Root Water Relations Research Articles

Influence of plant growth promoting haloalkaliphilic bacteria on mitigation salt and alkali stresses in pistachio seedlings (Pistacia vera L.)

Pistachio (Pistacia vera L.) tolerates salinity stress, but its yield decreases with increasing salinity. The present study was conducted to investigate the effect of Khorasan Razavi (Iran) native haloalkaliphile bacterial strains on the vegetative growth, biochemical parameters, and nutrient concentration of pistachio seedlings under orchard conditions. The concentration of ammonia production, tri-indole acetic acid, and ACC deaminase production were measured for Virgibacillus marismortui (61.89, 17.59 mg l-1, and 203.59 µM l-1), and Alkalibacillus haloalkaliphilus (61.55, 36.04 mg l-1 and 512.97 µM l-1), respectively. Most of the vegetative traits decreased up to 12 dS m-1 salinity and then they increased with increasing salinity to 16 dS m-1. The Akbari cultivar was superior in all studied traits except the root-to-shoot ratio. The inoculation with AlkaliBacillus Haloalkalophilus had a stronger impact on nutrient concentrations, while the mixed bacteria treatment had a greater effect on vegetative and biochemical parameters. The effect of bacteria inoculation on a sensitive cultivar (Daneshmandi) was higher in 16 dS m-1. The AlkaliBacillus Haloalkalophilus increased phosphorus, potassium, and boron to 5, 10, and 12.1 mg kg-1 while decreasing sodium to 69 mg kg-1 and Na+/K+ ratio to 0.0028 compared to the mixed bacteria treatment. The highest correlation was found between root volume and stem length (r=0.639) and diameter (r=0.629), indicating the impact of bacteria inoculation on root growth and water relations in saline and sodic conditions. Stem length and diameter growth in young pistachio seedlings are crucial for grafting and economic productivity, so two bacterial treatment mixtures are recommended. 16 dS m-1), two pistachio cultivars (Daneshmandi and se production were measured for Virgibacillus marismortui (61.89, 17.59 mg l-1 and 203.59 µM l-1), and Alkalibacillus haloalkaliphilus (61.55, 36.04 mg l-1 and 512.97 µM l-1), respectively. Results showed that most of the vegetative traits decreased up to 12 dS m-1 salinity and then they increased with increasing salinity to 16 dS m-1. The Akbari cultivar was superior in all studied traits except the root-to-shoot ratio. The inoculation with AlkaliBacillus Haloalkalophilus had a stronger impact on nutrient concentrations, while the mixed bacteria treatment had a greater effect on vegetative and biochemical parameters. The effect of bacteria inoculation on a sensitive cultivar (Daneshmandi) was higher in 16 dS m-1. The AlkaliBacillus Haloalkalophilus increased phosphorous (5 mg kg-1), potassium (10 mg kg-1), and boron (12.1 mg kg-1) concentration and decreased sodium (69 mg kg-1) and Na+/K+ ratio (0.0028) than the mixed bacteria treatment. Inoculation with AlkaliBacillus Haloalkalophilus, two mixed of strain and VirgiBacillus Marismorti treatments caused a 15.1%, 13.8%, and 7.6% reduction in Na+/K+ ratio compared to the control. AlkaliBacillus Haloalkalophilus had a greater effect on reducing the concentration of toxic elements (Na+ and Cl-) and the ratio of sodium to potassium. The highest correlation coefficient was observed between root volume and stem length (r = 0.639) and diameter (r = 0.629), indicating the impact of bacteria inoculation on root growth and water relations in saline and sodic conditions. Due to the importance of the stem length and diameter increase in the early stages of the pistachio seedlings’ growth to grafting and achieve economic productivity, the two mixtures of bacteria treatment were recommended as the maximum stem length, diameter, and leaf area with 55.2, 10.8 and 18.5 cm2, respectively.

Fungal Aquaporins in Ectomycorrhizal Root Water Transport.

Ectomycorrhizal fungi influence root water transport of host plants. To delineate the exact mechanisms of how fungal partner alters root water relations, it is important to understand the functions of fungal transmembrane water channels, i.e., aquaporins, the key component in the symplastic pathways. In this paper, we discussed what roles the fungal aquaporins may play in root water transport. We also highlighted the opportunities of using integrated approaches to address rising questions in future hotspots of aquaporin and root water relations research.

Going with the Flow: Multiscale Insights into the Composite Nature of Water Transport in Roots.

