Response of yield and quality of wheat with different gluten content to altitude above sea level and nitrogen treatment.

Wheat (Triticum aestivum L.) yield and processing quality varied across environments, especially along altitudinal gradients. This study evaluated the combined effects of altitude above sea level and nitrogen (N) topdressing on yield and quality traits of winter wheat with strong, medium and weak gluten content. Six cultivars were tested for two growing seasons at Renqiu (4 m), Beijing (40 m) and Lhasa (3688 m). Raw-data verification showed that Lhasa reduced mean grain yield by 44.1% compared with Beijing, mainly through reductions in spike number, grains per spike and thousand-grain weight. High altitude increased total grain protein by 17.5% compared with Beijing, especially through increases in albumin and globulin fractions, but this increase did not translate into better processing quality. Strong and medium gluten wheat showed reduced gluten index, shorter dough stability time and higher weakening degree at Lhasa, whereas weak gluten wheat maintained relatively better stability under high-altitude stress. Nitrogen responses differed among gluten types: strong gluten wheat benefited more from 240 kg/ha N, medium gluten wheat performed similarly under 180-240 kg/ha N, and weak gluten wheat showed a more stable response under high-altitude conditions. Multivariate analyses separated the Lhasa environment from Renqiu and Beijing and indicated a clear yield-quality trade-off. These results suggested that cultivar selection and N management should be adjusted jointly according to altitude above sea level and gluten type.