Microbial inoculation of seeds characteristically shapes the rhizosphere microbiome in <Emphasis Type="Italic">desi</Emphasis> and <Emphasis Type="Italic">kabuli</Emphasis> chickpea types

Purpose

Chickpea is generally cultivated after seed treatment with host-specific Mesorhizobium ciceri, the nitrogen-fixing bacterium forming root nodules. Some species of free-living cyanobacteria are capable of nitrogen fixation. We examined the rhizosphere microbiota changes and the potential for plant growth promotion by applying a free-living, nitrogen-fixing cyanobacterium and the biofilm formulation of cyanobacterium with M. ciceri, relative to M. ciceri applied singly, to two each of desi and kabuli varieties of chickpea.

Materials and methods

Denaturing gradient gel electrophoresis (DGGE) profiles of archaeal, bacterial and cyanobacterial communities and those of phospholipid fatty acids (PLFAs) were obtained to evaluate the changes of the microbial communities in the chickpea rhizosphere. Plant growth attributes, including the pod yields and the availabilities of soil macronutrients and micronutrients, were monitored.

Results and discussion

The DGGE profiles showed distinct and characteristic changes due to the microbial inoculation; varietal differences exerted a marked influence on the archaeal and cyanobacterial communities. However, bacterial communities were modulated more by the type of microbial inoculants. Abundance of Gram-negative bacteria (in terms of notional PLFAs) differed between the desi and the kabuli varieties inoculated with M. ciceri alone, and the principal component analysis of PLFA profiles confirmed the characteristic effect of microbial inoculants tested. Microbial inoculation led to increases in the 100-seed weight and differential effects on the concentrations of available nitrogen and phosphorus, and those of iron, zinc and copper, suggesting their increased cycling in the rhizosphere.

Conclusions

Microbial inoculation of chickpea brought out the characteristic changes in rhizosphere microbiota. Consequently, the growth promotion of chickpea and nutrient cycling in its rhizosphere distinctively differed. Further studies are needed to analyse the association and dynamic changes in the microbial communities to define the subset of microorganisms selected by chickpea in its rhizosphere and the influence of microbial inoculation.

     

The foliar spray of <Emphasis Type="Italic">Rhodopseudomonas palustris</Emphasis> grown under <Emphasis Type="Italic">Stevia</Emphasis> residue extract promotes plant growth via changing soil microbial community

Purpose

The extract of Stevia residue is an ideal substitute for cultivation of the purple nonsulfur bacterium, like Rhodopseudomonas palustris (R. palustris). But the influence of R. palustris grown under residue extract on its downstream application is still not well-characterized. The objective of this study was to assess the effect of foliar spray of R. palustris grown under Stevia residue extract on the plant growth and soil microbial properties.

Materials and methods

A pot experiment was carried out under the greenhouse condition, consisting of four treatments varying in the sprayed substances: sterilized water (control), R. palustris grown under the chemical medium supplemented with L-tryptophan (SyT), R. palustris grown under Stevia residue extract supplemented with L-tryptophan (ExT), and R. palustris grown under Stevia residue extract supplemented with NH₄Cl (ExT). The net photosynthesis rate of the uppermost leaves was measured with a portable photosynthesis system. Soil microbial activity was analyzed by microcalorimetry. Soil bacterial community components were determined by real-time quantitative PCR (qPCR) and high-throughput sequencing techniques.

Results and discussion

Compared with SyT, the R. palustris grown under Stevia residue extract not only improved the plant biomass and the net photosynthetic rate to a large extent, but also increased soil microbial metabolic activity and altered community compositions as well. The treatments receiving R. palustris, especially ExT and ExN, increased the relative abundances of some functional guilds involved in C turnover and nutrient cycling in soil, including Acidobacteria, Actinobacteria, Proteobacteria, Gemmatimonadaetes, Nitrospirae, and Planctomycetes.

Conclusions

R. palustris grown under the Stevia residue extract showed advantages over that under the chemical medium on both plant growth and soil microbial properties. One of the possible reasons could result from the increases in microbial activity and several bacterial keystone guilds involved into C and nutrient cycling, both of which potentially contribute to the improved plant growth. The results would be conducive to the downstream application of R. palustris in an economical way.

     

Combined bioremediation of soil co-contaminated with cadmium and endosulfan by <Emphasis Type="Italic">Pleurotus eryngii</Emphasis> and <Emphasis Type="Italic">Coprinus comatus</Emphasis>

Purpose

The subjects of this study were to investigate the remediating potential of the co-cultivation of Pleurotus eryngii and Coprinus comatus on soil that is co-contaminated with heavy metal (cadmium (Cd)) and organic pollutant (endosulfan), and the effects of the co-cultivated mushrooms on soil biochemical indicators, such as laccase enzyme activity and bacterial counts.

