Table 1_Biochar raises soil health and reduces greenhouse gas emissions in arid lands.docx

Biochar is increasingly recognized as a multifunctional amendment capable of restoring soil health and mitigating greenhouse gas (GHG) emissions, particularly in arid and semi-arid regions, where fragile soils, high salinity, and erratic moisture regimes exacerbate climate vulnerability. Despite the growing global interest, only ~3% of biochar studies target arid lands, leaving a critical knowledge gap in understanding its mechanisms under harsh edaphoclimatic conditions. This review synthesizes over 120 studies and provides a meta-analysis on the interplay between soil and biochar properties affecting GHG fluxes in arid agroecosystems. Biochar reduces CO2, CH4, and N2O emissions in non-arid climates by −18%, −38%, and −40%, respectively, relative to unamended control soils, though the effects are less pronounced in arid and semiarid lands (-8%, -21%, and -33%, respectively), modulated by soil and biochar physico-chemical properties, as well as application rates. The meta-analysis revealed that the reduction in CO2 emissions by biochar was significantly different between non-arid and arid or semiarid climates (P < 0.05); however, this was not the case for CH4 and N2O. Specifically, biochars are characterized by a high surface area and large porosity, enhancing soil aeration and oxygen diffusion while buffering soil pH. Together, these properties create conditions that favor nitrification over denitrification, and suppress N2O formation, reduce methanogenesis, and promote CH4 oxidation. Similarly, increased aeration and redox modulation reduce methanogenesis and increase CH4 oxidation, particularly in sandy and saline soils. The inherent long-term stability of biochar organic carbon (C) plays a central role in the long-term C retention in soils. Microbial responses, such as the expression of functional genes, enzyme activities, and the archaeal-to-bacterial ammonia oxidizer ratio, serve as key bioindicators for tracking the performance of biochar in reducing GHG emissions. Our synthesis provides a mechanistic and data-driven framework to inform biochar use in arid agroecosystems, supporting a shift toward circular, climate-smart land management in some of the world’s most sensitive landscapes.