The   highly toxic effects of ammonium on Arthrospira hinder its utilization as a   nitrogen source in Arthrospira cultivation and severely limit its application   in treating high-ammonium wastewater. This study revealed that both   short-term (12 d) and long-term (270 d) ammonium acclimation significantly   improved the ammonium tolerance of Arthrospira platensis HN5, with biomass   productivities of 0.14 and 0.11 g L-1 d-1, respectively, and net   photosynthetic oxygen evolution rates exceeding 60 and 50 mu mol O2 center   dot mg-1 center dot Chla center dot h-1 under a lethal ammonium concentration   of 15 mM. Furthermore, the ammonium tolerance of the long-term acclimated   strain exhibited heritable characteristics. Additionally, nitrate (NaNO3)   concentrations of >= 0.1 mM were demonstrated to effectively enhance the   ammonium tolerance of A. platensis HN5 in a concentration-independent manner.   This study highlighted the role of acclimation and nitrate supplementation in   improving the ammonium tolerance of A. platensis HN5, offering efficient and   reliable strategies for ammonium utilization in the Arthrospira industry and   for treating high-ammonium wastewater using Arthrospira.