Responses of lake phytoplankton communities to changing inorganic nitrogen supply forms

Abstract

A shift has been predicted in future nitrogen emission scenarios from nitrous oxide to higher proportions of ammonium compounds. To investigate the interaction between increasing nitrogen load and varying nitrate:ammonium ratios (NO 3 − :NH 4 +), we performed a mesocosm experiment in an oligotrophic lake in southern Germany. We fertilized mesocosms with both roughly natural and four times the natural nitrogen wet deposition amounts in molar NO 3 − :NH 4 + ratios of 4:1 and 1:4. We observed greater phytoplankton biomass in treatments with a relatively higher ammonium supply, but not in those with nitrate and total nitrogen load. Ammonium significantly increased the total chlorophyll a concentrations, and especially the growth of small nanophytoplankton species. The effects observed indicate that NH 4 + was taken up preferentially and that spring phytoplankton in oligotrophic lakes appear to be able to respond to variations in nitrogen forms (available NO 3 − :NH 4 + ratios) by adjusting their community composition. Such communal changes at the base of the food web may affect higher trophic levels. Therefore, the effects of varying available forms of nitrogen should also be considered in primarily phosphoruslimited aquatic systems.

Succession of Microbial Community in a Small Water Body within the Alluvial Aquifer of a Large River

“…The most abundant chlorophyte was Scenedesmus quadricauda, a small coenobium-forming and ammonium-tolerant species [97][98][99] with higher uptake abilities for ammonium under nitrogen limitation than species of the genus Microcystis and with competitive superiority in the large-pulse, low-frequency nutrient recharging [100], as was present in our study area. With regard to size, small algae can be more competitive than larger species, because they have high surface area to volume ratios, resulting in greater specific uptake and growth under low nutrient concentrations, when even slight NH 4 + additions can be enough to promote the growth of small algae [101]. Secondly, the most dominant species during the summer period was Microcystis spp., with the culmination of dominance (surface bloom) in August, which was connected with the maximum of phytoplankton biomass and number of cells per liter.…”

Improvement of In Vivo Fluorescence Tools for Fast Monitoring of Freshwater Phytoplankton and Potentially Harmful Cyanobacteria

“…Due to these characteristics and based on the results obtained here (i.e., higher accuracy and lower variation), more accurate data with ALA than with the other probes could be expected, as after sampling, this tool can be run under controlled laboratory conditions. As for ALA, few data are reported in the literature, and most of them are related to its use in research experiments to determine Chl- a content and photosynthetic efficiency, rather than for a comparison among detection methodologies [ 48 , 49 , 50 , 51 , 52 ], whereas a strong correlation between cyanobacterial biomass and ALA Chl- a was found in a Swedish lake [ 53 ]. Nonetheless, a general inconsistency between Chl- a quantification methodologies has been previously discussed [ 54 ], and discrepancies among in vivo fluorescence and extraction procedures have been related to the calibration of the bbe Moldaenke probes that are based on HPLC pigment analysis, by which the separation onto chromatograms of distinct Chl- a allomers occurs, resulting in an apparent lower Chl- a content [ 5 ].…”

Macrosystem community change in lake phytoplankton and its implications for diversity and function

“…The relatively strong temporal signal, reflected here in the linear effect of year (fixed effect) also suggests that there may be a set of important unmeasured environmental parameters that have not been included in our study, such as more detailed inorganic nutrient fractions that have been shown to explain phytoplankton community properties partly better than only including total concentrations (Ptacnik et al . 2010; Trommer et al . 2020).…”