Department of Forest Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi, Tokyo 113-8657, Japan.
Department of Subtropical Agro-Environmental Sciences, Faculty of Agriculture, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan.
Proc Natl Acad Sci U S A. 2023 Oct 17;120(42):e2301596120. doi: 10.1073/pnas.2301596120. Epub 2023 Oct 9.
Carbon dioxide and water vapor exchanges between tropical forest canopies and the atmosphere through photosynthesis, respiration, and evapotranspiration (ET) influence carbon and water cycling at the regional and global scales. Their inter- and intra-annual variations are sensitive to seasonal rhythms and longer-timescale tropical climatic events. In the present study, we assessed the El Niño-Southern Oscillation (ENSO) influence on ET and on the net ecosystem exchange (NEE), using eddy-covariance flux observations in a Bornean rainforest over a 10-y period (2010-2019) that included several El Niño and La Niña events. From flux model inversions, we inferred ecophysiological properties, notably the canopy stomatal conductance and "big-leaf" maximum carboxylation rate (). Mean ET values were similar between ENSO phases (El Niño, La Niña, and neutral conditions). Conversely, the mean net ecosystem productivity was highest during La Niña events and lowest during El Niño events. Combining Shapley additive explanation calculations for nine controlling factors with a machine-learning algorithm, we determined that the primary factors for ET and NEE in the La Niña and neutral phases were incoming shortwave solar radiation and , respectively, but that canopy stomatal conductance was the most significant factor for both ET and NEE in the El Niño phase. A combined stomatal-photosynthesis model approach further indicated that differences between ENSO phases were the most significant controlling factor for canopy photosynthesis, emphasizing the strong need to account for ENSO-induced ecophysiological factor variations in model projections of the long-term carbon balance in Southeast Asian tropical rainforests.
二氧化碳和水蒸气通过光合作用、呼吸作用和蒸散（ET）在热带林冠层和大气之间进行交换，影响区域和全球尺度的碳和水循环。它们的年际和年内变化对季节性节律和更长时间尺度的热带气候事件敏感。在本研究中，我们利用婆罗洲热带雨林 10 年（2010-2019 年）的涡度相关通量观测数据，评估了厄尔尼诺-南方涛动（ENSO）对 ET 和净生态系统交换（NEE）的影响，其中包括几次厄尔尼诺和拉尼娜事件。通过通量模型反演，我们推断出了生理生态特性，特别是冠层气孔导度和“大叶片”最大羧化速率（）。在 ENSO 阶段（厄尔尼诺、拉尼娜和中性条件），平均 ET 值相似。相反，净生态系统生产力在拉尼娜事件期间最高，在厄尔尼诺事件期间最低。我们结合 Shapley 加法解释计算的九个控制因素和机器学习算法，确定了拉尼娜和中性阶段 ET 和 NEE 的主要因素分别为入射短波太阳辐射和，而在厄尔尼诺阶段，冠层气孔导度是 ET 和 NEE 的最重要因素。综合气孔-光合作用模型方法进一步表明，ENSO 阶段之间的差异是冠层光合作用的最主要控制因素，强调在东南亚热带雨林的长期碳平衡模型预测中，需要考虑 ENSO 引起的生理生态因素变化。
