Analysis of canopy light utilization efficiency in high-yielding rapeseed varieties

The photosynthetic mechanism responsible for the differences in yield between different rapeseed varieties remains unclear, and there have been no consensus and definite conclusions about the relationship between photosynthesis and yield. Representation of the whole plant by measuring the photosynthetic performance at a single site may lead to biased results. In this study, we comprehensively analyzed the main photosynthetic organs of four high-yielding rapeseed varieties at the seedling, bud, flowering, and podding stages. The canopy photosynthetic parameters were derived by measuring the photosynthetic area, net photosynthetic rate, and chlorophyll content, and canopy photosynthetic capacity was used to evaluate the light utilization efficiency of different rapeseed varieties to establish the relationship between canopy photosynthetic traits and yield. The results showed that there were significant differences in photosynthetic traits among different parts of rapeseed plants. The photosynthetic trait parameters of the whole plant differed significantly when represented by leaves at different positions among different varieties, and different rapeseed varieties exhibited significantly different sensitivity to light intensity. The whole-plant study showed that the canopy photosynthetic capacity was the highest and second highest at the seedling and bud stage, respectively, both of which were closely and positively correlated with rapeseed yield, and ZY501 had higher canopy photosynthetic capacity than other varieties at these two stages due to its larger canopy photosynthetic area. Canopy chlorophyll content was also positively correlated with canopy photosynthetic capacity. These results indicated that investigation of photosynthetic characteristics at single sites in rapeseed might lead to biased results of photosynthetic capacity in different varieties, and provided a new evaluation index for studying the light utilization efficiency of rapeseed. Our results also clarified that canopy photosynthetic area has significantly greater contribution to canopy photosynthetic capacity than canopy photosynthetic efficiency, and provided a theoretical basis for investigating the photosynthesis mechanism underlying high crop yield.