3.1. Precipitation and fine root distribution
The cumulative frequency of annual total precipitation
(PT) and growing-season precipitation
(PG) are shown in Figure S3, from 1960 to 2012 at the
study site. The medians of PT and PGwere 479.7 and , respectively, which are similar to the annual means of
PT () and PG () during this period.
PT in 2014 (), 2015 () and 2016 () corresponded to
55.6%, 84.1% and 59.0%, respectively, in terms of cumulative
frequency. PG amounted to 56.6%, 98.7% and 67.0% in
2014 (), 2015 () and 2016 (), respectively. Thus, 2014 was considered to
be a normal year, whereas 2015 and 2016 were classified as a severe and
moderate drought year, respectively. It is noteworthy that the
percentages for PG in 2015 and 2016 were clearly lower
than for PT, indicating that less precipitation occurred
than in the 2014 growing season.
Figure 2 shows temporal patterns of daily and monthly precipitation for
different water years. It was clear that there was a severe spring
(April and May) and summer (June and July) drought in 2015. The total
precipitation for spring and summer 2015 accounted for only 60.1% and
21.1%, respectively, of that in 2014. In July 2015, the total
precipitation amounted to only and no water was made available to the
jujube trees as a result of almost all of the eight rainfall events
(precipitation< ). There was a moderate autumn drought in
2016. The total precipitation in August and September 2016 accounted for
only 54.8% and 39.9% of that in 2014 and 2015, respectively.
/Figure 2/
The distribution of fine root length density (FRLD) down the soil
profiles from 0 to 500 cm is shown in Figure 3. In general, the FRLD
decreased exponentially with soil depth. The top 300 cm accounted for
89.9% of the total fine root length down the entire profile (0-500 cm),
indicating that this is the main fine root layer. The top 100 cm
contained 52.5% of fine root length. Therefore, we studied soil water
storage dynamics and soil water use within the top 300 cm, with the top
100 cm defined as the shallow layer and below this was the deep layer.
/Figure 3/