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As a drought tolerant plant, jujube ( Ziziphus jujuba Mill.) is commonly planted in Chinese semiarid Loess Plateau Region under rain-fed conditions. To evaluated the effectiveness of branch removal to conserve water resources in rain-fed jujube plantations in the region, two degrees of branch removal treatments (T1–two main branches removed; T2–one main branch removed) were compared with control treatment (none of the three main branches removed) and the effects on water use in Jujube plantations were analyzed. Sap flow was monitored (using the Granier-type thermal dissipation probes) along with meteorological factors, soil water content, vessel diameter, crown projection area and leaf area index, with soil moisture condition divided into water stress and non-water stress. Results showed that branch removal was an efficient way of conserving water resources in jujube plantations. a) It improved soil water content by reducing water loss via total evapotranspiration ( ET ) during jujube growth period. Total ET values were 452, 463 and 478 mm respectively for T1, T2 and the control treatments during jujube growth period in 2012; 408, 426 and 451 mm respectively for T1, T2 and the control treatments during jujube growth period in 2013 and 374, 381 and 392 mm respectively for T1, T2 and the control treatments during jujube growth period in 2014. b) Branch removal not only decreased transpiration per unit ground area (stand transpiration: T g ), but also increased the sensitivity of T g to environmental variables. In contrast, the removal of two (out of three) branches increased transpiration per unit leaf area (leaf transpiration: T l ), making it less sensitive to soil water content. c) Treatment T1 significantly increased the sensitivity of canopy conductance ( G c ) to vapor pressure deficit ( VPD ), which effect was not significant under T2. Isohydric regulation of water loss through G c response to VPD was the same for the three treatments, regardless of the different tree canopy sizes and soil water conditions, but reference canopy conductance ( G cref : canopy conductance at VPD = 1 kPa) was treatment-specific. d) Branch removal improved the tolerant of jujube tree to negative water potential and xylem cavitation by decreasing average vessel lumen diameters. Compared with the control, both branch removal treatments (T1 and T2) resulted in a significant decrease in average vessel lumen diameter at 15 mm below the cambium (40.74, 42.53 and 46.81 μm respectively for T1, T2 and the control treatments). Similarly, T1 and T2 reduced mean vessel lumen diameter at 5 mm below the cambium (43.20, 47.44 and 48.39 μm respectively for T1, T2 and the control treatments). e) Branch removal significantly decreased the fresh fruit yield and water use efficiency except in 2013, during which differences were not significant. Fresh fruit yield values were 8082, 8964 and 11293 kg ha −1 respectively for T1, T2 and the control treatments in 2012; 5691, 5426 and 6000 kg ha −1 respectively for T1, T2 and the control treatments in 2013; 6804, 8341 and 10589 kg ha −1 respectively for T1, T2 and the control treatments in 2014. WUE values were 1.79, 1.94 and 2.36 kg m −3 in 2012; 1.40, 1.28 and 1.33 kg m −3 in 2013; 1.82, 2.19 and 2.70 kg m −3 in 2014. T1 treatment was recommended in terms of improving soil water storage as well as maintaining a certain amount of productivity in jujube plantations in Chinese semiarid Loess Plateau Region. The result of the study is critical for the development of effective water management strategies in jujube plantations ensure that the fragile ecology of the Loess Plateau is sustained. [ABSTRACT FROM AUTHOR]

