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Drip irrigation allows plants to be watered by slowly wetting the soil on a small surrounding area using special devices that distribute water drop by drop. The main advantage of drip irrigation compared to classic irrigation methods is that the necessary water amount is considerably reduced by wetting the soil strictly in the area that contains the roots for the plant. This allows a rigorous dose of the distributed water amount. On a clay loam cambic chernozem in the Cracau Plain that has a present moisture content of 19% g/g, field capacity of 23.2 % g/g, wilting coefficient of 14.8% g/g and bulk density of 1.36 g/cm³ (mean values for a depth range of 0 - 80 cm), we performed water irrigation for a duration of 10 hours using spiral microtube dripping devices. The total water discharge per dripping unit ranged from 19.6 – 36.1 l, and the water flux ranged from 1.96 – 3.65 l/hour. Twenty-four hours after irrigation, we observed that the distribution of about 20 l of water, with a water flux of about 2 l/hours, provided soil wetting of the zone under the dripping device at higher values than the field capacity at a depth of 80 – 90 cm. The diameter of the wetting contour ranged from 60 – 100 cm at a depth from 40 – 50 cm, and the border diameter of the wetting zone ranged from 100 – 400 cm at a depth from 50 – 70 cm. Higher water flux values or longer irrigation durations resulted in a longer overwetting state in the upper half of the active layer of the soil and in water loss by percolation. [ABSTRACT FROM AUTHOR]

The research was conducted at the "El Jaguey" belonging to the Cooperative Credit and Service "Ramón López Peña" of the Council Popular Cortés, Sandino, Pinar de Río, with the aim of determining vegetative and yield development in five cultivars of onion (Allium cepa L.). The established cultivars were 'Caribe 71', 'Diandra F1', 'Regent F1', 'Red Creole' and 'Texas Early Grain E 502', which were distributed in a completely randomized block design with three replications. The planting was carried out in rows, at a distance of 0.30 x 0.10 m, with homogeneous seedlings of each cultivar. Evaluations were carried out at 32 and 60 days after transplantation, where the variables plant height, number of active leaves, diameter of the false stem and total fresh mass were characterized. At harvest time, the fresh mass, the equatorial and polar diameters and the humidity were determined in the bulbs. The crop yield was also estimated. The results showed greater vegetative development in the cultivars 'Texas Early Grano E 502' and 'Red Creole', although the former reached yields above 35 t ha-1 and significantly exceeded the other cultivars. The equatorial diameter of the bulb determined its fresh mass in more than 85%, with the exception of the cultivar 'Texas Early Grano E 502', while the percentage of humidity of the bulb exceeded 75% in all cases and was infiuenced by the color of the same. [ABSTRACT FROM AUTHOR]

Tuber ultimate compressive strength (UCS) is a very important sensory property of tuber products. The UCS depends significantly on tuber moisture content and cooking degree. Therefore, it is necessary to monitor the UCS of tuber products during the industrial production. In the present study, Fourier transform mid-infrared spectra and UCS reference values of tuber samples at different drying times were collected. The fitting functions between tuber UCS and drying time were evaluated. Moreover, the fingerprint spectral matrices (1500–900 cm−1) were studied by pre-treatment methods and principal component analysis. Then, the spectral features were linked to the tuber UCS based on multivariate calibration models in terms of principal component regression and support vector machine regression (SVMR). It has been confirmed that tuber UCS values fitted by specific exponential function could be successfully used to develop robust SVMR model. [ABSTRACT FROM AUTHOR]

Lentil is now an integral part of prairie cropping systems. Climate forecasts point to variable and increased drought frequency, putting lentil production in jeopardy. Future lentil genotypes will require root systems that can extract more water under drought conditions. This study focuses on root diameter and root tip number, traits known to play an important role in water uptake during drought. We compared the total root length (TRL) in three soil horizons of both wild and cultivated lentil genotypes for three root diameter classes when plants were grown under moderate or severe drought, and when re-watered after exposure to moderate drought conditions. Our study demonstrates that roots of both wild and cultivated lentil genotypes can be categorized into very fine, fine and small diameter classes. Some wild lentil genotypes had significantly higher TRL in the B and C soil horizons when grown under severe or moderate drought and therefore, could act as resources for the transfer of root traits to cultivated lentil genotypes. Further evaluations focused on the root systems of interspecific recombinant inbred lines under drought conditions will be required to determine whether these traits are heritable. [ABSTRACT FROM AUTHOR]

