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Keywords:

  • land-use change;
  • llanos;
  • seasonally dry;
  • trace gases;
  • tropical soil

Abstract

The study investigates the effect of land-use change on nitrous oxide (N2O) and methane (CH4) fluxes from soil, in savanna ecosystems of the Orinoco region (Venezuela). Gas fluxes were measured by closed static chambers, in the wet and dry season, in representative systems of land management of the region: a cultivated pasture, an herbaceous savanna, a tree savanna and a woodland (control site). Higher N2O emissions were observed in the cultivated pasture and in the herbaceous savanna compared with the tree savanna and the woodland, and differences were mainly related to fine soil particle content and soil volumetric water content measured in the studied sites. Overall N2O emissions were quite low in all sites (0–1.58 mg N2O-N m−2 day−1). The cultivated pasture and the woodland savanna were on average weak CH4 sinks (−0.05±0.07 and −0.08±0.05 mg CH4 m−2 day−1, respectively), whereas the herbaceous savanna and the tree savanna showed net CH4 production (0.23±0.05 and 0.19±0.05 mg CH4 m−2 day−1, respectively). Variations of CH4 fluxes were mainly driven by variation of soil water-filled pore space (WFPS), and a shift from net CH4 consumption to net CH4 production was observed at around 30% WFPS. Overall, the data suggest that conversion of woodland savanna to managed landscape could alter both CH4 and N2O fluxes; however, the magnitude of such variation depends on the soil characteristics and on the type of land management before conversion.