From surface interception to biological stabilization: successional controls on lead immobilization and microbial...

Biocrusts regulate heavy metal fate in drylands, yet how lead (Pb) immobilization mechanisms evolve along ecological succession remains unresolved. Here, Pb retention, speciation, and microbial responses were examined across algal, lichen, and moss biocrusts under acute (30 min) and chronic (28 days) exposure regimes. Acute retention was dominated by rapid physicochemical interception, with stage-dependent capacities primarily controlled by texture and electrical conductivity. Chronic exposure over a 28-day period activated biologically reinforced stabilization, resulting in convergent high Pb retention efficiencies (>89%) across all successional stages despite pronounced structural differences. Pb progressively transformed from labile to stable fractions via distinct pathways, including phosphate-driven mineralization in algal crusts, coupled phosphate-carbonate biomineralization in lichen crusts, and dominant organic sequestration in moss crusts. Microbial responses revealed increasing resistance with succession, ranging from severe community simplification in algal crusts to functional reorganization and network robustness in mature crusts. These results demonstrate a successional transition from surface interception to biological stabilization, highlighting mature biocrusts as potentially effective biogeochemical buffers against atmospheric Pb contamination.