Presented in this paper is a proposed model describing the variation in the rehydration ratio with rehydration time for yam slices. The 'new' model describes the relationship between the moisture content of yam slices with time when rehydrated. The changes in mass and moisture content data with rehydration time, during the rehydration process, were recorded. Rehydration was carried out at 27 °C, 40 °C, 60 °C, and 80°C for 3.0 mm thick dehydrated yam slices. Regression analysis established that the variation in rehydration ratio vs rehydration time data, better fitted a two-term exponential equation rather than a quadratic equation. Also, regression analysis done on variation in rehydration ratio vs rehydration time data of cube sweet potatoes found it literature, further validated that the rehydration ratio vs rehydration time data better fitted a two-term exponential equation rather than a quadratic equation. For the recorded moisture content versus rehydration time data, a better fit was obtained for the new model rather than the Weibull, Peleg, and Exponential models. This study is essential for a better understanding of the rehydration characteristics of yam slices during the rehydration process. Information about rehydration characteristics of the yam slices presented in this work will also be valuable to optimise and characterise the soaking conditions, design yam-processing equipment and predict water absorption as a function of time and temperature. The rehydration process clearly indicates that rehydration occurs very rapidly in the first few minutes of the rehydration process, and this process is faster as the rehydration temperature increases. [ABSTRACT FROM AUTHOR]

Graphene, a new type of nanomaterial, has unique physical properties and important potential biological applications. However, few studies have been conducted on the environmental impact of graphene. Therefore, to explore the effect of graphene on plants, three-week-old, tissue-cultured ‘Gala’ apple plants ( Malus domestica ) were treated with different concentrations (0, 0.1, 1, 10 mg/L) of graphene oxide (GO) and examined after 40 days. Results indicated that adventitious root length, moisture content and the number of lateral roots were all inhibited by 0.1–10 mg/L GO. At 0.1 and 1 mg/L GO, however, the number of adventitious roots and the rooting rate exhibited a significant increase, relative to the control (no GO). Treatment with GO increased the activities of oxidative stress enzymes including catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) in the apple plants, relative to controls. Malondialdehyde (MDA) levels were also significantly decreased at 10 mg/L GO. Treatment of apple plantlets with 0.1 mg/L GO increased the transcript abundance of auxin efflux carrier ( PIN7, ABCB1 ) genes and auxin influx carrier ( LAX2, LAX3 ) genes but inhibited the transcript levels of the ARR3 gene, which involved in cytokinin biosynthesis. Additionally, the transcript levels of ARRO1 , ARF19 , and TTG1 , which play roles in the formation of adventitious roots, lateral roots, and root hairs, respectively, were all decreased in response to treatment with 1 and 10 mg/L GO. Collectively, the results indicate that treatment of ‘Gala’ apple plants with 0.1 mg/L GO had a positive effect on root formation but a negative effect on root growth. This response may be related to the negative impact of GO on cellular structure and function. [ABSTRACT FROM AUTHOR]

Ever since Darwin postulated that the tip of the root is sensitive to moisture differences and that it "transmits an influence to the upper adjoining part, which bends towards the source of moisture" [Darwin C, Darwin F (1880) The Power of Movement in Plants, pp 572-574], the signal underlying this tropic response has remained elusive. Using the FRET-based Cameleon Ca2+ sensor in planta, we show that a water potential gradient applied across the root tip generates a slow, long-distance asymmetric cytosolic Ca2+ signal in the phloem, which peaks at the elongation zone, where it is dispersed laterally and asymmetrically to peripheral cells, where cell elongation occurs. In addition, the MIZ1 protein, whose biochemical function is unknown but is required for root curvature toward water, is indispensable for generating the slow, long-distance Ca2+ signal. Furthermore, biochemical and genetic manipulations that elevate cytosolic Ca2+ levels, including mutants of the endoplasmic reticulum (ER) Ca2+-ATPase isoform ECA1, enhance root curvature toward water. Finally, coimmunoprecipitation of plant proteins and functional complementation assays in yeast cells revealed that MIZ1 directly binds to ECA1 and inhibits its activity. We suggest that the inhibition of ECA1 by MIZ1 changes the balance between cytosolic Ca2+ influx and efflux and generates the cytosolic Ca2+ signal required for water tracking. [ABSTRACT FROM AUTHOR]

