Cyanobacterial communities of rice straw left on the soil surface of a paddy field

To estimate diversity, seasonal variation, and phylogeny of the cyanobacterial communities in rice straw placed in nylon mesh bags and left on the soil surface of a paddy field, total DNA was extracted from straw, amplified by polymerase chain reaction targeting 16S rRNA genes of cyanobacteria, and the amplicons were separated by denaturing gradient gel electrophoresis (DGGE). These DGGE bands were sequenced. The paddy field was under flooded condition after transplanting of rice (Experiment 1) and under drained conditions after harvest (Experiment 2). The residual samples on the soil surface under upland conditions were collected just before spring plowing and were placed again on the soil surface after transplanting under flooded conditions. DGGE band patterns of cyanobacterial communities of rice straw were different under drained conditions, under flooded conditions when fresh rice straw samples were placed (Experiment 1), and under flooded conditions when residual rice straw samples were replaced (Experiment 2), indicating that the communities were influenced by both water regime of the paddy field and the degree of the rice straw decomposition. Sequence analysis of DGGE bands indicated that most of the cyanobacteria in rice straw on the soil surface in the paddy field were filamentous members belonging to Subsections III and IV. Filamentous cyanobacterial cells were observed in rice straw under flooded conditions by epifluorescence microscopy.     

Eukaryotic communities associated with the decomposition of rice straw compost in a Japanese rice paddy field estimated by DGGE analysis

To estimate the succession and phylogenetic composition of the eukaryotic communities responsible for the decomposition of rice straw compost under flooded conditions during the cultivation period of paddy rice, denaturing gradient gel electrophoresis (DGGE) analysis targeting 18S rDNA followed by sequencing was conducted in a Japanese paddy field. The eukaryotic communities in rice straw compost incorporated into the flooded paddy field were influenced by the mid-season drainage and mainly composed of fungi (Ascomycota, Zygomycota, and Chytridiomycota) and protozoa (Ciliophora, Euglyphida, and Dactylopodida), most of which existed continuously during the cultivation period of paddy rice. The results indicated that these eukaryotic members were associated with the decomposition of rice straw compost in paddy field soil directly or indirectly.     

Bacterial Communities Responsible for the Decomposition of Rice Straw Compost in a Japanese Rice Paddy Field Estimated by DGGE Analysis of Amplified 16S rDNA and 16S rRNA Fragments

To estimate the succession and phylogenetic composition of the bacterial communities responsible for the decomposition of rice straw compost under flooded conditions during the cultivation period of paddy rice, denaturing gradient gel electrophoresis (DGGE) analyses targeting 16S rDNA and 16S rRNA, followed by sequencing were conducted in a Japanese paddy field. The DGGE bands of the bacterial communities in the rice straw compost were significantly more numerous in the DNA samples than in the RNA samples. Although the band number of the DNA samples was almost constant throughout the period, RNA samples showed fewer DGGE bands after mid-season drainage than before it. Thus, about 81% of the bacteria present in rice straw compost were considered to be metabolically "active" before mid-season drainage and about 62% after it. The changes in the DGGE patterns of bacterial DNA and RNA before and after mid-season drainage, respectively, were also revealed by cluster analysis and principal component analysis of the DGGE patterns. These results indicated that the bacterial communities of rice straw compost incorporated into flooded paddy fields changed gradually along with the decomposition, except for the period of mid-season drainage, but that they were influenced by mid-season drainage. Members of β-, γ- and δ-Proteobacteria, Cytophaga-Flavobacterium-Bacteroides (CFB) group, Chlorobia, Verrucomicrobia, Chloroflexi, Spirochaetes, Firmicutes (clostridia) and Actinobacteria were present during the decomposition of rice straw compost. Characteristic "active" bacteria among them were as follows: Clostridium, Acinetobacter (γ-Proteobacteria) and β-Proteobacteria before mid-season drainage, Flavobacterium, Chondromyces , Chlorflexi and δ-Proteobacteria after mid-season drainage, and Spirochaeta and myxobacteria throughout the period.     

