Study On The Law Of Water And Salt Transport And Plant Response Under Microtopography In Saline-sodic Soil Region Of The Songnen Plain

In arid and semi-arid regions,microtopography is one of the important factors affecting the properties of salinization soil and plant distribution.Microtopography is widely distributed in saline-sodic soil area in Songnen Plain.The existence of microtopography intensifies soil salinization,and microtopography leads to the redistribution of soil moisture and salt,further affecting the growth and development of plants,and aggravating the degradation process of soda saline soil.In order to further understand the spatial variation characteristics of soil physical and chemical properties and plant response to the saline-sodic soil under microtopography in Northeast China,the spatial variation characteristics of relative elevation,soil physical properties(bulk density,total soil porosity,soil mass water content),soil chemical properties(p H,electrical conductivity,sodium adsorption ratio)and plant biomass in the saline-sodic soil with typical microtopography characteristics were studied by combining classical statistics and geostatistics.The spatial distribution map was drawn by spatial interpolation.The classical statistics showed that the coefficients of variation of soil physical and chemical properties under the microtopography were less than 0.7,indicating moderate and weak spatial variation;The geostatistical analysis demonstrated that the nugget coefficients of soil physical and chemical properties were smaller than 75%,indicating moderate and strong spatial autocorrelation.In addition,soil physical indexes(mass water content)had a stronger spatial autocorrelation than soil chemical indexes(p H,electrical conductivity,sodium adsorption ratio).In other words,microtopography had a more intense effect on soil moisture.The spatial interpolation map exhibited that the spatial distribution of soil indexes was striped or patchy.The measured soil physical and chemical properties were significantly correlated with relative elevation(P < 0.01),while plant biomass and relative elevation was negatively correlated(P < 0.05).The correlation coefficient of microtopography to soil moisture was greater than that of soil physical and chemical properties,while the correlation coefficient was the least between microtopography and plant biomass.Therefore,it is suggested that the microtopography leads to the difference of soil moisture at different elevations on the slope,and then changes the soil physical and chemical properties,which indirectly affects the plant changes.The regression analysis showed that there was a quadratic function relationship between the soil physical and chemical indexes and the relative elevation,and the soil salinity reached the highest threshold with the lowest plant biomass when the elevation of the micro-topography was 50-60 cm.The discovery of elevation threshold provides a theoretical basis for differential remediation and tillage management of saline-sodic soils.By setting up the artificial microtopography test area of saline-sodic soil,the microtopography is simply divided into two types,namely,terrance and slope land.Then,different elevation gradients are set for the two micro-topography,and the soil moisture is observed at a fixed point.The saline-alkali indexes of soil samples are measured to describe the movement law of water and salt.The results showed that the soil water content decreased first and then increased with the increase of soil layer depth in the profile in different elevation platform treatments and different elevation positions on the slope.The minimum values appeared in the 20 cm soil layer of the soil profile,and the values were less than 10 %.The water content in the surface layer(10 cm)of the soil was maintained at 10 % ? 30 %,while that in the deep layer(below 30 cm)was maintained at 30 % ? 45 %.Soil p H and EC showed an increasing trend,and the change range of soil p H was smaller than that of soil EC.There were differences in other saline-alkali indexes among treatments,and the difference of slope treatment was greater than that of platform treatment.And the data value of platform processing is greater than slope processing.Four plants were widely distributed in the two treatments,including Leymus chinensis,Phragmites australis,Artemisia scoparia and Echinacea purpurea.Except for H0(0 cm)treatment,Leymus chinensis was distributed in each plot,but the distribution ratio was different.The Margalef richness index,Pielou evenness index and Shannon-Wiener diversity index of platform treatment were larger than those of slope treatment at different elevation positions except H1(20 cm).Overall,the biodiversity of platform treatment was better than that of slope treatment.Through field experiments,the real dynamic characteristics of water and salt were understood,and the research content of soda saline soil under micro-topography was enriched.