The seeds cannot fully sprout owing to the seed quality and environmental differences. So it is difficult to provide seedling pots without empty seedling holes for automatic transplanting. In order to reduce the number of seedling shortage and the manual labor intensity of seedling supplement, and to improve transplanting quality, a method for supplementing seedlings in cotyledon phase was presented in the paper. According to the delicate seedling, undeveloped root system and the unconsolidated substrate in pot, a new type of end-effector for supplementing pot-seedling in cotyledon phase with 4 seedling shovels was designed. The 4 angular seedling shovels were synchronously driven up and down by stepper motor moving the X-shaped press rod. They can shape enveloping surface when they are inserted into the lower limit position of the whole pot and surrounded the seedlings from the 4 sides of seedling substrates during seedling. And then the pot seedling was taken out from seedling hole and transplanted to the target hole. The seedling supplementing was finished while the pot seedling was left in the target pot hole and the seedling spades lifted it up along the inclined guide. The 3 factor and 3 level orthogonal tests were conducted respectively with the Zheza809 tomato pot seedlings in cotyledon phase with the seedling age of 16, 21 and 26 d cultivated in standard seedling tray with 72 holes. In the test, the velocities of inserting and taking out of matrix for the shovels were measured by speedtro-50 laser velometer, and the average velocities were 29.85 and 31.12 m/s respectively. The mixture ratio of peat, vermiculite and perlite in nursery matrix, the moisture content of the substrate and the seedling age were chosen as factors. The matrix net rate, which is the percentage of the weight of pot seedling taken out from the pot holes by the end-effector in the total mass of the pot seedling in the pot hole, was set as index. The results indicate that the net rate of taking out the free substrate without seedlings or the pot seedlings in cotyledon phase is affected significantly by the pot seedling age and the mixture ratio of peat, vermiculite and perlite in nursery matrix. The net rate increases with the seedling age, which reaches the highest value at the end of cotyledon phase and the mixture ratio of peat, vermiculite and perlite in nursery matrix of 2:2:1. The effect of matrix water content from 67.1% to 79.2% on the net rate is not significant, while the net rate keeps a high value owing to good cohesive force and plasticity of the substrate when the moisture content of the substrate is 74.1%. When the growth age is 26 d, the mixture ratio of peat, vermiculite and perlite in nursery matrix is 2:2:1 and the moisture content of the substrate is 74.1%, the average net rate reaches the maximum of 89.5% and the shape and volume of the seedling pot keep complete. To further verify the optimal combination obtained by the test, the experiments of seedling taking out and supplementing were carried out with tomato pot seedlings with the age of 26 d, the mixture ratio of peat, vermiculite and perlite in nursery matrix of 2:2:1 and suitable substrate moisture content. The results show that the success rates for the free substrate without seedlings and pot seedlings are both 100%, which can take out the pot seedlings in cotyledon phase with crisp plant and loose matrix as a whole and fill them into target hole on the seedling pot completely. [ABSTRACT FROM AUTHOR]

To investigate the response of root architecture and nitrogen metabolism of apple rootstock to glucose supply in low-carbon (C) soil, Malus baccata (L.) Borkh. in gravel soil was treated with glucose C equal to the soil microbial biomass carbon (MBC)-C value (G1), five times the soil MBC value (G2), or with no glucose (CK). The roots samples were harvested after treatments for 7, 15 and 30 days. The roots tended to become larger, more dichotomous and showed a larger link branching angle in G1 and G2 than in CK, especially in the G1 treatment for 30 days. Plant height and biomass were increased by G1. Nitrate (NO-3-N) and nitrite (NO-2-N) contents were increased, but ammonium (NH+4-N) concentration was decreased in the roots treated with G1 and G2 in all treatment periods. Also, the activities and transcript levels of nitrate reductase, glutamine synthetase, glutamate dehydrogenase, glutamate synthase were generally increased in roots treated with glucose, especially under G1. The activities of glutamic oxalacetic transaminases and glutamic-pyruvic transaminase were higher under G1 than under either G2 or CK. Exogenous carbon source that equals to the native MBC effectively regulated the root architecture and supported increasing nitrogen absorption and metabolism in plants growing under carbon-restricted conditions. [ABSTRACT FROM AUTHOR]

Aims: Root-specific responses to stress are not well-known, and have been largely based on indirect measurements of bulk soil water extraction, which limits mechanistic modeling of root function.Methods: Here, we used neutron radiography to examine in situ root-soil water dynamics of a previously droughted black cottonwood (Populus trichocarpa) seedling, contrasting water uptake by the two major components of the root system that differed in initial recovery rate as apparent by ‘new’ (whiter, thinner), or ‘old’ (darker, thicker) parts of the fine root system.Results: The smaller diameter ‘new’ roots had greater water uptake per unit surface area than the larger diameter ‘old’ roots, but they had less total surface area leading to less total water extraction; rates ranged from 0.0027-0.0116 g cm−2 h−1. The finest most-active roots were not visible in the radiographs, indicating the need to include destructive sampling. Analysis based on root-free bulk soil hydraulic properties indicated substantial redistribution of water via saturated/unsaturated flow and capillary wicking across the layers - suggesting water uptake dynamics following an infiltration event may be more complex than approximated by common soil hydraulic or root surface area modeling approaches.Conclusions: Our results highlight the need for continued exploration of root-trait specific water uptake rates in situ, and impacts of roots on soil hydraulic properties - both critical components for mechanistic modeling of root function. [ABSTRACT FROM AUTHOR]

The ability of plants to take up water from the soil depends on both the root architecture and the distribution and evolution of the hydraulic conductivities among root types and along the root length. The mature maize (Zea mays L.) root system is composed of primary, seminal, and crown roots together with their respective laterals. Our understanding of root water uptake of maize is largely based on measurements of primary and seminal roots. Crown roots might have a different ability to extract water from the soil, but their hydraulic function remains unknown. The aim of this study was to measure the location of water uptake in mature maize and investigate differences between seminal, crown, and lateral roots. Neutron radiography and injections of deuterated water were used to visualize the root architecture and water transport in 5-week-old maize root systems. Water was mainly taken up by crown roots. Seminal roots and their laterals, which were the main location of water uptake in younger plants, made a minor contribution to water uptake. In contrast to younger seminal roots, crown roots were also able to take up water from their most distal segments. The greater uptake of crown roots compared with seminal roots is explained by their higher axial conductivity in the proximal parts and by the fact that they are connected to the shoot above the seminal roots, which favors the propagation of xylem tension along the crown roots. The deeper water uptake of crown roots is explained by their shorter and fewer laterals, which decreases the dissipation of water potential along the roots. [ABSTRACT FROM AUTHOR]

