3.3. Spatiotemporal patterns of soil water use
Soil water use by jujube trees was calculated based on the daily soil water data (Figure S4) acquired using the EC 5 sensors. The depth density of water uptake (DWU) under the four plots in the three different years is shown in Figure 5. The DWU generally decreased exponentially with soil depth, matching the FRLD distribution (Figure 3), and the values approached zero below a depth of 100 cm. The normal year of 2014 generally had higher DWU values than the two drought years in the top , with the exception of the MST plot where values were very similar for the three years. On the other hand, the drought years of 2015 and 2016 had clearly higher DWU values than the normal year 2014.
/Figure 5/
The proportion of soil water use (PWU) relative to the entire profile (0) is presented in Figure 6, for the shallow layer (0) and three different deep layers (100-160, 160-220 and 220). Overall, the shallow layer was responsible for the majority of water uptake in the profile and the PWU of this layer was generally higher than 63%, irrespective of plot and year. Significant annual variations in PWU were observed under all plots. In the normal year, the PWU values for the shallow layer ranged from 77.5% to 87.7%, and decreased by 15.6±5.3% and 15.9±7.9% (relative ratio; mean ± one standard deviation) in the drought years of 2015 and 2016, respectively. In contrast, the PWUs in the deep layers dramatically increased in both drought years compared with the normal year. In the serious drought year, the PWUs increased by 78.3±73.6%, 124.7±36.9%, and 127.1±74.8% (relative ratio; mean ± one standard deviation) in the 100-160, 160-220, and 220 layers, respectively. In the moderate drought year, even higher relative ratios were observed in the JBT plot.
/Figure 6/