Succession and Phylogenetic Profile of Eubacterial Communities in Rice Straw Incorporated into a Rice Field: Estimation by PCR-DGGE Analysis

PCR-DGGE analysis followed by sequencing was conducted to estimate the succession and the phylogenetic profile of the eubacterial communities responsible for the decomposition of rice straw (RS) that was incorporated into a rice field. Leaf sheath and leaf blade parts were separately put in nylon mesh bags, and were placed in the rice field soil under drained conditions during the off-cropping season and under flooded conditions after transplantation of rice. In addition, RS samples that had been placed under drained conditions in the off-cropping season were placed again in flooded rice field soil after transplantation of rice. DGGE patterns of the bacterial communities in the RS samples were classified into two groups, namely leaf sheaths and leaf blades. Principal component analysis of the DGGE patterns revealed the succession along with the duration of placement. These results indicated that the RS part (sheath or blade) mainly determined the structure of the bacterial communities responsible for the RS decomposition, followed by the duration of placement. Sequence analysis of the characteristic DGGE bands indicated that most of the closest relatives associated with the bands belonged to α-, β-, γ-, and δ-Proteobacteria, CFB group, and Spirochaetes. Some bands were closely related to Acidobacteria and Verrucomicrobia. CFB members and α-Proteobacteria predominated commonly in both RS parts, while γ- and δ-Proteobacteria, and Spirochaetes and β-Proteobacteria specifically colonized sheath and blade parts, respectively. In addition, Proteobacteria and CFB members characterized the differences in the bacterial communities under flooded or drained conditions. These results suggest that Proteobacteria, CFB group, and Spirochaetes were responsible for RS decomposition in rice field soil under both flooded and drained conditions.     

Microbial communities responsible for the decomposition of rice straw compost in a Japanese rice paddy field determined by phospholipid fatty acid (PLFA) analysis

To identify the microbial communities responsible for the decomposition of rice straw compost in soil during the rice cultivation period, phospholipid fatty acid (PLFA) composition of rice straw compost was determined by periodically sampling the compost from a Japanese rice field under flooded conditions. About 21% of the compost was decomposed within a period of 3 months. The total amount of PLFAs, as an indicator of microbial biomass, was significantly lower under drained conditions than under flooded conditions and was relatively constant during the flooding period. This indicates that the microbial biomass in the compost samples did not increase during the gradual decomposition of rice straw compost under flooded conditions. The proportion of branched-chain PLFAs (biomarker of Grampositive and anaerobic Gram-negative bacteria) slightly decreased during the early period after placement, and increased gradually afterwards. Among the branched-chain PLFAs, i15:0, ail5:0, i16:0 and i17:0 PLFAs predominated and their proportions increased gradually except for i16:0. The proportion of straight mono-unsaturated PLFAs (biomarker of Gramnegative bacteria) was almost constant throughout the period, and 18:1ω9 and 18:1ω7 PLFAs predominated. The proportion of straight poly-unsaturated PLFAs as a biomarker of eukaryotes including fungi was also constant throughout the period, except for a decrease under drained conditions. Straight poly-unsaturated PLFAs consisted mainly of 18:2ω6c PLFA. Therefore, these results suggest that the proportions of Gram-positive and anaerobic Gram-negative bacteria increased during the decomposition of rice straw compost in flooded paddy field. Statistical analyses enabled to divide PLFA patterns of microbiota in the rice straw compost into two groups, one group consisting of rice straw compost samples collected before mid-season drainage and the other of samples collected after mid-season drainage. Small squared distances among samples in cluster analysis indicated that the community structure of microbiota was similar to each other as a whole. These results suggest that the microbial communities changed gradually during the period of placement, and that mid-season drainage may have affected the community structure of microbiota. Principal component analysis of the PLFA composition suggested that the succession of microbiota along with the decomposition in flooded soil was similar between rice straw compost and rice straw and that the changes in the community structure during the decomposition in flooded soil were more conspicuous for rice straw than for rice straw compost.     