Spatially averaged models of root-soil interactions are often used to calculate plant water uptake. Using a combination of X-ray computed tomography (CT) and image-based modelling, we tested the accuracy of this spatial averaging by directly calculating plant water uptake for young wheat plants in two soil types. The root system was imaged using X-ray CT at 2, 4, 6, 8 and 12 d after transplanting. The roots were segmented using semi-automated root tracking for speed and reproducibility. The segmented geometries were converted to a mesh suitable for the numerical solution of Richards' equation. Richards' equation was parameterized using existing pore scale studies of soil hydraulic properties in the rhizosphere of wheat plants. Image-based modelling allows the spatial distribution of water around the root to be visualized and the fluxes into the root to be calculated. By comparing the results obtained through image-based modelling to spatially averaged models, the impact of root architecture and geometry in water uptake was quantified. We observed that the spatially averaged models performed well in comparison to the image-based models with <2% difference in uptake. However, the spatial averaging loses important information regarding the spatial distribution of water near the root system. [ABSTRACT FROM AUTHOR]

The linkage between root zone soil moisture and groundwater is either neglected or simplified in most land surface models. The fully-coupled subsurface-land surface model TerrSysMP including variably saturated groundwater dynamics is used in this work. We test and compare five data assimilation methodologies for assimilating groundwater level data via the ensemble Kalman filter (EnKF) to improve root zone soil moisture estimation with TerrSysMP. Groundwater level data are assimilated in the form of pressure head or soil moisture (set equal to porosity in the saturated zone) to update state vectors. In the five assimilation methodologies, the state vector contains either (i) pressure head, or (ii) log-transformed pressure head, or (iii) soil moisture, or (iv) pressure head for the saturated zone only, or (v) a combination of pressure head and soil moisture, pressure head for the saturated zone and soil moisture for the unsaturated zone. These methodologies are evaluated in synthetic experiments which are performed for different climate conditions, soil types and plant functional types to simulate various root zone soil moisture distributions and groundwater levels. The results demonstrate that EnKF cannot properly handle strongly skewed pressure distributions which are caused by extreme negative pressure heads in the unsaturated zone during dry periods. This problem can only be alleviated by methodology (iii), (iv) and (v). The last approach gives the best results and avoids unphysical updates related to strongly skewed pressure heads in the unsaturated zone. If groundwater level data are assimilated by methodology (iii), EnKF fails to update the state vector containing the soil moisture values if for (almost) all the realizations the observation does not bring significant new information. Synthetic experiments for the joint assimilation of groundwater levels and surface soil moisture support methodology (v) and show great potential for improving the representation of root zone soil moisture. [ABSTRACT FROM AUTHOR]

The soil moisture dynamics of the root zone and its hydrological interactions with the vadose zone below in deep groundwater table condition has not been thoroughly elucidated to date, thereby hampering our adaption of irrigation in farmlands with a deep groundwater table. In this study, vadose zone modelling detailing the soil moisture dynamics of the root zone in farmland with a deep groundwater table in the North China Plain, was presented to investigate the regular pattern of the soil hydrological processes during crops growing periods and to examine its implications for adjustment of irrigation applications of wheat and maize. Deep percolation reached over 30% of the total water input while root zone hardly obtain any moisture supplement from the vadose zone below, during the crops growing period, from April to September in 2012 and 2013, both being typical wet years. Corresponding to the seasonal distribution of precipitation, the soil evaporation and deep percolation were concentrated in the growing period of maize, rather than in the growing period of wheat. Additionally, soil water storage in the root zone before irrigation applications in the growing periods of wheat can be 100–120 mm less than it in growing periods of maize. On the basis of these soil hydrology characteristics in the root zone, the current irrigation scheduling for wheat could be adjusted to be more adequate but less frequent, while intensity and frequency of irrigation applications for maize should both be decreased to reduce deep percolation and soil evaporation. An example simulation in the crop growing period of 2012, showed that deep percolation and soil evaporation can be decreased by 36% and 18% respectively, with little impacts on crops transpiration, under the adjusted irrigation practice. This research suggests the direction and potential of adjustment of irrigation scheduling in farmlands with a deep groundwater table from the perspective of soil hydrological processes. [ABSTRACT FROM AUTHOR]