Materials and methods

A pot experiment was conducted to investigate the combined bioremediation effects on co-contaminated soil. After the mature fruiting bodies were harvested from each pot, the biomass of mushrooms was recorded. In addition, bacterial counts and laccase enzyme activity in soil were determined. The content of Cd in mushrooms and soil was detected by the flame atomic absorption spectrometry (FAAS), and the variations of Cd fractions in soil were determined following the modified BCR sequential extraction procedure. Besides, the residual endosulfan in soil was detected by gas chromatography-mass spectrometry (GC-MS).

Results and discussion

The results indicated that co-cultivation of P. eryngii and C. comatus exerted the best remediation effect on the co-contaminated soil. The biomass of mushroom in the co-cultivated group (T group) was 1.57–13.20 and 19.75–56.64% higher than the group individually cultivated with P. eryngii (P group) or C. comatus (C group), respectively. The concentrations of Cd in the fruiting bodies of mushrooms were 1.83–3.06, 1.04–2.28, and 0.67–2.60 mg/kg in T, P, and C groups, respectively. Besides, the removal rates of endosulfan in all treatments exceeded 87%. The best bioremediation effect in T group might be caused by the mutual promotion of these two kinds of mushrooms.

Conclusions

The biomass of mushroom, laccase activity, bacterial counts, and Cd content in mushrooms were significantly enhanced, and the dissipation effect of endosulfan was slightly higher in the co-cultivated group than in the individually cultivated groups. In this study, the effect of co-cultivated macro fungi P. eryngii and C. comatus on the remediation of Cd and endosulfan co-contaminated soil was firstly reported, and the results are important for a better understanding of the co-remediation for co-contaminated soil.

     

Trace elements bioavailability to <Emphasis Type="Italic">Triticum aestivum</Emphasis> and <Emphasis Type="Italic">Dendrobaena veneta</Emphasis> in a multielement-contaminated agricultural soil amended with drinking water treatment residues

Purpose

The in situ stabilization of multielement-contaminated agricultural soils has limited effectiveness when using common single amendments. This study examined the use of drinking water treatment residues (WTR), based on (hydr)oxides of Fe, Al, or Mn, as a cost-effective solution to optimize the immobilization of metals (Cd, Pb, Zn) and As.

Materials and methods

Trace elements (TE) bioavailability was assessed under semi-controlled conditions in a pot study cultivating winter wheat (Triticum aestivum L. cv. Tiger) until maturity. An Fe-based WTR and a Mn-based WTR, applied at rates of 0.5 and 1% (m/m), were related to effects of lime marl (LM) application. Additionally, a bioassay with earthworms (Dendrobaena veneta) was conducted. Both bioassays were compared with measurements of NH₄NO₃-soluble, diffusive gradients in thin film (DGT)-available and soil solution TE concentrations, representing well-established surrogates for mimicking the bioavailable element fractions in soil.

Results and discussion

The application of the Fe-based WTR reduced As accumulation in vegetative wheat tissues (by up to 75%) and earthworms (by up to 41%), which corresponded with the findings from soil chemical analyses and improved plant growth and earthworm body weight. However, As concentrations in cereal grains were not affected, Cd or Pb accumulation by wheat was not mitigated, and Zn uptake was enhanced. By contrast, the Mn-based WTR effected the greatest reduction in Pb uptake, and lowered Cd transfer to wheat grain (by up to 25%). Neither the NH₄NO₃-soluble nor DGT-available concentrations matched with Cd and Zn accumulation in plants or earthworms, indicating interferences due to competition for binding sites according to the biotic ligand model.

Conclusions

The results obtained in this study suggest that a bioassay with key species prior to field application should be mandatory when designing in situ stabilization options. The application of WTR to an agricultural soil strongly affected TE bioavailability to plants and earthworms. Low application rates tended to improve biomass production of biota. Higher application rates involved risks (e.g., P fixation, TE inputs), and none of the amendments tested could immobilize all targeted elements.

     

Soil quality assessment under different <Emphasis Type="Italic">Paulownia fortunei</Emphasis> plantations in mid-subtropical China

Purpose

Paulownia, one of the fastest growing broad-leaved tree species in the world, is widely distributed in the warm temperate regions of China. However, there are few commercial-scale Paulownia plantations, and there is only limited information available about the most suitable soil quality for Paulownia fortunei growth in mid-subtropical, Hunan Province, China.

Materials and methods

To understand the effect of the growth of P. fortunei on soil conditions, 25 soil property parameters under Paulownia plantations were studied in Hunan Province, China. Seventy-two standard plots of eight different stand types were analyzed by three statistical approaches to assess soil quality (SQ) in the different P. fortunei plantations.

