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PubMed2004

[Diversity of microbial genes in paddy soil stressed by cadmium using DGGE].

Variations of diversity of microbial genes in submerged paddy soil stressed by heavy metal cadmium were studied using modern molecular biotechnology which includes directly extracting total DNA from paddy soil, amplifying 16S rDNA and their V3 variable region by PCR, the denaturing gradient gel electrophoresis (DGGE). Two methods for extraction and purification of microbial DNA were compared. Bacterial communities were quantified by analyzing the DGGE band patterns. The genetic clusters and correlative comparison of bacterial communities were analyzed based on the DGGE finger-print. The results showed that there are some significant differences between bacterial communities in paddy soils treated with different concentrations of cadmium. The information about effect of cadium on microbial population based on molecular biological techniques are conformed with that from traditional methods, but that obtained about variations of microbial genes in paddy soil is much more than results based on the latter methods. It could provide a new way and foundation to research microbial gene diversity in contaminated environment.

Biodiversity↗

PubMed2006

Major and trace elements in paddy soil contaminated by Pb-Zn mining: a case study of Kocani Field, Macedonia.

The objective of this study was to assess the bulk chemical composition as well as the extent and severity of heavy metal contamination in the paddy soil of Kocani Field (eastern Macedonia). The results revealed that the paddy soil of the western part of Kocani Field is severely contaminated with Pb, Zn, As and Cd in the vicinity of the Zletovska River due to irrigation with riverine water that is severely affected by acid mine and tailing effluents from the Pb-Zn mine in Zletovo. The detected total concentrations of these metals are far above the threshold values considered to be phytotoxically excessive for surface soil. The paddy soil in the vicinity of the Zletovska River was also found to exhibit elevated levels of Ba, Th, U, V, W, Mo, Cu, Sb, Bi, Ag, Au, Hg and Tl, with concentrations above their generally accepted median concentration values obtained during this study. A correlation matrix revealed that the Mn and Fe oxides/hydroxides are the most important carrier phase for several trace elements, with the exception of rare earth elements (REEs). These also represent a major sink for the observed heavy metal pollution of the soil. REEs are mostly associated with two phases: light (L)REEs are bound to K-Al, while heavy (H)REEs are bound to Mg-bearing minerals. Although there is no direct evidence of a health risk, the paddy soil in the vicinity of Zletovska River needs further investigation and an assessment should be made of its suitability for agricultural use, particularly in view of the highly elevated concentrations of Pb, Zn, As and Cd.

Environmental Monitoring↗

PubMed2026

Electron shuttles facilitate methane-dependent arsenate reduction in paddy soils.

Methane-dependent arsenate reduction (M-AsR) occurs widely in paddy soils and can substantially enhance arsenic mobilization, posing potential ecological risks. However, the role of electron shuttles in this process remains poorly understood. In this study, we investigated the influence of anthraquinone-2,6-disulfonate (AQDS) on M-AsR in paddy soils. Fourteen-day incubation showed that 1 mmol/L AQDS facilitated 50.88 % of arsenate reduction and 31.31 % of methane oxidation. Quantitative polymerase chain reaction analysis revealed that AQDS significantly increased the abundance of functional genes associated with arsenate reduction (arrA, arsC) and anaerobic methane oxidation (mcrA) (P < 0.05). Microbial community analysis revealed that AQDS addition enriched Cloacibacterium, Sphingorhabdus, and Methylocystis, while decreasing the relative abundance of Methylobacter and Methylomonas. These findings indicate that electron shuttles facilitate M-AsR by modulating functional microbial populations, providing valuable insights into arsenic biogeochemistry and the coupled cycling of methane and arsenic in paddy soils.

Methane↗

PubMed1997

Peculiar archaea found in Japanese paddy soils.

Archaeal 16S rDNA clones retrieved from paddy soil DNA were sequenced. Among 100 clones, 88 clones were assigned to methanogens and nine clones were assigned to crenarchaeota. However, three of the nine clones were phylogenetically far from the cultured crenarchaeota and closely related to marine planktonic archaea. The other three clones showed extremely novel 16S rDNA sequences and were phylogenetically far from both Crenarchaeola and Euryarchaeota. This paper reports the ubiquitous presence of crenarchaeotal and extremely novel clones in paddy soils.

Archaea↗

PubMed2003

[Seasonal variation of fixed ammonium content of paddy soils in Hunan Province and its bioavailability].

