Sulfite Lignin Enhances Seed Germination and Salt Stress Tolerance

Abstract

Humic acids (HA), with their irregular polymeric structures and largely existing in grassland, present challenges in quality control due to significant variations in biological activities depending on extraction sources. To address this, we explored industrial byproducts as potential alternatives mimicking HA-like bioactivities. This study evaluates sulfite lignin, a byproduct of the pulp industry, as an eco-friendly biostimulant for enhancing plant growth and stress tolerance. Sulfite lignin demonstrated HA-like bioactivities, promoting seed germination and salt stress tolerance in Arabidopsis thaliana. Germination assays revealed that sulfite lignin significantly improved radicle and cotyledon emergence, particularly at low concentrations (8.6 mg L⁻¹), outperforming HA and kraft lignin. Additionally, under salt stress conditions, sulfite lignin-treated plants exhibited healthier phenotypes and maintained higher chlorophyll content compared to control treatments, similar to HA and kraft lignin. The findings highlight sulfite lignin as a promising, sustainable, and cost-effective biofertilizer, effectively replicating HA's biological functions while leveraging industrial byproducts.