# Physiological and molecular insights into nitrogen rate and planting density interactive regulation of black sesame nitrogen use efficiency, growth, yield, and seed quality

## TL;DR

This study explores how adjusting planting density and nitrogen levels can improve black sesame growth, yield, and seed quality in a sustainable way.

## Contribution

The study identifies optimal planting conditions and candidate genes for nitrogen use efficiency in black sesame under specific agronomic practices.

## Key findings

- Moderate nitrogen (≤90 kg/ha) with dense planting (330,000 plants/ha) improved yield and seed quality in two black sesame varieties.
- Genes AMT1 and NRT2.13A were identified as key regulators of nitrogen metabolism under these conditions.
- The optimal regime reduced environmental risk compared to high-nitrogen practices.

## Abstract

Optimizing nitrogen (N) application and planting density is a green and efficient agronomic strategy to increase crop yield and nitrogen use efficiency (NUE). However, the sesame responses to the interactive effects of N dose and planting density have not been fully elucidated. Here, we investigated the effects of different planting densities and N rates on the growth performances, physiological traits, N and carbon metabolism, yield components, and seed quality of two black sesame varieties (JHM and PYH). Two-year field experiments were conducted combining three planting densities (110,000, 160,000, and 330,000 plants.ha− 1) and three nitrogen rates (45, 90, and 135 kg.ha− 1).

Analyses revealed that sesame’s response to the combined effects of planting density and N rate is developmentally regulated and varietal-specific. Notably, we found that a moderate nitrogen dose of ≤ 90 kg.ha⁻¹ coupled with dense planting of ⁓330,000 plants per hectare improved sesame growth, NUE, yield, and seed quality. This optimal planting condition significantly improved N allocation to seeds, maximized the yield of JHM and PYH to 3.47 t·ha⁻1 and 3.84 t·ha⁻1, respectively, and considerably enhanced seed oil and unsaturated fatty acid contents. AMT1 and NRT2.13 A were identified as promising candidate regulatory genes of sesame NUE and modulators of N metabolism under dense planting density and moderate N rate. Other candidate N regulatory and sucrose metabolism-related genes were also identified.

This study exposes the complexity of mechanisms underlying sesame response to dual effects of planting density and N rate, and identifies a potential optimal planting condition to improving yield per unit area and seed quality. This agronomic optimization is likely to reduce environmental risk compared with high-N regimes. However, the proposed regime is optimal for the two tested varieties and the specific soil–climate conditions studied, and it should be validated in additional germplasm and environments before broader extrapolation. .

The online version contains supplementary material available at 10.1186/s12870-026-08114-8.