Home About us Contact
|
Home About us Contact | ||
|
|
||
Paddy Fields (paddy + field)
Kinds of Paddy Fields Selected AbstractsAPPLICATION OF DIFFUSIVE TANK MODEL IN DRAINAGE ANALYSIS OF PADDY FIELDS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2004Rong-Song Chen ABSTRACT: A diffusive tank model has been successfully applied to the simulation of runoff from paddy fields in Japan because it can well describe the features of local water flows. The main goal of the study is to evaluate the performance of the diffusive tank model with the calibrated parameters obtained in Jyau-Shi to simulate discharge from paddy fields in two experimental catchments located in the areas of Shing-Ying and Ta-Liao, Southwestern Taiwan. The simulations were verified by comparing the model results with observed runoff data from the two experimental catchments. The model predicted the discharge from the paddy fields well. This indicates that the model with the calibrated parameters may be used in other paddy fields in Taiwan. [source] Contrasting infection frequencies of Neotyphodium endophyte in naturalized Italian ryegrass populations in Japanese farmlandsGRASSLAND SCIENCE, Issue 2 2010Masayuki Yamashita Abstract Neotyphodium endophytes often confer benefits to their host grasses and may enhance invasiveness of some grasses. The knowledge of infection frequencies of endophytes among invading weed populations is necessary to understand the relationships between endophyte infection and invasiveness. Here we present data on infection frequencies of Italian ryegrass (Lolium multiflorum Lam.), an important weed in some farmlands in Japan, persisting in contrasting farmlands: a terraced paddy field and a wheat-soybean double-cropped field in the western region of Shizuoka prefecture, Japan. The terraced paddy site is a mosaic of several landscape elements such as paddy fields, levees, fallow and abandoned fields, with a high percentage of non-crop area. Rice (Oryza sativa L.) has been cultivated for more than a decade with no application of chemical fertilizers, pesticides and fungicides. The wheat-soybean field is characterized by the aggregation of large-scaled fields that were originally reconstructed paddy fields, showing a low percentage of non-crop area. Wheat and soybean have been grown as winter and summer crops, respectively, using chemical fertilizers and herbicides. We examined the presence or absence of endophytes in a total of 1200 seeds sampled from the two Italian ryegrass populations. The terraced paddy population exhibited a markedly high infection frequency (91.0%), due possibly to selective feeding of non-infected seeds by insects. In contrast, the wheat-soybean farmland population showed almost no infection (1.1%), whereas the putative source of the invasion in the proximity exhibited a relatively high infection rate (64.4%). Such a micro-scale variation in infection frequencies may be attributable to a loss in endophyte viability within the wheat-soybean field. The findings suggest that endophyte infection frequency may markedly differ among the Italian ryegrass populations even within the same region, presumably depending on the abundance of the seed-eating insects, farmland management regimes and/or environmental conditions such as soil humidity. [source] Influences of meteorological and vegetational factors on the partitioning of the energy of a rice paddy fieldHYDROLOGICAL PROCESSES, Issue 8 2005Hiroki Oue Abstract Observations made in a paddy field were analysed to show the influences of meteorological and vegetational factors on the crop's energy budget. Energy budget in the paddy field was characterized by the major partitioning to latent heat flux LE and by the negative Bowen ratio B mostly in the afternoon. Canopy resistance rc, estimated with the Penman,Monteith equation, was related to the influences of solar radiation SR, vapour pressure deficit VPD and plant height. The results demonstrated that rc could not directly account for B but that critical canopy resistance rcc, defined as the canopy resistance when B = 0, could be used to standardize rc, and that rc , rcc proved to be a good parameter to account for B. Influences of bulk stomatal response on energy partitioning were assessed as follows: the Bowen ratio dropped below zero, while the bulk stomatal aperture dwindled with the increase of VPD. In addition, stomata of a big leaf acted to promote the partitioning to LE against the rise of SR in the condition of higher VPD. Copyright © 2004 John Wiley & Sons, Ltd. [source] SEXUAL PROCESSES AND PHYLOGENETIC RELATIONSHIPS OF A HOMOTHALLIC STRAIN IN THE CLOSTERIUM PERACEROSUM,STRIGOSUM,LITTORALE COMPLEX (ZYGNEMATALES, CHAROPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 2 2010Yuki Tsuchikane Members of the Closterium peracerosum,strigosum,littorale (C. psl.) complex are unicellular charophycean algae in which there are two modes of zygospore