A study on effects of leaf and root characteristics on plant root water uptake

Water uptake intensity (WUI), which depicts the relationship between the rate of plant root water uptake per unit soil volume and soil matric suction, has been commonly used to analyse the transpiration-induced soil hydrological changes in civil infrastructure. However, the effects of plant characteristics on WUI are not clear, causing difficulties when estimating the effects of vegetation on soil moisture/suction changes. The aim of this study is to examine any correlations between plant characteristics and WUIs. Changes in suction and volumetric water content due to transpiration of eight tree individuals (Schefflera heptaphylla) vegetated in compacted silty sand were monitored to estimate the distribution of WUI within the root zone. Results show that the WUI remains a maximum and constant when suction is less than a threshold value of suction, beyond which the WUI decreases approximately linearly. The threshold suction is similar within the root zone of each tree individual, but it has a negative correlation with the ratio of leaf area (LA) and root length (RL). The reduction rate of WUI is positively correlated with root length density (RLD). This suggests that plants with a lower LA/RL ratio and lower RLD may be more capable of maintaining their water uptake ability, as high suction is induced.