\documentclass[10pt]{article}

\usepackage{fullpage}
\usepackage{setspace}
\usepackage{parskip}
\usepackage{titlesec}
\usepackage[section]{placeins}
\usepackage{xcolor}
\usepackage{breakcites}
\usepackage{lineno}
\usepackage{hyphenat}





\PassOptionsToPackage{hyphens}{url}
\usepackage[colorlinks = true,
            linkcolor = blue,
            urlcolor  = blue,
            citecolor = blue,
            anchorcolor = blue]{hyperref}
\usepackage{etoolbox}
\makeatletter
\patchcmd\@combinedblfloats{\box\@outputbox}{\unvbox\@outputbox}{}{%
  \errmessage{\noexpand\@combinedblfloats could not be patched}%
}%
\makeatother


\usepackage{natbib}




\renewenvironment{abstract}
  {{\bfseries\noindent{\abstractname}\par\nobreak}\footnotesize}
  {\bigskip}

\titlespacing{\section}{0pt}{*3}{*1}
\titlespacing{\subsection}{0pt}{*2}{*0.5}
\titlespacing{\subsubsection}{0pt}{*1.5}{0pt}


\usepackage{authblk}


\usepackage{graphicx}
\usepackage[space]{grffile}
\usepackage{latexsym}
\usepackage{textcomp}
\usepackage{longtable}
\usepackage{tabulary}
\usepackage{booktabs,array,multirow}
\usepackage{amsfonts,amsmath,amssymb}
\providecommand\citet{\cite}
\providecommand\citep{\cite}
\providecommand\citealt{\cite}
% You can conditionalize code for latexml or normal latex using this.
\newif\iflatexml\latexmlfalse
\providecommand{\tightlist}{\setlength{\itemsep}{0pt}\setlength{\parskip}{0pt}}%

\AtBeginDocument{\DeclareGraphicsExtensions{.pdf,.PDF,.eps,.EPS,.png,.PNG,.tif,.TIF,.jpg,.JPG,.jpeg,.JPEG}}

\usepackage[utf8]{inputenc}
\usepackage[ngerman,greek,english]{babel}



\usepackage{float}








\begin{document}

\title{Impact of land management practices on tree water use strategy and
responses to drought in a dryland plantation}



\author[1]{Xiaodong Gao}%
\author[2]{Hongchen Li}%
\author[1]{Xining Zhao}%
\affil[1]{Northwest Agriculture and Forestry University}%
\affil[2]{Ludong University}%


\vspace{-1em}



  
  \date{March 13, 2025}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
Extreme droughts of increased frequency due to climate change poses
great challenges to the sustainability of plantations in drylands
worldwide. Millions of plantations on China's Loess Plateau which are
mainly in drylands are threatened by serious degradation due to water
scarcity. Here we aim to disentangle the impacts of combinations of
terracing and mulching on water use strategy and its response to extreme
droughts in a rainfed jujube (Ziziphus jujuba) plantation on the
semiarid Loess Plateau, using three-year in situ field observations.
Pruned jujube branches and maize straw were mulched on half-moon
terraces to form two combined treatments, referred to as JBT and MST,
respectively. The efficacy of these two combinations on the water use
strategy of jujube trees was compared with terracing alone (SHT) and
control (no terrace). We found that extreme drought clearly reduced soil
water storage (SWS) under all treatments. However, the combined
treatments showed significantly (P\textless{}0.05) higher SWS than the
SHT and control. Furthermore, the combined treatments enhanced soil
water use in deep layers during both normal and drought years, thus
helping jujube trees to resist droughts. Moreover, the extreme drought
significantly reduced transpiration whereas the moderate drought
increased transpiration at both seasonal and annual scales. Nonetheless,
the combined treatments were associated with enhanced transpiration
compared to the SHT and control during drought periods. Finally, jujube
trees exhibited isohydric behavior which also helped them to cope with
prolonged droughts. Overall, the findings here may provide insights into
land management of dryland plantations worldwide under climate change.%
\end{abstract}%



\sloppy


\textbf{Impact of land management practices on tree water use strategy
and responses to drought in a dryland plantation}

Running title: Tree water use in relation to land management practices
and droughts

Xiaodong Gao\textsuperscript{1,2}, Hongchen Li\textsuperscript{3},
Xining Zhao\textsuperscript{1,2}*

1. Institute of Soil and Water Conservation, Northwest A\&F University,
Yangling 712100, Shaanxi Province, China

2. Institute of Soil and Water Conservation, Chinese Academy of Sciences
and Ministry of Water Resources, Yangling 712100, Shaanxi Province,
China

3. College of Resources and Environment, Ludong university, Yantai
264065, Shandong Province, China.

*Corresponding author: Xining Zhao (\emph{zxn@nwafu.edu.cn})

\textbf{Acknowledgement}

This work was jointly supported by the National Key Research and
Development Plan (No. 2016YFC0400204), the National Natural Science
Foundation of China (No. 41771316), and the `111'Project (No. B12007).

\textbf{Abstract} Extreme droughts of increased frequency due to climate
change poses great challenges to the sustainability of plantations in
drylands worldwide. Millions of plantations on China's Loess Plateau
which are mainly in drylands are threatened by serious degradation due
to water scarcity. Here we aim to disentangle the impacts of
combinations of terracing and mulching on water use strategy and its
response to extreme droughts in a rainfed jujube (\emph{Ziziphus jujuba}
) plantation on the semiarid Loess Plateau, using three-year\emph{in
situ} field observations. Pruned jujube branches and maize straw were
mulched on half-moon terraces to form two combined treatments, referred
to as JBT and MST, respectively. The efficacy of these two combinations
on the water use strategy of jujube trees was compared with terracing
alone (SHT) and control (no terrace). We found that extreme drought
clearly reduced soil water storage (SWS) under all treatments. However,
the combined treatments showed significantly (\emph{P} \textless{}0.05)
higher SWS than the SHT and control. Furthermore, the combined
treatments enhanced soil water use in deep layers during both normal and
drought years, thus helping jujube trees to resist droughts. Moreover,
the extreme drought significantly reduced transpiration whereas the
moderate drought increased transpiration at both seasonal and annual
scales. Nonetheless, the combined treatments were associated with
enhanced transpiration compared to the SHT and control during drought
periods. Finally, jujube trees exhibited isohydric behavior which also
helped them to cope with prolonged droughts. Overall, the findings here
may provide insights into land management of dryland plantations
worldwide under climate change.