Community structure of bacteria and fungi responsible for rice straw decomposition in a paddy field estimated by PCR-RFLP analysis

Rice straw including leaf sheaths and blades put in nylon mesh bags was placed in the plow layer of a Japanese paddy field after harvest under upland conditions and after transplanting of rice seedlings under flooded conditions. In addition, rice straw that was decomposed under the upland conditions during the off-crop season in winter was placed again in soil at the time of transplanting. The materials were collected periodically to analyze the community structure of the bacteria and fungi responsible for rice straw decomposition by PCR-RFLP analysis. The PCR products with 27f and 1492r primers designed for bacterial 16S rDNA and with EF3 and EF4 primers designed for fungal 18S rDNA were digested with four restriction endonucleases (Hinf I, Sau3A I, Hae III, EeoR I). Bacterial communities in the decomposing rice straw were different from each other between upland and flooded conditions, between leaf sheaths and blades, and between straw samples with and without decomposition under upland conditions during the off-crop season. Fungal communities in the decomposing rice straw were also different between the leaf sheaths and blades under upland soil conditions. Score plots of bacterial and fungal communities in the principal component analysis were separated from the plot of the straw materials along with the duration of the placement, indicating the succession of bacterial and fungal communities in decomposing rice straw with time.     

Microbial community responsible for the decomposition of rice straw in a paddy field: estimation by phospholipid fatty acid analysis

To estimate the microbial communities responsible for rice straw decomposition in paddy field, phospholipid fatty acid (PLFA) composition of leaf sheaths and blades was analyzed during the decomposition of both residues under upland conditions after harvest and under flooded conditions at the time of transplanting of rice plants. In addition, rice straw that had been placed in the field under upland conditions (November to April) was taken out in spring, and placed again in the same field under flooded conditions at the time of transplanting. High proportions of the branched-chain PLFAs were observed under flooded conditions (June to September); the proportions of straight mono-unsaturated and straight poly-unsaturated PLFAs were high under upland conditions in the winter season for 4 months. The dominant PLFAs in straight mono-unsaturated, straight poly-unsaturated and branched-chain PLFA groups were 18:19, 18:17 and 16:17c, 18:26c and i15:0, i17:0 and ai15:0, respectively, under both upland and flooded conditions. These findings indicated the important roles of Gram-negative bacteria and fungi under upland conditions and of Gram-positive bacteria and anaerobic Gram-negative bacteria under flooded conditions. Cluster analysis of PLFA composition showed the difference of community structure of microbiota in rice straw between upland and flooded conditions. In addition principal component analysis revealed the difference between leaf sheaths and blades under upland conditions and indicated that the content of straight unsaturated PLFAs (sheaths > blades) characterized their community structures.     

Molecular characterization of methane-oxidizing bacteria associated with rice straw decomposition in a rice field

Abstract

Methane-oxidizing bacteria (MOB) are crucial to the reduction of CH₄ emitted to the atmosphere. However, it is unclear how MOB in rice straw are affected by straw decomposition processes. In a Japanese rice field, a year-round experiment was set up to study the effects of agricultural practice (rice cultivation/winter fallow), straw parts (leaf sheath/blade) and the site of straw placement (plow layer/soil surface) on MOB communities in rice straw using denaturing gradient gel electrophoresis (DGGE) and DNA sequencing analyses of key MOB functional genes (pmoA and amoA). Thirty-eight different DGGE bands were observed over the entire investigation period. Principal component analysis of DGGE pattern suggested that agricultural practice is the key factor regulating the MOB communities. Sequencing of dominant DGGE bands showed that: (1) during the rice cultivation period, methanotrophs (particularly type I methanotrophs) dominated the MOB community, (2) during the winter fallow season both type I and type II methanotrophs were dominant in sheath segments placed both on the soil surface and in the plow layer, whereas ammonia oxidizers seemed to dominate blade segments placed in the plow layer. Alignment of diagnostic amino acid sequences of MOB suggested the presence of novel ammonia oxidizers in rice straw in rice fields.     

