Remediation of multi-metal contaminated soil using cow dung and its biochar: Effects on heavy metal uptake and soil microbiome in Triticum aestivum L

Multi-metals contamination in agriculture soil poses a significant challenge, threatening wheat quality. The effects of cow dung (CD) and cow dung biochar (CDB) applied to contaminated soil on heavy metal (HM) uptake and microbial diversity in wheat were tested with pot experiment. CD and CDB applications reduced soil Cd/Zn ratio by 30% and inhibited Cd uptake by wheat roots. Compared to the CK, CD doses of 0.5%, 1%, and 2% reduced Cd content in grains by 12.7%, 37.0%, and 35.3%, respectively, and CDB doses of 0.05%, 0.1%, and 0.2% reduced it by 16.7%, 27.7%, and 51.9%, respectively. CD and CDB changed the HM fraction distribution in the soil and reduced the proportion of acid-extractable and Fe-Mn oxidized fractions. The significant negative correlation between the acid-extractable fractions of Cd and Pb in soil and pH, confirming that increased pH reduces the acid-extractable fraction of HMs in soils. CD reduced the α-diversity of soil microorganisms, but the total number of edges, nodes, and microbial taxa positive correlation ratio increased by 168%, 34.5%, and 9.97%, respectively, resulting in more complex and tightly packed soil microbial network structure. Signature microorganisms such as Alphaproteobacteria , Mycobacterium spp . and Rhizobium spp. appeared in 1% and 2% of the dosage CD treatments, furthermore the abundance of metabolism-related genes such as amino acid synthesis, organic matter metabolism and citrate cycle were upregulated, which was favorable for soil nutrient cycling and transformation. Applying CD can mitigate wheat HMs uptake, improving crop safety and soil health and promoting eco-friendly agricultural practices. • Increasing soil pH is the main mechanism for HMs immobilization by cow dung-based amendments • Cow dung and its biochar improve rhizosphere microbes and inhibit HMs transfer from soil to wheat • Cow dung increases microbial genes for wheat HMs detoxification • The addition of zinc introduced by cow dung and its biochar forms competitive adsorption of zinc with cadmium, inhibiting cadmium uptake by wheat.