The purpose of the present research, was evaluating the performance of HYDRUS-3D model for simulating soil moisture under field conditions for corn and durum wheat in a Mediterranean climate. Furthermore, the PILOTE model was also used for accounting root water extraction. Soil moisture at different depths was measured by a neutron probe before irrigation. Observed soil moisture values were compared with simulated data using statistical indices i.e., the root mean square error (RMSE) and the normalized root mean square error (NRMSE). The ranges of water content NRMSE were between 6.3 and 7.5%. The performance of the model based on calculated NRMSE values have been placed in the excellent category for simulation of the soil water content. Ranges of RMSE were obtained between 0.0174 and 0.0190 cm3 cm-3, though the values are very low. The results of these two statistical indices indicated the high ability of the model in simulating soil water content. [ABSTRACT FROM AUTHOR]

Background and aims: Evidence for impacts of environmental changes on belowground net primary production (BNPP) from long-term experiments is rather scarce. We aimed to understand how long-term changes in water and nitrogen availability affect production and vertical allocation of roots in semi-arid grasslands and its consequence on carbon (C) and nitrogen (N) cycles. Methods: We investigated changes of BNPP and its vertical allocation along the soil profile to 40 cm in depth in response to simultaneous increases in water and N availability over 11 years in an old-field grassland in northern China. Results: Water addition increased BNPP in all soil layers (0-10 cm, 10-20 cm, and 20-40 cm), and enhanced the percentage BNPP in the upper soils but decreased that in 10-20 cm soil layer. Nitrogen addition decreased BNPP in 10-20 cm and 20-40 cm soil layers as well as total BNPP in 0-40 cm, and increased the percentage BNPP in the upper soil layer but decreased that in 10-20 cm soil layer. Water addition increased soil total C and N concentrations in 0-10 cm and 10-20 cm soil layers, while N addition only marginally decreased soil C:N ratio in 0-10 cm and 20-40 cm soil layers. Both soil total N concentration and soil C:N ratio were closely related to BNPP. Conclusions: Our results highlight the importance of environmental factors, especially water availability, in determining BNPP, and in turn controlling soil nutrient accumulation in semi-arid grasslands, although the specific mechanisms remain unclear. The projected increase in precipitation in those semi-arid grasslands would enhance soil C and N sequestration. The increased allocation of BNPP in upper soils with long-term precipitation increment and N deposition may accelerate the cycles of C and N in these ecosystems, and thus increase the risk of soil C and N loss. [ABSTRACT FROM AUTHOR]

Vegetation water use is closely related to its biophysical functioning and is often under stress from various environmental factors. However, commonly used root water uptake models only consider the stress from root zone moisture availability. There is a need to incorporate the stress from both the above-ground factors and root zone water condition. In this study, a newly developed coupled supply- and demand-induced (S&D) root water uptake model is examined with measurements on two tree species, Guihua in the subtropical monsoon climate and Drooping Sheoak in the Mediterranean climate. The results show that the S&D model outperforms a supply-constraint water stress function (the S-shape model) for both studied species. The S&D model predicts 67% and 84% temporal variability in the measured water stress for Guihua and Drooping Sheoak, respectively. The improvement of the S&D model over the S-shape model is more significant for Guihua than for Drooping Sheoak, which might be associated with the specific climate conditions. A two-step parameterization approach is adopted in this study for the S&D model, and is recommended for future applications. These results further support the validity of the S&D model, and should be considered for the root water uptake modeling. [ABSTRACT FROM AUTHOR]

Belowground herbivory under nutrient-poor conditions is known to significantly decrease plant biomass and root:shoot ratios. However, the mechanisms behind the changes in belowground plant–herbivore interactions that occur under different nutrient conditions remain unclear. We performed a pot experiment using Lolium perenne L. and the third-instar larva of Popillia japonica Newman. The experiment used a three-way factorial randomized-block design; the three factors were nutrient amount (rich/poor), nutrient heterogeneity (homogeneous/ heterogeneous), and belowground herbivore (present/absent). Relative water content (RWC) of shoots under nutrient-poor conditions was smaller than that under nutrient-rich conditions, and a single herbivory significantly reduced the RWC under the nutrient-poor conditions. Plant biomass was larger under nutrient-rich conditions than under nutrient-poor conditions. A herbivore decreased plant biomass more under nutrient-poor conditions than under nutrient-rich conditions. Nutrient heterogeneity had no effect on plant biomass, but herbivory and nutrient amount interactively affected root proliferations to nutrient patches. Plants were smaller under nutrient-poor conditions; thus, a larger proportion of the roots was removed by a belowground herbivore. A loss of a larger proportion of roots would cause the small RWC, which restricts compensatory growth. Consequently, growth of L. perenne is more severely limited by a belowground herbivore under nutrient-poor conditions. [ABSTRACT FROM AUTHOR]

The central moments of soil water content (SWC) variability at the field scale are determined by soil texture, considering both smooth topography and groundwater table position. The characteristics of variability are governed by other soil factors like soil structure, micro relief, preferred water flow paths, root system characteristics, rock content, etc. This paper shows the integral effect of all these hardly quantifiable factors on SWC variability simulated by the processes of evapotranspiration and groundwater–root zone interaction using the HYDRUS ET model. SWC and soil hydraulic characteristics were spatially determined over a 4.5 ha field during two sampling campaigns under different atmospheric and groundwater conditions, and data distributions were compared to SWC distributions provided by mathematical modeling. The entire spring–summer period of 2003 was then examined for changes of SWC spatial variability. It was found that evapotranspiration influences SWC spatial variability only if SWC is under the critical value when wetter parts of the field evaporate more water than drier parts, resulting in smoothed SWC variability. Under wet conditions the spatial variability of SWC increases by drainage, as those parts of the soil with coarser texture drain faster than finer-textured parts. [ABSTRACT FROM PUBLISHER]

