Original paper

Short-term responses of photosynthesis to temperature and irradiance in the freshwater red alga Compsopogon coeruleus

Necchi, Orlando


Short-term responses of photosynthetic characteristics to temperature and irradiance was analysed in the freshwater red alga Compsopogon coeruleus under field and laboratory conditions. Diurnal variation of "in vivo" chlorophyll fluorescence parameters was measured in two contrasting seasons (winter and fall, dry and rainy season, respectively) at one site located in a tropical region of southeastern Brazil (20°11'10" S, 49°41'05" W). Photosynthesis-irradiance and dark/light (induction) curves were tested in laboratory under simulating winter and fall field conditions. Field and experimental data revealed characteristics of shade-adapted macroalgae: relatively low values of ETR (electron transfer rate) and high of NPQ (non-photochemical quenching) indicating, respectively, a low capacity of photosystem (PII) energy conversion and a high capacity of heat dissipation of absorbed energy by reaction centres. Some mechanisms to cope with high irradiances were also evidenced: a negative correlation of EQY (effective quantum yield, F/Fm') with photosynthetically active radiation (PAR), suggesting a high excitation pressure on PII; and a fast up and down regulation of NPQ, as heat dissipation of the excessive energy captured by reaction centre. Three other general characteristics were observed: 1) dynamic photoinhibition, indicated by a decrease followed by an increase of ETR in the induction curve under winter conditions (lower PAR); 2) positive correlation of ETR with temperature, i.e. an increase of PII energy conversion by electron transfer directly coupled to a temperature increase, suggesting a temperature-dependent mechanism; 3) similar or higher values of EQY and PQY at the end of the day, suggesting good recovery capacity and lack of irreversible photodamage to the photosynthetic apparatus due to exposure to high PAR. The short-term responses suggest that C. coeruleus is a shade-adapted alga with a combination of some characteristics of sun-adapted algae to cope with high PAR and temperature in order to avoid irreversible damages to the photosynthetic apparatus.


chlorophyll fluorescencediurnal variationmacroalgaeparphotosynthesistemperature