Modeling long-term transfers of radiocesium in farmland under different tillage and cover crop treatments.

The 2011 nuclear accident at Japan's Fukushima Daiichi Nuclear Power Plant (FDNPP) prompted inquiries about the long-term transfer of Cesium-137 (137Cs) from soil to agricultural plants. In this context, numerical modeling is particularly useful for the long-term evaluation of the consequences of agroecosystem contamination. Agricultural practices, such as tillage and cover cropping, play key roles in 137Cs recycling in agroecosystems. In this study, we used 10-year monitoring data to develop a dynamic model to predict 137Cs redistribution (via uptake, litterfall, translocation, and percolation) under different tillage (no-tillage, NT; rotary cultivation, RC; moldboard plow, MP) and cover crop (rye; hairy vetch; fallow weed) treatments. The verification exercise and assessment results indicated the model's reliability, as the temporal dynamics of predicted values agreed with observed values. Tillage significantly influenced the 137Cs distribution in soil, thereby decreasing plant uptake of 137Cs, whereas cover crop exerted a minimal effect on 137Cs cycling. Furthermore, while the 137Cs concentrations in soybean grain under RC and NT treatments were comparable 62 years after the FDNPP accident, the concentration under MP treatment remained consistently the lowest. Despite natural decay being the main cause of the decreased global 137Cs level in the agroecosystem, with minimal losses from percolation to deeper soil layers and soybean harvesting, adopting an appropriate tillage practice was shown to promote a long-term reduction of 137Cs concentration in crops. Finally, to improve the model's accuracy, further research should consider incorporating the effects of soil properties and extreme weather events on 137Cs flow into the model, as these factors are essential for realizing improved agroecosystem predictions.

Radiocesium distribution caused by tillage inversion affects the soil-to-crop transfer factor and translocation in agroecosystems.

This study reports the translocation of cesium-137 (137Cs) into deep soil layers, and the 137Cs transfer from soil to soybean in farmland under three tillage (no tillage, NT; rotary cultivation, RC; moldboard plow; MP) treatments and an undisturbed grassland (GL) at eight years after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident on 11 March 2011 in Japan. Tillage influences the 137Cs distribution in the 0-30 cm of soil; the distribution of 137Cs in the soil was uniform under RC and MP treatments, while in the grassland, most 137Cs was concentrated on the soil surface (0-2.5 cm). The center of vertical 137Cs radioactivity concentration (the thickness of the soil from surface which containing half of the 137Cs inventory) in GL was 5.5 cm, which was shallower than that in farmland (9.5 cm in NT, 13.6 cm in RC and 15.2 cm in MP). Hence, the total translocation distance of 137Cs 8 years after FDNPP accident showed the following trend: GL (2.4 cm) < NT (7.0 cm) < RC (10.0 cm) < MP (12.3 cm). Meanwhile, a significant positive correlation was observed between 137Cs radioactivity concentration and organic carbon and nitrogen content in the soil. However, the 137Cs radioactivity concentration in soybean grains was negatively correlated with the center of vertical 137Cs radioactivity concentration but positively correlated with the ratio of exchangeable 137Cs (ExCs) and K content in the soil. The ExCs/K and 137Cs distributions in the soil were combined into a statistical model to predict the 137Cs radioactivity concentration in soybean grain. The results revealed the magnitude of the impact of 137Cs distribution on the 137Cs transfer from soil to crop. The addition of the 137Cs distribution dramatically improved the accuracy of the prediction model of 137Cs radioactivity concentration in soybean.

Metabolome Analysis Identified Okaramines in the Soybean Rhizosphere as a Legacy of Hairy Vetch.

Inter-organismal communications below ground, such as plant-microbe interactions in the rhizosphere, affect plant growth. Metabolites are shown to play important roles in biological communication, but there still remain a large number of metabolites in soil to be uncovered. Metabolomics, a technique for the comprehensive analysis of metabolites in samples, may uncover the molecules that intermediate these interactions. We conducted a multivariate analysis using liquid chromatography (LC)-mass spectrometry (MS)-based untargeted metabolomics in several soil samples and also targeted metabolome analysis for the identification of the candidate compounds in soil. We identified okaramine A, B, and C in the rhizosphere soil of hairy vetch. Okaramines are indole alkaloids first identified in soybean pulp (okara) inoculated with Penicillium simplicissimum AK-40 and are insecticidal. Okaramine B was detected in the rhizosphere from an open field growing hairy vetch. Okaramine B was also detected in both bulk and rhizosphere soils of soybean grown following hairy vetch, but not detected in soils of soybean without hairy vetch growth. These results suggested that okaramines might be involved in indirect defense of plants against insects. To our knowledge, this is the first report of okaramines in the natural environment. Untargeted and targeted metabolomics would be useful to uncover the chemistry of the rhizosphere.

