Table_1_Spatiotemporal Heterogeneity of Chlorophyll Content and Fluorescence Response Within Rice (Oryza sativa L.) Canopies Under Different Nitrogen Treatments.DOCX

Accurate acquisition of plant phenotypic information has raised long-standing concerns in support of crop breeding programs. Different methods have been developed for high throughput plant phenotyping, while they mainly focused on the canopy level without considering the spatiotemporal heterogeneity at different canopy layers and growth stages. This study aims to phenotype spatiotemporal heterogeneity of chlorophyll (Chl) content and fluorescence response within rice leaves and canopies. Multipoint Chl content and high time-resolved Chl a fluorescence (ChlF) transient (OJIP transient) of rice plants were measured at different nitrogen levels and growth stages. Results showed that the Chl content within the upper leaves exhibited an increasing trend from the basal to the top portions but a decreasing pattern within the lower leaves at the most growth stages. Leaf Chl content within the rice canopy was higher in the lower leaves in the vegetative phase, while from the initial heading stage the pattern gradually reversed with the highest Chl content appearing in the upper leaves. Nitrogen supply mainly affects the occurrence time of the reverse vertical pattern. This could be the result of different nutritional demands of leaves transforming from sinks to sources, and it was further confirmed by the fall of the JI phase of OJIP transient in the vegetative phase and the rise in the reproductive phase. We further deduced that the vertical distribution of Chl content could have a defined pattern at a specific growth stage. Furthermore, the reduction of end acceptors at photosystem I (PSI) electron acceptor side per cross section (RE0/CS) was found to be a potential sensitive predictor for identifying the vertical heterogeneity of leaf Chl content. These findings provide prior knowledge on the vertical profiles of crop physiological traits, which explore the opportunity to develop more efficient plant phenotyping tools for crop breeding.

精准获取植物表型信息，长期以来都是支撑作物育种项目的核心关注点。目前已开发出多种高通量植物表型分析方法，但此类方法大多聚焦于冠层整体水平，未考虑不同冠层层次及生长阶段下的时空异质性。本研究旨在解析水稻叶片及冠层内叶绿素（Chl）含量与荧光响应的时空异质性表型特征。研究在不同氮素水平及生长阶段下，对水稻植株的多点叶绿素含量与高时间分辨率叶绿素a荧光（ChlF）瞬态（OJIP瞬态）信号进行了测定。结果显示，在多数生长阶段中，水稻上部叶片的叶绿素含量从叶基到叶尖呈递增趋势，而下部叶片则呈现递减模式。水稻冠层内的叶片叶绿素含量在营养生长期表现为下部叶片更高，而从始穗期开始，该分布模式逐渐反转，上部叶片的叶绿素含量达到最高。氮素供给主要影响这种垂直分布反转模式的出现时间。这一现象可能源于叶片从库器官转变为源器官过程中的差异化营养需求，而营养生长期OJIP瞬态的J-I相下降、生殖生长期该相上升的结果进一步验证了上述推论。我们进一步推测，在特定生长阶段下，叶绿素含量的垂直分布可能存在固定模式。此外，本研究发现，单位截面光系统I（PSI）电子受体侧的末端受体数量（RE0/CS）可作为识别叶片叶绿素含量垂直异质性的潜在敏感指标。本研究结果为作物生理性状的垂直分布特征提供了先验知识，同时为开发更高效的作物育种用植物表型分析工具开辟了新路径。