\textbf{Key words} : water source; soil moisture; transpiration; land
development; drought

\textbf{1. Introduction}

Drylands cover more than 40\% of the Earth's land surface and 72\% of
them are in undeveloped regions that are home to 2.5 billion people, or
38\% of the world's total population (Huang et al., 2017). Water
scarcity impedes the sustainable development of agriculture, economy and
society in global drylands (Vohland and Barry, 2009; Schwaerzel et al.,
2020). It is projected that climate change is amplifying the intensity
and frequency of droughts, causing greater stress on water availability
particularly in arid and semiarid areas (Thornton et al., 2014) where it
could cause massive tree mortality (Choat et al., 2018). The
productivity and sustainability of agroecosystems in drylands during
prolonged droughts greatly depend on each crop's capacity to exploit
water resources (Grossiord et al., 2017), and on soil management to
increase infiltration and minimize evaporation (Zhao et al., 2009).

Understanding the seasonal and annual patterns associated with plants'
water use strategies is critical if we are to disentangle how plants
acclimate and respond to varying water situations. The seasonal water
sources usually vary depending on plant species, wetness, and topography
(Allen et al., 2019). Generally, plants can modify their water sources,
transpiration rate, or leaf water status under changing conditions in
order to cope with drought (Gow et al., 2018). It has been demonstrated
that tree species usually shift water use to deep-layer soil water (Gao
et al., 2018a; Tang et al., 2018) or groundwater (Barbeta et al., 2016)
during prolonged drought, by concentrating more fine roots at greater
depths in order to avoid hydraulic failure (Wang et al., 2020). In fact,
plants have evolved complex water use strategies in order to adapt to
different climates and water regimes, and these include isohydric and
anisohydric behavior (McDwell et al., 2008; Luo et al., 2017).
Schmidt-Walter et al. (2014) found that the transpiration of a mature
poplar (\emph{Populus} spp\emph{.} ) plantation was strongly controlled
by the stomata, with the plants exhibiting isohydric behavior and a
conservative water use strategy in response to drought at two sites with
a subhumid climate in Germany. In contrast, Luo et al. (2016) found that
two evergreen tree species (\emph{Osmanthus fragrans}
and\emph{Cinnamomum camphora} ) both exhibited anisohydric behavior in
response to an extreme summer drought at a humid site in central
southern China. Nevertheless, the information about the water use
strategies employed by trees in response to real-world droughts in
drylands remains limited. Furthermore, there appears to be few
integrated studies considering water source, transpiration and leaf
water potential for a given species.

A variety of mulching and terracing measures have been introduced in
drylands to reduce water loss through evaporation and runoff. It has
been clearly demonstrated that mulching has a great effect on water
balance, in terms of increasing soil water content and soil temperature,
reducing soil evaporation, and enhancing transpiration and water use
efficiency (e.g., Zhang et al., 2007; Singh et al., 2011; Liu et al.,
2014). However, little is known about how mulching influences seasonal
water use within soil profiles. For hilly regions in drylands, various
types of terraces have been used to reduce runoff and to promote
infiltration (Arn\selectlanguage{ngerman}áez et al., 2015; Wei et al., 2016; Chen et al., 2017).
However, just terracing without mulching the soil surface could increase
soil evaporation during inter-rainfall periods (Li et al., 2018). A
combination of terracing and mulching may be a better alternative to
either terracing or mulching alone on dryland hillslopes. However, the
impact of such a combination on plant water use strategy has not been
examined.

The Loess Plateau (LOP), of which almost 100\% can be classified as
dryland, is one of the most undeveloped regions in China due to severe
soil erosion. Therefore, the Chinese government launched the ``Grain for
Green'' project to reduce both soil erosion and rural poverty. This
project encouraged farmers to plant jujube trees (\emph{Ziziphus
jujuba}Mill.) on hillslopes to deliver both ecological and economic
benefits (Gao et al., 2018b). The planting area and output value of
jujube trees exceeded 54.5×10\textsuperscript{4} hm\textsuperscript{2}
and 9.4 billion RMB in 2013 (Wang et al., 2016) and supported the
livelihood of more than 1 million farmers. However, the sustainability
of jujube trees is greatly hindered by water scarcity and the increasing
frequency of extreme droughts. Therefore, the main objectives of this
study are (1) to investigate the impacts of mulching and terracing
combinations on soil moisture and the water use strategy of jujube trees
in a semiarid plantation, and (2) to apply the results to address the
issues of extreme drought in real world situations.

\textbf{2. Materials \& methods}

\textbf{2.1. Study site}

The study site was located in the Yuanzegou catchment (37°14\selectlanguage{english}' N, 110\selectlanguage{ngerman}°20\selectlanguage{english}'
E) in the hilly region of the Loess Plateau, China (Figure 1). This site
has a semiarid climate: the mean annual precipitation is 481 mm,
approximately 70\% of which falls in July, August and September (wet
season); the mean annual temperature is 8.6 , with the maximum of in
July and the minimum of in January (Gao et al., 2014). The catchment is
covered by thick loess soils (silt loam) (Gao et al., 2014). The basic
soil properties of the study site are presented in Table 1.

/Figure 1/

The area of the whole catchment is approximately 0.6
km\textsuperscript{2}. The uplands comprise three main land use types,
i.e., jujube plantations which account for approximately 50\% of the
uplands, cropland, and grassland at two different growing stages (Figure
1). The jujube tree is used primarily as a shade tree that also bears
fruit. The majority of the jujube trees in this catchment were planted
in 2007 at a density of approximately 1650 trees per hectare, in order
to improve both green cover and the farmer's income (Gao et al., 2014).
The jujube trees on hillslopes were planted in half-moon terraces (also
known locally as fish-scale pits), which is one of the primary methods
of planting trees on the Loess Plateau (Wei et al., 2016). The size and
layout of these terraces is shown in Figure S1. In general, jujube
plantations in the hilly region of the Loess Plateau are rainfed because
of the high cost of irrigation, which would require runoff water
collected in gully bottoms to be pumped upslope. Therefore, the jujube
plantations here usually suffer seasonal droughts.

\textbf{2.2. Precipitation data}

Historical precipitation data for the period 1960 to 2012 at the study
site was derived from the China Meteorological Forcing Dataset (CMFD; He
and Yang, 2011). The CMFD was developed by the Institute of Tibetan
Plateau Research, Chinese Academy of Science, and include data on air
temperature, air pressure, relative humidity, wind speed, downward
short-wave radiation, downward long-wave radiation and precipitation at
the land surface. The datasets are available \emph{via} the following
link:\emph{http://westdc.westgis.ac.cn/data/7a35329c-c53f-4267-aa07-e0037d913a21}.

