Language：Japanese   Publishing type：Research paper (scientific journal)   Participation form：Joint(The main charge)  

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Participation form：Joint(The vice charge)  

Publishing type：Research paper (scientific journal)   Publisher：Association of Rural Planning  

DOI： 10.2750/arp.36.59

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Participation form：Joint(The vice charge)  

Publishing type：Research paper (scientific journal)   Publisher：United Graduate School of Agricultural Science  

DOI： 10.7831/ras.5.56

Publishing type：Research paper (scientific journal)   Publisher：United Graduate School of Agricultural Science  

DOI： 10.7831/ras.4.21

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Journal of Rainwater Catchment Systems  

DOI： 10.7132/jrcsa.22_1_1

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Journal of Rainwater Catchment Systems  

DOI： 10.7132/jrcsa.21_2_1

Publishing type：Research paper (scientific journal)  

This article is discussing the impacts of land cover change from paddy field to barren land in small scale area (1,516.5 km2), on the surrounding local climate components in central Java, Indonesia. Data of several climate components from 2000-2010 were collected from weather stations that located separately. The land covers were dominated with cropland and little forest on eastern site, and settlements (urban) on western site. This study confirmed that the decrease in 13.1% of paddy field and the increase in 12.4% of barren land had significantly resulted in low daily actual vapor pressure (ea) during dry months with low rainfalls. The eastern areas that were originally occupied by croplands and trees, responded to the decrease of paddy fields by the increasing of air temperatures. The air temperatures and their variations at urban areas located in the western part were not distinctly affected by the land cover change.

DOI： 10.4137/ASWR.S21560

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Participation form：Joint(The vice charge)  

Authorship：Last author,　Corresponding author   Publishing type：Research paper (scientific journal)  

Soil salinization has provided a serious threat for global agriculture throughout human history. It is becoming ever more prevalent as human land use intensifies in recent years, and the reclamation is one of major challenges in agroecology. Flood irrigation is a typical method for leaching saline soil. Yet the practice needs a large amount of water, and it is difficult to remove salt uniformly throughout soil layers. In this study, an experiment was conducted to evaluate leaching efficiencies of four different methods, namely: flood irrigation, spray irrigation, paper-covered flood irrigation, and puddling irrigation. Flood irrigation was applied at three plots with different infiltration capacities. Spray irrigation, paper-covered flood irrigation, and puddling irrigation were applied at other three plots with medium infiltration capacities. Results showed that salt removal rates of flood irrigation tended to be higher near the surface of soil with smaller infiltration capacity, and that spray irrigation, paper-covered flood irrigation, and puddling irrigation were more efficient in removing salt than flood irrigation. Paper-covered irrigation was the only leaching method that reduced horizontal heterogeneities in salt content, while flood irrigation and puddling irrigation significantly increased the horizontal heterogeneities. The present study indicated that leaching efficiencies were highly affected by irrigation intensity and also by irrigation water volume only when irrigation intensity was considerably low, and that paper-covered irrigation is an efficient method in removing salt homogeneously from soil profile. Further studies need to be conducted to optimize irrigation intensity and water volume for given soil and water environmental conditions.

DOI： 10.1007/s10333-014-0417-3

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Trehalose confers protection against various environmental stresses on yeast cells. In this study, trehalase gene deletion mutants that accumulate trehalose at high levels showed significant stress tolerance to acetic acid. The enhancement of trehalose accumulation can thus be considered a target in the breeding of acetic acid-tolerant yeast strains.

DOI： 10.1016/j.jbiosc.2014.06.021

Scopus

PubMed

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：United Graduate School of Agricultural Science  

DOI： 10.7831/ras.3.46

Language：Japanese   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

To analyze genetic diversity of endangered medaka (<i>Oryzias latipes</i>), primers for PCR (polymerase chain reaction) were constructed that could amplify ten microsatellite loci of medaka genome based on the contig/scaffold sequences published. DNA was extracted from the caudal fin of medaka collected at six different sampling points in Wanouchi Town, Gifu Prefecture. Genetic diversity within each sampling point was relatively high, whereas genetic differentiation between sampling points was small (pairwise <i>F_ST </i>= 0.023-0.086) but significant for all except three pairs of the sampling points. The genetic difference between the populations of the sampling points could be explained not only by the geographical distances but by the waterway connectivity between the points. These results indicated the importance of planning agricultural channel corrections considering migration of medaka between populations, to conserve genetic features of medaka in this study site where within-population genetic diversity is not much deteriorated yet.