formation, heterothallic and homothallic. A homothallic strain of Closterium (designation, kodama20) was isolated from a Japanese rice paddy field. Based on alignment of the 1506 group-I introns, which interrupt nuclear SSU rDNAs, homothallic kodama20 is most closely related to the heterothallic mating group II-B, which is partially sexually isolated from group II-A. Time-lapse photography of the conjugation process in kodama20 revealed that most of the observed zygospores originated from one vegetative cell. The sexual conjugation process consisted of five stages: (1) cell division resulting in the formation of two sister gametangial cells from one vegetative cell, (2) formation of a sexual pair between the two sister gametangial cells (or between gametangial cells of another adjoined individual), (3) formation of conjugation papillae, (4) release of gametic protoplasts from both members of a pair, and (5) formation of the zygospore by protoplast fusion. For conjugation to progress, the cell density and light condition in the culture was critical. We suggested the presence of a conjugation promotion factor. [source] Nocturnal migration of dragonflies over the Bohai Sea in northern ChinaECOLOGICAL ENTOMOLOGY, Issue 5 2006HONG-QIANG FENG Abstract 1.,A sudden increase and subsequent sharp decrease of catches of dragonflies in a searchlight trap, with Pantala flavescens Fabricius (Odonata: Libellulidae) predominating, observed at Beihuang Island in the centre of the Bohai Gulf, in 2003 and 2004, indicated a seasonal migration of these insects over the sea during the night in China. The movements were associated with the onset of fog. 2.,Simultaneous radar observations indicated that the nocturnally migrating dragonflies generally flew at altitudes of up to 1000 m above sea level, with high density concentrations at about 200,300 or 500 m; these concentrations were coincident with the temperature inversion. 3.,During early summer, the dragonflies oriented in a downwind direction, so that the displacement direction varied between different altitudes. In contrast, during late summer, the dragonflies were able to compensate for wind drift, even headwind drift, so as to orient south-westward no matter how the wind changed, and thus the displacement direction was towards the south-west. 4.,The duration of flight, estimated from the variation of area density derived from radar data and hourly catches in the searchlight trap through the night, was about 9,10 h. The displacement speed detected using radar was ,5,11 m s,1. Therefore, the dragonflies might migrate 150,400 km in a single flight. 5.,The dragonflies were thought to originate in Jiangsu province and they migrated into north-east China to exploit the temporary environment of paddy fields in early summer. Their offspring probably migrated back south during late summer and autumn. [source] Biogeography of wetland rice methanotrophsENVIRONMENTAL MICROBIOLOGY, Issue 4 2010Claudia Lüke Summary We focused on the functional guild of methane oxidizing bacteria (MOB) as model organisms to get deeper insights into microbial biogeography. The pmoA gene was used as a functional and phylogenetic marker for MOB in two approaches: (i) a pmoA database (> 4000 sequences) was evaluated to obtain insights into MOB diversity in Italian rice paddies, and paddy fields worldwide. The results show a wide geographical distribution of pmoA genotypes that seem to be specifically adapted to paddy fields (e.g. Rice Paddy Cluster 1 and Rice Paddy Cluster 2). (ii) On the smaller geographical scale, we designed a factorial experiment including three different locations, two rice varieties and two habitats (soil and roots) within each of three rice fields. Multivariate analysis of terminal restriction fragment analysis profiles revealed different community patterns at the three field sites, located 10,20 km apart. Root samples were characterized by high abundance of type I MOB whereas the rice variety had no effect. With the agronomical practice being nearly identical, historical contingencies might be responsible for the field site differences. Considering a large reservoir of viable yet inactive MOB cells acting as a microbial seed bank, environmental conditions might have selected and activated a different subset at a time thereby shaping the community. [source] Contrasting infection frequencies of Neotyphodium endophyte in naturalized Italian ryegrass populations in Japanese farmlandsGRASSLAND SCIENCE, Issue 2 2010Masayuki Yamashita Abstract Neotyphodium endophytes often confer benefits to their host grasses and may enhance invasiveness of some grasses. The knowledge of infection frequencies of endophytes among invading weed populations is necessary to understand the relationships between endophyte infection and invasiveness. Here we present data on infection frequencies of Italian ryegrass (Lolium multiflorum Lam.), an important weed in some farmlands