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1.
Graham Zemunik Hans Lambers Benjamin L. Turner Etienne Laliberté Rafael S. Oliveira 《Plant and Soil》2018,424(1-2):255-271
Background and aims
We sought to describe the species and functional composition of Brazilian campos rupestres plant communities on severely nutrient-impoverished white sands, to test hypotheses relating plant communities and physiological adaptations to infertile soils. Based on recently-published information on a south-western Australian dune chronosequence, we hypothesised that campos rupestres plant communities would similarly contain a relatively large proportion of non-mycorrhizal species, because of the phosphorus-(P) impoverished nature of the soils. We also sought to test the hypothesis that many of these non-mycorrhizal species have high leaf manganese (Mn) concentrations as a consequence of carboxylate exudation to mobilise soil P.Methods
We conducted flora surveys and quantified mycorrhizal status and foliar Mn concentrations in field sites with strongly-weathered sandy soils. Rhizosphere carboxylates were collected from glasshouse-grown plants to assess a potential correlation of carboxylates and leaf Mn concentrations.Results
Soils were depleted of all major plant nutrients. Non-mycorrhizal plants were abundant in most field sites (mean relative cover = 48%). Vellozia species were dominant aboveground; belowground, roots were colonised more by dark septate endophytic fungi than by mycorrhizal fungi. From the field sites, foliar Mn concentrations in non-mycorrhizal species increased with decreasing soil P concentrations, but only when soil Mn concentrations were above a minimum threshold (exchangeable [Mn] above detection limit). Across all species, however, there was no relationship of foliar Mn concentrations with soil P concentrations.Conclusions
Our hypothesis that white-sand campos rupestres communities contain a relatively large proportion of non-mycorrhizal plants was supported. Comparison with similar ecosystems in south-western Australia suggests that plant communities on severely P-impoverished sandy soils, despite differing evolutionary histories and little overlap in plant families, follow convergent evolutionary paths towards increasing abundance of non-mycorrhizal species.2.
Background and aims
In Australia’s Mediterranean hyperdiverse vegetation, species that produce cluster roots to mobilise poorly-available nutrients (e.g. Banksia spp.) are an important functional and structural component. Cluster roots are only active during the wet season, indicating a strong dependence on suitable surface soil moisture conditions. Winter rainfall in this region is declining due to global climate change, with a delayed commencement of rains and a decline in precipitation. It is unknown how lower soil moisture levels will affect the root dynamics of these globally-significant plant communities.Methods
We determined the root dynamics and root lifespan with minirhizotrons with or without irrigation to simulate reduced rainfall scenarios.Results
We found a major effect of irrigation on the early production (0.24 m m?2 d?1 increase), occurrence (97% increase) of cluster roots and only slight effects on lifespan (~10 days less) of all root types. With irrigation, the resultant greater soil moisture levels increased the deployment of cluster roots. Apart from cluster roots, the dynamics of other roots did not decline at lower soil moisture levels, suggesting that this system shows some resilience to decreased rainfall.Conclusions
Future research should focus on assessing if climate-altered cluster-root activity may be promoting compositional shifts in plant communities with additional restraining effects on root trait diversity.3.
4.
Aim
This work aimed to investigate the role of arbuscular mycorrhizal fungi (AMF) in the uptake and accumulation of silicon (Si) in banana plants. Si is recognized as a significant element that helps plants resist stresses.Methods
A pot experiment compared the growth, Si and P accumulation of banana plants pre-colonized or not by an AMF and exposed or not to Si added to the growth substrate.Results
A marked increase in Si was noticed in pseudostem, leaves and roots of pre-colonized banana plants, in presence as well as in absence of Si added to the growth substrate. Without Si addition, this accumulation was 60 % and 45 % higher in pseudostem and leaves, respectively, while it was 47 % and 41 % in presence of Si added to the substrate. In roots, this increase was 23 % and 52 % in presence and absence of Si added to the substrate, respectively. Phosphorus content in shoots and roots was likewise significantly increased in presence of AMF or Si.Conclusion
Our findings revealed that pre-colonized banana plants accumulated more Si in shoot and roots than non-mycorrhizal plants and may thus represent a potential novel avenue to explore banana resistance to pests and diseases.5.
