丛的蒸腾耗水。该研究选择在中间锦鸡儿株丛的主根安装“热扩散探针”来测定整株丛的蒸腾耗水。结果表明: 中间锦鸡儿整株丛液流量的日变化可划分为4个阶段: 1)液流量迅速上升阶段(8:00~11:30), 其液流量占全天液流量的21.21%; 2)液流量最高而相对稳定阶段(12:00~18:00), 液流量占全天液流量的58.84%; 3)液流量迅速降低阶段(18:30~21:00), 液流量占全天液流量的10.62%; 4)液流量最低而稳定阶段(21:30~次日8:00), 液流量占全天液流量的9.32%。从所观测的中间锦鸡儿整株丛液流量的日变化可以看出: 在午间(12:00~14:00), 中间锦鸡儿整株丛蒸腾虽因环境因子的影响(如云朵遮阴)会发生较小的波动, 但并没有出现明显的“午休”现象, 而是保持相对稳定的高蒸腾速率。环境因子对中间锦鸡儿整株丛液流量影响的强弱次序依次为: 太阳辐射>空气温度>水蒸气压亏缺>空气相对湿度>土壤温度>风速。液流量对环境因子变化的响应存在着明显的时滞现象。根据所测大、中、小3个中间锦鸡儿整株丛树干液流量数据, 计算出一个中等大小(株高为110 cm, 冠幅为0.6 m², 叶片总干重为51.82 g)的中间锦鸡儿整株丛在测定时间内的日蒸腾耗水量为2.2 kg · d^-1。

Aims Caragana intermedia is an excellent wind-breaking and sand-fixing shrub species. There are many reports of transpiration measurements of C. intermedia, most of which extrapolated the transpiration water consumption of entire shrubs from measurement of a single leaf or shoot. Our objective was to study diurnal changes of sap flow for entire individuals of C. intermedia.
Methods We selected three C. intermedia plants in the Mu Us Sandy Land of north-central China and measured sap flow with a thermal dissipation probe, also called Granier sap-flow probe. The sap-flow sensor includes two probes, each of them containing a copper constantan thermocouple. We inserted the probes into the taproot, with one probe about 4-5 cm above the other, used solar film to seal the top of the cover against the bark to prevent rainwater from entering and obtained continuous measurements.
Important findings The diurnal changes of sap flow in C. intermedia individuals can be divided into four phases: 1) rapid ascending phase (8:00-11:30), 2) stationary high phase (12:00-18:00), 3) rapid descending phase (18:30-21:00) and 4) stationary low phase (21:30-8:00) of the next day, accounting for 21.21%, 58.84%, 10.62% and 9.32% of the sap flow, respectively. From 12:00 to 14:00, however, transpiration fluctuated slightly because of the environment (e.g., clouds), but there was no obvious “noon break”, as the transpiration rate remained high. The sequence of environmental factors that impacted sap flow was: solar radiation > air temperature > vapor pressure deficit > air relative humidity > soil temperature > wind, and there was an obvious time lag between the sap flow and the environment factors. Based on the diurnal change data, we calculated that the transpiration water consumption of an individual C. intermedia shrub is 2.2 kg·d^-1.