Soil texture and management jointly control the Birch effect under repeated drying–rewetting cycles

Climate projections predict an increase of frequency and/or intensity of extreme precipitation and drought events in temperate agroecosystems, leading to more pronounced drying–rewetting cycles (DWC). These moisture fluctuations trigger pulses of CO2 emissions from soil microbial activity—the Birch effect—which may destabilize soil organic carbon (SOC) stocks. However, large variability in the magnitude of this effect persists across studies, suggesting a strong influence of soil properties and land management, as well as methodological differences (e.g. lack of continuous CO2 measurement, inconsistent controls).

We addressed this issue through a controlled incubation of undisturbed soil cores from three French agricultural sites with contrasting textures (sandy, loamy, clayey) and management (conventional cropping, organic farming, conservation agriculture, permanent grassland). Soils were subjected to (i) five successive temperate DWC (1 week drying, 1 week rewetting, 70 days), (ii) five successive semi-arid DWC (6 weeks drying, 1 week rewetting, 245 days) and (iii) a constant moisture control. For each texture and management, the water content of the control was set to the mean value calculated over the temperate DWC. CO2 fluxes were monitored continuously, including during drying phases, enabling unbiased comparison of cumulative SOC mineralization across moisture regimes.

For both temperate and semi-arid scenarios, all soils showed pronounced CO₂ pulses upon rewetting, with declining amplitudes across successive cycles and strong modulation by soil texture and management. Relative to the constant-moisture control over the 70-day incubation, temperate DWC increased cumulative SOC mineralization for loamy soils managed conventionally and organically, and in sandy soils under permanent grassland. These differences were primarily explained by soil texture and water retention properties, with management effects depending on their interaction with clay content. Prolonged drought did not systematically increase SOC mineralization, indicating a context-dependent saturation of the Birch effect. Microbial biomass generally declined under longer droughts, whereas the metabolic quotient—defined as the ratio of cumulative mineralization during the last rewetting to final microbial biomass—increased with drought duration, except in grassland soils.

These results indicate a buffering effect of finer-textured and structurally stable soils, consistent with a joint biotic–abiotic control of the Birch effect shaped by soil texture and its interaction with land management. Recurrent DWC may progressively deplete labile SOC and destabilize protected SOC pools, with implications for SOC persistence under future climates. More mechanistic understanding is needed to improve predictions across soils, land uses, and management systems, and to integrate these dynamics into SOC models.

Keywords Drying–rewetting cycles ; Birch effect ; Soil texture ; Land use ; Agricultural management; Carbon mineralization ; Soil organic carbon; Climate change.