[Intensive Citrus Cultivation Suppresses Soil Phosphorus Cycling Microbial Activity].

Soil microbes are key drivers in regulating the phosphorus cycle. Elucidating the microbial mineralization process of soil phosphorus-solubilizing bacteria is of great significance for improving nutrient uptake and yield of crops. This study investigated the mechanism by which citrus cultivation affects the soil microbial acquisition strategy for phosphorus by measuring the abundance of the phoD gene, microbial community diversity and structure, and soil phosphorus fractions in the soils of citrus orchards and adjacent natural forests. The results showed that citrus cultivation could lead to a decrease in soil pH and an accumulation of available phosphorus in the soil, with a content as high as 112 mg·kg-1, which was significantly higher than that of natural forests (3.7 mg·kg-1). Citrus cultivation also affected the soil phosphorus fractions, with citrus soil having higher levels of soluble phosphorus (CaCl2-P), citrate-extractable phosphorus (Citrate-P), and mineral-bound phosphorus (HCl-P). The phosphorus fractions of natural forest soils were significantly lower than those of citrus soils, whereas the phoD gene abundance and alkaline phosphatase activity were significantly higher in natural forest soils than in citrus soils. High-throughput sequencing results showed that the Shannon diversity index of phosphate-solubilizing bacteria in citrus soils was 4.61, which was significantly lower than that of natural forests (5.35). The microbial community structure in natural forests was also different from that of citrus soils. In addition, the microbial community composition of phosphate-solubilizing bacteria in citrus soils was also different from that of natural forests, with the relative abundance of Proteobacteria being lower in natural forest soils than in citrus soils. Therefore, citrus cultivation led to a shift of soil microbial acquisition strategy for phosphorus, with external phosphorus addition being the main strategy in citrus soils, whereas microbial mineralization of organic phosphorus was the main strategy in natural forest soils to meet their growth requirements.

[Interaction and Transport Characteristics of Lead and Cadmium in Different Soil-wheat Systems].

In this study, four groups of lead(Pb) and cadmium(Cd) combined treatments with different concentration ratios were set up in Hailun black soil, Xianning brown-red soil, and Changwu Heilu soil, and wheat(Zhengmai 9023) was planted for a five-month pot experiment to analyze the Pb-Cd interaction behavior on heavy metal bioaccumulation in wheat under three soil-wheat systems. The low pH brown-red soil had the highest water-soluble Cd and Pb contents with significant Pb-Cd interactions in the soil, whereas the black soil with high organic matter and Heilu soil with high calcium carbonate content exhibited lower Cd and Pb activities. Among the three soils, wheat height and dry weight showed the poorest growth performance in the Heilu soil, but the wheat height increased by 2.68-8.49 cm compared with that in the control under the Pb-Cd combined treatment, whereas Pb-Cd interaction had the least effect on wheat height and dry weight in black soil and inhibited the growth of wheat in the brown-red soil. In the transport process of Cd or Pb in wheat, Pb-Cd interaction showed quite different effects in the three soil-wheat systems. Under the 125 mg·kg-1 and 250 mg·kg-1 Pb treatments, the Pb content in wheat grain planted in brown-red soil significantly increased by 73.2% and 19.1% with the addition of Cd, respectively, and therefore there was a synergistic effect between Pb and Cd. Under the 0.3 mg·kg-1 and 0.6 mg·kg-1 Cd treatments, the Cd content in wheat grains planted in black soil decreased by 51% and 33% with the addition of Pb, respectively; therefore, there was an antagonist effect between Pb and Cd. In the Heilu soil, a synergistic effect of Cd on Pb transport in wheat leaves was only observed under high Pb treatment. Therefore, pH and organic matter content were the key factors that determined the interaction behavior of Pb and Cd. The wheat food security risk of Pb and Cd combined pollution was higher than that of single metal pollution in acidic brown-red soil and lower in high organic matter black soil, whereas the interaction of Pb and Cd had little impact on the wheat food security risk of alkaline Heilu soil.