Pei-Chun Lisa Hsu Maureen O’Callaghan Leo Condron Mark R. H. Hurst 《Plant and Soil》2018,425(1-2):43-55
Aims
The mechanisms by which rhizosphere bacteria increase the availability of mineral P precipitates for plant use are understudied. However, Paraburkholderia bryophila Ha185 is known to solubilize inorganic phosphate in vitro via a novel process. Therefore, this study aimed to demonstrate P solubilization by Ha185 in association with roots of perennial ryegrass (Lolium perenne L.).Methods
We developed a gnotobiotic plant assay to assess P solubilization by Ha185 on ryegrass roots under various nutrient conditions. A green fluorescent protein (GFP)-tagged derivative of Ha185 was used in conjunction with fluorescent microscopy and confocal microscopy to visualize colonization of ryegrass roots.Results
Ha185 solubilized mineral P (hydroxyapatite) in association with ryegrass roots and increased ryegrass growth by 20% under P-limited conditions. The GFP-tagged Ha185 strain colonized the rhizoplane and penetrated the primary root of ryegrass, possibly through “crack entry” at the point of lateral root emergence, but also by entering the epidermal cells via root hairs.Conclusions
Ha185 supported ryegrass growth under P-limited conditions, indicating this strain may improve availability of soil P for uptake by ryegrass. Tools developed in this study have broad application in the study of rhizobacteria-plant interactions.6.
Background and Aims
Phosphorus (P) is an essential nutrient for plants but its low availability often necessitates amendments for agronomical issues. Objectives were to determine P spatial distribution and speciation that remain poorly understood in cultivated soils.Methods
Aquic Argiudoll soil samples developed on a calcareous loam glacial till were collected from experimental plots submitted to contrasting crop rotations and amendments. Micro-X-ray fluorescence (μ-XRF) maps were collected on undisturbed samples. X-ray absorption near edge structure (XANES) spectra were collected on bulk samples and on fractions thereof, and on points of interests selected from μ-XRF maps. Results were compared with chemical analyses and extraction techniques results.Results
Chemical analyses show variations in total and exchangeable P contents depending on the samples but no significant difference is observed in terms of P distribution and speciation. P distribution is dominated by a low-concentration diffuse background with a minor contribution from minute hot spots. P speciation is dominated by phosphate groups bound to clay-humic complexes. No modification of P distribution and speciation is observed close to roots.Conclusions
This study evidenced minor effect of cropping and fertilizing practices on P speciation in cultivated soils. Despite analytical challenges, the combined use of μ-XRF and XANES provides relevant information on P speciation in heterogeneous soil media.7.
8.
Sara Varela-Cervero Álvaro López-García José M. Barea Concepción Azcón-Aguilar 《Plant and Soil》2016,405(1-2):107-123
Background and aims
Arbuscular mycorrhizal fungi (AMF) appear differentially represented among propagule forms [intraradical mycelium (IRM) in colonized roots, spores and extraradical mycelium (ERM)]. However, spring to autumn changes in the AMF communities harboured in the different propagule forms has not been studied, being this the aim of the present study.Methods
A terminal restriction fragment length polymorphism approach was used to monitor, in spring and autumn, the AMF community composition present in the three propagule types associated to five shrub species in a semi-arid Mediterranean environment.Results
The AMF community composition in roots was significantly different between spring and autumn; however, no significant differences were detected in soil propagules (spores and ERM). Different trends were identified according to the preferential biomass allocation patterns of AMF phylotypes, suggesting different life strategies: those allocating mainly into IRM (belonging to the Glomeraceae), ERM (Diversisporaceae and Gigasporaceae) or spores (Pacisporaceae and Paraglomeraceae).Conclusions
Differences of AMF taxa in the biomass allocation patterns among propagules are maintained throughout the year. Progress in the knowledge of functional features of AMF communities and their responses to seasonal variations are important for the AMF application in Mediterranean ecosystems.9.
