| Testate amoebae are an ubiquitous group of shelled eukaryotic micro-organisms, mainly living in aquatic or moist habitats, such as estuaries, lakes, rivers, wetlands, soils, litter and moss. They are small(20-200μm), abundant(1000-10000 individuals g-1 dry moss), and diverse(~2000 described species, 10-30 species in any given sample), with proteinaceous, calcareous, or siliceous test(shell). Due to short life time and rapid reproduction rate, testate amoebae play a vital role in nutrient cycling in ecosystems. Because of their species-specific sensitivity to hydrology and their decay-resistant and morphologically distinct shells, testate amoebae are often used in a variety of ecological and palaeoecological studies in a variety of ecosystems globally. However, relatively little attention has been given to study the ecology and palaeoecology of testate amoebae in China. In this paper, field sampling and statistics methods were performed to explore the biodiversity of testate amoebae in different seasons in peatland from Sanjiang Plain, to identify the most important environmental factor for testate amoebae assemblages and build the transfer function between testate amoebae and the selected environmental factor. The potential of using testate amoebae based transfer function to reconstruct the local water table depth was also discussed. These results from this study provide important insights into the biodiversity of Sanjiang Plain and the local palaeoenvironmental reconstruction. The main results of this paper were showed as follows:(1) Species richness of testate amoebae is very high in peatland from Sanjiang Plain, 47 species belong to 18 genus were encountered. An average of 19 species in each sample was recorded. The average density was 1.2×105 individuals g-1 dry moss, and average biomass was 1.1×103 μg C g-1 dry moss. For density, testate amoebae was dominated by Euglypha(32.4%), Trinema(16.8%), Tracheleuglypha(12.0%), Arcella(11.7%) and Centropyxis(11.4%) in genus level; Trinema complanatum type(13.2%), Euglypha strigosa type(12.6%), Euglypha rotunda type(12.2%) and Tracheleuglypha dentata(12.0%) in species level. For biomass, testate amoebae were dominated by Centropyxis(37.9%), Euglypha(19.4%) and Arcella(11.7%) in genus level; Centropyxis cassis type(14.2%), Euglypha tuberculata(14.0%) and Centropyxis aculeata type(11.5%) in species level.(2) Clear seasonal patterns of testate amoebae communities were observed. Species number was highest in June and August(p<0.05), 11.6 and 12.7 in average respectively. Significant(p<0.05) peak density and biomass were observed in August, 6.2×104 individuals g-1 dry moss and 6.9×102 μg C g-1 dry moss respectively. High trophic position testate amoebae(shell-aperture size/body size ratio>0.18; i.e. primarily predators of protists and micro-metozoa) account for 60% of the total density and 91% of biomass. Community size structure consistently declined(p<0.05) from June to October. Depth to water table(DWT) was identified to be the most important environmental factor, which influenced testate amoebae assemblages in June, August and October.(3) Redundancy analysis(RDA) showed testate amoebae community structure was strongly correlated to DWT(15.4% of variance, Monte-carlo significance tests p<0.01) than the other physiochemical variables. Testate amoebae-DWT transfer function developed by WAPLS model performed the best, with the lowest RMSEP(RMSEPLOSO=4.97 cm) and highest R2(R2 LOSO=0.75).(4) We attempted to reconstruct the palaeohydrological history using the developed testate amoebae-DWT transfer function in Sanjiang Plain. Result showed a gradually raised DWT during the past 3000 years, but fluctuated in recent 1000 years. |
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