[Oxidation Process of Dissolvable Sulfide by Manganite and Its Influencing Factors].

As one of the manganese oxides, which are easily generated and widely distributed in supergene environment, manganite participates in the oxidation of dissolvable sulfide (S²â»), and affects the migration, transformation, and the fate of sulfides. In the present work, the redox mechanism was studied by determining the intermediates, and the influence of initial pH and oxygen atmosphere on the processes were studied. The chemical composition, crystal structures and micromorphologies were characterized by XRD, FTIR and TEM. The concentration of S²â» and its oxidation products were analyzed using spectrophotometer, high performance liquid chromatograph and ion chromatograph. The results indicated that elemental sulfur was formed as the major oxidation product of S²â» oxidation, and decreased pH could accelerate the oxidation rate of S²â» in the initial stage, however, there was no significant influence on final products. Elemental S could be further oxidized to S2O3²â» when the reaction system was bubbled with oxygen, and manganite exhibited excellent catalytic performance and chemical stability during the oxidation of dissolvable sulfide by oxygen. After reaction of more than 10 h, the crystal structure of manganite remained stable.

[Sorption and desorption characteristics of different structures of organic phosphorus onto aluminum (oxyhydr) oxides].

The sorption and desorption characteristics of four kinds of organic phosphorus with different molecular structures (glycerophosphate (GP), glucose-6-phosphate (G6P), adenosine triphosphate (ATP), and myo-inositol hexakisphosphate (IHP)) on three kinds of aluminum (oxyhydr)oxides (amorphous Al(OH)3, boehmite, and alpha-Al2O3) were studied. The underlying mechanisms were also illustrated. Results showed that the maximum sorption amounts of OP onto Al (oxyhydr)oxides, on a per gram dry weight basis, decreased as following: amorphous Al(OH)3 > boehmite > alpha-Al2O3. This mainly related to the mineral crystallinity and surface heterogeneity. With the exception of sorption of IHP on amorphous Al (OH)3, the maximum sorption density decreased with increasing molecular weight (MW) of OP, following the order: GP > G6P > ATP > IHP. However, the sorption amount of IHP on amorphous Al (OH)3 was much higher than those of other OP, due to the transformation of surface complexes of IHP to surface precipitation and thus enhancing the sorption. The sorption kinetics results showed that sorption of OP underwent the first onset rapid sorption, i. e. a certain amount of sorption occurred within an onset extremely short period, and a following long and slow sorption process. Amorphous Al (OH)3 had the greatest onset rapid sorption density, and the onset rapid sorption density of OP on Al (oxyhydr) oxides decreased with increasing MW. Desorption capacities of OP by KCl and citrate solutions related to the surface affinity between OP and boehmite. Initial desorption percentages by KCl decreased in the order: G6P (10.53%) > GP(6.91%) > ATP (3.06%) > IHP (0.8%). The maximum desorption percentages of OP by citrate were 4-5 times greater than those by KCl. During resorption process of P by KCl, the maximum desorption rate achieved after a fast desorption in a few hours, followed by diffusion-resorption during which the desorption percentage gradually decreased. Specially, both diffusion-resorption and surface precipitation promoted the resorption of IHP on mineral surface. Conclusively, the strong specific sorption of OP occurs on the surface of Al (oxyhydr) oxides, and molecular structure and size of OP as well as the crystallinity and crystal structure of minerals are the key factors affecting the interfacial reactions and environmental behaviors of OP.

Sorption of tetracycline on organo-montmorillonites.

