Tree plantations on a grassland region: effects on methane uptake by soils

We assessed the rates of methane uptake (CH₄) by soils of different tree plantations and a control to provide information regarding potential greenhouse gas sequestration by tree plantations of pines, mixed deciduous species and eucalyptus in a natural grassland around 37S, 59W (Argentinean Pampa). A naturalized pasture was used as control. All sites had been agricultural and livestock lands. Each site was sampled three times from December 2012 to May 2013, using five static chambers randomly distributed across an area of ~100 m² in each site. In the control, methane fluxes were very weak; both negative (uptake) and positive (emission) values were found. Below tree plantations, fluxes were always negative, with statistically significant intersite differences. The highest uptake rates were observed in the mixed deciduous plantation (~10 ng m^?2 s^?1), followed by pines and eucalyptus plantations. Intrasite differences associated with spatial variation were also found. A significant inverse correlation between CH₄ uptake and soil water content was found in the pine and deciduous species plantations (R² > 0.94, p < 0.1).