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.

Purpose

The aim of this work was to assess the concentrations of potentially toxic elements and to evaluate the soil quality of a typical Prosecco Denomination of Controlled and Guaranteed Origin vineyard of the Veneto region, NE Italy.

Materials and methods

Soil samples and leaves of Taraxacum officinale and Vitis vinifera were collected during spring–summer 2014. Element determination (Al, Cd, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, V, and Zn) were performed with ICP-OES after microwave digestion of samples. Soil quality was assessed via the biological soil quality (BSQ-ar) index. Lipid peroxidation test was performed to evaluate the vegetation oxidative stress, based on malondialdehyde (MDA) content via spectrophotometer.

Results and discussion

High concentrations of Al, Mg, and P were identified in soil, while high contents of Al, Cu, Fe, and Zn were found in V. vinifera leaves. The high concentrations in soil are probably due to agricultural activities, whereas those in leaves are probably due to atmospheric deposition and repeated use of foliar sprays in viticulture. The bioconcentration factor showed an effective transport of Cu, P, and Zn, from soil to leaf. The BSQ-ar values registered were similar to those obtained in preserved soils; hence, the biological class (VI) of these soils is high. The MDA content in T. officinale and V. vinifera leaves was below the reference value for T. officinale (2.9?±?0.2 μM), suggesting that the metal content did not stress the vegetation in the investigated site.

Conclusions

The MDA value for V. vinifera (1.1?±?0.7 μM) could be adopted as another control value for soil quality, which in our case is of “good quality.” Moreover, our results suggest that high concentrations of elements detected in the analyzed samples do not influence negatively the quality of soil, but a better agronomic management could improve soil quality in the studied area.

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.

Purpose

This study aimed at evaluating the acute effects of arsenic and zinc to the warmwater aquatic oligochaete Branchiura sowerbyi. Relative sensitivity with the coldwater species Tubifex tubifex was compared. Implications for the use of B. sowerbyi in the risk assessment of sediments in the tropics are discussed.

Materials and methods

Water-only (96 h) and sediment (14 days) toxicity tests were conducted with both species evaluating a concentration series of arsenic and zinc. The tests were conducted considering the environmental conditions in the natural habitat of T. tubifex (predominantly temperate) and B. sowerbyi (predominantly tropical). Both lethal and sublethal endpoints (autotomy of the posterior body parts, abnormal behavior and appearance) were determined in the tests. The lethal (LC₁₀ and LC₅₀) and effect (EC₁₀ and EC₅₀) concentrations were also determined to assess metal sensitivity for both species.

Results and discussion

Both test species were more sensitive to Zn than As in water-only tests, which is in agreement with previous studies evaluating the toxicity of these metals to aquatic oligochaetes. Sublethal effects were generally noted at concentrations lower than those leading to mortality. The warmwater oligochaete B. sowerbyi was more sensitive to both metals tested than the coldwater species T. tubifex.

Conclusions

Study findings support the need for using indigenous tropical species in risk assessments in the tropics. In addition, sublethal effect parameters should be included in toxicity testing with aquatic oligochaetes.

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.

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.

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.

Purpose

Fruiting vegetables are generally considered to be safer than other vegetables for planting on cadmium (Cd)-contaminated farms. However, the risk of transferring Cd that has accumulated in the stems and leaves of fruiting vegetables is a major issue encountered with the usage of such non-edible parts. The objective of this study was to resolve the contribution of arbuscular mycorrhizal (AM) fungi to the production of low-Cd fruiting vegetables (focusing on the non-edible parts) on Cd-contaminated fields.

Materials and methods

An 8-week pot experiment was conducted to investigate the acquisition and translocation of Cd by cucumber (Cucumis sativus L.) plants on an unsterilized Cd-contaminated (1.6 mg kg^?1) soil in response to inoculation with the AM fungus, Funneliformis caledonium (Fc) or Glomus versiforme (Gv). Mycorrhizal colonization rates of cucumber roots were assessed. Dry biomass and Cd and phosphorus (P) concentrations in the cucumber shoots and roots were all measured. Soil pH, EC, total Cd, phytoavailable (DTPA-extractable) Cd, available P, and acid phosphatase activity were also tested.

