Tree stem methane emissions from subtropical lowland forest (Melaleuca quinquenervia) regulated by local and seasonal hydrology
Tree stem methane emissions from subtropical lowland forest (Melaleuca quinquenervia) regulated by local and seasonal hydrology
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DOI：
10.1007/s10533-020-00726-y
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发表时间：
2020-11-09
期刊：
影响因子：
4
通讯作者：
Johnston, Scott G.
中科院分区：
文献类型：
--
作者：
Jeffrey, Luke C.;Maher, Damien T.;Johnston, Scott G.
树干介导的甲烷排放是大气甲烷的潜在重要但约束不严的来源。在这里，我们首次对五叶白千层（Melaleuca quinquenervia）的树干甲烷排放量进行了量化，白千层是一种广泛分布的澳大利亚低地标志性树种，也是全球入侵物种。在两种不同的水文条件（潮湿和干燥）下，我们捕获了 431 个树干通量测量值，涵盖沿着 50 m 地形梯度样线的 6 个不同的垂直茎高度，分为三个不同的水文区（上部、过渡和下部）。树干甲烷通量密切反映了当地的地形/水文，范围为 - 30.0 至 123,227 mu mol m(-2) day(-1)，其中最大值是迄今为止报告的最高值之一。在潮湿条件下、被淹没的下部区域以及树干基部和地下水位附近观察到甲烷排放量最高。与干燥条件相比，过渡区和下部区域每棵树的平均甲烷通量（按茎的 1 m 计算）在潮湿条件下分别高出 52 倍和 46 倍，而上部区域的排放量在季节之间变化不大。邻近土壤通量沿着水文梯度遵循类似的趋势，上部区域树干排放抵消了邻近土壤甲烷汇容量。甲烷排放量随茎高度急剧减少的明显趋势表明土壤甲烷起源。较低区域内两棵树的 45 小时时间序列显示出三到四倍的昼夜变化，并且早晨通量有所增加。总体而言，该研究表明，季节性水文条件和地形梯度在很大程度上调节了M. quinquenervia的甲烷排放，并且这一先前被忽视的途径应在湿地甲烷预算中加以考虑，特别是在淹没条件下。
Tree stem mediated methane emissions represent a potentially important yet poorly constrained source of atmospheric methane. Here we present the first ever quantification of tree stem methane emissions from Melaleuca quinquenervia, a widespread iconic Australian lowland tree and globally invasive species. Under two distinct hydrological conditions (wet and dry) we captured 431 tree stem flux measurements encompassing six different vertical stem heights along a 50 m topo-gradient transect, separated into three distinct hydrological zones (upper, transitional and lower). The tree stem methane fluxes closely reflected local topography/hydrology and ranged from - 30.0 to 123,227 mu mol m(-2) day(-1), with the maximum values amongst the highest values reported to date. The highest methane emissions were observed during wet conditions, within the inundated lower zone and from near the tree stem bases and water table. The average methane flux per tree (scaled to 1 m of stem) for the transitional and lower zones was 52-fold and 46-fold higher during wet conditions compared to dry, whereas the upper zone emissions changed little between seasons. Adjacent soil fluxes followed similar trends along the hydrology gradient with the upper zone tree stem emissions offsetting the adjacent soil methane sink capacity. A clear trend of sharply decreasing methane emissions with stem-height suggests a soil methane origin. A 45-h time-series of two trees within the lower zone revealed three to fourfold diel variability, with elevated morning-time fluxes. Overall, the study revealed that seasonal hydrological conditions and topo-gradient substantially regulated the methane emissions from M. quinquenervia and that this previously overlooked pathway should be accounted for within wetland methane budgets, especially during inundated conditions.