Evaluation of canopy photosynthetic rate in erect-panicle rice using a photosynthetic model

Erect-panicle rice has the potential to improve rice production owing to its unique leaf canopy structure and high leaf nitrogen content (LNC). However, limiting information is available regarding its canopy photosynthesis of erect-panicle rice. In this study, we aimed to investigate the effects of leaf canopy structure and LNC on photosynthesis in erect-panicle rice under various cultivation management conditions. Field experiments were conducted using three rice cultivars – Shennong265 (erect-panicle rice), Nipponbare, and Takanari – grown under different fertilizer and planting density treatments. A modeled canopy photosynthetic rate, based on a photosynthetic model that incorporates nitrogen distribution, was used to evaluate the influence of leaf canopy structure and LNC on canopy photosynthesis. Compared to other cultivars, Shennong265 exhibited significantly higher LNC, particularly in the lower stratum, which enhanced the modeled photosynthetic rate during the ripening stage. The erect configuration of its panicles and leaves allowed increased light transmittance within the canopy and may have contributed to the maintenance of LNC in the lower stratum. Nonetheless, the canopy photosynthetic rate of Shennong265 decreased under high planting density compared with that under normal density, indicating the importance of optimizing planting density for this cultivar. These findings underscore the critical role of LNC distribution in determining the productivity of erect-panicle rice. The distinctive canopy structure of erect-panicle rice enabled sustained LNC in the lower canopy, thereby improving photosynthetic capacity. Our results demonstrate the need to carefully consider in the cultivation of erect-panicle rice to maximize its productivity advantages.