In order to select suitable evapotranspiration (ET) models for rainfed and sparsely cultivated jujube ( Ziziphus jujuba Mill.) plantations in the Loess Plateau, this study used Bayesian analysis to compare the performances (accuracies and uncertainties) of the Shuttleworth–Wallace (SW) model, the Penman–Monteith (PM) model and the Penman–Monteith equation with a variable surface canopy resistance (PMv) model in terms of daily and hourly ET. To determine seasonal variations and soil water dependence, probabilistic analyses were independently used to calibrate the SW and PM model parameters at every growth stages and the PMv model parameters for different soil water conditions in the growth season of rainfed jujube plantations in 2013. Finally, data for the growth season in 2012 were used to validate the calibrated models. The results showed that the posterior distributions of the parameters of the three models narrowed down at both daily and hourly scales, suggesting decreasing uncertainties in the parameters. Some model parameters varied with season (increasing for the last two growth seasons) or soil water condition (decreasing with increasing soil moisture). The performances of the ET models also varied with time scale, generally less precise at hourly than at daily time scale. Irrespectively, the three ET models met the evaluation criteria (mean relative error (MAE) < 20% and coefficient of determination ( R 2 ) > 0.8 and Willmott index of agreement ( D ) > 0.8) with acceptable accuracy and uncertainty at the daily time scale in both calibration (with R 2 , MAE and D values of 0.94, 6.78% and 0.94 for the SW model; 0.94, 7.52% and 0.94 for the PM model; and 0.89, 8.49% and 0.83 for the PM V model, respectively) and validation periods (with R 2 , MAE and D values of 0.94, 5.77% and 0.92 for the SW model; 0.93, 5.15% and 0.91 for the PM model; and 0.89, 10.26% and 0.86 for the PM V model, respectively). Where only climate data were available, the PM V model was recommended for estimation of daily ET in the study area due to less complexity, low data requirements, and high accuracy. Where sufficient monitoring data were available, the PM model was preferred for estimation of the daily ET in the study area due to less complexity and small differences in performance with the SW model. All three models met the evaluation criteria for calibration period(with R 2 , MAE and D values of 0.92, 16.04% and 0.92 for the SW model; 0.96, 14.37% and 0.94 for the PM model; and 0.89, 18.56% and 0.91 for the PM V model, respectively) while only the SW model met the evaluation criteria for validation period (with R 2 , MAE and D values of 0.87, 16.33% and 0.88 for the SW model; 0.85, 20.70% and 0.85 for the PM model; and 0.85, 23.95% and 0.83 for the PM V model, respectively) at the hourly time scale. Based on model accuracy and uncertainty at the hourly time scale, the SW model was recommended for use in estimating ET in jujube plantations in the Loess Plateau. [ABSTRACT FROM AUTHOR]

Highlights: [•] Jujube, a drought tolerant plant which was seldom studied, was used as material. [•] Water-use strategy of rainfed jujube characterized by dry climate was researched. [•] Relative sap flow (SF R ), rather than absolute sap flow (SF) was used. [•] The changing process of SF R in a day contains two different periods. [•] Soil water content mainly influence the first period of SF R changing process. [Copyright &y& Elsevier]

The widely adopted practice of clean-cultivation in rainfed orchards in the Loess Plateau has led to serious soil erosion and degradation problems. Agroforestry is a promising management practice for solving these problems, but may reduce available soil water. Thus, reasonable soil and water management strategies should be developed for agroforestry systems in this region. The objective of this study was to determine whether adopting proper mowing management of the understory intercrop limited soil drying in a rainfed jujube (Ziziphus jujuba Mill.) orchard in this region. Various mowing intensities (3-, 6-, 9-cm stubble height and unmowed treatments) were imposed on three intercrop species: bluegrass (Poa pratensis L.), white clover (Trifolium repens L.), and hairy vetch (Vicia villosa Roth) to investigate and compare their root characteristics and soil moisture responses to mowing under greenhouse and field conditions. Based on the results, the most promising intercrop species and mowing intensity to be used in a jujube orchard were selected for field validation. The results showed that mowing effectively regulated intercrop root amount and distribution, as well as associated soil moisture conditions. However, the sensitivities of root characteristics and soil moisture to mowing and growth environment were species-specific. Bluegrass mowed to a 3-cm stubble height produced the minimum root amount, the shallowest root depth, and the greatest soil water content. When this treatment was applied to a rainfed jujube orchard during the 2015 and 2016 growing seasons, average soil moisture in the 0–300 cm soil layer was essentially unaffected, while fruit yield was increased. Consequently, bluegrass mowed to a stubble height of 3 cm when intercropped with jujube trees in the Loess plateau is a feasible practice to increase jujube yield and avoid extra soil drying. • Mowing altered root amount, depth and vertical distribution of intercrop species. • Proper mowing limited intercrop root growth and improved soil water condition. • Mowing effects differed among intercrop species and growth environment. • Bluegrass with 3-cm stubble height was selected for use in rainfed jujube orchard. • Selected agroforestry did not increase soil drying than jujube clean-cultivation. [ABSTRACT FROM AUTHOR]

