Spatio-Temporal variability of CO2 efflux from stony soil under a seasonally dry tropical forest

Abstract

Quantifying the variability of soil CO₂ efflux (SCE) in stony soils, such as the Leptosol of the Brazilian semi-arid region is essential to obtain accurate measurements of SCE and improve its global estimate. The objective of our study was to assess the temporal and spatial variability of the SCE in a Caatinga forest. The SCE was measured at 42 randomly selected sampling points in a 0.72 ha plot. The average SCE varied from 0.47 to 4.14 μmol of CO₂ m⁻² s⁻¹ in a dry and wet season, respectively. The temporal variability of SCE is explained by 93 % volumetric soil water content, while soil temperature explained 52 % independently. The non-linear relationship between volumetric soil water content and soil temperature explains 87 % of the variability. The autocorrelation spatial distance of SCE oscillated from 5.7 to 64.3 m and was smaller during the wet season. The spatial variability of SCE is related to SOC, C:N, pH, clay, volumetric soil water content, and soil temperature, but the type of relationship differs with season. The temporal variability of SCE is mainly controlled by the volumetric soil water content. To quantify SCE, a distance between points greater than 64.3 m must be adopted for the measurements to be considered statistically independent. Individually, soil attributes and environmental variables explain some SCE spatial variability, especially in the dry season. Landscape heterogeneity linked to rock fragments, Leptosols, and microtopography modulates SCE by altering moisture, temperature, and organic matter. Given the complexity of these interactions, future studies should account for such variability in Caatinga stony soils.