Influence of Soil Chemical Properties on Adsorption and Oxidation of Phenolic Acids in Soil Suspension

Relationships between abiotic oxidation and adsorption of phenolic acids added to soils and soil chemical properties were investigated by using 32 soil samples and ferulic, vanillic, and p-hydroxybenzoic acids. Soil properties studied were as follows: (as adsorption factors) contents of acid oxalate extractable Al (Alo), Fe (Feo), dithionite-citrate-bicarbonate (DCB) extractable Fe (Fed), total carbon and clay, and (as oxidation factors) level of soil oxidative activity (Cr oxidation) determined by the amount of Cr(VI) converted from Cr(III) added to soils. Soil samples were divided into 3 types based on chemical properties: Andosols A (A horizon of Andosols), Andosols B (B horizon of Andosols and light-colored Andosols), and non-Andosols.

The recovery of all phenolic acids (RPA) was negatively correlated with the total carbon and Feo contents in Andosols A and B, respectively, which suggested adsorption onto soil organic matter in Andosols A and onto Feo in Andosols B. It was considered that almost no oxidation of phenolic acids occurred in Andosols A, because a very small amount of Cr(VI) was obtained. The recovery of ferulic acid (RFA) and vanillic acid (RVA), however, was negatively correlated with Cr oxidation in non-Andosols, suggesting that these phenolic acids were oxidized, while almost all of the p-hydroxybenzoic acid was recovered.

These results were also supported by the comparison between RFA and recovery of dissolved organic carbon (RTOC). RFA was very similar to RTOC in Andosols A and B, which indicated that adsorption occurred, whereas RFA was lower than RTOC in the non-Andosols that showed a high level of Cr oxidation, indicating that oxidation took place. Manganese dissolution which occurred when phenolic acids were added to soils was also examined.     

Isolation and partial characterization of endophytic diazotrophs associated with Japanese sugarcane cultivar

Endophytic bacteria were isolated from the juice of a 6 month-old sugarcane cv. NiF-8, which was collected from Miyako, Okinawa and planted in a field lysimeter in Tsukuba, Ibaraki, Japan. The most probable number of N₂-fixing endophytes was 4.5 × 10⁵ cells per gram of fresh weight sample and 21 isolates have a positive reaction for ARA in an N₂-free semi-solid medium with 10% crystallized sugarcane sugar and 0.5% sugarcane juice. Analyses of some of the biochemical properties of the N₂-fixing isolates indicated that 13 isolates were putative strains of Acetobacter diazotrophicus, 4 isolates showed similar characteristics to those of Herbaspirillum seropedicae, and 4 isolates consisted of Herbaspirillum rubribalbicans-like strains. This study confirmed the existence of N₂-fixing endophytic bacteria in the Japanese sugarcane cv. NiF-8.     

Adequate range of boron nutrition is more restricted for root nodule development than for plant growth in young soybean plant

A pot experiment was conducted under growth chamber conditions to determine the lower and upper critical levels of boron (B) for plant growth, nodule development, and nodule acetylene reduction activity (ARA) in young soybean plants. Plants of a soybean cultivar, Tachinagaha, were grown in pots containing river sand to which a nutrient solution with different B levels was added and were inoculated with Bradyrhizobium japonicum A1017. At 8, 12, and 16 d after sowing (DAS), among the plants supplied with the solution at 0, 1.0, and 2.0 mg B L^-1 , plants with 1.0 mg B L^-1 showed the highest values for dry shoot and fresh root weight, root length, total number of developing nodules and meristematic nodules (DMN), and ARA. At 20 DAS plants grown with 11 B levels (0-2.0 mg L^-1) were compared. The B critical deficiency levels for soybean dry shoot weight, fresh root weight, root length, DMN, number of complete nodules, and ARA were approximately 46, 35, 34, 57, 60, and 50 mg B kg^-1 dry matter, and the critical toxicity levels were approximately 114, 137, 134, 97, 104, and 89 mg B kg^-1 dry matter, respectively. The optimum B levels for the growth characters were approximately 34 to 137 mg B kg^-1 dry matter. The optimum range of B levels for nodule formation and function was more restricted than that for the growth characters. Based on the results of treatments with various B concentrations, 0.4 mg B L^-1 was found to be the concentration most beneficial for all the growth characters including nodule formation at the early stage (20 DAS) of development of soybean plants.     

