Spatial heterogeneity analysis of silique chlorophyll a fluorescence-based photosynthetic traits for rapeseed yield and quality assessment

Abstract

Photosynthesis is an important process that contributes to capturing light energy and transforming it into chemical energy in plants. To date, most studies on the photosynthetic traits focus on plant leaves, while the photosynthetic response of non-foliar organs such as siliques of oilseed rapes at the vertical distribution of the canopy, and their contribution to yield and quality traits remain poorly understood. Therefore, this study aims to elucidate the spatial heterogeneity of silique chlorophyll a fluorescence features and estimate targeted rapeseed yield and quality traits in a non-destructive manner before harvest. Field experiments were conducted for silique chlorophyll a fluorescence, morphological traits, yield and quality traits measurements within different spatial layers under varied nitrogen treatment levels. Correlation analysis and random forest (RF) algorithm were applied to identify crucial JIP-test parameters in different spatial layers and to evaluate their performance on rapeseed yield and quality evaluation. Our results found that several JIP-test parameters (ABS/RC, TRo/RC, and ETo/RC) of the siliques at the top layer related to the activity of reaction center (RC) presented superior photoprotection and photosynthetic capacities compared to those in the middle and bottom layers, indicating a significant spatial heterogeneity of the primary photosynthesis of siliques. As for yield and quality traits, rapeseeds had the highest oil content at the bottom layer followed by the middle and top layers, whereas protein content and yield traits were completely opposite to this tendency. RF model further confirmed that the JIP-test parameters acquired from siliques of the upper layers were more sensitive to the yield and protein content prediction, while the oil content can be better estimated using the JIP-test parameters of siliques at the bottom layer. Furthermore, a relatively weak relationship was identified between the glucosinolates and erucic acid content and JIP-test parameters. We expect that findings in this study could provide a new way to understand the spatial heterogeneity of silique photosynthetic traits, which might be useful for developing high yield and quality cultivars in rapeseed breeding.