Higher nitrogen application during rice growth increased yield and the biosynthesis of 2-acetyl-1-pyrroline under low light conditions

Some of the major challenges facing rice researchers are how to improve yield and also increase the aroma content of fragrant rice. It has been established that light and Nitrogen (N) management affect the accumulation of 2-acetyl-1-pyrroline (2AP) in fragrant rice. However, the ability of N to improve yield in fragrant rice and improve its 2AP content has not been established. Nevertheless, N promotes rice growth and improves rice yield, which has the ability to compensate for the negative impact of low light on fragrant rice yield. The aim of this study was to investigate the impact of N application rates on rice yield and 2AP accumulation under shading conditions. Field experiments were conducted between May and September from 2019 to 2021. The experiments were conducted in ambient light condition (AL) and low light condition (LL); using four different levels of N－0 kg N ha−1 (N0), 20 kg N ha−1 (N1), 40 kg N ha−1(N2),and 60 kg N ha−1 (N3)－which were applied during the booting stage. The grain yield, 2AP content, photosynthetic related indicators, N content in rice, Malondialdehyde (MDA) content, antioxidant enzyme activity and the biochemical parameters related to 2AP formation were all investigated. Our results showed that shading reduced yield by 5.00 % and increased 2AP content by 23.40 %. In addition, shading reduced net photosynthetic rate (Pn), leaf area index (LAI), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and N content in rice, and increased proline, γ-aminobutyric acid (GABA), and pyrroline-5-carboxylic acid (P5C), proline dehydrogenase (PDH), △1-pyrroline-5-carboxylic acid synthetase (P5CS), malondialdehyde (MDA). Although increased N application levels increased the yield, 2AP, Pn, LAI, proline, P5C, GABA, PDH, P5CS, SOD, CAT, POD and N content of rice, the ornithine aminotransferase (OAT), diamine oxidase (DAO) and MDA levels all decreased. The findings of this study showed that shading increased 2AP content of fragrant rice, but reduced its yield. However, increase in N application under shading conditions increased both the biosynthesis of 2AP and yield in rice. •Increasing N application under shading further promoted the biosynthesis of 2AP.•N application at booting stage somewhat compensated the effect of shading on yield.•Both shading and N application enhanced the pathway for 2AP synthesis from Glu and Pro.•Rising N application at booting stage restricted the pathway of Orn to synthesize 2AP.•Optimizing N applicatio