Physiological evaluation of nitrogen use efficiency of different apple cultivars under various nitrogen and water supply conditions

Nitrogen (N) deficiency is a common problem for apple (Malusxdomestica) production in arid regions of China. However, N utilization efficiency (NUE) of different apple cultivars grown under low N conditions in arid regions has not been evaluated. In this study, NUE was assessed for one-year-old seedlings of six apple cultivars, Golden Delicious, Qinguan, Jonagold, Honeycrisp, Fuji and Pink Lady, grafted onto Malus hupehensis Rehd. rootstocks. Four treatments were used, including control water with control N (CWCN), limited water with control N (LWCN), control water with low N (CWLN) and limited water with low N (LWLN). Our results showed that growth indices such as biomass, plant height and stem diameter, and photosynthetic rate of all cultivars decreased in the order CWCN>CWLN>LWCN>LWLN. When subjected to LWLN treatment, Qinguan showed better growth and photosynthetic characters than other tested cultivars. Additionally, Qinguan and Pink Lady had higher NUE, while Honeycrisp and Jonagold had lower NUE, based on the determination of biomass, photosynthetic parameters, chlorophyll content, the maximal photochemical efficiency of PSII (F-v/F-m), N-15 and N contents.