Full data set from ENSO effects on the transpiration of eastern Amazon trees

Tree transpiration is important in the recycling of precipitation in the Amazon and might be negatively affected by El Niño–Southern Oscillation (ENSO)-induced droughts. To investigate the relative importance of soil moisture deficits versus increasing atmospheric demand (VPD) and determine if these drivers exert different controls over tree transpiration during the wet season versus the dry season (DS), we conducted sap flow measurements in a primary lowland tropical forest in eastern Amazon during the most extreme ENSO-induced drought (2015/2016) recorded in the Amazon. We also assessed whether trees occupying different canopy strata contribute equally to the overall stand transpiration (Tstand). Canopy trees were the primary source of Tstand. However, subcanopy trees are still important as they transpired an amount similar to other biomes around the globe. Tree water use was higher during the DS, indicating that during extreme drought trees did not reduce transpiration in response to low soil moisture. Photosynthetically active radiation and VPD exerted an overriding effect on water use patterns relative to soil moisture during extreme drought, indicating that light and atmospheric constraints play a critical role in controlling ecosystem fluxes of water. Our study highlights the importance of canopy and subcanopy trees to the regional water balance and highlights the resilience to droughts that these trees show during an extreme ENSO event.This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.树木蒸腾在亚马逊流域的降水循环中发挥着关键作用，且可能受到厄尔尼诺-南方涛动（El Niño–Southern Oscillation, ENSO）引发的干旱的负面影响。为探究土壤水分亏缺与不断升高的大气水汽压亏缺（Vapor Pressure Deficit, VPD）的相对重要性，并明确这两类驱动因子在湿季与旱季（dry season, DS）对树木蒸腾的调控作用是否存在差异，我们在亚马逊东部的一处原生低地热带森林中，于亚马逊有记录以来最极端的ENSO驱动干旱事件（2015/2016年）期间开展了树液流量测量。我们同时评估了处于不同冠层层次的树木对整体林分蒸腾（Tstand）的贡献是否一致。冠层树木是林分蒸腾的主要贡献源，但亚冠层树木同样发挥着重要作用，其蒸腾量与全球其他陆地生物群系的树木蒸腾水平相当。旱季期间的树木水分消耗量更高，这表明在极端干旱条件下，树木并未因土壤水分不足而降低蒸腾速率。相较于土壤水分，光合有效辐射与水汽压亏缺对极端干旱期间的树木水分利用模式具有主导调控作用，这表明光照与大气约束因子在调控生态系统水分通量中发挥着关键作用。本研究强调了冠层与亚冠层树木对区域水平衡的重要意义，同时揭示了这些树木在极端ENSO事件中展现出的干旱耐受能力。本文属于专题讨论会议专辑《2015/2016年厄尔尼诺对陆地热带碳循环的影响：模式、机制与启示》的一部分。