Carbon absorption capacity determines the response of algal competitiveness to elevated atmospheric CO2

<p><span>Although many studies have focused on </span><span>the effects of elevated </span><span>atmospheric</span> <span>CO₂</span><span> on algal growth</span><span>, few studies have demonstrated how </span><span>CO2</span><span> interacts with carbon absorption capacity to determine the algal competition at the population level</span><span>.</span><span> We conducted a pairwise competition experiment of <em>Phormidium</em></span><span><em> </em>sp., <em>Scenedesmus quadricauda</em>, <em>Chlorella vulgaris, </em>and <em>Synedra ulna</em>. The results showed that when the </span><span>CO₂</span><span> concentration increases from 400 to 760 ppm, the competitiveness of <em>S. quadricauda</em> increased, the competitiveness of <em>Phormidium </em>sp. and <em>C. vulgaris</em> decreased, and the competitiveness of <em>S. ulna</em> was always the lowest. we constructed a model</span><span> to explore whether interspecific differences in affinity and flux rate for CO₂ and HCO₃⁻ could explain changes of </span><span>competitiveness</span><span> between algae species along the gradient of atmospheric </span><span>CO₂</span><span> concentration.</span><span> Affinity and flux rate are the capture capacity and transport capacity of substrate, respectively, which are inversely proportional to each other. Low resource concentration is beneficial to the growth and reproduction of algae with high affinity. The simulation results showed that when the atmospheric </span><span>CO₂</span><span> concentration was low</span><span>, </span><span>species with high affinity for both </span><span>CO₂ and </span><span>HCO₃⁻ (HCHH) had the highest </span><span>competitiveness, followed by the species with high affinity for </span><span>CO₂ and low affinity for </span><span>HCO₃⁻ (HCLH), </span><span>the species with low affinity for </span><span>CO₂ and high affinity for </span><span>HCO₃⁻ (LCHH) and the species </span><span>with low affinity for both </span><span>CO₂ and </span><span>HCO₃⁻ (LCLH); when the CO2 concentration was high, the species were ranked according to the competitive ability: LCHH &gt; LCLH &gt; HCHH &gt; HCLH</span><span>. Thus, with the increase of atmospheric </span><span>CO₂ concentration, the competitive advantage changed from </span><span>HCHH</span> <span>species to </span><span>LCHH</span> <span>species.</span><span> These results indicate the important species types contributing to water bloom under the background of increasing global atmospheric </span><span>CO₂, highlighting the importance of carbon absorption characteristics in understanding, predicting and regulating population dynamics and community composition of algae.</span></p>