Discovery of Trigonopyxis arcula in Hani Mire and Its Implication in Paleoenvironmental Reconstruction

Testate amoebae are a group of protists livings in peatlands,wet soil and freshwater lake.They are covered with tests(shells).This decay-resistant shell can be preserved for millennia and allows species-level identification long after death.Currently testate amoebae are very useful environmental indicators in ecological and palaeoecological studies from peatlands.Their advantages are as follows: ① They have the clearly environmental significance.The assemblage of testate amoebae in peatlands is mainly controlled by hydrological variation not only in ombrotrophic bogs but also in minerotrophic fens. Their defined ecological niches make it easy to interpret the result of paleoenvironmental reconstruction.②Because of their endurable tests the relative abundance of testate amoebae can keep steady during the process of fossilization.This allows direct comparison between modern and fossil communities.③ The reproduction of testate amoebae is a relatively fast process and this should make them temporally sensitive indicators of paleoenvironmental changes.Because of these advantages testate amoebae draw more and more attention of scientists in paleoenvironmental studies.Trigonopyxis arcula is one of common taxa in peatlands.It is often found on the top of hummock where the depth to water is low.Therefore Trigonopyxis arcula is regarded as a typical indicator of drier condition along the hydrological gradient in peatlands.Hani mire(42°13′7″N,126°30′7″E) has the deepest peat deposition(9.6 m) in Northeast China and is an ideal site for paleoenvironmental reconstruction.Much work has been done based on the peat sampled from here. Trigonopyxis arcula discovered in Hani mire was presented in this paper.The samples were collected in June,2007.The preparation method is water-based sieving techniques following Charman.The test found here is 115～133 μm in diameter,pale yellowish brown,circular in dorsal view,hemispherical in lateral view.The shell is composed of mineral particles bounded by organic cement.The aperture is central,typical trianglar,20～30 μm in diameter,invaginated and surrounded by a collar of organic cement.This test is also discovered on the top of a hummock of Sphagnum nemoreum where the depth to watertable is about 45 cm,which means a dry condition.This is the first report of discovering the testate amoebae in sphagnum bog in China.More significantly,this consistent agreeing with other studies of peatlands worldwide indicates a great potentiality of testate amoebae used as a proxy for paleohydrology in peat-based paleoenvironmental reconstruction in China.Peatlands are widely distributed in Northeast China and peat deposits are always the important archives of regional environmental changes.It is believed that in the future testate amoebae will be a significant proxy in paleoenvironmenta studied in Northeast China.