Currently, there are several space missions capable of measuring surface soil moisture, owing to the relevance of this variable in meteorology, hydrology and agriculture. However, the Plant Available Water (PAW), which in some fields of application could be more important than the soil moisture itself, cannot be directly measured by remote sensing. Considering the root zone as the first 50 cm of the soil, in this study, the PAW at 25 cm and 50 cm and integrated between 0 and 50 cm of soil depth was estimated using the surface soil moisture provided by the Soil Moisture Ocean Salinity (SMOS) mission. For this purpose, the Soil Water Index (SWI) has been used as a proxy of the root-zone soil moisture, involving the selection of an optimal T (T opt ), which can be interpreted as a characteristic soil water travel time. In this research, several tests using the correlation coefficient (R), the Nash-Sutcliffe score (NS), several error estimators and bias as predictor metrics were applied to obtain the T opt , making a comprehensive study of the T parameter. After analyzing the results, some differences were found between the T opt obtained using R and NS as decision metrics, and that obtained using the errors and bias, but the SWI showed good results as an estimator of the root-zone soil moisture. This index showed good agreement, with an R between 0.60 and 0.88. The method was tested from January 2010 to December 2014, using the database of the Soil Moisture Measurements Stations Network of the University of Salamanca (REMEDHUS) in Spain. The PAW estimation showed good agreement with the in situ measurements, following closely the dry-downs and wetting-up events, with R ranging between 0.60 and 0.92, and error values lower than 0.05 m 3 m −3 . A slight underestimation was observed for both the PAW and root-zone soil moisture at the different depths; this could be explained by the underestimation pattern observed with the SMOS L2 soil moisture product, in line with previous studies. Nevertheless, the results obtained in this research showed an encouraging improvement of the PAW estimation. Despite the need for more research on this issue, the results of this study show that this methodology can be useful for applications of great interest in agriculture and hydrology. [ABSTRACT FROM AUTHOR]

Background and aims: Water is often heterogeneously distributed in soils. Understanding roots' responses to this soil-water heterogeneity is a key parameter defining plant survival in dry climates. To determine local root water uptake for partly dry conditions in a plant's root system, we prepared soil patches with different water contents, then used neutron radiography to monitor daily changes in root structure and water uptake. Methods: Lupin plants were grown in 30 × 25 × 1 cm aluminum containers filled with sandy soil. In two partitioning set-ups, the soil-root zone was divided into either two or nine hydraulically-isolated soil compartments. This was done by packing layers of coarse sand as capillary barriers, by which vertical and/or horizontal soil water heterogeneity as well as homogeneous well-watered treatments were applied for control. Daily changes in soil water content in each compartment, water uptake and root growth were monitored non-invasively and quantified by neutron radiography during a period of 15 consecutive days. Results: In optimal homogeneously-wet soil, lateral roots in the top 10 cm of the root system showed the highest water uptake rate, up to around 10 mg/(mm. root. day), which on average was twice as much as that for younger lateral roots in lower position and taproot. In heterogeneous treatments, root water uptake declined strongly in compartments with the soil water content below 0.13-0.10 cm/cm while in parallel an enhanced uptake rate, rising by up to 100 %, was observed for the roots in wet compartments, presumably to compensate for roots in dry compartments and, therefore, sustain the total transpiration. Also, our observations showed that in the drying compartment a reduction of soil water content to 0.10-0.15 triggered local cluster root formation. Conclusions: With the experimental set-up presented the pattern of water uptake across a lupin root system can be quantified and normalized to root length. Water uptake was shown to be highly variable in different parts of the root system. A threshold for water stress to cause cessation of local water uptake was identified, and the considerable amount of compensation by water uptake in other parts identified. The dynamic trade-off among different parts of the root system seems to regulate total root uptake also during water stress to sustain the daily transpirational demand. [ABSTRACT FROM AUTHOR]

