Soil carbon stocks of Ultisols under different land use in the Atlantic rainforest zone of Brazil

Reforestation has a great potential on soil carbon sequestration resulting from continuous deposition of plant residues above- and belowground. The purpose of this study was to answer the following questions: (1) did reforestation with 35 years old rubber tree plantation and 3 and 5 years old eucalyptus plantations enhance SOC accumulation up to 1 m depth? (2) How much did the conversion of forest into pasture changed the origin of SOC accumulated up to 1 m depth? (3) How much did the conversion of pasture into eucalyptus plantation changed the origin of SOC accumulated up to 1 m depth? The experimental area in this study was: 3-year-old eucalyptus plantation; 5-year-old eucalyptus plantation; 35-year-old rubber tree plantation and 50-year-old unfertilized pasture. SOC was determined by dry combustion in six layers (0-10, 10-20, 20-40, 40-60, 60-80 and 80-100 cm). The natural abundance of C-13 technique was used to determine the relative contributions of C3 and C-4 plants derived C to the total SOC accumulated up to 100 cm. Rubber tree showed significantly higher SOC stock (219 Mg ha(-1)) at a depth of 0-100 cm. Pasture (176Mg C ha(-1)) and 3 (148Mg C ha(-1)) and 5 years old (160Mg C ha(-1)) eucalyptus plantations had smaller C stocks and were similar to secondary forest (168 Mg C ha(-1)) and there was a narrow variation of SOC storage over the soil profile. The differences in delta C-13 valueswere more pronounced in the upper soil layers and below 40 cm these differences progressively decreased until a very small delta C-13 variation up to 100 cm. Rubber tree plantation, compared to secondary forest, enhanced around 46 Mg ha(-1) the SOC stored up to 1 m depth and 2 year old gap between the two eucalyptus plantations was enough to enhance the SOC accumulation in 14 Mg ha(-1). The accumulation of SOC decreased slightly from 40 to 100 cm. 50 years after the conversion of forest into pasture allowed the incorporation around 33 Mg ha(-1) of C-4-derived C up to 100 cm and around 14% of SOC accumulated in eucalyptus plantations was C-4-derived C up to 100 cm. The accumulation of SOC in all vegetable covers is still derived from the previous vegetation at a depth deeper than 60 cm. (c) 2016 Published by Elsevier B.V.