in Japan, persisting in contrasting farmlands: a terraced paddy field and a wheat-soybean double-cropped field in the western region of Shizuoka prefecture, Japan. The terraced paddy site is a mosaic of several landscape elements such as paddy fields, levees, fallow and abandoned fields, with a high percentage of non-crop area. Rice (Oryza sativa L.) has been cultivated for more than a decade with no application of chemical fertilizers, pesticides and fungicides. The wheat-soybean field is characterized by the aggregation of large-scaled fields that were originally reconstructed paddy fields, showing a low percentage of non-crop area. Wheat and soybean have been grown as winter and summer crops, respectively, using chemical fertilizers and herbicides. We examined the presence or absence of endophytes in a total of 1200 seeds sampled from the two Italian ryegrass populations. The terraced paddy population exhibited a markedly high infection frequency (91.0%), due possibly to selective feeding of non-infected seeds by insects. In contrast, the wheat-soybean farmland population showed almost no infection (1.1%), whereas the putative source of the invasion in the proximity exhibited a relatively high infection rate (64.4%). Such a micro-scale variation in infection frequencies may be attributable to a loss in endophyte viability within the wheat-soybean field. The findings suggest that endophyte infection frequency may markedly differ among the Italian ryegrass populations even within the same region, presumably depending on the abundance of the seed-eating insects, farmland management regimes and/or environmental conditions such as soil humidity. [source] Assessment of land-use impact on streamflow via a grid-based modelling approach including paddy fieldsHYDROLOGICAL PROCESSES, Issue 19 2005Seong Joon Kim Abstract To investigate the hydrologic impacts of land-use changes on streamflow for an urbanizing watershed with paddy fields, a grid-based daily hydrologic model was adopted. The model was calibrated with two years (2000,2001) of observed streamflow data and validated using 5 months (2001) of measured soil moisture data and 1 year (2002) of observed streamflow data. After the model was tested, it was run to estimate impacts of urbanization on each hydrologic component with the land-use data sets for 1986, 1994, and 2002 generated from Landsat TM satellite images. Total runoff increased from 41·4% (1986) to 44·9% (2002) for a 5·4% increase in urban area, implying that direct runoff increase exceeded baseflow decrease. Urbanization affected the proportions of direct runoff for each land-use category more than the change in total runoff and the ratio of direct runoff to total runoff. The change proportions in direct runoff for urban areas, paddy fields, and forest were 14·3%, ,9·8% and ,6·7% respectively for a 5·4% increase, 4·6% decrease and 3·4% decrease in each land-use area respectively. The results indicate that paddy fields play an important role in runoff regulation, and the evaluation method can assist regional policy makers in developing land management strategies that minimize hydrologic impacts on streamflow. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis of rainfall-runoff relation in paddy fields by diffusive tank modelHYDROLOGICAL PROCESSES, Issue 13 2003Rong-Song Chen Abstract Due to the occurrence of ponding during the period of rice growth, the analyses of rainfall-runoff in paddy fields are different from those in general lands. The diffusive tank model has been successfully applied in rainfall-runoff simulations in paddy fields because it can well describe the features of the local water flow. In most of the applications of this model, although the determination of the related model parameters is important, detailed investigations on each individual parameter are definitely needed to improve the accuracy of the results. In the study, an improved procedure is proposed to determine certain variables involved in the diffusive tank model and the application is conducted in a field area in Taiwan. In the application, the roughness of the river channel was assessed according to the actual field conditions. Instead of using the observed water levels in each rainfall event, the notch width of the rectangular contracted weir per unit area was evaluated by direct field measurements to calibrate the discharge coefficient. Test results from the selected field in six rainfall events showed that the local average value of the notch width of the rectangular contracted weir per unit area was 1·025 m/ha. Compared to the results of field measurements, the relative errors of the predictions were within 3% in all tests of rainfall events. In addition, for different types of catchment partitions, it was found that the corresponding weir discharge coefficients remained roughly unchanged. Copyright © 2003 John Wiley & Sons, Ltd. [source] Daily streamflow modelling