Results and discussion

The results revealed that a majority of the soil characteristics when intercropping with oilseed rape and the pure P. fortunei (plantation III) were better than intercropping with Camellia oleifera, orange trees, and Cunninghamia lanceolata (Lamb.). Available calcium, available magnesium, available potassium, available phosphorus, soil thickness, slope, soil organic matter, available sulfur, available copper, dehydrogenase, and available zinc were selected as the minimum data set (MDS). The SQ index (SQI) showed that three classes for soil quality among the eight P. fortunei plantations ranged from 0.48 to 0.88 and these were correlated with standing volume (p?<?0.05).

Conclusions

From the results, we concluded that selected MDS indicators can describe the soil fertility quality of P. fortunei plantations, and that the relationship between SQI and standing volume has a biological significance. P. fortunei plantations intercropped with Camellia oleifera, orange trees, and Cunninghamia lanceolata (Lamb.) caused a deterioration in SQ, but intercropping oilseed rape and pure P. fortunei plantations produced an improvement in SQ.

     

Dissipation of fomesafen in biochar-amended soil and its availability to corn (<Emphasis Type="Italic">Zea mays</Emphasis> L.) and earthworm (<Emphasis Type="Italic">Eisenia fetida</Emphasis>)

Purpose

Biochar application has been shown to be effective in improving soil fertility and sequestering soil contaminants. However, the impact of biochar amendments on the environmental fate of pesticides and the bioavailability of pesticides to living organisms in the soil environment is still not fully understood.

Materials and methods

Dissipation of fomesafen and its bioavailability to corn (Zea mays L.) and the earthworm Eisenia fetida in an agricultural soil amended with three different rates of rice hull biochar (0.5, 1, and 2 % (w/w)) under laboratory conditions was investigated.

Results and discussion

Biochar amendment significantly increased the DT₅₀ of fomesafen from 34 days in unamended soil to 160 days in 2 % biochar-amended soil. Furthermore, biochar amendment decreased fomesafen concentration in soil pore water resulting in lower plant uptake of the pesticide. In this case, total plant residue and soil pore water concentrations of fomesafen in 2 % biochar-amended soil decreased to 0.29 % and 0.28–45 % of that in the control, respectively. Similar results were obtained for bioavailability of fomesafen in earthworms, as the earthworm residue and soil pore water concentration of fomesafen in 2 % biochar-amended soil declined to 0.38–45 and 0.47–0.50 % compared to the level of the control, respectively.

Conclusions

As biochar could markedly reduce the concentration of fomesafen in soil pore water and subsequently reduce plant and earthworm uptake of fomesafen from contaminated soil, biochar amendment could be considered an appropriate option for immobilizing fomesafen in soils, protecting nontarget organisms from fomesafen contamination.

     

Effect of <Emphasis Type="Italic">Bacillus subtilis</Emphasis> QST713 and <Emphasis Type="Italic">Trichoderma asperellum</Emphasis> T34 on P uptake by wheat and how it is modulated by soil properties

Purpose

The effect on P uptake by plants after inoculation with P-mobilizing microorganisms may be modulated by soil properties, including natural microbiota. However, to put this theory into practical use, research is needed to shed new light on the soil factors which affect the capability of improving P nutrition in plants. The aim of this study was to assess how two P-mobilizing microorganisms, Trichoderma asperellum T34 and Bacillus subtilis QST713, influence P uptake by wheat plants in different soils; this will allow us to identify the soil properties which affect the efficiency of P nutrition in plants.

Materials and methods

In a completely randomized experiment, wheat was grown in pots in a growing chamber in soils with Olsen P values ranging from 4.8 to 8.7 mg kg^?1. The plants were inoculated with three treatments: T34, B. subtilis, and a non-inoculated control.

Results and discussion

Overall, B. subtilis was more effective in increasing plant P uptake and in mobilizing soil P (measured as Olsen P values) than T34. In some soils, B. subtilis was the only treatment which increased Olsen P in the rhizosphere after cultivation. However, the effect of both microorganisms differed depending on the soil. For B. subtilis, phytase hydrolysable P, Olsen P, carbonates, the Fe_ca/Fe_cbd ratio, and citrate-soluble P accounted for 92% of the variation in P uptake in inoculated plants (compared with the non-inoculated control). Most of these soil properties also accounted for 87% of the variation in the levels of shoot dry matter (DM) in B. subtilis-inoculated plants compared with shoot DM in the control plants. In addition, Olsen P, the Fe_ca/Fe_cbd ratio, and phytase hydrolysable P in the NaOH extracts accounted for 82 and 74% of the variation in the effect of T34 on P uptake and shoot DM, respectively. Overall, the lower the initial Olsen P in the soil, the higher the P uptake caused by microorganisms.