Results and discussion

Both Fc and Gv significantly increased (P?<?0.05) root mycorrhizal colonization rates and P acquisition efficiencies, and thus the total P acquisition and biomass of cucumber plants, whereas only Fc significantly increased (P?<?0.05) soil acid phosphatase activity and the available P concentration. Both Fc and Gv significantly increased (P?<?0.05) root to shoot P translocation factors, inducing significantly higher (P?<?0.05) shoot P concentrations and shoot/root biomass ratios. In contrast, both Fc and Gv significantly decreased (P?<?0.05) root and shoot Cd concentrations, resulting in significantly increased (P?<?0.05) P/Cd concentration ratios, whereas only Gv significantly decreased (P?<?0.05) the root Cd acquisition efficiency and increased (P?<?0.05) the root to shoot Cd translocation factor. Additionally, AM fungi also tended to decrease soil total and phytoavailable Cd concentrations by elevating plant total Cd acquisition and soil pH, respectively.

Conclusions

Inoculation with AM fungi increased the P acquisition and biomass of cucumber plants, but decreased plant Cd concentrations by reducing the root Cd acquisition efficiency, and resulted in a tendency toward decreases in soil phytoavailable and total Cd concentrations via increases in soil pH and total Cd acquisition by cucumber plants, respectively. These results demonstrate the potential application of AM fungi for the production of fruiting vegetables with non-edible parts that contain low Cd levels on Cd-contaminated soils.

Purpose

The present paper concerns the distribution and mobility of heavy metals (Cu, Pb, Zn and Fe) in the soils of some abandoned mine sites in Italy and their transfer to wild flora.

Materials and methods

Soils and plants were sampled from mixed sulphide mine dumps in different parts of Italy, and the concentrations of heavy metals were determined.

Results and discussion

The phytoremediation ability of Salix species (Salix eleagnos, Salix purpurea and Salix caprea), Taraxacum officinale and P?lantago major for heavy metals and, in particular, zinc was estimated. The results showed that soils affected by mining activities presented total Zn, Cu, Pb and Fe concentrations above the internationally recommended permissible limits. A highly significant correlation occurred between metal concentrations in soils.

Conclusions

The obtained results confirmed the environmental effects of mine waste; exploring wild flora ability to absorb metals, besides metal exploitation, proved a useful tool for planning possible remediation projects.

Purpose

This work investigated changes in priming effects and the taxonomy of soil microbial communities after being amended with plant feedstock and its corresponding biochar.

Materials and methods

A soil incubation was conducted for 180 days to monitor the mineralization and evolution of soil-primed C after addition of maize and its biochar pyrolysed at 450 °C. Responses of individual microbial taxa were identified and compared using the next-generation sequencing method.

Results and discussion

Cumulative CO₂ showed similar trends but different magnitudes in soil supplied with feedstock and its biochar. Feedstock addition resulted in a positive priming effect of 1999 mg C kg^?1 soil (+253.7 %) while biochar gave negative primed C of ?872.1 mg C kg^?1 soil (?254.3 %). Linear relationships between mineralized material and mineralized soil C were detected. Most priming occurred in the first 15 days, indicating co-metabolism. Differences in priming may be explained by differences in properties of plant material, especially the water-extractable organic C. Predominant phyla were affiliated to Acidobacteria, Actinobacteria, Chloroflexi, Gemmatimonadetes, Firmicutes, Planctomycetes, Proteobacteria, Verrucomicrobia, Ascomycota, Basidiomycota, Blastocladiomycota, Chytridiomycota, Zygomycota, Euryarchaeota, and Thaumarchaeota during decomposition. Cluster analysis resulted in separate phylogenetic grouping of feedstock and biochar. Bacteria (Acidobacteria, Firmicutes, Gemmatimonadetes, Planctomycetes), fungi (Ascomycota), and archaea (Euryarchaeota) were closely correlated to primed soil C (R ²?=??0.98, ?0.99, 0.84, 0.81, 0.91, and 0.91, respectively).

