Shoot Xylem Research Articles

Complete genome sequence of Microbacterium sp. che218, an endophyte isolated from Vitis vinifera cv. Chardonnay shoot xylem.

Microbacterium species are bacterial endophytes that live inside plants. We report the complete genome sequence of Microbacterium sp. che218, an endophyte isolated from the shoot xylem of the wine grape Vitis vinifera cv. Chardonnay.

Anthocyanin Accumulation in Grape Berry Skin Promoted by Endophytic Microbacterium sp. che218 Isolated from Wine Grape Shoot Xylem.

Grape berry skin coloration is a key determinant of the commercial value of red wines. Global warming caused by climate change has inhibited anthocyanin biosynthesis in berry skins, leading to poor coloration. Through two-year field experiments, the endophyte che218 isolated from grape shoot xylem promoted anthocyanin accumulation in berry skins. The che218 enhanced anthocyanin biosynthesis in grapevine cultured cells. In the 2022 growing season, applying che218 to grape bunches enhanced anthocyanin accumulation in berry skins on day 20 post-treatment. However, the anthocyanin accumulation enhancing effect of che218 became negligible at harvest. In the 2023 growing season, che218 enhanced anthocyanin accumulation in berry skins on day 15 post-treatment and at harvest (day 30 post-treatment) and also upregulated the transcription of mybA1 and UFGT, two genes that regulate anthocyanin biosynthesis in berry skins. Whole genome sequencing demonstrated that che218 is an unidentified Microbacterium species. However, it remains unknown how che218 is involved in the biosynthesis of anthocyanin in berry skins. This study provides insights into the development of an eco-friendly endophyte-mediated technique for improving grape berry skin coloration, thereby mitigating the effects of global warming on berry skin coloration.

Decreased irrigation volume, not irrigation placement, promotes accumulation of multiple hormones in cotton leaves during partial rootzone drying

While ABA is often assumed to mediate partial stomatal closure as the soil dries, other plant hormones and hydraulic signals may also be involved. We tested whether irrigation volume (% of crop evapotranspiration, ET) and placement (partial rootzone drying [PRD] or deficit irrigation [DI], which irrigate part or all of the rootzone respectively) affect this signalling by measuring stomatal conductance (gs), leaf and shoot water potential (Ψleaf, Ψshoot), shoot xylem sap ABA concentration ([X-ABA]shoot) and various foliar hormones (ABA, IAA, SA, JA, JA-Ile and cis-OPDA) in cotton plants exposed to different irrigation volumes (100 %ET or 50 %ET) and placements (DI or PRD). Partial rootzone drying caused stomatal closure coincident with sustained foliar ABA accumulation and minimal changes in Ψshoot, but continued soil drying of the dry compartment reversed partial stomatal closure (with gs of 100 %ET PRD plants sometimes greater than well-watered plants). With 100 %ET PRD, partial stomatal closure correlated with decreased soil moisture of the dry compartment and increased [ABA]leaf, but neither Ψleaf nor [X-ABA]shoot. Irrespective of irrigation placement, 50 %ET significantly decreased gs, Ψleaf and Ψshoot, but significantly increased [ABA]leaf, [X-ABA]shoot, [SA]leaf, [IAA]leaf and [cis-OPDA]leaf, with stomatal closure of 50 %ET PRD plants occurring earlier than 50 %ET DI plants. While stomatal closure at 50 %ET correlated with foliar accumulation of multiple plant hormones, foliar ABA dynamics best explained transient stomatal closure at 100 %ET PRD but not stomatal re-opening with prolonged soil drying. Thus, stomatal sensitivity to drying soil (and putative regulatory signals such as ABA) depended on irrigation volume and placement.

