Comparison of As sequestration in iron plaque and uptake by different genotypes of rice plants grown in As-contaminated paddy soils

Background and aims

Limited information is available on comparing the iron plaque formation capabilities and their effect on arsenic (As) uptake by different rice plant genotypes grown in As-contaminated soils. This study investigates the effect of iron plaque on As uptake in different rice genotypes grown in As-contaminated soils from the Guandu Plain of northern Taiwan.

Methods

Twenty-eight rice genotypes including 14 japonica and 14 indica genotypes were used in this study. Rice seedlings were grown in As-contaminated soils for 38 days. The iron plaque formed on the rice roots were extracted using dithionite–citrate–bicarbonate. The concentrations of As, Fe, and P in soil solutions, iron plaque, and plants were measured. The speciation of As in the root’s iron plaque was determined by As K-edge X-ray absorption near-edge structure spectroscopy (XANES).

Results

The amounts of iron plaque formation on roots were significantly different among 28 tested rice genotypes, and 75.7–92.8 % of As uptake from soils could be sequestered in iron plaque. However, there were no significant negative correlations between the amounts of Fe or As in the iron plaque and the content of As accumulated in rice plants of tested genotypes. XANES data showed that arsenate was the predominant As species in iron plaque, and there were difference in the distribution of As species among different rice genotypes.

Conclusions

The iron plaque can sequester most of As uptake from soils no matter what rice genotypes used in this study. However, the iron plaque alone did not control the extent of As accumulation in rice plants from As-contaminated soils among 28 tested rice genotypes. Low As uptake genotypes of rice selected from this study can be recommended to be grown in the As-contaminated soils.     

Properties of anthropogenic soils in ancient run-off capturing agricultural terraces in the Central Negev desert (Israel) and related effects of biochar and ash on crop growth

Background and aims

In the Central Negev hills (Israel) many ancient terraced wadis exist, which captured run-off and caused gradual soil aggradation, which enabled agricultural practices. In these terraces, dark colored soil horizons were observed, containing charcoal, as can be found in Terra Preta soils, suggesting higher fertility compared to natural soils. The aim of our investigation was to investigate these anthropogenic soils and to study the effects of charcoal and ash addition on soil properties and crop growth.

Methods

We investigated 12 soil profiles, focusing on possible differences between light and dark colored soil horizons. We also investigated the effects of amendment of charcoal and ash on the growth of wheat (Triticum Aestivum L.) in a 40-day pot experiment involving two water regimes.

Results

Results show that charcoal content in light and dark horizons were both low (<0.2 %), but significantly lower bulk densities were found in dark colored horizons. In the crop experiment, charcoal addition resulted in decreased crop growth, while, in the water deficit regime, ash addition resulted in increased crop growth.

Conclusions

Considering the observed charcoal and the results from the crop experiment, we hypothesize that, in ancient run-off capturing agricultural systems, ash was purposefully added as fertilizer.     

Evidence for progressive phosphorus limitation over long-term ecosystem development: Examination of a biogeochemical paradigm

Aims

To test predictions of ecosystem theory for changes in P cycling over primary succession, we determined soil phosphorus (P) in labile, primary mineral, organic, and occluded forms along a chronosequence of five wave cut terraces known as the “Ecological Staircase”. The Ecological Staircase terraces (T1-T5) transition naturally from fertile native coastal forests in California, USA, to diminutive pygmy vegetation over the span of?>?500,000 years of pedogenesis.

Methods

Soil P fractions were quantified to a depth of 40 cm on T1-T5 using a modified Hedley P fractionation procedure.

Results

Overall results confirmed the Walker and Syers Model of Phosphorus Transformations During Pedogenesis: total P declined from youngest (194 mg/kg P) to oldest (127 mg/kg P) sites; primary-mineral P decreased sharply from T1 to older sites; and occluded P dominated P pools at the oldest pygmy sites (T3-T5). In addition, foliar P concentrations declined markedly in the pygmy forest, and N/P of vegetation (T1: 6.03, T5: 14.4) and N/P_organic of mineral soils (T1: 6.10, T5: 25.3) increased significantly over time.