The precipitation data during the study period (2014-2016) were recorded
by a portable weather station (AR5, Avolon Scientific, USA) located at
the study site. The data logger recorded primary meteorological
variables including precipitation, wind speed, solar radiation, air
temperature and relative humidity every 30 min.

\textbf{2.3. Experimental design}

In order to enhance the ability of jujube trees to resist extreme
seasonal droughts, a mulching experiment was conducted at this site in
2013. First, branches pruned from jujube trees during normal management
and maize stems were trimmed to lengths of approximately 20 cm and then
used as mulch on the surface of half-moon terraces, applied at a
thickness of 15 cm, resulting in two combinations of terracing and
mulching (Figure S1), hereafter JBT and MST, respectively. The mulch
material can be washed off the terraces by rapid overland flow during
heavy rainstorms or blown away by strong winds. Therefore, new branches
or maize stems were added to terraces every spring to maintain a
constant thickness. Two other treatments, just half-moon terracing (SHT)
and the traditional hillslope (control) land management practices, were
also examined. Each treatment included four replicates, and each
replicate comprised a 24-m\textsuperscript{2} plot (4 m \selectlanguage{ngerman}× 6 m),
including three jujube trees. Therefore, there was a total of 16 plots
in the experiment.

\textbf{2.4. Fine root data}

A portable hand auger (\selectlanguage{greek}Φ\selectlanguage{english}=90mm) was employed to collect fine roots from
two different jujube trees outside the 16 plots. Samples were collected
down to 500 cm vertically, at 20 cm intervals. To reduce sampling
uncertainty caused by spatial variability, for each jujube tree, root
samples were collected at four locations: two of them along the contour
line and the other two downslope from the stem (Figure S2). As shown in
the figure, the distance of A and C locations was 0.5 m to the trunk of
jujube tree and it was 1.0 m for the B and D locations. Mixed root
samples were sealed in bags and stored immediately in a refrigerator at
4 \selectlanguage{ngerman}°C. In the lab, root samples were gently washed in a 2-mm sieve, and
the roots retained on the sieve were removed with tweezers. A Vernier
caliper with a precision of 1×10\textsuperscript{-2} mm was used to
separate fine roots (\selectlanguage{english}[?]2 mm) from coarse roots (\textgreater{} 2 mm). The
determination of fine roots and the calculations of fine root length
density (FRLD) are given in Li et al. (2017).

\textbf{2.5. Soil moisture data}

A TRIME-IPH TDR system (IMKO, Germany) was employed to sample soil
moisture in each plot in the 0 depth range. In order to capture detailed
temporal patterns of soil water use of jujube trees in the main root
soil profiles, soil water content was also recorded using EC-5 sensors
(Decagon Inc., USA) every 10 minutes in one plot for each of the four
treatments. To install soil moisture sensors, a 320-cm-deep pit was dug
and the soil moisture sensors were inserted horizontally at depths of
10, 20, 40, 60, 100, 160, 220, and under each of the four plots. Soil
water data for the first month after sensor installation were excluded.

The soil moisture outputs (\selectlanguage{greek}\emph{θ\textsubscript{E}}\selectlanguage{english} ) obtained
\emph{via the} EC-5 sensors were calibrated at the study site in order
to improve accuracy. According to Li et al. (2018), the calibration
equation was:

(1)

where denotes volumetric soil water content derived by multiplying
gravimetric water content by dry soil bulk density.

In this study, daily soil water observations were used to analyze
temporal patterns of water use by jujube trees. Daily soil water data
clearly has less noise than the 10-minute and hourly data; however,
using daily data can obscure the effect of gravity drainage following
rainstorms when quantifying soil water use, because the relatively high
infiltration capacity of loess soil means that gravity drainage is
expected to last less than one day (Zhu et al., 1983). Daily soil
moisture data were derived by arithmetically averaging soil moisture
data at the 10-min resolution over a whole day.

Here, the 0-100 cm soil layer was defined as ``shallow'', because this
layer clearly exhibits higher temporal variations in soil moisture (Gao
et al., 2014) and higher fine root density (Li et al., 2017) than the
layers below 100 cm. Furthermore, this definition of a shallow layer can
also be found in other regions (e.g., Broedel et al., 2017; Yang et al.,
2017).

\textbf{2.6. Ecophysiological data}

Sap flow rate of stems was used as a proxy for the canopy transpiration
rate of jujube trees. For each treatment, three jujube trees were
randomly selected from three different plots for sap flow measurements.
Therefore, a total of 12 jujube trees were used for this experiment. A
FLGS-TDP XM1000 system (Dynamax Co., USA) was used for measuring sap
flow rate; this includes 12 thermal dissipation probes (TDPs) with two
needles (30 mm in length and 2 mm in diameter) and one CR1000 data
logger. The installation of the equipment was completed in early March
of 2014. On the north side of the trunk and at 20 cm above the ground on
each of the 12 selected trees, one TDP sensor was uniformly and
horizontally inserted into the 0--30 mm sapwood layer after peeling off
the bark layers; it was then packed using silver membrane. From early
March 2014 to the end of 2016, sap flow rate was recorded continuously
for all 12 jujube trees. The data from the first two weeks were
discarded. Sap flow density (\emph{J\textsubscript{s}} ) was calculated
based on the equation introduced by Granier (1987). The sap flow rate
(\emph{SF} ) was then derived using the following equation, with an
assumption of a constant \emph{J\textsubscript{s}} across the sapwood
profile.

(2)

where K denotes a unit conversion coefficient, equal to
0.00864;\emph{A\textsubscript{S}} denotes sapwood area,
cm\textsuperscript{2}.

Mid-day leaf water potential (\selectlanguage{greek}Ψ\selectlanguage{english}\textsubscript{L}) was measured on 18
June, 18 July, 18 August, and 18 September in 2015 and on 19 June, 17
July, 19 August, and 19 September in 2016, using a PMS Model 1000
pressure chamber (PMS Instrument, USA).

