Effect of intermittent shade on nitrogen dynamics assessed by 15N trace isotopes, enzymatic activity and yield of Brassica napus L.

Abstract

Modern era of agriculture is concerned with the environmental influence on crop growth and development. Shading is one of the crucial factors affecting crop growth considerably, which has been neglected over the years. Therefore, a two-year field experiment was aimed to investigate the effects of shading at flowering (S1) and pod development (S2) stages on nitrogen (N) dynamics, carbohydrates and yield of rapeseed. Two rapeseed genotypes (Chuannong and Zhongyouza) were selected to evaluate the effects of shading on 15N trace isotopes, enzymatic activities, dry matter, nitrogen and carbohydrate distribution and their relationship with yield. The results demonstrated that both shading treatments disturbed the nitrogen accumulation and transportation at the maturity stage. It was found that shading induced the downregulation of the N mobilizing enzymes (NR, NiR, GS, and GOGAT) in leaves and pods at both developmental stages. Shading at both growth stages resulted in reduced dry matter of both varieties but only S2 exhibited the decline in pod shell and seeds dry weight in both years. Besides this, carbohydrates distribution toward economic organs was declined by S2 treatment and its substantial impact was also experienced in seed weight and seeds number per pod which ultimately decreased the yield in both genotypes. We also revealed that yield is positively correlated with dry matter, nitrogen content and carbohydrates transportation. In contrast to Chuannong, the Zhongyouza genotype performed relatively better under shade stress. Overall, it was noticed that shading at pod developmental stage considerable affected the transportation of N and carbohydrates which led to reduced rapeseed yield as compared to shading at flowering stage. Our study provides basic theoretical support for the management techniques of rapeseed grown under low light regions and revealed the critical growth stage which can be negatively impacted by low light.

Low Light at Specific Growth Stage Affects Photoassimilates Transportation, Seed Quality and Yield in Brassica napus L.

“…Hence, we may propose that the employment of low light at pod stage considerably inhibited the translocation of carbohydrates to the economic organ, which ultimately resulted in a drop in both genotypes' yield. Previous research revealed that shade during grain filling reduces the grain's volume and weight, as well as the starch deposition (Javed et al 2022;Lu et al 2013;Shi et al 2018;Yang et al 2016). Seed starch deposition was similarly diminished as a result of ear shading (Cui et al 2012).…”

“…Previous research revealed that shade during grain filling reduces the grain's volume and weight, as well as the starch deposition (Javed et al. 2022; Lu et al. 2013; Shi et al.…”

“…After the maturity stage, pods and seed samples were collected from main stem of both genotypes and carbohydrates were measured by a previously published method (Javed et al. 2022).…”