College of Agronomy & Biotechnology, Yunnan Agricultural University, Kunming, 650201, China.
Key Laboratory of Medicinal Plant Biology of Yunnan Province, Yunnan Agricultural University, Kunming, 650201, China.
Photosynth Res. 2021 Mar;147(3):283-300. doi: 10.1007/s11120-021-00823-5. Epub 2021 Feb 15.
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), photosynthetic N use efficiency (PNUE), maximum carboxylation rate (V) and maximum electron transport rate (J) 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/F), 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 P (P) 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，在阴生且对氮敏感的物种（如三七）中，高氮驱动对光合效率和光保护的抑制机制仍不清楚。本研究比较分析了中度氮（MN）和高氮（HN）处理下，耐荫且对氮敏感的三七叶片叶绿素（Chl）含量、核酮糖-1,5-二磷酸羧化酶加氧酶（Rubisco）活性和含量、光合器官中的氮分配、光合性能和 Chl 荧光。结果表明，HN 个体的 Rubisco 含量、Chl 含量和比叶氮（SLN）较高。与 MN 个体相比，暴露于 HN 下的 Rubisco 活性、净光合速率（A）、光合氮利用效率（PNUE）、最大羧化速率（V）和最大电子传递速率（J）较低。在 MN 水平下，叶片氮的很大一部分分配给羧化组分。只有在 HN 个体中，更多的氮仅作为氮储存的形式，而不参与光合作用。与 MN 植株相比，HN 植株的 PSII 最大光量子产量（F/F）、PSII 非光化学猝灭（NPQ）、有效量子产量和电子传递速率明显降低，MN 植株的循环电子流（CEF）显著增强。HN 和 MN 个体之间的最大光氧化 P（P）没有显著差异。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）中的 K 相高于 MN 个体。研究结果表明，高氮可能主要通过失活的 Rubisco 抑制光合能力，而高氮诱导的光保护抑制可能是由 PSII 放氧复合物供体侧的光损伤引起的。