Three paddy soils with higher content of fixed ammonium in Hunan Province were used as test soils in pot experiment to study the seasonal variation of their fixed ammonium content and its bioavailability during rice growth period. The results showed that the fixed ammonium content in the paddy soils changed constantly during rice growth. Applying N fertilizer and organic manure increased the fixed ammonium content, which was decreased through the N uptake by rice plants. The recently fixed ammonium was almost fully available to rice, while the native fixed ammonium was partly available. The release of fixed ammonium during rice growth was newly alluvial sandy soil > purple clayey soil > alluvial sandy soil, and was greater a early growth stage than at later growth stage.

Biological Availability↗

PubMed2002

[Health-quality problems of paddy soil in the Taihu region].

The concept of soil health quality was discussed from the angle of sustainable and safe agricultural production and nutritive agricultural products. Based on the data of 13 higher-yield rice-farms and its corresponding irrigated rivers in the Taihu region, problems of health quality occurred in paddy soil were discussed. Owing to the high application of inorganic fertilizers in those farms, high available P and N were observed in paddy soil and river sediments. The contents of heavy metals such as Pb, Cu, Ni and Co in paddy soil were still at the level of background values. However, it was found that some rivers were seriously polluted by Cu, Zn and Pb. Several cases of point-source pollution of heavy metal were found in paddy soil in the region. The contents of DDT and HCH in soils and river sediments were lower than their maximum allowable concentrations. The results of lower selenium content in agricultural product owing to lower content in paddy soil indicted that the Taihu region is a selenium-deficient area.

China↗

PubMed2005

[Aging of spiked pyrene in two paddy soils and their particle-size fractions after soil incubation and changes in extractability and bio-availability to earthworm].

Effect of aging on bioavailability and extractability of persistent organic pollutants has recently been paid much attention in environmental studies. This study deals with aging of spiked pyrene, a four-ring polycyclic hydrocarbon, in two paddy soils and their particle-size fractions under laboratory incubation and change in its extractability and bioavailability. The bioavailability of aged pyrene was tested by an assay of exposure to earthworms (Eisenia foetida). The extractability of spiked pyrene was decreased by 15% to 23%, and the bioavailability to earthworm was decreased by 37% to 67% after incubation for 90 d compared to under no incubation. Meanwhile, there was no significant difference in the pyrene extractability between incubation with different size fractions of a single soil. Soil incubation resulted in lower extractability and, thus, lower environmental risk of the organic pollutants after incorporation in paddy soils and their aggregates. The different size fractions of paddy soils may exert different bioavailability when exposure to soil fauna. Thus, content and chemical extractability may not be appropriate index for assessing the potential environmental risk and bioavailability to soil fauna for persistent organic pollutants in paddy soils.

Animals↗

PubMed2000

Copper contamination in paddy soils irrigated with wastewater.

Copper (Cu) contamination was investigated in paddy soils where Cu-rich wastewater (12 mg Cu/l) was used for irrigation. The results showed that Cu contamination increased the soil Cu content from 17.0 mg Cu/kg in the non-wastewater irrigated soils (NWIS) to 101.2 mg Cu/kg in the wastewater irrigated soils (WIS), and Cu accumulated mostly in the surface layer (0-10 cm) of the paddy soil. The average Cu contents in brown rice, rice hull and rice straw from NWIS were 1.4, 7.3 and 14.5 mg Cu/kg, while those from WIS were 15.5, 133.2, and 101.4 mg Cu/kg, respectively. Correlation analysis revealed that the relationship between the Cu content in the rice straw and the rice hull with the total Cu content of the soil could be described by an exponential function (R2 = 0.921 and 0.831, respectively; P <0.01). Rice plants grown in the WIS showed symptoms of black roots, less effective tiller, etc. Subsequently, the rice yield decreased by 18-25%, compared with that grown in NWIS.

Agriculture↗

PubMed2006

Organic phosphorus fractions in organically amended paddy soils in continuously and intermittently flooded conditions.