Flooding effects on soil phenol oxidase activity and phenol release during rice straw decomposition

Phenol oxidase (Pox) plays a key role in soil C cycle and its presence may affect soil C mineralization during crop residue decomposition. To examine soil dynamics and relationships between Pox, phenols, Fe²⁺, and C mineralization, we designed a 53‐d laboratory experiment conducted with and without rice straw addition and under non‐flooded and flooded conditions. The results demonstrate that rice straw can indeed decompose faster under flooded conditions. The addition of rice straw significantly increased soil Pox activity (up to 15‐fold), but only under flooded conditions. Rice straw application increased alkali extractable phenol (AEP) concentration by 129% at day 4. However, flooded conditions reduced soil AEP by 61% and 49% at day 53 with and without rice straw application, respectively. Phenol oxidase activity was positively correlated with dissolved organic C and Fe²⁺, while negatively related to AEP, which itself was positively correlated with C mineralization (i.e., CO₂ emission rates). Also, all relationships between soil Pox, AEP, Fe²⁺, and C were stronger under flooded conditions. We therefore conclude that flooded conditions in paddy soil may promote straw decomposition as a result of the stimulation of Pox activity and phenol decomposition.     

Effect of Application of Rice Straw and Compost on the Bacterial Communities Associated with Moina sp. in the Floodwater of a Paddy Soil Microcosm: Estimation Based on DGGE Pattern and Sequence Analyses

Bacterial communities associated with Moina sp. in the floodwater of a paddy field microcosm were examined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA. Eighteen out of 20 eubacterial DGGE bands were sequenced. The associated eubacterial communities mainly consisted of the Cytophaga-Flavobacterium-Bacteroides group and α-, β-, and γ-Proteobacterial groups, irrespective of the application of rice straw and rice straw compost. The effect of the application of rice straw and compost on the communities was not appreciable, compared with host specificity. An uncultured Cytophagales bacterium was estimated to be specifically associated with Moina sp. Presence of bacteria that are specific to rice straw treatment was also estimated.     

广谱抗真菌蛋白转基因水稻秸秆模拟还田对土壤真菌群落结构的影响

为探讨广谱抗真菌蛋白转基因水稻秸秆降解对土壤真菌群落结构的影响,本文在室温条件下进行田间秸秆还田模拟试验,设不添加秸秆(S)、添加转基因水稻‘转品1’秸秆(S-Z1)、添加转基因水稻‘转品8’秸秆(S-Z8)、添加非转基因水稻‘七丝软粘’秸秆(S-CK)4个土壤处理,采用传统的平板计数法和变性梯度凝胶电泳(denatured gradient gel electrophoresis,DGGE)技术,分析广谱抗真菌蛋白转基因水稻秸秆模拟还田过程中土壤可培养真菌数和土壤真菌群落的变化情况。平板计数结果表明,在秸秆降解的第40 d,转基因水稻秸秆处理(S-Z1、S-Z8)与非转基因水稻秸秆处理(S-CK)土壤之间的可培养真菌数差异显著,但秸秆降解中后期(50~90 d),S-Z1、S-Z8和S-CK之间土壤可培养真菌数的差异均不显著。真菌18S r RNA的PCR-DGGE图谱显示,S-Z1、S-Z8和S-CK在秸秆降解过程中没有显著不同的条带出现,仅有个别条带在亮度上存在差异。DGGE图谱条带多样性分析结果表明,在秸秆降解的个别时间段,S-Z1、S-Z8和S-CK之间在丰富度和Shannon-Wiener多样性指数上存在显著差异,而在秸秆降解的整个过程均匀度指数差异均不显著。对DGGE主要条带和差异性条带进行克隆测序后发现,子囊菌占最大比重,其次为担子菌、壶菌,而在转基因和非转基因土壤处理间亮度上存在差异的条带属于子囊菌。以上研究结果表明,广谱抗真菌蛋白转基因水稻秸秆降解对土壤真菌群落结构的影响是短暂的、不持续的。     

Comparison of community structures of microbiota at main habitats in rice field ecosystems based on phospholipid fatty acid analysis

