DIURNAL AND SEASONAL PHOTOSYNTHETIC CHARACTERISTICS OF POPULUS-DELTOIDES MARSH LEAVES

Diurnal and seasonal changes in photosynthetic characteristics of popl ar (Populus deltoides L.) leaves were studied with an aim to understan d the adaptation mechanisms/strategies employed by the leaves in order to deal with fluctuation in environmental conditions. The net rates o f CO2 (P-N) uptake were different in different seasons and varying CO2 compensation concentrations explained these changes, at least partly. The leaves showed a major shift in the temperature optima for CO2 ass imilation to suit the changing temperature conditions. Although the ac tual rates of uncoupled electron transport in thylakoids varied in par allel with P-N, they were not limiting for photosynthesis. The chlorop hyll (Chl) and carotenoid (Car) contents did not show a major change b ut the amount of Car in relation to Chl was considerably higher in sum mer leaves. The leaves primarily responded by seasonal shift of the te mperature optimum for photosynthesis to deal with the changing irradia nce and temperature. These changes in different seasons were coupled w ith fluctuations in CO2 compensation concentration, changes in the rat es of electron transport and to some extent with pigment composition.