Tolerance to Nitrogen ions enrichment in a Gulf of Mexico's freshwater submerged grass

Abstract

BackgroundTolerance to the enrichment of ionic nitrogen (N) with ammonium (NH 4 ) and nitrate (NO 3 ) needs to be distinguished in a submerged grass ecotype-species of freshwater wetlands. Concentrations of total Nitrogen (TN: 500 to 2000 µgL -1 ) and three N sources (NS: NH 4 , NO 3 , 1:1 NH 4 :NO 3 ratio) in an overlaying aqueous phase, using local tap water as control (174 µgL -1 TN), were evaluated in rooted autotrophic juvenile Vallisneria americana established in vitro in two-phase culture medium. The treatments ranged from 7 to 111 µM TN. Phenotypes changes, pH and ionic strength in the aqueous phase were registered at 15 days. In addition, biomass of lyophilized leaf and root as well as N contents (gas and high-performance liquid chromatography) were analysed to estimate accumulations of N-NH 4 , N-NO 3 and N-NO 2 .ResultsAll individuals showed phenotypic similarities. Accumulation of N-NH 4 was discarded, but the accumulations of N-NO 3 and N-NO 2 in both tissues were significantly different (p<0.001 and 0.0001), revealing so much that the maximum cumulative responses coincided with a deficit of N as both showed a linear decrease in their cumulative capacity linked to an increase in micromolar TN. ConclusionsThe results provide direct evidence of the tolerance to N enrichment with three different N sources in the focal ecotype at the seedling stage, based mainly on its cumulative capacity of N-NO 3 and N-NO 2 under eutrophic conditions. The findings imply that NO 2 is a relevant ion in the tolerance to N enrichment in overlaying water with NH 4 and NO 3 ions. Future studies of N cumulative effect with an in vitro approximation will be to support stress predictions by N enrichment. Keywords : Hydrocharitaceae. Eutrophization. Stress in vitro. Ammonium. Nitrate. Nitrogen endogenous