and assessment based on the curve-number techniqueHYDROLOGICAL PROCESSES, Issue 16 2002Jin-Yong Choi Abstract A cell-based long-term hydrological model (CELTHYM) that can be integrated with a geographical information system (GIS) was developed to predict continuous stream flow from small agricultural watersheds. The CELTHYM uses a cell-by-cell soil moisture balance approach. For surface runoff estimation, the curve number technique considering soil moisture on a daily basis was used, and release rate was used to estimate baseflow. Evapotranspiration was computed using the FAO modified Penman equation that considered land-use-based crop coefficients, soil moisture and the influence of topography on radiation. A rice paddy field water budget model was also adapted for the specific application of the model to East Asia. Model sensitivity analysis was conducted to obtain operational information about the model calibration parameters. The CELTHYM was calibrated and verified with measured runoff data from the WS#1 and WS#3 watersheds of the Seoul National University, Department of Agricultural Engineering, in Hwaseong County, Kyounggi Province, South Korea. The WS#1 watershed is comprised of about 35·4% rice paddy fields and 42·3% forest, whereas the WS#3 watershed is about 85·0% forest and 11·5% rice paddy fields. The CELTHYM was calibrated for the parameter release rate, K, and soil moisture storage coefficient, STC, and results were compared with the measured runoff data for 1986. The validation results for WS#1 considering all daily stream flow were poor with R2, E2 and RMSE having values of 0·40, ,6·63 and 9·69 (mm), respectively, but validation results for days without rainfall were statistically significant (R2 = 0·66). Results for WS#3 showed good agreement with observed data for all days, and R2, E2 and RMSE were 0·92, 0·91 and 2·23 (mm), respectively, suggesting potential for CELTHYM application to other watersheds. The direct runoff and water balance components for watershed WS#1 with significant areas of paddy fields did not perform well, suggesting that additional study of these components is needed. Copyright © 2002 John Wiley & Sons, Ltd. [source] Olfactory response of Trigonotylus caelestialium (Het.: Miridae) to rice plant and gramineous weedsJOURNAL OF APPLIED ENTOMOLOGY, Issue 8 2007T. Niiyama Abstract:, The olfactory response of Trigonotylus caelestialium, to rice, Oryza sativa L., and two species of gramineous weeds, Poa annua and Digitaria ciliaris, was investigated with an olfactometer to clarify the role of host-plant odours as olfactory cues in their host-finding behaviour. Third-instar nymphs and adult males were significantly attracted to whole plants (above ground parts) of P. annua. However, adult females were not significantly attracted to whole plants of P. annua. Attractancy of rice to T. caelestialium differed with the growth stage and part of the plant. Adult females were significantly attracted to stems and leaves in the panicle-formation stage, and panicles in the flowering stage. They were not attracted to stems and leaves in the fourth-leaf stage and flowering stage, or to panicles in the milk-and full-ripe stages. Although adult males were significantly attracted to stems and leaves in the panicle-formation stage, they were not attracted to the other rice structures tested. Both females and males were significantly attracted to stems and leaves, as well as panicles of D. ciliaris in the flowering stage. The findings suggest that T. caelestialium use host-plant volatiles as olfactory cues to find their host plants and their invasion to paddy fields were caused by olfactory responses to rice plant. [source] Bacillus cereus is common in the environment but emetic toxin producing isolates are rareJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2006M. Altayar Abstract Aims:, To determine the incidence of emetic toxin producing Bacillus cereus in soil, animal faeces and selected vegetable produce to compare the results with the previously reported high incidence in rice paddy fields. To examine whether the emetic toxin has antibiotic activity. Methods and Results:, The incidence of emetic toxin producing B. cereus was evaluated by plating on selective agar 271 samples of soils, animal faeces, raw and processed vegetables. Overall, 45·8% of samples were positive for B. cereus. One hundred and seventy-seven B. cereus isolates were recovered at 30°C with the grand mean spore count being 2·6 ± 1·7 log10 CFU g,1 and 148 B. cereus isolates were recovered at 7°C with the grand mean spore count being 2·2 ± 1·2 log10 CFU g,1 of the177 B. cereus isolated at 30°C, only 3 were positive for emetic toxin production at a titre of 1/64, 1/32, 1/16, respectively. Also, 1 of 148 B. cereus isolated at 7°C was positive for emetic toxin production to a titre of 1/128. All positive isolates came from washed or unwashed potato skins, one was psychrotrophic