Colleen M. Iversen Joanne Childs Richard J. Norby Todd A. Ontl Randall K. Kolka Deanne J. Brice Karis J. McFarlane Paul J. Hanson 《Plant and Soil》2018,424(1-2):123-143
Background and aims
Fine roots contribute to ecosystem carbon, water, and nutrient fluxes through resource acquisition, respiration, exudation, and turnover, but are understudied in peatlands. We aimed to determine how the amount and timing of fine-root growth in a forested, ombrotrophic bog varied across gradients of vegetation density, peat microtopography, and changes in environmental conditions across the growing season and throughout the peat profile.Methods
We quantified fine-root peak standing crop and growth using non-destructive minirhizotron technology over a two-year period, focusing on the dominant woody species in the bog: Picea mariana, Larix laricina, Rhododendron groenlandicum, and Chamaedaphne calyculata.Results
The fine roots of trees and shrubs were concentrated in raised hummock microtopography, with more tree roots associated with greater tree densities and a unimodal peak in shrub roots at intermediate tree densities. Fine-root growth tended to be seasonally dynamic, but shallowly distributed, in a thin layer of nutrient-poor, aerobic peat above the growing season water table level.Conclusions
The dynamics and distribution of fine roots in this forested ombrotrophic bog varied across space and time in response to biological, edaphic, and climatic conditions, and we expect these relationships to be sensitive to projected environmental changes in northern peatlands.10.
M. Victoria Vignale Leopoldo J. Iannone J. Martín Scervino M. Victoria Novas 《Plant and Soil》2018,422(1-2):267-281
Background and aims
We studied, through exudates employment, the effect of Epichloë (endophytic fungi), both independently and in association with Bromus auleticus (grass), on arbuscular mycorrhizal fungi (AMF) colonization, host and neighbouring plants biomass production and soil changes.Methods
Through in vitro and greenhouse experiments, Epichloë endophytes effect on AMF development was evaluated. In vitro studies of exudates effect on Gigaspora rosea and Rhizophagus intraradices were performed using root or endophyte exudates. A 6-month greenhouse experiment was conducted to determine Bromus auleticus endophytic status effect and endophyte exudates role in biomass production, neighbouring plants mycorrhizal colonization and soil properties.Results
Endophyte exudates and E+ plant root exudates promoted in vitro AMF development in the pre-infective stage of G. rosea and in carrot root culture mycelium of R. intraradices in a dose-response relationship, while control media and E- plants exudates had no effect. R. intraradices colonization and plant growth was clearly increased by endophytes and their exudates.Conclusions
This is the first work evidencing the direct effect of Epichloë endophytes and infected plants root exudates on AMF extramatrical development. While higher levels of AMF colonization were observed in E+ plants, no clear effect was detected in neighbouring plants colonization, plant biomass or soil properties.11.
Sabine Güsewell 《Plant and Soil》2017,415(1-2):57-72
Aims
Dauciform roots (DR) are formed by some Cyperaceae under phosphorus (P) deficiency. To advance our understanding of their physiological function, I ask: Is DR formation regulated by shoot P status or external P supply? How does it respond to nitrogen (N)? Do DR enhance root monoesterase, diesterase or phytase activities and ability to utilize organic P?Methods
Greenhouse experiments were carried out with two Carex species grown in sand with (1) different combinations of N and P supply, (2) local supply of N or P to root halves, and (3) different organic P forms.Results
Carex flava produced DR in all treatments. The density of DR and phosphatase activities increased with N supply; they were regulated by shoot P status and external N (but not P) supply. All phosphatase activities increased with DR density. Carex muricata produced no DR and had lower diesterase activity than C. flava but both species grew equally well with diester-P.Conclusions
DR and phosphatase activities are regulated by both N and P supply. Similar growth responses to nutrients in both species suggest small costs and benefits of DR under experimental conditions but confirmation is needed for plants grown on natural soils.12.
