Lidan Liu

Change characters of Phragmites australis phytolith in Northeast China: Change characters of Phragmites australis phytolith in Northeast China

Aims Our objective is to study the change rules of the main phytolith morphotypes in Phragmites australis from June to October.Methods We selected similarly sized leaves of P.australis in 12 sampling sites and extracted phytoliths with the wet-ashing method.Important findings The main phytolith morphotypes in P.australis could be classified into five categories.There is little change about the phytolith assemblages in P.australis during different growth periods and different combination of temperature and humidity.This implies that phytolith morphotypes of the same plant species are stable and therefore can be used to effectively reconstruct paleo-vegetation.The maximum value of the saddle percentage appears in July and then slightly decreases.While the maximum value of the percentage and concentration of the bulliform appears in August or September,with its minimum value in July.This indicates that the saddle formation may be more controlled by plant photosynthesis and transpiration,while the bulliform formation may be closely associated with the support of bulliform cells.The result also shows that the phytolith concentration in P.australis does not gradually accumulate from June to October.Its maximum value appears in August and its minimum value in September,so the change rules of the phytolith concentration may be concordant with the need of silicon for plants in different growth periods.Furthermore,the maximum value of the saddle concentration in P.australis also appears in August,with its minimum value in September.This trend is similar to changes of the phytolith concentration in P.australis.

Holocene Artemisia-Chenopodiaceae-dominated grassland in North China: Real or imaginary?

The Songnen grasslands were traditionally thought to be dominated by Artemisia and Chenopodiaceae plants as early as the late Pleistocene. However, increasing evidence has called that interpretation into question. To shed new light on the paleovegetation evolution of the arid and semi-arid steppe in North China, phytolith assemblages preserved in the region’s sand-paleosol sequence (section Daike) are used as a proxy for paleovegetation structure. Results show that both the sand and paleosol layers in the Songnen grassland sections contain well-preserved phytoliths attributed to different families of grass. This is the first direct evidence of the nature of the vegetation that existed during the sandy layer episodes. Moreover, the phytolith evidence represented in the samples indicates that plant successions happened within the subfamilies of Poaceae through the time. Referring to phytoliths in modern plants and topsoils, and using statistical analyses, we propose that phytolith assemblages in the section Daike originated from Poaceae-dominant communities rather than an Artemisia-Chenopodiaceae ecosystem. The phytoliths, and evidence from the historical and modern pollen-vegetation relationships, lead to rejection of the hypothesis of a past widespread Artemisia-Chenopodiaceae ecosystem in the Songnen grasslands. Using published radiocarbon and thermoluminescence data, it is proposed that the present Poaceae-dominated grasslands developed as early as the early Holocene. This study also highlights the usefulness of phytolith analysis in paleovegetation reconstruction in arid and semi-arid lands.

Spatial and Temporal Distribution Differences Among Phytoliths of Phragmites Communis in Northeast China

Phragmites communis phytoliths were extracted from the xerophytic habitat of 12 sampling sites in northeast (NE) China during June–October in 2011 and 2012. The changes of P. communis phytolith concentrations in different temperature zones and growth stages were used to reveal the ecological environmental significance of P. communis phytoliths. The purpose of the study is to provide a scientific reference for quantitative reconstruction of paleoenvironment and studies of phytolith formation. The main phytolith types extracted from the 12 sampling sites and different growth stages were identical; however, the phytolith concentrations differed markedly. In NE China, from the temperate to the warm temperate zone, as temperature increased, the saddle phytoliths, bulliform phytoliths and the silicified stomata concentrations all increased, whereas the lanceolate phytolith concentration decreased. Moreover, in the humid, semi-humid and semi-arid areas, there were different responses of P. communis phytolith concentrations to temperature. Consequently, the spatial results showed that P. communis phytolith concentrations in NE China were closely related to temperature, which enabled inference of the change in temperature from phytolith concentration; however, they were also somewhat affected by humidity. During June–October, the temporal variation results of P. communis phytolith concentrations revealed that there were high lanceolate and bulliform phytolith concentrations in September or October; whereas the saddle phytolith concentration was high in July or August, and the maximum concentration for silicified stomata was in July. These findings may improve the understanding of phytolith formation, and provide useful information to further interpret phytolith assemblages in sediments.