Gharahi Ghehi, N., Werner, C.,
Cizungu Ntaboba, L., Mbonigaba Muhinda, J. J., Van Ranst, E.,
Butterbach-Bahl, K., Kiese, R., and Boeckx, P.: Spatial variations of
nitrogen trace gas emissions from tropical mountain forests in Nyungwe,
Rwanda, Biogeosciences, 9, 1451-1463, doi:10.5194/bg-9-1451-2012, 2012.
Abstract.
Globally, tropical forest soils represent the second largest source of
N2O and NO. However, there is still considerable uncertainty on the
spatial variability and soil properties controlling N trace gas emission.
Therefore, we carried out an incubation experiment with soils from 31
locations in the Nyungwe tropical mountain forest in southwestern Rwanda. All soils
were incubated at three different moisture levels (50, 70 and 90 % water
filled pore space (WFPS)) at 17 °C. Nitrous oxide emission varied between
4.5 and 400 μg N m−2 h−1, while NO emission varied from
6.6 to 265 μg N m−2 h−1. Mean N2O emission at
different 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 carbon
and nitrogen indicate a biological control over N2O and NO production.
But interestingly N2O and NO emissions also showed a positive
correlation with free iron and a negative correlation with soil pH (only
N2O). The latter suggest that chemo-denitrification might, at least for
N2O, be an important production pathway. In conclusion improved
understanding and process based modeling of N trace gas emission from
tropical forests will benefit from spatially explicit trace gas emission
estimates linked to basic soil property data and differentiating between
biological and chemical pathways for N trace gas formation.
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