Background
The current literature establishes the importance of gene functional category and expression in promoting or suppressing duplicate gene loss after whole genome doubling in plants, a process known as fractionation. Inspired by studies that have reported gene expression to be the dominating factor in preventing duplicate gene loss, we analyzed the relative effect of functional category and expression.Methods
We use multivariate methods to study data sets on gene retention, function and expression in rosids and asterids to estimate effects and assess their interaction.Results
Our results suggest that the effect on duplicate gene retention fractionation by functional category and expression are independent and have no statistical interaction.Conclusion
In plants, functional category is the more dominant factor in explaining duplicate gene loss.13.
Lenin D. Sarabia Berin A. Boughton Thusitha Rupasinghe Allison M. L. van de Meene Damien L. Callahan Camilla B. Hill Ute Roessner 《Metabolomics : Official journal of the Metabolomic Society》2018,14(5):63
Introduction
Mass spectrometry imaging (MSI) is a technology that enables the visualization of the spatial distribution of hundreds to thousands of metabolites in the same tissue section simultaneously. Roots are below-ground plant organs that anchor plants to the soil, take up water and nutrients, and sense and respond to external stresses. Physiological responses to salinity are multifaceted and have predominantly been studied using whole plant tissues that cannot resolve plant salinity responses spatially.Objectives
This study aimed to use a comprehensive approach to study the spatial distribution and profiles of metabolites, and to quantify the changes in the elemental content in young developing barley seminal roots before and after salinity stress.Methods
Here, we used a combination of liquid chromatography–mass spectrometry (LC–MS), inductively coupled plasma mass spectrometry (ICP–MS), and matrix-assisted laser desorption/ionization (MALDI–MSI) platforms to profile and analyze the spatial distribution of ions, metabolites and lipids across three anatomically different barley root zones before and after a short-term salinity stress (150 mM NaCl).Results
We localized, visualized and discriminated compounds in fine detail along longitudinal root sections and compared ion, metabolite, and lipid composition before and after salt stress. Large changes in the phosphatidylcholine (PC) profiles were observed as a response to salt stress with PC 34:n showing an overall reduction in salt treated roots. ICP–MS analysis quantified changes in the elemental content of roots with increases of Na+ and decreases of K+ content.Conclusion
Our results established the suitability of combining three mass spectrometry platforms to analyze and map ionic and metabolic responses to salinity stress in plant roots and to elucidate tolerance mechanisms in response to abiotic stress, such as salinity stress.14.
Sheng Qin Wei-Wei Feng Tian-Tian Wang Peng Ding Ke Xing Ji-Hong Jiang 《Plant and Soil》2017,415(1-2):117-130
Background and aims
Xylem-tapping mistletoes may experience relaxed selective pressure to use water efficiently during photosynthesis because of lower per-unit costs for water acquisition than experienced by host plants. As a result, we hypothesised that mistletoes would exhibit parallel but dampened leaf-level adaptations and responses to aridity, compared to those seen in hosts.Methods
Photosynthetic traits, leaf dark respiration, nutrient concentrations and specific leaf area (SLA) were measured on 42 mistletoe-host species-pairs sampled from five sites in Australia and Brazil that vary widely in aridity.Results
Mistletoes exhibited similar trait-shifts to hosts in relation to site aridity. In both groups, arid-site species showed stronger control over stomatal water loss, larger drawdown of CO2 during photosynthesis (lower ci: ca), higher leaf N and P concentrations per unit leaf area, and lower SLA. Nevertheless, mistletoes were profligate water users compared to their hosts and showed substantially less efficient use of water during photosynthesis. On average, mistletoes showed twice higher leaf dark respiration rates at a given photosynthetic capacity, suggesting relatively higher leaf maintenance costs for these parasitic plants.Conclusions
Despite fundamental differences in lifestyle and in photosynthetic traits, mistletoes exhibit trait responses and adaptations to site aridity in parallel and to approximately the same extent as their hosts.15.
