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MIKI AIDA KAZUYUKI ITOH HIROAKI IKEDA NAOKUNI HARADA YASUO ISHII KENJI USUI 《Weed Biology and Management》2004,4(3):127-135
Paddy herbicides have the potential to cause adverse effects on non-target plants. Susceptibilities of some aquatic ferns ( Azolla japonica Franch. et Savat., Isoetes japonica A. Braun, Marsilea quadrifolia L. and Salvinia natans All.) and duckweeds ( Lemna minor L. and Spirodela polyrhiza Schleid.) to paddy herbicide bensulfuron methyl (BSM) were evaluated with a 20 day exposure experiment using 200 cm2 pots. The BSM concentrations in the surface water of monitoring pots with no plants dissipated exponentially with half lives of 3.5 and 3.9 days at application rates of 15 and 150 g ha−1 , respectively. The BSM concentrations in the surface water 1 day after application in the culture pots were comparable among plant species, and were lower than those in the monitoring pots. Bensulfuron methyl reduced the plant growth in all species. I . japonica showed the lowest intrinsic relative growth rate (RGR) and the lowest susceptibility with an effective dose resulting in 50% growth inhibition (ED50 ) of 21 g ha−1 . Except for I . japonica , the RGR of the duckweeds was similar to the ferns, and ED50 for the duckweeds was higher than the ferns. ED50 for Sa . natans , A . japonica and M . quadrifolia were 1.1, 1.8 and 1.2 g ha−1 , respectively, which were smaller than 1/20 of the recommended field dose (51–75 g ha−1 ) and ranged from 1/2 to 1/6 of ED50 for L . minor and Sp . polyrhiza (6.5 and 3.2 g ha−1 , respectively). These results suggest that BSM application in paddy fields and its runoff in some localities is expected to have adverse effects on the growth of Sa . natans , A . japonica and M . quadrifolia . 相似文献
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YUGO SHIMIZU KAZUTAKA TAKAHASHI SHIN-ICHI ITO SHIGEHO KAKEHI HIROAKI TATEBE ICHIRO YASUDA AKIRA KUSAKA TOMOHARU NAKAYAMA 《Fisheries Oceanography》2009,18(5):312-327
The lateral transport of organic carbon in large grazing copepods ( Neocalanus cristatus, Neocalanus flemingeri, Neocalanus plumchrus and Eucalanus bungii ) from the Oyashio area to the mixed water region (MWR) by the coastal Oyashio intrusion was estimated using the data of VMPS (vertical multiple plankton sampler) and 1500 dbar-referred geostrophic transport from the CTD (conductivity temperature depth sensor) data of five cruises during June 2001 to April 2002 on a repeat observation section OICE (Oyashio Intensive observation line off Cape Erimo), which extends southeastward from Hokkaido Island, Japan. The transport to MWR by the coastal Oyashio intrusion was estimated to be 5.3 × 1011 g C for the four species. Data from profiling floats also indicated that the copepods were advected from OICE to MWR by the coastal Oyashio intrusion within about 2 months. This transport is considered to be one of the significant sources of organic carbon in MWR as it is larger than the amount of large zooplankton consumed by Pacific saury ( Cololabis saira ) in MWR, one of the dominant copepod predators in this region. 相似文献
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MAKOTO TERAZAKI HIROAKI SAITO HIROMI KASAI TOKIHIRO KONO YASUHIRO KAWASAKI SATORU TAGUCHI 《Fisheries Oceanography》1995,4(2):158-170
The spatial distribution and seasonal variability of epipelagic chaetognaths along the Kurile Islands and off south-east Hokkaido, in the western subarctic Pacific Ocean. were investigated during the period from May 1990 to October 1992. Sagitta elegans was the dominant species among the epipelagic chaetognaths in the study area. Juvenile S. elegans were distributed mainly along the path of the mixed water which was determined by the acceleration potential anomaly (APA) at the iso-pycnal density surface of 26.6 σθ. The location of the path of The mixed water meandered around cyclonic and anticyclonic eddies. Catches of S. elegans were made at temperatures ranging from 4.5 to 22.2C. The juvenile distribution, however, was mostly restricted to between 1 and 4C of the potential temperature determined at the isopycnal density surface of 26.6 σθ. Variability in the juvenile abundance within the path of the mixed water could be caused by predation rather than by food limitation because microzooplankton, which are known to he prey for juveniles, were abundant enough to meet the food requirements of juveniles in the study area. Adults occurred in spring (April-May) and young individuals (juvenile and stage 1) were abundant in summer (June-July), when a strong thermocline developed. The main spawning period appears to be during April-May, with a possible second spawning period in the autumn. 相似文献
