Study On Soil Solute Transport Characteristics And Water Sources Of Typical Sand-control Plants In Water-wind Erosion Crisscross Region

As a key ecological factor of restricting agricultural and forestry production and ecosystem stability in arid and semi-arid areas,water resources have a crucial impact on the survival and evolution direction of regional vegetation.Understanding the characteristics of soil solute transport and its influencing factors under different vegetation types and to reveal water sources and water use characteristics of typical sand-control plants in water-wind erosion crisscross region is critical to rational allocation of vegetation,efficient utilization of water resources and sustainable development of ecosystems.In this study,the characteristics of Cl^-transport under different soil types（sandy soil,loam soil）and vegetation types（arbor,shrub,grass）in Liudaogou and Gechougou watershed in water-wind erosion crisscross region were studied by using the method of field observation and indoor analysis.At the same time,the characteristics and influencing factors of soil water recharge under different groundwater levels（GWL）in three types of woodland（Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pcdunculata Pall.）was analyzed based on the stable isotope tracer technique.In addition,seasonal variations and influencing factors of water uptake by typical plants（Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pcdunculata Pall.）were studied by Bayesian mixing model Mix SIAR.The main results and conclusions of the study are as follows:（1）TS,TE,V and D of Cl^-all varied with soil texture,vegetation type and soil depth in the range of 12～80 min,75～480 min,0.52～1.98 cm?h^-1 and 0.75～2.55 cm²?h^-1,respectively.Mean V and D in 0～1 m soil profile the same in texture varied with vegetation cover,showing a decreasing order of S-AR>S-GR>S-SH and L-AR>L-SH>L-GR,while mean TS and TE did too,but showing opposite trends.Mean V and D in 0～1 m soil profile the same in vegetation cover varied with soil texture,showing orders of S-AR>L-AR;S-SH>L-SH and S-GR>L-GR,while mean TS and TE did too,but showing reverse patterns.Soil bulk density,number of macro-pores,connectivity density,and contents of organic carbon,sand,silt and clay were all significantly related to V,TS and TE.Soil properties and vegetation types were major factors affecting the characteristics of Cl^-transport in soils.（2）During the monitored period（June-November）,theδD andδ¹⁸O of soil water in Salix psammophila（0～20 cm）,Pinus sylvestris L.var.mongholica Litv.（0～40 cm）and Amygdalus pedunculata Pall.（0～40 cm）woodland exhibited depletion of heavy isotopes and enrichment of light isotopes,which were significantly positive correlated（P<0.05）with the hydrogen and oxygen isotopic compositions of precipitation,suggesting that the shallow soil water（<40 cm）under different woodland was mainly affected by precipitation infiltration and evaporation.The mean values ofδD andδ¹⁸O of the deep soil water in different types of woodland（Salix psammophila（>180 cm）,Pinus sylvestris L.var.mongholica Litv.（>60 cm）and Amygdalus pedunculata Pall.（>120 cm））were close to those of the groundwater,andδD andδ¹⁸O of soil water increased with depth tended to be more stable（CV<10%）.The depth of soil water recharge by groundwater in the three types of woodland（Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pedunculata Pall.）was respectively about 73～80 cm,27～33 cm,and 52～56 cm according to the correlations ofδ¹⁸O between soil water and groundwater.（3）According to the SWC and coefficient variation（CV）of SWC in different soil depths,the soil profile was divided into three layers in the studied three types of woodland（Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pcdunculata Pall.）:the active layer（1%<SWC<8%,10%<CV<30%）,the stable layer（2%<SWC<5%,CV<10%）and the moist layer（SWC>8%,CV>30%）,respectively.The depth of active layer in Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pcdunculata Pall.was 0～100 cm,0～30 cm and 0～60 cm,respectively;the depth of stable layer was 100～200 cm,30～60 cm and 60～120 cm,respectively;and the depth of moist layer was 200 cm to GWL,60 cm to GWL and 120 cm to GWL,respectively.The Mix SIAR model shows that in June Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pedunculata Pall.mainly used the soil water in the moist layer and groundwater.During July to September,due to the increase of rainwater recharge,the water absorption of plant roots gradually shifted from moist layer and groundwater to active layer and stable layer,and the absorption of soil water in the two layers increased by 36.14%,32.98%and 25.52%,respectively.From October to November,with the decrease of rainwater recharge and temperature,Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pedunculata Pall.mainly used soil water in the stable layer and moist layer.In the growing season,Pinus sylvestris L.var.mongholica Litv.has the highest dependence on groundwater（30.16%）.The proportion of water absorbed in active layer by Salix psammophila showed great variation and was more sensitive to precipitation,showing a high ecological adaptability.However,Amygdalus pedunculata Pall.tended to use soil water in stable layer and moist layer.Salix psammophila,Pinus sylvestris L.var.mongholica Litv.and Amygdalus pedunculata Pall.have different emphasis on the absorption of potential water,which may be attributed to the dimorphism of plant root system.In addition,the infiltration and recharge of precipitation and the seasonal fluctuation of GWL may also contribute to the specific water use patterns for different plants.