This study determined the physical granulometric fractionation evaluated the mineralizable carbon within and around forest fragments of the Atlantic Forest biome located in the state of Paraná. Soil samples were collected at three three internal points of the fragments: the edge (E), the half radius (HR) and the center (CF); and one point in no-tillage system (NTS) areas around the fragments, in four replicates. The contents of total organic carbon (TOC), particulate fraction carbon (C-POM) and mineral fraction (C-MOM) were determined, and the %POM and %MOM and the stocks of POM (StockPOM) and MOM (StockMOM) were calculated, in addition to the indices: carbon stock index (CSI), lability (L), lability index (LI) and carbon management index (CMI), also evaluating CO2 emission, daily and accumulated. The highest TOC levels were observed in the CF point. The highest C-POM contents were observed in the E and CF points of fragment 1, in the CF point of fragment 2, and the highest C-MOM contents were expressed in the CF points of both fragments. CMI showed a distinct pattern among the fragments. The NTS areas showed lower C-CO2 emissions, with 39.8% and 28.3% less total emission compared to CF. The results of physical granulometric fractionation show the CF point favors the quality of SOM and the mineralizable carbon analysis indicated that the conversion of native areas into NTS compromises soil microbial activity.

No abstract

No abstract

No abstract

Conversions of natural vegetation into pasture can, in a short time, change the carbon stock and the natural abundance of δ13C in the soil. The objective of this study was to evaluate changes in carbon (C) and nitrogen (N) stocks, as well as in the natural abundance of δ13C and δ15N of Argissolo Vermelho distrófico (Acrisol), in an area of natural vegetation and planted pasture in the Cerrado region of Aquidauana (MS), Brazil. In order to do this, an area of pasture (PA), cultivated for 25 years with Urochloa brizantha, and an area of natural vegetation (NV) were evaluated. Soil samples were collected at intervals of 0.05 m up to 0.60 m depth, and physical attributes, C and N stocks (CSt and NSt) and isotopic variations of δ13C and δ15N of soil were determined. In the 0–0.05 m layer, the highest C and N stocks occurred in NV, 21.99 and 1.9 Mg ha-1, respectively. In the conversion to PA, 14.62 Mg ha-1 of CSt and 1.36 Mg ha-1 of NSt were lost in the 0–0.05 m layer. The area with PA had greater isotopic enrichment of δ13C in the layers of 0–0.05 and 0.05–0.10 m, with values of -18.3 and -17.4‰, respectively, while in the other layers the isotopic values decreased with the mixture between C of C3 and C4 plants. NV showed enrichment in the isotopic signals, in the layers from 0.25–0.30 m up to 0.40–0.45 m, with values between -21.74 and -21.54‰, respectively, which is characteristic of mixed vegetation of C3 and C4 plants. The values of δ15 N showed isotopic enrichment as depth increased, indicating greater mineralization of soil organic matter in both areas. The conversion of Cerrado into pasture and its consequent fragmentation causes negative impacts on the C and N sequestration and storage capacity, both in pasture and in natural vegetation.