Temporal dynamics of 137Cs distribution in soil and soil-to-crop transfer factor under different tillage systems after the Fukushima Daiichi Nuclear Power Plant accident in Japan.

The accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) in Japan in 2011 released a large amount of radionuclides, primarily radiocesium-137 (137Cs; half-life: 30 years), resulting in long-term contamination of soil and consequently crops. Tillage is a common agricultural management practice that alters the vertical distribution of nutrients in the soil. However, the effect of tillage on 137Cs contamination in soil and crops over time remains unclear. In this study, we investigated the temporal changes in the vertical distribution of 137Cs in the soil, concentration of 137Cs in soybean and cover crops, and the transfer factor (TF) of 137Cs from the soil to crops under three tillage systems (rotary cultivation [RC], moldboard plow [MP], and no tillage [NT]; main factors) using three cover crops (hairy vetch, winter rye, and fallow weeds; side factors). The amount of 137Cs in the soil decreased exponentially with soil depth under the NT and RC treatments. By contrast, 137Cs showed uniform distribution at each soil depth tested under the MP treatment since 2012. The exchangeable 137Cs demonstrated a similar tendency as 137Cs. The 137Cs concentration in soybean (including grain and residue) and cover crops decreased exponentially with time. Consistently higher 137Cs concentration was observed in soybean grains under the NT treatment, suggesting that tillage continuously reduced the concentration of 137Cs in soybean over 7 years since the FDNPP accident. The TF of 137Cs from soil to soybean and cover crops decreased continuously over time; however, 137Cs concentration of soybean grain showed a positive linear correlation with its annual variation rate. Additionally, TF showed a positive logarithmic correlation with 137Cs relaxation depth in the soil. These results enhance our understanding of the long-term behavior and radioecology of 137Cs in agroecosystems in Japan since the radionuclide accident.

Physical properties, structure, and shape of radioactive Cs from the Fukushima Daiichi Nuclear Power Plant accident derived from soil, bamboo and shiitake mushroom measurements.

We conducted an elution experiment with contaminated soils using various aqueous reagent solutions and autoradiography measurements of contaminated bamboo shoots and shiitake mushrooms to determine the physical and chemical characteristics of radioactive Cs from the Fukushima Daiichi Nuclear Power Plant accident. Based on our study results and data in the literature, we conclude that the active Cs emitted by the accident fell to the ground as granular non-ionic materials. Therefore, they were not adsorbed or trapped by minerals in the soil, but instead physically adhere to the rough surfaces of the soil mineral particles. Granular Cs* can be transferred among media, such as soils and plants. The physical properties and dynamic behavior of the granular Cs* is expected to be helpful in considering methods for decontamination of soil, litter, and other media.

Isolation and molecular characterization of a multicellular cyanobacterium, Limnothrix/Pseudanabaena sp. strain ABRG5-3.

A cyanobacterium, semi-filamentous multicellular strain ABRG5-3, was isolated and its unique nature was characterized. This axenic strain formed colonies and was motile on an agarose plate. The 16S rRNA gene of ABRG5-3 exhibited similarities to those of the Limnothrix and Pseudanabaena strains, which are known as filamentous and nonheterocystous cyanobacteria. Peaks in absorbance for the accumulation of chlorophyll a, phycocyanin, and phycoerythrin were observed in the cell extract. Natural separation of the pigments occurred in the supernatant of the autolysed cells. The cell lysis was promoted by osmotic shocks and lysozyme treatments. Chlorophyll a and total DNA were abundantly recovered from the cells. Analysis of the restriction-modification system for genomic DNA revealed novel diversity. Moreover, we made a successful attempt to create antibiotic-resistant strains by conjugation with a foreign plasmid, which indicates that strain ABRG5-3 is transformable.

