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

Abstract

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 Thalassiosira weissflogii, a coastal diatom, in response to different N sources (Nitrate, NO₃⁻; Ammonium, NH₄⁺; urea, CH₄N₂O) and availabilities (45 and 5 μM). Our findings demonstrate that T. weissflogii 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 (μ) is higher (1.18 ± 0.01) under NH₄⁺-high treatment compared to NO₃⁻-high (1.01 ± 0.01). The carrying capacity (K) 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 T. weissflogii to varying N conditions, shedding light on the ecological success and resilience of this species in highly variable coastal environments.