The present study compares the community structures of microbiota at different habitats in Japanese rice fields by comparing their phospholipid fatty acid (PLFA) compositions to understand the contribution of different habitats to microbiological diversity. The data were collected from four neighboring rice fields. Comparison was made for the PLFA compositions extracted from the floodwater, percolating water, rice soils under flooded and drained conditions, rice straw (RS) placed in flooded and drained rice soils, RS in the composting process, and RS compost placed in a flooded rice field. Average amounts of PLFAs were 33 μg L⁻¹ in the floodwater, 17.1 μg L⁻¹ in the percolating water from plow layers, 34.6 μg L⁻¹ in the percolating water from subsoil layers, 108 μg g⁻¹ dry weight basis (dw) in flooded rice soils, 382 μg g⁻¹ dw in RS materials, 2,510 μg g⁻¹ dw in RS composts, 2,850 μg g⁻¹ dw in RS composts after application to a flooded rice soil, 222 μg g⁻¹ wet weight basis (ww) in RS in drained rice soils, and 284 μg g⁻¹ ww in RS in flooded rice soils. The total amount of PLFAs to the soil depth of 10 cm was estimated to be about 12 g m⁻². The PLFA compositions were different from each other depending on the habitats. Rice soils were characterized by the predominance of actinomycetes and Gram-positive bacteria in comparison with the other habitats. In contrast, the microbial communities in the floodwater and percolating water were characterized by the predominance of Gram-negative bacteria and eukaryotes (presumably algae), and Gram-negative bacteria, respectively. The microbial community of RS materials was dominated by fungi. Gram-positive bacteria became predominant in RS after application to flooded rice soils, while RS placed in a drained rice field after harvesting rice was characterized by the predominance of Gram-negative bacteria and fungi. The community structures at respective habitats were stable and specific, irrespective of the season of sampling and the duration of decomposition of RS.     

Comparison of bacterial community structures at main habitats in paddy field ecosystem based on DGGE analysis

Bacterial communities at different habitats in a Japanese paddy field ecosystem were compared to understand the bacterial world in the ecosystem as a whole by analyzing data of the denaturing gradient gel electrophoresis (DGGE) band patterns and the sequenced DGGE bands. The habitats were floodwater, percolating water, microcrustacean inhabiting in floodwater, plow layer soil, rice roots, rice straw and rice straw compost incorporated in soil, rice straw placed on the soil surface, plant residues in paddy fields, and rice straw under composting process. Phylotype (band) richness, diversity, evenness, and stability of the bacterial communities at the respective habitats were evaluated based on the DGGE profile data. Phylotype richness was greater near plant residues, rice straw buried in soil and rice straw placed on soil surface, while it was smaller at microcrustacean and rice straw compost buried in soil. The samples from plow layer soil and rice straw compost buried in soil showed considerably higher index values for diversity, evenness, and stability, while those from rice straw placed on soil surface and microcrustacean had lower values of the indices than other habitats. Sequences of totally 250 DGGE bands were assigned to phyla or classes. Distribution of bacterial members to phylogenetic taxa was different among the respective habitats. Inhabitants in plow layer soil were most widely distributed among the groups (nine phyla: Proteobacteria, Chloroflexi, Chlorobi, Verrucomicrobia, Acidobacteria, Nitrospira, candidate division OP10, Cyanobacteria, and Actinobacteria), while those in floodwater and microcrustacean were restricted to only three phyla (Proteobacteria, Bacteroidetes, and Actinobacteria). Proteobacteria and Bacteroidetes were found at all the habitats and the habitats except for plow layer soil, respectively, whereas abundant members belonged to Chloroflexi and Actinobacteria in plow layer soil. “Comprehensive mapping” of DGGE fragments was conducted by principal component analysis based on evolutionary distances of the fragments to 202 reference bacterial strains to overview phylogenetic relationships of bacterial members among the respective habitats. The score plots with the first and second principal components distinctly characterized bacterial members at the respective habitats, and the similarity between the respective communities was clearly demonstrated. Overall, bacterial communities at the respective habitats were distinct and different in the diversity and stability to each other, which may have contributed to the diversity of overall bacterial communities in the paddy field ecosystem.     