Split root experiments have the potential to disentangle water transport in roots and soil, enabling the investigation of the water uptake pattern of a root system. Interpretation of the experimental data assumes that water flow between the split soil compartments does not occur. Another approach to investigate root water uptake is by numerical simulations combining soil and root water flow depending on the parameterization and description of the root system. Our aim is to demonstrate the synergisms that emerge from combining split root experiments with simulations. We show how growing root architectures derived from temporally repeated X-ray CT scanning can be implemented in numerical soil-plant models. Faba beans were grown with and without split layers and exposed to a single drought period during which plant and soil water status were measured. Root architectures were reconstructed from CT scans and used in the model R-SWMS (root-soil water movement and solute transport) to simulate water potentials in soil and roots in 3D as well as water uptake by growing roots in different depths. CT scans revealed that root development was considerably lower with split layers compared to without. This coincided with a reduction of transpiration, stomatal conductance and shoot growth. Simulated predawn water potentials were lower in the presence of split layers. Simulations showed that this was related to an increased resistance to vertical water flow in the soil by the split layers. Comparison between measured and simulated soil water potentials proved that the split layers were not perfectly isolating and that redistribution of water from the lower, wetter compartments to the drier upper compartments took place, thus water losses were not equal to the root water uptake from those compartments. Still, the layers increased the resistance to vertical flow which resulted in lower simulated collar water potentials that led to reduced stomatal conductance and growth. [ABSTRACT FROM AUTHOR]

Aims: In agroforestry systems, root activity of trees may either reduce nutrient leaching beneath neighboring crops or compete with them. A previous study reveals high chloride (Cl) accumulation in the soil under a bottomland oak hedgerow in western France. Our study tests whether Cl can be used as an indicator of the spatial extent of tree root activity. Methods: Cl was analyzed in soil profiles up to 2 m deep along transects perpendicular to hedgerows. One site was explored in detail to examine the role of hedgerow position on the slope, supplemented with multi-annual and multi-site studies on bottomland hedgerows. Results: Upslope Cl accumulation was highest near the tree line (and up to 6 m away) and around 1 m deep. Downslope it extended up to 18 m from the tree line and near the surface. This difference was caused by differences in water availability or physical soil constraints. Cl accumulation was found in both temporal (multi-annual) and spatial (multi-site) studies. Conclusions: Cl accumulation under oak hedgerows can be used to identify the lateral extent and depth of water uptake by roots. It results from root activity over many years. The method is more suitable for poorly drained soils. [ABSTRACT FROM AUTHOR]

This work presents an assessment of potential advantages of drought tolerance in maize (Zea mays L.) production. A higher water uptake resulting from an enhanced root exploration at deep soil layers seems to be the most promising mechanism. The potential field-level impacts of this mechanism is assessed in two contrasting agroecological areas of the Argentine Pampas using the CERES-Maize model. The soil root growth factor parameter (SRGF) was manipulated to represent a modified maize hybrid with higher density of deep roots. Enhanced root exploration increased maize transpiration and consequently biomass production and yields. Benefits of the modified hybrid tend to be higher under low water availability conditions (low soil water content at sowing and/or rains during crop cycle). Although higher yield responses to root architecture changes were initially expected in the marginal semiarid area (Pilar), the opposite was observed: the average yield increases were 4.7 and 11.7% for Pilar and Pergamino, respectively. The modified hybrid showed lower yields than the current one in approximately 10% of the simulated situations. There were no yield penalties for the modified hybrid in cropping cycles with high water availability. This work shows strong interactions between root architecture and the environmental conditions in which crops are grown that affect potential field-level benefits. We highlight the need for assessing attributes tied to drought tolerance in the context of agroecological conditions in which plants will be grown to identify which drought-tolerance mechanisms might prove effective under different water-stress conditions. [ABSTRACT FROM AUTHOR]

Breeding for enhanced rooting depth and root biomass in deeper soil layers is a promising strategy to adapt wheat (Triticum aestivum L.) plants to drought periods. We evaluated (1) the extent of indirect selection of root traits during the last century of wheat breeding and (2) how it affected the variety performance under well-watered conditions compared to gradually developing drought stress. Fourteen bread wheat genotypes covering 100 years of Swiss wheat breeding were grown in 1.6 m tall columns in the greenhouse under well-watered and drought conditions. Root parameters, such as rooting depth and root biomass and above ground parameters were determined at flowering and maturity. Rooting depth showed a negative trend in response to year of release under well-watered conditions but not under early water stress. Modern varieties responded with enhanced root allocation to deeper soil layers. Consequently, rooting depth was positively correlated with plant height at well-watered conditions but not under early water stress. Considerable genetic variation for rooting depth among modern varieties indicates that the trait is selectable without strong alteration of plant height. We conclude that modern varieties adjusted rooting depth to water demand. [ABSTRACT FROM AUTHOR]

Plant roots play a key role in stabilizing slopes, particularly in the Mediterranean region, characterized by rough and unstable terrain. However, forest species differ in their stabilizing capacities. The purpose of this study is to fill the gap of knowledge on root biomechanical properties of relevant Mediterranean trees and shrubs in relation to slope stability. Root specimens of typical montane Mediterranean tree and shrub species were sampled in Southern Italy. Root characteristics, such as tensile strength (Tr) and root area ratio (RAR), were assessed from live roots sampled in trenches, while root cohesion was calculated. Power law functions yielded the best fit for the relationship of Tr versus root diameter; however, no significant relationship was found between root strength and root moisture content. RAR varied amongst different tree and shrub species. Roots of Quercus cerris L. were the most resistant to breaking under tension, while roots of Ilex aquifolium L. had the highest tensile strength among all shrub species. Results provide quantitative information on the role of root systems of montane Mediterranean forest species in stabilizing soils and will improve modeling of landslide susceptibility to the prevention and mitigation of natural hazards in mountain environments. [ABSTRACT FROM AUTHOR]

