Abstract
BackgroundThe primary sources of nitrogen for plants have been suggested to be nitrate (NO3−) and ammonium (NH4+). However, when both nitrate and ammonium are simultaneously available to plants, it is very difficult to differentially quantify NO3−/NH4+ utilization in culture media or soil. Consequently, the contribution of NO3−/NH4+ to total inorganic nitrogen assimilation cannot be determined.ResultsWe developed a method called the bidirectional stable nitrogen isotope tracer to differentially quantify the nitrate and ammonium utilization by Orychophragmus violaceus (Ov) and Brassica napus (Bn) plantlets in vitro. The utilization efficiency of nitrate was markedly lower than the utilization efficiency of ammonium for plantlets of both Ov and Bn. In both Ov and Bn, the proportion of NO3−/NH4+ utilization did not show a linear relationship with inorganic nitrogen supply. The Ov plantlets assimilated more nitrate than the Bn plantlets at the lowest inorganic nitrogen concentration.ConclusionsQuantifying the utilization of nitrate and ammonium can reveal the differences in nitrate and ammonium assimilation among plants at different inorganic nitrogen supply levels and provide an alternate way to conveniently optimize the supply of inorganic nitrogen in culture media.
Highlights
The primary sources of nitrogen for plants have been suggested to be nitrate (NO3−) and ammonium (NH4+)
The Orychophragmus violaceus (Ov) plantlets had a greater biomass than the Brassica napus (Bn) plantlets at the lowest total nitrogen supply
Considering the low inorganic nitrogen concentration in karst regions, where nitrate is more abundant than ammonium [54], the Ov plantlets, with their strong ability to assimilate nitrate at low nitrate concentrations, would have an advantage in acquiring available nitrogen to survive in karst regions
Summary
The primary sources of nitrogen for plants have been suggested to be nitrate (NO3−) and ammonium (NH4+). When both nitrate and ammonium are simultaneously available to plants, it is very difficult to differentially quantify N O3−/NH4+ utilization in culture media or soil. The primary sources of nitrogen for plants generally have been suggested to be nitrate (NO3−) and ammonium (NH4+) [1,2,3]. Compared with the assimilation of ammonium, the assimilation of nitrate requires more energy [7, 8]. Ammonium assimilation leads to acidification [9], and an excess supply of ammonium causes ion disorder in plants, which is harmful to plant growth [11, 12]. Most plants grow well if both nitrate and ammonium are available [13]
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