Qingke (Hordeum vulgare L. var. nudum Hook. f.), a staple crop in the Tibetan Plateau, suffers from severe yield reduction under continuous cropping (by 38.67%), yet the underlying mechanisms remain unclear. This study systematically investigated the effects of 23-year continuous cropping (23y-CC) on the nutrient dynamics, carbohydrate metabolism, and enzymatic activities in Qingke leaves across five developmental stages (T1: seedling; T2: tillering; T3: jointing; T4: flowering; T5: filling). Compared to the control (first-year planting), 23y-CC significantly reduced leaf nitrogen (N), phosphorus (P), and potassium (K) contents by 60.94%, 47.96%, and 60.82%, respectively, at early growth stages. Key nitrogen-metabolizing enzymes, including glutamate synthase (GOGAT), glutamine synthase (GS), and nitrate reductase (NR), exhibited reduced activities under 23y-CC, indicating impaired nitrogen assimilation. Carbohydrate profiling revealed lower starch and glucose contents but higher sucrose accumulation in later stages (T4–T5) under 23y-CC, accompanied by the dysregulation of sucrose synthase (SS) and invertase activities. These findings elucidate how continuous cropping disrupts nutrient homeostasis and carbon allocation, ultimately compromising Qingke productivity. This study provides novel insights into agronomic strategies for mitigating continuous cropping obstacles in Qingke.

The young stem of rapeseed is a highly nutritional vegetable, but there is a lack of information on quality regulation by slow-release fertilizers (SRFs). This study aims to evaluate the effects of SRFs on nutritional contents, including vitamin and sugar profiles and regulatory mechanisms, using enzymatic activity and gene expression analysis. A field experiment was conducted with a split-plot design, in which treatments with two fertilizers (traditional compound fertilizer (TF) and SRF) served as the main plot and two harvesting stages (main stem harvesting (S1) and the first branch harvesting (S2)) served as the sub-plot. The results showed that vitamin E (VE) content under the SRF treatment was 48.31% and 18.44% higher than that under the TF treatment at both stages. The contents of vitamin C (Vc) at the S2 stage and vitamin B6 (VB6) at the S1 stage under the TF treatment were 7.56% and 2.95% higher than under SRF treatments. Water-soluble sugar (WSS) and glucose contents under the SRF treatment were significantly higher than under the TF treatment at both stages, while fructose, trehalose, and sorbitol contents exhibited the opposite trend. The offset effect of the activity of ascorbate oxidase (AAO) and dehydroascorbate reductase (DHAR) between the two fertilizers resulted in a non-significant difference in Vc content at the S1 stage. Under the TF treatment, sucrose phosphate synthase had greater activity as compared to the SRF treatment. The selected key genes involved in vitamin and carbohydrate metabolism were generally in agreement with the changes in enzymatic activity. This study highlights the importance of SRF for the quality formation of young stems of rapeseed as a vegetable.

Early-stage, accurate and high-throughput phenotyping‌ through leaf area estimation is ‌critical‌ for future rapeseed breeding, but faces