Conclusions

Results point to P as the primary limiting nutrient in the pygmy forest, exemplifying the terminal steady-state of ecosystem retrogression that underlies the persistence of this unique ecosystem.     

Effect of the aerenchymatous helophyte Glyceria maxima on the sulfate-reducing communities in two contrasting riparian grassland soils

Aims

The research aimed at studying the effect of flooding with sulfate-rich water on the activity, abundance and diversity of sulfate-reducing micro-organisms present in the root zone of an oxygen-releasing plant growing on two riparian grassland soils with contrasting amounts of iron.

Methods

A series of microcosms was used to investigate the effects. Plants were grown under controlled conditions in microcosms containing a rhizosphere and bulk soil compartment for a period of 12 weeks in the presence of sulfate-rich flood water. Molybdate-treated systems served as non-sulfate-reducing controls.

Results

At harvest, activity and numbers of sulfate-reducing micro-organisms were higher in the absence of molybdate, but a rhizosphere effect and an impact of the presence of high levels of iron were not observed on activity and numbers. Both soils had in common a diverse community of sulfate-reducing micro-organisms covering all major cultured bacterial taxa. The appearance of members of the Desulfovibrionaceae exclusively in the rhizosphere of G. maxima was the only unambiguous indication of a plant effect.

Conclusion

The presence of sulfate-rich flood water stimulated the activity and growth of a part of the sulfate-reducing community leading to a change in community composition. The proximity of aerenchymatous plant roots and the abundance of iron in the soil had a negligible effect on the sulfate-reducing community.     

Effects of nano-sized zero-valent iron on DDT degradation and residual toxicity in soil: a column experiment

Background and aims

Nanoscale zero-valent iron (nZVI) application is a promising technology for degradation of chlorinated contaminants in soil. Plants also play an important role in soil remediation and nZVI should not adversely affect plants growing on treated soils. Large amounts of DDT are still found in certain soils and means to remediate these soils are limited. Our aims were to investigate the effect of nZVI on DDT degradation and evaluate possible negative effects of nZVI on plants.

Methods

Columns with spiked (20 mg DDT kg^?1) soil were percolated with nZVI (1 g nZVI L^?1) and leached with five pore volumes of water to assess leaching of nZVI and residual toxicity of leachates and soil to plants using seed germination and plant growth tests (barley, flax).

Results

Addition of nZVI led to degradation of 45 % of the added DDT. Percolation with water significantly oxidized and transported iron through the columns. The first leachates had negative effects on plant development, but after leaching with 4 pore volumes, neither soil nor leachates affected plant negatively.

Conclusions

nZVI is efficient for degradation of DDT and adverse effects of nZVI on plants seem ephemeral and are alleviated after oxidation mediated by percolating water.     

Effect of selenium fertilization on the accumulation of cadmium and lead in rice plants

Background and Aims

The accumulation of cadmium and lead in rice (Oryza sativa L.) grains is a potential threat to human health. In this study, the effect of selenium fertilization on the uptake and translocation of cadmium and lead in rice plants was investigated.

Methods

Rice plants were cultivated using cadmium and lead contaminated soils with selenium addition at three concentrations (0, 0.5 and 1 mg kg^?1). At maturity, plants were harvested, and element concentrations in rice tissues were analyzed by using ICP-MS.

Results

Selenium application significantly increased selenium accumulation in rice grain, and markedly decreased cadmium and lead concentrations in rice tissues. In brown rice grains, selenium application reduced cadmium concentrations by 44.4 %, but had no significant effect on lead accumulation. Selenium application significantly decreased metal mobility in soils, at 0.5 mg kg^?1 treatment, the translocation factor of cadmium and lead from soil to iron plaque decreased by 71 and 33 % respectively.

Conclusions

The mechanism of selenium mitigating of heavy metal accumulation in rice could be decreasing metal bioavailability in soil. Selenium fertilization could be an effective and feasible method to enrich selenium and reduce cadmium levels in brown rice.     