Soil organic phosphorus (SOP) can greatly contribute to plant-available P and P nutrition. The study was conducted to determine the effects of organic amendments on organic P fractions and microbiological activities in paddy soils. Samples were collected at the Changshu Agro-ecological Experiment Station in Tahu Lake Basin, China, from an experiment that has been performed from 1999 to 2004, on a paddy soil (Gleysols). Treatments consisted of swine manure (SM), wheat straw (WS), swine manure plus wheat straw (SM + WS), and a control (chemical fertilization alone). Organic amendments markedly increased soil total organic phosphorus (TOP) and total organic carbon (TOC), especially in continuously flooded conditions. Based on the fractionation of SOP, organic amendments significantly increased soil labile organic phosphorus (LOP), moderately labile organic phosphorus (MLOP), and moderately stable organic phosphorus (MSOP) compared with the control. For SM and SM + WS treatments, LOP in continuously flooded soils decreased by 30.1 and 36.4%, respectively, compared to intermittently flooded soils. In organically amended soils, continuous flooding showed significantly lower microbial biomass phosphorus (MBP) and alkaline phosphatase activities (APA) than intermittent flooding. In intermittently flooded conditions, incorporating organic amendments into soil resulted in greater P uptake and biomass yield of rice than the control. In the intermittently flooded soils, APA (P < 0.05) and MBP (P < 0.01) were significantly and positively related to TOP, LOP, MLOP, and MSOP, whereas in continuously flooded soils, there was a significant (P < 0.05) negative relationship between MBP, TOP, and MSOP. Based on soil organic P fractions and soil enzymatic and microbiological activities, continuous flooding applied to paddy soils should be avoided, especially when swine manure is incorporated into paddy soil.

Crops, Agricultural↗

PubMed2006

Aerobic and anaerobic biodegradation of phenol derivatives in various paddy soils.

Microbiological degradation of phenol and some of its alkyl-derivatives (p-cresol, 4-n-propylphenol, 4-i-propylphenol, 4-n-butylphenol, 4-sec-butylphenol, 4-t-butylphenol, and 4-t-octylphenol) was examined under both aerobic and anaerobic conditions in seven Japanese paddy soils. Aerobic biodegradation of phenol derivatives was detected in all the paddy soils examined. The half-lives ranged from 2 to 19 days. The aerobic degradation rate of 4-t-octylphenol was correlated inversely with the total carbon contents of paddy soils, and there were significant inverse correlations between the aerobic degradation rate and the size of alkyl groups of alkylphenols. Anaerobic biodegradation of phenol and p-cresol was detected in three soils with the half-lives ranging from 24 to 260 days for phenol and from 11 to 740 days for p-cresol, respectively. The three soils were characterized by low contents of nitrate and iron oxides. Other soil properties did not show any significant correlations with the anaerobic degradation rates. In one soil, we found for the first time anaerobic biodegradation of 4-n-propylphenol. However, the other five compounds (4-i-propylphenol, 4-n-butylphenol, 4-sec-butylphenol, 4-t-butylphenol and 4-t-octylphenol) were not degraded over 224 days of incubation. These results suggest that phenol and all the alkylphenols were degraded within several days when paddy soil is not flooded and so under aerobic conditions. Under flooded and anaerobic conditions, 4-n-propylphenol would be degraded as well as phenol and p-cresol while alkylphenols with long and branched alkyl chains were hardly degraded at all.

Agriculture↗

PubMed2004

Nitrous oxide emission and reduction in a laboratory-incubated paddy soil response to pretreatment of water regime.

A laboratory incubation experiment was conducted to investigate nitrous oxide (N2O) emission and reduction in a paddy soil (Stagnic Anthrosol) response to the pretreatment of water regime. The paddy soil was maintained under either air-dried (sample D) or submerged (sample F) conditions for 110 d before the soil was adjusted into soil moisture of 20% , 40% , 60% , 80% and 100% water holding capacity (WH(-2)) respectively, and then incubated with or without 10% (v/v) acetylene for 138 h at 25 degrees C. At lower soil water content (< or = 60% WHC), N2O emission from the sample F was 2.29 times higher than that from the sample D (P < 0.01). While, N2O emission from the sample F was only 29 and 14 percent of that from the sample D at the soil moisture of 80% and 100% WHC, respectively (P < 0.01). The maximal N2O emissions observed at soil moisture of 80% WHC were about 24 and 186 times higher than the minima obtained at the soil moisture of 20% WHC for the sample F and D, respectively. But at the soil moisture of 80% and 100% WHC, N2O emission from the sample F with acetylene (F + ACE) was comparable to that of the sample D with acetylene (D + ACE). The results showed that the F sample produced N2O ability in denitrification was similar to the sample D, however, the sample F was in the better reduction of N2O to N, than the sample D even after the soil moisture was adjusted into the same level of 80% or 100% WHC. Therefore, the pretreatment of water regime influenced the strength and product composition of denitrification and N2O emission from the paddy soil.

Agriculture↗

PubMed1978

The influence of water-logging stage upon the paddy soil mycoflora in the Ukraine.

