The impact of fast-growing eucalypt plantations on C emissions in tropical soil: effect of belowground and aboveground C inputs

Planted forest soils can have great potential for CO 2 -C sequestration, mainly due to belowground C inputs, which impact deep soil C (DSC) accumulation. However, there are still gaps in understanding the CO 2 emission dynamics in eucalypt plantations. Therefore, we used isotopic techniques to investigate the dynamics of the soil surface CO 2 -C flux and CO 2 -C concentration with depth for a eucalypt plantation influenced by different C inputs (above- and belowground). The gas evaluations were carried in depth the root to valuation of root priming effect (RPE) was calculated. In addition, measurements of the plant (C-fine root and C-litterfall) and soil (total organic carbon – TOC, total nitrogen – TN, soil moisture – SM, and soil temperature – ST) were performed. After planting the eucalypt trees, there was an increase in the soil surface CO 2 -C flux with plant growth. Root growth contributed greatly to the soil surface CO 2 -C flux, promoting greater surface RPE over time. In comparison to the other factors, SM had a greater influence on litterfall decomposition and root respiration. It was not possible to detect losses in TOC and TN in the different soil layers for the 31-month-old eucalypt. However, the 40-month-old eucalypt showed a positive RPE with depth, indicating possible replacement of DSC (“old C”) by rhizodeposition-C (“new C”) in the soil. Thus, in eucalyptus plantations, aboveground plant growth influences CO 2 emissions on the soil surface, while root growth and activity influence C in deeper soil layers. This information indicates the need for future changes in forest management, with a view to reducing CO 2 emissions.