The influence of ammonium to nitrate ratio on the thermal responses of early life stages of the giant kelp Macrocystis pyrifera

Abstract

<p>The distribution and productivity of <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/kelp" title="Learn more about seaweeds from ScienceDirect's AI-generated Topic Pages">seaweeds</a>, including kelps, are strongly influenced by changes in temperature and inorganic nitrogen (Ni) availability. However, their tolerances, sensitivities, and capacity to adjust to these changes can vary across their complex life cycle (microscopic and macroscopic stages). For the early life stages of <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/macrocyst" title="Learn more about Macrocystis from ScienceDirect's AI-generated Topic Pages">Macrocystis</a>, this study investigated the effect of the nitrate: ammonium ratio on <a href="https://www.sciencedirect.com/topics/engineering/physiological-trait" title="Learn more about physiological traits from ScienceDirect's AI-generated Topic Pages">physiological traits</a> and gametophyte development at a range of temperatures (6.5 to 26.5 °C). Thermal performance curves (TPCs) were utilized to determine and predict the effect of temperature on meiospore germination success (%), gametophyte size (μm2), sex ratio and <a href="https://www.sciencedirect.com/topics/engineering/physiological-trait" title="Learn more about physiological traits from ScienceDirect's AI-generated Topic Pages">physiological traits</a> (photosynthetic efficiency and nitrate and ammonium uptake rates). We found that the presence of NH4+ led to negative NO3− uptake rates in <em>Macrocystis pyrifera</em> gametophytes and reduced growth rates, and results suggest that <a href="https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/critical-thermal-maximum" title="Learn more about thermal tolerance from ScienceDirect's AI-generated Topic Pages">thermal tolerance</a> windows might vary between developmental stages and physiological traits. Our findings indicate that reduced meiospore germination and gametophyte size induced by suboptimal temperatures and increased NH4+concentrations can lead to lower physiological performance that might subsequently affect adult individuals and populations. Knowledge of the <a href="https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/nitrogen-uptake" title="Learn more about Ni uptake from ScienceDirect's AI-generated Topic Pages">Ni uptake</a> kinetics and source preferences across different life cycle phases can be crucial for conservation and aquaculture purposes as it might increase species productivity and persistence in a changing ocean.<br></p>