Freeze–Thaw Dynamics in Postindustrial Soil: Implications for Metal Stability and Soil Enzymatic Activity During Phytostabilization

Abstract

Phytostabilization, a key strategy in addressing heavy metal contamination, faces challenges in regions with frequent temperature fluctuations. The challenges arise from the impact of temperature variations on microbial activity, plant metabolism, and metal bioavailability. Acknowledging the sensitivity of soil dynamics, amendments, and ecological interactions to temperature variations underscores the importance of considering these factors for effective phytostabilization strategies in dynamic environmental conditions. The aim of this study is to explore the effect of phytostabilization assisted with diatomite, halloysite, and biochar with and without freeze–thaw conditions on metal stability (as distribution patterns), and microbial activity (as dehydrogenase activity, DHA). The experiment comprised two variants. In the first, conducted without FTC, Lolium perenne seeds were sown in pots filled with soil from a contaminated area, both with and without amendments (3%), lasting for 52 days. The second variant replicated the process with 16 freeze–thaw cycles (FTC) and extended the duration to 116 days. Results revealed that FTC alters the distribution of heavy metals in soil compared to conditions without the FTC cycle. Diatomite reduces Cu mobility but may potentially increase Cd mobility. Halloysite enhances Cu exchangeability, restricts Cd mobility, and increases Pb retention in a stable form. Biochar exhibits mixed effects on Cu and Cd mobility, showcasing the influence of FTC on these soil amendments. As a vital microbial indicator, soil DHA responds dynamically to varying temperatures. The applied amendments seem to mitigate the adverse effects of FTC cycles by supporting DHA. Notably, halloysite exhibits a more favorable influence without FTC, while biochar and diatomite showcase enhanced stimulatory effects post-FTC. It emphasises the need for a nuanced understanding of temperature–microbe interactions and the role of amendments in enhancing the sustainability of phytostabilization in metal-contaminated environments.