Influence Of The Evolution Of Root System And Soil Pore Structure Of Artificial Caragana Korshinskii In Desert Grassland On Preferential Flow

It is important to investigate the influence of soil macropore and root topology evolution characteristics on preferential flow after the introduction of artificial Caragana Korshinskii in desert grassland to further understand the subsurface ecological processes in arid areas.In this study,grassland(CK)and 9,14,24 and 35-year-old artificial Caragana Korshinskii stands in the same habitat were selected as the study area in a typical desert grassland area in Yanchi County,Ningxia.In-situ soil column acquisition,CT scanning and image processing analysis were performed separately to obtain the geometric distribution characteristics of soil macropores and roots,and to quantify structural parameters such as their number,length,volume,surface area,equivalent diameter and connectivity.The study of the influence of heterogeneous soil root system and pore structure evolution characteristics on preferential flow after the introduction and during the continuous growth of Caragana Korshinskii sticks led to the following main conclusions:(1)It can be seen from the 3D images that in the 0-200 mm soil vertical profile,the number of large pores in the 9a and 14a samples is overall less compared to the CK samples,while the number of large pores in the 24a and 35a samples is significantly more and more complex in structure.For the root system,compared with CK,the main roots were less distributed and surrounded by fine roots in the 14a sample plot,a large number of fine roots in the 9a and 24a sample plots,and a thicker root system with a few fine roots around in the 35a sample plot.It can be seen that as the age of the Caragana Korshinskii stand increased,the number of thick roots increased significantly,while the number of fine roots decreased.(2)The effect of stand age on the geometric characteristics parameters and macropore structure parameters of the Caragana Korshinskii root system was significant(P<0.05).For the root system,as the age of the Caragana Korshinskii stand increased,the root number density and mean equivalent diameter decreased,while the surface area density,bulk density,and connectivity increased subsequently.Meanwhile,root number density and length density showed an overall trend of decreasing with increasing soil depth,while bulk density,surface area density,equivalent radius and connectedness increased with increasing soil depth.For macropores,the number density,length density,bulk density,surface area density,equivalent diameter and connectivity of soil macropores showed an increasing trend as the age of the Caragana Korshinskii stand increased,while their parameters showed an increase with the depth of the soil layer.(3)Differences in maximum staining depth,staining area ratio,coefficient of variation and degree of preferential flow were found in different stand age Caragana Korshinskii samples.The analysis revealed that the soil preferential flow staining depth showed 35a>CK>14a and 24a>9a.The maximum staining area ratio of the five samples showed 35a>9a>CK>14a>24a.The coefficients of variation of soil staining area ratio in different stand age Caragana Korshinskii samples showed 9a>14a>24a>35a>CK,and their preferential flow degrees were rapid change,sub-active,active,sub-active,and sub-active,respectively.(4)Root system geometric characteristics parameters and macropore structure parameters had significant(P<0.05)effects on preferential flow characteristics.Root number density,length density and surface area density were significantly and positively correlated with staining area ratio(P<0.05),and equivalent diameter and connectivity were significantly and negatively correlated with staining area ratio(P<0.01).Number density and length density were significantly positively correlated with length index and coefficient of variation(P<0.01)and negatively correlated with connectivity and equivalence radius(P<0.01).Macropore number density,length density,and surface area density were significantly and positively correlated(P<0.05)with matrix flow depth,coefficient of variation,length index,and staining area ratio,and equivalent diameter and connectivity were significantly and negatively correlated(P<0.01)with matrix flow depth.