Case Studies on the Seasonal Changes of Diatom Community in Paddy Fields

As a case study, the seasonal changes of diatom community in flooded water of paddy fields were discussed. The investigations were conducted on Andosols (Field 1) at Field Science Center, Tohoku University, and on Fluvisols (Field 2) at Furukawa Agricultural Experimental Station, located at Miyagi Prefecture, Japan, during the rice-growing season of 2004. The results obtained are as follows: 1) Diatom cell density at Field 1 ranged between 2.1x10^5 and 1.1x10^6 cells L^. There was no large difference during the experimental period in Field 1. Diatom cell density in Field 2 ranged between 4.3x10^5 and 5.3x10^6 cells L^. Diatoms in Field 2 were low in the end of May, and increased gradually thereafter. 2) Nineteen genera were observed in Field 1 and twenty-four genera in Field 2. In general, Nitzschia was predominated genus in the both fields. In Field 1, Melosira became predominated from June to August. In Field 2, Navicula was also predominated in July

Diatoms composing benthic microbial mats in freshwater lakes of Skarvsnes ice-free area, East Antarctica

Diatoms composing benthic microbial mats in Skarvsnes lakes, East Antarctica, were studied in terms of their taxonomy and relationship to environmental factors. Samples were collected from 13 freshwater lakes in the area. Amphora sp. (cf. veneta) was dominant in 11 of the 13 samples, while Craticula sp. (cf. molesta) and Diadesmis sp. (cf. perpusilla) were respectively dominant in the remaining 2 samples. Navicula ectoris Van de Vijver was also reported here for the first time in continental Antarctica. Mosses in the microbial mats did not have a significant effect on the diatom species composition. Redundancy analysis revealed that the main environmental gradient for diatoms was electric conductivity, despite its relatively narrow range (18-390 mS m^(-1)). Our results suggest that Diadesmis sp. and Psammothidium metakryophilum are halophobes, whereas Amphora sp. is a halophile