Implications of seasonal variation in nitrate export from forested ecosystems: a review from the hydrological perspective of ecosystem dynamics

In recent decades, the seasonal variation in NO₃ ^? discharge from forest ecosystems has been used increasingly by ecologists and hydrologists as a diagnostic indicator of the nutrient status of ecosystems. Major factors underlying the seasonal patterns of stream NO₃ ^? concentration include seasonal variations in (1) ecosystem nutrient demand, (2) solute transport capability of the hydrological condition, and (3) in-stream nutrient usage and supply. In this article I show how case studies have helped elucidate the dominant controlling factors by comparing data from Japanese catchments with previously compiled data from studies in North America and Europe. Moreover, I explain the different influences that hydrological and biogeochemical controls exert in regions with rainy (Japan) and dry (northeastern United States and Europe) summers. The seasonal variation in hydrological conditions is the predominant controlling factor in Japanese forests, whereas nutrient demand may predominate in the northeastern United States and Europe. I emphasize the importance of comparing seasonal patterns among regions with differing climates to obtain more universal explanations of seasonal variations in NO₃ ^?-related biogeochemical and hydrological dynamics in a forest ecosystem. In addition, multi-scale investigations will be needed to provide insight into the relative contributions of hillslope biogeochemical effects and in-stream biological activities.     

Effective dose conversion coefficients for radionuclides exponentially distributed in the ground

In order to provide fundamental data required for dose evaluation due to environmental exposures, effective dose conversion coefficients, that is, the effective dose rate per unit activity per unit area, were calculated for a number of potentially important radionuclides, assuming an exponential distribution in ground, over a wide range of relaxation depths. The conversion coefficients were calculated for adults and a new-born baby on the basis of dosimetric methods that the authors and related researchers have previously developed, using Monte Carlo simulations and anthropomorphic computational phantoms. The differences in effective dose conversion coefficients due to body size between the adult and baby phantoms were found to lie within 50?%, for most cases; however, for some low energies, differences could amount to a factor of 3. The effective dose per unit source intensity per area was found to decrease by a factor of 2–5, for increasing relaxation depths from 0 to 5?g/cm², above a source energy of 50?keV. It is also shown that implementation of the calculated coefficients into the computation of the tissue weighting factors and the adult reference computational phantoms of ICRP Publication 103 does not significantly influence the effective dose conversion coefficients of the environment. Consequently, the coefficients shown in this paper could be applied for the evaluation of effective doses, as defined according to both recommendations of ICRP Publications 103 and 60.     

Phylogenetic Analysis of Isolates of Pasteurella pneumotropica from Laboratory Animals Based on the gyrB Gene Sequence.

Phylogenetic analysis using the gyrB sequence was performed to investigate the genetic relevance among 49 isolates of P. pneumotropica. In the phylogeny, the isolates were clearly classified into three groups as follows: group A for the isolates of biotype Jawetz derived from mice, group B for the isolates of biotype Jawetz derived from rats, and group C for the isolates of biotype Heyl. These results suggest that the gyrB sequence of P. pneumotropica differs between the isolates of two biotypes, and also between the isolates derived from mice and rats in the biotype Jawetz.     

Applying hydraulic lift in an agroecosystem: forage plants with shoots removed supply water to neighboring vegetable crops

When a plant encounters spatially heterogeneous soil moisture within its root system, usually drier surface and moister subsurface soils, water can move between these layers through the root system, a plant process known as hydraulic lift or redistribution. The water thus transferred is available not only for the plant itself but also for its neighbors. We examined application of this process as a possible biological irrigation tool. As ??donors??, we used perennial forage plants with their shoots removed to minimize the effect of light-interception by them on the ??receiver?? plants growing alongside them. In a horizontally split-root experiment, where an upper container was filled with sand and a lower one with water, superior donor species could maintain the upper sand in a fully hydrated condition for several weeks, increasing stomatal conductance in the receivers. The effects were also confirmed in a water-limited agricultural field, as significant differences were found in canopy temperature and yield in neighboring crop plants in the presence or absence of donor root systems. These results suggest that deep-rooting associate plants with their shoots removed function as an irrigation tool and improve crop production in water-scarce environments.     