Conclusions

The initial availability of P and organic P in soil, in addition to other properties affecting P dynamics in the soil, may explain the triggering and efficiency of the P-mobilizing mechanisms in microorganisms. These are crucial in explaining the potential benefits to crops and, as a result, their practical use as a bio-fertilizer.

     

Effect of <Emphasis Type="Italic">Eucalyptus</Emphasis> forests on understory vegetation and soil quality

Purpose

Eucalyptus forest plantations are normally devoid of understory vegetation that is often assumed to be associated with Eucalyptus allelopathic effects. The objective of this study was to determine the influence of high soil compaction and low soil moisture content on inhibition of the germination of understory seeds in Eucalyptus forests and thus would result in the scarcity of understory vegetation.

Materials and methods

The soil water content above the depth of 1 m of six major understory vegetation types was analyzed to determine if there was a correlation between soil water content and understory vegetation. The effects of soil treatment (soil-loosening vs. no soil-loosening) and water supply amount (2500, 2000, 1500, 1000, 500, 250, or 0 ml of water per day) on the seed germination rate of Stylosanthes sp. were explored using an artificial climate chamber experiment. Influence of soil source (five Eucalyptus forest soils vs. two non-Eucalyptus forest soils) and water supply (0, 50, 150, 200, or 400 ml of water every day) on the germination rate of five types of seed were assessed using a three-factor analysis of variance (ANOVA).

Results and discussion

Soil-loosening and water supply significantly (P?<?0.05) increased seed germination rate with the contribution rates of 26.14 and 42.93 %, respectively. Analysis of variance for three-factor experiments revealed a significant (P?<?0.05) effect of water supply and vegetation seed type on the germination rate of plant seeds. No significant effect of soil type was observed on germination rate, indicating that germination rate was not affected by soils in Eucalyptus forest.

Conclusions

The conservation of soil characteristics, such as water content and compaction, during the development of a Eucalyptus forest plantation may be an effective strategy for encouraging the growth of understory vegetation. This study highlights the importance that in dry areas or areas prone to long-term drought, it would be preferable to retain native vegetation.

     

Response of <Emphasis Type="Italic">Piptatherum miliaceum</Emphasis> to co-culture with a legume species for the phytostabilisation of trace elements contaminated soils

Purpose

The presence of high concentrations of trace elements (TEs) in mine soils like those in the Sierra Minera of La Unión-Cartagena (SE Spain) limits the development of a vegetation cover on such sites, and pollution dispersion by water and wind erosion represents a serious risk for the surrounding ecosystems. The aim of this study was to evaluate different phytostabilisation procedures based on the co-culture of a legume (Bituminaria bituminosa) and a high-biomass (Piptatherum miliaceum) species for this type of soils.

Materials and methods

A pot experiment was carried out where B. bituminosa was tested as a soil pre-treatment strategy. Five different procedures were followed to study the growth stimulation or competition of both species in a contaminated soil from the Sierra Minera: (i) sowing of P. miliaceum without B. bituminosa (control treatment), (ii) sowing of P. miliaceum for co-cultivation of both species, (iii) sowing of P. miliaceum and co-cultivation of both species in soil with compost, (iv) harvesting and elimination of the aerial part of the plants before sowing of P. miliaceum and (v) harvesting and incorporation to the soil of the aerial part of B. bituminosa before sowing of P. miliaceum.

Results and discussion

The results showed that the co-culture of both species favoured the growth of P. miliaceum, whilst incorporating the aerial part of the legume to the soil increased nitrogen concentration in P. miliaceum but reduced its growth. The use of compost improved both the growth and N uptake of P. miliaceum and did not inhibit nodulation in B. bituminosa. TE extractability in the soils and accumulation in the plants were rather low and very little affected by the addition of the amendments or by co-culture of species.

Conclusions

Nitrogen availability plays an important role in P. miliaceum growth in TE-contaminated mine soils. The addition of compost together with legume cultivation is proposed as an effective combination for the cultivation of P. miliaceum in these soils, as both plant growth and soil conditions were improved following this procedure.

     

A comparative study to evaluate efficiency of EDTA and calcium in alleviating arsenic toxicity to germinating and young <Emphasis Type="Italic">Vicia faba</Emphasis> L. seedlings

Purpose

This study delineated the effect of calcium (Ca) and ethylenediaminetetraacetic acid (EDTA) addition on arsenic (As) accumulation and physiological attributes of Vicia faba L.

Materials and methods

Two separate experiments were performed. In the first experiment, V. faba seedlings, grown under hydroponic conditions, were exposed to three levels of As (25, 125 and 250 μM) in the presence and absence of three levels of EDTA (25, 125, 250 μM) and calcium (CaCl₂: 1, 5 and 10 mM). The effect of EDTA and Ca on As accumulation and physiological attributes of V. faba was assessed by determining As contents in roots and shoot, chlorophyll contents, H₂O₂ contents, and lipid peroxidation in young and old leaves. In the second experiment, V. faba seeds were grown in As-contaminated sand culture using the same treatment plan.

