Speciation Of Calcium In Soil And Plants' Leaves In Karst Ecosystem And Its Ecological Significance

Laboratory analysis was carried out to study the speciations of calcium(Ca), magnesium(Mg),manganese(Mn) and zinc(Zn) of the limestone soils and red soils,which occure both in Maocun of Guilin city and are under the same climate condition,and to study the speciations of Ca in leaves of four kinds of common plants in Maocun, Loropetalum chinense, Liquidamlar formosana Hance, Vitex negundo L., Euchlaena mexicanna Schrad.Their ecological significances were discussed.Research on karst ecosystem has been hot these years.And soils in karst environment was intensified by defining the karstification system as process in rock-water-soil-air interface instead of rock-water-air interface.Meanwhile,there has been increasing interest in the status of Ca in soils in karst areas,which has been well revealed to be the most abundent metal element in karst ecosystem.As is well known to us,bio-availability ,toixcity and mobiliziation of a certain element largely depend on its speciation.But it was rarely reported before in the literatures to study the spciation of Ca in karst areas.It remains to be a problem to understand the behavior of elements in soil-water-plant system in karst environment.Speciation was defined as the process leading to the identification and determination of the forms of a element in a sample by IUPAC.Speciation analysis may provide more information about toxicological and bio-availability of elements than total concentration.To know more about why Ca has a great significance in karst ecosystem,speciation of Ca in karst soils was analysised and that in nonkarst soils was done the same way. Meanwhile , speciation analysis of Mn and Zn was carried out to acquire a further understanding of the effect of Ca on the distribution and bioavailability of micro-elements in the limestone soils.Furthermore,speciation of Ca in leaves of the said plants were made to primarily reveal how the plants in karst areas adapt themselves to the karst soils with a high concentration of Ca. The results were showed as follows:(1)The limestone soils contain a large amount of not only total concentration of Ca,but also activated fraction of Ca,including exchangeable form,carbonate and humic-acid bounded form.This leads to the good mobilization of Ca in water-soil system and a great effect on the soil environment,such as soil pH.(2)Limestone soils contain a higher total concentration of Mn and Zn than red soils,but lack of exchangeable form of Mn and Zn as a result of the effect of a high content of Ca.