As water often limits crop production, a more complete understanding of plant water capture and transport is necessary. Here, we developed MECHA, a mathematical model that computes the flow of water across the root at the scale of walls, membranes, and plasmodesmata of individual cells, and used it to test hypotheses related to root water transport in maize (Zea mays). The model uses detailed root anatomical descriptions and a minimal set of experimental cell properties, including the conductivity of plasma membranes, cell walls, and plasmodesmata, which yield quantitative and scale-consistent estimations of water pathways and root radial hydraulic conductivity (k r). MECHA revealed that the mainstream hydraulic theories derived independently at the cell and root segment scales are compatible only if osmotic potentials within the apoplastic domains are uniform. The results suggested that the convection-diffusion of apoplastic solutes explained most of the offset between estimated k r in pressure clamp and osmotic experiments, while the contribution of water-filled intercellular spaces was limited. Furthermore, sensitivity analyses quantified the relative impact of cortex and endodermis cell conductivity of plasma membranes on root k r and suggested that only the latter contributed substantially to k r due to the composite nature of water flow across roots. The explicit root hydraulic anatomy framework brings insights into contradictory interpretations of experiments from the literature and suggests experiments to efficiently address questions pertaining to root water relations. Its scale consistency opens avenues for cross-scale communication in the world of root hydraulics.

Connecting the dots between computational tools to analyse soil–root water relations

In recent years, many computational tools, such as image analysis, data management, process-based simulation, and upscaling tools, have been developed to help quantify and understand water flow in the soil-root system, at multiple scales (tissue, organ, plant, and population). Several of these tools work together or at least are compatible. However, for the uninformed researcher, they might seem disconnected, forming an unclear and disorganized succession of tools. In this article, we show how different studies can be further developed by connecting them to analyse soil-root water relations in a comprehensive and structured network. This 'explicit network of soil-root computational tools' informs readers about existing tools and helps them understand how their data (past and future) might fit within the network. We also demonstrate the novel possibilities of scale-consistent parameterizations made possible by the network with a set of case studies from the literature. Finally, we discuss existing gaps in the network and how we can move forward to fill them.

Root growth potential, water relations and carbohydrate status of ash alternative species following pre-plant storage

The catastrophic loss of ash (Fraxinus spp.) trees in the midwestern United States due to emerald ash borer has emphasized the need for greater diversity in urban and community forests. However, the availability of some important Fraxinus alternative species may be limited due to difficulties in nursery production. We conducted two trials to examine growth and physiological responses of bare-root tree liners to pre-plant storage and handling. In both trials, bare-root liners were given one of four treatments for three weeks prior to planting: 1) control, 2) cold storage (4°C), 3) sweating (warm, moist storage), or 4) heeled-in (outdoor storage). Subjecting trees to a warm, moist environment before planting (sweating) increased shoot dieback of Celtic occidentalis trees. Root growth potential was very low for Quercus spp. trees and varied by treatment for Celtis occidentalis trees. Taxodium distichum trees had a relatively high root growth potential in all treatments. Stem water potential measured immediately before and after pre-plant treatments indicated that Quercus spp. trees and T. distichum trees were able to rehydrate during sweating while water stress in C. occidentalis trees remained high (stem water potential <−2.0MPa). The results suggest that poor transplanting success reported for Quercus spp. trees may be related to low root growth potential, whereas poor establishment of Celtis occidentalis trees is related to a combination of factors including desiccation, poor root regeneration and poor carbohydrate status. None of the pre-plant treatments reduced shoot dieback compared to control trees that were not stored prior to planting.

Supplementary calcium ameliorates ammonium toxicity by improving water status in agriculturally important species.