Positive correlation between the number of root nodule primordia and seed sugar secretion in soybean (Glycine max L.) seedlings inoculated with a low density of Bradyrhizobium japonicum

Sufficient rhizobium population in the rhizosphere of legume seedlings is required for early and enough setting of root nodules. Potential of seed and seedling root exudates for proliferation of Bradyrhizobium japonicum PNT119 was evaluated in the soybean cvs. Enrei and Tachinagaha. In both cultivars, seed exudates showed a higher potential than root exudates. In the seed exudates, a low-molecular high-polarity fraction including sugars and amino acids showed a higher potential than both high-molecular fraction and low-molecular low-polarity fraction. The correlations between the sugar or amino acid contents of seed exudates and the number of root nodule primordia at 7 d after sowing were investigated among 12 soybean cultivars. When seeds were inoculated with a low rhizobium density, a high correlation coefficient was detected between them. However, there was no positive correlation in the plants inoculated with a high rhizobium density. These results suggest that the amount of low molecular substances in the seed exudates determines the number of root nodule primordia through rhizobium proliferation around seed and young roots when the rhizobium density is the limiting factor. The genetic trait relating to seed coat secretion should be considered as a possible key factor contributing to adequate root nodulation in soybean seedlings cultivated in fields with a low rhizobium density.     

Effect of the Fukushima Daiichi nuclear power plant accident on radiocesium distribution in tea fields in Saitama Prefecture: Intercultivar differences

We investigated radiocesium distribution in tea plants (Camellia sinensis L. var. sinensis) of Saitama Prefecture, located approximately 200–250 km away from Tokyo Electric Power Company’s Fukushima Daiichi nuclear power plant. In 2012, more than 2500 samples of tea plants were analyzed. We found differences in radiocesium concentration among tea plant cultivars, which appeared to be attributable mainly to the leaf morphology and depth of the leaf layer in tea plants. Furthermore, the radiocesium concentration in the first tea crop showed a strong correlation with that in spring skiffing.     

The effects of rice (Oryza sativa L. ssp. japonica) husk biochar on nitrogen dynamics during the decomposition of hairy vetch in two soils under high-soil moisture condition

ABSTRACT

Legumes, including hairy vetch (Vicia villosa Roth), are widely used as green manures. They fix nitrogen (N) and provide the N to other crops when they decompose, and thus are considered alternatives for chemical N fertilizers. However, N-rich plant residues, including hairy vetch, are also sources of soil nitrous oxide (N₂O) emissions, a greenhouse gas. On one hand, rice (Oryza sativa L. ssp. japonica) husk biochar is widely used as a soil conditioner in Japan and has been reported as a tool to mitigate soil N₂O emissions. We conducted a soil core incubation experiment (1.5 months) to compare the N₂O emissions during the decomposition of surface-applied hairy vetch (0.8 kg dried hairy vetch m^?2 soil) under semi-saturated soil moisture conditions (~100% water-filled pore space (WFPS)), using two soil types, namely Andosol and Fluvisol. Throughout the incubation period, the use of biochar suppressed soil NH₄⁺-N concentrations in Andosol, whereas the effect of biochar on NH₄⁺-N was not clear in Fluvisol. Biochar increased the nitrate (NO₃^?-N) levels both in Andosol and Fluvisol, suggesting a negative influence on denitrification and/or a positive influence on nitrification. Biochar application did not influence the cumulative N₂O emissions. Our study suggests that rice husk biochar is not a good option to mitigate N₂O emissions during the decomposition of surface-applied hairy vetch, although this study was performed under laboratory conditions without plants. However, the trends of the inorganic-N concentration changes followed by the addition of hairy vetch and biochar were markedly different between the two soil types. Thus, factors behind the differences need to be further studied.     

