Acid rain continues to cause persistent soil acidification, leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More vital nutrients and altering soil organic nitrogen dynamics in forest ecosystems worldwide. Alkaline biochar made from plant litter offers a practical solution to counter these environmental impacts. In a recent publication in Biochar, authors Yuanyuan Feng, Yuanhao Liu, Jiaxuan Liu, Haibo Hu, Meijia Zhou, Yanfang Feng, and Lihong Xue examined how biochar derived from oak litter regulates acid-hydrolyzable nitrogen fractions in a forest plantation subject to simulated acid rain over two years. Their research provides new insight into the biological mechanisms that control bioavailable soil nitrogen accumulation.

The field experiment demonstrated that simulated acid rain alone substantially depleted soil nitrogen pools and increased acidity. However, incorporating oak litter biochar into the topsoil under acid rain conditions successfully increased soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More by nearly two-tenths of a unit and elevated total acid-hydrolyzable nitrogen by roughly sixty-five percent compared to acid rain alone. The individual fractions of nitrogen responded with remarkable gains. Specifically, acid-ammonia nitrogen expanded by forty-five percent, acid-amino sugar nitrogen grew by over sixty-one percent, and acid-amino acid nitrogen surged by over eighty percent. Unidentified hydrolyzable nitrogen components also saw a sixty percent increase. These substantial gains demonstrate that biochar effectively mitigates acid-induced nutrient loss by converting active inorganic nitrogen into stable, bioavailable organic pools.

To explain these dramatic improvements, the researchers evaluated both chemical properties and biological factors across the treated soils. Statistical modeling showed that soil chemo-biological interactions accounted for up to forty percent of the variation in nitrogen fractions, with biological drivers exerting a far greater influence than chemical properties alone. Microbial biomass nitrogen was identified as the key determinant controlling the accumulation of microbial-derived amino sugars and amino acids. Additionally, microbial nitrogen use efficiency primary governed changes in acid-ammonia nitrogen levels. Biochar helped relieve environmental stress on soil microbes, allowing them to assimilate free nitrogen into microbial biomass and subsequently return it to the soil through natural turnover.

The study also revealed key shifts in the soil microbiome architecture under combined stress and biochar treatments. Biochar application under acid rain maximized bacterial network complexity, fostering greater co-occurrence and cooperative interactions among bacterial groups such as nitrogen-fixing Proteobacteria. Conversely, fungal network connectivity decreased under the same conditions, indicating a shift toward specialized fungal communities focused on organic matter decomposition. Crucially, partial least squares path modeling confirmed that the positive regulatory influence of biochar on soil nitrogen dynamics consistently surpassed the negative impacts inflicted by acid rain stress.

Ultimately, these findings show that biochar amendment works primarily by stimulating soil biological activity rather than just altering baseline chemistry. By optimizing microbial nitrogen use efficiency and reconfiguring soil microbial networks, biochar transforms acid rain-stressed soils into productive reservoirs capable of retaining bioavailable nitrogen. This biological regulation provides a sustainable strategy for managing forest soil fertility and restoring damaged ecosystems facing ongoing atmospheric pollution.

Source: Feng, Y., Liu, Y., Liu, J., Hu, H., Zhou, M., Feng, Y., & Xue, L. (2026). Biochar-driven biological regulation dominates acid-hydrolyzable nitrogen accumulation in plantation soils under acid rain stress. Biochar, 8(1), 55.