Results and discussion

The accumulation and toxicity of As to V. faba plants increased with increasing As levels in nutrient solution. Arsenic exposure enhanced the production of reactive oxygen species (ROS) in both roots and leaves, which resulted in lipid peroxidation and decreased chlorophyll contents. The presence of both EDTA and Ca, in general, significantly decreased As accumulation by V. faba seedlings, Ca being more effective than EDTA. Both the amendments decreased As-induced reactive oxygen species (ROS) production and lipid peroxidation. In the case of chlorophyll contents, EDTA significantly decreased chlorophyll contents, while Ca significantly increased chlorophyll contents compared to As. The effect of all the treatments was more pronounced in roots than leaves and in young leaves compared to old leaves.

Conclusions

It is proposed that EDTA and Ca greatly affect As accumulation and toxicity to V. faba, and the effect varies greatly with their applied levels as well as type and age of plant organs. The germinating seedlings of V. faba may be preferred for risk assessment studies, while transplanting 1-week-old V. faba seedlings to As-contaminated soils can decrease its toxicity.

     

Physiological and biochemical responses of <Emphasis Type="Italic">Dolichos lablab</Emphasis> L. to cadmium support its potential as a cadmium phytoremediator

Purpose

This study aims to investigate the response of a high biomass producer non-hyperaccumulator legume plant species, Dolichos lablab L., to cadmium (Cd) stress for phytoremediation process.

Materials and methods

Three individual experiments were carried out to assess physiological and biochemical parameters to support the use of this plant species as a phytoremediator. The first experiment was carried out in Cd-contaminated soil while the second and third experiments were conducted in sand in which Cd was applied to study biochemical responses. Analysis of mineral nutrition, phytoremediation parameters, antioxidant response, and protein identification by gel-based proteomics were performed.

Results and discussion

Good tolerance to Cd under moderate level of contamination was observed. Mineral nutrition was little affected, and phytoremediation index was satisfactory. Additionally, biochemical responses based on antioxidant enzyme analysis were well responsive in roots, reflecting the capacity of Cd stress attenuation in this organ. A proteomic analysis revealed positive regulation of root proteins involved in carbohydrate, amino acids, nitrogen metabolism, and abiotic/biotic stress response, which together may contribute to create a scenario to overcome Cd-induced stress.

Conclusions

Based on the physiological and biochemical results, we concluded that D. lablab L. is suitable for phytoremediation/phytostabilization purposes.

     

High Zn concentration does not impair biomass,cutting radial growth,and photosynthetic activity traits in <Emphasis Type="Italic">Populus alba</Emphasis> L.

Purpose

Evaluate the efficiency of Populus alba clone Villafranca in the uptake and translocation of Zn from contaminated soils.

Materials and methods

The effects of 48 days of zinc treatment (Zn _t ) on the growth and the photosynthetic activities of P. alba L. clone Villafranca were studied using ZnSO₄ (375 ppm per unit of soil dry weight) added in sand and peat moss substrate at the beginning of the treatment (T ₀) and again after 30 days (T ₁) in order to reach a target Zn concentration of 375 ppm at T ₀ and 750 ppm at T ₁ per unit of soil dry weight.

Results and discussion

Zn uptake in the different organs was analyzed after 30 (T ₁) and 48 days (T ₂) from the beginning of treatment, showing the following order: root ? leaves ≥ woody cutting = stem. The leaf area increased by 12 % in comparison to control plants at the end of second treatment (48 days). Cutting radial growth showed a high synchronicity in the growth rate fluctuation among control and Zn _t plants, but a higher increase in radial diameter of Zn _t cutting was observed starting from day 38 (after 8 days of second Zn _t ) reaching after 48 days 38 % higher than control plants.

Conclusions

Although our data of leaf Zn concentration were in the range usually reported as toxic for plants, Villafranca clone in Zn _t substrate were unaffected in terms of net CO₂ assimilation and stomatal conductance to water vapor.

     

Eco-restoration of a mine technosol according to biochar particle size and dose application: study of soil physico-chemical properties and phytostabilization capacities of <Emphasis Type="Italic">Salix viminalis</Emphasis>

Purpose

Anthropic activities induce severe metal(loid)s contamination of many sites, which is a threat to the environment and to public health. Indeed metal(loid)s cannot be degraded, and thus accumulate in soils. Furthermore, they can contaminate surrounding ecosystems through run-off or wind erosion. This study aims to evaluate the phytostabilization capacity of Salix viminalis to remediate As and Pb highly contaminated mine site, in a biochar-assisted phytoremediation context and to assess biochar particle size and dose application effects.