Effects of exogenous salicylic acid on alleviation of arsenic-induced oxidative damages in rice

Salicylic acid (SA) is a phenolic phytohormone that plays a vital role in plant development and mediates plant responses to plenty of adversity including arsenic (As) stress. The effects of exogenous addition of SA on As tolerance and As accumulation were assessed in two cultivars of rice (Oryza sativa L.) Nipponbare and Zhongzao 39, hydroponically grown with Kimura B nutrient solution under arsenite [As (III)] and dimethylarsonic acid (DMA) exposure. In the second ex-periment, the influence of soaking seed with SA on As uptake and As damages was investigated in rice (cv. Nipponbare) exposed to As (III) and DMA. The results showed that exogenous addition of SA significantly decreased the concentrations of hydrogen peroxide (H2O2) and malondialdehyde (MDA) in both As (III)- and DMA-stressed rice, indicating that SA alleviates As-induced oxidative damages in rice. SA increased the activity of antioxidant enzymes and, moreover, increased the relative amount of glutathione (GSH) and ascorbate (ASA) by accelerating the GSH-ASA circle system. Exogenous addition of SA significantly decreased the As concentration in both roots and shoots of rice under As(III) stress by influencing the expression of genes encoding As transporters, viz. OsLsi1, OsLsi2. The addition of SA significantly decreased the As content in shoots under DMA stress, which may be related to the expression of OsPTR7 involved in shoot xylem unloading. This finding may foster a novel perspective for reducing As accumulation in rice grains.

Diversity of endophytic bacterial microbiota in grapevine shoot xylems varies depending on wine grape-growing region, cultivar, and shoot growth stage

Next-generation sequencing technology may clarify microbiota that are as yet poorly understood in the soil, the rhizosphere, and the phyllosphere of vineyards. To provide new information on the interaction between grapevine and microorganisms, we focused on the endophytic microbiota in grapevine. We performed endophytic microbiome analysis of the shoot xylems of four cultivars, Vitis vinifera cvs. Chardonnay, Pinot Noir, Cabernet Sauvignon, and Vitis sp. cv. Koshu, grown in eleven vineyards in Japan. The number of endophytic fungal species was small in the grapevine shoot xylems and could not be analyzed further, whereas a total of 7,019,600 amplicon sequences (46,642–285,003 per shoot xylem) and 1305 bacterial operational taxonomic units were obtained by analysis of the V3–V4 region of the bacterial 16S rRNA gene. Gammaproteobacteria was predominant in the shoot xylems at the shoot elongation stage irrespective of the cultivar, whereas Alphaproteobacteria and Oxyphotobacteria were predominant at véraison. Actinobacteria, Bacteroidia, Bacilli, and Clostridia were also detected in the shoot xylems. The endophytic bacterial microbiota in Koshu and Pinot Noir shoot xylems were similar irrespective of the grapevine-growing region. In contrast, the endophytic bacterial microbiota in Chardonnay and Cabernet Sauvignon showed diversity and complexity among grapevine-growing regions. Alpha diversity analysis revealed that Koshu shoot xylems had a higher diversity of endophytic bacterial microbiota than Pinot Noir, Chardonnay, and Cabernet Sauvignon shoot xylems, and that grapevine shoot xylems at the shoot elongation stage had a higher diversity of endophytic bacterial microbiota than those at véraison. Principal coordinate analysis (PCoA) demonstrated that the profiles of the endophytic bacterial microbiota in grapevine shoot xylems at véraison were relatively uniform compared with those at the shoot elongation stage. Multidimensional scaling analysis showed that the plots of all cultivars were generally apart from each other at the shoot elongation stage and then became close to each other at véraison. The plots of all grapevine-growing regions cultivating Koshu were close to each other, whereas those of grapevine-growing regions cultivating Chardonnay and Cabernet Sauvignon were apart from each other. The findings of this study suggest that the endophytic bacterial microbiota in grapevine shoot xylems varied depending on the cultivar and the grapevine-growing region even for the same cultivars, and that the microbiota fluctuated depending on the shoot growth stage.

Isolation and Characterization of Endophyte Bacillus velezensis KOF112 from Grapevine Shoot Xylem as Biological Control Agent for Fungal Diseases.

