Nitrate boosts arsenic accumulation in hyperaccumulator Pteris vittata by coupling nitrogen assimilation with arsenic detoxification

Nitrogen is a critical macronutrient for plant growth including As-hyperaccumulator Pteris vittata . Being common N fertilizers, both NO 3 ⁻ and NH 4 + enhance As accumulation in P. vittata , but the underlying mechanisms remain unclear. Based on 0.2-strength Hoagland nutrient solution (0.2X HNS, NO 3 ⁻ /NH 4 + = 2.8 mM/0.2 mM), we investigated the impacts of 3.0 mM NO 3 ⁻ or NH 4 + by growing P. vittata in sand-vermiculite culture for 7 weeks under 50 µM As exposure. Besides plant growth and nutrient uptake, we determined As speciation (arsenate-AsV and arsenite-AsIII), N assimilation and As-metabolism gene expression in P. vittata . Though 0.2X HNS control produced greater plant biomass, NO 3 ⁻ and NH 4 + treatments increased frond As and P contents by 89–113 and 39–76%. While NO 3 ⁻ enhanced N assimilation via nitrate reductase, glutamine synthetase, and free amino acids by 61–157%, 24–65%, and 1.6–5.7 fold, the corresponding increases for NH 4 + treatment were 28–125%, 23%, and 2.8-fold. Although both NH 4 + and NO 3 ⁻ promoted greater As/P uptake and translocation associated with 1.3–2.4 fold upregulation of P-transporters PvPht1;2/1;4 and AsIII-antiporter PvACR3;1 , NO 3 ⁻ showed greater arsenate reduction and detoxification via 1.4–2.1 fold upregulation of AsV-reductase PvHAC1 and AsIII-antiporters PvACR3/3;2 . Overall, NO 3 ⁻ is more effective than NH 4 + in enhancing As accumulation in P. vittata , which is related to improved N assimilation and As metabolism. This study suggests potential application of NO 3 ⁻ to improve phytoremediation of As-contaminated sites based on P. vittata .