\textbf{2.7. Identification of growing seasons}

At our study site, in normal years, the jujube trees sprout generally in
middle April and leaf-fall occurs in mid-October, by which time the
fruit are mature. Root growth, however, generally commences earlier and
ceases later than shoot growth (Gregory, 2006). Therefore, for this
study, we defined the growing season of jujube trees as being from April
10 to October 20. Each growing season was divided into four different
growth periods based on records from several years, i.e., the sprouting
(SPR) period from April 10 to May 20, the blossom \& young fruit (BYF)
period from May 21 to July 10, the fruit swelling (FRS) period from July
11 to September 10, and the fruit maturation (FRM) period from September
11 to October 20.

\textbf{2.8. Characterizing the soil water use pattern}

Soil water use by jujube trees in a given layer during the growing
season was quantified on the basis of daily changes in soil water
storage (SWS) in that layer (Broedel et al., 2017; Christina et al.,
2017) because the groundwater is far beyond the plant's rooting depth at
our site. The SWS for each layer was computed by multiplying the mean
soil water content in this layer () by the layer depth
(\emph{D\textsubscript{i}} ). In the 0 layer, the soil water content at
10 cm was used as the mean soil water content. For other depth
intervals, the mean soil water content was defined as the arithmetic
mean of soil water content at the upper and lower depths. Soil water
loss in the 0 layer is generally the result of soil evaporation (He et
al., 2013) although this may be small in mulched plots. Nevertheless, in
order to ensure consistency between the different plots, the SWS in the
0-10 cm layer was excluded when quantifying soil water use here. We then
computed daily changes () in SWS at eight depth intervals (10-20, 20-40,
40-60, 60-100, 100-160, 160-220, and 220) during the growing season in
each year. A negative indicates the use of soil water by jujube trees.
The sum of negativein one layer over the growing season was defined as
the total water uptake during the growing season from that layer.

Because of the non-uniform depth intervals between the different layers
considered, the concept of depth density of water use (DWU) was
introduced in order to compare soil water use at different depths. The
DWU is defined as the amount of water use per centimeter depth.
Furthermore, we calculated the proportion of water use source (PWU) for
the shallow (10) and deep (100-280 cm) layers relative to those of the
profile as a whole (10) in different years and growing periods to reveal
temporal patterns at annual and seasonal scales.

One-way analysis of variance (ANOVA) was used to examine the impacts of
combinations of mulching and terracing on SWS, transpiration and mid-day
leaf water potential, using the \emph{nlme} package in R (v.3.5.3, R
Core Team 2019). The graphs presented in this paper were drawn using
Origin 2016 (OriginLab, Massachusetts, USA).

\textbf{3. Results}

\textbf{3.1. Precipitation and fine root distribution}

The cumulative frequency of annual total precipitation
(P\textsubscript{T}) and growing-season precipitation
(P\textsubscript{G}) are shown in Figure S3, from 1960 to 2012 at the
study site. The medians of P\textsubscript{T} and P\textsubscript{G}were
479.7 and , respectively, which are similar to the annual means of
P\textsubscript{T} () and P\textsubscript{G} () during this period.
P\textsubscript{T} in 2014 (), 2015 () and 2016 () corresponded to
55.6\%, 84.1\% and 59.0\%, respectively, in terms of cumulative
frequency. P\textsubscript{G} 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 P\textsubscript{G} in 2015 and 2016 were clearly lower
than for P\textsubscript{T}, 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\textless{} ). 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/

\textbf{3.2. Temporal dynamics of soil water storage}

The time series for soil water storage (SWS) during the study period
under different treatments are shown in Figure 4. It is clear that both
the extreme drought in 2015 (dry spell I) and the moderate drought in
the 2016 (dry spell II) greatly decreased the SWS at all soil depths
under the different treatments, with a clear lag in the 180-280 cm layer
for dry spell I. In particular, the soil water content in the 0-20 cm
layer under the SHT and control fell below the permanent wilting point
(Table 1). Generally, the treatments that combined terraces and mulches
(JBT and MST) exhibited higher SWS values than terraces alone (SHT) or
the control. Furthermore, the differences between the combined
treatments and the others seemed to be greater during the two dry
spells.

/Figure 4/

The annual average SWS was clearly lower in 2015 and 2016 than in 2014
in the 0-20 cm layer but not in the deeper layers, indicating the
effects of seasonal droughts on SWS at the annual scale are probably
only apparent in the surface layer. In the 0-20 cm layer, the combined
treatments had, on average, 14.6\% and 30.4\% higher SWS than the SHT
and control, respectively, and the difference between these treatments
and the control was statistically significant (\emph{P} \textless{}0.05)
in 2014 and 2015. In the 20-100 cm layer, the combined treatments had,
on average, 20.7\% and 36.0\% higher SWS than the SHT and control,
respectively, for the different years. The difference was highly
significant (\emph{P} \textless{}0.01) for all years, highlighting the
advantage of combining terracing and mulching in order to retain soil
water.

\textbf{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\selectlanguage{ngerman}±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/

\textbf{3.4. Canopy transpiration and physiological response}

The change in daily transpiration rate (T\textsubscript{d}) over time
during the study period under different treatments is presented in
Figure 7. Overall, T\textsubscript{d} showed clear seasonal patterns
independent of year and treatment; T\textsubscript{d} progressively
increased with leaf development in late Spring, peaked from middle
Summer to early Autumn (late July to mid-September), and decreased
sharply with leaf fall in mid-autumn. The severe drought (dry spell I)
clearly reduced T\textsubscript{d} in spring and summer 2015; the
transpiration in the BYF period decreased by 22.6\% on average compared
to that in 2014. However, the moderate drought in 2016 had negligible
negative effects on the time series for T\textsubscript{d}, although the
SWS obviously decreased (Figure 4). Nonetheless, this moderate drought
seemed to enhance the differences in T\textsubscript{d} between the
different treatments; the combined treatments had apparently higher
T\textsubscript{d} than the SHT and the control.

/Figure 7/

The amount of transpiration was calculated for the four growing periods
-- SPR, BYF, FRS, and FRM (Figure 8). As expected (based on Figure 7),
the FRS period had the highest transpiration and accounted from 45.2\%,
on average, of the whole growing season considering all treatments in
different years, while the SPR had the lowest, accounting for only
4.9\%, on average. The combined treatments significantly enhanced the
transpiration during the four growing periods, with the exception of the
SPR in 2015; the FRS period had the highest level (\emph{P}
\textless{}0.001) of significant difference whereas the SPR had the
lowest level. At the annual scale, the transpiration during the four
different growing stages was summed to derive the transpiration for the
whole growing season. As shown in Figure 8, 2016 had the highest amount
of transpiration, amounting to 206.5 mm on average, while 2015 had the
lowest, with 172.6 mm on average. Moreover, the combined terracing and
mulching also had significantly (\emph{P} \textless{}0.01 or 0.001)
higher annual transpiration than the other treatments; the MST treatment
had the greatest value of 213.5 mm, whilst the control had only 152.3
mm.

