Minquartia guianensis Aubl. is a slow-growing species with several uses. In the juvenile state, it is well-adapted to low light conditions of the forest understory. However, it is still unknown how climate variability affects transpiration of this species, particularly under drought stress. In this study, we aimed to assess the effect of climatic variability on sap flow rates (SFR). SFR and radial growth were measured in six trees (14‒50 cm diameter) in 2015 and 2016. Climate (precipitation, irradiance, relative humidity and temperature) and soil water content (SWC) data were also collected. SFR tended to increase in the dry season, with a negative relationship between SFR and SWC and precipitation (p < 0.001), while there was a positive association between radial growth and monthly precipitation (p = 0.004). Irradiance and temperature were the environmental factors more closely correlated with SFR during daytime (p < 0.001), whereas relative humidity and vapor pressure deficit were the most important factors at night (p < 0.001). Although negative SFR were sometimes recorded at night, the mean nocturnal sap flow was positive and across trees the nighttime sap flow accounted for 12.5% of the total daily sap flow. Increased transpiration during the dry season suggests that the root system of Minquartia was able to extract water from deep soil layers. These results widen our understanding of the ecophysiology of Amazonian trees under drought and provide further insight into the potential effect of the forecasted decline in precipitation in the Amazon region.

Minquartia guianensis Aubl。是一种生长缓慢的物种，具有多种用途。在幼年时期，它非常适合森林林下的弱光条件。然而，仍然不清楚气候变化如何影响该物种的蒸腾作用，特别是在干旱胁迫下。在这项研究中，我们旨在评估气候变化对汁液流量（SFR）的影响。在2015年和2016年对6棵树木（直径14‒50厘米）的SFR和径向生长进行了测量。还收集了气候（降水，辐照度，相对湿度和温度）和土壤含水量（SWC）数据。干旱季节SFR趋于增加，SFR和SWC与降水之间呈负相关关系（p <0.001），而径向生长与月降水量之间呈正相关（p  = 0.004）。白天的辐照度和温度是与SFR更为紧密相关的环境因素（p  <0.001），而夜间的相对湿度和蒸气压不足是最重要的因素（p  <0.001）。尽管有时在夜间记录的SFR为负，但夜间的平均树液流量为正，并且夜间树木的树液流量占每日总树液流量的12.5％。干旱季节的蒸腾作用增加表明，Minquartia的根系能够从深层土壤中提取水。这些结果拓宽了我们对干旱下亚马逊树木生态生理的理解，并提供了对预测的亚马逊地区降水下降的潜在影响的进一步了解。