DOI： 10.11408/jsidre.83.I_99

CiNii Books

Other Link： https://jlc.jst.go.jp/DN/JLC/20011867485?from=CiNii

Language：Japanese   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

The amount of irrigation water, soil temperature and population density of a pathogenic bacterium <i>Ralstonia solanacearum </i>before and after soil solarization were investigated in 6 greenhouses (located at Kaizu city, Gifu, Japan) in order to obtain the basic information of water requirement for the control of <i>R. solanacearum </i>via soil solarization in managing tomato cultivation. Our results showed that the soil temperature was influenced by airtight state of a glasshouse, temperature differences between inside and outside of a greenhouse, and duration and climatic conditions of the solarization period. The density of <i>R. solanacearum </i>decreased markedly after soil solarization with daily average soil temperature greater than 40°C for consecutive 10 days or 3 days under anaerobic condition, which was consistent with previous studies. The amount of irrigation water ranged from 155.6 to 495.2 mm (average: 291.3 mm) for 2 greenhouses where soil solarization was effective, which corresponded to 104 - 346% (average: 218%) of the amount of water requirement from some state to become saturation state.

DOI： 10.11408/jsidre.82.433

CiNii Books

CiNii Research

Other Link： http://id.ndl.go.jp/bib/026011790

Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)  

We analyzed a model of phytoplankton competition for light in a well-mixed water column. The model, proposed by Gerla et al. (Oikos 120:519-527, 2011), assumed inhibition of photosynthesis at high irradiance (photoinhibition). We described the global behavior through mathematical analyses, providing a general solution to the multi-species competition for light with photoinhibition. We classified outcomes of 2- and 3-species competitions as examples, and evaluated feasibility of the theoretical predictions using empirical relationships between photosynthetic production and irradiance. Numerical simulations with published p-I curves indicate that photoinhibition may often lead to strong Allee effects and competitive facilitation among species. Hence, our results suggest that photoinhibition may play a major role in organizing phytoplankton communities.

DOI： 10.1007/s11538-013-9852-3

Scopus

PubMed

Language：Japanese   Publisher：The Japanese Society of Irrigation, Drainage and Rural Engineering  

It is important to evaluate tensile strength characteristics of foundation and embankment material of fill dam in order to examine conditions for crack development which is one of the causes for the hydraulic fracturing. While it is possible to evaluate tensile strength of hard rock by fixing both ends of the specimen with chucks and applying the force directly, it is not possible to use the same method for soft material like cohesive soil. In this study, we designed an I-shaped plate specimen by the FEM analysis so that it contains parts where stress acts almost uniformly. The direct tensile test was performed with the specimen made of volcanic ashes loam and the tensile strain was measured by image instrumentation using digital cameras. Our tensile test method enabled continuous measurement of tensile stress and strain with soft material like cohesive soil.

DOI： 10.11408/jsidre.81.377

CiNii Research

Publishing type：Research paper (scientific journal)  

A recent theory of the vertical distribution of phytoplankton considers how interacting niche construction processes such as resource depletion, behavior, and population dynamics contribute to spatial heterogeneity in the aquatic environment. In poorly mixed water columns with opposing resource gradients of nutrients and light, theory predicts that a species should aggregate at a single depth. This depth of aggregation, or biomass maximum, should change through time due to depletion of available resources. In addition, the depth of the aggregation should be deeper under low amounts of nutrient loading and shallower under higher amounts of nutrient loading. Theory predicts total biomass to exhibit a saturating relationship with nutrient supply. A surface biomass maximum limited by light and a deep biomass maximum limited by nutrients or co-limited by nutrients and light is also predicted by theory. To test this theory, we used a motile phytoplankton species (Chlamydomonas reinhardtii ) growing in cylindrical plankton towers. In our experiment, the resource environment was strongly modified by the movement, self-shading, nutrient uptake, and growth of the phytoplankton. Supporting predictions, we routinely observed a single biomass maximum at the surface throughout the course of the experiment and at equilibrium under higher nutrient loading. However, at equilibrium, low nutrient loading led to a non-distinct biomass maximum with the population distributed over most of the water column instead of the distinct subsurface peak predicted by theory. Also supporting predictions, total biomass across water columns was positively related to nutrient supply but saturating at high nutrient supply conditions. Further supporting predictions, we also found evidence of light limitation for a surface biomass maximum and nutrient limitation for the deep biomass when no surface maximum was present. In addition, the light level leaving the bottom of the water column declined through time as the phytoplankton grew and was negatively related to nutrient loading. Nutrients were strongly depleted where biomass was present by the end of the experiment. This experimental study shows that the vertical distribution of phytoplankton may be driven by intraspecific resource competition in space. © 2012 by the Ecological Society of America.