As the use of chemical fungicides has raised environmental concerns, biological control agents have attracted interest as an alternative to chemical fungicides for plant-disease control. In this study, we attempted to explore biological control agents for three fungal phytopathogens causing downy mildew, gray mold, and ripe rot in grapevines, which are derived from shoot xylem of grapevines. KOF112, which was isolated from the Japanese indigenous wine grape Vitis sp. cv. Koshu, inhibited mycelial growth of Botrytis cinerea, Colletotrichum gloeosporioides, and Phytophthora infestans. The KOF112-inhibited mycelial tips were swollen or ruptured, suggesting that KOF112 produces antifungal substances. Analysis of the 16S rDNA sequence revealed that KOF112 is a strain of Bacillus velezensis. Comparative genome analysis indicated significant differences in the synthesis of non-ribosomal synthesized antimicrobial peptides and polyketides between KOF112 and the antagonistic B. velezensis FZB42. KOF112 showed biocontrol activities against gray mold caused by B. cinerea, anthracnose by C. gloeosporioides, and downy mildew by Plasmopara viticola. In the KOF112–P. viticola interaction, KOF112 inhibited zoospore release from P. viticola zoosporangia but not zoospore germination. In addition, KOF112 drastically upregulated the expression of genes encoding class IV chitinase and β-1,3-glucanase in grape leaves, suggesting that KOF112 also works as a biotic elicitor in grapevine. Because it is considered that endophytic KOF112 can colonize well in and/or on grapevine, KOF112 may contribute to pest-management strategies in viticulture and potentially reduce the frequency of chemical fungicide application.

Complete Genome Sequence of Bacillus velezensis KOF112, an Antifungal Endophytic Isolate from Shoot Xylem of the Indigenous Japanese Wine Grape Vitis sp. cv. Koshu.

ABSTRACTBacillus species are the most well-studied biological control agents and produce a large variety of antibiotics that exert antifungal activity against phytopathogens and induce defense responses in plants. Here, we introduce the genome sequence of Bacillus velezensis KOF112, an antifungal endophytic isolate from the shoot xylem of a wine grape.

Constitutive and insect-induced transcriptomes of weevil-resistant and susceptible Sitka spruce.

Spruce weevil (Pissodes strobi) is a significant pest of regenerating spruce (Picea) and pine (Pinus) forests in North America. Weevil larvae feed in the bark, phloem, cambium, and outer xylem of apical shoots, causing stunted growth or mortality of young trees. We identified and characterized constitutive and weevil-induced patterns of Sitka spruce (Picea sitchensis) transcriptomes in weevil-resistant (R) and susceptible (S) trees using RNA sequencing (RNA-seq) and differential expression (DE) analyses. We developed a statistical model for the analysis of RNA-seq data from treatment experiments with a 2×3 factorial design to differentiate insect-induced responses from the effects of mechanical damage. Across the different comparisons, we identified two major transcriptome contrasts: A large set of genes that was constitutively DE between R and S trees, and another set of genes that was DE in weevil-induced S-trees. The constitutive transcriptome unique to R trees appeared to be attuned to defense, while the constitutive transcriptome unique to S trees was enriched for growth-related transcripts. Notably, a set of transcripts annotated as "fungal" was detected consistently in the transcriptomes. Fungal transcripts were identified as DE in the comparison of R and S trees and in the weevil-affected DE transcriptome of S trees, suggesting a potential microbiome role in this conifer-insect interaction.

Interactive Effect of Elevated CO2 and Moisture Stress on Anatomical Configuration in Brassica Species

Free-Air CO2 Enrichment (FACE) was developed as a means to study the crops response to elevated level of CO2 under the fully open-air field conditions. In this study, results of FACE experiments are summarized by disusing the root and shoot anatomy. Result indicated that elevated Co2 significantly altered the root and shoot xylem and phloem characters such as both proto and meta xylem and phloem; vessels, character of root and shoots which are vital for the transpiration regulation, along with leaves photosynthesis as a whole. The coexistence of two ontogenetically different phloem sieve element in Brassica plant under elevated CO2 might have possibility of two different transport functions at the same time. One may be involved in supplying for the structural development (leaf size, stem girth and root volume) and other may cater the need of increased new sinks. Though these parameters were found to decrease under moisture stress condition but these impacts of stress were reduced at higher level of atmospheric CO2.

