Monitoring Nitrogen Leaf Resorption Kinetics by Near-Infrared Spectroscopy during Grain Filling in Durum Wheat in Different Nitrogen Availability Conditions

In wheat (Triticum spp.), the N content of leaves during the grain filling period (GFP) plays a key role in maintaining photosynthetic activity and determining the amount of N available for grain protein content (GPC). We documented flag N leaf resorption in durum wheat (Triticum turgidum L.) plants under a nonlimiting level of N in 2010 and under two different levels of N fertilization in 2011. During the GFP, we monitored changes in flag leaf N content by a nondestructive method based on near-infrared spectroscopy. The data-sets were modeled for each plant; parameters were extracted and analyzed to determine which source of variation (genotype and/or N availability) predominated. Different genotypic profiles were highlighted opposing Ixos versus Primadur when comparing two different levels of N availability, with Ixos flag leaves being the most affected by a low level of N preanthesis. High postanthesis N availability delayed the beginning of N resorption (t0) and there was a strong negative correlation between t0 and the resorption duration. Delayed N resorption was associated with better grain yield components. A high proportion of the variation of grain yield per spike and GPC was explained by multiple linear regressions combining the width of the flag leaf and N dynamic parameters under the nonlimiting N availability. The negative correlation between yield and GPC may result from the initiation of N resorption during grain filling, potentially increasing yield if delayed or increasing GPC if occurring early.