The nitrogen (N) management is crucial to stevia growth and steviol glycoside (SG) production. Although previous studies have concentrated on the impacts caused by N fertilization rates, very few studies are concerning N topdressing strategies. We hypothesized that stevia biomass and SG productivity can be effectively increased by altering the ratio of base fertilization:first topdressing at the seedling stage:second topdressing at the branching stage. The current plot experiment was undertaken to evaluate such effects. Compared with one-time basal fertilization, optimized N topdressing ratios (especially the 5:3:2 and 4:3:3 ratios) significantly enhanced the leaf biomass formation and aboveground N accumulation. Different results were observed for the leaf SG concentrations, and increasing the topdressing proportions critically reduced the total leaf SG concentrations (3.3–24.7%) at the harvest stage. The highest values for total SG accumulation were exhibited under the 6:4:0 and 5:3:2 topdressing strategies, which depend on the changes in biomass and SG concentration. Moreover, a significant negative correlation between leaf SGs and the N concentration was observed at all growth stages, but a positive correlation was observed with the leaf C/N ratio and soluble sugar concentrations. Our results suggest the potential for increasing SG productivity by optimizing N fertilization regimes, especially with an appropriate reduction in the topdressing ratio after the vegetative growth stage. Our findings further expanded the effect of topdressing strategies on SG production based on the N fertilization levels.

中文翻译：

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优化的氮肥追肥策略提高了甜菊 (Stevia rebaudiana Bertoni) 植物中甜菊糖苷的生产力

氮 (N) 管理对甜菊糖的生长和甜菊糖苷 (SG) 的生产至关重要。尽管以前的研究集中在施氮率造成的影响上，但很少有研究涉及施氮策略。我们假设通过改变基础施肥：幼苗期第一次追肥：分枝期第二次追肥的比例可以有效提高甜菊糖生物量和SG生产力。目前的小区实验是为了评估这种效果。与一次基施相比，优化的施氮比例（尤其是5:3:2和4:3:3的比例）显着提高了叶片生物量的形成和地上氮的积累。对于叶片 SG 浓度观察到不同的结果，在收获阶段增加追肥比例会显着降低总叶片 SG 浓度（3.3-24.7%）。总 SG 积累的最高值出现在 6:4:0 和 5:3:2 追肥策略下，这取决于生物量和 SG 浓度的变化。此外，在所有生长阶段都观察到叶片SGs与N浓度之间显着负相关，但观察到与叶片C/N比和可溶性糖浓度正相关。我们的结果表明，通过优化施氮方式，特别是在营养生长阶段后适当降低追肥率，可以提高 SG 生产力。我们的研究结果进一步扩大了追肥策略对基于施氮水平的 SG 生产的影响。