Wheat Development, Productivity, and Nitrogen Use Are Unaffected by Stable Isotope Form of the Nitrogen Source

Under conditions where an adequate amount of isotopic (15)N is supplied, it is not known whether wheat (Triticum aestivum) plants have a preference for (14)N against the heavy isotope. A pot experiment was conducted for 2 yr with manually controlled nitrogen (N) supply to assess crop development, dry matter production, and N acquisition and partitioning in spring wheat plants grown in plastic pots filled with Ottawa sand. A set of plants were supplied with N from an (14)N source (0.37 atom % (15)N) throughout the growing period, while another set of plants received the same amounts of N from an (15)N-enriched fertilizer source (91.2 atom % (15)N). At crop maturity, about 60% of the applied (15)N was recovered in different plant parts, and 65% of the total N content in the plant was enriched with (15)N compared with <0.5% in the control treatment. There were not any visual differences between the two sets of plants, neither was there a difference in quantitative traits such as plant height, leaf greenness, dry matter production, N acquisition and partitioning. This study demonstrated that given similar concentrations of the two N treatments that differed markedly in their (15)N enrichment, there was no differentiation in N uptake and partitioning resulting from isotopic enrichment of the two N sources. This indicated that there is no preference against (15)N by the wheat plants, and the greater natural abundance of the (14)N is the main reason why plant tissues are dominated with (14)N isotope.