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The Yellow River Delta,one of China′s three major river deltas,has recently been the subject of numerous important research projects.Soil is an important environmental factor in the delta and heavily influences plant physiology and vegetation distribution.In previous studies,soil salinity and moisture have been proven to be main driving forces of terrestrial vegetation succession in the Yellow River Delta.However,vegetation in the Yellow River Delta is prone to retrograde succession and secondary succession resulting from both natural forces and human disturbance.Currently,changing salinity patterns and soil conditions in the Yellow River Delta are causing a deeper penetration of salinity into the soil.This change in soil salinity has been brought on by a rise in sea level and other natural or societal causes such as dredging,shoreline modifications,and so on,and the local vegetation is adapting to these changes out of necessity.Our research looked at the relationships between community diversity and soil conditions as well as analyzing the classification of the coastal meadows in the Yellow River Delta.Gaining an understanding of these relationships will not only enlighten us on the relationships between vegetation and soil;it also has theoretical significance for vegetation conservation and restoration in the Yellow River Delta.Sixty-seven vegetation quadrats were selected in June,2010,and nine soil characteristics were analyzed,including soil moisture content(MC),soil electrical conductivity(EC),soil pH(pH),total carbon(TC),total nitrogen(TN),total phosphorus(TP),available nitrogen(AN),available phosphorus(AP) and available potassium(AK).Vegetative analysis of the quadrants found 52 species,belonging to nineteen families and forty-six genera.The abundance of Compositae,Gramineae and Chenopodiaceae,the three plant families with the largest number of species found during this study,demonstrates their wide range of adaptability.Also,the species of the Chenopodiaceae are mostly salt-tolerant,and some of them are edificators,or environment-forming species,in some communities,so this family is of special importance to the Yellow River Delta vegetation communities.Many past ecological studies confirm the rationality of the wide use of Canonical Correspondence Analysis(CCA) and Two-way Indicator Species Analysis(TWINSPAN) in quantitative vegetation ecology.Canonical Correspondence Analysis was performed to analyze the relationships between the vegetation quadrats and the nine soil factors.The CCA results show the first two axes explained 46.4% of the variance within the species-environmental relationships,and electrical conductivity and moisture content most heavily influenced the community distribution.Using TWINSPAN,we classified the quadrats into seven communities as follows: Community.Aeluropus sinensis,Com.Phragmites australis,Com.Imperata cylindrica+Phragmites australis,Com.Cynanchum chinense,Com.Phragmites australis-Suaeda glauca,Com.Phragmites australis-Suaeda salsa and Com.Suaeda salsa.The seven communities were classified into three groups along the first axis of the CCA: Com.Suaeda salsa,Com.Phragmites australis-Suaeda salsa and other meadow communities.The results indicate the succession series of coastal meadow in the Yellow River Delta develops along the salinity gradient,and may also indicate a transitional role for the Com.Phragmites australis-Suaeda salsa,a role which should be explored in the future studies.The Shannon-Wiener(H′) and Simpson(D) indices were calculated.Correlation analysis shows species diversity had a highly significant negative correlation with EC,AP and AK(P0.01),and a significant positive correlation with pH(P0.05).In this study,the combination of CCA and TWINSPAN performed well since classification increased the effectiveness of ordination,and ordination helped one understand the classification results.These findings helped the authors develop a theoretical basis for vegetation conservation and restoration in the Yellow River Delta.

The Achnatherum splendens community is an important vegetation resource in arid and semi-arid regions.A mosaic A.splendens community often exists in the slightly lower topographical parts of typical steppe regions in Inner Mongolia,and often adjoins the low-lying wetlands.At present,little research has been done on suitable habitat for the A.splendens community.Four representative study areas of typical steppe in the Xilinguole Grassland were selected to study the suitable habitat for this community in the steppe region of Inner Mongolia: 1 and 2) Huahushuo and Borenaobao of Baiyinxile Ranch,3) Laomaodeng hamlet of Maodeng Ranch,and 4) Xinlinhaote′s penal farm.We selected an area in each plot to measure the local topography by using an optical theodolite(TDJ6E),including the length,width,and heigh of each plot.Also we surveyed the vegetation of the A.splendens community and its adjacent communities,which were zonal Stipa communities and wet meadow communities.When possible,we measured the underground water level in wells in the plots using the optical theodolite(TDJ6E) at the topographic control point;a soil sample 1 meter in depth was collected,and divided into 10 equal layers.Soil conductivity was tested using a Multi-340i multi-parameter measuring instrument.The soil pH value was tested with a DELTA320-type pH meter produced by the Mettler Toledo Company.Soil texture feature was assessed by testing soil grain size with a Microtrac S3500 Particle Size Analyzer.By comparing the above indices with the other adjacent communities,some conclusions can be made.The A.splendens community of typical steppe in Inner Mongolia is a result of an elevation gradient.It has a kind of zonal distribution among the communities of A.splendens,zonal Stipa communities,and wet meadow communities.First,it is clear the A.splendens community occurs in areas with groundwater at 1—3 m below the surface,in addition to surface runoff.The deep root system of A.splendens reaches the groundwater directly.Secondly,it is also relevant to the soil pH value and the soil conductivity tests reflect the soil salt content.The salt tolerance of A.splendens community is well known to be very high.Soil salinity,low at the soil surface,was relatively higher as depth increased.The soil pH is significantly higher in this community than in the adjacent wet meadow community and zonal Stipa community.However,it can be concluded that the formation of the A.splendens community suitable habitat is unrelated to soil texture.