Response of soil enzyme activity, microbial community and root exudates in wheat rhizosphere to copper hydroxide...

Despite growing evidence regarding the effects of copper hydroxide (Cu(OH)₂) nanopesticides on soil microbes and enzyme activity, its effects on root exudates, microbial communities and enzyme activities at the plant-soil interface remain unclear. This study investigated alterations in enzyme activities, root exudates and bacterial communities in wheat rhizosphere soil treated with a commercial Cu(OH)₂ nanopesticide formulation (NPF), its nanosized active ingredient (AI), or its ionic analog (CuSO₄). At 70 mg/kg Cu, representing short-term use, the changes in enzyme activity were negligible. At 500 mg/kg Cu, representing long-term accumulation, NPF, AI and CuSO₄ increased fluorescein diacetate hydrolase activity, reduced N-acetylglucosaminidase and leucine aminopeptidase activities, and had minimal effects on urease activity. These treatments also affected the root exudation profiles, increasing the excretion of benzoxazinoids and chemoeffectors such as xanthine. Furthermore, microbial diversity decreased, whereas the relative abundance of metal-tolerant and nitrogen-cycling bacteria, including Brevundimonas and Cupriavidus, increased. Correlation analysis suggested that the modified exudation patterns under Cu(OH)₂ nanopesticide exposure may facilitate the recruitment of these bacteria, which may impact soil enzyme activity. Notably, in the NPF treatment, this response was predominantly triggered by the nanosized Cu(OH)₂. These findings highlight the potential long-term ecological effects of Cu(OH)₂ nanopesticides at the soil-plant interface.