Abstract

Estimating plant water use is an important step in assessing the effects of increasing vegetation cultivation on the hydrological cycle especially in arid and semi-arid regions. In this study, meteorological measurements combined with sap flow techniques provided a low-cost option to study the canopy physiological transpiration of Platycladus orientalis response to environmental factors on a continuous basis. Canopy transpiration (E_c) was measured by thermal dissipation method of Granier, and canopy conductance (g_c) was calculated by inverting the Penman-Monteith equation. The results showed that the transpiration ofP. orientalis was strongly controlled by stomatal conductance, and g_c was a comprehensive and compounded environmental variable. An improved Jarvis-type model, based on a series of environmental control functions, explained 85% of the variation observed in g_c. Cross validation showed that this model provided good predictions of canopy conductance and transpiration for P. orientalis. Such a methodology offers a reasonable estimation of water use in the determination of water balance for land water resources planning, vegetation management and impact assessments of rehabilitation.

Key words: Sap flow, canopy transpiration, canopy conductance, model, Penman-Monteith equation, Platycladus orientalis, semi-arid region.