Soil CO 2 concentration, efflux, and partitioning in a recently afforested grassland

Relatively few studies have documented the impacts of afforestation, particularly production forestry, on belowground carbon dioxide (CO 2 ) effluxes to the atmosphere. We evaluated the changes in the soil CO 2 efflux—a proxy for soil respiration (Rs)—for three years following a native grassland conversion to eucalypt plantations in southern Brazil where minimum tillage during site preparation created two distinct soil zones, within planting row (W) and between-row (B). We used root-exclusion and carbon (C)- isotopic approaches to distinguish Rs components (heterotrophic-Rh and autotrophic-Ra respirations), and a CO 2 profile tube (1-m deep) to determine the concentration ([CO 2 ]) and isotopic C signature of soil CO 2 (δ 13 [CO 2 ]). The soil CO 2 efflux in the afforested site averaged 0.37 g CO 2 m −2 h −1 , which was 56% lower than the soil CO 2 efflux in the grassland. The δ 13 CO 2 in the afforested site ranged from − 14.1‰ to − 29.4‰, indicating a greater contribution of eucalypt-derived respiration (both Rh and Ra) over time. Higher soil CO 2 efflux and lower [CO 2 ] were observed in W than B, indicating that soil preparation creates two distinct soil functional zones with respect to C cycling. The [CO 2 ] and δ 13 [CO 2 ] decreased in both zonal positions with eucalypt stand development. Although the equilibrium in C fluxes and pools across multiple rotations is needed to fully account for the feedback of eucalypt planted forests to climate change, we provide quantitative information on soil CO 2 dynamics after afforestation and show how soil preparation can leverage the feedback of planted forests to climate change.