Seedless okra production by indole 3-acetic acid micro syringe injection on flower bud, ovary and shoot xylem and its vitamin and mineral content development: An innovation

The study was conducted to evaluate the effect of different concentrations of indole 3-acetic acid (IAA) on the okra growth and seedless production. The micro syringe injection technology applied on the flower bud, ovary and shoot xylem was an innovative technique of growth regulator application (IAA) and used in this experiment rather than spray as common and traditional method. Flower bud injection technique was applied on the flower before flowering (Expt. 1), flower ovary injection technique was applied on the flower after anthesis of flower (Expt. 2) and shoot xylem injection technique was applied on the main shoot (stem) before flowering (vegetative stage) using IAA at 0, 25, 50, 100 and 200 mg/L concentrations (Expt. 3). The concentrations of 25, 50 and 100 mg/L IAA greatly exhibited higher pod setting percent compared with the 0 and 200 mg/L in the case of flower bud, ovary and shoot xylem injection. The higher pod length, diameter, weight, size, total soluble solids and vitamin C, chlorophyll and Photosynthetic yield (Fv/Fm) was found in 50 and 100 mg/L compared with 0, 25 and 200 mg/L concentrations in the case of all experiments. The highest (100 %) seedless was observed at 100 and 200 mg/L concentration in ovary and flower bud injection. The relationship between IAA concentrations (mg/L) and seedless percentage per pod was R√ = 0.905. It was found that concentrations of IAA 50 and 100 mg/L) increased potassium (K), calcium (Ca), magnesium (Mg), sodium (Na) and iron (Fe) content compared to the control (0) and 200 mg/L concentration in the case of all experiments. The result seemed that IAA 100 and 200 mg/L concentrations were the effective for seedless okra production in flower bud and ovary injection technique which was an innovation for okra.

The existence of cellulose and lignin chemical connections in ginkgo traced by 2H-13C dual isotopes

To elucidate the covalent association between the celluloses and lignins found in gymnosperms, they were labeled with stable isotopes (deuterium and carbon-13) at specific positions and traced via mass spectroscopy and nuclear magnetic resonance (NMR). Both the 2H-labeled cellulose precursor (UDP-glucose-[6-2H2]) and the 13C-labeled lignin precursor (coniferin-[α-13C]) were added to a growing ginkgo plant, in combination with a 4-coumarate-CoA ligase inhibitor. The detection of abundance of 13C and 2H revealed that the lignin precursor and cellulose precursor deposited more actively in 300 to 1300 μm and 100 to 900 μm distance from cambium, respectively. The lignin-carbohydrate complexes (LCCs) were isolated from the newly-formed ginkgo shoot xylem and further degraded with cellulase and hemicellulase to obtain enzymatically degraded lignin-carbohydrate complexes (EDLCCs). Analysis of the solid-state cross polarization / magic angle spinning (CP/MAS) 13C-NMR of the newly-formed xylem, liquid-state 13C-NMR, and 1H-NMR of the EDLCCs confirmed that the major connection between celluloses and lignins was a benzyl ether bond (between cellulose C6 and lignin Cα). A minor ester bond was also found between the hydroxyl group (at the 6-position of cellulose) and ferulic acid (at the γ position in lignins).

ANATOMICAL STRUCTURE OF VEGETATIVE ORGANS OF NITRARIA SCHOBERI L. (SULAKSKY POPULATION, DAGESTAN)

Aim. The article is devoted to the study of the anatomical structure of the vegetative organs of Nitraria schoberi L. growing on saline soils in the Caspian lowland of Dagestan and to the analysis of some of its features in relation with its habitat. Methods. Were studied 10 samples of leaves, stems and roots of N. schoberi. Preparations of temporary specimen as well as the description of tissues and cells of vegetative organs of N. schoberi were carried out in accordance with conventional methods. Results. The main tissues of leaf, stem and root of N. schoberi are described; their quantitative estimation is given; ecologically significant adaptive anatomical signs are also identified. Conclusion. The presence of a thin cuticle, dense mesophyll, water-preserving tissue, large stomata and deposition of excess salts in containers to maintain high osmotic pressure of the protoplasm is associated with the phreatophytic nature of N. schoberi which allows the species grow on saline soils at high air temperatures. The increase of the proportion of vessels in the xylem of shoots with age in comparison with the cells of the libriform is associated with an increase in water demand for successful photosynthetic processes and thermoregulation in the conditions of the Caspian lowland. The obtained data can be used in a comparative evaluation with other ecotypes of N. schoberi and of the genus Nitraria.

