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https://doi.org/10.1016/s0168-1923(98)00078-1
Copy DOIJournal: Agricultural and Forest Meteorology | Publication Date: Jun 1, 1998 |
Citations: 46 |
In order to evaluate the stomatal control on the canopy evapotranspiration, diurnal variations in stomatal conductance ( g s) of individual plants and bulk surface conductance ( G s) of the canopy were measured independently in the Sarobetsu mire of northern Japan. During July–August 1993 and 1994, g s was measured for four species ( Sasa palmata, Moliniopsis japonica, Myrica gale L. var. tomentosa and Ilex crenata var. paludosa) growing in the mire. In July and August 1995, G s was determined using Penman–Monteith equation. In this equation, evapotranspiration rate was determined by the Bowen ratio/energy balance method. Diurnal hysteresis curves of g s in relation to leaf-to-air vapor pressure deficit ( ν) followed different courses from day to day according to the magnitude of ν, and daily maximum g s was correlated negatively with daily maximum ν except for Ilex crenata var. paludosa. Similar clockwise hysteresis curves were observed between G s and vapor pressure deficit at the mean evaporative surface ( D 0), and daily maximum G s decreased with daily maximum D 0 in mid-summer. In particular, on days when daily maximum D 0 increased up to 1.9 kPa, the large decrease in G s decreased the evapotranspiration rate, despite high irradiance levels. Thus, stomatal control by individual plant leaves strongly affects evapotranspiration from the canopy and prevents excessive water loss on days when vapor pressure deficit is high, even when soil water is plentiful. On the rising limb of the diurnal course of the transpiration rate ( T r), increases in T r with change in ν, Δ T r/Δ ν varied from day to day, in particular for M. gale L. var. tomentosa. Further, a negative relationship was found between Δ T r/Δ ν and the rate of increase of ν for unit change in time. We believe that the change of the daily course of g s and T r was caused by the response of stomata to the increased rate of change of ν. Thus, in order to predict the diurnal variation of g s, the magnitude and tendency of ν for each day must be considered.
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