Spatial variations of nitrogen trace gas emissions from tropical mountain forests in Nyungwe, Rwanda

[摘要] Globally, tropical forest soils represent the second largest source ofN₂O and NO. However, there is still considerable uncertainty on thespatial variability and soil properties controlling N trace gas emission.Therefore, we carried out an incubation experiment with soils from 31locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soilswere incubated at three different moisture levels (50, 70 and 90 % waterfilled pore space (WFPS)) at 17 °C. Nitrous oxide emission varied between4.5 and 400 μg N m⁻² h⁻¹, while NO emission varied from6.6 to 265 μg N m⁻² h⁻¹. Mean N₂O emission atdifferent moisture levels was 46.5 ± 11.1 (50 %WFPS), 71.7 ± 11.5(70 %WFPS) and 98.8 ± 16.4 (90 %WFPS) μg N m⁻² h⁻¹,while mean NO emission was 69.3 ± 9.3 (50 %WFPS), 47.1 ± 5.8 (70 %WFPS)and 36.1 ± 4.2 (90 %WFPS) μg N m⁻² h⁻¹. The latter suggests that climate (i.e. dry vs. wet season)controls N₂O and NO emissions. Positive correlations with soil carbonand nitrogen indicate a biological control over N₂O and NO production.But interestingly N₂O and NO emissions also showed a positivecorrelation with free iron and a negative correlation with soil pH (onlyN₂O). The latter suggest that chemo-denitrification might, at least forN₂O, be an important production pathway. In conclusion improvedunderstanding and process based modeling of N trace gas emission fromtropical forests will benefit from spatially explicit trace gas emissionestimates linked to basic soil property data and differentiating betweenbiological and chemical pathways for N trace gas formation.

[学科分类] 地球化学与岩石