Abstract
Soil amendment with biochar alleviates the toxic effects of heavy metals on microbial functions in single-metal contaminated soils. Yet, it is unclear how biochar application would improve microbial activity and enzymatic activity in soils co-polluted with toxic metals. The present research aimed at determining the response of microbial and biochemical attributes to addition of sugarcane bagasse biochar (SCB) in cadmium (Cd)-lead (Pb) co-contaminated soils. SCBs (400 and 600 °C) decreased the available concentrations of Cd and Pb, increased organic carbon (OC) and dissolved organic carbon (DOC) contents in soil. The decrease of metal availability was greater with 600 °C SCB than with 400 °C SCB, and metal immobilization was greater for Cd (16%) than for Pb (12%) in co-spiked soils amended with low-temperature SCB. Biochar application improved microbial activity and biomass, and enzymatic activity in the soils co-spiked with metals, but these positive impacts of SCB were less pronounced in the co-spiked soils than in the single-spiked soils. SCB decreased the adverse impacts of heavy metals on soil properties largely through the enhanced labile C for microbial assimilation and partly through the immobilization of metals. Redundancy analysis further confirmed that soil OC was overwhelmingly the dominant driver of changes in the properties and quality of contaminated soils amended with SCB. The promotion of soil microbial quality by the low-temperature SCB was greater than by high-temperature SCB, due to its higher labile C fraction. Our findings showed that SCB at lower temperatures could be applied to metal co-polluted soils to mitigate the combined effects of metal stresses on microbial and biochemical functions.
Highlights
Soil contamination with cadmium (Cd) and lead (Pb) is an important environmental concern because of their high toxicity and non-biodegradable nature, as well as different source contributions in the soil–plant system (Alloway 2013; Smolders and Mertens 2013; Steinnes et al 2013; Wang et al 2020)
The DTPA-extractable metal (Cd and Pb) concentrations were considerably higher with the co-presence of metals compared with the single metals, regardless of the biochar application (Fig. 1)
The amount of soil organic carbon (OC) was significantly increased by 94–100% after addition of both biochars across contaminated soils compared to the control, from 4.61 g kg−1 in the unamended soil to 8.93 g kg−1 in by slow pyrolysis at 400 (B400)-amended soils and 9.23 g kg−1 in B600-amended soils (Fig. 1)
Summary
Soil contamination with cadmium (Cd) and lead (Pb) is an important environmental concern because of their high toxicity and non-biodegradable nature, as well as different source contributions in the soil–plant system (Alloway 2013; Smolders and Mertens 2013; Steinnes et al 2013; Wang et al 2020). These highly mobile and potentially toxic elements enter into soils mainly through anthropogenic activities such as metal-mining/smelting activities and land application of sewage sludge (Alloway 2013; Palansooriya et al.2020). It was reported that the co-contamination of Cd and Pb inhibited
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