Distribution And Transformation Of Sulfur In Soil-plant System Of Coastal Wetland In Yancheng,Jiangsu Province

The cycles of nutrient elements are the focus of modern wetland ecology research.The process of sulfur biogeochemical cycle plays an important role in wetland systems.In order to understand the distribution of sulfur in wetland system,four typical coastal wetlands in Jiangsu province were taken as objects to research the spatial and temporal distribution of content and reserve of different forms of sulfur in soil,the seasonal dynamic of content and cumulate of plant sulfur,and the dynamic of sulfur in decomposing process of plant in typical wetlands,by means of field sampling,in-situ test and laboratory test.Then key process of sulfur cycle in soil-plant system of typical coastal wetland was studied.The main results are as follows:?1?Sulfur in the coastal wetland soil showed a significantly spatial pattern and an obvious layered characters,which was mainly affected by the content of organic matter in the soil.With barely human disturbance and abundant rainfall leaching effect,soil total sulfur content in our study were lower than most coastal estuary wetland in China,the total sulfur content in the soil of Spartina alterniflora wetland reached 0.8 mg?g^-1,and the total sulfur content in the soil of the other three wetlands was lower than the world average value.Organic sulfur is the main form of sulfur in soil,which accounted for 54.32%?75.29%of total soil sulfur,and it is beneficial to sulfur storage.The inorganic sulfur sources in the soil of Phragmites australis wetland and Suaeda salsa wetland are mainly from the mineralization of organic sulfur,while the inorganic sulfur sources in the S.alterniflora wetland and the mudflat are diverse,with more exogenous sulfur input;Soil sulfur content has obvious vertical zonation and seasonal change,and there are great differences among various points,which is mainly related to the growth process of vegetation.Soil sulfur reserves in the S.alterniflora wetland were significantly higher than those in other sites,plant invasion had a great impact on the sulfur reserves in the wetland.?2?The total sulfur content in the organs of three plants showed obvious seasonal variation,which generally increase at the early stage and then decrease,the variation trend was consistent with the growth rhythm of plants.Sulfur accumulates in the root system of plants and then transfers to aboveground organs,root is an important“collecting and distributing repository”of plant nutrient elements.S.alterniflora and S.salsa have higher tolerance to sulfur.?3?During the decomposition of the litter of 220 days,the decomposition rate of all three plants were fast at first and then slower down.S.alterniflora contains more soluble substances and decomposes faster in early stage in compared with P.australis and Suaeda salsa.The decomposition rate of the root system of P.australis and S.alterniflora was higher than that of the aboveground part,while little difference between the above and the underground parts of Suaeda salsa.During the decomposition process,the total sulfur content of each plant component changed alternately with time,and the release mode was leaching-fixation-release,the C/S ratio of litter was the determining factor.The difference of the initial and critical values of C/S determines the change characteristics of sulfur in different plants and organs.?4?The adsorption characteristics of SO₄^2-to different soils can be fitted by Langmuir isothermal adsorption curve.With the increase of the concentration of adsorption liquid,the amount of adsorption and desorption increased,while the adsorption rate decreased and the desorption rate increased,there was a maximum value of SO₄^2-adsorption of soil.Soil desorption capacity was mainly affected by the amount of adsorption.When the adsorption amount of soil is small,the absolute amount and desorption rate of desorption are small,and vice versa.?5?Incubation temperature,water condition and soil initial sulfur content have great influence on the mineralization of soil organic sulfur.Under the condition of aerobic,soil organic sulphur mineralization quickly in the early stage,then mineralization rate decreased?15?and 25??;At 35?,the mineralization rate relatively stable throughout the incubation period.Generally,the mineralization amount were lowest at 25?,and the highest at 35?.The mineralization amount of S.alterniflora wetland soil increased with the increase of incubation temperature.Under the condition of waterlogging,the mineralization amount of the first two week accounted for about 50%of the total mineralization amount of the whole incubation period,and the rate of mineralization in the later period of incubation was greatly decreased.The mineralization potential of soil organic sulfur is higher in the deep layer and fluctuates with the increase of incubation temperature,it provides support for the evaluation of soil sulfur supply capacity.?6?The circulation and accumulation of sulfur in the key processes of soil-plant cycle in a typical coastal wetland are estimated.The net outflow of sulfur from the soil system to the plant system is positive,P.australis wetland:1.149 g?m^-2?a^-1;S.salsa wetland:0.046 g?m^-2?a^-1;S.alterniflora wetland:0.512 g?m^-2?a^-1.Soil sulfur pool is the source of plant sulfur pool,but its effluent amount is very little compared with the total soil sulfur pool,and plant absorption has little effect on the whole soil sulfur pool Soil sulfur pool accounts for more than 97%of the whole soil-plant system.The roots of P.australis,the leaves of S.salsa,and the stems of S.alterniflora are the main sulfur reservoirs of their subsystems.The sulfur stock in soil-plant system was increased by the invasion of Spartina alterniflora,and the stability of sulfur in the system was also enhanced.