Tetracycline (TC) is a veterinary antibiotic that is frequently detected as pollutant in the environment. Powerful adsorbents are required for removing TC. The present paper compares the TC adsorption capacity of Na-montmorillonite (Na-mont) with six organo-montmorillonites (organo-monts). Three quaternary ammonium cations (QACs) with different alkyl-chain lengths were used as modifiers. Powder X-ray diffraction indicated that the d(001) values of organo-monts increased with increasing the QACs loading and alkyl-chain length. The CECs of the organo-monts were substantially lower than that of Na-mont and decreased with QACs chain length and increased loading. The modeling of the adsorption kinetics revealed that the processes of TC adsorption on the tested samples could be well fitted by the pseudo-second-order equation. The maximum adsorption capacities of TC on the organo-monts (1000-2000mmol/kg) were considerably higher than that on Na-mont (769mmol/kg). Both the Langmuir and Freundlich model could fit the adsorption isotherms. The TC adsorption to the organo-monts increase significantly with decreasing the pH below 5.5 because of the electrostatic interaction, and a high QACs loading performed better than a low loading at around pH 3.

[Lead adsorption and arsenite oxidation by cobalt doped birnessite].

In order to study the effects of transition metal ions on the physic-chemical properties of manganese dioxides as environmental friendly materials, three-dimensional nano-microsphere cobalt-doped birnessite was synthesized by reduction of potassium permanganate by mixtures of concentrated hydrochloride and cobalt (II) chloride. Powder X-ray diffraction, chemical analysis, N2 physical adsorption, field emission scanning electron microscopy (FE-SEM) and X-ray photoelectron spectra (XPS) were used to characterize the crystal structure, chemical composition and micro-morphologies of products. In the range of molar ratios from 0.05 to 0.20, birnessite was fabricated exclusively. It was observed that cobalt incorporated into the layers of birnessite and had little effect on the crystal structure and micromorpholgy, but crystallinity decreased after cobalt doping. Both chemical analysis and XPS results showed that manganese average oxidation state decreased after cobalt doping, and the percentage of Mn3+ increased. Co(III) OOH existed mainly in the structure. With the increase of cobalt, hydroxide oxygen percentage in molar increased from 12.79% for undoped birnessite to 13.05%, 17.69% and 17.79% for doped samples respectively. Adsorption capacity for lead and oxidation of arsenite of birnessite were enhanced by cobalt doping. The maximum capacity of Pb2+ adsorption increased in the order HB (2 538 mmol/kg) < CoB5 (2798 mmol/kg) < CoB10 (2932 mmol/kg) < CoB20 (3 146 mmol/kg). Oxidation percentage of arsenite in simulated waste water by undoped birnessite was 76.5%, those of doped ones increased by 2.0%, 12.8% and 18.9% respectively. Partial of Co3+ substitution for Mn4+ results in the increase of negative charge of the layer and the content of hydroxyl group, which could account for the improved adsorption capacity of Pb2+. After substitution of manganese by cobalt, oxidation capacity of arsenite by birnessite increases likely due to the higher standard redox potential of Co3+/Co2+ than those of Mn4+/Mn3+/Mn2+. Therefore, Co-doped birnessite is more applicable for the remediation of water polluted with heavy metal ions, implying new methods of modification of manganese dioxides in practice.

[Adsorption of heavy metals on the surface of birnessite relationship with its Mn average oxidation state and adsorption sites].

Adsorption characteristics of mineral surface for heavy metal ions are largely determined by the type and amount of surface adsorption sites. However, the effects of substructure variance in manganese oxide on the adsorption sites and adsorption characteristics remain unclear. Adsorption experiments and powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) were combined to examine the adsorption characteristics of Pb2+, Cu2+, Zn2+ and Cd2+ sequestration by birnessites with different Mn average oxidation state (AOS), and the Mn AOS dependent adsorption sites and adsorption characteristics. The results show that the maximum adsorption capacity of Pb2+, Cu2+, Zn2+ and Cd2+ increased with increasing birnessite Mn AOS. The adsorption capacity followed the order of Pb2+ > Cu2+ > Zn2+ > Cd2+. The observations suggest that there exist two sites on the surface of birnessite, i. e., high-binding-energy site (HBE site) and low-binding-energy site (LBE site). With the increase of Mn AOS for birnessites, the amount of HBE sites for heavy metal ions adsorption remarkably increased. On the other hand, variation in the amount of LBE sites was insignificant. The amount of LBE sites is much more than those of HBE sites on the surface of birnessite with low Mn AOS. Nevertheless, both amounts on the surface of birnessite with high Mn AOS are very close to each other. Therefore, the heavy metal ions adsorption capacity on birnessite is largely determined by the amount of HBE sites. On birnessite surface, adsorption of Cu2+, Zn2+, and Cd2+ mostly occurred at HBE sites. In comparison with Zn2+ and Cd2+, more Cu2+ adsorbed on the LBW sites. Pb2+ adsorption maybe occupy at both LBE sites and HBE sites simultaneously.

