要旨
We compare independent data sets of the maximum stomata1 conductance (gsmax, for single leaves) and bulk surface conductance (Gsmax for a vegetated surface including the plant canopy
and soil) for evaporation. Data were obtained from field measurements, restricted to periods
with plentiful soil water, adequate light, high relative humidity and moderate temperature. The
data encompass most major vegetation types and a wide range of leaf area index (A). Observed
G smax is not systematically dependent on A; and takes average values of 20 and 33 mm pro s for
natural vegetation and agricultural crops. A similar pattern exists in the g,,, data, which yield
remarkably consistent average values of 6 and 12 mm s-1, respectively, for natural vegetation
and crops. Overall, the ratio Gmax/gmax is consistently close to 3, for seven major vegetation
types of diverse structure. A simple model accounts for the close relationship between gsmax and
G smax, and in particular how G smax is conservative against A because of the compensating
decrease in plant canopy evaporation and increase in soil evaporation as A diminishes. The
results are important for development of parameters for biosphere-atmosphere interactions in models.