/Figure 8/

The relationship between annual transpiration and the corresponding mean
SWS for different treatments and years is shown in Figure 9. Clearly,
the annual transpiration significantly (\emph{P} \textless{}0.01) and
positively correlated with the mean SWS in both the shallow (0-100 cm)
and deep (100-280 cm) soil layers. This means that the higher
transpiration in the combined treatments could be due to the greater
soil water availability.

/Figure 9/

The mid-day leaf water potential (\selectlanguage{greek}Ψ\selectlanguage{english}\textsubscript{L}) during the growing
seasons in 2015 and 2016 is presented in Figure 10. Overall,
\selectlanguage{greek}Ψ\selectlanguage{english}\textsubscript{L} showed relatively moderate temporal variation during
the growing seasons, ranging from -1.04\selectlanguage{ngerman}±0.007 to -1.67±0.068 MPa, even
in the extreme drought in July 2015 and the moderate autumn drought in
2016. This suggests that the jujube trees exhibited isohydric behavior
and a conservative water use strategy in response to extreme droughts.
In addition, the combined treatments generally had higher
\selectlanguage{greek}Ψ\selectlanguage{english}\textsubscript{L} than the SHT and control, especially during the dry
spells.

/Figure 10/

\textbf{4. Discussion}

\textbf{4.1. Tree water use strategy and response to drought}

Soil water is the primary water source for plants in semiarid regions
where the ground water is usually deep; this is very much the case on
China's Loess Plateau. Because of the paucity of precipitation, plants
in drylands usually develop deep root systems to acquire water from deep
in the soil or from the groundwater (Gao et al., 2018b). It is predicted
that the frequency and intensity of droughts will increase in drylands
as a result of climate change (Zhang et al., 2019). The occurrence of
extreme droughts increases potential water demand, with intensive soil
evaporation and canopy transpiration. Here the extreme spring and summer
drought in 2015 reduced soil water storage, particularly in the shallow
soil layers (Figure 4). The decrease in shallow water availability
increased soil water use from the deep layers during droughts (Figure 5
and 6), supporting the findings of Gao et al. (2018b) based on a stable
isotopic method. The shift in water use to exploit deep water sources
indicates that jujube trees have a flexible water use strategy. This is
often ascribed to dimorphic rooting systems, meaning that deep roots
become active as shallow roots experience reversible embolism due to
severe water stress (Williams and Ehleringer, 2000; West et al., 2012;
Gao et al., 2018a). Deep soil water has been considered to be the
critical water resource for plants coping with extreme droughts,
allowing them to avoid hydraulic failure and mortality, and this applies
not just to drylands (Grossoird et al., 2017) but also to subtropical
and tropical regions (Choat et al., 2018). However, for drylands where
ground water is far beyond the rooting depth, use of deep soil water
could result in serious soil desiccation (Jia et al., 2019) which would
undermine ecosystem sustainability.

In our study, the peak daily transpiration under the control was gently
higher than that recorded for jujube trees without mulching at another
study site on the Loess Plateau (Ma et al., 2019). This is because our
site has a 6.7\% higher annual mean precipitation as well as higher air
temperature compared to the site investigated by Ma et al. (2019).
Despite the increase in deep-layer water use during the extreme drought
in 2015 (Figure 6), the prolonged drought significantly (\emph{P}
\textless{}0.01) reduced the amount of transpiration in the blossom \&
young fruit (BYF) period (Figure 8) and the daily transpiration rate
(Figure 7). This can be attributed to the decrease in water availability
over the whole soil profile during the BYF period. However,
Schmidt-Walter et al. (2014) found that water availability did not
greatly restrict transpiration rate in a full-grown mature poplar
plantation; we think it likely that they did not consider soil water
content in layers below 120 cm. In contrast, the moderate autumn drought
did not limit the transpiration rate and was actually associated with
enhanced transpiration during the fruit swelling (FRS) period (Figure 7
and 8). This could be explained by the high SWS in the 0-280 cm profile,
indicating that there was abundant water provision for transpiration
(Figure 8), prior to the occurrence of drought (Figure 4). At the annual
scale, there was lower transpiration during the extreme drought year and
significantly higher transpiration during the moderate drought year
compared to the normal year (Figure 8). This may imply that moderate
rather than extreme drought may favor transpiration by trees. However,
the jujube trees in this study were not mature and were increasing in
size during the study period; the jujube trees in 2016 had a larger
canopy basal diameter and tree height than in 2014 and 2015, which would
contribute to the higher transpiration in 2016.

The jujube trees tended to exhibit isohydric behavior in response to the
prolonged droughts, with moderate variation in mid-day leaf water
potential during the study period (Figure 10). In contrast to
ansiohydric behavior, which could place plants at a great risk of
dieback or mortality during extreme droughts (McDwell et al., 2008; Luo
et al., 2016), isohydric behavior usually results in a conservative
water use strategy and allows plants to avoid hydraulic failure
(Schmidt-Walter et al., 2014). In our study, specifically, no dieback
was observed in the jujube trees under any treatment after the extreme
drought in 2015. Nevertheless, an in-depth investigation is needed to
understand the effects of extreme droughts on the hydraulic system of
jujube trees, as this is critical to understanding the mechanism of
drought impacts (Choat et al., 2018) and to predict how jujube trees
will respond to future extreme climates.

\textbf{4.2. Effects of combined terracing and mulching on water use
strategy}

Terraces, including the half-moon terracing considered here, have been
shown to be efficient in interrupting runoff paths, reducing soil and
water loss and enhancing infiltration (Wei et al., 2016; Chen et al.,
2017). However, terraces alone can enhance soil evaporation and reduce
soil water content compared to hillslopes during dry spells (Li et al.,
2011). Our results demonstrate that the advantage of half-moon terraces
(SHT) compared to a control gradually reduced over the whole soil
profile during an extreme drought (Figure 4). In contrast, the efficacy
of mulching in reducing soil evaporation has been widely reported, and a
variety of mulching materials -- films, straw, branches and gravel --
have been shown to be effective in enhancing soil water availability (et
al., Zhang et al., 2007; Singh et al., 2011; Sun et al., 2012; Liu et
al., 2014). In the current study, two common local materials, pruned
jujube branches and corn stalks, were mulched on the surface of
fish-scale pits to form the combined treatments of terracing and
mulching. We found that they significantly increased soil water storage
compared to the SHT and the control in both the surface (0-20 cm) and
subsurface (20-100 cm) layers (Figure 4).

