Unprecedentedly high soil carbon stocks and their spatial variability in a seasonally dry Atlantic Forest in Brazil

There is a significant gap in the literature concerning the potential of tropical soils to stock carbon in the Brazilian Atlantic Forest biome. Furthermore, the key drivers responsible for the variability in carbon storage in tropical soils remain unknown. Therefore, experimental studies are crucial to highlight the importance of Atlantic Forests in storing organic matter, considering that forest soils are one of the most important carbon reservoirs on Earth. This study aimed: (i) to determine soil carbon stocks at the depths of 0-5 cm, 5-10 cm, 10-20 cm, 20-30 cm, 30-40 cm, 40-60 cm, and 60-100 cm in a forest fragment located in the Atlantic Forest hotspot; (ii) to describe the temporal variability of soil carbon stocks; and (iii) to identify the main biotic and abiotic drivers that influence their temporal and spatial variations. Soil carbon stocks at a 1-meter depth ranged from 201 to 396 Mg C/ha, with a spatial variability of 22.3 %. The highest accumulation of soil carbon in the 1-meter depth was in December (290.8 Mg C/ha), while the lowest was in August (246.1 Mg C/ha), highlighting the soil carbon stocks' seasonality in the Atlantic Forest. Concerning the vertical distribution, similar to 50 % of the soil carbon stocks were found in the 0-30 cm layer. The main drivers of carbon spatial distribution varied across different soil layers: (i) litterfall and long-term spatiotemporal patterns of throughfall were the primary drivers in the shallower layers (0-5 cm and 5-10 cm), while (ii) variability in tree sizes and long-term temporal dynamics of soil moisture were the main drivers in the deeper layers. Oxisols' characteristics were crucial for the unprecedently high carbon stocks observed in the deep layers (67.7 Mg C/ha). Thus, the Atlantic Forest-Oxisol association is a prominent strategy to improve carbon stocks in Brazilian tropical soils.

Automated summary

There is a lack of research on the potential of tropical soils in the Brazilian Atlantic Forest biome to store carbon. This study aimed to determine the soil carbon stocks at different depths, describe their temporal variability, and identify the main drivers that influence their variations. The results showed significant spatial and seasonal variability in soil carbon stocks, with a high accumulation in December and a low accumulation in August. The study also found that litterfall, throughfall, tree sizes, and soil moisture were important factors affecting the distribution of soil carbon.