Materials and methods

To achieve this, mesocosm experiments were conducted using the contaminated technosol and four different size fraction of one biochar as amendment, at two application rates (2 and 5%). Non-rooted cuttings of Salix viminalis were planted in the different mixtures. In order to characterize the mixtures, soil pore waters were sampled at the beginning and at the end of the experiment and analyzed for pH, electrical conductivity, and metal(loid) concentrations. After 46 days of Salix growth, roots, stems, and leaves were harvested and weighed, and As and Pb concentrations and distributions were measured.

Results and discussion

Soil fertility improved (acidity decrease, electrical conductivity increase) following biochar addition, whatever the particle size, and the Pb concentration in soil pore water decreased. Salix viminalis did not grow on the non-amended contaminated soil while the biochar amendment permitted its growth, with a better growth with the finest biochars. The metal(loid)s accumulated preferentially in roots.

Conclusions

Fine biochar particles allowed S. viminalis growth on the contaminated soil, allowing this species to be used for technosol phytostabilization.

     

Root plasticity,whole plant biomass,and nutrient accumulation of <Emphasis Type="Italic">Neyraudia reynaudiana</Emphasis> in response to heterogeneous phosphorus supply

Purpose

The aims of this study were to examine the adaptive mechanisms of Neyraudia reynaudiana, a pioneer species rapidly colonizing degraded sites, to heterogeneous phosphorus (P) distribution, and how foraging P distributed in patches affects whole-plant biomass and nutrient accumulation.

Materials and methods

Plants were grown in equally divided sand-culture boxes using different concentrations of P applied either heterogeneously (0/5, 0/15, 5/15, 0/30, and 15/30 mg KH₂PO₄ solution/kg dry soil) or homogeneously (2.5/2.5, 7.5/7.5, 10/10, 15/15, and 22.5/22.5 mg kg^?1) to each of the split boxes.

Results and discussion

After 4 months of treatment applications, a significant (p < 0.05) variation in specific root length plasticity was detected between patches of heterogeneous P availability. The largest patch strength difference (0/30 mg/kg) induced the greatest change in specific root length relative to the smallest patch strength difference (0/5 mg/kg). Root P content was not changed by the heterogeneous treatments. Although the whole plant biomass was unaffected by the P distribution pattern, the accumulation of P in the whole plant was slightly higher in the homogeneous treatment than in the heterogeneous treatment.

Conclusions

Plasticity of root morphological appears to be the main adaptation mechanism by which this species forages patchily distributed P. The benefit of this strategy is not reflected in increased whole-plant productivity or nutrient accumulation when P is heterogeneously distributed. The results are fundamental to understanding the mechanisms of foraging nutrient-patches and adapting to poor soil conditions.

     

Geographic distance and amorphous iron affect the abundance and distribution of <Emphasis Type="Italic">Geobacteraceae</Emphasis> in paddy soils in China

Purpose

Geobacteraceae are important dissimilatory Fe (III)-reducing microorganisms, influencing the cycling of metals, nutrients as well as the degradation of organic contaminants. However, little is known about their distribution, diversity, and abundance of Geobacteraceae and the effects of environment factors and geographic distance on the distribution and diversity of Geobacteraceae in paddy soils remain unclear. Therefore, the objectives of this study were to investigate the distribution, diversity, and abundance of Geobacteraceae in paddy soils and to determine key factors in shaping the Geobacteraceae distribution, environmental factors, geographic distance, or both and to quantify their contribution to Geobacteraceae variation.

Materials and methods

Illumina sequencing and quantitative real-time PCR using a primer set targeting 16S rRNA genes of bacteria affiliated with the family Geobacteraceae were employed to measure the community composition, diversity, and abundance patterns of 16S rRNA genes of Geobacteraceae in 16 samples collected from north to south of China. MRT, Mantel test, and VPA were used to analyze the relationship between communities of Geobacteraceae and environmental factors and geographic distance.

Results and discussion

Quantitative PCR showed that the abundance of 16S rRNA genes of Geobacteraceae ranged from (1.20?±?0.18)?×?10⁸ to 1.13?×?10⁹?±?2.25?×?10⁸ copies per gram of soil (dry weight) across different types of soils. Illumina sequencing results showed Geobacter was the dominant genus within the family of Geobacteraceae. Multivariate regression tree (MRT) analysis showed that soil amorphous iron contributed more (22.46 %) to the variation of dominant species of Geobacteraceae than other examined soil chemical factors such as pH (14.52 %), ammonium (5.12 %), and dissolved organic carbon (4.74 %). Additionally, more geographically distant sites harbored less similar communities. Variance partitioning analysis (VPA) showed that geographic distance contributed more to the variation of Geobacteraceae than any other factor, although the environmental factors explained more variation when combined. So, we detected the uneven distribution of Geobacteraceae in paddy soils of China and demonstrated that Geobacteraceae community composition was strongly associated with geographic distance and soil chemical factors including aFe, pH, Fe, DOC, C:N, and NO₃ ^?-N. These results greatly expand the knowledge of the distribution of Geobacteraceae in environments, particularly in terrestrial ecosystems.

