Study On Soil Moisture And Salinity Dynamics And Their Influence On Plant Community In Hui River Wetland

Soil moisture plays a vital role in the formation,accumulation and distribution of salinity.Changes in soil moisture caused by wetland hydrological processes can directly affect salinity transport and thus alter the characteristics of wetland salinization.Significant changes in hydrological processes as a result of future climate change will further exacerbate its impact on wetland salinity,with potential risks and great uncertainty about the impact on wetland vegetation and the ecosystem as a whole.In this study,five sections,namely,Zhangzisong（ZZS）,Muqiao（MQ）,Chagan mountain（CGM）,Xiboqiao（XBQ）and Temohuzhu（TMHZ）were selected from upstream to downstream in Hui River Wetland of Hulunbuir grassland,which were classified into three flooding conditions,wetted（W）,wetting-drying（WD）and dried（D）plot,based on hydrological characteristics.Soil water-salt dynamics of riverine wetlands in grassland and their impact on plant community were explored through field sampling and indoor analysis from July to September 2020 and 2021.The main conclusions are as follows:（1）28.33%of the soil area in Hui River Wetland was salinized.The degree of soil salinization gradually increased from the source（ZZS）to the catchment（TMHZ）,it also gradually increased as the degree of flooding decreases,and moved towards the deeper layers.The soil salinization type was dominated by sulphate saline soil,with a transition from sulphate saline soil to chloride-sulphate saline soil as the degree of flooding decreased.60%of the soil salinity profile types showed a surface accumulated profile,while the rest showed a bottom accumulated profile and even distribution profile.The main characteristic factors of soil salinity in Hui River Wetland are Na⁺,SO₄^2-and SAR,and the degree of salinization is mainly influenced by the salinity composition,alkalinity characteristics and soil structure.（2）There were significant differences in soil physicochemical properties and salinity with seasonal variation in the TMHZ plot of Hui River Wetland.In the wetted plot,the soil salinity content varied seasonally as July>June>September>August,and the profile distribution type was bottom accumulated in Jun.,Jul.and Sep.,and even distribution in Aug..In the wetting-drying plot,it showed that June>September>July>August,and the profile distribution type changed from surface accumulated（Jun.-Aug.）to bottom accumulated（Sep.）.In the dried plot,it showed that September>August>July>June,and the profile distribution changed from surface accumulated（Jun.and Jul.）to bottom accumulated（Aug.and Sep.）.The degree of soil salinization with seasonal changes gradually decreased in the wetted and wetting-drying plot,while decreased in the topsoil,and increased in the deeper soil of the dried plot.In terms of soil salinization type,the wetted plot was mainly chlorine-sulfate saline soil in Jul.and Sep.,and sulfate saline soil in other months.In the wetting-drying plot,it changed from sulfate saline soil（Jun.）to chlorine-sulfate saline soil（Jul.）in the depth of 0-30 cm,and then gradually shifted to sulphate saline soil from deep to surface.In the dried plot,chloride-sulphate saline soil decreased with seasonal changes and moved to deeper layers.（3）The aboveground biomass of plant community was significantly higher in the medium-water and high-salt gradient than in the other water-salt gradients,with no significant differences in the high-water and non-salt,medium-water-salt gradients,the total biomass and belowground biomass of plant community were significantly higher in the high-water and non-salt gradient than in the other water-salt gradients,with no significant differences in the medium-water and high-salt gradient,medium-water-salt gradient.There was no significant difference in root-shoot ratio of plant community under different water-salt gradients.The relationship between soil moisture content and aboveground biomass of plant community followed a Gaussian model,while it was not significantly positively correlated with belowground biomass and total biomass.The relationship between soil total salinity and aboveground biomass of plant community was significantly positively correlated;while the relationship with total biomass and belowground biomass followed a logistic model.（4）Theα-diversity of plant community under different water-salt gradients showeda"V"-shaped distribution.Theα-diversity index of plant community were significantly lower in the medium-water and high-salinity gradient than in other water-salt gradients.In the high-water and non-salt gradient,the Shannon-Winner index in the medium-water-salt gradient was significantly lower than in the medium-water-salt gradient,while the Pielou index was significantly higher than in the medium-water-salt gradients.The Simpson index and Margalef index were not significantly different in the high water and non-salt gradient,medium-water-salt gradient.The relationship between soil moisture content and Simpson index,Shannon-Winner index and Margalef index was consistent with binomial distribution respectively,while the relationship with Pielou index showed a non-significant correlation.Soil total salinity was significantly and negatively correlated with theα-diversity index of wetland plant community.（5）The soil factors affecting plant community characteristics differed among water-salt gradients.The soil factors in the high-water and non-salt gradient was soil SMC and Ca²⁺,the effects of soil factors on plant community characteristics in the medium-water and high-salinity gradient were not significant,and soil factors in the medium-water-salt gradient was soil SMC,Ca²⁺and Mg²⁺.