Effects of biochar amendment on root traits and contaminant availability of maize plants in a copper and arsenic impacted soil

Background and aims

Biochar has been proposed as a tool to enhance phytostabilisation of contaminated soils but little data are available to illustrate the direct effect on roots in contaminated soils. This work aimed to investigate specific root traits and to assess the effect of biochar amendment on contaminant availability.

Methods

Amendment with two different types of biochar, pine woodchip and olive tree pruning, was assessed in a rhizobox experiment with maize planted in a soil contaminated with significant levels of copper and arsenic.

Results

Amendment was found to significantly improve root traits compared to the control soil, particularly root mass density and root length density. Copper uptake to plants and ammonium sulphate extractable copper was significantly less in the biochar amended soils. Arsenic uptake and extractability varied with type of biochar used but was not considered to be the limiting factor affecting root and shoot development.

Conclusions

Root establishment in contaminated soils can be enhanced by biochar amendment but choice of biochar is key to maximising soil improvement and controlling contaminant availability.     

The temporal development and additivity of plant-soil feedback in perennial grasses

Background

Current knowledge of plant-soil feedback is based largely on single end point studies with soils conditioned by monocultures, but accounting for variability in the ecological impacts of feedback effects may require understanding how feedback develops over time and in multi-species plant communities.

Methods

To examine temporal development and additivity of feedback, two pairs of native and non-native congeneric grasses were grown alone or in mixtures to create six soil conditioning treatments. We measured plant growth and feedback on the soils over 19 months and addressed whether plant biomass was additive or non-additive between soils treated by mixtures and their constituent monocultures.

Results

For native grasses, plant-soil feedback either became progressively more negative through time or switched from neutral to negative. Feedback to non-native grasses was variably neutral to positive. Final biomass of the grasses growing on soils conditioned by mixtures was generally an additive function of growth on soils conditioned by the component monocultures, except native grasses growing in soils conditioned by their own congener mixtures, which were non-additive.

Conclusions

Temporal variation and non-additivity in feedback suggest that extrapolation to communities may be complex. More work is needed to assess the generality of temporal and scaling effects.     

Morphological and growth altering effects of Cisplatin in C. albicans using fluorescence microscopy

Background

Extrapulmonary manifestations of tuberculosis have become increasingly important in the era of HIV/AIDS.

Case presentation

We describe a case of tuberculosis (TB) dactylitis in a patient with AIDS who originated from the Ivory Coast. The diagnosis was established by direct visualization of acid-fast bacilli on joint fluid and bone biopsy of the proximal phalanx. Imaging of the chest revealed multiple bilateral nodules. Confirmation of the diagnosis was made by isolation of Mycobacterium tuberculosis from sputum and bone cultures.

Conclusion

Tuberculosis should be considered in patients with unusual soft tissue or skeletal lesions, especially when an immunosuppressive condition is present. Ziehl-Neelsen staining and culture of tissue obtained via surgical biopsy offer the most direct approach to diagnosis.     

Effect of phosphate status on the sorption and desorption properties of some soils of northern India

Aims

Enormous quantities of phosphate have been applied to world soils, yet we know little about effects of phosphate status on sorption properties.

Methods

We measured sorption and desorption of phosphate on soils from fertilized tea plantations from northern India and compared them with unfertilized soils. We also incubated phosphate at high temperature with a previously unfertilized soil and measured the effects.

Results

Sorption of phosphate was less marked on soils of high phosphate status whether derived from inherent fertility or fertilizer application. This occurred because high phosphate status made the surface charge on the reacting surfaces more negative. Phosphate status also affected desorption. The higher the phosphate status, the smaller the difference between sorption and desorption curves. This occurred because on soils of high phosphate status the pathways by which adsorbed anions diffuse were saturated and the slow reaction that follows adsorption was stopped.

Conclusions

When low-phosphate soils are first fertilized, it is necessary to supply more phosphate than is removed in produce. However, after long-term phosphate fertilization, it is sufficient to only replace phosphate lost in produce. We need to find how much phosphorus it takes to reach this state and how many of the world’s soils have already reached it.     