Conclusions

Our results showed that geographic distance and amorphous iron played important roles in shaping Geobacteraceae community composition and revealed that both geographic distance and soil properties governed Geobacteraceae biogeography in paddy soils. Our findings will be critical in facilitating the prediction of element cycling by incorporating information on functional microbial communities into current biogeochemical models.

     

Enhanced <Emphasis Type="Italic">Scirpus triqueter</Emphasis> phytoremediation of pyrene and lead co-contaminated soil with alkyl polyglucoside and nitrilotriacetic acid combined application

Purpose

This study aimed to evaluate the effect of combination of alkyl polyglucoside (APG) and nitrilotriacetic acid (NTA) on improving the efficiency of phytoremediation for pyrene and lead (Pb) co-contaminated soil by Scirpus triqueter.

Materials and methods

Seedlings of S. triqueter with a similar size and biomass (3 g/pot) were grown on 2-month aged soil contaminated with 184.5 mg kg^?1of pyrene and 454.3 mg kg^?1 of Pb at pH?=?8.3. After growth for 10 days, different doses of APG and NTA were added into the soil. After 60 days, the height of plants, Pb concentrations in plants, and pyrene amounts in soil were determined.

Results and discussion

Combined application of NTA and APG with lower dosage (1 + 1 g kg^?1 soil and 1 + 2 g kg^?1 soil) had no notable negative influence on the growth of S. triqueter. Moreover, significant synergy on Pb accumulation in S. triqueter was achieved with APG and NTA combined application. Besides, the dissipation of pyrene from soil after 60-day planting was increased in APG and NTA treatments when compared with the control treatments. Application of APG alone or combined with NTA had greater effect on enhancing dissipation of pyrene from soil than NTA alone.

Conclusions

This study demonstrated that the remediation of Pb and pyrene co-contaminated soil by S. triqueter can be enhanced by combined application of APG and NTA. Long-term evaluation of this strategy is needed in co-contaminated field sites.

     

Rhizosphere effects of <Emphasis Type="Italic">Populus euramericana</Emphasis> Dorskamp on the mobility of Zn,Pb and Cd in contaminated technosols

Purpose

This study aimed at investigating the rhizosphere effects of Populus euramericana Dorskamp on the mobility of Zn, Pb and Cd in contaminated technosols from a former smelting site.

Materials and methods

A rhizobox experiment was conducted with poplars, where the plant stem cuttings were grown in contaminated technosols for 2 months under glasshouse conditions. After plant growth, rhizosphere and bulk soil pore water (SPW) were sampled together. SPW properties such as pH, dissolved organic carbon (DOC) and total dissolved concentrations of Zn, Pb and Cd were determined. The concentrations of Zn, Pb and Cd in plant organs were also determined.

Results and discussion

Rhizosphere SPW pH increased for all studied soils by 0.3 to 0.6 units compared to bulk soils. A significant increase was also observed for DOC concentrations regardless of the soil type or total metal concentrations, which might be attributed to the plant root activity. For all studied soils, the rhizosphere SPW metal concentrations decreased significantly after plant growth compared to bulk soils which might be attributed to the increase in pH and effects of root exudates. Zn, Pb and Cd accumulated in plant organs and the higher metal concentrations were found in plant roots compared to plant shoots.

Conclusions

The restricted transfer of the studied metals to the plant shoots confirms the potential role of this species in the immobilization of these metals. Thus, P. euramericana Dorskamp can be used for phytostabilization of technosols.

     

Biotite weathering by <Emphasis Type="Italic">Aspergillus niger</Emphasis> and its potential utilisation

Purpose

Biotite, as a type of associated mineral, is normally applied as a filling material for buildings, or is discarded as tailings. However, as a potassium-bearing phyllosilicate mineral, biotite can be easily weathered by fungi, which leads to its internal potassium being released for agricultural production (1), and the mineral residues being weathered by the fungus may be applied for adsorption of heavy metal ions (2).

Materials and methods

This work investigates the weathering of biotite by Aspergillus niger through the analysis of the differences in ion dissolution from biotite, producing of organic acids, the change of mineral morphology and composition by inductively coupled plasma optical emission spectrometry (ICP-OES), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), and X-ray diffraction (XRD). Besides, the mineral residues were applied for adsorption of heavy metal ions.

