School of Environment, Earth & Ecosystem Science, The Open University, Milton Keynes, UK.
Lancaster Environment Centre, Lancaster University, Lancaster, UK.
Glob Chang Biol. 2019 Jan;25(1):361-372. doi: 10.1111/gcb.14498. Epub 2018 Nov 14.
Tropical forests on upland soils are assumed to be a methane (CH ) sink and a weak source of nitrous oxide (N O), but studies of wetland forests have demonstrated that tree stems can be a substantial source of CH , and recent evidence from temperate woodlands suggests that tree stems can also emit N O. Here, we measured CH and N O fluxes from the soil and from tree stems in a semi-evergreen tropical forest on upland soil. To examine the influence of seasonality, soil abiotic conditions and substrate availability (litter inputs) on trace greenhouse gas (GHG) fluxes, we conducted our study during the transition from the dry to the wet season in a long-term litter manipulation experiment in Panama, Central America. Trace GHG fluxes were measured from individual stem bases of two common tree species and from soils beneath the same trees. Soil CH fluxes varied from uptake in the dry season to minor emissions in the wet season. Soil N O fluxes were negligible during the dry season but increased markedly after the start of the wet season. By contrast, tree stem bases emitted CH and N O throughout the study. Although we observed no clear effect of litter manipulation on trace GHG fluxes, tree species and litter treatments interacted to influence CH fluxes from stems and N O fluxes from stems and soil, indicating complex relationships between tree species traits and decomposition processes that can influence trace GHG dynamics. Collectively, our results show that tropical trees can act as conduits for trace GHGs that most likely originate from deeper soil horizons, even when they are growing on upland soils. Coupled with the finding that the soils may be a weaker sink for CH than previously thought, our research highlights the need to reappraise trace gas budgets in tropical forests.
旱地热带森林被认为是甲烷（CH ）的汇和氧化亚氮（N O）的弱源，但湿地森林的研究表明，树干可以是 CH 的重要来源，最近来自温带林地的证据表明，树干也可以排放 N O。在这里，我们测量了旱地半常绿热带森林中土壤和树干中的 CH 和 N O 通量。为了研究季节性、土壤非生物条件和基质可用性（凋落物输入）对痕量温室气体（GHG）通量的影响，我们在中美洲巴拿马的一项长期凋落物处理实验中，在从旱季向雨季过渡期间进行了研究。痕量 GHG 通量是从两种常见树种的单个树干基部和同一棵树下的土壤中测量的。土壤 CH 通量从旱季的吸收变化到雨季的少量排放。旱季土壤 N O 通量可忽略不计，但在雨季开始后显着增加。相比之下，树干基部在整个研究过程中排放 CH 和 N O。尽管我们没有观察到凋落物处理对痕量 GHG 通量的明显影响，但树种和凋落物处理相互作用，影响了树干的 CH 通量和树干及土壤的 N O 通量，表明树种特性和分解过程之间存在复杂的关系，这可能会影响痕量 GHG 动态。总的来说，我们的结果表明，即使在旱地生长，热带树木也可以作为痕量温室气体的通道，这些气体很可能来自更深的土壤层。再加上土壤可能比以前认为的更弱的 CH 汇的发现，我们的研究强调需要重新评估热带森林的痕量气体预算。
