Metals In Rhizosphere Research Articles

Speciation Distribution and Influencing Factors of Heavy Metals in Rhizosphere Soil of Miscanthus Floridulus in the Tailing Reservoir Area of Dabaoshan Iron Polymetallic Mine in Northern Guangdong

Through field investigation and experimental analysis, the forms, contents and distribution of heavy metals (Zn, Pb, Cu, Cd, Ni, Cr) in rhizosphere and non-rhizosphere soils of Miscanthus floridulus growing everywhere in Tielongwei mine pond (sample plot 1), Caoduikeng tailings pond (sample plot 2), Donghua tailings pond (sample plot 3) and Small tailings pond (sample plot 4) in Dabaoshan, Guangdong Province were studied. The results showed that the main forms and distributions of heavy metals in rhizosphere and non-rhizosphere soils are basically the same, which shows that the mineral content accounts for most of the total amount of heavy metals, while the exchange content is low. Compared with non-rhizosphere soil, the proportion of exchangeable and organic heavy metals in rhizosphere soil increased significantly, in which the proportion of organic-bound Cu increased by 53.25%, the proportion of organic-bound Cd and Pb increased by more than 17%, and the proportion of Zn increased by 5.67%. At the same time, the contents of carbonate-bound and iron manganese oxide-bound decreased. Statistical analyses showed that the morphological distribution of Zn, Pb, Cu, Cd, Ni and Cr in rhizosphere soil was closely related to soil pH value, organic matter content, plant growth and other factors. The results of this study provided a basis for the restoration of heavy metal-contaminated sites by Miscanthus.

Relative distribution of rare-earth metals alongside alkaline earth and alkali metals in rhizosphere of agricultural soils in humid tropical environment.

The study of trace and major elements in the biosphere has traditionally focused on the transition and basic metals; the rare earth (REMs), alkaline earth (AEMs) and alkali metals (AMs) that equally constitute environmental contaminants are rarely considered especially in the tropics. The levels and spatial variation of some REMs, AEMs and AMs in the 0-50-cm layer of agricultural soils of Ikwo in southeastern Nigeria typing a humid tropical environment were studied. Soil sampling was undertaken at five zones namely north, south, east, west and centre (covering over 60% of the land area) in the 2017 dry season. Four soil samples were collected from each of the four cardinal points (with evidence of mining and agricultural activities), and two from the centre (serving as reference zone), totalling 18. Metal concentrations were determined using inductively coupled plasma atomic emission spectroscopy. The metals were grouped into REMs (Ce, La, Sm), AEMs (Ba, Ca, Mg, Sr) and AMs (Cs, K, Na, Rb). All metals increased in concentration from the north, or the south (for Ce and Sm only), towards the centre. Overall, they were reasonably similar in distribution pattern among the five zones. Cationic ratios did not vary markedly, reflecting the greater role of pedogenesis than anthropogenic activities in the area. Nevertheless, their variations showed more K, Ca, Sr and La enrichments over the other metals. Enrichment factor and pollution index of the REMs showed healthy levels of these elements in the soils. The data from this preliminary study may add to the data pool on levels and occurrence of REMs, AEMs and AMs in largely disturbed ecosystems of the humid tropics.

Water managements limit heavy metal accumulation in rice: Dual effects of iron-plaque formation and microbial communities

Understanding the mechanisms on how water management can minimize the concentrations of heavy metals in rice grains is important. Two water managements were concerned in our studies, including continuously flooding and alternate wetting and drying (AWD). Compared to AWD, a continuously flooded culture reduces the concentration of cadmium and other metals in the rice grains by reducing the root-to-shoot translocation and the availability of metals in rhizosphere. In a flooded environment, the rice rhizosphere was characterized by an increased soil pH, reduced fluorescein diacetate (FDA) activity, and lower metal bioavailability. In addition, flooding significantly decreased the iron plaque on the root surface and reduced the affinity for metals in rhizosphere. Water managements significantly changed soil microbial diversity, especially the proportion of anaerobic bacteria, including the iron-reducing bacteria Latescibacteria, Desulfuromonadales, and Geobacteraceae. Interestingly, these bacteria exhibited a significant correlation with cadmium that was adsorbed on the root. This study revealed that continuously flooded culture is a valuable strategy for minimizing heavy metal accumulation in rice grains. By increasing the abundance of unique bacterial community, iron plaque formation and the affinity of metals in rhizosphere were reduced, and the uptake and accumulation of heavy metals in rice plants was finally mitigated.

