Biochar-driven biological regulation dominates acid-hydrolyzable nitrogen accumulation in plantation soils under acid rain stress

Abstract

Acid-hydrolysable nitrogen (AHN), a crucial fraction of bioavailable soil organic nitrogen (N), is highly sensitive to soil acidification. Alkaline biochar (BC) has been shown to effectively mitigate acid rain (AR)-induced soil acidification. However, its regulatory effects and underlying mechanisms on AHN fractions remain largely unexplored. In this study, a field-scale simulated AR experiment was conducted in a Quercus acutissima plantation, utilizing BC derived from Q. acutissima litter to evaluate its impacts on AHN fractions and associated soil chemical-biological drivers. The results showed that after 2 years of simulated AR spraying, BC application elevated soil pH by 0.19 units under AR stress and increased total AHN content by 64.8%. Specifically, acid-ammonia N, acid-amino sugar N, acid-amino acid N, and acid-hydrolyzable unidentified N increased by 45.0%, 61.3%, 80.6%, and 60.7%, respectively. BC-amended soils under AR exhibited the highest bacterial network complexity (0.8), whereas fungal network connectivity was reduced. Soil chemo-biological interactions explained 23.1−39.7% of the variations in AHN fractions. Random forest modeling identified microbial N use efficiency as the primary factor influencing acid-ammonia N, and microbial biomass N as the key factor governing the accumulation of acid-amino acid N and acid-amino sugar N. Furthermore, the regulatory effects of BC on AHN fractions (0.77–0.98) surpassed those of AR stress. This study elucidates the mechanistic pathways through which BC modulates acid-induced N dynamics, providing insights for sustainable N management in plantation ecosystems affected by AR.

Keywords

Biochar / Acid rain / Plantation soil / Acid-hydrolyzable nitrogen / Bacteria and fungi

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Funding

Natural Science Foundation of Jiangsu Province(BK20250692)

National Positioning Observation and Research Project of Farmland Protection Forest Ecosystem in Changjiang River Delta(2024132077)

Jiangsu Province Carbon Peak and Carbon Neutrality and Technology Innovation Special Fund Project(BE2022305)

Natural Science Foundation of the Jiangsu Higher Education Institutions of China(25KJB210009)

RIGHTS & PERMISSIONS

The Author(s)