To our knowledge, this study is the first attempt to investigate the
effects of agronomic practices on soil water use strategy. We found that
the combinations of terracing and mulching clearly modified soil water
use patterns, enhancing depth density of water uptake (Figure 5) and the
proportion of soil water drawn from the deep layers (Figure 6). This can
be attributed to the higher SWS of the subsurface soils in the combined
treatments (Figure 4). The increase in soil water availability may
promote the growth of fine roots that forage water, due to their
hydrotropic nature (Takahashi, 1997), thus enhancing subsurface water
use. The combined treatments also significantly increased transpiration
rate at daily, seasonal and annual scales (Figures 7 and 8). This can be
explained by the strong relationship between SWS and transpiration
(Figure 9). The greater soil water storage further promoted tree growth
and hence more transpiration occurred to meet water demand. Moreover,
the higher SWS may also be responsible for the higher mid-day leaf water
potential under the combined treatments (Figure 10).

\textbf{4.3. Implications}

Since the initiation of the Grain for Green project in 1999, extensive
commercial plantations of jujube, apple (\emph{Malus domestica} ),
walnut (\emph{Juglans regia} ), and peach (\emph{Prunus persica} ),
among others, have been planted on the Loess Plateau, with the aim of
delivering ecological and economic benefits (Gao et al., 2014). For
example, the area of planted apple trees reached 130 million ha by 2017
(Gao et al., under review). On the Loess Plateau, these commercial
plantations are primarily run by smallholder farmers. Because of the
complex topography and high cost of irrigation, most of these
plantations are rainfed (Gao et al., 2018b). Therefore, efficient use of
rainwater and improved SWS are critical to their success. Our results
indicate that, compared to traditional hillslopes and terraces alone,
the combination of terracing and mulching clearly increases SWS,
enhances deep-layer water use and transpiration, and results in higher
mid-day leaf water potential, particularly during drought periods.
Therefore, the combination of terraces and mulches is strongly
recommended for use in commercial plantations on the Loess Plateau, and
potentially also in drylands worldwide, thus helping to deliver
Sustainable Development Goals (United Nations, 2015).

\textbf{5. Conclusions}

We studied how the combination of terracing and mulching influences
water use by jujube trees and their response to droughts in three
different years on the semiarid Loess Plateau of China. We found that
both the extreme and moderate droughts clearly reduced soil water
storage and modified soil water use patterns, causing a sharp increase
in the use of water from deep layers. Furthermore, the extreme rather
than moderate drought resulted in a significant decrease in
transpiration at both seasonal and annual scales. In addition, the
jujube trees exhibited isohydric behavior during the drought periods;
this allowed them to cope with extreme drought. Moreover, the combined
treatments effectively enhanced soil water availability, deep-layer soil
water and canopy transpiration, indicating higher water use efficiency
than with traditional land management. These results demonstrate that
the combination of terracing and mulching can help jujube trees to
survive extreme droughts. These findings provide insights into the
effective management of hillslope plantations in drylands, particularly
in the context of global warming.

\textbf{Conflict of interest}

The authors declare that they have no conflict of interest.

\textbf{References}

Allen, S.T., Kirchner, J.W., Braun, S., Siegwolf, R.T.W., \& Goldsmith,
G.R. (2019). Seasonal origins of soil water used by trees. \emph{Hydrol.
Earth Syst. Sci.} , 23, 1199-1210.

Arn\selectlanguage{ngerman}áez, J., Lana-Renault, N., Lasanta, T., Ruiz-Flano, P., \&
Castroviejo, J. (2015). Effects of farming terraces on hydrological and
geomorphological processes. A review. \emph{Catena} 128, 122-134.

Barbeta, A., Mejía-Chang, M., Ogaya, R., Voltas, J., Dawson, T.E., \&
Peñuelas J. (2015). The combined effects of a long-term experimental
drought and an extreme drought on the use of plant-water sources in a
Mediterranean forest. \emph{Glob. Chang. Biol.} , 21(3), 1213-1225.

Biswas, A. (2014). Landscape characteristics influence the spatial
pattern of soil water storage: Similarity over times and at
depths.\emph{Catena} , 116, 68-77.

Broedel, E., Tomasella, J., Cândido, L.A., \& von Randow, C. (2017).
Deep soil water dynamics in an undisturbed primary forest in central
Amazonia: Differences between normal years and the 2005
drought.\emph{Hydrol. Process.} , 31, 1749--1759.

Chen, D., Wei, W., \& Chen, L.D. (2017). Effects of terracing practices
on water erosion control in China: A meta-analysis. \emph{Earth Sci.
Rev} ., 173, 109-121.

Choat, B., Brodribb, T.J., Brodersen, C.R., Duursma, R.A., Lopez, R., \&
Medlyn, B.E. (2018). Triggers of tree mortality under
drought.\emph{Nature} , 558, 531-539.

Christina, M., Nouvellon, Y., Laclau, J., Stape, J.L., Bouillet, J.,
Lambais, G.R., \& le Maire, G. (2017). Importance of deep water uptake
in tropical eucalypt forest. \emph{Funct. Ecol} ., 31, 509-519.

Gao, X., Wu, P., Zhao, X., Wang, J., \& Shi, Y. (2014). Effects of land
use on soil moisture variations in a semi-arid catchment: implications
for land and agricultural water management. \emph{Land Degrad. Dev.} ,
25, 163-172.

Gao, X.D., Zhao, X.N., Li, H.C., Guo, L., Lv, T., \& Wu, P.T. (2018a).
Exotic shrub species (Caragana korshinskii) is more resistant to extreme
natural drought than native species (Artemisia gmelinii) in a semiarid
revegetated ecosystem. \emph{Agr. Forest Meteorol} ., 263, 207-216.

Gao, X.D., Liu, Z.P., Zhao, X.N., Ling, Q., \& Huo, G.P. (2018b).
Extreme natural drought enhances interspecific facilitation in semiarid
agroforestry systems. \emph{Agric. Ecosyst. Environ} ., 265, 444-453.

