Effects of Drought on Partitioning of Nitrogen in Two Wheat Varieties Differing in Drought-tolerance

Abstract

A model was constructed to describe the translocation and partitioning of nitrogen on the seventh day after anthesis for well-watered and droughted plants of two wheat varieties (Triticum aestivum L. cv. Warigal and Condor). The glasshouse-grown plants were detillered so that a simplified model could be derived for the main stem. A 9-d drought treatment was imposed just after anthesis and this coincided with the period of endosperm cell division in the grains. Warigal, which had a higher grain yield than Condor under drought, absorbed up to 15-times more nitrogen and translocated 1.5-fold more nitrogen to the shoot via the xylem. In both varieties, nitrogen redistributed from vegetative organs accounted for more than 60 per cent in control and 70 per cent in droughted plants of the nitrogen needed for ear growth. The net loss of nitrogen increased by 4-3 per cent in the leaves, but decreased by 60 per cent in the stem under drought. Stem and roots appeared to play an important role in the nitrogen economy of droughted plants: less nitrogen was translocated directly to the grains from the senescing leaves and 40–60 per cent more nitrogen was translocated to the roots. Nearly all the nitrogen reaching the roots in the phloem was reloaded into the xylem stream and translocated back to the shoot. The transfer of nitrogen through the stem was reduced under drought and this resulted in a constant C:N ratio of the grains which may be important in the regulation of endosperm cell division.