Author(s)

Jean Dalmo de Oliveira Marques^1*, Flávio Jesus Luizão², Wenceslau Geraldes Teixeira³, Euler Melo Nogueira², Philip Martin Fearnside², Max Sarrazin⁴

¹Federal Institute of Education, Science and Technology of the Amazonas (IFAM), Campus Center of Manaus, Manaus, Brazil.
²National Institute for Research in Amazonia (INPA), Manaus, Brazil.
³National Center for Soil Research, Brazilian Agricultural Research Corporation (EMBRAPA), Rio de Janeiro, Brazil.
⁴IRD, UMR BIOEMCO, Route de Montabo, Cayenne Cedex, French Guiana.

Transformations of natural ecosystems in tropical regions, which are usually covered by high-biomass forests, contribute to increased atmospheric CO2. Much of the carbon in forest ecosystems is stored in the soil. This study estimates soil carbon stock in a dense forest in central Amazonia from sets of soil samples collected in three topographic positions (plateau, slope and valley bottom). Soil organic matter (SOM) was fractionated by density and particle size, thus obtaining the free light fraction (FLF), intra-aggregated light fraction (IALF), sand fraction (F-sand), clay fraction (F-clay) and silt fraction (F-silt). Soil organic carbon (SOC) stocks on the plateaus (Oxisol), slopes (Ultisol) and valley bottoms (Spodosol) were 98.4 ± 7.8 Mg·ha^-1, 72.6 ± 5.4 Mg·ha^-1 and 81.4 ± 8.9 Mg·ha^-1, respectively. Distribution of carbon in soil fractions was: 112.6 ± 15 Mg·ha^-1 (FLF), 2.5 ± 0 Mg·ha^-1 (ILAF), 40.5 ± 1.5 Mg·ha^-1 (F-silt), 68.5 ± 4.2 Mg·ha^-1 (F-clay) and 28.3 ± 1.4 Mg·ha^-1 (F-sand), totaling 252.4 ± 22.1 Mg·ha^-1 of carbon. Carbon is largely in labile form and near the soil surface, making it liable to release from deforestation or from climate change. Spodosols are more susceptible to soil carbon losses, demonstrating the need to preserve forested areas close to Amazonian rivers and streams.

Fractionation of Carbon, Carbon Stocks, Soil Physics, Global Warming, Amazon Rainforest, Brazil

de Oliveira Marques, J. , Luizão, F. , Teixeira, W. , Nogueira, E. , Fearnside, P. and Sarrazin, M. (2017) Soil Carbon Stocks under Amazonian Forest: Distribution in the Soil Fractions and Vulnerability to Emission. Open Journal of Forestry, 7, 121-142. doi: 10.4236/ojf.2017.72008.