Dataset Information

Origin and hydrodynamics of xylem sap in tree stems, and relationship to root uptake of soil water.

ABSTRACT: Although 10 years have passed since Japan's Fukushima nuclear accident, the future radiation risk from ¹³⁷Cs contamination of wood via root uptake is a serious concern. We estimated the depth at which the roots of evergreen coniferous sugi (Cryptomeria japonica) and broadleaf deciduous konara (Quercus serrata) trees actively take up soil water by using positive δD values from the artificial D₂O tracer and seasonal changes in the δ¹⁸O values of soil water as a natural environmental tracer. We compared the tracer concentration changes in xylem sap with those in the soil water and ascertained that both tree species primarily took up water from a depth of 20 cm, though with mixing of water from other depths. Using sap hydrodynamics in tree stems, we found that water circulation was significantly slower in heartwood than in sapwood. Heartwood water was not supplied by direct root uptake of soil water. The measured diffusion coefficients for D₂O, K⁺, Cs⁺, and I^- in xylem stems were greater in sapwood than in heartwood, and their magnitude was inversely correlated with their molecular weights. The distribution of D₂O and ¹³⁷Cs concentrations along the radial stem could be explained by simulations using the simple advective diffusion model.

SUBMITTER: Mahara Y

PROVIDER: S-EPMC8052340 | biostudies-literature | 2021 Apr

REPOSITORIES: biostudies-literature

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Origin and hydrodynamics of xylem sap in tree stems, and relationship to root uptake of soil water.

Mahara Yasunori Y Ohta Tomoko T Ohshima Jyunichi J Iizuka Kazuya K

Scientific reports 20210416 1

Although 10 years have passed since Japan's Fukushima nuclear accident, the future radiation risk from 137Cs contamination of wood via root uptake is a serious concern. We estimated the depth at which the roots of evergreen coniferous sugi (Cryptomeria japonica) and broadleaf deciduous konara (Quercus serrata) trees actively take up soil water by using positive δD values from the artificial D2O tracer and seasonal changes in the δ18O values of soil water as a nat ...[more]

PMID: 33863961

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Project description:BackgroundSubstance transport in higher land plants is mediated by vascular bundles, consisting of phloem and xylem strands that interconnect all plant organs. While the phloem mainly allocates photoassimilates, the role of the xylem is the transport of water and inorganic nutrients from roots to all aerial plant parts. Only recently it was noticed that in addition to mineral salts, xylem sap contains organic nutrients and even proteins. Although these proteins might have important impact on the performance of above-ground organs, only a few of them have been identified so far and their physiological functions are still unclear.ResultsWe used root-pressure xylem exudate, collected from cut Brassica napus stems, to extract total proteins. These protein preparations were then separated by high-resolution two-dimensional gel electrophoresis (2-DE). After individual tryptic digests of the most abundant coomassie-stained protein spots, partial peptide sequence information was deduced from tandem mass spectrometric (MS/MS) fragmentation spectra and subsequently used for protein identifications by database searches. This approach resulted in the identification of 69 proteins. These identifications include different proteins potentially involved in defence-related reactions and cell wall metabolism.ConclusionThis study provides a comprehensive overview of the most abundant proteins present in xylem sap of Brassica napus. A number of 69 proteins could be identified from which many previously were not known to be localized to this compartment in any other plant species. Since Brassica napus, a close relative of the fully sequenced model plant Arabidopsis thaliana, was used as the experimental system, our results provide a large number of candidate proteins for directed molecular and biochemical analyses of the physiological functions of the xylem under different environmental and developmental conditions. This approach will allow exploiting many of the already established functional genomic resources, like i.e. the large mutant collections, that are available for Arabidopsis.

Project description: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.

Dataset Information

Origin and hydrodynamics of xylem sap in tree stems, and relationship to root uptake of soil water.

Publications

Origin and hydrodynamics of xylem sap in tree stems, and relationship to root uptake of soil water.

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