Soil-mediated local adaptation alters seedling survival and performance

Background and aims

Soils can act as agents of natural selection, causing differential fitness among genotypes and/or families of the same plant species, especially when soils have extreme physical or chemical properties. More subtle changes in soils, such as variation in microbial communities, may also act as agents of selection. We hypothesized that variation in soil properties within a single river drainage can be a selective gradient, driving local adaptation in plants.

Methods

Using seeds collected from individual genotypes of Populus angustifolia James and soils collected from underneath the same trees, we use a reciprocal transplant design to test whether seedlings would be locally adapted to their parental soil type.

Results

We found three patterns: 1. Soils from beneath individual genotypes varied in pH, soil texture, nutrient content, microbial biomass and the physiological status of microorganisms. 2. Seedlings grown in local soils experienced 2.5-fold greater survival than seedlings planted in non-local soils. 3. Using a composite of height, number of leaves and leaf area to measure plant growth, seedlings grew ～17.5% larger in their local soil than in non-local soil.

Conclusions

These data support the hypothesis that variation in soils across subtle gradients can act as an important selective agent, causing differential fitness and local adaptation in plants.     

The impact of changing moisture conditions on short-term P availability in weathered soils

Background and Aims

Bioavailable phosphorus (P) represents a primary constraint on productivity in many ecosystems on highly-weathered soils. Soil moisture can be important to determining P bioavailability and net primary productivity in these systems. However, hydrologic controls on P availability remain poorly understood.

Methods

We used “resins” (anion-exchange membranes) to quantify the response of labile P, an estimate of bioavailable P, to soil moisture conditions in two highly-weathered soils (rendzina, ultisol). The resins were either incubated in soil or shaken with a soil-water slurry.

Results

Resin incubations in aerobic soil effectively quantified labile P in soils under changing moisture conditions, extracting significant amounts of labile P while avoiding the disturbance imposed by slurries. Wetting field-moist soils resulted in pulsed labile P, with lagged peaks occurring days after the largest moisture additions. Re-wetting air-dried soils enhanced labile P immediately, with the largest amounts observed at the highest moisture levels; labile P steadily declined following the moisture addition.

Conclusions

Soil moisture levels and history strongly impacted labile P, indicating the importance of both variables when interpreting labile P measurements. These results also suggest that P availability is linked to both the amount and timing of rainfall, with implications for plant productivity in regions exposed to changing moisture regimes.     

Metal mobilization from soils by phytosiderophores – experiment and equilibrium modeling

Aims

To test if multi–surface models can provide a soil-specific prediction of metal mobilization by phytosiderophores (PS) based on the characteristics of individual soils.

Methods

Mechanistic multi-surface chemical equilibrium modeling was applied for obtaining soil-specific predictions of metal and PS speciation upon interaction of the PS 2’-deoxymugineic acid (DMA) with 6 soils differing in availability of Fe and other metals. Results from multi-surface modeling were compared with empirical data from soil interaction experiments.

Results

For soils in which equilibrium was reached during the interaction experiment, multi-surface models could well predict PS equilibrium speciation. However, in uncontaminated calcareous soils, equilibrium was not reached within a week, and experimental and modeled DMA speciation differed considerably. In soils with circum-neutral pH, on which Fe deficiency is likely to occur, no substantial Fe mobilization by DMA was predicted. However, in all but the contaminated soils, Fe mobilization by DMA was observed experimentally. Cu and Ni were the quantitatively most important metals competing with Fe for complexation and mobilization by DMA.

Conclusion

Thermodynamics are unable to explain the role of PS as Fe carrier in calcareous soils, and the kinetic aspects of metal mobilization by PS need to be closer examined in order to understand the mechanisms underlying strategy II Fe acquisition.     

Dynamics of plant metal uptake and metal changes in whole soil and soil particle fractions during repeated phytoextraction

Aims

Phytoextration of metal polluted soils using hyperaccumulators is a promising technology but requires long term successive cropping. This study investigated the dynamics of plant metal uptake and changes in soil metals over a long remediation time.

