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.     

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.     

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.     

Succession and phylogenetic profile of eukaryotic communities in rice straw incorporated into a rice field: Estimation by PCR-DGGE and sequence analyses

Abstract

Succession and the phylogenetic profile of eukaryotic communities associated with rice straw decomposition in a rice field were studied using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis followed by 18S rDNA sequencing. Nylon mesh bags containing leaf sheaths or blades were buried in the plow layer of a rice field under flooded conditions after transplanting (Experiment 1) and under drained conditions during the off-crop season (Experiment 2). In addition, rice straw samples in Experiment 2 were taken out before plowing in spring and re-placed in the rice field under flooded conditions at transplanting. Statistical analyses based on DGGE patterns showed that eukaryotic communities were divided into two groups, namely group A before the placement in soil, after the mid-season drainage in Experiment 1 and under the drained conditions in Experiment 2 and group B before the mid-season drainage in Experiment 1 and under the flooded conditions in Experiment 2. Based on the sequence analysis of DGGE bands, which characterized the eukaryotic communities, succession of the communities was revealed, that is, most of the bands in group A were closely related to fungi, whereas the bands in group B were closely related to protozoa. These results indicated that eukaryotic communities associated with rice straw decomposition in the rice field are mainly affected by soil conditions, such as oxic or reduced conditions, irrespective of rice straw parts (leaf sheaths and blades).     

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.     

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.     

Modeling a long-term effect of rice straw incorporation on SOC content and grain yield in rice field

ABSTRACT

The long-term effects of rice straw incorporation on soil organic carbon (SOC) content and rice yield were evaluated from rice cultivation with different treatments: no rice straw (control), rice straw (RS), and rice straw compost (RSC) as a main-plots; five levels of nitrogen (N) fertilizer application: 0, 100, 150, 200, and 250 of N (kg ha^?1) as a sub-plots. The denitrification and decomposition (DNDC) model was employed to simulate changes in SOC content and rice grain yield over 35 years. Additionally, scenario analysis on continuous or discontinuous RS incorporation in rice fields was conducted using the DNDC model. The long-term results indicated that RS and RSC treatments played a crucial role in increasing grain yields by 9% and 11% due to the increased SOC contents compared to control treatment. The validated DNDC model on SOC contents and yields showed a good agreement between the observed and simulated values based on the normalized root mean square errors. The model predicted a rapid decline of SOC contents without RS incorporation. Results suggested that incorporating rice straw or amending manure to paddy soils is a preferred practice for maintaining SOC contents.     

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。     

Soil microbial community responses to Bt transgenic rice residue decomposition in a paddy field

Purpose

Genetic modifications (GM) of commercial crops offer many benefits. However, microbial-mediated decomposition might be affected by GM crop residues in agricultural ecosystems. The objective of this study was to assess the possible impacts of cry1Ab gene transformation of rice on soil microbial community composition associated with residue decomposition in the paddy field under intensive rice cultivation.

Materials and methods

A 276-day field trial was set up as a completely randomized design for two types of rice residues, KMD (Bt) and Xiushui 11 (non-Bt parental variety) in triplicate by conventional intensive rice cropping system. The litterbag method was used in the rice residue decomposition and a total of 120 straw and root litterbags were either placed on the soil surface or buried at 10 cm depth in the field on Dec. 24, 2005. The litterbags were sampled periodically and their soil bacterial and fungal communities were determined by terminal restriction fragment length polymorphism (T-RFLP). The additive main effects with multiplicative interaction (AMMI) model were performed for the analysis of T-RFLP on binary variables of peak presence (presence/absence). The analysis of variance and linear regressions were performed for analysis of AMMI data.

Results and discussion

Total AMMI model analysis revealed that microbial community composition in the litterbags was affected by temporal and spatial factors. Compared with the non-Bt rice residue treatment, Bt rice straw had no significant effects on the soil bacterial and fungal community composition during the study period, regardless of the litterbags being placed on the surface or buried in the soil. There were no significant differences in the bacterial community composition profiles in root decomposition between Bt transgenic and non-Bt varieties. However, significant differences in soil fungal community composition between the buried Bt and non-Bt rice roots were observed in soils sampled on days 31, 68, and 137, indicating that Bt roots incorporated into paddy soil may affect soil fungal community during the initial stage of their decomposition.

Conclusions

There were some significant differences in fungal community composition between Bt rice root and non-Bt root treatments at the early stage of root decomposition in the paddy field. It is important that, before Bt rice is released for commercial production, more research should be conducted to evaluate the ecological effects of the Bt rice residues returned to paddy field upon grain harvesting.     

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.     

不同耕作方式下覆草旱作稻田土壤肥力的特征

通过始建于2003年中国南方季节性干旱区(江西省余江县)的双季稻田定位试验,于2005～2007年研究了水稻覆草旱作和免耕覆草旱作对稻田土壤理化性质和生物学性质的影响。结果表明,覆草旱作、免耕覆草旱作的耕层土壤容重和总孔隙度与常规水作的差异不显著。与常规水作相比,免耕覆草旱作显著提高土壤有机质、全氮、碱解氮和土壤基础呼吸;与常规水作相比,覆草旱作和免耕覆草旱作均显著提高土壤微生物生物量碳含量、脲酶和蔗糖酶活性。由此可知,覆草旱作和免耕覆草旱作可以作为该区积极推行的具有培肥地力作用的节水型稻作栽培模式。     

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。     

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.     