Conclusions

Quality of plant materials (especially labile C) shifted microbial community (specific microbial taxa) responses, resulting in a distinctive priming intensity, giving a better understanding of the functional role of soil microbial community as an important driver of priming effect.

Purpose

This study investigated the extent of metal accumulation by plants colonizing a mining area in Yazd Province in Central Iran. It also investigated the suitability of these plants for phytoextraction and phytostabilization as two potential phytoremediation strategies.

Materials and methods

Plants with a high bioconcentration factor (BCF) and low translocation factor (TF) have the potential for phytostabilization, whereas plants with both BCFs and TFs >1 may be appropriate for phytoextraction. In this study, both shoots and roots of 40 plant species and associated soil samples were collected and analyzed for total concentrations of trace elements (Pb, Zn, and Ag). BCFs and TFs were calculated for each element.

Results and discussion

Nonnea persica, Achillea wilhelmsii, Erodium cicutarium, and Mentha longifolia were found to be the most suitable species for phytostabilization of Pb and Zn. Colchicum schimperi, Londesia eriantha, Lallemantia royleana, Bromus tectorum, Hordeum glaucum, and Thuspeinantha persica are the most promising species for element phytoextraction in sites slightly enriched by Ag. Ferula assa-foetida is the most suitable species for phytostabilization of the three studied metals. C. schimperi, L. eriantha, L. royleana, B. tectorum, M. longifolia, and T. persica accumulated Ag, albeit at low level.

Conclusions

Our preliminary study shows that some native plant species growing on this contaminated site may have potential for phytoremediation.

Purpose

We determined the relationship of a planktonic algal bloom with spatial and temporal changes in sediment bacterial communities in a eutrophic urban river in the Taihu Basin, China.

Materials and methods

Surface sediments from different locations on the river, including with and without an algal bloom, were collected monthly for 1 year. Sediment bacterial communities were assessed by sequencing 16S rRNA gene amplicons using an Illumina MiSeq.

Results and discussion

There were distinct spatial and temporal changes in sediment bacterial community structure. Significant decrease in the Shannon diversity corresponded with the peak chlorophyll a (Chl a) concentration. Proteobacteria, Chloroflexi, and Bacteroidetes were the dominant phyla throughout the year; however, their relative abundances changed seasonally. At the time of peak Chl a concentrations, Proteobacteria and Bacteroidetes comprised a greater proportion of the bacterial community. Bacterial community structure also varied spatially at the operational taxonomic unit (OTU) level according to canonical correspondence analysis (CCA), especially in locations with an algal bloom compared with those without an algal bloom. There were positive correlations between multiple bacterial genera and Chl a content, suggesting the potential for facilitative relationships between phytoplankton and bacteria. Based on the CCA, water temperature, NH₄ ⁺-N, TN, NO₃ ^?-N, and TP in the sediment and Chl a contents in the water column were significantly correlated with sediment bacterial community structure (P < 0.05).

Conclusions

Planktonic algal blooms may influence sediment bacterial community structure at all taxonomic levels in urban rivers. This work emphasizes the need for more comprehensive studies regarding the impact of planktonic algal blooms on sediment bacterial communities.

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.

Purpose

The scope of this article was to investigate the spatial and temporal variability of enantiomeric fractions (EFs) of persistent organic pollutants (POPs) in soil compared to the uncertainty of the analytical data.

Materials and methods

Soil samples were taken with high spatial resolution at two sites in Czech Republic in 2008 to investigate variability on a small spatial scale. In addition, composite soil samples were taken from ten sites in 2005 and 2008 to investigate temporal variations. All samples were analysed for a suite of soil properties as well as concentrations and EFs of polychlorinated biphenyl (PCB) -95, PCB-132 and PCB-149; α-hexachlorocyclohexane (HCH); o,p′-dichlorodiphenyltrichloroethane (DDT); and o,p′-dichlorodiphenyldichloroethane (DDD).

