| Abstract: | In order to gain a better understanding of the factors responsible for changes in cyanobacterial species composition in the Alberche River (central Spain), which is characterized by spatiotemporal N and P variability, we undertook P‐limitation studies on two isolated N2‐fixing species that are well represented in the river: Calothrix elenkinii (Kosinskaja) UAM 225 and Nostoc punctiforme (Kützing) UAM 220. We examined differences in phosphorus‐storage capacity, phosphate uptake, and phosphatase activity between the two isolates grown under N2‐fixing conditions. Although they shared a similar pattern of phosphate uptake, C. elenkinii cultures had a greater phosphorus storage capacity and greater phosphatase activity than those of N. punctiforme. The former showed a stronger response when cultured under low P concentrations. The two species showed specific differences in the rates of intracellular polyphosphate granule utilization and phosphatase activity. Our results suggest that C. elenkinii might be particularly well suited to river environments in which nutrient concentrations are generally low, but which experience episodic pulses of high P supply (inorganic and/or organic), favoring “luxury uptake” and storage strategies. |
