ABSTRACT

Deforestation and land-use change are accelerating in the Congo Basin and elsewhere in the tropics affecting the soil-atmosphere exchange of greenhouse gases (GHG). There is a lack of data from Central Africa. We quantified fluxes of CO₂, CH₄, and N₂O at the soil-atmosphere interface in a secondary forest, a cocoa agroforest, and an unfertilized cropland. Soil respiration was highest in the secondary forest (15.37 ± 3.42 Mg C ha⁻¹ y⁻¹), intermediate in the cacao agroforest (12.26 ± 2.91 Mg C ha⁻¹ y⁻¹) and the lowest in the unfertilized cropland (8.74 ± 2.62 Mg C ha⁻¹ y⁻¹). Likewise, N₂O fluxes were highest in the secondary forest (2.17 ± 0.20 kg N ha⁻¹ y⁻¹), intermediate in the cacao agroforest (1.40 ± 0.08 kg N ha⁻¹ y⁻¹) and lowest in the unfertilized cropland (1.04 ± 0.15 kg N ha⁻¹ y⁻¹). Soils were a sink for atmospheric CH₄ and sink strength was high in the secondary forest (−3.60 ± 1.83 kg CH₄ ha⁻¹ y⁻¹) and cacao agroforest (−3.61 ± 2.09 kg CH₄ ha⁻¹ y⁻¹) and low in the unfertilized cropland (−1.9 ± 1.59 kg CH₄ ha⁻¹ y⁻¹). Variation in soil water content rather than temperature was the dominant driver of seasonal variations of the fluxes at all study sites and N availability affected both N₂O and CH₄ fluxes. Our results suggest that tropical land-use change is decreasing soil respiration, decreasing the strength of the soil CH₄ sink and decreasing N₂O emissions, in landscapes that do not practice agriculture with chemical fertilization.

摘要

刚果盆地和热带其他地区的森林砍伐和土地利用变化正在加速，影响土壤-大气中温室气体的交换（GHG）。中部非洲缺乏数据。我们量化了次生林，可可农林和未耕地的土壤-大气界面处的CO ₂，CH ₄和N ₂ O通量。次生林的土壤呼吸最高（15.37±3.42 Mg C ha ^-1 y ^-1），可可杂粮林的土壤呼吸中等（12.26±2.91 Mg C ha ^-1 y ^-1），未耕地的土壤呼吸最低（8.74± 2.62 Mg C ha ^-1 y ^-1）。同样，N ₂次生林中的O通量最高（2.17±0.20 kg N ha ^-1 y ^-1），可可杂粮林中的O通量（1.40±0.08 kg N ha ^-1 y ^-1）中等，未耕地的最低（1.04±0.15） kg N ha ^-1 y ^-1）。土壤是大气中CH _4的汇聚处，次生林（−3.60±1.83 kg CH ₄ ha ^-1 y ^-1）和可可农林（−3.61±2.09 kg CH ₄ ha ^-1 y ^-1）的汇聚强度很高。且在未施肥的农田中较低（−1.9±1.59 kg CH ₄ ha ^-1 y^-1）。在所有研究地点，土壤含水量而不是温度的变化是通量季节性变化的主要驱动因素，氮的有效利用会影响N ₂ O和CH _4的通量。我们的研究结果表明，在不使用化学肥料进行农业耕作的景观中，热带土地利用变化正在减少土壤呼吸，降低土壤CH ₄汇的强度并减少N ₂ O排放。