Physiological performances of two populations of Compsopogon caeruleus (Rhodophyta) to inorganic nitrogen and phosphorus impoverishment

Abstract

Studies on the effects of inorganic nutrients manipulation (specially nitrogen and phosphorus) in freshwater macroalgae are scarce. Physiological responses (growth, photosynthesis, and pigment contents) to nitrogen and phosphorus impoverishment (nitrate and phosphates, respectively) were analyzed under culture conditions in two populations of Compsopogon caeruleus coming from environments with distinct levels of saprobity (oligosaprobic and mesosaprobic, designated isolates o and m, respectively). The aim was to evaluate the isolate responses (decrease or increase in physiological performance) to decrease in inorganic nitrogen and phosphorus concentrations. Three dilutions in original concentration of nitrogen and phosphorus of Bold Basic Medium were tested. For the nitrogen treatments, the isolate m had a more pronounced decrease in general performance in comparison to isolate o: lower values of effective quantum yield and phycobiliprotein concentrations in all nitrogen dilutions. Phycobiliprotein degradation is a typical and widely reported response of red algae under nitrogen scarcity. For the phosphorus experiments, the isolate o showed a more pronounced decrease in general performance in comparison to isolate m: lower values of maximum photosynthetic rate (Pmax) and photosynthetic efficiency (a), besides lower phycobiliprotein concentrations in all dilutions. The best performance of C. caeruleus was found at higher nutrient concentrations, confirming previous records as a good bioindicator of enriched environments. Nevertheless, the two populations differed in the mode that they use these resources, thus suggesting a possible phenotypic difference between them. Physiological responses of these isolates to nitrogen and phosphorus impoverishment seem to be more related to the type of limiting nutrient than to saprobity.