Dose-dependent Responses of Soil Enzyme Activities and Zinc Availability to Zinc Oxide Nanoparticles in Acidic Tea Plantation Soil
1Debajit Saikia2*, Pradip Kumar Baruah², Satya Ranjan Sarmah³, and Shafiqul I. Bhuyan4*
1Department of Botany, University of Science and Technology Meghalaya (USTM), Ri-Bhoi, Techno City, Killing Road, Baridua - 793101 (India) 2Department of Botany, CNB College, Bokakhat, Golaghat - 785612 (India) 3Department of Mycology and Microbiology, Tocklai Tea Research Institute, Cinnamara, Jorhat - 785008 (India) 4Department of Botany, Pandit Deendayal Upadhayay Aadarsha Mahavidyalaya, Behali Rotowa, Biswanath - 784184 (India) *Corresponding Authors : Debajit Saikia: debajitsaikia79@gmail.com Shafiqul I. Bhuyan: safibhuyan@gmail.com
ABSTRACT
Zinc oxide nanoparticles (ZnO-NPs) are increasingly explored as alternative zinc inputs in agriculture; however, their influence on soil biochemical functioning in acidic, perennial plantation systems remains poorly constrained. This study examined the concentration- and timedependent responses of selected soil enzymes and zinc availability following ZnO-NP amendment in acidic tea plantation soil under controlled incubation conditions. Non-sterile sandy loam soil was amended with ZnO-NPs at 150, 300, and 450 mg kg-1 soil and incubated for 14 and 30 days. Dehydrogenase, urease, and phosphatase activities were quantified as functional indicators of microbial oxidative metabolism and nitrogen and phosphorus transformation processes, while DTPAextractable zinc was measured as an operational index of bioavailable Zn. ZnO-NP amendment produced enzyme-specific and non-linear responses. Dehydrogenase activity was significantly lower in all ZnONP-treated soils compared with the untreated control, indicating reduced microbial oxidative activity, with the greatest suppression observed at the intermediate ZnO-NP concentration. Urease activity was not significantly affected by ZnO-NP treatment and varied primarily with incubation time, indicating limited responsiveness within the tested concentration range. Phosphatase activity showed pronounced treatment- and time-dependent variation, displaying a non-monotonic response across ZnO-NP concentrations