Lachgasemissionen aus Böden und Baumstämmen von tropischen Regenwäldern und Kakao Agroforstsystemen im Kongobecken, Kamerun
Zusammenfassung der Projektergebnisse
The conversion of forests to extensively managed, mature (>20 years old) CAF systems had no effect on stem and soil GHG emissions, because of similarities in soil moisture and texture, absence of fertilizer application, and comparable abundance of leguminous trees and basal area in both land uses. Tree stems consistently emitted N2O and CH4 throughout the measurement period. The annual total (soil + stem) N2O emissions were 1.55 ± 0.20 kg N ha^−1 yr^−1 from the forest and 1.15 ± 0.10 kg N ha^−1 yr^−1 from CAF, with tree N2O emissions contributing 11 to 38% for forests and 8 to 15% for CAF. The balance between the soil and stem CH4 fluxes indicated that there was a net CH4 sink in both land uses. The mean annual soil CH4 uptake was -2.95 ± 0.40 for the forest and -3.42 ± 0.44 for the CAF, with tree emissions offseting 6–23% of the soil sink in the forest, and 4–42% of the soil CH4 sink in the CAF. 2% of our measured trees were “hot spots” of CH4 emission, with two orders of magnitude larger emissions than the remaining trees in our sites. These substantial contributions of tree stems to total N2O and CH4 fluxes highlight the importance of including tree-mediated fluxes in ecosystem GHG budgets. Annual soil CO2 emissions were 10.1 ± 0.27 Mg C ha^−1 yr^−1 for the forest, and 10.3 ± 0.42 Mg C ha^−1 yr^−1 for the CAF. In contrast to findings from other studies, stem N2O and CH4 emissions did not differ among the different tree species in our study, which supported our spatial extrapolation based on diameter at breast height (DBH) of trees in our sites. N-isotope tracing from soil mineral N to stem-emitted 15N2O and correlations between stem and soil N2O, vapour pressure deficit and other drivers suggest that stem-emitted N2O originated predominantly from the soil. Our results also points a possible soil origin of tree stem CH4 emissions, driven by transpiration. Considering the biophysical conditions of our forest sites, which represented two-thirds of the Congo Basin, our extrapolated emissions from the Congo Basin rainforest area were 0.18 ± 0.05 Tg N2O-N yr^−1 and -0.28 ± 0.04 Tg CH4-C yr^−1. As many of the studied trees had buttresses, we measured stem emissions at trunk heights of 1.3 m above the ground, leaving an open question about lower stem N2O and CH4 emission rates. Our measurements of decreasing stem N2O and CH4 emissions with increasing tree height suggest that there may be high emissions occurring at lower tree height, and possibly an underestimation of tree stem emissions from this important tropical region. Further research efforts are necessary to provide additional insights into mechanisms of stem N2O and CH4 production and magnitudes, in order to improve regional and global GHG budget estimations.
Projektbezogene Publikationen (Auswahl)
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2019. Changes in soil organic carbon and nutrient stocks in conventional selective logging versus reduced-impact logging in rainforests on highly weathered soils in Southern Cameroon. Forest Ecology and Management, 451, p.117522
Lontsi, R.T., Corre, M.D., van Straaten, O. and Veldkamp, E.
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2020. Soil greenhouse gas fluxes following conventional selective and reduced-impact logging in a Congo Basin rainforest. Biogeochemistry, 151(2), pp.153-170
Lontsi, R.T., Corre, M.D., Iddris, N.A. and Veldkamp, E.
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2020. Stem and soil nitrous oxide fluxes from rainforest and cacao agroforest on highly weathered soils in the Congo Basin. Biogeosciences, 17(21), pp.5377-5397
Iddris, N.A.A., Corre, M.D., Yemefack, M., van Straaten, O. and Veldkamp, E.
