Pyrogenic carbon stocks and its spatial variability in soils from savanna-forest ecotone in amazon

Keywords Carbon stocks; Seasonal forests; Spatial distribution; Forest fires Highlights * In forest fragments of Northern Amazon, the pyrogenic C with size * A high variability in pyrogenic C stocks was observed at the edge of forest fragments. * Pyrogenic C stocks may be part of an in-depth discussion in the context of national C reports in Brazil. Abstract Forest fragments from Amazon are important long-term carbon (C) reservoirs with an essential role in the global C balance. They are often impacted by understory fires, deforestation, selective logging and livestock. Forest fires convert soil organic matter into pyrogenic carbon (PyC), but little is known about its distribution and accumulation along the soil profile. Thus, the objective of this study is to estimate the refractory carbon stocks derived from PyC accumulated in the soil vertical profile of different seasonal forest fragments in the Amazon. Sixty-nine soil cores (1 m deep) were collected in 12 forest fragments of different sizes considering edge and interior gradients. The mean total organic C (TOC) and PyC contents for the edge and interior gradients were 0.84% and 0.009%, respectively. The PyC/TOC ratio ranged from 0.53% to 1.78%, with an average of 1.32% and increasing in depth, being low when compared with other studies, where the contribution of PyC to TOC ranges from 1 to 9%. PyC stocks on the edge (1.04 [plus or minus] 0.04 Mg ha.sup.-1) differed significantly from the interior (1.46 [plus or minus] 0.03 Mg ha.sup.-1). The analyzed forest fragments presented a weighted PyC stock of 1.37 [plus or minus] 0.65 Mg ha.sup.-1. The vertical distribution of PyC declined in depth with 70% of PyC concentrated in the surface soil layers (0--30 cm). These results indicate that the PyC accumulated in the vertical profile of soils in forest fragments in Amazonia are important, and they need to be considered in Brazilian and global reports on carbon stocks and fluxes. Author Affiliation: (a) Institute of Agricultural Sciences, Federal of Viçosa University - Campus Florestal, Road LMG 818 Km 06, Florestal, MG, 35690-000, Brazil (b) Department of Soil Sciences (DSC), College of Agricultural Sciences, Federal University of Ceará, CE, 60356-001, Brazil (c) Department of Environmental Dynamics, Roraima Office (NPRR), National Institute for Research in Amazonia (INPA), Rua Coronel Pinto 315, 69301-150, Boa Vista, Roraima, Brazil (d) Department of Geochemistry, Fluminense Federal University, Niterói, RJ 24020-150, Brazil * Corresponding author. Libério Junio da Silva Institute of Agricultural Sciences, Federal of Viçosa University - Campus Florestal, Road LMG 818 km 06, Florestal, MG 35690-000, Brazil. Article History: Received 15 February 2023; Revised 13 April 2023; Accepted 17 April 2023 Byline: Libério Junio da Silva [liberiojunior25@gmail.com] (a,*), Dener Márcio da Silva Oliveira (a), Gabriel Nuto Nóbrega (b), Reinaldo Imbrózio Barbosa (c), Renato Campello Cordeiro (d)