Nitrogen Allocation with Altered Sink Demand in Wheat

Abstract

Wheat (Triticum aestivum L.) grain N is derived concurrently from mobilization of vegetative N accumulated prior to anthesis and soil N absorbed after anthesis. The effect of main stem spike removal on N redistribution, total tiller grain yield, and total grain N yield was determined to assess the relationship between N utilization and reproductive sink demand. The soft red winter wheat cultivar ‘Hart’ was field grown on a Maury silt loam soil (fine, mixed, mesic, Typic Paleudalf). Net changes in tissue N contents and allocation of 50 μmol of 99 atom % 15N‐NH+4 injected into the main stem penultimate internode were determineduring grain fill. Senescence of main stem vegetative tissues, as indicated by net loss of vegetative N, was equivalent for plants with main stem spikes intact (control) and plants with only main stem spikes removed (‐spike). However, after anthesis negligible main stem injected 15N was allocated to control tillers, whereas the tillers of the ‐spike treatment contained 69% of the aboveground excess 15N at maturity. Even though the main stem vegetative N of the ‐spike treatment was allocated to the tillers, grain yield was not significantly increased compared to the control. There was a trend for increased tiller N yield such that total N yield of the ‐spike treatment was 12% less than the control, whereas plant total grain yield of the ‐spike treatment was 21% less than the control. These results indicate that senescence proceeds normally in stems lacking a reproductive sink, provided that alternate tiller sinks are present. Furthermore, effects of reduced sink demand appear to have a greater impact on plant grain yield than on plant N yield.