Methods

A soil slightly polluted with metals (S1) was mixed with highly polluted soil (S4) to give two intermediate pollution levels (S2, S3). The four resulting soils were repeatedly phyto-extracted using nine successive crops of Cd/Zn-hyperaccumulator Sedum plumbizincicola over a period of 4 years.

Results

Shoot Cd concentration decreased with harvest time in all soils but shoot Zn declined in S1 only. Similar shoot Zn concentrations were found in S2, S3 and S4 although these soils differed markedly in metal availability, and their available metals decreased during phytoextraction. A possible explanation is that plant active acquisition ability served to maintain plant metal uptake. Plant uptake resulted in the largest decrease in the acid-soluble metal fraction followed by reducible metals. Oxidisable and residual fractions were less available to plants. The coarse soil particle fractions made the major contribution to metal decline overall than the fine fractions.

Conclusion

Sedum plumbizincicola maintained long term metal uptake and the coarse soil particles played the most important role in phytoextraction.     

Influence of serpentine abundance on the vertical distribution of available elements in soils

Background and Aim

Biotic and abiotic factors contribute in shaping the distribution through the soil profile of elements released by mineral weathering; among them, leaching and biocycling dominate in temperate environments. We evaluated if the intensity of leaching and biocycling of nutrients can be modulated by element deficiencies linked to the abundance of serpentine in the soil parent material, i.e. if the most deficient elements are more efficiently retained.

Methods

We selected twelve poorly developed soils from Northern Italian beech stands, with variable amounts of serpentinites in the parent material, and determined total and exchangeable Ca, Mg and K, as well as an index of abundance of serpentine minerals.

Results

The total element content depended on the abundance of serpentines, while only exchangeable Mg was related to the parent material. The vertical trend of Ca and K indicated the role of biocycling in all soils, but the relative availability of Ca (ratio between exchangeable and total content) was much higher in the top horizons of serpentine-rich soils.

Conclusions

The different element availability among soils suggested that the vertical distribution of available elements was linked to the parent material and that losses were limited in serpentine-rich soils, probably because plants take up the deficient elements as soon as they are released from litter and thus limit their leaching in deeper soil horizons.     

Soil chemical properties affect the concentration of elements (N,P, K,Ca, Mg,As, Cd,Cr, Cu,Fe, Mn,Ni, Pb,and Zn) and their distribution between organs of Rumex obtusifolius

Background and aims

The ionome (elemental composition) of grassland species has rarely been studied at the level of individual organs and little is known about effects of soil chemical properties on the ionome. Using the model oxalate plant Rumex obtusifolius, we asked how its biomass production and the distribution of elements between its organs is affected by soil chemical properties.

Methods

We established a pot experiment with R. obtusifolius planted in acidic non-contaminated control and in slightly acidic and alkaline soils anthropogenically contaminated by the risk elements As, Cd, Pb, and Zn. Both contaminated soils were untreated and treated by lime and superphosphate. We determined biomass production and the concentrations of elements in its organs.

Results

Biomass production was negatively related to the mobility of micro- and risk elements. Restricted transport of micro- and risk elements from belowground organs into leaves was recorded in untreated contaminated soils. In both lime-treated soils and in superphosphate-treated alkaline soil, elevated transport of micro- and risk elements from belowground organs into leaves was recorded in comparison to untreated contaminated soils. The lowest concentrations of micro- and risk elements were recorded in stems and seeds, followed by belowground organs and leaves.

Conclusions

R. obtusifolius is an As-, Cd-, Pb-, and Zn-excluder and is sensitive to high availability of micro- and risk elements in the soil. Soil chemical properties affect the distribution of essential elements within the plant greatly.     

Assessment of the relationship between geologic origin of soil, rhizobacterial community composition and soil receptivity to tobacco black root rot in Savoie region (France)

Background and aims

In Morens (Switzerland), soils formed on morainic deposits (which contain vermiculite clay and display particular tobacco rhizobacterial community) are naturally suppressive to Thielaviopsis basicola-mediated tobacco black root rot, but this paradigm was never assessed elsewhere. Here, we tested the relation between geology and disease suppressiveness in neighboring Savoie (France).