Effects of Pseudomonas fluorescens Seed Bioinoculation on Heavy Metal Accumulation for Mirabilis jalapa Phytoextraction in Smelter-Contaminated Soil

Some Pseudomonas fluorescens strains, consistently isolated from the rhizosphere of wild plants grown in a soil that was highly polluted with illegal waste of smelter residues, were utilised for Mirabilis jalapa seed bioinoculation to verify their effects on seed germination and on promoting a higher heavy metal accumulation in the plant rhizosphere and/or uptake in the leaves. The high content of heavy metals in the soil induced a decrease in either the leaf dry weight or photosynthetic pigment concentration during all vegetative phase of M. jalapa. Bioinoculation with P. fluorescens strains significantly increased the germination of seeds and the root length in the contaminated soil. In some bacterial strain/seed combination, bioinoculation significantly increased the accumulation of heavy metals in M. jalapa rhizosphere. For Cd, the concentration of this metal in the rhizospheres of bioinoculated plants ranged from 270 to 910 μg g−1 of dry weight compared with 200 μg g−1 of dry weight for the non-coated plants. Two P. fluorescens strains, AA27 and MO49, which were isolated from Artemisia annua and Melilotus officinalis, respectively, induced a significantly higher rhizosphere availability also for Cr, Cu, Ni and Zn. However, despite the relevant accumulation of the heavy metals in the plant rhizosphere, generally the metal uptake into the leaves was rather low. Both analysis of variance and principal component analysis confirmed this finding. However, one P. fluorescens strain, CD1, which was isolated from the multi-metal accumulator Cynodon dactylon, significantly promoted the M. jalapa leaf uptake for Cr, Cu and Zn. The plant metal uptake assessment, confirmed the per se capability of M. jalapa to effectively uptake Cd (30 %) and Cu (12.72 %) from the rhizosphere to the leaves, whereas the uptake for the other metals was low: Ni (2.66 %), Zn (2.46 %), Cr (1.75 %), Pb (0.73 %).

Terrestrial Biotic Ligand model to predict bioavailability of heavy metals in rhizosphere

Terrestrial Biotic Ligand model to predict bioavailability of heavy metals in rhizosphere

The application of diffusive gradient technique (DGT) for assessment of changes in Cd, Pb, and Zn mobility in rhizosphere

Diffusive Gradient in Thin Films (DGT) technique was applied to determine Cd, Pb and Zn concentrations in rhizosphere of four different plant species: hyperaccumulator Penny-cress (Thlaspi caerulescens J. et C. Presl), trees with a good accumulation capacity willow (Salix dasyclados Vimm.) and poplar (Populus nigra L.) and crop maize (Zea mays L.). Moreover, the effect of two chelating agents (ethylendiaminetetraacetic acid – EDTA, and S,S-ethylendiaminedisuccinic acid – EDDS) on element mobility in rhizosphere like soil was investigated. DGT was able to register even small changes in heavy metal concentrations in rhizosphere according to individual crop and/or soil treatments. A particularly significant effect of EDTA application to enhance solubility of metals bound to solid phase into the soil solution was observed resulting in increased concentrations of mobile metals in rhizosphere. The suitability of DGT technique for evaluation of heavy metal behavior in the environment was demonstrated with reasonable results.

Physical and chemical properties in rhizosphere and bulk soils of Tsuga and Yushania in a temperate rain forest

The objectives of this study were to investigate selected physical and chemical properties, and availability of metals in rhizosphere and bulk soils of Tsuga and Yushania of alpine forests. The pH of rhizosphere soils was lower than bulk soils. Mean CEC, organic carbon, carbon/nitrogen (C/N) ratio, and clay contents in rhizosphere soils were greater than in bulk soils Concentrations of exchangeable potassium (K) and magnesium (Mg) were also greater in rhizosphere soils than in bulk soils. The availability of aluminum (Al), iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) in rhizospheres was influenced by the ionic species and concentrations, which depend on the pH change and chemical compositions of root exudates.