Community structure of methanogenic archaea in paddy field soil under double cropping (rice-wheat)

Community structure of methanogenic archaea in paddy field soil under double cropping (rice [Oryza sativa L.] and wheat [Triticum aestivum L.]) was studied by the denaturing gradient gel electrophoresis (DGGE) method. Soil samples under flooded and upland conditions were collected 7 and 6 times, respectively, from two paddy fields throughout a year, and two primer sets, 0357F-GC/0691R and newly designed 1106F-GC/1378R, were used for DGGE analysis. The 25 and 29 different bands were observed on the DGGE gels with the primers 0357F-GC/0691R and 1106F-GC/1378R, respectively. DGGE band patterns of the methanogenic archaeal community were stable throughout a year including the cultivation periods of rice under flooded conditions and of wheat under upland conditions. Cluster analysis and principal component analysis suggested that the difference in the soil type (sampling region) largely influenced the community structures of methanogenic archaea in paddy field soil, while the effects of sampling period and different fertilizer treatments on them were small. Most of the sequences obtained from the DGGE bands were closely related to Methanomicrobiales, Methanosarcinaceae, Methanosaetaceae and Rice cluster-I.     

接种菌剂腐熟稻草育秧基质提高机插稻秧苗素质及产量

为探明稻草育秧基质在机插稻生产中的应用效果,该文以水稻土（CK）为对照,研究了接种自制腐秆菌剂的稻草基质（T1）、不接种腐秆菌剂的稻草基质（T2）2种基质理化性状及其对机插稻秧苗素质、机插质量及产量形成的影响。结果表明,T1、T2容重显著低于CK,含水量、孔隙度（通气孔隙度和持水孔隙度）和养分含量则显著高于CK;接种腐秆菌剂改善了稻草育秧基质的理化性状,可降低基质有机质含量、提高速效养分浓度及减小碳氮比（C/N）。与T2和CK相比,T1培育出的秧苗综合素质较好、机插质量高,有利于促进大田分蘖早生快发,同时增加了各时期叶面积指数、干物质质量及N、P、K吸收量,可形成较多的有效穗和充足的总颖花量,最终促进水稻高产的形成。T1产量比CK提高了4.37%,增产效果显著。可见,接种腐秆菌剂的稻草基质能满足水稻秧苗正常生长,与当前机插技术兼容性强,有利于提高机插稻产量及稻草的资源化利用,是一种较为理想的机插稻育秧基质。     

淹水条件下FACE处理的水稻以及小麦秸秆的分解及产物

Winter wheat and rice straw produced under ambient and elevated CO2 in a China rice-wheat rotation free-air CO2 enrichment (FACE) experiment was mixed with a paddy soil at a rate of 10 g kg-1 (air-dried), and the mixture was incubated under flooded conditions at 25 ℃ to examine the differences in decomposition as well as the products of crop residues produced under elevated CO2. Results showed that the C/N ratio and the amount of soluble fraction in the amended rice straw grown under elevated CO2 (FR) were 9.8% and 73.1% greater, and the cellulose and lignin were 16.0% and 9.9% lesser than those of the amended rice straw grown under ambient CO2 (AR), respectively. Compared with those of the AR treatment, the CO2-C and CH4-C emissions in the FR treatment for 25 d were increased by 7.9% and 25.0%, respectively; a higher ratio of CH4 to CO2 emissions induced by straw in the FR treatment was also observed. In contrast, in the treatments with winter wheat straw, the CO2-C and CH4-C productions, the ratio of straw-induced CH4 to CO2 emissions, and the straw composition were not significantly affected by elevated CO2, except for an 8.0% decrease in total N and a 9.7% increase in C/N ratio in the wheat straw grown under elevated CO2. Correlation analysis showed that the net CO2-C and CH4-C emissions from straw and the ratio of straw-induced CH4 to CO2 emissions were all exponentially related to the amount of soluble fraction in the amended straw (P < 0.05). These indicated that under flooded conditions, the turnover and CH4 emission from crop straw incorporated into soil were dependent on the effect of elevated CO2 on straw composition, and varied with crop species. Incorporation of rice straw grown under elevated CO2 would stimulate CH4 emission from flooded rice fields, whereas winter wheat straw grown under elevated CO2 had no effect on CH4 emission.     

