Effects Of Typical Herb Roots On Soil Infiltration And Spatial Differences In The Loess Plateau

Owing to the fragile ecological environment and worse soil erosion,the Loess Plateau is one of the regions which suffer from the serious looser soil surface and ecological environment degradation in China and even in the world.As an important part of eco-hydrological processes,rainfall infiltration determines soil water storage and runoff formation,and plays a crucial role in hydrological responses such as water cycle and potential soil and water loss.Studying the eco-hydrological process of the Loess Plateau will be beneficial to the improvement in regional ecological environment and function of soil system in this region.With respect to vegetation restoration in the Loess Plateau,plant root activity is an important driving factor that ameliorates soil properties and improves soil infiltration and water storage capacity.Moreover,soil texture also affects the change degree of root-induced soil hydrodynamic characteristics.Therefore,it is of great scientific significance to study the effect and mechanism of typical herbaceous plant roots on soil properties and soil infiltration capacity.In this study,three study regions in different soil types from north to south of the Loess Plateau,namely,Liudaogou（with sandy loess texture in Shenmu）,Fangta（with loess texture in Ansai）,and Yongshouliang（with clay loess texture in Yongshou）,were selected as the study area.Two natural vegetation communities,including Stipa bungeana（S.bungeana）with fibrous root systems and Artemisia gmelinii（A.gmelinii）with tap root systems,were selected as research objects,and abandoned land（farmland left fallow for one year）was used as the control.Then,based on in-situ double-ring infiltration methods in the field and experimental analysis in the laboratory,the effect of roots on soil properties and the quantitative response of soil infiltration to plant roots and soil properties under different conditions were quantitatively analyzed.This work could improve the understanding of the root-soil interaction and its influence on the infiltration process in the vegetation restoration in the Loess Plateau,and provide a scientific reference for the selection of suitable vegetation to improve infiltration rate,to reduce the loss of surface water,and to prevent soil erosion disasters in these areas.The main conclusions are as follows.（1）Vegetation restoration significantly improved soil infiltration capacity.Under the same soil texture,the infiltration rates（initial infiltration rate,stable infiltration rate,and average infiltration rate）and soil infiltration capacity index（SIC）showed a relationship in Liudaogou and Yongshouliang as follow:S.bungeana>A.gmelinii>abandoned land.In Fangta,however,they showed the relationship of A.gmelinii>S.bungeana>abandoned land.With respect to the same vegetation community,the infiltration rates and the SIC of Yongshouliang were significantly higher than those of another two regions.Compared with the abandoned land under the same soil texture condition,the improvement degree in soil infiltration ability of vegetation community was the highest in Liudaogou region concerning the different regions and more obvious for the S.bungeana community concerning the different vegetation communities.（2）Vegetation communities have a positive effect in ameliorating soil physical properties.For the same vegetation community,the soil structure of Yongshouliang is better than that of another two regions.The root characteristic parameters（root mass density,root length density,root surface area density and root volume density）decreased sharply and then decreased slowly with the increase of soil depth,showing a pronounced surface aggregation.Under the same soil texture,root characteristic parameters of A.gmelinii community were higher than those of S.bungeana community,except for root length density.However,for the same vegetation community,the root characteristic parameters in Yongshouliang were higher than those in Fangta and Liudaogou regions.（3）The growth of plant roots could improve soil structure and soil water-holding capacity,including the decrease of bulk density,the increase of soil porosity,and the increase of soil water-holding capacity.Under the same soil texture,the correlations between root parameters and soil properties for A.gmelinii community were stronger than those for S.bungeana community.For the same vegetation community,the correlations between root parameters and soil properties gradually increased from Liudaogou region in the north of the Loess Plateau to Yongshouliang region in the south of the Loess Plateau.On the whole,root surface area density exhibited the strongest effect on soil physical properties,which is followed by root length density and root volume density,and root mass density showed the weakest effect but had the strongest correlation with soil non-capillary porosity.（4）The growth of root and the amelioration of soil structure collectively contribute to the increase of soil infiltration rates in vegetation community.Soil physical properties had a positive effect on the improvement of soil infiltration capacity,while the effect of root growth on soil infiltration capacity was complex,which was affected by soil texture and root diameter.Under the same soil texture condition,the correlations between soil infiltration and root parameters,soil properties were stronger for S.bungeana.For the same vegetation community,the correlation intensity between soil infiltration and rootsoil interactions indicated a relationship of Fangta>Yongshouliang>Liudaogou.Furthermore,In the Loess Plateau,the stepwise regression analysis results showed that the proportion of soil particle size（clay and silt）,soil porosity（CP and NCP）,soil saturated water-holding rate,and root characteristics（RSAD and RVD）were the main factors that controls soil infiltration capacity,which explained 47.9%,90.7%,72.0%,and 80.2%of initial infiltration rate（IIR）,stable infiltration rate（SIR）,average infiltration rate（AIR）,and soil infiltration capacity index（SIC）,respectively.