Sap flow rates of Minquartia guianensis in central Amazonia during the prolonged dry season of 2015–2016

Abstract

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.