Molecular characterization of fungal communities in non-tilled, cover-cropped upland rice field soils.

This study aimed to characterize soil fungal communities in upland rice fields managed with tillage/non-tillage and winter cover-cropping (hairy vetch and cereal rye) practices, using PCR-based molecular methods. The study plots were maintained as upland fields for 5 years and the soils sampled in the second and fifth years were analyzed using T-RFLP (terminal restriction fragment length polymorphism) profiling and clone libraries with the internal transcribed spacer (ITS) region and domain 1 (D1) of the fungal large-subunit (fLSU) rRNA (D1(fLSU)) as the target DNA sequence. From the 2nd-year-sample, 372 cloned sequences of fungal ITS-D1(fLSU) were obtained and clustered into 80 nonredundant fungal OTUs (operational taxonomic units) in 4 fungal phyla. The T-RFLP profiling was performed with the 2nd- and 5th-year-samples and the major T-RFs (terminal restriction fragments) were identified using a theoretical fragment analysis of the ITS-D1(fLSU) clones. These molecular analyses showed that the fungal community was influenced more strongly by the cover-cropping than tillage practices. Moreover, the non-tilled, cover-cropped soil was characterized by a predominance of Cryptococcus sp. in the phylum Basidiomycota. We provided a genetic database of the fungal ITS-D1(fLSU)s in the differently managed soils of upland rice fields.

Detection of betaproteobacteria inside the mycelium of the fungus Mortierella elongata.

Microscopic and molecular analyses showed the presence of endobacteria inside the mycelia of four out of twelve nitrous oxide (N(2)O)-producing fungal isolates identified as Mortierella elongata. The 16S rRNA gene was successfully amplified with DNA extracted directly from the endobacterium-containing fungal strains and all sequences were related to that of Candidatus Glomeribacter gigasporarum in the family Burkholderiaceae. Bacterial endotoxin was detected in the endobacterium-positive fungal strains but only trace levels were found in endobacterium-negative strains. No significant relationship was found between the fungal N(2)O-producing activity and the presence of endobacteria.

Relationships between Fungal Biomass and Nitrous Oxide Emission in Upland Rice Soils under No Tillage and Cover Cropping Systems.

The relationships between soil microbial properties and nitrous oxide emission were examined in upland soil under different tillage systems [no tillage (NT), rotary and plow tillage] and cover crop systems (fallow, cereal rye, and hairy vetch) in 2004 and 2005. Microbiological analyses included the determination of soil ergosterol as an indicator of fungal biomass, bacterial plate counting, and MPN estimations of ammonia oxidizers and denitrifiers. The combined practice of NT with rye-cover crop treatment increased fungal biomass but not bacterial populations in 0-10 cm deep soils. Such increase in fungal biomass was not found in 10-20 cm and 20-30 cm deep cover-cropped NT soil. The combined practice of NT with rye-cover cropping resulted in higher in situ N(2)O emission rates compared with rotary- and plow-till treatments. N(2)O flux was positively correlated with soil ergosterol content but not with denitrifier MPN and other soil chemical properties. These results suggested a significant contribution of fungi to N(2)O emission in cover-cropped NT soils.

Archaeal Diversity of Upland Rice Field Soils Assessed by the Terminal Restriction Fragment Length Polymorphism Method Combined with Real Time Quantitative-PCR and a Clone Library Analysis.

The PCR amplification-based analysis of microbial diversity is subject to potential problems. In this study, to minimize the bias toward a 1:1 ratio in multitemplate PCR, a real-time PCR assay was carried out using a quenching fluorescence dye primer and amplification efficiency was monitored. Then terminal-restriction fragment length polymorphism (T-RFLP) profiling was performed using the PCR product with minimized PCR bias. This method was applied to an analysis of the diversity of the archaeal community in an upland rice field under different tillage systems and winter cover cropping. Terminal restriction fragments (T-RFs) of PCR-amplified archaeal 16S rRNA genes were assigned to the gene sequences recovered from the same soil by using an archaeal 16S rRNA gene clone library. Our results indicated that soil archaeal members were not influenced but the relative abundance of archaeal species particularly those belonging to Crenarchaeota which changed between the tillage and non-tillage treatments.