Stem nitrogen accumulation through vegetative storage proteins and mobilization to seeds supports high-yielding soybean

Abstract

The role of stems as a source of nitrogen (N) for growing seeds has received little attention in soybean. This study evaluatedN storage and mobilization from stems to seeds across 42 high-yielding environments under contrasting N supply:a ‘zero-N’ treatment, in which crops relied on soil and biological N fixation, and a ‘full-N’ treatment consisting ofample N fertilizer. We measured the accumulated N per organ before seed filling and subsequent N mobilization fromvegetative organs to seeds. Vegetative storage protein (VSP) abundance in stems was quantified via proteomics. Yieldranged from 4.2 to 7.3 Mg ha−1, with +11% yield in full-N (6.1 Mg ha−1) compared with zero-N (5.5 Mg ha−1). The full-Ntreatment resulted in more mobilized N from stems (+42%) and leaves (+22%) to seeds than zero-N treatment, whichwas attributed to the larger amount of N stored in stems and leaves before seed filling (+37% and +21%, respectively).Among the 5335 identified proteins at the peak of N accumulation, VSPα (+1.4%) and VSPβ (+0.8%) showed the greatestincrease in full-N. We conclude that N stored in stems as VSPs before seed filling plays a key role in meeting the seed Ndemand in high-yielding soybean crops.