Phosphorus availability and microbial community in the rhizosphere of intercropped cereal and legume along a P-fertilizer gradient 总被引：5，自引：0，他引：5
Xiaoyan Tang Sarah A. Placella Florent Daydé Laetitia Bernard Agnès Robin Etienne-Pascal Journet Eric Justes Philippe Hinsinger 《Plant and Soil》2016,407(1-2):119-134
Background and aims
Positive below-ground interactions (facilitation) should be more pronounced when resources limit crop growth, according to the stress-gradient hypothesis. Our aim was to test this hypothesis for intercropped durum wheat and faba bean along a P-fertilizer gradient.Methods
A field experiment was conducted in a long-term P-fertilizer trial with three rates of P-fertilization (No, Low and High P). Microbial biomass was assessed by chloroform fumigation-extraction. Quantitative PCR was applied to evaluate the abundance of relevant microbial groups.Results
Phosphorus availability and microbial biomass systematically increased in the rhizosphere compared to bulk soil. P-fertilization resulted in higher abundance of targeted bacterial phyla, whole bacterial and fungal communities, and depressed mycorrhizal colonization of durum wheat, but not faba bean. Microbial biomass carbon significantly increased in the rhizosphere only in P-fertilized treatments, pointing to P limitation of microbial communities. Intercropping yielded a significant effect on rhizosphere microbial properties only at High P. Microbial biomass P increased in the rhizosphere of intercropped faba bean only at No P level, and was thus the sole finding supporting the stress-gradient hypothesis.Conclusions
P-fertilization was the main driver of microbial communities in this field trial, and P-fertilizer application modulated the species-specific effect in the intercrop. Plant performance did not validate the stress-gradient hypothesis as positive plant-plant interactions occurred regardless of the level of P-fertilization.16.
Orpheus M. Butler Mehran Rezaei Rashti Tom Lewis James J. Elser Chengrong Chen 《Plant and Soil》2018,431(1-2):191-202
Background and aims
The current study was undertaken to investigate the mechanism underlying Boron (B)-alleviated phosphate (P) deficiency in Arabidopsis thaliana. Furthermore, we were interested to explore whether this alleviation of P deficiency by B could extend to Brassica crops.Methods
Arabidopsis thaliana or Brassica oleracea plants were grown under P-sufficient or -deficient condition with or without extra B for 7 days, then shoots and roots of B. oleracea were sampled for analysis of soluble P content while those of A. thaliana were harvested for analysis of total P content, soluble P content and nitric oxide (NO) as well as for cell wall extraction and RNA isolation.Results
A. thaliana plants showed reduced root growth and decreased P content in the root under P-deficient conditions, but improved root growth when supplemented with additional B. Further analysis revealed that exogenous B elevated the cell wall pectin content and facilitated the release of P in P-deficient seedlings, thus more soluble P was available to sustain growth under P deficiency. Furthermore, B supplement also increased soluble P in P-deficient cabbage (Brassica oleracea var. capitata L.), an economically important vegetable crop. P deficiency alone was sufficient to induce NO accumulation, and in combination with B application further enhanced NO accumulation, while exogenous application of NO scavenger c-PTIO [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide] counteracted this positive effect of B, indicating that NO is positively involved in B-mediated alleviation of P deficiency.Conclusions
Our study reveals the critical role of B in improving the growth of P-deficient plants, and also provides evidence implicating the involvement of NO signal.17.