Granier, A. (1987). Evaluation of transpiration in a Douglas-fir stand
by means of sap flow measurements. \emph{Tree Physiol} ., 3 (4),
309-320.

Gregory, P. (2006). Plant roots: Growth, activity and interaction with
soils (Eds.). Blackwell Publishing, .

Gow, L.J., Barrett, D.J., O'Grady, A.P., Renzullo, L.J., \& Phinn, S.R.
(2018). Subsurface water-use strategies and physiological responses of
subtropical eucalypt woodland vegetation under changing
water-availability conditions. \emph{Agr. Forest Meteorol} ., 248,
348-360.

Grossiord, C., Sevanto, S., Dawson, T.E., Adams, H.D., Collins, A.D.,
Dickman, L.T., Newman, B.D., Stockton, E.A., \& McDowell, N.G. (2017).
Warming combined with more extreme precipitation regimes modifies the
water sources used by trees. \emph{New Phytol} ., 213, 584-596.

Huang, J., Yu, H., Dai, A., Wei Y., \& Kang, L. (2017). Drylands face
potential threat under 2\selectlanguage{english} degC global warming target. \emph{Nat. Clim.
Chang} ., 7, 417-422.

He, J., \& Yang, K. (2011). China Meteorological Forcing Dataset. Cold
and Arid at , 2011. doi:10.3972/westdc.002.2014.db.

Jia, Y.H., Li, T.C., Shao, M.A., et al. (2019). Disentangling the
formation and evolvement mechanism of plants-induced dried soil layers
on China's Loess Plateau. \emph{Agr. Forest Meteorol} ., 269-270, 57-70.

Li, H.J., Si, B.C., Wu, P.T., \& McDonnell, J. (2019). Water mining from
deep critical zone by apple trees growing on loess. \emph{Hydrol.
Process} . 33,320-327.

Li, L., Gao, X., Wu, P., Zhao, X., Li, H., Ling, Q., \& Sun, W. (2017).
Soil water content and root patterns in a rain-fed jujube plantation
across stand ages on the Loess Plateau of China. \emph{Land Degrad.
Dev.} , 28, 207-216.

Li, P., Zhu, Q.K., Zhao, L.L., Chang, C., \& Zhou, Y. (2011). Soil
moisture of fish-scale pit during rainy season in Loess hilly and gully
region. \emph{T. Chinese Soc. Agr. Eng} ., 27 (7), 76-81.

Liu, X.E., Li, X.G., Hai, L., Wang, Y.P., \& Li, F.M. (2014). How
efficient is film fully-mulched ridge--furrow cropping to conserve
rainfall in soil at a rainfed site? \emph{Field Crop Res} ., 169,
107-115.

Luo, D.D., Wang, C.K., \& Jin, Y. (2017). Plant water-regulation
strategies: Isohydric versus anisohydric behavior. \emph{Chin. J. Plant
Ecol} ., 41, 1020-1032.

Luo, Z.D., Guan, H.D., Zhang, X.P., Zhang, C.C., Liu, N., \& Li, G.
(2016). Responses of plant water use to a severe summer drought fortwo
subtropical tree species in the central southern China. \emph{J. Hydrol.
Reg. Stud} ., 8, 1-9.

Ma, L.H., Wang, X., Gao, Z.Y., Wang, Y.K., Nie, Z.Y., \& Liu, X.L.
(2019). Canopy pruning as a strategy for saving water in a dry land
jujube plantation in a loess hilly region of China. \emph{Agric. Water.
Manag} ., 216, 436-443.

McDowell, N., Pockman, W.T., Allen, C.D., Breshears, D.D., Cobb, N.,
Kolb, T., Plaut, J., Sperry, J., West, A., Williams, D.G., \& Yepez,
E.A. (2008). Mechanisms of plant survival and mortality during drought:
why do some plants survive while others succumb to drought? \emph{New
Phytol} ., 178 (4), 719-739.

Schmidt-Walter, P., Richter, F., Herbst, M., Schuldt, B., \& Lamersdorf,
N.P. (2014). Transpiration and water use strategies of a young and a
full-grownshort rotation coppice differing in canopy cover and leaf
area. \emph{Agr. Forest Meteorol} ., 195-196, 165-178.

Schwaerzel, K., Zhang, L.L., Montanarella, L., Wang, Y.H., \& Sun, G.
(2020). How afforestation affects the water cycle in drylands: A
process-based comparative analysis. \emph{Glob. Chang. Biol.} , 26(2),
944-959.

Singh, B., Eberbach, P.L., Humphreys, E., \& Kukal, S.S. (2011). The
effect of rice straw mulch on evapotranspiration, transpiration and soil
evaporation of irrigated wheat in Punjab, India. \emph{Agric. Water
Manag.} , 98, 1847-1855.

Tang, Y.K., Wu, X., Chen, Y.M.,, Wen, J., Xie, Y.L., \& Lu, S.B. (2018).
Water use strategies for two dominant tree species in pure andmixed
plantations of the semiarid Chinese Loess Plateau. \emph{Ecohydrology} ,
11, e1943.

Takahashi, H. (1997). Hydrotropism: The current state of our
knowledge.\emph{J. Plant Res.} , 110, 163-169.

Thornton, P.K., Ericksen, P.J., Herrero, M., \& Challinor, A.J. (2014).
Climate variability and vulnerability to climate change: a
review.\emph{Glob. Chang. Biol.} , 20, 3313-3328.

United Nations (UN). Transforming our World: the 2030 Agenda for
Sustainable Development Annex A/RES/70/1,
https://sustainabledevelopment. un.org/post2015/transformingourworld
(UN, 2015).

Vohland, K., \& Barry, B. (2009). A review of in situ rainwater
harvesting (RWH) practices modifying landscape functions in African
drylands. \emph{Agric. Ecosyst. Environ} ., 131, 119-127.

Wang, J.H. (2016). Effects of climate change on jujube industry and its
application on the Loess Plateau. China Meteorological Press, Beijing,
China.

Wang, P., Huang, K., \& Hu, S. (2020). Distinct fine root responses to
precipitation changes in herbaceous and woody plants: a
meta-analysis.\emph{New Phytol.} , 225, 1491-1499.

Wei, W., Chen, D., Wang, L.X., Daryanto, S., Chen, L.D., Yu, Y., Lu,
Y.L., Sun, G., \& Feng, T.J. (2016). Global synthesis of the
classifications, distributions, benefits and issues of
terracing.\emph{Earth Sci. Rev.} , 159, 388-403.

