Nitrogen and Carbon Isotope Composition of Wheat Grain: Alteration due to Sink-source Modifications at Flowering

Abstract

An experiment of sink-source modifications was performed in field-grown wheat at flowering on five varieties (four Triticum aestivum and one T. durum); among these, two varieties were non-awned. The sink-source modifications were blade removal (treatment B) and blade deletion and stalk and sheaths darkening (treatment C). Intact plants (treatment A) acted as a control. In the three awned varieties, the effect of awn removal was also analysed. Two lots of tests were initially performed, with awns (treatments A+, B+, C+) or with awns removed (treatments A−, B−, C−). Yields and carbon and nitrogen isotope compositions were then determined on seeds harvested at maturity. Blade deletion reduced the yield by one third whereas additional stalk and sheaths darkening led to a two thirds decrease. Nitrogen yield was similarly affected but the deprivation due to treatment C was less marked for nitrogen than for carbon. Thus, treatment C produced grains which were notably richer in nitrogen than plants which had received treatment A and B. For each of the five varieties, the decrease in yield was highly correlated with a 13C enrichment of grains (roughly from −28 to −25‰). In contrast with the 13C variations, there was no general trend for 15N evolution among treated plants. The final yield for treated T. durum plants was strongly modified when the awns were removed at flowering whereas no significant variations were noted in the other T. aestivum awned varieties. T. durum seeds obtained from plants deprived of awns were notably depleted in 13C and in 15N compared to control plants. Isotope compositions of C and N of the different pools supplying the grain filling were estimated and discussed in the context of the physiology of the mother plants between flowering and maturity.