The study “Biochar application alleviates drought-induced oxidative stress by activating the salicylic acid-mediated glutathione synthesis pathway in Brassica napus,” published in BMC Plant Biology, authors Bok-Rye Lee, Sang-Hyun Park, and colleagues explored the precise mechanisms by which biochar helps Brassica napus plants cope with drought. The study focused on how biochar application influences the hormonal and antioxidant defense systems, particularly the regulation of glutathione-based redox control under conditions of moderate drought stress over 43 days.

Drought stress is a major constraint on plant productivity, primarily by disrupting the cellular environment and leading to the excessive accumulation of reactive oxygen species (ROS), such as superoxide anion and hydrogen peroxide . This leads to severe cellular damage, indicated by increased lipid peroxidation, measured as malondialdehyde (MDA) levels. The researchers confirmed that drought alone drastically reduced key physiological indicators, causing an $84.0\%$ reduction in shoot biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More and a reduction in relative water content (RWC) compared to the well-watered control. These physical stresses were accompanied by a significant 88.3% reduction in the critical antioxidant ratio of reduced to oxidized glutathione , signaling severe oxidative stress and a collapse of the cellular redox homeostasis.

Biochar application provided a powerful, two-pronged defense. First, the application of rice husk biochar significantly improved the soil’s water retention capacity, which directly eased the physical stress on the plants. The drought-plus-biochar treatment (Drought+Biochar) resulted in a less pronounced reduction in soil water content—a 48.1% decrease relative to the control, compared to a 64.0% decrease in drought alone. This improvement in water status led to enhanced RWC, greater preservation of chlorophyll, and substantial improvement in shoot biomass.

The second, and more crucial, part of the defense involved activating the plant’s internal biochemical signaling pathways. Under drought alone, the plants exhibited an Abscisic Acid (ABA)-dominant profile, marked by an increase in ABA and the upregulation of ABA signaling genes . This hormonal state correlated with the heightened oxidative stress. Biochar application effectively antagonized this stress response. Compared to drought alone, biochar treatment elevated the protective hormone Salicylic Acid (SA) content and simultaneously reduced ABA content.

This shift in the hormonal balance activated the plant’s antioxidant system. Biochar application dramatically enhanced the master antioxidant Glutathione (GSH), increasing its level by 2.9-fold and restoring the ratio by more than 4.5-fold compared to drought alone. This restoration of the redox balance was achieved by activating the SA-mediated GSH synthesis pathway. Specifically, biochar treatment upregulated the expression of the SA biosynthesis gene and the SA signaling gene. This SA activation subsequently promoted the expression of the key GSH biosynthesis gene, (4.2-fold upregulation), while suppressing GPX7 (a gene associated with GSH consumption) by 60.7%. This transcriptional and hormonal switch, as supported by correlation analysis, proves that biochar-induced drought tolerance relies on integrating improved water conditions with this SA-mediated redox regulatory signature.

The findings demonstrate that rice husk biochar application offers an important strategy for enhancing drought stress tolerance in agriculture, not just through simple physical improvements to the soil, but primarily by modulating complex phytohormone-mediated redox control.

Source: Lee, B.-R., Park, S.-H., Muchlas, M., Bae, D.-W., & Kim, T.-H. (2025). Biochar application alleviates drought-induced oxidative stress by activating the salicylic acid-mediated glutathione synthesis pathway in Brassica napus. BMC Plant Biology, 25(1582).