as determined by PCR and growth at 7°C on subculture. The emetic toxin was not shown to have any antibiotic effects in growth inhibition studies. Conclusions:, While B. cereus was a common isolate, the incidence of the emetic strain was rare. This is in contrast to previous findings of the high incidence in rice paddy fields and the processing environment, which may suggest rice is a selective area for growth of the emetic strain of B. cereus. Significance and Impact of Study:, The finding that a psychrotrophic isolate of B. cereus can produce emetic toxin is the first ever such observation and suggests the possibility that psychrotrophic isolates could grow in refrigerated fresh foods and cause emesis. The incidence of emetic B. cereus strains in rice paddy fields now requires further study for comparison with the low incidence found in other soils. The emetic toxin failed to inhibit the growth of other bacterial, fungal and yeast species. Whether the toxin (which is similar in structure to the antibiotic valinomycin) plays a competitive role in the environment therefore remains unclear. [source] Influence of host plant odours on invasion of the rice leaf bug Trigonotylus caelestialium into paddy fieldsAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2010Tatsuya Fujii 1The host-odour preferences of the rice leaf bug Trigonotylus caelestialium between the rice plant Oryza sativa L. and four species of graminaceous weeds, Poa annua, Alopecurus aequalis, Digitaria ciliaris and Eleusine indica, were investigated with an olfactometer aiming to clarify the influence of these odours on invasion of the bug to paddy fields at the flowering stage of rice. 2Both female and male adults significantly preferred the graminaceous weed A. aequalis in the flowering stage to rice in the fifth-leaf stage. The bugs also significantly preferred flowering P. annua and A. aequalis to rice in the panicle-formation stage. However, the bugs showed no preferences between rice in the flowering and grain-filling stages and the flowering graminaceous weeds P. annua, D. ciliaris and E. indica. 3The preference of the rice leaf bug for the flowering graminaceous weeds before rice flowering coincides with the fact that these bugs mainly live on these weeds before rice flowering. It is considered that the bug's similar preference for flowering rice panicles as the flowering graminaceous weeds causes the intense invasion of the bug into paddy fields at this rice developmental stage. [source] Material Flows in a Social Context: A Vietnamese Case Study Combining the Materials Flow Analysis and Action-in-Context FrameworksJOURNAL OF INDUSTRIAL ECOLOGY, Issue 1 2007Marieke HOBBES Summary Materials flow analysis (MFA) is one of the central achievements of industrial ecology. One direction in which one can move MFA beyond mere accounting is by putting the material flows in their social context. This "socially extended MFA" may be carried out at various levels of aggregation. In this article, specific material flows will be linked to concrete actors and mechanisms that cause these flows,using the action-in-context (AiC) framework, which contains, inter alia, both proximate and indirect actors and factors. The case study site is of Tat hamlet in Vietnam, set in a landscape of paddy fields on valley floors surrounded by steep, previously forested slopes. Out of the aggregate MFA of Tat, the study focuses on material flows associated with basic needs and sustainability. The most important actors causing these material flows are farming households, politicians, traders, and agribusiness firms,of which local politicians turned out to be pivotal. The study shows the value of combining MFA with actor-based social analysis. MFA achieves the balanced quantification of the physical system, thus helping to pinpoint key processes. Actor-based analysis adds the causal understanding of what drives these key processes, leading to improved scenarios of the future and the effective identification of target groups and instruments for policy making. [source] APPLICATION OF DIFFUSIVE TANK MODEL IN DRAINAGE ANALYSIS OF PADDY FIELDS,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 1 2004Rong-Song Chen ABSTRACT: A diffusive tank model has been successfully applied to the simulation of runoff from paddy fields in Japan because it can well describe the features of local water flows. The main goal of the study is to evaluate the performance of the diffusive tank model with the calibrated parameters obtained in Jyau-Shi to simulate discharge from paddy fields in two experimental catchments located in the areas of Shing-Ying and Ta-Liao, Southwestern Taiwan. The simulations were verified by comparing the model results with observed runoff data from the two experimental catchments. The model predicted the discharge from the paddy fields well. This indicates that the model with the calibrated parameters may be used in other