Impacts of MnO2 on tomato (Lycopersicon esculentum Mill.) growth: A study with MnO2-amended organic fertilizer

Manganese dioxide (MnO 2 ), as a catalyst in composting processes, can accumulate in soil over multiple fertilization. However, its impact on crop growth remains to be explored. In this study, a pot experiment was conducted to investigate the impacts of MnO 2 on the tomato plant performance across various growth stages. Results showed that MnO 2 reduced the plant height, leaf number and length by 35.53 %, 27.61 %, and 37.00 %, respectively, and decreased the fruit weight (23.16 %) and sugar-acid ratio (29.7 %) of fruits compared to the MnO 2 -free control. The adverse impacts of MnO 2 on plant growth might be attributed to the inhibition of microbial activity in soil reflected by the reduction of soil urease (9.30 %) and acid phosphatase (12.52 %) activities, which decreased the efficiency of nutrients conversion and uptake. The decrease of nutrient elements in roots resulted in oxidative stress in the plant, inhibiting the plasma membrane H + -ATPase activity thereby reducing the translocation of nutrients (e.g., calcium, magnesium, and phosphorus) translocation from roots to leaves. Furthermore, the phytohormones indolebutyric acid, gibberellin, and jasmonic acid of leaves were disturbed. This study reveals the risks associated with the application of MnO 2 -containing organic fertilizers.