# Modulating alfalfa growth: impacts of plant growth regulators on physiology, architecture, and seed yield

## TL;DR

This study explores how plant growth regulators can improve alfalfa seed yield by altering plant structure and metabolism.

## Contribution

The study identifies an optimal concentration of DPC that significantly enhances alfalfa seed yield and plant architecture.

## Key findings

- A single spray of 0.35 g L−1 DPC increased chloroplast volume, starch granules, and photosynthetic capacity in alfalfa.
- DPC treatment improved carbon-nitrogen metabolism and increased seed yield to 329.76 kg·hm−2.
- The 0.35 g L−1 DPC treatment had the highest membership degree of effectiveness in plant architecture optimization.

## Abstract

Alfalfa seed yield is severely restricted by its indeterminate growth habit, with actual average yield only reaching 4% of potential yield in field production. Plant growth regulators (PGRs) can modulate the balance between vegetative and reproductive growth, yet research on PGR application for alfalfa plant architecture optimization and seed yield improvement remains limited. To address this gap, this study treated “XinMu No.4” alfalfa (Medicago sativa L.) with three PGRs at specific concentration gradients: flumetralin (CAG: 0.5/1.0/1.5 g L− 1), 1,1-dimethyl-piperidinium chloride (DPC: 0.25/0.35/0.45 g L− 1), and compound sodium nitrophenolate (CSN: 0.15/0.20/0.25 g L− 1), to investigate their effects on growth, photosynthetic characteristics, carbon-nitrogen metabolism, and seed yield.

Key findings showed that a single spray of 0.35 g L− 1DPC resulted in complete cell structure, significantly increased chloroplast volume (by 23.6%), enhanced starch granule number (by 41.2%), and improved photosynthetic capacity (chlorophyll content increased by 47.5% and net photosynthetic rate (Pn) increased by 32.8%). This treatment also elevated nitrate reductase activity by 37.5% and sucrose synthase activity by 29.4%, enhancing carbon-nitrogen metabolic capacities. By increasing branch number to 63 branches/plant, inflorescences per plant increased by approximately 28 Pcs/Plant, ultimately boosting seed yield to 329.76 kg·hm− 2. Comprehensive membership function evaluation indicated this treatment had the highest average membership degree (0.918).

Comprehensive analysis showed that 0.35 g L− 1 DPC was the most effective in shaping plant architecture and boosting seed yield.

The online version contains supplementary material available at 10.1186/s12870-026-08173-x.