Root clumping may affect the root water potential and the resistance to soil-root water transport

1992 ◽  
Vol 140 (2) ◽  
pp. 291-301 ◽  
Author(s):  
F. Tardieu ◽  
L. Bruckler ◽  
F. Lafolie
Keyword(s):  
Water Potential ◽  
Water Transport

Leaf Gas Exchange and Water Relations of Lupins and Wheat. II. Root and Shoot Water Relations of Lupin During Drought-Induced Stomatal Closure

1989 ◽  
Vol 16 (5) ◽  
pp. 415 ◽  
Author(s):  
CR Jensen ◽  
IE Henson ◽  
NC Turner
Keyword(s):  
Water Potential ◽  
Soil Water ◽  
Water Transport ◽  
Water Uptake ◽  
Water Relations ◽  
Leaf Gas Exchange ◽  
Stomatal Closure ◽  
Soil Water Potential ◽  
Root Water Uptake ◽  
Leaf Conductance

Plants of Lupinus cosentinii Guss. cv. Eregulla were grown in a sandy soil in large containers in a glasshouse and exposed to drought by withholding water. Under these conditions stomatal closure had previously been shown to be initiated before a significant reduction in leaf water potential was detected. In the experiments reported here, no significant changes were found in water potential or turgor pressure of roots or leaves when a small reduction in soil water potential was induced which led to a 60% reduction in leaf conductance. The decrease in leaf conductance and root water uptake closely paralleled the fraction of roots in wet soil. By applying observed data of soil water and root characteristics, and root water uptake for whole pots in a single-root model, the average water potential at the root surface was calculated. Potential differences for water transport in the soil-plant system, and the resistances to water flow were estimated using the 'Ohm's Law' analogy for water transport. Soil resistance was negligible or minor, whereas the root resistance accounted for 61-72% and the shoot resistance accounted for about 30% of the total resistance. The validity of the measurements and calculations is discussed and the possible role of root- to-shoot communication raised.

scholarly journals Hypernodulating soybean mutant line nod4 lacking ‘Autoregulation of Nodulation’ (AON) has limited root-to-shoot water transport capacity

2019 ◽  
Vol 124 (6) ◽  
pp. 979-991 ◽  
Author(s):  
Emile Caroline Silva Lopes ◽  
Weverton Pereira Rodrigues ◽  
Katherine Ruas Fraga ◽  
José Altino Machado Filho ◽  
Jefferson Rangel da Silva ◽  
...  
Keyword(s):  
Plant Growth ◽  
Water Potential ◽  
Water Transport ◽  
Leaf Water Potential ◽  
Root Nodules ◽  
Leaf Water ◽  
Transport Capacity ◽  
N Content ◽  
Photosynthetic Rates ◽  
Root Conductance

AbstractBackground and AimsAlthough hypernodulating phenotype mutants of legumes, such as soybean, possess a high leaf N content, the large number of root nodules decreases carbohydrate availability for plant growth and seed yield. In addition, under conditions of high air vapour pressure deficit (VPD), hypernodulating plants show a limited capacity to replace water losses through transpiration, resulting in stomatal closure, and therefore decreased net photosynthetic rates. Here, we used hypernodulating (nod4) (282.33 ± 28.56 nodules per plant) and non-nodulating (nod139) (0 nodules per plant) soybean mutant lines to determine explicitly whether a large number of nodules reduces root hydraulic capacity, resulting in decreased stomatal conductance and net photosynthetic rates under high air VPD conditions.MethodsPlants were either inoculated or not inoculated with Bradyrhizobium diazoefficiens (strain BR 85, SEMIA 5080) to induce nitrogen-fixing root nodules (where possible). Absolute root conductance and root conductivity, plant growth, leaf water potential, gas exchange, chlorophyll a fluorescence, leaf ‘greenness’ [Soil Plant Analysis Development (SPAD) reading] and nitrogen content were measured 37 days after sowing.Key ResultsBesides the reduced growth of hypernodulating soybean mutant nod4, such plants showed decreased root capacity to supply leaf water demand as a consequence of their reduced root dry mass and root volume, which resulted in limited absolute root conductance and root conductivity normalized by leaf area. Thereby, reduced leaf water potential at 1300 h was observed, which contributed to depression of photosynthesis at midday associated with both stomatal and non-stomatal limitations.ConclusionsHypernodulated plants were more vulnerable to VPD increases due to their limited root-to-shoot water transport capacity. However, greater CO2 uptake caused by the high N content can be partly compensated by the stomatal limitation imposed by increased VPD conditions.