Decomposition of Bacillus thuringiensis (Bt) transgenic rice residues (straw and roots) in paddy fields

Background, aim, and scope  

Genetic modification of commercial crops may affect their decomposition and nutrient cycling processes in agricultural ecosystems. Intensive rice cultivation under partially submerged conditions (paddy rice) is an important and widespread cropping system, particularly in the tropics, yet there is little data on the decomposition of Bt rice residue under field conditions. We investigated straw and root decomposition of rice modified to express the Cry1Ab protein of Bacillus thuringiensis (Bt) to kill lepidopteran pests, compared with a parental non-Bt isoline. The objective of this study was to assess the possible impacts of cry gene transformation of rice on residue decomposition under intensive rice cultivation with long period of submergence.     

稻草还田条件下水田和旱地土壤有机碳矿化特征与差异

采用14C示踪技术,通过100 d的原状土柱室内模拟试验,得出以下研究结果:培养100 d后,有34.74%(水田覆盖)、17.85%(水田翻埋)、35.68%(旱地覆盖)和36.06%(旱地翻埋)的稻草碳被矿化,水田和旱地土壤分别有0.99%～1.17%和2.25%～2.53%的原有有机碳被矿化。土地利用和稻草还田方式及两因素的交互作用,对添加稻草碳的矿化速率和累积矿化率均有显著影响(p<0.01),但对于土壤原有有机碳的矿化速率和累积矿化量,只有土地利用方式对其有显著影响(p<0.01);添加稻草后,土壤总累积矿化量没有发生显著变化(旱地翻埋除外),因为稻草还田抑制了土壤原有有机碳的降解,使100 d的累积矿化量相对于各自对照减少了13.95%(水田覆盖)、15.68%(水田翻埋)、11.04%(旱地覆盖)和3.34%(旱地翻埋)。水田翻埋和旱地覆盖是稻草资源合理利用的较好方式,更有利于土壤有机碳的积累;添加的稻草碳和土壤原有有机碳在水田的矿化速率均显著低于旱地,是水田有机碳含量通常高于同一景观单元旱地的主要原因之一。     

Effect of the long-term application of organic matter on soil carbon accumulation and GHG emissions from a rice paddy field in a cool-temperate region,Japan. -I. Comparison of rice straw and rice straw compost -

ABSTRACT

The influence of the long-term combination of rice straw removal and rice straw compost application on methane (CH₄) and nitrous oxide (N₂O) emissions and soil carbon accumulation in rice paddy fields was clarified. In each of the initial and continuous application fields (3 and 39?51 years, respectively), three plots with different applications of organic matter were established, namely, rice straw application (RS), rice straw compost application (SC) and no application (NA) plots, and soil carbon storage (0?15 cm), rice grain yield and CH₄ and N₂O fluxes were measured for three years. The soil carbon sequestration rate by the organic matter application was higher in the SC plot than in the RS plot for both the initial and continuous application fields, and it was lower in the continuous application field than in the initial application field. The rice grain yield in the SC plot was significantly higher than those in the other plots in both the initial and continuous application fields. Cumulative CH₄ emissions followed the order of the NA plot < the SC plot < the RS plot for both the initial and continuous application fields. The effect of the organic matter application on the N₂O emissions was not clear. In both the initial and continuous application fields, the increase in CH₄ emission by the rice straw application exceeded the soil carbon sequestration rate, and the change in the net greenhouse gas (GHG) balance calculated by the difference between them was a positive, indicating a net increase in the GHG emissions. However, the change in the GHG balance by the rice straw compost application showed negative (mitigating GHG emissions) for the initial application field, whereas it showed positive for the continuous application field. Although the mitigation effect on the GHG emissions by the combination of the rice straw removal and rice straw compost application was reduced by 21% after 39 years long-term application, it is suggested that the combination treatment is a sustainable management that can mitigate GHG emissions and improve crop productivity.     

Changes in natural 15N abundance in paddy soils under different,long-term soil management regimes in the Tohoku region of Japan

Abstract

Long-term temporal changes in natural ¹⁵N abundance (δ¹⁵N value) in paddy soils from long-term field experiments with livestock manure and rice straw composts, and in the composts used for the experiments, were investigated. These field experiments using livestock manure and rice straw composts had been conducted since 1973 and 1968, respectively. In both experiments, control plots to which no compost had been applied were also maintained. The δ¹⁵N values of livestock manure compost reflected the composting method. Composting period had no significant effect on the δ¹⁵N value of rice straw compost. The δ¹⁵N values increased in soils to which livestock manure compost was successively applied, and tended to decrease in soils without compost. In soils to which rice straw compost was successively applied, the δ¹⁵N values of the soils remained constant. Conversely, δ¹⁵N values in soils without rice straw compost decreased. The downward trend in δ¹⁵N values observed in soils to which compost and chemical N fertilizer were not applied could be attributed to the natural input of N, which had a lower δ¹⁵N value than the soils. Thus, the transition of the δ¹⁵N values in soils observed in long-term paddy field experiments indicated that the δ¹⁵N values of paddy soils could be affected by natural N input in addition to extraneous N that was applied in the form of chemical N fertilizers and organic materials.     

秸秆施用后土壤溶解性有机质的动态变化

采用室内培养方法研究了水稻秸秆腐解对土壤溶解性有机质（Dissolved Organic Matter,DOM）含量及其化学组成的动态影响。结果表明,秸秆腐解的前7 d显著增加了土壤溶解性有机碳（DOC）含量,7 d后则无明显影响;同时,秸秆腐解增加了土壤中溶解性糖（DS）、溶解性酚酸（DP）以及芳香族化合物含量。随着腐解时间的延长,溶解性糖在DOC中所占比例下降,而芳香族化合物逐渐上升,表明秸秆腐解不同阶段DOM的化学组成发生了变化。溶解性总氮（TDN）的变化表明,秸秆腐解增加土壤氮素的固定。