钾素营养对油菜叶片和角果皮光合特性的影响及其机制

Potassium (K) fertilization is one of the most indispensable cultivations of winter oilseed rape production. It can promote crop growth, increase the numbers of pods per plant and seeds per pod, which is closely related to the improvement of photosynthesis due to K fertilization. Many studies about the effects of K fertilizer on photosynthesis have been conducted, nevertheless, the studies focus on the major limiting factors of crop photosynthesis and the changes of K concentration on this process are usually neglected. Furthermore, both leaf and pod wall are the dominant photosynthetic organs; their structures and functions are quite different. But the influences and mechanisms of K fertilization on the photosynthesis characteristics of leaf and pod wall of oilseed rape are unclear. Therefore, the succession patterns of these photosynthetic organs and their responses to K fertilization are ascertained through the field experiments. With the combination of the analysis of morphology characteristics, photosynthetic capacity and metabonomics, the influences of K fertilization on the photosynthetic characterizes of leaf and pod wall are clarified. Moreover, the correlations between crop K concentration and the limiting factors of photosynthesis (stomatal, mesophyll conductance and biochemical limitations) are quantified to determine the principal limitations of oilseed rape photosynthesis under different K stress. Then the mechanisms of K fertilization on photosynthesis are revealed depending on the modern technologies including the electron microscope, the fluorescent probes etc. Finally, the critical K concentrations based on the crop photosynthesis characteristics are established. This will provide the theoretical basis and technical support of optimizing K fertilization and expanding the potential yield of oilseed rape.

施钾是冬油菜生产中重要的栽培措施，它能促进油菜的生长，增加角果数和每角粒数，这与施钾改善油菜的光合作用紧密联系。钾对作物光合作用的影响已有广泛的研究，但研究中往往关注某个限制因子是造成光合速率降低的主因，而忽视钾素浓度的变化对这个过程的影响。叶片和角果皮作为油菜主要的光合器官，其结构和功能存在明显差异，而钾对它们光合作用的影响及机制并不明晰。本研究通过田间监测明确施钾对油菜主要光合器官演替规律的影响，结合形态特征、光合能力以及光合代谢产物的分析，阐明油菜叶片和角果皮光合特性的差异及其对钾素营养的响应；进一步量化作物钾素浓度和光合作用各限制因子（气孔导度、叶肉导度和生化因子）的关系，确定不同钾素胁迫下油菜光合作用的主要限制因子，利用电镜、荧光探针等技术揭示各限制因子影响光合作用的机制，最终建立基于光合作用变化的临界钾素浓度阈值，为合理施用钾肥，充分挖掘油菜生产潜力提供理论和技术支撑

钾肥施用能明显改善光合作用，提高作物的产量。关于钾对作物光合作用的影响已有广泛的研究，但研究中往往忽视钾素浓度的变化对整个过程的影响。叶片和角果皮作为油菜主要的光合器官，其结构和功能存在明显差异，但钾对它们光合作用的影响及机制并不明晰。因此本研究利用不同钾素供应的田间和水培试验研究了油菜主要光合器官（叶片和角果皮）的演替规律、光合能力的差异及其对施钾的响应，量化了不同钾素供应下油菜主要光合器官的限制因子，从叶面积变化、CO2传导、Rubisco酶特性以及代谢产物的差异等角度揭示了钾素调控作物光合作用的生理机制，为优化作物钾素养分管理提供理论支撑。主要结果表明，（1）冬油菜生长过程中存在明显光合器官演替现象，油菜叶面积指数（LAI）在花期达到最大（3.4-4.8）；进入角果期后，LAI快速下降，角果皮指数（PAI）在结角后25天达到最高（3.5-4.1）。钾肥施用对LAI和PAI调控作用一致，LAI和PAI均随施钾量增加而增加。（2）油菜叶片和角果皮的光合特性存在明显差异，饱和光强下叶片的净光合速率是角果皮的2.6-2.9倍，但角果皮对高温和高光强有更高的适应能力。角果皮的气孔数量少于叶片，但角果皮的气孔长、宽以及单个气孔面积高于叶片。缺钾胁迫显著降低了油菜主要光合器官的光合速率及关键光合特征参数，两者的趋势相似，叶片降低的幅度大于角果皮。（3）光合作用限制因子随着叶片和角果皮钾含量的增加而显著降低。轻度缺钾时，影响叶面积的关键结构参数（S/W值）早于影响叶片光合能力的结构参数的变化，导致叶面积降低先于光合速率降低。随着缺钾胁迫增加，叶绿体面向细胞空隙的面积减小导致CO2在叶肉细胞中传输阻力增加。TCA循环中上调的柠檬酸被分配给苹果酸和富马酸的合成，亚细胞pH值降低了SBPase酶和Rubisco酶的活性，阻碍了RuBP的再生。严重缺钾胁迫时光呼吸速率降低，加剧了光损伤和生化限制。（4）油菜叶片净光合速率变化的钾浓度阈值为1.2%-1.3%，但15~20叶龄的新叶钾含量低于3.0%时，已面临“隐性”缺钾症状。因此基肥充足的钾肥供应，不仅能维持叶面积的扩张，同样保证了高的光合能力和光合持续期。新叶钾含量以及叶面积的大小是作物钾素营养诊断需要关注的关键指标。