Floodwater Of Paddy Field Research Articles

Frequency of phage-infected bacterial cells in the floodwater of a Japanese paddy field

In aquatic environments, viruses play an important role in the microbial food web through microbial mortality from viral lysis. Bacteriophages (phages) compose the majority of viral communities in the floodwater of paddy fields. The present study evaluated bacterial mortality from phage lysis in the floodwater of a Japanese paddy field based on the frequency of phage-infected bacterial cells by transmission electron microscopy. Floodwater was sampled five times during the rice cultivation period from two plots of NPK plus lime (no-compost plot) and NPK plus lime and compost (compost plot) under a long-term and ongoing fertilizer trial that began in 1925. The frequency of visibly infected cells in the compost plot was larger, ranging from 2.4 to 3.6% (average 3.0%), than that in the no-compost plot, which ranged from 1.6 to 2.9% (average 2.0%). The fractions of bacterial mortality from phage lysis in the floodwater samples were estimated to range from 12.8 to 27.3% (average 17.2%) and from 21.7 to 35.0% (average 27.9%) for the samples collected from the no-compost plot and the compost plot, respectively. This is the first study to estimate bacterial mortality from phage lysis in the paddy field ecosystem, and the frequency of phage lysis in floodwater was found to be within the frequency ranges observed in other aquatic environments.

Phosphorus interception in floodwater of paddy field during the rice-growing season in TaiHu Lake Basin

A field experiment located in TaiHu Lake Basin in China was conducted, by application of superphosphate or a mixture of superphosphate with manure, to elucidate the interception of P export during a typical rice growing season through ‘zero-drainage water management’ combined with sound irrigation, rainfall forecasting and field drying. P concentrations in floodwater rapidly declined before the first event of field drying, and subsequently tended to return to the background levels. Before the first field drying TPP was the predominant P form in floodwater on fields with no P input, DRP on plots that received superphosphate only, and DOP on plots treated with the mixture of superphosphate and manure. Thereafter TPP became the major form. No P export was found from the paddy fields, but a retention of 0.65 kg ha −1, mainly due to soil P sorption. The results recommend the zero-drainage water management for full-scale areas for minimizing P export.

Effect of Free-Air CO2 Enrichment (FACE) on the Community Structure of Aquatic Organisms in Floodwater of a Japanese Paddy Field during the Flooding Period of Rice Cultivation

In the present study, the effect of free-air CO2 enrichment (FACE) on the diversity and the community structure of aquatic organisms in the floodwater of a paddy field in northern Japan was evaluated. The varieties and the number of aquatic organisms ranging from 30 μm to 2 cm were compared four times at intervals of 20 d between the FACE (599 ppm CO2) and ambient air (384 ppm CO2) plots during the flooding period of rice cultivation. Aquatic organisms were classified mainly at the order level. Twenty-eight taxonomical groups were detected, and the number of groups in the FACE plots was significantly lower than that in the ambient plots. Zygnematales and Chaetonotida were less frequently detected in the FACE plots. The population densities of Zygnematales, and Chaetonotida also tended to be lower in the FACE plots than in the ambient plots in the late flooding period (after 50 d of flooding). No groups showed a significantly higher population density and frequency of presence in the FACE plots than in the ambient plots. The seasonal variations in the number of taxonomical groups and the community structure of aquatic organisms were less conspicuous in the FACE plots than in the ambient plots. We concluded that the FACE conditions adversely affected the communities of aquatic organisms in paddy fields.

Effect of application of rice straw and compost on the community structure of bacteria associated with microcrustaceans in the floodwater of a paddy field microcosm

A microcosm experiment was conducted to study the effect of the application of rice straw and compost to a soil on the bacterial communities associated with five species of microcrustaceans in the floodwater of paddy fields based on RFLP analysis. PCR products for bacterial 16S rDNA were digested with four restriction endonucleases (Hinf I, Sau3A I, Hae III, EcoR I). The results showed that the RFLP patterns of the bacterial communities were distinctly different among the microcrustaceans, although DNA fragments common to Tanycypris sp., Cypretta sp., and Heterocypris sp. were recognized. Bacterial communities associated with Tanycypris sp. showed the smallest number of fragments among the microcrustaceans studied. Rice straw and compost application exerted a negligible effect on the band patterns from Cypretta sp. and Moina sp., respectively. Cluster analysis and principal component analysis enabled to separate the band patterns into 2 groups with a total of 4 subgroups: I-1. Moina sp., I-2. Mesocyclops sp., II-1. Tanycypris sp. and Cypretta sp., and II-2. Heterocypris sp. The results indicated that the bacterial association with the microcrustaceans was primarily determined by the genus and species of hosts. Effects of rice straw and compost application on the bacterial communities associated with Moina sp. and Cypretta sp. and the duration of flooding on the bacterial communities associated with all the micro crustaceans were also observed, although the effects were not appreciable compared to those of the kind of host microcrustaceans.

Bacterial communities associated with aquatic organisms in the floodwater of a Japanese paddy field estimated by RFLP pattern analysis

Bacterial communities associated with crustacean (Tanycypris, Cladocera, Cyclopoida), Diptera (larvae of Cricotopus sp.), and roots of duckweed (Lemna paucicostata Hegelm) in the floodwater of a paddy field were analyzed based on the RFLP patterns of 16S rDNA. A larger number of RFLP bands was obtained from the bacterial communities in the floodwater and that associated with Cyclopoida than from the bacterial community associated with the other host organisms. The bacterial community associated with Tanycypris gave the smallest number of bands compared with the other habitats. DNA fragments common to Tanycypris, Cladocera, Cyclopoida, and Diptera and specific to the respective organisms were recognized. The RFLP pattern of the bacterial communities in the floodwater was markedly different from and more complex than those from aquatic organisms. The RFLP pattern of the bacterial community associated with Lemna roots was also specific. Cluster analysis and principal component analysis enabled to clearly separate the RFLP patterns of the bacterial communities associated with aquatic organisms from one another. The effect of sampling time on the bacterial communities was not appreciable compared to the effect of host organisms.