Results and discussion

Results showed that the mycelia envelope the mineral and form fungal–mineral aggregates. The fungus can secrete a variety of organic acids including citric acid and oxalic acid; these attacked the surface and cleavage of biotite to release ions (Al³⁺, Fe³⁺, Mg²⁺, and K⁺). During incubation with A. niger, biotite weathered as shown by the relative decrease in biotite content and increase in interlayer spacing. Moreover, a certain concentration of phytic acid and tween-80 could promote the release of K⁺, and the fermentation liquid of rice bran has the same effect. Biotite residues showed a good adsorption for Cd²⁺, Pb²⁺, Zn²⁺, and Cu²⁺.

Conclusions

The results indicate that biotite can be biotransformed and release K⁺, of which the production can be acted as heavy metal ion adsorbent. It provides a reference for application of biotite in agriculture and control of heavy metal ion pollution in soil.

     

Changes in methane emission and methanogenic and methanotrophic communities in restored wetland with introduction of <Emphasis Type="Italic">Alnus trabeculosa</Emphasis>

Purpose

The dynamics and uncertainties in wetland methane budgets affected by the introduction of Alnus trabeculosa H. necessitate research on production of methane by methanogenic archaea and consumption by methane-oxidizing microorganisms simultaneously.

Materials and methods

This study investigated methane emission in situ by the closed chamber method, and methanogenic and methanotrophic communities using denatured gradient gel electrophoresis (DGGE) and quantitative PCR based on mcrA (methyl coenzyme M reductase), pmoA (particulate methane monooxygenase) genes in the rhizosphere and non-rhizosphere soils in the indigenous pure Phragmites australis T., and A. trabeculosa–P. australis mixed communities in Chongxi wetland.

Results and discussion

Methane flux rate from the pure P. australis community was 2.4 times larger than that of A. trabeculosa–P. australis mixed community in the rhizosphere and 1.7 times larger in the non-rhizosphere, respectively. The abundance of methanogens was lower in the mixed community soils (3.56?×?10³–6.90?×?10³ copies g^?1 dry soil) compared with the P. australis community (1.47?×?10⁴–1.89?×?10⁴ copies g^?1 dry soil), whereas the methanotrophs showed an opposite trend (2.08?×?10⁶–1.39?×?10⁶ copies g^?1 dry soil for P. australis and 6.20?×?10⁶–1.99?×?10⁶ copies g^?1 dry soil for mixed community soil). A liner relationship between methane emission rates against pmoA/mcrA ratios (R ²?=?0.5818, p?<?0.05, n?=?15) was observed. The community structures of the methane-cycling microorganism based on mcrA and pmoA suggested that acetoclastic methanogens belonging to Methanosarcinaceae and a particular type II methanotroph, Methylocystis, were dominant in these two plant communities.

Conclusions

The introduction of A. trabeculosa would promote the proliferation of methanotrophs, especially the dominant Methylocystis, but not methanogens, ultimately diminishing methane emission in the wetland.

     

Comparison of ammonium fertilizers,EDTA, and NTA on enhancing the uptake of cadmium by an energy plant,Napier grass (<Emphasis Type="Italic">Pennisetum purpureum</Emphasis> Schumach)

Purpose

The aim of this study was to quantify the effect of enhanced agronomic practices on cadmium (Cd) accumulation in the high-biomass energy plant Napier grass (Pennisetum purpureum Schumach).

Materials and methods

Potted-plant experiments were performed to investigate the effects of ammonium fertilizers and chelating agents, alone or in combination, on the growth, accumulation of Cd, and phytoextraction efficiency of P. purpureum on Cd-contaminated soil. The fertilizers included ammonium nitrate, ammonium sulfate, and ammonium chloride. The chelating agents included ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA).

Results and discussion

The addition of ammonium fertilizers and chelating agents generally stimulated growth of P. purpureum, and the shoots accounted for 90.1–94.1% of the total biomass. The concentrations of Cd in different parts of P. purpureum plants were in the order root > leaf > stem. Ammonium chloride alone showed effectiveness in increasing root and shoot Cd concentrations compared to other amendments alone. Both EDTA alone and NTA alone significantly decreased root Cd concentration and increased shoot Cd concentration, while EDTA alone was more efficient on shoot and total Cd accumulation than that by NTA alone. The total accumulation of Cd in P. purpureum ranged from 1.10 to 2.05 mg per plant with 47.3–73.5% of Cd accumulation concentrated in shoots. The results indicate that P. purpureum can remove more Cd through phytoextraction than that by other hyperaccumulators.

Conclusions

Ammonium chloride led to the highest total Cd accumulation. Ammonium chloride applied alone or in combination with either EDTA or NTA resulted in the most effective agronomic approaches for P. purpureum phytoextraction of soil Cd.