Assessing the potential of using biochar in mine rehabilitation under elevated atmospheric CO2 concentration

Purpose Re-establishment of soil nitrogen (N) capital is a priority in mine rehabilitation. We aimed to evaluate the effects of biochar addition on improving mine spoil N pools and the influence of elevated CO2 concentration on mine rehabilitation. Materials and methods We assessed the effects of pinewood biochar, produced at three temperatures (650, 750 and 850 °C, referred as B650, B750 and B850, respectively), on mine spoil total N concentrations with five different plant species, including a tree species (Eucalyptus crebra), N-fixing shrubs (Acacia floribunda and Allocasuarina littoralis) and C3 and C4 grasses (Austrodanthonia tenuior and Themeda australis) incubated at ambient (400 μL L−1 ) and elevated (700 μL L−1 ) atmospheric CO2 concentrations, as well as the effects of elevated CO2 on mine rehabilitation. Results and discussion Soil total N significantly improved following biochar incorporation under all plant species (P < 0.05) except for T. Australis. E. crebra had the highest soil total N (0.197%, 0.198% and 0.212% for B650, B750 and B850, respectively). Different from the negligible influence of elevated CO2 on soil properties under the grasses and the Nfixing shrubs, elevated CO2 significantly increased soil water and hot water extractable organic C (WEOC and HWEOC, respectively) and decreased total C under E. crebra, indicating that the nutrient demands were not met. Conclusions Biochar addition showed the potential in mine rehabilitation in terms of improving soil N pool, especially with E. crebra. However, it would be more difficulty to rehabilitate mine spoils in future with the rising atmospheric CO2 concentration