# Reducing nitrogen with dense planting increase sweetpotato storage roots quantity via favoring starch synthesis over lignification

## TL;DR

Reducing nitrogen and using dense planting improves sweetpotato root growth by boosting starch production and reducing lignin.

## Contribution

The study reveals how medium nitrogen with dense planting enhances sweetpotato root development through hormonal and genetic mechanisms.

## Key findings

- MDMN increased root number, length, and volume compared to traditional low-density high-N methods.
- MDMN upregulated genes for starch synthesis and downregulated lignin-related genes.
- MDMN altered hormone levels to favor starch accumulation over lignification.

## Abstract

Excessive nitrogen (N) inhibits crop development, yet the synergistic effects of reducing nitrogen with dense planting on sweetpotato storage root (SR) formation remain unclear. This study evaluated four N levels (0, 23, 46, and 69 mg N kg−1 soil) and three planting spacings (0.25, 0.20, and 0.15 m). Results indicated that medium density with medium N (MDMN) significantly outperformed the traditional low-density high-N (LDHN) treatment. From 15 to 30 days after planting (DAP), MDMN enhanced root number, length, and volume, while by 45 DAP it increased SR number, root activity, and N accumulation. MDMN upregulated IbKNOX1 and IbARF5, elevating ZR and IAA levels while reducing GA3, thereby promoting starch accumulation via increased IbSUS and IbAGP expression. Concurrently, lignin biosynthesis was suppressed through downregulation of IbPOD and lignin-related genes. Collectively, MDMN promotes SR formation by optimizing hormonal balance to favor starch synthesis over lignification.

•MDMN improved storage root number, and N uptake vs. high-N low density•MDMN increased ZR and IAA but decreased GA3 during storage root formation•MDMN upregulated starch biosynthesis genes, boosting sucrose and starch accumulation•MDMN suppressed lignin biosynthesis, lowering lignin and promoting storage root initiation

MDMN improved storage root number, and N uptake vs. high-N low density

MDMN increased ZR and IAA but decreased GA3 during storage root formation

MDMN upregulated starch biosynthesis genes, boosting sucrose and starch accumulation

MDMN suppressed lignin biosynthesis, lowering lignin and promoting storage root initiation

Agricultural science; Agronomy; Agricultural techniques; Agricultural plant products