Nitrogen source and availability regulate plastic population dynamics in the marine diatom Thalassiosira weissflogii

Abstract

<p>Variation in nitrogen (N) availability significantly influences population dynamics and the productivity of marine phytoplankton. As N availability in the ocean is conditioned by the N source, it is important to understand the capacity of phytoplankton organisms to adjust their physiology and dynamics under different N conditions. We investigated the growth dynamics of <em>Thalassiosira weissflogii</em>, a coastal diatom, in response to different N sources (Nitrate, NO3-; Ammonium, NH4+; urea, CH4N2O) and availabilities (45 and 5 <em>μ</em>M). Our findings demonstrate that <em>T. weissflogii</em> can display plastic adjustments in population dynamics to different N sources. These responses evidenced a greater preference for NH4+ and urea than NO3-, particularly under high N availability. The relative growth rate (<em>μ</em>) is higher (1.18 ± 0.01) under NH4+-high treatment compared to NO3--high (1.01 ± 0.01). The carrying capacity (<em>K</em>) varied only among concentrations, indicating equal N utilization efficiency for biomass production. No effects of N source were detected under the low concentration, suggesting that the preference for NH₄⁺ and urea was diminished by limited nitrogen supply due to potential interactions. These results provide valuable insights into the physiological flexibility of <em>T. weissflogii</em> to varying N conditions, shedding light on the ecological success and resilience of this species in highly variable coastal environments.</p>