Abstract:

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.

Key words: Caragana intermedia, sap flow, transpiration of an individual shrub, thermal dissipation probe method