The toxin-producing, bloom-forming cyanobacterial genera Microcystis and Planktothrix require fixed nitrogen (N), such as nitrate, ammonium, or organic N (e.g., urea) for growth and production of microcystins (MC). Bioavailable N can enter lakes in pulses via tributary discharge and through in-lake recycling, which can maintain low N concentrations. Additionally, light intensity has been suggested to play a role in MC production. This study examined how three forms of N (nitrate, ammonium, and urea) interacted with N loading rate (one large pulse vs. many small pulses) and light intensity to stimulate Microcystis and Planktothrix growth and MC production using nutrient enrichment experiments. Enrichments of nitrate, ammonium, and urea resulted in greater cyanobacterial biovolumes and MC concentrations than phosphorus-only enrichments, and there was no difference between pulse (100 μmol/L) and press treatments (8.3 μmol/L every 4 h). Analysis of mcyD transcripts showed significant up-regulation within 4 h of ammonium and urea enrichment. High light intensities (300 μmol photons/m²/s) with N enrichment resulted in greater cyanobacterial biovolumes and MC concentrations than lower light intensities (30 and 3 μmol photons/m²/s). Overall, the results suggest Microcystis and Planktothrix can use many forms of N and that high light intensities enhance MC production during elevated N concentrations. Moreover, the results here further demonstrate the importance of considering N, as well as P, in management strategies aimed at mitigating cyanobacterial blooms.

产生毒素，形成水华的蓝藻属微囊藻和浮游藻类需要固定的氮（N），例如硝酸盐，铵或有机氮（例如尿素）才能生长和生产微囊藻毒素（MC）。可生物利用的氮可以通过支流排放和湖内循环利用而以脉冲形式进入湖泊，这可以保持低氮浓度。另外，已经提出光强度在MC产生中起作用。这项研究检查了三种形式的氮（硝酸盐，铵和尿素）如何与氮的加载速率（一个大脉冲对许多小脉冲）和光强度相互作用，以刺激微囊藻和浮游藻类使用营养富集实验进行生长和MC生产。硝酸盐，铵和尿素的富集比仅磷的富集产生更大的蓝细菌生物量和MC浓度，脉冲处理（100μmol/ L）和压榨处理（每4小时8.3μmol/ L）之间没有差异。对mcyD转录本的分析显示，在铵和尿素富集的4 h内显着上调。与较低的光强度（30和3μmol光子/ m ² / s）相比，具有N富集的高光强度（300μmol光子/ m ² / s）导致更大的蓝细菌生物量和MC浓度。总体而言，结果表明微囊藻和浮游藻可以使用多种形式的氮，并且高的光强度会在氮浓度升高的情况下增强MC的产生。而且，这里的结果进一步证明了在旨在减轻蓝藻水华的管理策略中考虑N和P的重要性。