Prolonged drying cycles stimulate ABA accumulation in Citrus macrophylla seedlings exposed to partial rootzone drying

Partial rootzone drying (PRD) establishes discrete wet and dry parts of the rootzone (for example using parallel drip lines on either side of the crop row), and alternates them to stimulate root growth and root-to-shoot ABA signalling. To assess whether alternation frequency affects plant physiological responses, Citrus macrophylla Wester seedlings were grown with the root system split between two pots and 5 irrigation treatments applied: Control, PRD-Fixed (where wet and dry parts of the rootzone were not alternated) and three alternate PRD treatments where the wet and dry parts were swapped at 3 (PRD1), 6 (PRD2) and 12 (PRD3) days intervals, to dry the soil to different degrees before alternating the irrigation. Water was equally distributed between both pots in Control plants, whereas only one pot was watered and the other allowed to dry in PRD plants, with all plants receiving the same irrigation volume. After 24 days, soil water content (θv), leaf water potential (Ψleaf), root water potential (Ψroot), abscisic acid (ABA) concentration in roots ([ABA]root), leaves ([ABA]leaf) and shoot xylem sap ([X-ABA]shoot), biomass allocation and leaf area were measured. Higher soil water availability of the dry side (PRD1 and PRD2) had no significant effects on leaf water relations, ABA status and plant biomass allocation. However, increasing the duration of exposure of part of the root system to dry soil (PRD3 and PRD-Fixed) further decreased Ψroot and stimulated root ABA accumulation, while decreasing Ψleaf and increasing [ABA]leaf of PRD3 plants compared to the other treatments. Differences in physiological response between PRD3 and PRD-Fixed plants were attributed to differences in the proportion of root mass exposed to drying soil: PRD3 plants had a lower Ψleaf and a higher [ABA]leaf with a smaller proportion of their root mass in wet soil. Since long drying cycles were required to alter plant biomass allocation and physiological responses in PRD plants, these should be implemented in designing suitable PRD strategies for field application.

Drought Stress Induces Flowering and Enhances Carbohydrate Accumulation in Averrhoa Carambola

Star fruit (Averrhoa carambola) is an important fruit tree in tropical and subtropical Asia. The tree blooms several times and fruits accordingly within one year. Controlling the flowering time and understanding the physiological mechanism of the induction of floral buds in A. carambola are indispensable to the industry. In this study, A. carambola potted trees were subjected to drought stress in a growth chamber. To avoid excessive drought stress and leaf abscission, trees were watered every 7 d and were sprayed with water every 2 d. The flowering rate was recorded, and the carbohydrate contents of the leaves, phloem, and xylem tissues were determined during the treatment and after re-watering. The results showed that drought stress increased the flowering rate in both drooping and water shoots, increased the relative conductivity, decreased the relative water content (RWC) of leaves. The total soluble sugar, sucrose, fructose, and glucose in leaves of the drooping shoots were increased. The starch contents in the xylem of both drooping and water shoots were also increased by the treatment. The results indicated that drought stress enhances carbohydrate accumulation in A. carambola. This study provides a potential way by water control to induce flowering without chemical in A. carambola.

Amelioration of Soybean Plant from Saline-Induced Condition by Exopolysaccharide Producing <i>Pseudomonas</i>-Mediated Expression of High Affinity K<sup>+</sup>-transporter (HKT1) Gene

