Effects of post-flowering drought on nitrogen mobilization and growth of bread wheat (Triticum aestivum L.) using stable 15N isotope

Abstract

Water and nitrogen shortage are one of the main limiting factors of crop productivity such as wheat and cereals. Increased variation and changes in climate conditions are expected to dominate yield potential of wheat. Nitrogen isotope technique widely used in recent years provides useful information about mobilization and nitrogen use efficiency under environmental constraints. This study aimed to determine the effects of drought conditions applied during different growing periods on nitrogen uptake by using stable 15N isotope, yield and quality properties and stomatal conductivity of bread wheat. Environmental variation was obtained by designing 4 artificial practices (irrigated condition, rainfed condition, early drought (flowering-harvest) and late drought (grain filling-harvest) by rainout shelter with covering progress about drought in different growing periods. Number of grains per spike, 1000 grain weight, single spike yield, spike numbers per square meter, plant height, grain yield, biomass yield, stomatal conductance, protein, ash content and stem δ15N (‰), flag leaf δ15N (‰), grain δ15N (‰) values were determined. The drought period from the beginning of flowering till harvest of plants had adverse impact on grain yield and yield components. The results clearly indicated the practices that may cause drought stress in the generative period should be avoided. In addition, nitrogen use efficiency of bread wheat was disrupted with the decrease in the amount and efficiency of plant water use during drought periods. The results also revealed that contribution of nitrogen to crop yield decreased due to less consumption of nitrogen in plant metabolic activities during drought periods. Based on the results additional water supply decreased δ15N content in mature grains from 13420 ‰ to 9278 ‰. Nitrogen applied in stem elongation period had greater contribution to grain δ15N content (15269 ‰) compared to tillering growth stage (8975 ‰). Nitrogenous fertilizer application time suggested not to be delayed to improve nitrogen contribution in metabolic activities and to prevent postponing the tillering and stem elongation periods. The application of nitrogen improved mobilization and efficiency of nitrogen contribution to different plant parts during generative development stages of bread wheat.