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Stem and soil nitrous oxide fluxes from rainforest and cacao agroforest on highly weathered soils in the Congo Basin
Biogeosciences ( IF 4.9 ) Pub Date : 2020-11-10 , DOI: 10.5194/bg-17-5377-2020
Najeeb Al-Amin Iddris , Marife D. Corre , Martin Yemefack , Oliver van Straaten , Edzo Veldkamp

Although tree stems act as conduits for greenhouse gases (GHGs) produced in the soil, the magnitudes of tree contributions to total (soil + stem) nitrous oxide (N2O) emissions from tropical rainforests on heavily weathered soils remain unknown. Moreover, soil GHG fluxes are largely understudied in African rainforests, and the effects of land-use change on these gases are identified as an important research gap in the global GHG budget. In this study, we quantified the changes in stem and soil N2O fluxes with forest conversion to cacao agroforestry. Stem and soil N2O fluxes were measured monthly for a year (2017–2018) in four replicate plots per land use at three sites across central and southern Cameroon. Tree stems consistently emitted N2O throughout the measurement period and were positively correlated with soil N2O fluxes. 15N-isotope tracing from soil mineral N to stem-emitted 15N2O and correlations between temporal patterns of stem N2O emissions, soil–air N2O concentration, soil N2O emissions and vapour pressure deficit suggest that N2O emitted by the stems originated predominantly from N2O produced in the soil. Forest conversion to extensively managed, mature (>20 years old) cacao agroforestry had no effect on stem and soil N2O fluxes. The annual total 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 cacao agroforestry, with tree N2O emissions contributing 11 % to 38 % for forests and 8 % to 15 % for cacao agroforestry. These substantial contributions of tree stems to total N2O emissions highlight the importance of including tree-mediated fluxes in ecosystem GHG budgets. Taking into account that our study sites' biophysical characteristics represented two-thirds of the humid rainforests in the Congo Basin, we estimated a total N2O source strength for this region of 0.18 ± 0.05 Tg N2O-N yr−1.

中文翻译:

刚果盆地高风化土壤上雨林和可可杂粮林的茎和土壤一氧化二氮通量

尽管树茎充当土壤中产生的温室气体(GHG)的管道,但树木对严重风化土壤中热带雨林的总(土壤+ 茎)一氧化二氮(N 2 O)排放的贡献大小 仍然未知。此外,非洲热带雨林中对土壤温室气体通量的研究还很不足,土地利用变化对这些气体的影响被认为是全球温室气体预算中一个重要的研究空白。在这项研究中,我们量化了森林转化为可可农林业的茎和土壤N 2 O通量的变化。茎和土壤N 2在喀麦隆中部和南部三个地点的每个土地使用情况的四个重复样地中,每月(一年)(2017-2018)每月测量一次通量。在整个测量期间,树茎始终排放N 2 O,并且与土壤N 2 O通量呈正相关。从土壤矿质N到茎排放的15 N 2 O的15 N同位素示踪 以及茎N 2 O排放的时间模式,土壤-空气N 2 O浓度,土壤N 2 O排放和蒸气压亏缺之间的相关性表明N 2茎发出的O主要来自N 2O在土壤中产生。将森林转变为广泛管理,成熟(> 20 年以上)的可可农林业对茎和土壤的N 2 O通量没有影响。每年总共N 2个O排放分别为1.55  ±  0.20千克Ñ公顷-1 年-1 从森林和1.15  ±  0.10千克Ñ公顷-1 年-1从可可农林业,与树Ñ 2 O排放贡献11%至38%对于森林而言,则为8%至15%。这些树木茎对总N 2的重要贡献O排放强调了将树木介导的通量纳入生态系统GHG预算的重要性。考虑到我们研究地点的生物物理特征代表了刚果盆地三分之二的湿润雨林,我们估计该区域的总N 2 O源强度为0.18  ±  0.05 Tg N 2 O-N yr -1
更新日期:2020-11-12
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