Cropping patterns and plant population density alter nitrogen partitioning among photosynthetic components, leaf photosynthetic capacity and photosynthetic nitrogen use efficiency in field-grown soybean
Guowei Zhang, Zhikang Li, Qing Zhu, Changqin Yang, Hongmei Shu, Zhenzhen Gao, Xiangbei Du, Fei Wang, Lingfeng Ye, Ruixian Liu
Abstract
Soybean is essential for industrial applications, with its yield and production distribution significantly influencing global agricultural sectors. In maize-soybean strip intercropping (SI) systems, optimizing soybean yield requires a comprehensive understanding of photosynthetic physiology under conditions of limited light availability. This three-year study examined nitrogen (N) partitioning among photosynthetic components and photosynthetic N use efficiency (PNUE) in SI compared to soybean monocropping (Mono) system. Effects of different plant population densities (PPD) (8.3 ×10 4 plants ha −1 , 9.5 ×10 4 plants ha −1 and 11.1 ×10 4 plants ha −1 ) on photosynthetic N allocation, PNUE and their interrelationships in inner and border rows were also analyzed. Results indicated that, compared to Mono, SI increased chlorophyll and N content, allocating more N to the light-harvesting system while reducing N allocation to carboxylation, electron transfer systems, and the overall photosynthetic system. This shift in N allocation led to reduced photosynthetic capacity and PNUE. Higher PPD in SI further reduced the proportion of N allocation to carboxylation, electron transfer and total photosynthetic system, thereby reducing PNUE. In inner rows, N was more efficiently allocated to the photosynthetic system, particularly to the carboxylation and electron transfer systems, supporting a relatively higher photosynthetic capacity, PNUE and yield than border rows. A significant trade-off was observed between cell wall N and total photosynthetic system N in inner rows, while a quadratic relationship was noted in border rows. In conclusion, soybean leaves optimized photosynthetic capacity and PNUE by modulating N partitioning among photosynthetic components. Under SI system with a PPD of 9.5 × 10 4 plants ha −1 , soybean leaves demonstrated balanced photosynthetic N allocation, achieving the highest yield. These findings offer a theoretical basis for refining leaf N allocation strategies to maximize yield benefits in SI systems. • SI reduced PAR transmittance, Pn and PNUE in soybean leaves compared to Mono. • Leaf optimized P n and PNUE by adjusting N allocation among different components. • SI and increased PPD elevated P -nonphoto and P CW levels but decreased P -photo. • Differences in photosynthetic N allocation between border and inner rows influenced yield. • Elevated P -photo, particularly P B and P C benefits P n and PNUE in the SI system.