[Characterization of Pb2+ adsorption on the surface of birnessite treatment with Na4P2O7 at different pH and the study on the distribution of Mn(III) in the birnessite].

Acid birnessite was treated with Na4P2O7 at pH 2, 4, 5 respectively. After the treatments, the species and content of manganese ion in the complex solution, and the variation of average oxidation state (AOS) of Mn in birnessite, and the amount of adsorbed Pb2+ and released Mn2+, H+ during the Pb2+ adsorption were investigated. The results indicate that after acid birnessite, the AOS of Mn is 3.670 which is treated by Na4P2O7 at different pH, Mn( III) located in the layer edge and part of Mn(III) located in the interlayer are released to the solution through complexation with Na4P2O7. The content of Mn(III) in the structure of original birnessite is very low. Small amount of Mn(II), which accounts for 4.70%-7.46% in the molar percentage of total released Mn, is also released simultaneously. The AOS of Mn of birnessites after treatment increases to 3.783 (pH 2), 3.786 (pH 4), 3.824 (pH 5) respectively. While the crystal structure of birnessite does not change after treatment, the amount of Mn(III) located above or below vacant cation sites decreases, and the amount of H+ located above or below vacant cation sites goes up in the structure of birnessites. The amount of vacant cation sites responsible for Pb2+ adsorption increases, which lead to the increase of the maximum amount of adsorbed Pb2+. Additionally, the distribution of Mn(III) in the structure of acid birnessite is deduced. About one sixth of Mn(III) locates in the layer edge, and five sixths of Mn(III) locates in the interlayer and the non layer edge.

[Effects of Mn(III) on oxidation of Cr(III) with birnessites].

Cr(III) could be oxidized only by manganese oxide minerals as natural inorganic oxidants in nature, and so the rate and mechanism of interaction between manganese oxide minerals and Cr(III) were widely concerned. The effects of Mn(III) in birnessites, the most common Mn oxide mineral in the environment, on the rate of Cr(III) oxidation with birnessites and the kinetic characteristics were investigated through batch kinetic technique. The results show that Cr(III) oxidation rate follows a pseudo-first-order reaction, and the apparent rate constant K(obs), is 0.031 3 min(-1) when the average oxidation state (AOS) of Mn is about 3.50 in birnessite. When the birnessite is pretreated with Na4P2O7 solution, and the Mn(III) can be complexed out from the solid oxides. Therefore the content of Mn(III) in the birnessites decreases and the AOS of manganese increases. The AOSs of Mn for the pretreated birnessites increase from 3.50 to 3.63, 3.73 and 3.78 when the concentrations of Na4P2O7 are about 10, 20 and 50 mmol/L respectively. The Mn(III) content does not affect the initial oxidation rate of Cr(III) markedly, although oxidation amount of Cr(III) increases with the AOS of Mn. The apparent rate constants for the corresponding pretreated birnessites are 0.035 1, 0.032 5 and 0.0309 min(-1) respectively. The oxidation rate of Cr( III) is markedly influenced by the amount of Mn(III) produced in the transformation process of Mn(VN) --> Mn(III). The newly formed Mn(III) is complexed by Na4P2O7 and the oxidation rate decreases to 45%-88%. The lower content of Mn(III) in birnessites, the more Mn(III) newly formed from the transformation of Mn(IV) is complexed out from the minerals, and the greater amplitude in the decrease of Cr(III) oxidation rate. Thus the newly formed Mn(III) is highly active and possesses fast rate of electron transfer, however the rate of electron transfer in the transformation process of Mn(IV) --> Mn(III) is relatively slow. It could be deduced that the controlling step of initial oxidation rate of Cr(III) with birnessites may be the electron transfer process of Mn(IV) --> Mn(III).

