Carbon cycling in rice field ecosystems in the context of input, decomposition and translocation of organic materials and the fates of their end products (CO2 and CH4)

Rice fields are intensively managed, unique agroecosystems, where soil flooding is general performance for rice cultivation. Flooding the field results in reductive soil conditions, under which decomposition of organic materials proceeds during the period of rice cultivation. A large variety of organic materials are incorporated into rice soils according to field management. In this review, the kind and abundance of organic materials entering carbon cycling in the rice field ecosystem are evaluated first. Then, decomposition of plant residues and soil organic matter in rice fields is reviewed quantitatively. Decomposition of plant residues is shown to be the active process in carbon cycling in rice fields. Rice releases photosynthates into the rhizosphere (rhizodeposition), and they follow a different avenue of decomposition in soil from that of plant residues. Incorporation of rhizodeposition into microbial biomass and soil organic matter during the period of rice cultivation, and their fates after harvesting are evaluated quantitatively from ¹³C pulse labeled experiments. Percolating water transports inorganic and organic carbon from the plow layer to the subsoil layer. The amounts of their transport and accumulation in the subsoil layer are evaluated in relation to the amounts of soil organic C in the plow layer. Not only CO₂ but also CH₄ are produced in the decomposition process of organic materials in flooded rice fields. CH₄ evolution from rice fields is of global concern from the viewpoint of global warming. Origins of CH₄ evolved from rice fields are estimated first, followed by the fates of CH₄ in rice field ecosystems. Rhizodeposition is shown to be the main origin of CH₄ evolved from rice fields. Evolution to the atmosphere is not the sole pathway of CH₄ produced in rice fields. The amounts of CH₄ retained in soil, percolated to the subsoil layer and decomposed in soil are evaluated in the context of the amounts of CH₄ efflux. Thus, this review focuses on carbon cycling in the rice field ecosystem from the viewpoints of input, decomposition, and translocation of organic materials and the fates of their end products (CO₂ and CH₄).     

Chemical characteristics and potential source of fulvic acids leached from the plow layer of paddy soil

To understand better the chemical characteristics and source of dissolved organic matter (DOM) leached from the plow layer of rice paddies, a lysimeter study was conducted, which simulated submerged paddy topsoil during rice growth. The fulvic acid (FA) fraction in the percolation water from the lysimeter was collected by adsorption onto insoluble polyvinylpyrrolidone (PVP), and the temporal variations in its elemental composition, molecular size distribution, IR spectra, ¹³C CPMAS NMR spectra, and δ¹³C values were investigated. The proportion of the FA fraction to bulk DOM varied greatly, but the chemical characteristics of the FA fraction did not change appreciably during the experimental period. Thus, it is considered that the changes in the DOM composition in percolation water were mainly due to the differing contributions of the FA fraction. Further, to investigate the source of the FA fraction in the leachate, the chemical characteristics of the FA fraction in the leachate were compared with those extracted from the plow layer soil. A sequential extraction of the FA fraction was conducted using a sequence of water, 0.25 M Na₂SO₄, 0.1 M Na₄P₂O₇ (pH 7.0), 0.1 M Na₄P₂O₇ (pH 10.5), and NaBH₄+0.1 M Na₄P₂O₇ (pH 10.5). It was found that the water- and 0.25 M Na₂SO₄-extractable fractions, which were most mobile, were not the only source of the FA fraction in the leachate. The small molecular size sub-fraction of the NaBH₄+0.1 M Na₄P₂O₇ (pH 10.5)-extractable FAs, most of which are probably bound mainly to iron oxides, are considered to be another source of the FA fraction leached from the plow layer of paddy fields.     

Study on some functional and compositional properties of yak butter lipid

The present experiment was performed to determine some functional properties of yak butter lipids such as lipid class composition; conjugated linoleic acid (CLA) composition, differential scanning calorimetric (DSC) analysis, tyrosinase inhibition activity and antioxidant property. Yak butter lipids composition contained 98% triacylglycerols, 0.9% free fatty acids, 0.32% free sterols and 0.27% phospholipids. The CLA content in yak butter was 2.5% and the major portion was of cis‐9 and trans‐11 (90%). The DSC analysis of yak butter lipids showed a similar path for transition temperature as cow butter lipids, although the enthalpy of yak lipid was higher (40.0 mJ/mg) compared to cow butter lipids (32.0 mJ/mg). Melting point of yak butter was observed at 41°C. Yak butter with lactic acid, NaCl, citric acid and ascorbic acid showed pronounced tyrosinase inhibition activity. Vegetable oils blended with yak butter have extended the oxidation induction time.     