Fertilization of agricultural plants with ammonium [Formula: see text] is often desirable because it is less susceptible to leaching than nitrate [Formula: see text] reducing environmental pollution, risk to human health and economic loss. However, a number of important agricultural species exhibit a reduction in growth when fertilized with [Formula: see text] and increasing the tolerance to [Formula: see text] may be of importance for the establishment of sustainable agricultural systems. The present study explored the feasibility of using calcium (Ca) to increase the tolerance of bell pepper (Capsicum annuum) to [Formula: see text] fertilization. Although [Formula: see text] at proportions ≥25 % of total nitrogen (N) decreased leaf dry mass (DM), supplementary Ca ameliorated this decrease. Increasing [Formula: see text] resulted in decreased root hydraulic conductance (Lo) and root water content (RWC), suggesting that water uptake by roots was impaired. The [Formula: see text]-induced reductions in Lo and RWC were mitigated by supplementary Ca. Ammonium induced increased damage to the cell membranes through lipid peroxidation, causing increased electrolyte leakage; Ca did not reduce lipid peroxidation and resulted in increased electrolyte leakage, suggesting that the beneficial effects of Ca on the tolerance to [Formula: see text] may be more of a reflection on its effect on the water status of the plant. Bell pepper plants that received [Formula: see text] had a low concentration of [Formula: see text] in the roots but a high concentration in the leaves, probably due to the high nitrate reductase activity observed. Ammonium nutrition depressed the uptake of potassium, Ca and magnesium, while increasing that of phosphorus. The results obtained in the present study indicate that [Formula: see text] caused growth reduction, nutrient imbalance, membrane integrity impairment, increased activity of antioxidant enzymes and affected water relations. Supplementary Ca partially restored growth of leaves by improving root Lo and water relations, and our results suggest that it may be used as a tool to increase the tolerance to [Formula: see text] fertilization.

Root apoplastic transport and water relations cannot account for differences in Cl− transport and Cl−/NO3 − interactions of two grapevine rootstocks differing in salt tolerance

Grapevine is moderately sensitive to salinity and accumulation of toxic levels of Cl− in leaves is the major reason for salt-induced symptoms. In this study, apoplastic Cl− uptake and transport mechanism(s) were investigated in two grapevine (Vitis sp.) rootstock hybrids differing in salt tolerance; 1103 Paulsen (salt tolerant) and K 51–40 (salt sensitive). Increased external salinity caused high Cl− accumulation in shoots of the salt sensitive K 51–40 in comparison to Paulsen. Measurement of 15NO3 − net fluxes under high salinity showed that by increasing external Cl− concentrations K 51–40 roots showed reduced NO3 − accumulation. This was associated with increased accumulation of Cl−. In comparison to Paulsen, K 51–40 showed reduced NO3 −/Cl− root selectivity with increased salinity, but Paulsen had lower selectivity over the whole salinity range (0–45 mM). To examine if root hydraulic and permeability characterisations accounted for differences between varieties, the root pressure probe was used on excised roots. This showed that the osmotic Lpr was significantly smaller than hydrostatic Lpr, but no obvious difference was observed between the rootstocks. The reflection coefficient (σ) values (0.48–0.59) were the same for both rootstocks, and root anatomical studies showed no obvious difference in apoplastic barriers of the main and lateral roots. Comparing the uptake of Cl− with an apoplastic tracer, PTS (3-hydroxy-5,8,10-pyrentrisulphonic acid), showed that there was no correlation between Cl− and PTS transport. These results indicated that bypass flow of salts to the xylem is the same for both rootstocks (0.77 ± 0.2 and 1.05 ± 0.12 %) and hence pointed to differences in membrane transport to explain difference in Cl− transport to the shoot.

Root and leaf traits, water use and drought tolerance of maize genotypes

AbstractThe main components of drought tolerance of six maize genotypes were studied to evaluate crop performance in water limiting environments: (1) the postponement of dehydration by reduced transpiration rate (TR) and an increased efficiency of water acquisition from soil; (2) the tolerance of dehydration by effective physiological water use. The aim was to describe the genotype dependent response to drought in leaf and root traits and water relations using data from controlled environment and field experiments, and using dynamic simulation by the Swedish Coup model. High genetic variation was detected in the root density, acquisition efficiency and water use among the genotypes. The female parent lines had the greatest TR with the smallest dry matter accumulation in water deficiency, whereas hybrids could acquire more water from dryer soil while maintaining a lower TR. Hybrid Mv 444 increased water potential more strongly in leaves than hybrid Norma. The postponement of dehydration was observed for Norma, while more tolerance to dehydration characterized Mv 444. Simulation was an effective tool for testing hypotheses considering water acquisition efficiency and for summarizing the results of the measurements in a formalized structure; it helped to quantify the dynamics of water availability and the impact of drought on the growth of the maize genotypes.

