Calculation of CO2 gas phase diffusion in leaves and its relation to stomatal resistance

Abstract

Abstract. A new theory and experimental method was developed to measure the diffusion resistance to CO 2 in the gas phase of mesophyll leaf tissue. Excised leaves were placed in a chamber and their net evaporation and CO, assimilation rates measured at two different ambient pressures. These data were used to calculate CO, gas phase diffusion resistances. A variety of field grown leaves were tested and the effects of various experimental errors considered. Increasing the gas phase diffusion resistance decreased transpiration more than it decreased CO, assimilation. It was concluded that gas phase diffusion resistance associated with CO2 assimilation may sometimes be 100 or 200 s•m-1 greater than the resistance implied by transpiration rates. This may be due to longer path lengths for the CO, diffusion, constricted in places by the shape and arrangement of mesophyll cells.

RuP2 pool size indicated by CO2 assimilation following the abrupt loss of light

“…Transpiration and CO 2 uptake were measured by standard methods as previously described [1], except that the gas exchange chamber was modified to accomodate intact leaves on potted plants. This was accomplished by cutting a slit in the side of the outermost chamber so that the leaf could be passed through it and into the assimilation cell.…”