There is a consensus that soil salinization causes decreased agricultural production. Several plants may adapt to survive under high salt stress wherein glycophytes fail to grow. Among transporters in plants, the sodium transporter, also known as high-affinity K + -transporter ( HKT1 ) that comes under the HKT gene family, is involved in uptake of sodium through the roots and its recirculation from shoot to root. In the present study, we have examined the role of transporter HKT1 in soybean plants upon addition of 200 mM NaCl and treatment with Pseudomonas sp. strain AK-1. It is reported that HKT1 is permeable to K + /Na + and systemically alleviates salinity stress through upregulation of gene expression in shoots and down-regulation in roots. Higher transcription levels in shoot recirculate Na + from shoot xylem to root phloem whereas lower transcription levels in root do not allow sodium to enter the plants through root cells. We have also examined role of exopolysaccharide (EPS) produced by strain AK-1 which helps in the binding of free Na + from soil and thus makes Na + unavailable to the soybean plants. Strain with EPS showed decrease in electrical conductivity of soil from 1.1 to 0.9 dS/m in the presence of 200 mM NaCl. In conclusion, treatment with Pseudomonas sp. strain AK-1 exhibits significant rise in shoot/root length, number of lateral roots, shoot/root fresh weight and decreased Na + /K + ratio under salinity stress.

Early changes of the pH of the apoplast are different in leaves, stem and roots of Vicia faba L. under declining water availability

Changes in pH of the apoplast have recently been discussed as an important factor in adjusting transpiration and water relations under conditions of drought via modulatory effect on abscisic acid (ABA) concentration. Using Vicia faba L., we investigated whether changes in the root, shoot and leaf apoplastic pH correlated with (1) a drought-induced reduction in transpiration and with (2) changes in ABA concentration. Transpiration, leaf water potential and ABA in leaves were measured and correlated with root and shoot xylem pH, determined by a pH microelectrode, and pH of leaf apoplast quantified by microscopy-based in vivo ratiometric analysis. Results revealed that a reduction in transpiration rate in the early phase of soil drying could not be linked with changes in the apoplastic pH via effects on the stomata-regulating hormone ABA. Moreover, drought-induced increase in pH of xylem or leaf apoplast was not the remote effect of an acropetal transport of alkaline sap from root, because root xylem acidified during progressive soil drying, whereas the shoot apoplast alkalized. We reason that other, yet unknown signalling mechanism was responsible for reduction of transpiration rate in the early phase of soil drying.

Auxin Response Gene SlARF3 Plays Multiple Roles in Tomato Development and is Involved in the Formation of Epidermal Cells and Trichomes.

The auxin response factor (ARF) genes encode a large family of proteins involved in auxin signaling transduction. SlARF3, a member of the ARF gene family, encodes a protein containing two conserved domains, B3 and ARF, and lacking an Aux/IAA domain. Expression analysis showed that SlARF3 has a particularly high expression level in trichomes. In situ hybridization also detected the SlARF3 transcripts in epidermal pavement cells of leaves. The physiological function of SlARF3 was studied by using the RNA interference (RNAi) strategy. SlARF3-down-regulated plants exhibited decreased density of epidermal pavement cells and obviously reduced density of type I, V and VI trichomes of leaves, which indicates the important role of SlARF3 in the formation of trichomes and epidermal cells in tomato. The number of shoot xylem cells was also decreased in SlARF3-down-regulated lines. Furthermore, RNA-sequencing (RNA-Seq) analysis identified 51 differentially expressed genes (DEGs) belonging to 14 transcription factor (TF) families, such as MYB, bHLH, WD40 and C2H2 zinc finger. Twenty-seven DEGs were involved in the metabolism and signaling transduction of phytohormones, such as auxin, ethylene and gibberellin. These results indicated the important roles of the TFs and hormones in auxin-dependent transcriptional regulation of trichome formation in tomato. Taken together, our results demonstrate that SlARF3 plays an important role in the formation of epidermal cells and trichomes and reveal novel and specific functions for ARFs in tomato developmental processes.

Disruption of the rice nitrate transporter OsNPF2.2 hinders root-to-shoot nitrate transport and vascular development.

