We aim to identify the importance of vapour pressure deficit (VPD), soil water content (SWC) and photosynthetic photon flux density (PPFD) as drivers of tree canopy conductance, which is a key source of uncertainty for modelling vegetation responses under climate change. We use sap flow time series of 1858 trees in 122 sites from the SAPFLUXNET global database to obtain whole-tree canopy conductance (G). The driver importance, defined as the percentage of variance (R²) of G explained by the three main hydrometeorological drivers (VPD, SWC and PPFD), was evaluated using linear mixed models. For each driver we assess differences in their importance among biomes, and use multiple linear regression to explain how driver importance varies with climate, soil and vegetation structure. We found that in most areas tree canopy conductance is better explained by VPD than by SWC or PPFD, although results for drylands were inconclusive. Climate, soil and vegetation structure were common controls for the importance of all three hydrometeorological drivers, with wetter climates, fine-textured soils and tall vegetation being associated with stronger influence of the driver on G. Differences across sites in the importance of the hydrometeorological drivers of tree canopy conductance may affect predictions of ecosystem dynamics under future climates, and should be accounted for explicitly in models.

我们的目标是确定蒸汽压亏缺 (VPD)、土壤含水量 (SWC) 和光合光子通量密度 (PPFD) 作为树冠电导驱动因素的重要性，这是气候变化下植被响应建模不确定性的关键来源。我们使用 SAPFLUXNET 全球数据库中 122 个地点的 1858 棵树的树液流时间序列来获得全树冠层电导率 ( G )。驱动因素重要性，定义为G的方差百分比 ( R ² )由三个主要水文气象驱动因素（VPD、SWC 和 PPFD）解释，使用线性混合模型进行评估。对于每个驱动因素，我们评估它们在生物群落中的重要性差异，并使用多元线性回归来解释驱动因素的重要性如何随气候、土壤和植被结构而变化。我们发现，在大多数地区，VPD 比 SWC 或 PPFD 更好地解释了树冠导度，尽管旱地的结果尚无定论。气候、土壤和植被结构是所有三个水文气象驱动因素重要性的共同控制因素，潮湿的气候、质地细腻的土壤和高大的植被与驱动因素对G的影响更大有关. 不同地点在树冠传导的水文气象驱动因素的重要性方面的差异可能会影响对未来气候下生态系统动态的预测，并且应该在模型中明确说明。