Assessment of the methane mitigation potentials of alternative water regimes in rice fields using a process‐based biogeochemistry model

Rice production is a substantial source of atmospheric CH₄, which is second only to CO₂ as a contributor to global warming. Since CH₄ is produced in anaerobic soil environments, water management is expected to be a practical measure to mitigate CH₄ emissions. In this study, we used a process‐based biogeochemistry model (DNDC‐Rice) to assess the CH₄ mitigation potentials of alternative water regimes (AWR) for rice fields at a regional scale. Before regional application, we tested DNDC‐Rice using site‐scale data from three rice fields in Japan with different water regimes. The observed CH₄ emissions were reduced by drainage of the fields, but were enhanced by organic amendments. DNDC‐Rice gave acceptable predictions of variation in daily CH₄ fluxes and seasonal CH₄ emissions due to changes in the water regime. For regional application, we constructed a GIS database at a 1 × 1 km mesh scale that contained data on rice field area, soil properties, daily weather, and farming management of each cell in the mesh, covering 3.2% of the rice fields in Japan's Hokkaido region. We ran DNDC‐Rice to simulate CH₄ emissions under five simulated water regimes: the conventional water regime and four AWR scenarios with gradually increasing drainage. We found that AWR can reduce CH₄ emission by up to 41% compared with the emission under conventional water regime. Including the changes in CO₂ and nitrous oxide emissions, potential mitigation of greenhouse gas (GHG) was 2.6 Mg CO₂ Eq. ha^?1 yr^?1. If this estimate is expanded to Japan's total rice fields, expected GHG mitigation is 4.3 Tg CO₂ Eq. yr^?1, which accounts for 0.32% of total GHG emissions from Japan. For a reliable national‐scale assessment, however, databases on soil, weather, and farming management must be constructed at a national scale, as these factors are widely variable between regions in Japan.     

Hot spots of leaf breakdown within a headwater stream reach: comparing breakdown rates among litter patch types with different macroinvertebrate assemblages

1. Detecting hot spots of litter decomposition will promote understanding of litter processing in a heterogeneous system. To identify hot spots of leaf breakdown within a headwater stream reach, we examined the difference in leaf breakdown rate among four types of litter patches, one that formed in riffles and three that formed in pools (middle, alcove, edge), in different seasons. 2. Middle patches showed the highest breakdown rate in some seasons; the rate in middle patches was 1.5–4 times higher than in the other patches. Thus middle patches can be regarded as hot spots of leaf breakdown in the study reach. This result contrasted with other studies showing higher breakdown rate in riffles than in pools. 3. Significant relationships between abundance of caddisfly shredders and breakdown rate were observed in seasons when the rate differed among patch types. Greater abundance of Lepidostoma seems to be responsible for middle patches being hot spots of leaf breakdown. 4. It is expected that when the proportion of leaves retained in middle patches within a reach is higher, the breakdown rate of the entire reach will be increased. Clarifying how the proportion of leaves retained on middle patches within a reach varies temporally and spatially would improve our understanding of leaf breakdown in headwater streams.     

Morphological responses of Daphnia ambigua to different concentrations of a chemical extract from Chaoborus flavicans

1. Daphnia ambigua were reared individually with eight different concentrations of a chemical extract from larvae of Chaohorus flavicans, and the frequency of appearance of helmeted individuals and the helmet sizes were determined in the instars 1–6. 2. The animals developed most marked helmets in the second instar in response to the extract. The frequency of the helmeted individuals and helmet size in the second instar increased with increasing chemical concentration, although their dose-response curves differed between them. 3. The results may explain the cyclomorphosis of Daphnia, which develop the highest helmets in summer, when the predators are abundant and active, and the concentrations of the predator-released chemicals would presumably be high. 4. The extract became toxic to Daphnia at the highest concentration prepared.     

Maternal and paternal effects on the germination time of non‐dormant seeds of a monocarpic perennial species,Aster kantoensis (Compositae)

In plant species producing non‐dormant seeds, the germination time (from the start of imbibition to radicle emergence) is the main factor determining the timing of seedling emergence. We investigated maternal and paternal genetic effects on the germination time of non‐dormant seeds of a monocarpic perennial, Aster kantoensis Kitamura (Compositae). Three sets of reciprocal diallel crosses among five plants were conducted to produce genetic variation in seeds, and the germination time of the progeny of each parent was determined. The effects of the maternal parent and the interaction of maternal and paternal parents on the germination time of progeny were significant in all sets, and the effect of the paternal parent was significant in two of the three sets. This result means that the germination time of the progeny of a maternal or paternal parent can vary with the genotype of its mating partners. Because variation in the emergence time of seedlings contributes to avoiding seedling loss owing to unpredictable environmental changes, genetic variation in the germination time among the progeny of each parent mating with multiple partners could contribute to the establishment of the parent's seedlings in species producing non‐dormant seeds in the field.     