Challenges and opportunities for improving N use efficiency for rice production in sub-Saharan Africa

ABSTRACT

In sub-Saharan Africa (SSA), rice production from smallholder farms is challenged because of a lack of fertilizer inputs and nutrient-poor soils. Therefore, improving nutrient efficiency is particularly important for increasing both fertilizer use and rice yield. This review discusses how to improve the return from fertilizer input in terms of agronomic N use efficiency (AE_N), that is, the increase in grain yield per kg of applied N, for rice production in SSA. The AE_N values we summarized here revealed large spatial variations even within small areas and a certain gap between researcher-led trials and smallholder-managed farms. Experimental results suggest AE_N can be improved by addressing spatial variations in soil-related factors such as P, S, Zn, and Si deficiencies and Fe toxicity in both irrigated and rainfed production systems. In rainfed production systems, differences in small-scale topography are also important which affects AE_N through dynamic changes in hydrology and variations in the contents of soil organic carbon and clay. Although empirical evidence is further needed regarding the relationship between soil properties and responses to fertilizer inputs, recent agricultural advances have generated opportunities for integrating these micro-topographical and soil-related variables into field-specific fertilizer management. These opportunities include UAV (unmanned aerial vehicle) technology to capture microtopography at low cost, database on soil nutrient characteristics at high resolution and more numbers of fertilizer blending facilities across SSA, and interactive decision support tools by use of smartphones on site. Small-dose nursery fertilization can be also alternative approach for improving AE_N in adverse field conditions in SSA.

ABBREVIATIONS: AE_N: agronomic nitrogen use efficiency; FISP: farm input subsidy program; VCR: value cost ratio; SOC: soil organic carbon; SSA: sub-Saharan Africa; UAV: unmanned aerial vehicle     

Homoplastic occurrence of perforated pit membranes and torus-bearing pit membranes in ancestral angiosperms as observed by field-emission scanning electron microscopy

Recent studies demonstrated that perforated pit membranes (i.e., pit membranes with a large opening in their central portion) are commonly present between wood fibers in core eudicots. It is unclear whether this type of pit membranes might also occur in ancestral angiosperms. Therefore, structure of interfiber pit membranes was examined by field-emission scanning electron microscopy in nine species representing seven families that are located at more ancestral position than core eudicots. We found perforated pit membranes in three of the nine species. Our observations indicate that perforated pit membranes are relatively common even in ancestral groups of angiosperms. In the non-perforated pit membranes of the other six species, we found a range of structural variations. Thin-walled pit membranes without apparent intercellular layers were always found in three of the six species and the porosity of sheet-like pit membranes differed among the three species. Unlike the thin-walled pit membranes, interfiber pit membranes of Buxus microphylla var. japonica were thick-walled with obvious intercellular layers, and in Schisandra chinensis, we often observed torus-bearing pit membranes. Such variations in layered structure of pit membranes and homoplastic occurrence of torus-bearing pit membranes have not yet been reported for ancestral angiosperms. Our observations indicate that the structure of interfiber pit membranes might be more complicated than previous studies might suggest.     

Characterization of Rehmannia mosaic virus isolated from chili pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis>) in Japan

In 2010, severe necrotic mosaic disease and fruit distortion were observed on greenhouse-grown chili pepper (Capsicum annuum cv. Fushimi-amanaga) plants in Kyoto Prefecture, Japan. Electron microscopic imaging and genomic RNA sequencing indicated that the virus responsible was a new isolate of Rehmannia mosaic virus (ReMV), which had not been previously reported in Japan. Although ReMV systemically infected many Solanaceae species, including chili pepper and tomato (Solanum lycopersicum), tobamovirus-resistance genes from species of Capsicum (L ^1a , L ² , L ³ , and L ⁴ ) and tomato (Tm-1, Tm-2, and Tm-2 ^a ) conferred resistance against ReMV.