scholarly journals Rehydration rates and the prevalence of xylem-hydration of flowers

2018 ◽  
Author(s):  
Adam B. Roddy ◽  
Craig R. Brodersen
Keyword(s):  
Water Potential ◽  
Water Transport ◽  
Plant Canopy ◽  
Abiotic Conditions ◽  
Physiological Constraints ◽  
Diverse Species ◽  
Extant Species ◽  
Significant Difference ◽  
Potential Gradients ◽  
Floral Form

AbstractAngiosperm flowers are remarkably diverse anatomically and morphologically, yet they all must satisfy the physiological constraints of supplying sufficient amounts of water and carbon effectively promote pollination. Flowers often occur in the hottest, driest parts of the plant canopy and can face harsh abiotic conditions. Prior evidence suggests that extant species vary dramatically in how water is delivered to flowers, with some evidence that water may be imported into flowers by the phloem. Here we measured midday water potential gradients between flowers, leaves, and stems often phylogenetically diverse species. We further tested the likelihood of xylem-hydration by measuring rates of rehydration after experimentally induced desiccation. There was no significant difference in rehydration rates between leaves and flowers. These results are consistent with xylem-hydration of flowers and suggest that there has been little modification to the mechanisms of water transport despite the diversity of floral form.

Leaf hydraulic vulnerability protects stem functionality under drought stress in Salvia officinalis

2016 ◽  
Vol 43 (4) ◽  
pp. 370 ◽  
Author(s):  
Tadeja Savi ◽  
Maria Marin ◽  
Jessica Luglio ◽  
Francesco Petruzzellis ◽  
Sefan Mayr ◽  
...  
Keyword(s):  
Water Potential ◽  
Water Transport ◽  
Salvia Officinalis ◽  
Summer Drought ◽  
Plant Organs ◽  
Transport Efficiency ◽  
Drought Tolerant ◽  
Hydraulic Vulnerability ◽  
Stem Water ◽  
Salvia Officinalis L

Functional coordination between leaf and stem hydraulics has been proposed as a key trait of drought-resistant plants. A balanced water transport efficiency and safety of different plant organs might be of particular importance for plant survival in the Mediterranean climate. We monitored seasonal changes of leaf and stem water relations of Salvia officinalis L. in order to highlight strategies adopted by this species to survive in harsh environmental conditions. During summer drought, the water potential dropped below the turgor loss point thus reducing water loss by transpiration, whereas the photosynthetic efficiency remained relatively high. Leaves lost their water transport efficiency earlier than stems, although in both plant organs P50 (water potential inducing 50% loss of hydraulic conductivity) indicated surprisingly high vulnerability when compared with other drought-tolerant species. The fast recovery of leaf turgor upon restoration of soil water availability suggests that the reduction of leaf hydraulic conductance is not only a consequence of vein embolism, but cell shrinkage and consequent increase of resistance in the extra-xylem pathway may play an important role. We conclude that the drought tolerance of S. officinalis arises at least partly as a consequence of vulnerability segmentation.