Insecticidal activity and microsomal metabolism of biooxidizable lindane analogs

The insecticidal activity of lindane analogs, in which some chlorine atoms were replaced by other groups susceptible to microsomal oxidative metabolism, was determined against mosquitos, house flies, and German cockroaches. When tested with a synergist, piperonyl butoxide, one of the methylthio analogs was as active as lindane, whereas several others were also highly active. By examining the ratio of synergized and unsynergized LD₅₀ values (synergistic ratio value), the highly insecticidal methylthio, methoxy, and methyl analogs appear to undergo metabolic detoxication effectively in house flies. By means of in vitro metabolism experiments using microsomal fraction from house fly abdomen, the methoxy, ethoxy, and methylthio analogs were shown to be metabolized rapidly at similar rates. The synergized insecticidal activities of these compounds against various insect species relate linearly with each other, suggesting that the oxidative degradation is inhibited by the synergist to a similar extent and that the transport process to the site of action is not a limiting factor in determining the relative insecticidal activity.     

Effects of serpentine substrate on vegetation and soil development with special reference to Picea glehnii forest in Teshio district, Hokkaido, Japan

Characteristics of vegetation and soils in the serpentine area of northern Hokkaido were studied in comparison with non-serpentine areas of the same region, and with other serpentine areas of Japan and elsewhere in the world. The relationship between vegetation and soils is discussed.

Although forest vegetation of northern Hokkaido is generally represented by deciduous forest, coniferous forest, predominantly Picea glehnii, develops in the serpentine area. Deciduous trees are limited both in number and in size. Forest floor is densely covered with Sasa kurilensis. The shrub layer is also well developed, whereas the herb layer is poor but contains characteristic species. Soils developing in the serpentine area are determined as Podzol (Wet Iron Podzol), while Brown Forest Soil is commonly found in the non-serpentine areas of the region. The serpentine soils are shallow and moist, showing general morphology and chemistry of podzolic soil in upper horizons of the profile. In lower horizons, however, physico-chemical properties are strongly affected by the parent rock. In comparison with other serpentine areas of Japan and elsewhere, northern Hokkaido is unique in that the vegetation is represented by a relatively closed forest of fair-sized trees, and the soils by a podzol.

Such Picea glehnii forests and podzolic soils are considered an intrazonal phytogeocoenosis strongly affected by serpentine substrate. In this regard, the cool and humid climate as well as undulating relief of northern Hokkaido are also important factors for the development of the unique phytogeocoenosis.     

Male Pseudohermaphroditism in a raccoon dog (Nyctereutes procynoides)

A wild raccoon dog (Nyctereutes procynoides) which died due to a traffic accident on 18 October 2001, and was determined to be 4.5 years old, was examined. Visual appearance of the external genitalia in this animal showed to be female with a large penis-like clitoris protruding from the vulvar juncture. Visual examination of the internal genitalia revealed that the animal possessed both testes and uterus. Histological appearance of the removed gonads showed only Sertoli cells but no spermatogenesis. Using polymerase chain reaction with skin biopsy directed against the sex-determining region on the Y chromosome (SRY) gene, the genomic SRY gene was expressed as a single band and sequenced. Based on these findings, this raccoon dog was diagnosed as male pseudohermaphrodite.     

Changes in activities of enzymes related to energy metabolism in canine lymphoma cells

Alterations in the activities of enzymes related to energy metabolism in canine lymphoma cells were investigated. Cytosolic pyruvate kinase (PK) and mitochondrial malate dehydrogenase (MDH) activities in lymphoma cells were significantly higher than those in lymphocytes obtained from lymph nodes of healthy dogs, whereas cytosolic lactate dehydrogenase (LDH) activity was significantly lower in lymphoma cells. The cytosolic M/L ratio (MDH activity/LDH activity), which is considered to be a good indicator of energy metabolism related to glucose utilization in animal tissues, was significantly higher in lymphoma cells than in the normal lymphocytes.