Stomatal density of cowpea correlates with carbon isotope discrimination in different phosphorus, water and CO2 environments

* Stomatal formation is affected by a plant's external environment, with long-distance signaling from mature to young leaves seemingly involved. However, it is still unclear what is responsible for this signal. To address this question, the relationship between carbon isotope discrimination (Delta) and stomatal density was examined in cowpea (Vigna sinensis). * Plants were grown under various environments that combined different amounts of soil phosphorus (P), soil water, and atmospheric CO(2). At harvest, stomatal density was measured in the youngest fully expanded leaf. The (13)C : (12)C ratio was measured in a young leaf to determine the Delta in mature leaves. * Results indicated that stomatal density is affected by P as well as by amounts of water and CO(2). However, stomatal responses to water and CO(2) were complex because of strong interactions with P. This suggests that the responses are relative, depending on some internal factor being affected by each external variable. Despite such complicated responses, a linear correlation was found between stomatal density and Delta across all environments examined. * It is proposed that the Delta value is a good surrogate for the long-term mean of the intercellular (C(i)) to the atmospheric (C(a)) CO(2) concentration ratio (C(i) : C(a)) and may be useful in understanding stomatal formation beyond complicated interactions.     

Biochemical Characterization and Phylogenetic Analysis Based on 16S rRNA Sequences for V-Factor Dependent Members of <Emphasis Type="Italic">Pasteurellaceae</Emphasis> Derived from Laboratory Rats

Phylogenetic analysis based on 16S rRNA sequences with sequence data of some bacterial species of Pasteurellaceae related to rodents deposited in GenBank was performed along with biochemical characterization for the 20 strains of V-factor dependent members of Pasteurellaceae derived from laboratory rats to obtain basic information and to investigate the taxonomic positions. The results of biochemical tests for all strains were identical except for three tests, the ornithine decarboxylase test, and fermentation tests of D(+) mannose and D(+) xylose. The biochemical properties of 8 of 20 strains that showed negative results for the fermentation test of D(+) xylose agreed with those of Haemophilus parainfluenzae complex. By phylogenetic analysis, the strains were divided into two clusters that agreed with the results of the fermentation test of xylose (group I: negative reaction for xylose, group II: positive reaction for xylose). The clusters were independent of other bacterial species of Pasteurellaceae tested. The sequences of the strains in group I showed 99.7–99.8% similarity and the strains in group II showed 99.3–99.7% similarity. None of the strains in group I had a close relation with Haemophilus parainfluenzae by phylogenetic analysis, although they showed the same biochemical properties. In conclusion, the strains had characteristic biochemical properties and formed two independent groups within the “rodent cluster” of Pasteurellaceae that differed in the results of the fermentation test of xylose. Therefore, they seemed to be hitherto undescribed taxa in Pasteurellaceae.     

A flash-photolysis study of the reactions of acaa 3-ttype cytochrome oxidase with dioxygen and carbon monoxide

The time course of absorbance changes following flash photolysis of the fully-reduced carboxycytochrome oxidase fromBacillus PS3 in the presence of O₂ has been followed at 445, 550, 605, and 830 nm, and the results have been compared with the corresponding changes in bovine cytochrome oxidase. The PS3 enzyme has a covalently bound cytochromec subunit and the fully-reduced species therefore accommodates five electrons instead of four as in the bovine enzyme. In the bovine enzyme, following CO dissociation, four phases were observed with time constants of about 10 s, 30 s, 100 s, and 1 ms at 445 nm. The initial, 10-s absorbance change at 445 nm is similar in the two enzymes. The subsequent phases involving hemea and Cu_A are not seen in the PS3 enzyme at 445 nm, because these redox centers are re-reduced by the covalently bound cytochromec, as indicated by absorbance changes at 550 nm. A reaction scheme consistent with the experimental observations is presented. In addition, internal electron-transfer reactions in the absence of O₂ were studied following flash-induced CO dissociation from the mixed-valence enzyme. Comparisons of the CO recombination rates in the mixed-valence and fully-reduced oxidases indicate that more electrons were transferred from hemea ₃ toa in PS3 oxidase compared to the bovine enzyme.