Abstract
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.
Highlights
Rice (Oryza sativa L.) is a critical staple crop that feeds more than half of the world’s population
The variations of Chl content at the leaf level and its vertical distribution at the canopy level under different nitrogen treatments are shown in Figure 2 and Supplementary Table 1
No obvious change of the average Chl content was observed from the initial tillering (V1) to the jointing (V3) with the treatments of namely 0 (N0) and N1, while there was a considerable increase for plants under the N2 treatment
Summary
Rice (Oryza sativa L.) is a critical staple crop that feeds more than half of the world’s population. Leaf nitrogen concentration tended to be higher in photosynthetically active leaves of the upper layer, especially when nitrogen supply is deficient, and could theoretically track the within-canopy light gradient (Hikosaka, 2016; Pao et al, 2018). This vertical heterogeneity within crop canopies could be regarded as an adaptive strategy of continuous adjustment of between- and withinleaf partitioning to maximize canopy photosynthesis rate in response to limited nutritional resources and fluctuating environmental conditions (Adachi et al, 2017; Pao et al, 2018). Quantitative analysis of the spatiotemporal heterogeneity within the canopy is indispensable for accurate phenotyping
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