基于线粒体DNA序列探讨斑头鱼分类地位

测定了斑头鱼Agrammus agrammus和大泷六线鱼Hexagrammos otakii的线粒体COⅠ、Cyt b和16S rRNA基因的部分序列,结合从GenBank中获得的六线鱼属3种的同源序列,以单鳍多线鱼Pleurogrammus monopterygius为外群,运用邻接法(NJ)、最大简约法(MP)和贝叶斯法(BI)构建了分子系统树。同时联合了3个基因片段序列,运用贝叶斯联合模型综合探讨了六线鱼类的系统发育关系。结果显示:除16S rRNA基因外,其余2个基因片段以及联合模型所构建的系统树拓扑结构完全一致,即斑头鱼与大泷六线鱼亲缘关系最近,应归为六线鱼属,拉丁学名应为Hexagrammos agrammus。Cyt b基因片段序列分析结果显示,斑头鱼和大泷六线鱼分歧时间约为175万年。结合形态学研究资料,支持将斑头鱼归为六线鱼属的观点,斑头鱼和大泷六线鱼亲缘关系最近,属于六线鱼科中分化较晚的种类。     

Movements of Mitochondria Associated with Isolated Egg Cortex

Cortical tragments of Tubifex eggs undergoing ooplasmic segregation were isolated in plastic dishes with an oil droplet separating part of them from the dish. Except at the edges of fragments and at the base of the oil droplet, the nearly entire area of the cortex was firmly attached to the plastic surface. Many mitochondria were associated with the cortical actin lattice. On addition of ATP to the preparations, only nonadhering portions of the cortex exhibited contractions. At the base of oil droplets, some mitochondria moved in the same direction concurrently with cortical contractions. Contractile activities of isolated cortices were completely inhibited by their preincubation with N-ethylmaleimide-modified heavy meromyosin, suggesting the involvement of an actomyosin force-generating mechanism in the cortical contractions during ooplasmic segregation.     

Evidence for the Presence of a Low Molecular Weight Factor in Sera from Various Animals that Induces in vitro Maturation of Fish Oocytes

Studies were made on whether sera from various animals or serum components could induce in vitro maturation of medaka oocytes in the absence of any exogenous hormone. When intra-follicular oocytes were preincubated in medium containing serum of some mammals or chickens, and were then washed, they matured during further incubation in the same medium without the serum. In contrast, no remarkable stimulatory effect on oocyte maturation was recognized in sera from some other mammals and from reptiles, amphibian and fish. A dialysate of rabbit serum collected using a cellulose membrane (mol. wt. retention 3,500) also induced in vitro maturation of intra-follicular oocytes. This activity was stable on treatment with proteolytic enzymes or heat-treatment. Small molecular weight fractions with this activity were obtained by filtering the dialysate through Sephadex G-10. The oocytes matured by the serum factor were capable of developing normally beyond the stage of embryonic body formation.
From these results, it is concluded that the serum of higher vertebrates contains a low molecular weight factor that stimulates in vitro nuclear and cytoplasmic maturation of intrafollicular fish oocytes.     

β-Lactoglobulin Suppresses Melanogenesis in Cultured Human Melanocytes

The effects of whey proteins from bovine milk on melanogenesis in cultured human melanocytes were examined. Among the major protein components of milk whey including β-lactoglobulin (BLG), α-lactalbumin, serum albumin, and IgG, only BLG exhibited the depigmenting effect at a concentration of 1 mg/ml. Also, BLG suppressed the activity of tyrosinase in these cells. Retinol, to which BLG is known to bind, slightly increased the pigmentation of the cells at concentrations in the range of 1–100 nM, and retinoic acid, a metabolite of retinol, exhibited a strong pigmentation-promoting effect within the same concentration range. Treatment of the cells with 1 mg/ml BLG completely abrogated the pigmentation induced by these A vitamins. These results demonstrate a novel biological activity of BLG and suggest that this activity is dependent on its ability to bind retinol.     

Glycoproteins from Teratocarcinomas and Organs of Adult Mice: Analysis by Affinity Chromatography on Lectin-conjugated Agarose1

Glycoproteins were isolated from particulate fraction of four teratccarcinomas and several organs of adult mice by affinity chromatography on lectins conjugated with agarose [concanavalin A (Con A), wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA), peanut agglutinin (PNA) and Dolichos biflorus agglutinin (DBA)] and were compared by SDS gel electrophoresis. Glycoprotein components were found to be very similar in three lines of solid teratocarcinoma, namely F9, STT-2 and OTT-10A. Teratocarcinoma OTT6050, which is an ascitic form called embryoid bodies, also gave glycoprotein profiles somewhat similar to those of other teratocarcinomas. However, glycoprotein profiles of most adult organs were significantly different from those of teratocarcinomas. The following points were of special interest. 1) RCA receptors from the four teratocarcinomas gave a strong band with an apparent molecular weight 145,000 daltons, which was either weak or absent in the receptors from adult organs. 2) The WGA receptors of all adult organs except muscle and small intestine gave more intense bands than those of the teratocarcinomas. 3) Glycoproteins with molecular weights of more than 240,000 daltons were present in WGA receptors, RCA receptors and PNA receptors of teratocarcinoma OTT 6050, but not in the receptors of other teratocarcinomas.