Can Addition of Biochar and Zeolite to a Contaminated Calcareous Soil Mitigate the Pb-toxicity Effects on Spinach (Spinacia Oleracea L.) Growth?

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ABSTRACT Recently, the use of biochar for remediation of agricultural soils polluted with heavy metals to reduce their toxicity for plants has been expanded. This study aims to evaluate the impact of biochars and zeolite on the biochemical composition of spinach (Spinacia oleracea L.) grown in a Pb-contaminated calcareous soil under greenhouse conditions as completely randomized design. The first factor consists of biochars (without biochar application (CL), green compost (GB), municipal solid waste (MB) and poultry manure (PB) each at 3% (w/w)), and the second factor included zeolite levels (without zeolite application (Z0), 2% (w/w) (Z1) and 4% (w/w) (Z2)). With increasing the zeolite levels, shoot dry matter (3.1 fold), content of chlorophyll a (33.3%), chlorophyll b (37.0%), carotenoids (30.1%), and nutrients uptake (Zn (3 fold), Cu (3.3 fold), Fe (3 fold), Mn (3.7 fold), P (2.9 fold) and K (3.2 fold)) by spinach were significantly enhanced while the enzymes activity (catalase and peroxidase) and Pb concentration (2.9 fold) were reduced significantly. Among the biochars, the MB treatment was the best due to the highest increase in shoot dry matter (57.4%) and nutrients uptake (Zn, Cu, Fe, Mn, P and K) compared to the control. However, it had the lowest Pb concentration and catalase enzyme. Finally, it could be concluded that addition of biochar and zeolite to Pb-polluted calcareous soils can mitigate the Pb-toxicity effects on spinach growth through the reduction of Pb concentration, activity of antioxidant enzymes, and enhancement of the nutrients absorption.