Identification and differential induction of the expression of aquaporins by salinity in broccoli plants

Plant aquaporins belong to a large superfamily of conserved proteins called the major intrinsic proteins (MIPs). There is limited information about the diversity of MIPs and their water transport capacity in broccoli (Brassica oleracea) plants. In this study, the cDNAs of isoforms of Plasma Membrane Intrinsic Proteins (PIPs), a class of aquaporins, from broccoli roots have been partially sequenced. Thus, sequencing experiments led to the identification of eight PIP1 and three PIP2 genes encoding PIPs in B. oleracea plants. The occurrence of different gene products encoding PIPs suggests that they may play different roles in plants. The screening of their expression as well as the expression of two specific PIP2 isoforms (BoPIP2;2 and BoPIP2;3), in different organs and under different salt-stress conditions in two varieties, has helped to unravel the function and the regulation of PIPs in plants. Thus, a high degree of BoPIP2;3 expression in mature leaves suggests that this BoPIP2;3 isoform plays important roles, not only in root water relations but also in the physiology and development of leaves. In addition, differences between gene and protein patterns led us to consider that mRNA synthesis is inhibited by the accumulation of the corresponding encoded protein. Therefore, transcript levels, protein abundance determination and the integrated hydraulic architecture of the roots must be considered in order to interpret the response of broccoli to salinity.

Delayed soil thawing affects root and shoot functioning and growth in Scots pine

In boreal regions, soil can remain frozen after the start of the growing season. We compared relationships between root characteristics and water relations in Scots pine (Pinus sylvestris L.) saplings subjected to soil frost treatments before and during the first week of the growing period in a controlled environment experiment. Delayed soil thawing delayed the onset of sap flow or totally blocked it if soil thawing lagged the start of the growing period by 7 days. This effect was reflected in the electrical impedance of needles and trunks and in the relative electrolyte leakage of needles. Prolonged soil frost reduced or completely inhibited root growth. In unfrozen soil, limited trunk sap flow was observed despite unfavorable aboveground growing conditions (low temperature, low irradiance, short photoperiod). Following the earliest soil thaw, sap flow varied during the growing season, depending on light and temperature conditions, phenological stage of the plant and the amount of live needles in the canopy. The results suggest that delayed soil thawing can reduce tree growth, and if prolonged, it can be lethal.

Plant Aquaporins: Membrane Channels with Multiple Integrated Functions

Aquaporins are channel proteins present in the plasma and intracellular membranes of plant cells, where they facilitate the transport of water and/or small neutral solutes (urea, boric acid, silicic acid) or gases (ammonia, carbon dioxide). Recent progress was made in understanding the molecular bases of aquaporin transport selectivity and gating. The present review examines how a wide range of selectivity profiles and regulation properties allows aquaporins to be integrated in numerous functions, throughout plant development, and during adaptations to variable living conditions. Although they play a central role in water relations of roots, leaves, seeds, and flowers, aquaporins have also been linked to plant mineral nutrition and carbon and nitrogen fixation.

Intracellular ROS

Intracellular localization of stress induced reactive oxygen species (ROS) has emerged as an important aspect towards understanding of cellular responses to environmental stimuli. Our recent study published in the PNAS (103:18008–13)1 shows that NaCl-induced ROS appear within endosomes on the way to tonoplast as part of the vacuolar vesicle trafficking. In addition to showing ROS damage to the tonoplast, this finding may shed light upon recently reported aspects of root water relations during salt stress, suggesting a new signaling role for intracellular ROS in Arabidopsis root cells, during salt stress: ROS that are compartmentalized in endosomes are delivered by the vacuolar vesicle trafficking pathway to the tonoplast, resulting in oxidative gating of TIPs water channels. The closure of the tonoplast aquaporins contributes to the observed reduction in root hydraulic conductivity during salt stress.

Molecular mechanisms of water uptake and transport in plant roots: research progress with water channel aquaporins

Aquaporins (water channels) are membrane proteins which facilitate the transport of water and low molecular weight compounds across biological membranes. The author and collaborators identified barley aquaporins and investigated the level of transcripts in roots, water transport activity, tissue localization, expression reduction by salt stress, and diurnal changes in the expression of a particular aquaporin. Over-expression of a barley aquaporin, HvPIP2;1, increased the shoot/root ratio and raised salt sensitivity in transgenic rice plants. Aquaporin research is providing significant insights into the water relations of plant roots.

