Spatial variability of soil respiration in Archaeological Dark Earth areas in the Amazon

In natural ecosystems, soil respiration is one of the important components of carbon emission into the atmosphere – CO2 efflux. Soil CO2 efflux has both temporal (due to temperature and moisture changes) and spatial variability, which can be explained by different types of soil, soil use and management, as well as the influence of vegetation on CO2 efflux. The aim of this study was to measure the spatial variability of soil CO2 efflux, soil temperature and soil moisture in areas of archaeological dark earth cultivated with the guandu bean (GB) and pasture (PT), compared to soil use in natural forests (NF) in Amazonas state, Brazil. To that end, regular meshes were marked out in areas of forest (6×6m spacing), guandu bean (4×5m spacing) and pasture (8×8m spacing) measuring 2500m2, 1700m2 and 4800m2, respectively, with 88 sample points georeferenced in each area. Soil CO2 efflux (FCO2) and soil temperature (ST) were measured at the intersection points of the meshes, and soil samples were collected at a depth of 0.00–0.10m to determine soil moisture (SM) in the laboratory. FCO2 measurements were taken using LI-6400 systems. Soil temperature (ST) was measured at 0.00–0.10m, using a portable thermistor thermometer, and soil moisture (SM) using soil samples collected at 0.00–0.10m. FCO2 and ST were lower in the forest area, with higher SM content, no difference between FCO2 and ST in GB and PT, but with lower SM content in PT. The models of the experimental semivariogram were predominantly spherical, except for FCO2 in the NF and GB areas, and SM in the PT area, which were fit to the exponential model. The maps of spatial distribution patterns indicate a trend in concentration, with a positive correlation between FCO2 and SM and negative correlation between FCO2 and ST in natural forest. Positive correlations were observed between FCO2 and ST and SM in GB, but in PT, FCO2 correlations were restricted to SM.