Results and discussion

Median EFs of PCB-95 and PCB-149, α-HCH, o,p′-DDT and o,p′-DDD did not change significantly on the sites sampled in 2005 and again in 2008, while PCB-132 changed from EF?=?0.38 to EF?=?0.53. The sampling methodology is therefore very important, and composite samples will not be the best option if enantioselective degradation processes are investigated. Non-racemic EFs of POPs in the subsampled sites in 2008 were correlated to soil parameters, such as total organic carbon (TOC), total nitrogen and humic acids. These parameters are site specific and might vary on a small scale. This can explain why certain soil parameters are reported as significantly correlated with non-racemic EFs of chiral POPs in some studies, but not always in other similar studies.

Conclusions

While composite samples may still represent the overall prevailing EF range, they are not ideally suited to study enantiomeric degradation processes, which are taking place at a relative small scale, depending on the heterogeneity of soil parameters such as TOC, total organic nitrogen (TON) and humic acids.

Purpose

The use of municipal solid wastes (MSWs) as a low-cost source of organic matter for soils should be considered after discarding the environmental risks related to their metal(loid) load. The goal of this work was to assess the employment of a MSW as an organic amendment in two types of soil (an agricultural soil, A, and a metal(loid)-enriched mine tailings soil, T) attending to changes in soil properties and in plant growth, nutrition and metal(loid) translocation from roots to aerial parts of Zea mays L. (stalk, leaves, tassel, husk, cob and kernel).

Materials and methods

After a comprehensive characterisation of each soil treatment (A, A + MSW, T, T + MSW), a pot-designed experiment was carried out. Soil solution was monthly monitored throughout the experiment, and metal(loid) concentrations were measured.

Results and discussion

The MSW improved some fertility-related parameters in both soils, A and T: increased total and dissolved organic carbon, total nitrogen and soil microbiology. However, an increase in 0.01 M CaCl₂-extractable metal(loid) concentration was also observed. No differences in dry biomass were found between amended and not amended treatments. A fractionation of metal(loid) concentrations among plant organs occurred. For instance, the highest Cu and Pb concentrations were found in roots, while for Zn occurred in the stalk and the cob. The amended treatments favoured the accumulation of Mn in all plant organs. Kernels showed in general the lowest metal(loid) concentrations.

Conclusions

The addition of municipal solid wastes as organic amendment could be a suitable tool to increase soil fertility. However, due to the high metal(loid) content of this particular MSW, its use on agricultural soils would not be appropriate. By other hand, along with the improvement of soil fertility, the MSW was useful to promote plant development in the mine tailings soil which should be then considered as a potential tool to promote plant establishment in those metal(loid)-impacted soils.

Purpose

As a useful comprehensive index for reflecting nutrient cycling in soils, nitrogen (N) and phosphorus (P) stoichiometry is subject to influences of many external environmental and biological factors. Studies on such influences were limited, and the influential mechanism remains unclear. The purpose of this research is to investigate soil N and P stoichiometric variations and analyze “fertile island” effects of Tamarix chinensis Lour. (T. chinensis) in the coastal wetland of Laizhou Bay in China.

Materials and methods

Soil samples beneath clusters and communities of T. chinensis were collected respectively in July 2012. Amounts of ammonium, nitrate, and available phosphorus in the soil samples were measured through the corresponding standard methods for material measuring.

Results and discussion

In general, there were significant vertical variations in soil N and P stoichiometry beneath clusters and communities of T. chinensis. A downtrend was observed for N and P contents with the increase in soil depth. On the contrary, the N/P ratio revealed a trend of going up first and then dropping off along with the increase of the soil depth. Comparatively, the horizontal variations in the soil N and P stoichiometry beneath a single cluster of T. chinensis were greater in the topsoil than those in the subsoil. The N and P contents gradually decreased from the canopy center to the outside. On the contrary, an opposite trend was found for the N/P ratio. For the horizontal variations beneath T. chinensis communities, there were no significant differences for either N and P contents or N/P ratios.

