Characterization of Canopy Photosynthetic CO2 Flux and Leaf Stomatal Conductance Responses of Potato Crop to Changing Field Meteorological Conditions in Hokkaido

This study characterizes the response of canopy CO2 flux (FCO2) and leaf stomatal conductance (gs) of potato fields in the Tokachi plain in Hokkaido to changing meteorological factors, e.g. air temperature and vapor pressure deficit (VPDa). Measurements were made of FCO2 and meteorological conditions in August 1998. Also, upper crown sunlit leaf stomatal conductance response to air temperature and vapor pressure deficit (VPDc) inside the cuvette of a porometer were measured simultaneously on a number of days to determine their effects on gs. Results showed that at moderate summer temperatures in Hokkaido and free soil water stress, VPDa was the more significant factor affecting the depression in FCO2 in the potato crop. The depression is characterized by the difference of FCO2 from a curve tracing the maximum FCO2 response to light. A similar VPDc effect was also observed in gs. Above an optimum temperature of 25°C, stomatal closure and high depressions in photosynthetic CO2 exchange occurred even at low vapor pressure deficit. This fact implies a decrease in photosynthetic CO2 fixation and crop growth in cool temperate-climate regions under further global climate warming.