[Relation between average oxidation state of Mn of birnessite and the amount of Pb2+ adsorbed].

Vacant sites in Mn oxides, commonly occur in soils, play an important role in their heavy metal adsorption behavior. The dependence of Pb2+ adsorption capacity for the synthesized birnessites and their d110-interplanar spacing on the respective Mn average oxidation state (AOS), and the relationship between Pb2+ adsorption and the Mn2+, H+, K+ released during adsorption were investigated. The results show that Mn AOS of birnessites apparently reflects their amount of vacant sites which largely account for the Pb2+ adsorption. Significant positive correlation between Pb2+ adsorption capacity and the Mn AOS of corresponding birnessites (r = 0.9779 > 0.6614, n = 14, alpha = 0.01), negative correlation between d110 spacing and the Mn AOS (r = -0.9035 < -0.6614, n = 14, alpha = 0.01), and significant positive correlation between Pb2+ adsorption and the Mn2+, H+, K+ released during adsorption(r = 0.9962 > 0.6614, n = 14, alpha = 0.01) are found. The vacant sites amount increases with Mn AOS for birnessites, which causes the increase of Pb2+ adsorption. Therefore, the Pb2+ adsorption capacity of birnessite is largely determined by the amount of vacant sites, from which Mn2+, H+, and K+ released during adsorption are mostly derived.

Interaction between humic acid and lysozyme, studied by dynamic light scattering and isothermal titration calorimetry.

Interactions of purified Aldrich humic acid (PAHA) with the protein lysozyme (LSZ) are studied with dynamic light scattering and isothermal titration calorimetry by mixing LSZ and PAHA at various mass ratios. In solution LSZ is positive and PAHA is negative at the investigated pH values. Up to moderate KCl concentrations no aggregation occurs for LSZ and for PAHA aggregated particles with an average radius of 80 nm are present. Complexation of PAHA with LSZ starts as soon as PAHA is added to LSZ and is followed by aggregation when the isoelectric-point (IEP) of the complexes is approached. Aggregation is gradual for 50 mM KCl and sudden for low KCl concentrations. The aggregate size is at its maximum at the IEP of the complexes. At mass ratios beyond the IEP the aggregates partially disaggregate. Positively charged complexes of PAHA and LSZ, formed in the absence of salt strongly aggregate upon salt addition. Mixing of LSZ and PAHA is initially enthalpically driven. Near the IEP complexation and aggregation are due to hydrophobic forces (structural reorganization) and counterion release. The observations are relevant for other HA-protein systems when the protein is positively charged.

Adsorption and redox reactions of heavy metals on synthesized Mn oxide minerals.

Several Mn oxide minerals commonly occurring in soils were synthesized by modified or optimized methods. The morphologies, structures, compositions and surface properties of the synthesized Mn oxide minerals were characterized. Adsorption and redox reactions of heavy metals on these minerals in relation to the mineral structures and surface properties were also investigated. The synthesized birnessite, todorokite, cryptomelane, and hausmannite were single-phased minerals and had the typical morphologies from analyses of XRD and TEM/ED. The PZCs of the synthesized birnessite, todorokite and cryptomelane were 1.75, 3.50 and 2.10, respectively. The magnitude order of their surface variable negative charge was: birnessite> or =cryptomelane>todorokite. The hausmannite had a much higher PZC than others with the least surface variable negative charge. Birnessite exhibited the largest adsorption capacity on heavy metals Pb(2+), Cu(2+), Co(2+), Cd(2+) and Zn(2+), while hausmannite the smallest one. Birnessite, cryptomelane and todorokite showed the greatest adsorption capacity on Pb(2+) among the tested heavy metals. Hydration tendency (pK(1)) of the heavy metals and the surface variable charge of the Mn minerals had significant impacts on the adsorption. The ability in Cr(III) oxidation and concomitant release of Mn(2+) varied greatly depending on the structure, composition, surface properties and crystallinity of the minerals. The maximum amounts of Cr(III) oxidized by the Mn oxide minerals in order were (mmol/kg): birnessite (1330.0)>cryptomelane (422.6)>todorokite (59.7)>hausmannite (36.6).