A pump/leak model of growth: the biophysics of cell elongation in higher plants revisited

2017 ◽  
Vol 44 (2) ◽  
pp. 185 ◽  
Author(s):  
Lars H. Wegner
Keyword(s):  
Growth Rate ◽  
Plasma Membrane ◽  
Water Potential ◽  
Water Transport ◽  
Higher Plants ◽  
Hydraulic Conductance ◽  
Potential Difference ◽  
Metabolic Energy ◽  
Root Cells ◽  
Water Potential Difference

Current concepts of growth hydraulics in higher plants are critically revisited, and it is concluded that they partly fail to interpret the experimental data adequately, particularly in the case of hydroponics-grown roots. Theoretical considerations indicate that the growth rate in roots is controlled by the extensibility of the cell wall, excluding water availability (i.e. hydraulic conductance) as a major constraint. This is supported by the findings that the growth rate does not scale with turgor, and that no radial nor axial water potential gradients have been observed in the root elongation zone. Nevertheless, a water potential deficit ranging from –0.2 to –0.6 MPa has repeatedly been reported for growing cells that by far exceeds the shallow trans-membrane water potential difference required for the uptake of growth water. Unexpectedly, growth was also shown to depend on the hydraulic conductance (LP) of the plasma membrane of root cells, even though LP should generally be too large to have an impact on growth. For leaves, similar observations have been reported, but the interpretation of the data is less straightforward. Inconsistencies associated with the current model of growth hydraulics prompt the author to suggest a revised model that comprises, in addition to a passive mechanism of water transport across the plasma membrane of growing cells mediated by aquaporins (‘leak’) a secondary active water transport (‘pump’), in analogy to a mechanism previously demonstrated for mammalian epithelia and postulated for xylem parenchyma cells in roots. Water is hypothesised to be secreted against a trans-membrane water potential difference by cotransport with solutes (salts, sugars, and/or amino acids), taking advantage of the free energy released by this transport step. The solute concentration gradient is supposed to be maintained by a subsequent retrieval of the solutes from the apoplast and back-transport at the expense of metabolic energy. Water secretion tends to reduce the turgor pressure and retards growth, but turgor and, in turn, growth can be upregulated very rapidly independent from any adjustment in the osmolyte deposition rate by increasing LP and/or reducing secondary active water transport, e.g. when the root is exposed to mild osmotic stress, as confirmed by experimental studies.

Hydraulic traits of Neotropical canopy liana and tree species across a broad range of wood density: implications for predicting drought mortality with models

2020 ◽  
Author(s):  
Mark E De Guzman ◽  
Aleyda Acosta-Rangel ◽  
Klaus Winter ◽  
Frederick C Meinzer ◽  
Damien Bonal ◽  
...  
Keyword(s):  
Water Potential ◽  
Water Transport ◽  
Wood Density ◽  
Drought Resistance ◽  
Tree Species ◽  
Forest Site ◽  
Xylem Cavitation ◽  
Water Release ◽  
Trade Offs ◽  
Maximum Water

Abstract Wood density (WD) is often used as a proxy for hydraulic traits such as vulnerability to drought-induced xylem cavitation and maximum water transport capacity, with dense-wooded species generally being more resistant to drought-induced xylem cavitation, having lower rates of maximum water transport and lower sapwood capacitance than light-wooded species. However, relationships between WD and the hydraulic traits that they aim to predict have not been well established in tropical forests, where modeling is necessary to predict drought responses for a high diversity of unmeasured species. We evaluated WD and relationships with stem xylem vulnerability by measuring cavitation curves, sapwood water release curves and minimum seasonal water potential (Ψmin) on upper canopy branches of six tree species and three liana species from a single wet tropical forest site in Panama. The objective was to better understand coordination and trade-offs among hydraulic traits and the potential utility of these relationships for modeling purposes. We found that parameters from sapwood water release curves such as capacitance, saturated water content and sapwood turgor loss point (Ψtlp,x) were related to WD, whereas stem vulnerability curve parameters were not. However, the water potential corresponding to 50% loss of hydraulic conductivity (P50) was related to Ψtlp,x and sapwood osmotic potential at full turgor (πo,x). Furthermore, species with lower Ψmin showed lower P50, Ψtlp,x and πo,x suggesting greater drought resistance. Our results indicate that WD is a good easy-to-measure proxy for some traits related to drought resistance, but not others. The ability of hydraulic traits such as P50 and Ψtlp,x to predict mortality must be carefully examined if WD values are to be used to predict drought responses in species without detailed physiological measurements.

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