paddy fields in Taiwan. [source] Insecticide resistance spectra and resistance mechanisms in populations of Japanese encephalitis vector mosquitoes, Culex tritaeniorhynchus and Cx. gelidus, in Sri LankaMEDICAL AND VETERINARY ENTOMOLOGY, Issue 4 2000S. H. P. P. Karunaratne Summary Culex tritaeniorhynchus Giles and Cx. gelidus Theobald (Diptera: Culicidae), both vectors of Japanese encephalitis, were collected in 1984 and 1998 from two disease endemic localities in Sri Lanka: Anaradhapura and Kandy. Using wild-caught adult mosquitoes from light traps, log dosage-probit mortality curves for insecticide bioassays were obtained for three insecticides: malathion (organophosphate), propoxur (carbamate) and permethrin (pyrethroid). LD50 values showed that, in 1998, Cx. tritaeniorhynchus was ,100-fold more resistant to malathion and 10-fold more resistant to propoxur than was Cx. gelidus. This difference was attributed to Cx. tritaeniorhynchus breeding mostly in irrigated rice paddy fields, where it would have been exposed to pesticide selection pressure, whereas Cx. gelidus breeds in other types of aquatic habitats less prone to pesticide applications. Resistance in Cx. tritaeniorhynchus increased between 1984 and 1998, whereas Cx. gelidus remained predominantly susceptible. Propoxur inhibition of acetylcholinesterase (AChE) activity (the target site of organophosphates and carbamates) indicated that in 1998, frequencies of insensitive AChE-based resistance were 9% in Cx. gelidus and 2,23% in Cx. tritaeniorhynchus, whereas in 1984 this resistance mechanism was detected only in 2% of the latter species from Anaradhapura. The AChE inhibition coefficient (ki) with propoxur was 1.86 ± 0.24 × 105 m,1 min,1 for Cx. tritaeniorhynchus from Anaradhapura in 1998. Both species were tested for activity levels of detoxifying glutathione S-trans- ferases (GSTs) and malathion-specific as well as general carboxylesterases. High activities of GSTs and carboxylesterases were detected in Cx. tritaeniorhynchus but not Cx. gelidus. Malathion-specific carboxylesterase was absent from both species. Native polyacrylamide gel electrophoresis resolved two elevated general carboxylesterases, CtrEst,1 and CtrEst,1, from Cx. tritaeniorhynchus and none from Cx. gelidus. CtrEst,1 was the most intensely staining band. Gel inhibition experiments showed that both elevated esterases were inhibited by organophosphates and carbamates but not by pyrethroids. The major elevated esterase CtrEst,1 was partially purified (15-fold) by sequential Q-Sepharose and phenyl Sepharose column chromatography. The bimolecular rate constant (ka) and the deacylation rate constant (k3) for the malaoxon/ enzyme interaction were 9.9 ± 1.1 × 103 m,1 min,1 and 3.5 ± 0.05 × 10,4m,1 min,1, respectively, demonstrating that the role of this enzyme in organophosphorus insecticide resistance is sequestration. [source] Ecological distribution and phenology of an invasive species, Cardamine hirsuta L., and its native counterpart, Cardamine flexuosa With., in central JapanPLANT SPECIES BIOLOGY, Issue 1 2003YOSHINORI YATSU Abstract Cardamine hirsuta is a European species that was recently introduced into Japan and its wide distribution has been confirmed in the Kanto district. To understand mechanisms of the recent spread of C. hirsuta in Japan, a comparative study of the alien species and its native congeneric species, C. flexuosa, was conducted. Habitat preferences, phenology and seed germination were examined. Cardamine hirsuta and C. flexuosa showed distinctive habitat-preferences; the former was most common in open habitats created by recent man-made constructions, and the latter was common in rice paddy fields and surrounding areas. The results indicate that C. flexuosa is a year-long annual, with a mixed phenology of summer and winter germination and growth. Seed dormancy during summer was relatively weak for C. flexuosa, and some plants that germinated early in summer reproduced during the same summer,autumn period. Plants that germinated in late summer and autumn behaved as winter annuals. In rice paddy fields, C. flexuosa is a winter annual because germination is prevented by submergence during summer. Plants flower during the following spring and complete their life cycle before the fields are flooded for rice cultivation. Cardamine hirsuta showed strong seed dormancy during summer and behaved as a typical winter annual. Seeds of C. hirsuta were intolerant to submergence in water, a condition that breaks seed dormancy of C. flexuosa. The results explain the absence of C. hirsuta from rice paddy fields. It was concluded that the spread of C. hirsuta is attributable to the recent expansion of urban habitats created by human activity and has occurred without direct competition with C. flexuosa. Considering recent urbanization in many areas, it is suggested that C. hirsuta has been spreading rapidly in Japan. [source] | ||||||||||||||||