Stomatal Response Characteristics of Dry Evergreen and Dry Deciduous Forests in Kampong Thom, Cambodia

Abstract

We explored diurnal and seasonal variations in stomatal conductance in dry evergreen and dry deciduous forests in Cambodia and examined the stomatal response characteristics at two sites using a Jarvis-type model. Although stomatal conductance had maximum values at 9:00 (0900) or 10:00 (1000) in the morning and decreased continuously during the evening, transpiration showed peak values in the daytime and minimum values in the morning or evening at both sites in correspondence with the vapor pressure deficit. Stomatal conductance decreased in the rainy season to the late dry season; the pattern was clearer in the dry evergreen forest than in the dry deciduous forest. Stomatal conductance and volumetric soil water content had similar seasonal patterns, although these patterns differed between the dry evergreen and dry deciduous forests. The seasonal patterns of stomatal conductance and transpiration were different in the dry evergreen forest in the rainy season as a result of the moist air conditions. Clear differences were observed in maximum stomatal conductance and the function of the vapor pressure deficit between the two sites. In particular, compared to the results of other studies, the two sites showed large differences in their responses to the vapor pressure deficit. The functions of photosynthetically active radiation and the vapor pressure deficit showed wide daily change, suggesting that these factors may greatly impact the diurnal change of stomatal conductance. The vapor pressure deficit and volumetric soil water content also showed large seasonal variations and remarkable differences in function. The vapor pressure deficit had a large influence on stomatal conductance in the early dry season, whereas volumetric soil water content had a large effect in the late dry season.