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Variability in timing and magnitude of spring bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan 总被引：6，自引：0，他引：6
HIROMI KASAI HIROAKI SAITO AKIRA YOSHIMORI & SATORU TAGUCHI 《Fisheries Oceanography》1997,6(2):118-129
The spring bloom of phytoplankton is a well-established, regular, seasonal event in the western subarctic Pacific and is considered one of the most important conditions of massive production of pelagic fishes. A series of 12 cruises was conducted from 1990 to 1992 to examine the timing and magnitude of the spring phytoplankton bloom in the Oyashio region, the western subarctic Pacific off Hokkaido, Japan. An interannual variability in the bloom events was also analysed. On the basis of hydrographical characteristics, the study area was divided into three water masses: the Oyashio Water Mass, the Mixed Water Mass, and the Coastal Water Mass. Spring blooms were observed first in April in the Oyashio and the Coastal Water Masses, and continued to May in 1991 and 1992. However, no bloom was recorded in the Mixed Water Mass. High nutrient supply into the surface mixed layer during winter is likely to be one of the factors supporting an intense spring bloom in the Oyashio Water Mass. A significant positive relationship between log-transformed surface chlorophyll a concentration and maximum density gradient (MDG) within the euphotic layer was obtained in April, indicating the importance of vertical stability of the water column in the initiation of spring blooms in the Oyashio and the Coastal Water Masses. The spring blooms in 1991 were much more extensive and lasted longer than in 1990. It is suggested that meteorological conditions and abundance of grazers were responsible for this interannual difference. 相似文献
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YUKO SHIMAMOTO NAOFUMI NOMURA TOKUSHIRO TAKASO HIROAKI SETOGUCHI 《Weed Biology and Management》2011,11(3):118-126
The invasion of natural ecosystems by exotic species is a major threat to biodiversity on a local, regional, and global scale. Endemic island flora are particularly vulnerable to invasive species. Bidens pilosa var. radiata is a common invasive weed of roadsides, which are subject to clipping, on Japanese subtropical islands. To assess compensation by the weed to damage by clipping, a pot experiment was conducted under common garden conditions. The above‐ground parts were clipped with pruning shears at various frequencies, ranging from no clipping (the control) to clipping at 4–16 week intervals for 32 weeks in summer. The clipped individuals regenerated new branches from the axillary buds and flowered for ≤12 weeks after the clipping. The regeneration after the clipping gave rise to secondary reproduction, whereas minimal regeneration occurred in the unclipped individuals after the maturation of the fruit. Consequently, the total flower head mass, represented by the dry weight of the inflorescences throughout the experiment, was higher on the individuals that were clipped at 12 and 16 week intervals than on the unclipped individuals, suggesting overcompensation in fecundity. At the higher frequencies of above‐ground clipping, the flower head mass was suppressed at 8 week clipping intervals, while both the flower head mass and the productive biomass were suppressed at 4 week clipping intervals. This indicates that clipping at intervals of ≤8 weeks is required to prevent the reproduction of this weed. 相似文献
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MASAAKI TACHIBANA KAZUYUKI ITOH HIROAKI WATANABE SOICHI NAKAYAMA 《Weed Biology and Management》2010,10(1):9-15
This study was conducted to determine the reproductive characteristics of Barbarea vulgaris under different disturbance regimes (mowing and tilling) in two different habitats: a levee and a wheat field. On the levee, 77 of the 114 individuals that had had their floral stalks removed by the first mowing produced new rosettes at the basal part of the stem during the same growing season. The plants that were mowed four times per year had a significantly greater survival rate than the plants that were mowed twice per year. The levee population that was mowed without tillage was largely maintained by vegetative reproduction. These results suggest that mowing the levees promotes the vegetative reproduction of B. vulgaris and helps it to compete with tall-growing plants, thus facilitating its survival as a perennial. In spite of the high sprouting ability of the plant's root fragments, most of the root fragments did not regenerate when buried or when exposed to high soil moisture conditions in tilled wheat fields. The population of B. vulgaris in tilled wheat fields was maintained almost entirely by sexual reproduction. Barbarea vulgaris can survive under two different management regimes by altering its mode of reproduction. 相似文献