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

• 35-year-old rubber tree stored 46 Mg ha-1 of SOC more than the secondary forest.
• 2 year old gap between two eucalyptus plantations enhanced SOC in 14 Mg ha-1.
• Below 60 cm SOC storage in all systems is still derived from previous vegetation.

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 13C technique was used to determine the relative contributions of C3 and C4 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 (176 Mg C ha− 1) and 3 (148 Mg C ha− 1) and 5 years old (160 Mg 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 δ13C values were more pronounced in the upper soil layers and below 40 cm these differences progressively decreased until a very small δ13C 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 C4-derived C up to 100 cm and around 14% of SOC accumulated in eucalyptus plantations was C4-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.