The soil fungal flora of paddy soils from the southern districts of the Ukraine was investigated. From 287 soil samples 170 species were isolated. They belonged to the following genera: Oomycetes 1.2%, Zygomycetes 8.8%, Ascomycetes 5.8%, Deuteromycetes 84.2%. Certain fungi were found to be dominant forms, among them Mortierella alpina Peyron., Penicillium funiculosum Thom, P. rugulosum Thom, P. chrysogenum Thom, Acremonium strictum W. Gams, Acr. breve W. Gams, Alternaria alternata (Fr.) Riessler, Cladosporium brevi-compactum Pidopl. et Deniak, Gliocladium roseum (Link) Thom, Harposporium sp., Fusarium oxysporum Schlect. var. orthoceras (App. et Wr.) Bilai, Trichoderma lignorum (Tode) Harz etc. The total number of fungi decreased in the paddy fieldsoils. It was found low frequency of Penicillium, Aspergillus, and high frequency of Mucorales.

Ecology↗

PubMed2005

Transfer of 137Cs to rice plants from various paddy soils contaminated under flooded conditions at different growth stages.

Soil blocks from 18 paddy fields around three Korean nuclear power plant sites were put into lysimeters. Greenhouse experiments were carried out to investigate the (137)Cs transfer from these paddy soils to rice plants for its deposition at different growth stages. A solution of (137)Cs was applied to the flooded lysimeters at 2-3 different stages. The applied (137)Cs was mixed with the topsoil only at the pre-transplanting application. The transfer was quantified with a transfer factor based on the unit-area deposition (TF(a), m(2)kg(-1)-dry). The TF(a) in the pre-transplanting application showed a remarkable variation with the soils. However, the differences in the mean values among the study sites were not statistically significant. The straw TF(a) was 2-3 times higher than the corresponding seed value. The early-tillering stage and booting stage applications resulted in a higher transfer than the pre-transplanting application by factors of, on an average, 2 and 16 for the straws, and 3 and 25 for the hulled seeds, respectively. The (137)Cs transfer was found to correlate negatively with the soil pH and positively with the organic matter content. Based on the present results, the representative (137)Cs TF(a) values for the rice are proposed for use in the whole of Korea for the deposition at three different growth stages.

Cesium Radioisotopes↗

PubMed2006

Ancient paddy soils from the Neolithic age in China's Yangtze River Delta.

Identifying prehistoric irrigated rice fields and characterizing the beginning of paddy soil development are important for a better understanding of human development and agricultural history. In 2003, paddy soils and irrigated rice fields buried at a depth of 100-130 cm were excavated at Chuo-dun-shan in the Yangtze River Delta, close to Suzhou, China. The fields of sizes between 1.4 and 16 m(2) were surrounded with ridges that were connected to ditches/ponds via outlets to control the water level within the fields. Many carbonized and partly carbonized rice grains with an age of 3,903 B.C. (measured (14)C age 5,129+/-45 a BP) were recovered. The surface layers of these buried paddy fields showed a high content of soil organic matter and a considerable high density of rice opals. The latter were identified to derive from Oryza spp. Solid-state (13)C nuclear magnetic resonance spectroscopy revealed aromatic carbon (C) as the predominant organic C form in the fossil surface layer. This is expected, if the major source represents burnt rice and straw. In summary, our data are in agreement with new evidences indicating that in China, paddy soils and irrigated rice cultivation were initiated and developed more than 6,000 years ago.

Archaeology↗

PubMed2000

Fermentation pattern of methanogenic degradation of rice straw in anoxic paddy soil.

The anaerobic degradation of different fractions of rice straw in anoxic paddy soil was investigated. Rice straw was divided up into stem, leaf sheath and leaf blade. The different straw fractions were mixed with paddy soil and incubated under anoxic conditions. Fermentation of straw components started immediately and resulted in transient accumulation of acetate, propionate, butyrate, isobutyrate, valerate, isovalerate and caproate with much higher concentrations in the presence than in the absence of straw. Also some unidentified compounds with UV absorption could be detected. The maximum concentrations of these compounds were different when using different straw fractions, suggesting differences in the degradation pathway of these straw fractions during the early phase of incubation, i.e. with Fe(III) and sulfate serving as oxidants. When concentrations of the intermediates decreased to background values, CH(4) production started. Rates of CH(4)unamended soil. During the methanogenic phase, the percentage contribution of fermentation products to CH(4) production was determined by inhibition with 2-bromoethanesulfonate (BES). Acetate (48-83%) and propionate (18-28%) were found to be the main intermediates of the carbon flow to CH(4), irrespective of the fraction of the rice straw or its absence. Mass balance calculations showed that 84-89% of CH(4) was formed via acetate in the various incubations. Radiotracer experiments showed that 11-27% of CH(4) was formed from H(2)/CO(2), thus confirming that acetate contributed 73-89% to methanogenesis. Our results show that the addition of rice straw and the fraction of the straw affected the fermentation pattern only in the early phase of degradation, but had no effect on the degradation pathway during the later methanogenic phase.