DOI： 10.1890/11-0273.1

Scopus

Publishing type：Research paper (scientific journal)  

Effects of fish predation propagate through aquatic food webs, where the classical grazing food chain and microbial loop are interwoven by trophic interactions. The overall impact on aquatic food webs is further complicated because fish may also exert bottom-up controls through nutrient regeneration. Yet, we still have limited information about cascading effects among fish, zooplankton, phytoplankton, and microbes. In this study, we performed a mesocosm experiment to evaluate effects of fish introduction on plankton communities. Six plots were set in factorial combination with fish introduction and rice straw plowing in a paddy field, and the experiment was continued for 4 weeks. Introduction of fish significantly increased chlorophyll a concentrations in smaller size fractions (<15 μm) and abundances of filamentous bacteria (>5 μm in length) and heterotrophic nanoflagellates in 3-15 μm fraction. Microbes in 0.8-3 μm fraction showed increasing but not significant trends in response to fish introduction. These results indicate cascading effects of fish predation operating via two pathways, one through grazing food chain and the other through microbial food web. Phytoplankton community compositions shifted in similar fashion in all plots until 1 week after fish introduction, and then diverged between plots with and without fish thereafter. Bottom-up effects of fish introduction were suggested by increases of total chlorophyll a and inedible phytoplankton species in response to fish introduction. This study provides an example of how fish predation regulates biomass and structure of phytoplankton and microbial communities. © 2011 The Ecological Society of Japan.

DOI： 10.1007/s11284-011-0820-9

Scopus

Publishing type：Research paper (scientific journal)  

We compiled light utilization traits for 56 species of freshwater phytoplankton to analyze group differences, trait trade-offs, and allometric scaling relationships. We also used these traits to explain differences in major group distributions along the light availability gradient in 527 lakes in the continental United States. Major taxonomic groups differed significantly in their light utilization traits. Cyanobacteria had the highest initial slope of the growth-irradiance curve (α) and low irradiance at the onset of photoinhibition, indicating adaptation to low light environments. Green algae had the highest maximal growth rates and low a, indicating adaptation to higher light environments. Groups capable of mixotrophy had traits indicative of poor light competitive abilities and high light requirements. Key light utilization traits scaled allometrically with cell size and exhibited trade-offs leading to contrasting ecological strategies; a and cell size were conserved at the highest taxonomic level (domain), indicating a fundamental trait divergence between prokaryotic and eukaryotic phytoplankton. In line with these trait differences, major groups showed different responses to light availability in natural conditions. The relative abundances of low light-adapted groups declined with increasing light availability and vice versa. The genera mean values of the initial slopes of the growth-irradiance curves were significantly negatively correlated with the slopes of the relationships between the genus's relative abundance and light availability characterized by Secchi depth in 527 lakes. This indicates that light utilization traits can be used to explain phytoplankton distributions in nature. © 2011, by the American Society of Limnology and Oceanography, Inc.

DOI： 10.4319/lo.2011.56.2.0589

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

What determines the vertical distribution of phytoplankton in different aquatic environments remains an open question. To address this question, we develop a model to explore how phytoplankton respond through growth and movement to opposing resource gradients and different mixing conditions. We assume stratification creates a well-mixed surface layer on top of a poorly mixed deep layer and nutrients are supplied from multiple depth-dependent sources. Intraspecific competition leads to a unique strategic equilibrium for phytoplankton, which allows us to classify the distinct vertical distributions that can exist. Biomass can occur as a benthic layer (BL), a deep chlorophyll maximum (DCM), or in the mixed layer (ML), or as a combination of BL+ML or DCM+ML. The ML biomass can be limited by nutrients, light, or both. We predict how the vertical distribution, relative resource limitation, and biomass of phytoplankton will change across environmental gradients. We parameterized our model to represent potentially light and phosphorus limited freshwater lakes, but the model is applicable to a broad range of vertically stratified systems. Increasing nutrient input from the sediments or to the mixed layer increases light limitation, shifts phytoplankton towards the surface, and increases total biomass. Increasing background light attenuation increases light limitation, shifts the phytoplankton towards the surface, and generally decreases total biomass. Increasing mixed layer depth increases, decreases, or has no effect on light limitation and total biomass. Our model is able to replicate the diverse vertical distributions observed in nature and explain what underlying mechanisms drive these distributions.