The controlling effect of pH on oxidation of Cr(III) by manganese oxide minerals.

Oxidation of Cr(III) by three types of manganese oxide minerals (birnessite I, birnessite II, and todorokite) and effects of pH were investigated by chemical analysis, equilibrium redox, X-ray diffraction (XRD), and transmission electron microscopy. The effects of pH in the reaction systems on the oxidation of Cr(III) were similar among the three manganese oxide minerals. As pH increased from pH 2.0, the amount of Cr(III) oxidized by the tested manganese oxide minerals first increased, and then peaked at pH 3.0-3.5. While pH continually increased from 3.0 to 3.5, the amount of Cr(III) oxidized by the manganese oxide minerals sharply decreased. Until pH was higher than 5.0-5.5, the Cr(III) oxidation amounts changed to a small extent or kept stable. pH influenced the oxidation of Cr(III) mainly by altering the redox potential in the system, i.e., the concentration of H+, the species of Cr(III), and their distributions in the system. However, the surface charge of the manganese oxide minerals, subjected to the pH in the system, was not found to greatly influence the extent of the oxidation. When pH was below 5.0, oxidation of Cr(III) by the manganese oxide minerals was (or tended to be) an equilibrium reaction and was controlled thermodynamically. When pH was above 5.0-5.5, Cr(OH)3 precipitate was produced in the system and pH had little effect on the oxidation content of Cr(III).

Effects of Rebixiao granules on blood uric acid in patients with repeatedly attacking acute gouty arthritis.

OBJECTIVE: To observe the clinical effect of Rebixiao granule (RBXG) in treating repeatedly attacking acute gouty arthritis and through experimental study on blood uric acid to explore RBXG's therapeutic mechanism. METHODS: Ninety repeatedly attacking acute gouty arthritis patients were divided into the treated group (n = 60) and control group (n = 30). The treated group was treated with RBXG, and the control group was treated with Futalin tablets (diclofenac sodium). The baseline treatment including good rest, low purine diet, sufficient water drinking and urine alkalization, etc. was then given to both groups. Hypoxanthine 600 mg/kg and niacin 100 mg/kg was applied to hyperuricemic mice by gastrogavage to establish the animal models. RESULTS: The clinical effective rate of the treated group was 95.0% and that of the control 90.0%. Good therapeutic effects were won, insignificant difference (P > 0.05)was shown between the two groups. However, the cure rate of the treated group was 26.7% while that of the control group was 10.0%, with significant difference (P < 0.01) shown between them. The treated group had its blood uric acid lowered, which was significantly different (P < 0.05) from that of the control group. The animal experiment indicated that all the three groups treated with different dosages of RBXG, as well as the Ash bark and Smilax glabra rhizome groups had their blood uric acid content reduced in the hyperuricemic mice. CONCLUSION: RBXG has a quicker initiation and better treatment effects than sole anti-inflammatory and analgesic agents on the treatment of repeatedly attacking acute gouty arthritis, showing no obvious toxic or adverse reactions and therefore good for long-term administration and likely to be a safe TCM preparation to control the symptoms and reduce the onsets of repeatedly attacking of acute gouty arthritis. The animal experiment shows that both the compound preparation and part of the single ingredients in the recipe have the function of reducing blood uric acid. However, the compound recipe has better therapeutic effects, proving to be superior to single drugs.