Interactive effects of biochar addition and elevated carbon dioxide concentration on soil carbon and nitrogen pools in mine spoil

Purpose This study aimed to assess the effects of biochar on improving nitrogen (N) pools in mine spoil and examine the effects of elevated CO2 on soil carbon (C) storage. Materials and methods The experiment consisted of three plant species (Austrostipa ramossissima, Dichelachne micrantha, and Lomandra longifolia) planted in the N-poor mine spoil with application of biochar produced at three temperatures (650, 750, and 850 degrees C) under both ambient (400 mu L L-1) and elevated (700 mu L L-1) CO2. We assessed mine spoil total C and N concentrations and stable C and N isotope compositions (delta C-13 and delta N-15), as well as hot water extractable organic C (HWEOC) and total N (HWETN) concentrations. Results and discussion Soil total N significantly increased following biochar application across all species. Elevated CO2 induced soil C loss for A. ramossissima and D. micrantha without biochar application and D. micrantha with the application of biochar produced at 750 degrees C. In contrast, elevated CO2 exhibited no significant effect on soil total C for A. littoralis, D. micrantha, or L. longifolia under any other biochar treatments. Conclusions Biochar application is a promising means to improve N retention and thus, reduce environmentally harmful N fluxes in mine spoil. However, elevated CO2 exhibited no significant effects on increasing soil total C, which indicated that mine spoil has limited potential to store rising atmospheric CO2.