Background and aims
We evaluated the influence of plant species and life forms on soil aggregate distribution among size-classes, total macroaggregate mass and aggregate mean weight diameter (MWD), and examined how specific root traits were related to these aggregation variables.Methods
We analyzed the soil attached to the roots (i.e., rhizospheric soil) under 13 Mediterranean species grown in monocultures in a common garden experiment for four years, and compared it to a bare soil. The mass distribution of aggregates in six size-classes and aggregate MWD were calculated, both on a rhizospheric soil and root biomass basis.Results
Compared to bare soil, macroaggregate mass increased by an average of 13% in the presence of plants, with a strong effect of species and life forms (both P < 0.0001); some species such as Sanguisorba minor showing increases of up to ~40%. Although the soil under graminoids had a greater macroaggregate mass, their MWD was lower than under non-woody dicots. Large (2000–1000 μm) and intermediate (1000–500 μm) macroaggregate mass increased with root mass and length density and decreased with root lignin concentration, while very large macroaggregate (6000–2000 μm) mass and the MWD increased with root soluble compound concentration.Conclusions
Species and life forms differently influenced the distribution of macroaggregates among size-classes and aggregate MWD. Easily-decomposable roots with traits related to resource acquisition (i.e., high fine root length, high water-soluble compound concentration) are more favorable for the development of water-stable macroaggregates than roots traits related to resource conservation (high lignin concentration, thick roots).18.
P. A. García-Parisi F. A. Lattanzi A. A. Grimoldi M. Druille M. Omacini 《Plant and Soil》2017,412(1-2):151-162
Aims
Plants interact by modifying soil conditions in plant-soil feedback processes. Foliar endophytes of grasses exert multiple effects on host rhizosphere with potential consequences on plant-soil feedback. Here, we hypothesize that the grass-endophyte symbiosis impairs soil symbiotic potential, and in turn influences legume performance and nitrogen acquisition.Methods
Soil was conditioned in pots, growing Lolium multiflorum with or without the fungal endophyte Epichloë and with or without arbuscular mycorrhizal fungi (AMF). Then, Trifolium repens grew in all types of conditioned soils with high or low rhizobia availability.Results
Endophyte soil conditioning reduced AMF spores number and rhizobial nodules (?27 % and ?38 %, respectively). Seedling survival was lower in endophyte-conditioned soil and higher in mycorrhizal soils (?27 % and +24 %, respectively). High rhizobia-availability allowed greater growth and nitrogen acquisition, independent of soil conditioning. Low rhizobia-availability allowed both effects only in endophyte-conditioned soil.Conclusion
Endophyte-induced changes in soil (i) hindered symbiotic potential by reducing AMF spore availability or rhizobia nodulation, (ii) impaired legume survival irrespective of belowground symbionts presence, but (iii) mimicked rhizobia effects, enhancing growth and nitrogen fixation in poorly nodulated plants. Our results show that shoot and root symbionts can be interactively involved in interspecific plant-soil feedback.19.
Leaf litter thickness,but not plant species,can affect root detection by ground penetrating radar 总被引：1，自引：0，他引：1
Toko Tanikawa Hidetoshi Ikeno Masako Dannoura Keitarou Yamase Kenji Aono Yasuhiro Hirano 《Plant and Soil》2016,399(1-2):271-282
Aim
Ground penetrating radar (GPR), a nondestructive tool that can detect coarse tree roots, has not yet become a mature technology for use in forests. In this study, we asked two questions concerning this technology: (i) Does the leaf litter layer influence root detection and major indices based on the time interval between zero crossings (T) and the amplitude area (A)? (ii) Can GPR images discriminate roots of different plant species?Methods
Roots buried in a sandy bed, which was covered with different thicknesses of leaf litter, were scanned using a 900 MHz GPR antenna. Roots of four plant species in the bed were also scanned.Results
Leaf litter decreased root reflections without distorting the shape of the hyperbolas in the radar profile. A values decreased with increasing litter thickness, whereas T was independent of litter thickness. For all species combined, GPR indices were significantly correlated with root diameter.Conclusions
Leaf litter dramatically decreased root detection, but the influence of the litter could be ignored when the sum of T for all reflection waveforms (ΣT) is adopted to estimate root diameter. To use A values to detect roots, litter should be removed or equalized in thickness. Radar profiles could not reliably differentiate among roots belonging to plants of different species.20.