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Salt-affected soils urgently need to be remediated to achieve the goals of carbon neutrality and food security. Limited reviews are available on biochar performance in remediating salt-affected soils in the context of carbon neutrality and climate change mitigation. This work summarized the two pathways to achieve carbon neutrality during remediating salt-affected soils using biochars, i.e., biochar production from sustainable feedstock using thermal technologies, application for promoting plant productivity and mitigating greenhouse gas (GHG) emission. Converting biomass wastes into biochars can reduce GHG emission and promote carbon dioxide removal (CDR), and collection of halophyte biomass as biochar feedstocks, development of biochar poly-generation production systems with carbon neutrality or negativity could be promising strategies. Biochar can effectively improve plant growth in salt-affected soils, showing that the grand mean of plant productivity response was 29.3%, via improving physicochemical characteristics, shifting microbial communities, and enhancing plant halotolerance. Moreover, biochar can mitigate GHG emission via inducing negative priming effect, improving soil properties, changing microbial communities associated with carbon and nitrogen cycle, direct adsorption of GHG. However, biochar also may pose negative effects on plant growth because of stress of toxic compounds and free radicals, and deterioration of soil properties. The promoted GHG emission is mainly ascribed to positive priming effect, and provision of labile carbon and inorganic nitrogen fractions as microbial substrates. Finally, this review pointed out the gaps in the current studies and the future perspectives. Particularly, the development of “carbon neutral” or “carbon negative” biochar production system, balancing the relationship of biochar effectiveness and functionality with its environmental risks and costs, and designing biochar-based GHG adsorbents would be important directions for remediating salt-affected soils to achieve carbon neutrality and abate climate change. Graphical Abstract

Biochar is a solid carbonaceous residue from biomass pyrolysis under anaerobic conditions. It has been well-known that biochar enhances plant growth and improve soil quality as the soil amendment. However, for chili (Capsicum annuum L), it is unknown whether biochar addition has any effect on its productivity. Thus, we studied the effects of different dosages of biochar addition at rates of 1.5% and 3% (w/w,1.5%BC and 3%BC) on the germination and growth of chili using a pot experiment. The results show that the 3%BC increased the weight of fresh shoots and roots by 17.4% and 14.6%, respectively. However, the addition of biochar has no pronounced effect on the chili yield. Therefore, it is very important to choose the appropriate biochar and addition proportion for its application in agricultural soils.