Global warming, as well as europhication are predicted to promote cyanobacterial blooms, but how tropical phytoplankton communities from different trophic state systems respond to temperature variation is less known. To further explore the effect of temperature changes and nutrient addition on phytoplankton communities and to get insight in possible resistance to these effects, we tested the hypothesis that temperature variation will have a stronger effect on cyanobacteria dominance in eutrophic water than in oligo-mesotrophic. Hereto, we conducted an experiment with phytoplankton communities from two aquatic ecosystems differing in trophic state. Water samples from a eutrophic and an oligo-mesotrophic system were collected and incubated in 25 and 30ºC. Also, treatments that received additional surplus N and P were included that served as eutrophication treatments. Temperature variation itself did not promote cyanobacteria in either water from the oligo-mesotrophic or the eutrophic system. However, nutrient enrichment of water from the eutrophic system significantly boosted cyanobacteria, and biomass increased 10 times in both 25ºC and 30ºC treatments. In contrast, eutrophication of water from the oligo-mesotrophic system did not change the relative contribution of phytoplankton groups and response ratios were much lower than those for water from the eutrophic system. Although using a very simple experimental design, the results suggest that in eutrophic systems cyanobacteria dominance can be favoured by further addition of nutrients, independently of a direct temperature effect and that more pristine environments possess some resistance against eutrophication. Since global warming is assumed to intensify eutrophication symptoms indirectly, our study underscores the importance of nutrient control.
Both global warming and eutrophication are predicted to promote cyanobacterial blooms. At the same time, how tropical phytoplankton communities exhibiting different trophic state systems will respond to temperature variations is less clear. To investigate the effects of temperature changes and nutrient additions on phytoplankton communities, and gain insights regarding possible resistance to these effects, the present study focused on testing the hypothesis that temperature variations and nutrient additions will have a stronger effect on cyanobacteria dominance in eutrophic water system than in oligo‐mesotrophic water systems. Experiments were conducted with phytoplankton communities from two aquatic ecosystems exhibiting different trophic states. To this end, water samples from a eutrophic and oligo‐mesotrophic system were collected and incubated at 25 and 30ºC. Samples receiving additional surplus nitrogen (N) and phosphorus (P) inputs were included to serve as eutrophication treatments. The study results indicated that temperature variations alone did not promote cyanobacteria in water from either the oligo‐mesotrophic or eutrophic water system. However, nutrient enrichment of the water from the eutrophic system significantly boosted the cyanobacteria, with the biomass increasing by factor of 10 for both the 25°C and 30°C treatments. In contrast, eutrophication of the water from the oligo‐mesotrophic system did not change the relative contribution of phytoplankton groups, with the response ratios being much lower than those for the water from the eutrophic system. Although based on a simple experimental design, the results of the present study suggest that cyanobacteria dominance is favoured by further nutrient additions for eutrophic water systems, independently of any direct temperature effects, and that more pristine environments possess some resistance against eutrophication effects. Since global warming is assumed to indirectly intensify eutrophication symptoms, the results of the present study underscore the importance of nutrient control.
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