The spatiotemporal distribution of root water uptake (RWU) depends on the dynamics of the root distribution and compensatory uptake from wetter regions in the root zone. This work aimed to parameterize three RWU models with different representations of compensation: the Feddes-Jarvis model that uses an empirical function, the Feddes model without compensation, and the Couvreur model that is based on a physical description of water flow in the soil-root system. These models were implemented in HYDRUS-1D, and soil hydraulic parameters were optimized by inverse modeling using soil water content and potential measurements and observations of root distributions of winter wheat (Triticum aestivum L.) in horizontally installed rhizotubes. Soil moisture was equally well predicted by the three models, and the soil hydraulic parameters optimized by the models with compensation were comparable. The obtained RWU parameters of the Feddes-Jarvis model were consistent with data reported in the literature, although the pressure heads h$ and h^ for lower and higher transpirations rates, respectively, could not be uniquely identified. Response surfaces of the objective function showed that the root-related parameters of the Couvreur model could be identified using inverse modeling. Furthermore, these parameters were consistent with combined root architectural and hydraulic observations from the literature. The Feddes-Jarvis and Couvreur models simulated similar root-system-scale stress functions that link total RWU to the effective root zone water potential, suggesting that parameters may be transferable between the two models. Simulated RWU profiles differed due to different water redistribution by the root system, but the measurements were not sufficiently precise to observe this redistribution. [ABSTRACT FROM AUTHOR]

Design of efficient water irrigation strategies with a combination of high-quality water and saline water relies on accurate prediction of root water uptake. Macroscopic models are usually used to predict root water uptake at the field scale. However, they miss proper representation of stress processes at the plant scale. A fully mechanistic three-dimensional model was used to investigate the effect of root length density (RLD), transpiration rate and dynamics, potential leaching fraction (LF), and irrigation frequency and salinity on osmotic stress and gradients developed between the soil-root interface and the bulk soil. For the same LF and salinity level of the irrigation water, osmotic stress was larger at lower RLDs and higher transpiration rates. Roots were also more stressed when a sinusoidal transpiration boundary condition was considered. The variability of macroscopic parameters calculated forthe simulated data show that macroscopic functions need to take into account RLD and transpiration rate to adequately predict osmotic stress. Finally, small salt concentration gradients were observed in this single-root study where root density was assumed constant with depth. However, future work requires checking salt concentration gradients at the scale of a whole plant, where this assumption does not apply. [ABSTRACT FROM AUTHOR]

Predicting soil water availability to plants is important for agricultural and ecological models. Models that explicitly take into account root water uptake and transpiration reduction describe the ability of soil to supply water to plants based on soil hydraulic properties that depend on soil water content. The objective of this study was to further develop an existing single-layer root water uptake model based on matric flux potential to allow for multi-layer scenarios; and to illustrate its functionality using soil hydraulic properties from layered soils from two climate zones in Brazil: a semiarid zone and a humid zone. For each soil layer, the hydraulic properties were determined by inverse modeling of laboratory evaporation experiment data available for pressure heads between -165 and -1.5 m. The water supplying capacities of soils were evaluated using the newly developed multi-layer root water uptake model. Soils from the semiarid zone were able to supply water to plants over a wider range of pressure heads. Soils from the humid zone showed slightly stronger hydraulic restrictions for supplying transpirable water. For the analyzed soils, only a negligible increase in available water results from decreasing the root water potential below -150 m. Therefore, based on this analysis, it is reasonable to expect plant adaptation to move toward an increase of root length density rather than to a decrease of minimum root water potential. [ABSTRACT FROM AUTHOR]

This study tested a method to quantify and locate hydraulic lift (HL, defined as the passive upward water flow from wetter to dryer soil zones through the plant root system) by combining an experiment using the stable water isotope ¹H218Oas a tracer with a soil-plant water flow model. Our methodology consisted in (i) establishing the initial conditions for HL in a large rhizobox planted with Italian ryegrass (Lolium multiflorum Lam.), (ii) labeling water in the deepest soil layer with an 18O-enriched solution, (iii) monitoring the water O isotopic composition in soil layers to find out changes in the upper layers that would reflect redistribution of O-enriched water from the bottom layers by the roots, and (iv) comparing the observed soil water O isotopic composition to simulation results of a three-dimensional model of water flow and isotope transport in the soil-root system. Our main findings were that (i) the depth and strength of the observed changes in soil water O isotopic composition could be well reproduced with a modeling approach (RMSE = 0.2%o, i.e., equivalent to the precision of the isotopic measurements), (ii) the corresponding water volume involved in HL was estimated to account for 19% of the plant transpiration of the following day, i.e., 0.45 mm of water, and was in agreement with the observed soil water content changes, and (iii) the magnitude of the simulated HL was sensitive to both plant and soil hydraulic properties. [ABSTRACT FROM AUTHOR]