CHANGES IN APPARENT PHOTOSYNTHESIS, CO2 COMPENSATION POINT AND DARK RESPIRATION OF LEAVES OF SOME POACEAE AND CYPERACEAE SPECIES WITH SENESCENCE

CO2 exchange characteristics of detached mature and senescent flag leaves and of bracts in some Poaceae and Cyperaceae species, respectively, were studied using a closed IR system. Senescent leaves, 30 to 45 days after flowering, showed lower rates of apparent photosynthesis and dark respiration, and higher CO2 compensation points (CCP) than those measured at the flowering stage. In senescent C4-Poaceae, the increase of CCP was small (from 4.8 to 10.1 ppm on the average) with little influence of temperature, and the photorespiration level, 0.4 mg CO2/dm2/hr, was as low as that in mature leaf, indicating the presence of normal C4-characteristics. On the other hand, a C4-Cyperaceae, Cyperus microria Steud., showed extensive increases of CCP (from 9 to 41 ppm) and photorespiration (from 0.8 to 2.1 mg CO2/dm2/hr) with senescence. © 1979 Oxford University Press.