Nitrogen (N) is a primary factor limiting leaf photosynthesis. However, the mechanism of high-N-driven inhibition on photosynthetic efficiency and photoprotection is still unclear in the shade-tolerant and N-sensitive species such as Panax notoginseng. Leaf chlorophyll (Chl) content, Ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity and content, N allocation in the photosynthetic apparatus, photosynthetic performance and Chl fluorescence were comparatively analyzed in a shade-tolerant and N-sensitive species P. notoginseng grown under the levels of moderate nitrogen (MN) and high nitrogen (HN). The results showed that Rubisco content, Chl content and specific leaf nitrogen (SLN) were greater in the HN individuals. Rubisco activity, net photosynthetic rate (A_net), photosynthetic N use efficiency (PNUE), maximum carboxylation rate (V_cmax) and maximum electron transport rate (J_max) were lower when plants were exposed to HN as compared with ones to MN. A large proportion of leaf N was allocated to the carboxylation component under the levels of MN. More N was only served as a form of N storage and not contributed to photosynthesis in HN individuals. Compared with the MN plants, the maximum quantum yield of photosystem II (F_v/F_m), non-photochemical quenching of PSII (NPQ), effective quantum yield and electron transport rate were obviously reduced in the HN plants. Cycle electron flow (CEF) was considerably enhanced in the MN individuals. There was not a significant difference in maximum photo-oxidation P₇₀₀₊ (P_m) between the HN and MN individuals. Most importantly, the HN individuals showed higher K phase in the fast chlorophyll fluorescence induction kinetic curve (OJIP kinetic curve) than the MN ones. The results obtained suggest that photosynthetic capacity might be primarily inhibited by the inactivated Rubisco in the HN individuals, and HN-induced depression of photoprotection might be caused by the photodamage to the donor side of PSII oxygen-evolving complex.

氮 (N) 是限制叶片光合作用的主要因素。然而，高氮驱动抑制光合效率和光保护作用的机制在三七等耐阴和对氮敏感的物种中尚不清楚。比较分析了耐阴和氮敏感物种的叶片叶绿素 (Chl) 含量、1,5-二磷酸核酮糖加氧酶 (Rubisco) 活性和含量、光合装置中的氮分配、光合性能和 Chl 荧光。在中氮 (MN) 和高氮 (HN) 水平下生长的三七。结果表明，HN个体的Rubisco含量、Chl含量和比叶氮(SLN)更高。Rubisco 活性，净光合速率 (A _net )、光合氮利用效率 (PNUE)、最大羧化速率 ( V _cmax ) 和最大电子传输速率 ( J _max ) 当植物暴露于 HN 时低于暴露于 MN 的植物。在 MN 水平下，大部分叶 N 分配给羧化组分。更多的 N 仅作为 N 储存的一种形式，对 HN 个体的光合作用没有贡献。与 MN 植物相比，光系统 II 的最大量子产率 ( F _v / F _m)、PSII (NPQ) 的非光化学猝灭、有效量子产率和电子传输速率在 HN 植物中明显降低。MN 个体的循环电子流 (CEF) 显着增强。HN 和 MN 个体之间的最大光氧化 P ₇₀₀₊ ( P _m )没有显着差异。最重要的是，HN 个体在快速叶绿素荧光诱导动力学曲线（OJIP 动力学曲线）中显示出比 MN 更高的 K 相。获得的结果表明光合能力可能主要受到 HN 个体中灭活的 Rubisco 的抑制，并且 HN 诱导的光保护抑制可能是由 PSII 氧释放复合物的供体侧的光损伤引起的。