Effects of N-application on utilization of 15N and 13C and quality in two wheat cultivars

Influence of Sink Size on 15N and 13C Allocation during Different Phenological Phases of Spring Wheat Cultivars

The scientific objective of this study was to answer the question of whether sink limitation is also true for high quality wheat varieties. We examined the incorporation of 15N and 13C during phenological phases into vegetative parts and grains of Elite wheat Triso (E) and Quality wheat Naxos (A) when the spike is halved. Three splits of fertilizer were applied at EC 11, EC 30, EC 59, whereby 10% at EC 30 and EC 59 was 15N, and plants were also labelled with 13CO2. The application of only the third split as 15N, combined with spike-halving, resulted in a significantly higher 15N-content (+11%) of 0.486 mg 15N/g DM, compared to the control (0.437 mg15N/g DM). Labelling whole plants with 13CO2 at EC 59 resulted in a significantly higher 13C-content—40%—(0.223 mg 13C/g DM) of the grains of the control for Triso at the fully-ripe stage (EC 89), compared to Naxos (0.160 mg 13C/g DM). This superiority was reduced to 34%, and was also demonstrated by spike-halving (0.226 mg 13C/g DM, 0.169 mg 13C/g DM). Remobilization of 15N for control and spike-halving treatments were 68.2% and 61.1%, respectively. This clearly demonstrates that the reduction of the sink size by spike-halving leads to a 7% reduction in the remobilization of 15N from vegetative to reproductive tissues.

Effect of Late 15N-Fertilization and Water Deficit on Allocation into the Gluten of German and Mediterranean Spring Wheat Cultivars

In a split N-application system, the objective was to quantify N/15N in gluten and non-gluten proteins after the late application of 30 or 60 kg N, whereby 10% of the third split was applied as 15N. This fertilization was combined with a reduced water supply for 21 days (well-watered (ww); water deficit (wd)). German spring wheat cultivars, Elite wheat Taifun, Quality wheat Monsun and cultivars from the Mediterranean territory, Golia, Gönen, were examined. The protein content in gluten was for 30 kg N, ww, similar for Taifun, Golia, and Gönen, but markedly lower in Monsun (231, 245, 247, 194 mg protein/g DM). The water deficit increased the protein content in the gluten of Golia and Gönen and was higher than that of Taifun and Monsun (297, 257, 249, 202 mg protein/g DM). Fertilization of 60 kg N, ww, did not result in any change in the protein content in gluten and differences between the cultivars were not detectable. The 15N protein in gluten was for 30 kg N, ww, markedly higher in Gönen (2.32 mg 15N protein/g DM), compared to Golia and Monsun (1.93, 1.50 mg 15N protein/g DM), and similar in Taifun (1.64 mg 15N protein/g DM). 15N fertilizer uptake into gluten was stimulated by water deficit for 30 and 60 kg N, leading to significantly increased 15N protein in Golia and Gönen, (2.38, 2.99, 4.34, 5.87 mg 15N protein/g DM). Fertilization of 60 kg N led to a proportional two-time increase in the 15N gluten protein of the four cultivars, in ww and wd plants. Assessed on the basis of 15N fertilizer allocation under wd conditions into gluten proteins, Golia and Gönen have a stronger sink activity, compared to Taifun and Monsun.

15N allocation into wheat grains (Triticum aestivum L.) influenced by sowing rate and water supply at flowering under a Mediterranean climate

This study examined the effects of a reduced wheat sowing rate (250 vs. 500 grains m^-2) on grain yield, uptake of ¹⁵N into grains, and the incorporation into gluten and non-gluten proteins of wheat under field conditions in the Aegean region. A single ¹⁵N application was applied at stem elongation, at flowering, or at both developmental stages. Each ¹⁵N treatment included either additional water supply, or no additional water supply at flowering. Sowing rate (either 250 or 500 grains m^-2) had no impact on grain yield. Grain yield increased with additional water supply, but at the expense of protein quality, because of a decrease in the protein content of gluten. The ¹⁵N content of the gluten and non-gluten proteins at grain maturity was not different among cultivars. ¹⁵N applied at both stem elongation and flowering was found in comparable amounts in grains and protein fractions, irrespective of sowing rate.