Effects of water deficit and nitrogen application on leaf gas exchange, phytohormone signaling, biomass and water use efficiency of oat plants

Abstract

AbstractBackground: Water and nitrogen (N) are essential resources influencing plant growth and yield. To improve their efficiencies in crop production is challenging because the physiological mechanisms of water and N coupling and their interactive effect on crop water use efficiency (WUE) are not well understood yet.Aim: The aim of this study was to investigate the physiological responses and phytohormones signaling in oats in response to soil water status and N supply under fertigation, to explore the mechanisms regulating plant growth and WUE.Methods: Oat plants were subjected to the factorial combination of three soil moisture regimes (50, 70, and 90% of soil water holding capacity, SWHC) and three N levels (fertilized with 74, 149, and 298 mg kg−1).Results: The stomatal conductance (gs) was significantly decreased by soil water deficit, and also by the highest N level, whereas photosynthesis rate (An) was unaffected by neither water nor N. Consequently, intrinsic WUE (WUEint, An/gs) was highest under reduced irrigation and high N fertilization. This effect at stomatal level was affirmed by responses in whole plant WUE (WUEb), which was positively correlated with shoot δ13C. A positive correlation between δ18O and δ13C in shoots further indicated that decreases of gs rather than changes in An contributed to the enhanced WUE.Conclusion: Moderate soil water deficit and sufficient N supply is recommended for saving irrigation water and improving WUE on fertigated oat plants without compromising biomass accumulation to any large extent.