pH-dependent response of soil microbial community and multifunctionality to long-term low and moderate mercury pollution

Low and moderate concentrations represent the predominant forms of mercury pollution in contaminated regions. Nevertheless, the responses of soil microbial communities to these pollution levels are still poorly understood. Here, under field conditions, we evaluated the impact of long-term exposure to low and moderate Hg pollution (0.02-5.43 mg/kg) on soil bacterial communities based on 16S rRNA gene amplicon sequencing. Bacterial α-diversity and richness showed weakly associations with both total and available Hg content, while soil pH was a key factor influencing bacterial community composition. At pH 5.5-8.0, total Hg became a primary environmental variable shaping bacterial community structure. Soil multifunctionality increased along the Hg concentration gradient, with its relationship to Hg levels strongly dependent on soil pH. Available Hg had a stronger influence on soil multifunctionality at pH 4.0-5.5, while total Hg was more influential at pH 5.5-8.0. This study improves our understanding of bacterial community assembly in soils under long-term, low to moderate Hg pollution and demonstrates the critical effects of soil pH on the impact of Hg on soil multifunctionality.