Conclusions

Similar to the ecosystems in arid and semi-arid areas, vegetations in many semi-humid areas could also form fertile islands and exert significant influences on the soil nutrient cycle. The formation of fertile islands beneath a single cluster of T. chinensis could have significant influence on soil N and P stoichiometry. Under the influence of fertile islands beneath T. chinensis, the limiting element of the biogeochemical processes in the coastal wetland of Laizhou Bay might change from N to P. However, the influences of fertile island effects on soil N and P stoichiometry beneath T. chinensis communities were relatively small, illustrating that the influences of fertile island effects was not significant at the community level. Thus, the impacts of environmental factors on soil N and P stoichiometry might be greater than that of the fertile island effects in the wetland on a larger scale.

Purpose

Understanding how archaeal communities are affected by water-table drawdown is essential for predicting soil functional responses to future climate change and the consequences of the responses on the soil carbon cycle.

Material and methods

We investigated the effect of water-table drawdown, warming, drought, and combinations thereof on archaeal communities using terminal restriction fragment length polymorphism (T-RFLP) and quantitative PCR.

Results and discussion

Methanosarcinales, Methanosaeta, Methanomicrobiales, Methanobacteriales, uncultured Rice Cluster II (RC-II), and uncultured Crenarchaeota were detected. Water-table drawdown and drought exhibited significant effects on the archaeal communities. When the water table was at or above 10 cm, the archaeal abundance at 10 cm remained high (approximately 10⁹ cells per gram dry soil), whereas the archaeal abundance at 10 cm was reduced to approximately 10⁸ cells per gram dry soil where the water table was lowered to 20 cm or below. When the water table kept constant, warming caused a significant reduction in the archaeal abundance, whereas drought only caused a decrease in archaeal abundance when the water table was higher than ?20 cm.

Conclusions

Results suggest that changes in water table may directly impact archaeal community abundance and assemblage which can in turn influence methane emissions, potentially on a large scale. Our results also indicate that archaeal communities response to water-table drawdowns that are dependent on the initial ecohydrology.

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.

Purpose

This paper aims to study the ecological effects of rice-duck integrated farming on soil fertility and weed and pest control.

Materials and methods

A field experiment was carried out in the suburb of Shanghai in 2014, which included a rice-duck integrated treatment and non-duck treatment (CK) under organic management. Each treatment was in triplicate, and the experiment included six plots in total, with each plot 667 m² in area.

Results and discussion

(1) The number of weeds in the plots with the duck treatment was significantly lower than that with CK (p?<?0.01). (2) The incidence of stem borers (Chilo suppressalis) with the duck treatment was significantly lower than that with CK (p?<?0.05). The incidences of rice leaf rollers (Cnaphalocrocis medinalis), rice sheath blight (Rhizoctonia solani), and planthoppers with the duck treatment were extremely significantly lower than those with CK (p?<?0.01). (3) The contents of NH₄ ⁺-N, alkali-hydrolyzable N, available P, and available K in the soils with the duck treatment were higher than those with CK, and the activities of urease, phosphatase, sucrase, and catalase in the soils with the duck treatment were also much higher than those with CK. The grain yield with the duck treatment was 1.9 times that with CK. (4) The number of soil nematodes with the duck treatment was significantly higher than that with CK in the late rice growing stage (p?<?0.01).

Conclusions

Raising ducks in the paddy fields not only showed a potential of controlling weed hazards and reducing rice pests and diseases but also raised soil fertility, improved soil biodiversity, and increased grain yield effectively. Implementing the rice-duck integrated farming could highly reduce the amount of pesticides and herbicides and was beneficial to develop the organic rice farming in the suburbs of Shanghai, Southeast China.