Methods

Two morainic and two sandstone soils from Savoie were compared based on disease receptivity (T. basicola inoculation tests on tobacco), clay mineralogy (X-ray diffraction), tobacco rhizobacterial community composition (16S rRNA gene-based taxonomic microarray) and phlD ⁺ Pseudomonas populations involved in 2,4-diacetylphloroglucinol production (real-time PCR and tRFLP).

Results

Unlike in Morens, in Savoie the morainic soils were receptive to disease whereas T. basicola inoculation did not increase disease level in the sandstone soils. Vermiculite was not present in Savoie soils. The difference in rhizobacterial community composition between Savoie morainic and sandstone soils was significant but modest, and there was little agreement in bacterial taxa discriminating soils of different disease receptivity levels when comparing Morens versus Savoie soils. Finally, phlD ⁺ rhizosphere pseudomonads were present at levels comparable to those in Morens soils, but with different diversity patterns.

Conclusions

The morainic model of black root rot suppressiveness might be restricted to the particular type of moraine occurring in the Morens region, and the low disease receptivity of sandstone soils in neighboring Savoie might be related to other plant-protection mechanisms.     

Arthrobacter agilis UMCV2 induces iron acquisition in Medicago truncatula (strategy I plant) in vitro via dimethylhexadecylamine emission

Background and aims

Iron is an essential nutrient for plant growth. Although abundant in soil, iron is poorly available. Therefore, plants have evolved mechanisms for iron mobilization and uptake from the rhizospheric environment. In this study, we examined the physiological responses to iron deficiency in Medicago truncatula plants exposed to volatile organic compounds (VOCs) produced by Arthrobacter agilis UMCV2.

Methods

The VOC profiles of the plant and bacterium were determined separately and during interaction assays using gas chromatography. M. truncatula plants exposed to A. agilis VOCs and pure dimethylhexadecylamine were transferred to conditions of iron deficiency, and parameters associated with iron nutritional status were measured.

Results

The relative abundance of the bacterial VOC dimethylhexadecylamine increased 12-fold when in co-cultures of A. agilis and M. truncatula, compared to axenic cultures. Plants exposed to bacterial VOCs or dimethylhexadecylamine exhibited a higher rhizosphere acidification capacity, enhanced ferric reductase activity, higher biomass generation, and elevated chlorophyll and iron content relative to controls.

Conclusions

The VOCs emitted by A. agilis UMCV2 induce iron acquisition mechanisms in vitro in the Strategy I plant M. truncatula. Dimethylhexadecylamine is the signal molecule responsible for producing the beneficial effects.     

Influence of agricultural practices and seasons on the abundance and community structure of culturable pseudomonads in soils under no-till management in Argentina

Background and aims

Members of the genus Pseudomonas are common inhabitants of rhizospheres and soils, and it is known that soil types and crop species influence their population density and structure. 20?×?10⁶ ha are cultivated under no-tillage in Argentina and there is a need to find new biologically-based soil quality indexes to distinguish between sustainable and non-sustainable agricultural practices. Pseudomonads abundance and community structure were analyzed in no-till soils with different agricultural practices, in productive fields along 400 km of Argentinean Pampas.

Methods

We sampled soils and root systems from agricultural plots in which sustainable or non-sustainable agricultural practices have been applied. Samples were collected in summer and winter during 2010 and 2011. Culturable fluorescent and total pseudomonads were enumerated by plating on Gould’s selective medium S1. Colonies from these plates served as DNA source to carry out PCR-RFLP community structure analysis of the pseudomonads-specific marker genes oprF and gacA.

Results

Abundance of total and fluorescent culturable pseudomonads in bulk soils was influenced by seasonal changes and agricultural practices. Rhizospheric counts from the same crop were affected by agricultural treatments. Also, crop species influenced pseudomonads density in the rhizosphere. Combined PCR-RFLP profile of both genes showed a seasonal grouping of samples.

Conclusions

Sustainable soil management seems to promote pseudomonads development in soils, favoring root colonization of crops from those plots. Crop species influence total pseudomonads load of rhizospheres and its community structure. Total or relative pseudomonads load could function as soil quality indicator of good agricultural practices.