DOI： 10.1016/j.jtbi.2010.09.041

Scopus

PubMed

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10750-010-0341-5

Other Link： http://link.springer.com/article/10.1007/s10750-010-0341-5/fulltext.html

Publishing type：Research paper (scientific journal)  

Detailed cross-sectional temperature and oxygen distributions during winter were examined over 5 years (2003-2007) in large, warm, monomictic Lake Biwa. The distribution patterns showed year-to-year variation in the degree of spatial heterogeneity and indicated that both convective mixing and gravity currents contributed to the delivery of oxygen to the profundal zone. We encountered a warm winter in 2007, when deep-water oxygenation was delayed by more than a month relative to normal years. Data obtained during the period of oxygenation in 2007 suggest that the timing of complete oxygenation of the bottom water (or lower layers of the hypolimnion) was controlled by physical processes responsible for destruction of the weak thermal stratification near the bottom. This study revealed that Lake Biwa is sensitive to year-to-year variations in winter meteorological conditions. Specifically, the bottom environments are highly susceptible to a warm winter, especially when it follows a cold winter. © 2010 The Japanese Society of Limnology.

DOI： 10.1007/s10201-009-0307-3

Scopus

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s12237-009-9210-8

Other Link： http://link.springer.com/article/10.1007/s12237-009-9210-8/fulltext.html

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Phytoplankton compete for nutrients and light in a vertically heterogeneous environment determined by turbulent mixing. We analyzed a model of competition between two phytoplankton species in a stratified water column. We assume that the surface layer is uniformly mixed and that the deep layer is poorly mixed, as is commonly observed in lakes and oceans. We employed two analytical techniques, I(out) - (R)theory in the mixed surface layer and a game theoretical approach in the deep layer. Under our assumptions, at equilibrium, each species is either absent or resides in the benthic layer, the deep layer, or the surface layer. Assuming a trade-off between nutrient- and light-competitive abilities, we obtained five spatial configurations of coexistence and the corresponding parameter regions where they occur. Good light competitors show two distinct ecological niches: in mesotrophic conditions, they live as understory species below a layer of good nutrient competitors; in eutrophic conditions, they live as competitive dominants in the surface layer. Multiple regions of alternative stable states are possible in parameter space. This work extends previous phytoplankton competition theory to stratified water columns, as commonly found in lakes and oceans.

DOI： 10.1086/600113

Scopus

PubMed

Publishing type：Research paper (scientific journal)  

Diatoms are key players in the global carbon cycle and most aquatic ecosystems. Their cell sizes impact carbon sequestration and energy transfer to higher trophic levels. We report fundamental differences in size distributions of marine and freshwater diatoms, with marine diatoms significantly larger than freshwater species. An evolutionary game theoretical model with empirical allometries of growth and nutrient uptake shows that these differences can be explained by nitrogen versus phosphorus limitation, nutrient fluctuations and mixed layer depth differences. Constant and pulsed phosphorus supply select for small sizes, as does constant nitrogen supply. In contrast, intermediate frequency nitrogen pulses common in the ocean select for large sizes or the evolutionarily stable coexistence of large and small sizes. Size-dependent sinking interacts with mixed layer depth (MLD) to further modulate optimal sizes, with smaller sizes selected for by strong sinking and shallow MLD. In freshwaters, widespread phosphorus limitation, together with strong sinking and shallow MLD produce size distributions with smaller range, means and upper values, compared with the ocean. Shifting patterns of nutrient limitation and mixing may alter diatom size distributions, affecting global carbon cycle and the structure and functioning of aquatic ecosystems. © 2009 by The National Academy of Sciences of the USA.

