Distribution of soil salt ions around Tamarix chinensis individuals in the Yellow River Delta

Spatial heterogeneity is considered a ubiquitous feature of natural ecosystems.A typical example of spatial heterogeneity in ecosystems is the formation of salt islands,which form around small shrubs and are important local and regional salt reserves that influence community structure and ecosystem function.These salt islands are formed where salts accumulate under the shrub canopy.Soil salinity has been shown to vary significantly between areas covered by shrub canopies and interspaces.To quantify the effect of halophyte plants on the salinity characteristics of salt islands in saline and alkaline soil,the native Tamarix chinensis of the Yellow River Delta(YRD) was selected as a study species,and its soil salt ion composition and content were analyzed.Differences in the cation and anion contents and ratios among distances and horizons were analyzed using an analysis of variance and multiple comparisons.A correlation analysis was also conducted,to determine the relationships among different salt ions.The results show that salt islands are mainly distributed in the surface soil.Both the cations and the anions were present in higher concentrations near T.chinensis individuals.Of the cations,Na was found in the highest levels of the profile,followed by Ca and Mg in the lower layers,and K in the deepest part of the profile.Anions in all soil depths both showed Cl~- SO_4 HCO_3~-,but CO_3~(2-) was not detected.The distance from the center of the shrub to the sampling point had a significant effect on most salt ions and their ratios,with the exception of Ca~(2+),Mg~(2+),SO_4~(2-),Na~+/Ca~(2+),Ca~(2+) /Mg~(2+),and Cl /SO_4~(2-).The soil depth had a significant effect on almost all of ions and ratios,with the exception of the Na~+ /K~+ ratio.The interaction between distance and depth only had a significant effect on Cl~- and HCO_3~-.Na~+/K~+,Ca~(2+)/K~+,Mg~(2+)/K~+,and Ca~(2+)/Mg~(2+) increased in the 0-20 cm layer,while the Na~+ /Ca~(2+) and Na~+ /Mg~(2+) ratios decreased along the gradient between the canopied area and the interspace.Therefore,the cations enrichment due to the proximity of a T.chinensis individual was as follows:K~+ Na~+ Mg~(2+) Ca~(2+).However,anions enrichment was determined to occur as follows:HCO_3~- Cl~- SO_4~(2-) as Cl~-/SO_4~(2-)decreased and Cl~-/HCO_3~- and SO_4~(2-) /HCO_3~- increased in the 20-40 cm soil layer,along the gradient from the shrub center to the interspace.The total soluble salt content of the soil increased with depth.Howe