Biochar raises soil health and reduces greenhouse gas emissions in arid lands

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 CO 2 , CH 4 , and N 2 O 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 CO 2 emissions by biochar was significantly different between non-arid and arid or semiarid climates (P < 0.05); however, this was not the case for CH 4 and N 2 O. 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 N 2 O formation, reduce methanogenesis, and promote CH 4 oxidation. Similarly, increased aeration and redox modulation reduce methanogenesis and increase CH 4 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.