Heterocystous Cyanobacteria of the genus Nodularia form major blooms in brackish waters, while terrestrial Nostoc species occur worldwide, often associated in biological soil crusts. Both genera, by virtue of their ability to fix N₂ and conduct oxygenic photosynthesis, contribute significantly to global primary productivity. Select Nostoc and Nodularia species produce the hepatotoxin nodularin and whether its production will change under climate change conditions needs to be assessed. In light of this, the effects of elevated atmospheric CO₂ availability on growth, carbon and N₂ fixation as well as nodularin production were investigated in toxin and non-toxin producing species of both genera. Results highlighted the following:

• Biomass and volume specific biological nitrogen fixation (BNF) rates were respectively almost six and 17 fold higher in the aquatic Nodularia species compared to the terrestrial Nostoc species tested, under elevated CO₂ conditions.

• There was a direct correlation between elevated CO₂ and decreased dry weight specific cellular nodularin content in a diazotrophically grown terrestrial Nostoc species, and the aquatic Nodularia species, regardless of nitrogen availability.

• Elevated atmospheric CO₂ levels were correlated to a reduction in biomass specific BNF rates in non-toxic Nodularia species.

• Nodularin producers exhibited stronger stimulation of net photosynthesis rates (NP) and growth (more positive Cohen’s d) and less stimulation of dark respiration and BNF per volume compared to non-nodularin producers under elevated CO₂ levels.

This study is the first to provide information on NP and nodularin production under elevated atmospheric CO₂ levels for Nodularia and Nostoc species under nitrogen replete and diazotrophic conditions.

结节菌属的异型蓝藻在微咸水域中形成大量的花，而陆生的念珠菌种类遍布世界各地，通常与生物土壤结壳有关。这两个属都凭借其固定N ₂和进行含氧光合作用的能力，对全球初级生产力做出了重要贡献。某些Nostoc和Nodularia物种会产生肝毒素结核菌素，需要评估其产量在气候变化条件下是否会发生变化。鉴于此，大气中CO ₂利用率提高对生长，碳和N _2的影响研究了两个属的毒素和非毒素产生菌种的固定和结节菌素的产生。结果突出显示以下内容：

• 生物量和体积固有生物固氮（BNF）率分别为几乎6和17在水生倍的节球物种相比于地面发菜测试物种，升高的CO下₂的条件。

• 之间存在着直接相关性升高CO ₂，并在生长diazotrophically地面下降干重特异性细胞节球含量发菜物种，和水生节球种，不论氮可用性。

• 在无毒根瘤菌物种中，大气中CO ₂含量升高与生物量比BNF降低有关。

• 在升高的CO ₂水平下，与非结核菌素生产者相比，结核菌素生产者表现出更强的净光合速率（NP）和生长刺激（Cohen's阳性），对暗呼吸和每单位体积BNF的刺激更少。

本研究首次提供关于NP和节球下升高大气CO生产信息₂水平节球和发菜在氮气充满和固氮条件物种。