Soil Processes and Climate Solutions: From Carbon Cycling to Climate-Smart Land Management

Soil water availability governs both the assimilation of carbon by terrestrial vegetation and its return to the atmosphere through microbial decomposition, yet the two limbs of this control operate through different mechanisms, on different timescales and with different degrees of empirical support. Intensifying drought, more frequent compound dry and hot extremes, and the sharper wetting events that accompany a more intense hydrological cycle have moved soil moisture from a secondary environmental variable to a first-order determinant of the terrestrial carbon balance. This critical narrative review examines how drought and subsequent rewetting jointly shape the persistence of soil organic carbon and the strength of the land carbon sink, and evaluates whether current evidence supports the confident projections of moisture-driven carbon loss that increasingly appear in the literature. Sources were identified through structured searching of open scholarly databases and indexes, supplemented by backward and forward citation tracking, with critical appraisal directed at measurement scale, attribution strategy, temporal coverage and geographical representation. Four findings emerge. First, the suppression of heterotrophic respiration by drying and its stimulation by rewetting are asymmetric, so that the net carbon consequence of a dry–wet sequence depends on the antecedent moisture history, soil texture and event timing rather than on drought severity alone. Second, competing mechanistic explanations of the rewetting pulse remain only partially reconciled, and the microbial and physical hypotheses are not mutually exclusive. Third, ecosystem-scale attribution of carbon anomalies to soil moisture is confounded by the tight coupling between soil dryness, atmospheric demand and temperature, and different statistical treatments of this coupling yield materially different partitionings. Fourth, model projections of moisture-driven soil carbon loss remain sensitive to the choice of an empirical moisture response function that observations do not yet constrain. Confidence is highest for short-term flux responses and lowest for decadal changes in soil carbon stocks. Priorities include long-duration manipulations that impose realistic wetting sequences, coordinated measurement in tropical and dryland regions where observational coverage is sparse, and model evaluation against moisture-dependent flux behaviour rather than against mean stocks alone.