CO2 AND O-2 TRANSPORT IN THE AERENCHYMA OF CYPERUS-PAPYRUS L

Cyperus papyrus L. (papyrus) is an emergent wetland species with C-4 p hotosynthesis. Culms of papyrus possess numerous large intercellular a ir cavities and functional 'Kranz' chlorenchyma which are involved in CO2 recycling in the culm. In darkness, the CO2 concentration in the c ulms increased to 74 times that of the ambient air. In the light, the culms greatly reduce the intercellular CO2 concentrations by internal CO2 recycling via photosynthesis. Results suggest that 35-57% of the C O2 respired by the culm pith and rhizomes may be refixed by culm photo synthesis. The dynamics of O-2 transport in the intercellular spaces o f the culms and the rhizomes were also studied. Both illumination and prolonged darkness had significant effects on the O-2 concentrations i n the culm and rhizomes. While the water surrounding the rhizomes rema ined strongly hypoxic, the O-2 concentration in the submerged rhizomes was 15.1% during the day and 10.3% at night. The diffusive fluxes of CO2 and O-2 within the papyrus plant during the day and night were cal culated. Results suggest that rapid CO2 exchange occurs between the am bient air, internal atmosphere and the culm photosynthetic tissue. Als o, there is a high O-2 flux, particularly at night, which is generated in the intercellular air spaces between the culm and the rhizome.