Journal Article↗

PubMed1979

Studies on Propionibacterium isolated from paddy soils.

The anaerobic bacteria occurring in paddy soils sampled from fields belonging to the Rice Research Station at Ohmagari in Akita Prefecture, Japan, were surveyed from May to November, 1974. Irregularly shaped rods predominated which were found to be gram-positive, strictly anaerobic, catalase-positive and not heat-resistant; populations were estimated at 10(5)--10(-7) cells/g dry soil throughout the entire survey period. On the basis of their morphological and physiological characteristics these bacteria were identified as Propionibacterium. Most strains belonged to P. lymphophilum and P. granulosum.

Anaerobiosis↗

PubMed2001

Nitrate-dependent iron(II) oxidation in paddy soil.

Iron(III) profiles of flooded paddy soil incubated in the greenhouse indicated oxidation of iron(II) in the upper 6 mm soil layer. Measurement of oxygen with a Clark-type microelectrode showed that oxygen was only responsible for the oxidation of iron(II) in the upper 3 mm. In the soil beneath, nitrate could be used as electron acceptor instead of oxygen for the oxidation of the iron(II). Nitrate was still available 3 mm below the soil surface, and denitrifying activity was indicated by higher concentrations of nitrite between 3 and 6 mm soil depth. Nitrate was generated by nitrification from ammonium. Ammonium concentrations increased beneath 6 mm soil depth, indicating ammonium release and diffusion from deeper soil layers. High concentrations of ammonium were also found at the surface, probably resulting from N2 fixation by cyanobacteria. Experimental adjustment of the nitrate concentration in the flooding water to 200 microM stimulated nitrate-dependent iron(II) oxidation, which was indicated by significantly lower iron(II) concentrations in soil layers in which nitrate-dependent iron(II) oxidation was proposed. Soil incubated in the dark showed high iron(III) concentrations only in the layer where oxygen was still available. In this soil, the nitrogen pool was depleted because of the lack of N2 fixation by cyanobacteria. In contrast, soil incubated in the dark with 500 microM nitrate in the flooding water showed significantly higher iron(II) and significantly lower iron(II) concentrations in the anoxic soil layers, indicating nitrate-dependent iron(II) oxidation. Anoxic incubations of soil with nitrate in the flooding water also showed high concentrations of iron(II) and low concentrations of iron(II) in the upper 3 mm. As oxygen was excluded in anoxic incubations, the high iron(III) concentrations are a sign of the activity of nitrate-dependent iron(II) oxidizers. The presence of these bacteria in non-amended soil was also indicated by the most probable number (MPN) counts of nitrate-dependent iron(II) oxidizers in the layer of 3-4 mm soil depth, which revealed 1.6 x 10(6) bacteria g(-1) dry weight.

Anaerobiosis↗

PubMed2002

[Effect of iron oxides addition on organic acids content in paddy soil].

The addition of ferrihydrite into paddy slurries significantly reduced the concentration of acetate. In fresh paddy soil, due to the competitive consumption for acetate by addition of ferrihydrite, the concentration of acetate was reduced to 10-20 mumol.L-1 after 5d anaerobic incubation. However, in control slurries, the acetate concentration was still as high as more than 1200 mumol.L-1. In soil produced low acetate, the acetate was completely consumed by addition of ferrihydrite, resulting in a full inhibition of methane formation. Also, the application of lepidocrocite reduced methane genesis, but the reductive effect was less than ferrihydrite. The acetate was largely accumulated during a short-term anaerobic incubation from 1 to 10 days by hematite addition, but at the same time, the methane genesis was not extensively increased. The propionate concentration was also reduced under anaerobic incubation by addition of different iron oxides such as ferrihydrite, lepidocrocite and aluminum-substituted goethite, and the inhibitory effect was in order of ferrihydrite > lepidocrocite > Al-substituted goethite. The types and contents of organic acids in fresh soil were greatly different from those being incubated for 11 weeks under an anaerobic condition.

Fatty Acids↗