Plant diversity and its maintenance in Populus euphratica riparian forests in the Ejina Oasis,China

The dynamic environments in riparian zones support a variety of life-history strategies, which constitute a fundamental mechanism for development and maintenance of biodiversity in riparian forest ecosystems. To demonstrate the effect of life-history strategies on biodiversity, we investigated community-level diversity and its relationship to environmental variability in the riparian Populus euphratica forests of the Ejina Oasis. Communities were divided into 14 associations on the basis of their species impor- tance values. The Simpson＇s index, Shannon-Wiener index, Pielou＇s evenness index and the regional Whittaker＇s index were applied to calculate community diversity. An ordination of the sample plots was carried out by correspondence analysis （CA）. Biodiversity was relatively low across the entire study area, but there was high community diversity （flw = 8.09） due to the spatial heterogeneity of habitats in different plots. In addition, we investigated the relationship between biodiversity and several environmental factors, such as water availability, community components and soil conditions. We conclude that the heterogeneity of soil and water availability drives community diversity patterns in riparian zones and that community-level diversity favors the maintenance of species diversity in the P euphratica forests in the Ejina Oasis.

Influence of environmental,root,and stand parameters on soil surface CO_2 efflux in a Populus euphratica of desert forest in extreme arid region

Spatial variation in soil surface CO2 efflux was measured in a stand of Populus euphratica in the Ejina Oasis of desert riparian forest in the extreme arid region in northwestern China from April 2007 through October 2007.Measurements were taken with a gas-exchange analyzer linked to a soil-respiration chamber.The mean soil CO2 efflux in the stand was 2.71 μmol/(m2·s) during the growing season and 1.38 μmol/(m2·s) in the nongrowing season.The seasonal maximum (end of May through early June) andminimum (October) CO2 efflux were 3.38 and 0.69 μmol/(m2·s),respectively.The diurnal fluctuation of CO2 efflux was relatively small (< 20 percent),with theminimum appearing around 05:00 and the maximum around 15:00.Linear regression analysis showed soil-surface CO2 efflux to be most highly correlated with soil temperature (R2=0.435) and soil moisture (R2=0.213).When all variables were considered simultaneously,only soil temperature (R2=0.378),soil moisture (R2=0.147),and root volume density (R2=0.021) explained a significant amount of variance in soil surface CO2 efflux.Stand volumes were not correlated with soil CO2 efflux on our sites.

Why lowland riparian trees are difficult to use for streamflow reconstruction

Existing streamflow reconstructions based on tree-ring analysis mostly rely on species from upland,mainly montane areas,while lowland species(generally plain)areas are rarely used.This limits the understanding of streamflow change history in the lowlands,which is an important basis for water resource management.This study focused on Populus euphratica stands located along the main stream,eastern and western tributaries in the lower reaches of the Heihe River basin(HRb),in arid northwestern China.We investigated how streamflow regulation interferes with ripar-ian trees in lowlands when they used for streamflow recon-struction.Tree-ring width chronologies were developed and analyzed in conjunction with meteorological and hydrologic observation data.The results show streamflow regulation leads in sharp fluctuations in the streamflow allocation between the eastern tributaries and western tributaries.This resulted in instability of the correlation between streamflow at the two tributaries and at the Zhengyixia hydrologic station,with corresponding fluctuations in radial growth of poplar trees on the banks of the two tributaries and at the station.Streamflow regulation altered the natural patterns of seasonal streamflow below the station,changing the time window of poplar response.This study provides useful insight into tree-ring width based streamflow reconstruction in the lowlands.