Plants have evolved to express some members of the nitrate transporter 1/peptide transporter family (NPF) to uptake and transport nitrate. However, little is known of the physiological and functional roles of this family in rice (Oryza sativa L.). Here, we characterized the vascular specific transporter OsNPF2.2. Functional analysis using cDNA-injected Xenopus laevis oocytes revealed that OsNPF2.2 is a low-affinity, pH-dependent nitrate transporter. Use of a green fluorescent protein tagged OsNPF2.2 showed that the transporter is located in the plasma membrane in the rice protoplast. Expression analysis showed that OsNPF2.2 is nitrate inducible and is mainly expressed in parenchyma cells around the xylem. Disruption of OsNPF2.2 increased nitrate concentration in the shoot xylem exudate when nitrate was supplied after a deprivation period; this result suggests that OsNPF2.2 may participate in unloading nitrate from the xylem. Under steady-state nitrate supply, the osnpf2.2 mutants maintained high levels of nitrate in the roots and low shoot:root nitrate ratios; this observation suggests that OsNPF2.2 is involved in root-to-shoot nitrate transport. Mutation of OsNPF2.2 also caused abnormal vasculature and retarded plant growth and development. Our findings demonstrate that OsNPF2.2 can unload nitrate from the xylem to affect the root-to-shoot nitrate transport and plant development.

XYLEM ANATOMY AND HYDRAULIC TRAITS OF TWO CO-OCCURRING RIPARIAN DESERT PLANTS

Populus euphratica Oliv. and Tamarix ramosissima Ledeb. are the dominant riparian plants in desert ecosystems in China, where they play a significant role in maintaining ecological balance. To obtain a better insight into the ecological adaptations of xylem structure and hydraulic traits in desert phreatophytes to extremely drought-stressed environments, we investigated various quantitative features of the vessels and intervessel pits, as well as the xylem hydraulic efficiency (Ks(max)) and native embolism rate (PLC, %), in the woody shoots and lateral roots (all c. 2–4.5 mm in diameter) of P. euphratica and T. ramosissima from natural populations in the Heihe River Basin, northwestern China. The relationships between xylem anatomy and hydraulic traits are also discussed. There were significant anatomical differences between lateral root and woody shoot xylem within individual species. For lateral roots , arithmetic, hydraulic and maximum vessel diameter (D, Dh, Dmax), average vessel area (Va), intervessel wall thickness (Tvw), intervessel pit membrane and pit aperture areas (APM, APA), and intervessel pit membrane and pit aperture diameters (DPM, DPA), were larger than in woody shoots (P < 0.05).The mean Ks(max) values in lateral roots were 6–11 times greater than in woody shoots for P. euphratica and T. ramosissima, respectively (P < 0.01). Woody shoots of T. ramosissima had higher native PLC values (68%) than P. euphratica (39%).The different vessel grouping patterns in the two species seemed to be related to their different native embolism level. It is possible that the lateral roots of these two riparian desert plants could be more resistant to embolism than the woody shoots, and that cavitation resistance in the root xylem of T. ramosissima is higher than that of P. euphratica.

Water relations of wallum species in contrasting groundwater habitats of Pleistocene beach ridge barriers on the lower north coast of New South Wales, Australia

This study examined the water relations of sclerophyllous evergreen vegetation (wallum) on coastal sand barriers in eastern Australia. Many wallum species may be groundwater dependent, although the extent of this dependency is largely unknown. Twenty-six perennial tree, shrub and herb species were investigated in three groundwater habitats (ridge, open depression, closed depression). Pre-dawn and midday shoot xylem water potentials (ψx) were measured monthly between late autumn 2010 and late summer 2011. Pressure–volume curve traits were determined in mid- to late spring 2009, including the osmotic potential at full (π100) and zero (π0) turgor, and bulk modulus of elasticity (ε). Carbon isotope ratios (δ13C) were also determined in mid- to late spring 2009, to measure water-use efficiency (WUE). The species displayed a range of physiological strategies in response to water relations, and these strategies overlapped among contrasting growth forms and habitats. Linear relationships between osmotic and elastic adjustment were significant. A strong correlation between δ13C and distribution along the hydrological gradient was not apparent. Banksia ericifolia subsp. macrantha (A.S.George) A.S.George, Eucalyptus racemosa Cav. subsp. racemosa and Eucalyptus robusta Sm. displayed little seasonal variation in ψx and maintained a comparatively high pre-dawn ψx, and are therefore likely to be phreatophytic. Wetland vegetation in the lowest part of the landscape appeared to tolerate extreme fluctuations in water availability linked to a prevailing climatic pattern of variable and unreliable seasonal rainfall.