DOI： 10.1073/pnas.0810891106

Scopus

PubMed

Language：English   Publishing type：Research paper (bulletin of university, research institution)  

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Planktonic microorganisms are affected by various size-dependent processes both from the bottom up and from the top down. We developed a simple resource-consumer model to explore how size-dependent resource uptake and resource loss influence the growth of, and competition between, planktonic microorganisms. We considered three steps of resource uptake: diffusive transport of resource molecules, uptake by membrane transporters, and cellular enzymatic catalysis, and we investigated optimal cell size when one, two, or three of those steps limit resource uptake. Optimal cell size depends negatively on the size of resource molecules when resource uptake is limited by diffusive transport and membrane uptake. When competing for two resources of different molecular sizes, two different-sized consumers can coexist if the inputs of resources and sizes of consumers are correctly chosen. The model suggests that mixtures of various-sized resources can promote coexistence and size diversity of microorganisms even if the availability of one element, such as carbon, nitrogen, or phosphorus, limits the whole community. Model predictions include that bacteria grown on maltose or polysaccharides should be smaller compared with those grown on glucose under carbon limitation. Our results suggest that size of resource molecules can be an important factor in microbial resource competition in aquatic environments.

DOI： 10.1086/523950

Scopus

PubMed

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

A model of phytoplankton dynamics within a water column was analyzed with special consideration on the existence of a bifurcation set in the parameter space. We considered two resources, light and a limiting nutrient, for phytoplankton growth and assumed that the water column is separated into two layers by thermal and/or density stratification. It was shown that there exists a bifurcation set in the parameter space when the growth function meets several conditions that are general for growth functions of two essential resources. Specifically, these conditions include that a less abundant of the two resources limits the growth while the effect of the other is sufficiently small. Folded structure with two stable states separated by one unstable state appears in the catastrophe manifold when parameters move to a certain direction with a certain curvature from a point in the bifurcation set. These results suggest that occurrence of discontinuous transition between two alternative vertical patterns is possible nature of phytoplankton dynamics within a stratified water column.

DOI： 10.1007/s00285-005-0349-z

Scopus

PubMed

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

Phytoplankton response to nutrients was examined with a 26-yr database from the Delaware Estuary. Biomass-normalized primary production did not increase linearly with increasing nutrient concentrations and instead showed saturation at comparatively low nutrient concentrations and decreased at high concentrations. To separate the effects of light availability and temperature on primary production from those of other environmental variables, we developed an empirical model of areal primary production. The model equation was obtained for the entire dataset and the effect of the residual variables was expressed as correction factors of observed primary production to the model estimates. The model accounted for 67% of variability of observed primary production overall, indicating that production of the estuary was mainly controlled by light availability and temperature. In contrast, a similar model applied to a Chesapeake Bay database had shown a poorer fit, indicating consistent light limitation in the Delaware Estuary and varying strengths of light and nutrient limitation in the Chesapeake Bay. The relationships between nutrients and correction factors for the Delaware Estuary showed that the model underestimates primary production at low and mid nutrient concentrations and overestimates it at high concentrations. The model fit and correction factors for five regions of the estuary indicate a high-nutrient, low-growth situation in the Delaware Estuary because of varying influences of light limitation, proportions of nutrients, and probably toxic contaminants in areas with large anthropogenic inputs - including high nutrients. © 2006, by the American Society of Limnology and Oceanography, Inc.

DOI： 10.4319/lo.2006.51.1_part_2.0424

Scopus

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/03680770.2001.11901869

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

We showed a catastrophic transition between a surface maximum pattern and a subsurface maximum pattern of phytoplankton in a water column by a mathematical model considering the vertical distribution of phytoplankton and two resources, light and a limiting nutrient. In our model, we assumed that a water column consists of two layers: a complete mixing layer above a seasonal thermocline and an incomplete mixing layer below it. From numerical calculation of the model, we obtained that there are two stable vertical patterns of phytoplankton over a certain range of parameters of the model: a pattern having its maximum below the thermocline and another having its maximum above the thermocline. As other models having multiple stable equilibria, our model also exhibits a hysteresis effect and catastrophic transition when one of the parameters of the model changes continuously. These results indicate the possibility of the existence of alternative equilibria of vertical patterns of phytoplankton even if the trophic status and physical condition of the water column are similar. Moreover, the catastrophic transition between the steady states suggests one of the possible mechanisms of autumn algal blooms.

DOI： 10.1006/jtbi.2002.3007

Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Participation form：Joint(The main charge)  

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