Trace gas emissions from soil of the central highlands of Mexico as affected by natural vegetation: a laboratory study

In the central highlands of Mexico, mesquite (Prosopis laevigata) and huisache (Acacia schaffneri), N₂-fixing trees or shrubs, dominate the vegetation and are currently used in a reforestation program to prevent erosion. We investigated how natural vegetation or cultivation of soil affected oxidation of CH₄, and production of N₂O. Soil was sampled under the canopy of mesquite (MES treatment) and huisache trees (HUI treatment), outside their canopy (OUT treatment) and from fields cultivated with maize (ARA treatment) at three different sites while production of CO₂, and dynamics of CH₄, N₂O and inorganic N (NH₄⁺, and NO₃^–) were monitored in an aerobic incubation. The production of CO₂ was 2.3 times higher and significantly greater in the OUT treatment, 3.0 times higher in the MES treatment and 4.0 times higher in the HUI treatment compared to the ARA treatment. There was no significant difference in oxidation of CH₄ between the treatments, which ranged from 0.019 g CH₄–C kg^–1 day^–1 for the HUI treatment to 0.033 CH₄–C kg^–1 day^–1 for the MES treatment. The production of N₂O was 30 g N₂O–N kg^–1 day^–1 in the MES treatment and >8 times higher compared to the other treatments. The average concentration of NO₃^– was 2 times higher and significantly greater in the MES treatment than in the HUI treatment, 3 times greater than in the OUT treatment and 10 times greater than in the ARA treatment. It was found that cultivation of soil decreased soil organic matter content, C and N mineralization, but not oxidation of CH₄ or production of N₂O.