West, A.G., Dawson, T.E., February, E.C., Midgley, G.F., Bond, W.J., \&
Aston, T.L. (2012). Diverse functional responses to drought in a
Mediterranean-type shrubland in South Africa. \emph{New Phytol.} , 195,
396-407.

Yang, F., Feng, Z., Wang, H., Dai, X., \& Fu, X. (2017). Deep soil water
extraction helps to drought avoidance but shallow soil water uptake
during dry season controls the inter-annual variation in tree growth in
four subtropical plantations. \emph{Agr. Forest Meteorol.} , 234,
106-114.

Zhang, B.Q., AghaKouchak, A., Yang, Y.T., Wei, J.H., \& Wang, G.Q.
(2019). A water-energy balance approach for multi-category drought
assessment across globally diverse hydrological basins. \emph{Agr.
Forest Meteorol.} , 264, 247--265.

Zhang, S.L., Lovdahl, L., Grip, H., Jansson, P., \& Tong, Y. (2007).
Modelling the effects of mulching and fallow cropping on water balance
in the Chinese Loess Plateau. \emph{Soil Till. Res} ., 93, 283-298.

Zhao, X., Wu, P., Feng, H., Wang, Y., \& Shao, H. (2009). Towards
development of eco-agriculture of rainwater harvesting for supplemental
irrigation in the semi-arid Loess Plateau of China. \emph{J. Agron. Crop
Sci} ., 195, 399--407.

Zhu, X.M., Li, Y.S., Peng, X.L., \& Zhang, S.G. (1983). Soils of the
loess region in China. \emph{Geoderma} , 29, 237--255.

Table 1. The basic soil properties of the study site.\selectlanguage{english}
\begin{longtable}[]{@{}lllllllll@{}}
\toprule
Soil depth & Bulk density & Soil textural fractions (\%) & Soil textural
fractions (\%) & Soil textural fractions (\%) & K\textsubscript{sat} &
\selectlanguage{greek}θ\selectlanguage{english}\textsubscript{s} & \selectlanguage{greek}θ\selectlanguage{english}\textsubscript{FC} &
\selectlanguage{greek}θ\selectlanguage{english}\textsubscript{PWP}\tabularnewline
\midrule
\endhead
(cm) & (g cm\textsuperscript{-3}) & Sand & Silt & Clay & (mm
min\textsuperscript{-1}) & (cm\textsuperscript{3}
cm\textsuperscript{-3}) & (cm\textsuperscript{3} cm\textsuperscript{-3})
& (cm\textsuperscript{3} cm\textsuperscript{-3})\tabularnewline
0-20 & 1.27 & 19.1 & 64.7 & 16.2 & 1.21 & 50.4 & 27.5 &
6.6\tabularnewline
20-40 & 1.31 & 18.8 & 64.8 & 16.4 & 1.28 & 50.8 & 27.1 &
7.2\tabularnewline
40-60 & 1.31 & 17.9 & 63.1 & 19.0 & 1.16 & 53.1 & 28.4 &
7.1\tabularnewline
60-80 & 1.45 & 17.4 & 64.5 & 18.1 & 0.91 & 52.8 & 28.1 &
7.3\tabularnewline
80-100 & 1.37 & 18.7 & 62.8 & 18.5 & 0.85 & 52.3 & 27.8 &
8.1\tabularnewline
100-120 & 1.40 & 16.5 & 62.5 & 21.0 & 0.82 & 57.1 & 30.4 &
9.5\tabularnewline
120-140 & 1.37 & 16.1 & 63.2 & 20.7 & 0.92 & 55.8 & 30.2 &
9.2\tabularnewline
140-160 & 1.41 & 16.8 & 62.9 & 20.3 & 0.86 & 56.4 & 29.0 &
7.9\tabularnewline
160-180 & 1.46 & 16.2 & 64.1 & 19.7 & 0.94 & 55.4 & 29.2 &
8.8\tabularnewline
\bottomrule
\end{longtable}

Sand: 0.02-2 mm; Silt: 0.002-0.2 mm; Clay: \textless{}0.002 mm.
K\textsubscript{sat}: saturated hydraulic conductivity;
\selectlanguage{greek}θ\selectlanguage{english}\textsubscript{s}: saturated water content;

List of figures

Figure 1. The study site: the location of the Yuanzegou catchment on the
Loess Plateau (a), land use map (b), and a general view of the jujube
plantations (c).

Figure 2. Daily and monthly precipitation distribution at the study site
during the study period. The light orange shading indicates dry spells.

Figure 3. Fine root length density of jujube trees at the study site.

Figure 4. Temporal evolution of soil water storage (SWS) under different
treatments at different depth intervals during the study period. The
columns in the right panels show annual mean SWS for the different
treatments. The single, double, and triple asterisks indicate
significant differences at \emph{P} \textless{}0.05,\emph{P}
\textless{}0.01, and \emph{P} \textless{}0.001, respectively.

Figure 5. Depth density of water uptake (DWU) by jujube trees under
various treatments during different years.

Figure 6. The proportion of soil water use (PWU) in the studied profile
(0-280 cm) under various treatments during different years.

Figure 7. Time series for daily transpiration (T\textsubscript{d}) under
different treatments during the study period.

Figure 8. Seasonal and annual variation in transpiration under different
treatments during the study period. The single, double, and triple
asterisks indicate significant differences at \emph{P}
\textless{}0.05,\emph{P} \textless{}0.01, and \emph{P} \textless{}0.001,
respectively.

Figure 9. The relationship between annual transpiration and
corresponding mean soil water storage (SWS) in the shallow (0-100 cm)
and deep (100-280 cm) layers.

Figure 10. Mid-day leaf water potential variation for different
treatments in 2015 and 2016. The single, double, and triple asterisks
indicate significant differences at \emph{P} \textless{}0.05,\emph{P}
\textless{}0.01, and \emph{P} \textless{}0.001, respectively.

\textbf{Hosted file}

\verb`Figure 1.jpg`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 2.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 3.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 4.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 5.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 6.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 7.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 8.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 9.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\textbf{Hosted file}

\verb`Figure 10.tif`  available at \url{https://authorea.com/users/302566/articles/432677-impact-of-land-management-practices-on-tree-water-use-strategy-and-responses-to-drought-in-a-dryland-plantation}

\selectlanguage{english}
\FloatBarrier
\end{document}