Physiological and Anatomical Basis of Differential Tolerance to Soil Flooding of Lotus corniculatus L. and Lotus glaber Mill

Lotus corniculatus L. and Lotus glaber Mill. are warm-season legume species adapted to many kinds of environmental stress, including flooding conditions, whereas other popular forage legumes, like alfalfa or white clover, cannot thrive. This study evaluates the relationship between root aerenchyma, water relations and leaf gas exchange and the differential tolerance to soil flooding of L. corniculatus and L. glaber. Adult plants of these species, established independently in grasslands mesocosms, were subjected to 40 days of early spring flooding at a water depth of 6 cm. Both species presented constitutive aerenchyma tissue in the roots. Under flooding conditions, this parameter was 26.2% in L. glaber and 15.3% in L. corniculatus. In addition, flooded plants of L. glaber presented a leaf biomass 47.5% higher above water while L. corniculatus showed a leaf biomass 59.6% lower in the same layer, in comparison to control plants. Flooded plants of L. glaber maintained the stomatal conductance (gs) and transpiration rate (E) for 25 days, although these parameters reduce slightly to 40–60% in comparison to controls after 40 days of flooding. In this species, a reduction in photosynthesis (A) in flooding conditions was detected only on the last day of measurement. In L. corniculatus, the same parameters (gs, E and A) were affected by flooding since day 18 of treatment, and values reached 25–40% in comparison to control plants after 40 days of flooding. Flooding did not affect above-ground biomass in L. glaber; while in L. corniculatus, above-ground biomass was 35% lower than in control plants. Our results confirmed that L. glaber is more able to cope with flooding stress than L. corniculatus, even in the presence of natural competitors. On the whole, this experiment provides information that can aid in the identification of anatomical and physiological parameters associated with flood-tolerance in this forage legume species, with economic potential for the agricultural areas subject to periodic flooding.

Physiology of abscisic acid (ABA) in roots under stress—a review of the relationship between root ABA and radial water and ABA flows

Abscisic acid (ABA), the universal plant stress hormone, is accumulated in roots subjected to a range of external stresses, including drought, salinity, and nutrient deficiencies. This accumulation is regulated by ABA-metabolism (biosynthesis and degradation), -recirculation, and -exudation. Stress ABA serves as a long-distance signal regulating the water relations of shoots (stomata, meristems) and roots (hydraulic conductivity, root development, desiccation tolerance). Endogenous ABA, radial water flows (JV), and radial ABA flows (JABA) are closely coupled. Here we described the relations between these processes that are crucial factors for the role of ABA as a stress hormone and a long-distance stress signal. Crop varieties with high ABA concentrations exhibit an intensified long distance ABA signalling that reduces water consumption and, in the case of grapevine, improves the quality of the berries.

Drought resistance of Ailanthus altissima: root hydraulics and water relations.

Drought resistance of Ailanthus altissima (Mill.) Swingle is a major factor underlying the impressively wide expansion of this species in Europe and North America. We studied the specific mechanism used by A. altissima to withstand drought by subjecting potted seedlings to four irrigation regimes. At the end of the 13-week treatment period, soil water potential was -0.05 MPa for well-watered control seedlings (W) and -0.4, -0.8 and -1.7 MPa for drought-stressed seedlings (S) in irrigation regimes S1, S2 and S3, respectively. Root and shoot biomass production did not differ significantly among the four groups. A progressively marked stomatal closure was observed in drought-stressed seedlings, leading to homeostasis of leaf water potential, which was maintained well above the turgor loss point. Root and shoot hydraulics were measured with a high-pressure flow meter. When scaled by leaf surface area, shoot hydraulic conductance did not differ among the treated seedlings, whereas root hydraulic conductance decreased by about 20% in S1 and S2 seedlings and by about 70% in S3 seedlings, with respect to the well-watered control value. Similar differences were observed when root hydraulic conductance was scaled by root surface area, suggesting that roots had become less permeable to water. Anatomical observations of root cross sections revealed that S3 seedlings had shrunken cortical cells and a multilayer endodermal-like tissue that probably impaired soil-to-root stele water transport. We conclude that A. altissima seedlings are able to withstand drought by employing a highly effective water-saving mechanism that involves reduced water loss by leaves and reduced root hydraulic conductance. This water-saving mechanism helps explain how A. altissima successfully competes with native vegetation.

