GROWTH OF CHLORELLA OUTDOORS IN A CHANGING LIGHT ENVIRONMENT

Chlorella zofingiensis was grown in semi-continuous culture in an outd oor enclosed tubular photobioreactor. At the quasi steady state, the r esponse of the culture to changes in photosynthetically active radianc e (PAR) was studied by following closely the dissolved O-2 concentrati on, biomass concentration and the carbohydrate and protein content of the biomass. Generally, O-2 production and the output of carbon and ni trogen of the biomass showed a linear correlation with incident PAR, s uggesting that the cultures were light-limited. Photoinhibition was no t observed in high Light adapted cultures (on a sunny day), but was ob served in shade adapted cultures (cloudy days) when there was a sudden four-fold increase in PAR. The output rate of biomass nitrogen observ ed on sunny days was, however, lower than that measured on cloudy days . On sunny days, a rapid increase in the C/N ratio of the biomass was seen. We attribute the increase in C/N ratio on sunny days to a slower response of protein synthesis to big increases in PAR, compared to ca rbohydrate synthesis. The possible influence of this C and N response pattern on the productivity of outdoor algal cultures is discussed.