• Various constraint functions of environmental factors were used in Jarvis model. • Their ability to model daily transpiration of jujube orchard (T) was compared. • Bayesian approach, rather than traditional method was used for model comparison. • Different constraint functions of soil water achieved different T model performance. • Including soil water in Jarvis model was not always improved T model performance. The Jarvis canopy resistance sub-model is commonly used in transpiration modelling, although its optimal structure is rarely studied. It is still not fully clear that to what extent transpiration modeling may differ if using different constraint function forms for key environmental variable in Jarvis sub-model. In this study, various Jarvis canopy resistance sub-model configurations were embedded in the Penman-Monteith model to compare their ability to model daily transpiration of rain-fed jujube (Ziziphus jujuba Mill.) plantations where soil moisture is a key factor of tree water use. Parameters were calibrated using the Bayesian Markov Chain Monte Carlo (MCMC) simulation technique and model comparison was quantified using Deviance Information Criterion (DIC). The results showed significant differences in model performance between the constraint function forms of soil water content. The difference in DIC between the model with the best constraint function form and the other two forms reached 37.66–50.94, much higher than the evaluation criteria for significance (larger than 7). When the best constraint function form was used, the performance of the transpiration model improved. The model performance worsened when the other constraint function forms were used, even worse than those without consideration for soil water content. However, only slight differences in model performance were detected for the constraint function forms of temperature, vapor pressure deficit and photosynthetically active radiation. Using the best configuration of Jarvis canopy resistance sub-model, daily transpiration of jujube plantation was well estimated with overall good accuracy and acceptable uncertainty. The predictions and observations were highly correlated (R2 = 0.87 for calibration and R2 = 0.80 for validation). The results suggested that different constraint function forms of an environmental factor contributed differently to transpiration model performance, and the situation was different for different environmental factors. Including the key environmental factor in the Jarvis canopy resistance sub-model will not always improve the performance of transpiration models. [ABSTRACT FROM AUTHOR]

Soil desiccation occurs widely across China's Loess Plateau due to long-term water demand in excess of water supply. Hydraulic redistribution (HR) - the movement of water from wet to dry soil via roots - and canopy dew (CD) are crucial to water replenishment in dryland ecosystems. However, much is still not known about the response of CD and HR to soil water deficits (including no deficit, slight deficit, moderate deficit, and severe deficit water conditions) in dryland jujube (Ziziphus jujuba Mill.) plantations in China's Hilly Loess Region. To this end, the duration and intensity of dew were monitored using dielectric leaf wetness sensors to better understand the effects of soil water status on dew. Also, soil water content, sap flow, and meteorological variables were measured during the jujube growing seasons in 2017–2019. The results showed that the time of occurrence of CD under the no deficit condition came earlier than the time of occurrence of CD under slight, moderate, and severe soil water deficit conditions. Peak CD appeared at 5:00–6:30 am and ended at 6:30–9:00 am local time under the four soil water conditions. The amount, duration, and frequency of CD decreased with increasing soil water deficit. The amount and duration of CD under the no deficit condition were significantly higher than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). The amount and frequency of HR (in the 20–60 cm soil layer) increased with increasing soil water deficit. Under the no deficit condition, HR was significantly lower than under the slight, moderate, and severe soil water deficit conditions (p < 0.05). While HR was influenced by CD, CD enhanced HR under the no deficit condition, but inhibited HR under slight, moderate, and severe soil water deficit conditions. For the growing season, the contribution of CD to total actual evapotranspiration (ET c act , CD/ ET c act ratio) was highest under the no deficit condition (maximum CD/ ET c act ratio of 0.21). The contribution of HR to ET c act (HR/ ET c act ratio) was higher under slight, moderate, and severe soil water deficit conditions (maximum of 0.11). The mutual effects of CD and HR lessened soil water deficit, making them important ecohydrological processes affecting the response of dryland jujube plantations to soil desiccation. ● The amount and duration of canopy dew decreased with increasing soil water deficit. ● The hydraulic redistribution (HR) increased with increasing soil water deficit. ● HR was influenced by canopy dew. ● The mutual effect of canopy dew and HR lessened soil water deficit. [ABSTRACT FROM AUTHOR]