Effects of water deficit stress and recovery on the root water relations of trembling aspen ( Populus tremuloides) seedlings

Aspen ( Populus tremuloides Michx.) seedlings were grown in sand culture and subjected to mild and severe water deficit stress by withholding watering. Severely-stressed seedlings were also rewatered for 24 h to determine the effects of water deficit stress and stress recovery on root water flow properties. Both stress levels and stress recovery treatment reduced leaf stomatal conductance and shoot water potentials. However, root volume flux density and hydraulic conductivity were inhibited only by the severe water deficit stress and did not recover within 24 h following rewatering. The inhibition of root hydraulic conductivity in severely-stressed plants was accompanied by an increase in the proportion of apoplastic root water flow, as determined by the trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate fluorescent tracer dye. In all treatments and control, the mean activation energy values for root water flow were lower than 6 kcal mol −1, pointing to the presence of AQP-mediated transport. However, compared with earlier studies using solution culture-grown aspen seedlings, mercuric chloride had relatively little effect on root volume flux density. We interpreted this result as likely due to limited penetration of the root cortex by mercuric chloride through the exodermal layer.

Steady-state water relations of soybean seedling roots.

A previous four-compartment steady-state model of the root is extended to include the following: gradients of pressure (P) and osmotic pressure (Π) in the rooting medium, cortical apoplast and xylem; unloading of solutes to the xylem from internal stores; and apoplastic water flow across the endodermis. The model is tested by determining the steady-state relationship between applied pressure (Po) and volume flow rate (Qv) for excised roots of 4-day-old soybean seedlings under various conditions (vermiculite- versus water-cultured plants, different salt concentrations, permeant versus impermeant solutes). It is concluded that apoplastic volume flow across the endodermis is negligible. It is also argued that external or apoplastic gradients of P and Π tend to reduce the magnitude of the anomalous offset often observed in Po-Qv curves. The trans-root difference in water potential (ΔΨ) is shown to be a linear function of Qv at low Qv , but both ΔΨ(Qv) and Po(Qv) become nonlinear at high Qv . This unusual behavior may result from a nonlinear dependence of apoplastic pressure gradients and / or symplastic solute-concentration gradients on Qv . Alternatively, it might reflect saturation of water transport in plasmodesmata or aquaporins. The ΔΨ associated with growth-induced water uptake is shown to be negligible compared with the growth-induced water potentials measured in the stem elongation zone.

The origin of the exudate from cut maize roots

The exudate that wells out of the cut surface of detached roots is commonly thought to flow from the xylem and to be forced up the vessels by root pressure. Direct monitoring of the cut surface of maize ( Zea mays L.) roots by optical microscopy and cryomicroscopy of fast-frozen material showed that the liquid originated not only from cut vessels but was also exuded from living tissues and intercellular spaces over the entire cut surface. Indeed, exuded liquid usually appeared last over the vessels. This pattern of exudation was seen also from partially submerged segments of mature roots in which the lower end had been sealed. Exudation also occurred from similarly prepared root sleeves from which the stele had been removed. Measurements of rates of exudation often showed a periodicity of about 1 h. These observations add to earlier published descriptions of the phenomenon, particularly extensive 19th century studies, which remains unexplained by current understanding of root water relations.

Effects of postharvest mechanical and climatic stress on carrot tissue water relations

Abstract Using a ‘Scholander’-type pressure bomb, the effects of climatic or mechanical impacts on the water relations of carrots during postharvest handling were investigated to characterise the stresses during the different steps of the whole chain. Water potential (Ψ) provided a valuable means to easily, rapidly and repeatedly measure a large number of roots during an experiment. Water potential of freshly harvested carrots ranged between −0.2 and −0.6 MPa. Independent of whether the leaves were detached from the roots, Ψ declined by more than 200% (−0.8–−1.5 MPa) during two days of storage at 18°C even if the air humidity was very high (>98% RH). While osmotic potential (Ψπ) was unaffected, pressure potential (ΨP) decreased from approximately 0.7 to approximately 0.3 MPa, as determined by pressure–volume (PV) analysis or cryoscopy. Storing bunched carrots at moderate air humidity (85% RH) resulted in their water potential falling beyond the turgor loss point (i.e. ΨP=0 at Ψ≈−2.1 MPa in this experiment) within 2 days. Repeated falls from a conveyor belt onto either a steel plate or a belt did not enhance the reduction of Ψ in intact, leafless carrots relative to controls during subsequent storage. On the other hand, shaking roots on an oscillation table stress-simulator resulted in a significant decrease in Ψ, reflecting the degree of stress (i.e. time on the stress-simulator). In contrast to Ψ, changes in water content (from measuring dry mass) of randomly selected samples did not clearly indicate the effects of climatic and mechanical stress on root water relations.