Effects of rice‐straw and phosphorus application on production and emission of methane from tropical rice soil

Rice‐straw amendment increased methane production by 3‐fold over that of unamended control. Application of P as single superphosphate at 100 μg (g soil)^–1 inhibited methane (CH₄) production distinctly in flooded alluvial rice soil, in the absence more than in the presence of rice straw. CH₄ emission from rice plants (cv. IR72) from alluvial soil treated with single superphosphate as basal application, in the presence and absence of rice straw, and held under non‐flooded and flooded conditions showed distinct variations. CH₄ emission from non‐flooded soil amended with rice straw was high and almost similar to that of flooded soil without rice‐straw amendment. The cumulative CH₄ efflux was highest (1041 mg pot^–1) in rice‐straw‐amended flooded soil. Appreciable methanogenic reactions in rice‐straw‐amended soils were evident under both flooded and non‐flooded conditions. Rice‐straw application substantially altered the balance between total aerobic and anaerobic microorganisms even in non‐flooded soil. The mitigating effects of single‐superphosphate application or low‐moisture regime on CH₄ production and emission were almost nullified due to enhanced activities of methanogenic archaea in the presence of rice straw.     

Bacterial communities in manganese nodules in rice field subsoils: Estimation using PCR-DGGE and sequencing analyses

Abstract

The phylogenetic positions of bacterial communities in manganese (Mn) nodules from subsoils of two Japanese rice fields were estimated using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis followed by sequencing of 16S rDNA. The DGGE band patterns and sequencing analysis of characteristic DGGE bands revealed that the bacterial communities in Mn nodules were markedly different from those in the plow layer and subsoils. Three out of four common bands found in Mn nodules from two sites corresponded to Deltaproteobacteria and were characterized as sulfate-reducing and iron-reducing bacteria. The other DGGE bands of Mn nodules corresponded to sulfate and iron reducers (Deltaproteobacteria), methane-oxidizing bacteria (Gamma and Alphaproteobacteria), nitrite-oxidizing bacteria (Nitrospirae) and Actinobacteria. In addition, some DGGE bands of Mn nodules showed no clear affiliation to any known bacteria. The present study indicates that members involved in the reduction of Mn nodules dominate the bacterial communities in Mn nodules in rice field subsoils.     

秸秆覆盖旱作对稻田甲烷排放和水稻产量的影响

为较全面评价秸秆覆盖旱作水稻栽培模式的生态意义,采用田间试验研究了常规淹水（F）、秸秆覆盖旱作（NF-M）和无覆盖旱作（NF-ZM）3种栽培模式稻田甲烷排放、水稻产量及土壤养分的变化规律。结果表明：3种水稻栽培模式的甲烷排放均集中在水稻生育期的前20d;在水稻生育期内,秸秆覆盖旱作稻田甲烷的排放总量为11.12g·m^-2,显著高于常规淹水稻田的7.78g·m^-2和无覆盖旱作稻田的4.23g·m^-2。秸秆覆盖旱作稻田的水稻产量为8.60t·hm^-2,与常规淹水处理没有显著差异,但二者均显著高于无秸秆覆盖旱作处理的6.78t·hm^-2;与常规淹水处理相比,秸秆覆盖旱作还可以提高水稻单株生物量10g以上。秸秆覆盖旱作还可以显著提高稻田表层土壤有机质含量,维持和改善表层土壤养分状况,对实现农业可持续性有重要意义。因此,在水资源缺乏地区,秸秆覆盖旱作是一种值得考虑的替代传统淹水栽培的水稻栽培模式,同时秸秆覆盖旱作还田也是一种值得推广的稻田秸秆管理技术。