Soil Carbon-13 Natural Abundance under Native and Managed Vegetation in Brazil

Wilcke, Wolfgang; Lilienfein, Juliane

Soil Carbon-13 Natural Abundance under Native and Managed Vegetation in Brazil

2004

Wilcke, Wolfgang | Lilienfein, Juliane

The conversion of native Cerrado vegetation (a mixed C₃ and C₄ vegetation) to Pinus caribaea Morelet plantations (a pure C₃ vegetation) and to Brachiaria decumbens stapf pastures (a pure C₄ vegetation) likely affects the C cycle. We used the natural abundance of ¹³C (δ¹³C) in vegetation and soil to: (i) quantify the contributions of C₃ and C₄ plants to the organic matter input into the soil under Cerrado vegetation and (ii) determine the degree of the replacement of original Cerrado-derived C by Pinus plantations and pastures. The mean δ¹³C value of the soils (Anionic Acrustoxes) under Cerrado vegetation ranged from −20.5 to −19.7‰, which was dissimilar to the mass-weighted mean δ¹³C signal of the aboveground biomass (−25.8‰). This was because grasses being C₄ plants contributed 11% to the aboveground biomass but about 50% of the organic matter input to the soil, which was estimated with a simple mixing model of the C₃ and C₄ ¹³C signals. After 12 and 20 yr, only 30% of the original organic matter in the topsoil was replaced by new organic matter under pasture or Pinus plantation, respectively. This turnover took place without significantly changing the C storage of the top 2 m of the soil (17–19 kg m⁻²). The C replacement under Pinus affected only the top 0.15 m. Our results demonstrate that the C replacement in soils following land-use change in the Oxisols of this study takes several decades and is considerably slower under Pinus than under pasture.

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