氮钾互作调节叶片光合氮和存储氮分配提高油菜叶片光合作用的机理

Combination with nitrogen (N) and potassium (K) fertilization is one of the critical technologies for scientific fertilization in oilseed rape production. There have been extensive studies on the combination of N and K fertilizer to increase crop yield and shoot N uptake. It is inseparable between the increase of crop yield and the improvement of photosynthesis. The photosynthesis is not related to leaf N and K concentration, but also closely linked with leaf N forms, especially photosynthetic N pools. Potassium could promote protein synthesis and adjust leaf N transformation. However, the mechanism of N and K interaction to improve leaf photosynthesis through coordinating the transformation of leaf photosynthetic N pool is not clear. In the study, the method of leaf photosynthetic N and storage N pool is proposed and improved based on the photosynthetic N model and chemical extraction method. It is further optimized depending on the Simple Western and 15N labeling methods. Then the effects of N and K interaction on the photosynthetic pools, such as Rubisco, are studied using photosynthetic model, fluorescence probe and non-invasive micro-test techniques. Furthermore, the distribution of photosynthetic N and storage N influenced by N and K interaction are analyzed from single-leaf and canopy scales. It is helpful to reveal the mechanism by which N and K interactions could improve photosynthesis by increasing photosynthetic N pool, coordinating leaf photosynthetic N and storage N pools. Finally, the critical leaf N/K ratio and optimum distribution of photosynthetic N pools balancing higher photosynthesis and higher crop yield are proposed, which would provide theoretical support for nutrient management techniques of “enhancing N fertilizer by K fertilization”.

氮钾配施是油菜科学施肥的关键技术，关于氮钾配施提高作物产量和氮素吸收已有广泛的研究。作物产量的提高和光合作用改善密不可分，光合作用不仅与叶片氮钾含量密切相关，更与叶片氮素形态，尤其是光合氮库紧密相联。钾促进蛋白质合成，协调氮素转化，然而氮钾互作协调叶片光合氮库转化，提高叶片光合作用的机制并不明晰。本研究结合光合氮素模型和化学浸提方法，配合Simple Western和15N标记方法，提出并完善叶片光合氮和存储氮库分组方法。借助光合模型、荧光探针和非损伤微测等技术，研究氮钾互作对Rubisco等光合关键氮库的影响；进一步从单叶和冠层两个尺度分析氮钾配施对油菜叶片光合氮库和存储氮库分配影响，揭示氮钾互作通过提高光合氮库，协调叶片光合氮和存储氮库转化，提高光合作用的机制。最终提出协调油菜光合作用和高产的关键生育期叶片适宜氮钾比及叶片光合氮库配比，为“以钾促氮”的养分管理技术提供理论支撑。

氮钾配施是油菜科学施肥的关键技术，关于氮钾配施提高作物产量和氮素吸收已有广泛的研究，然而氮钾互作协调叶片光合氮库转化，提高叶片光合作用的机制并不明晰。因此本研究利用不同氮钾供应的田间和水培试验，在完善叶片氮库分组方法的基础上，探究了氮钾互作对叶片氮库的影响，解析了氮钾互作对叶片光合氮库库容和周转的影响，揭示了氮钾互作提高油菜叶片光合作用的机制，量化了油菜关键生育时期的氮钾比及叶片光合氮库配比，为“以钾促氮”的养分管理提供理论支撑。主要结果表明，（1）基于光合模型和化学浸提方法将叶片氮库分为光合氮、存储氮、结构氮和呼吸氮4个组分，分别占叶片全氮含量的12%-56%、26%-81%、6-19%和1%-3%。（2）Rubisco酶是叶片主要的光合氮库，施钾提高了叶片Rubisco酶含量，且随施氮量的增加钾对Rubisco含量的提升作用越明显，这与施钾提高叶肉细胞pH值增加Rubisco酶活性密切相关。光合氮库在叶片生长60天后达到最大，平均占叶片氮库的35%-55%。施钾后完全展开叶光合氮分配比例较不施钾平均增加了22%，存储氮的比例平均降低了16%。氮钾配施提升了光合氮和存储氮的周转，提高了其对叶叶片生长的贡献。（3）油菜叶片的净光合速率呈现明显的季节性变化，叶片CO2总导度（gtot）和羧化效率（Vcmax）是氮钾配施调节叶片光合季节性变化的主要因素，其中氮对CO2传导和同化的影响高于钾。施钾增加了羧化系统氮分配的比例，提高了叶片的羧化效率，协调了CO2传导和同化。（4）油菜最优氮肥和钾肥用量分别为165-220 kg N/hm2和103-148 kg K2O/hm2。油菜苗期最新完全展开叶适宜的氮钾比为2.4-2.7，其中钾含量不低于2.0%，氮含量在4.0%-5.4%（光合氮库占50%，其中羧化系统占30%）。综上所述，氮钾互作通过叶片光合氮库转化，增强叶片的光合能力，提高油菜产量和养分利用率。