Responses Of Soil Aggregates And Organic Carbon To Grazing Intensity In A Typical Steppe Of Inner Mongolia

The grassland ecosystem plays an important role in the stability of the global ecosystem.The Inner Mongolia grassland is an important ecological barrier in northern China.In recent decades,due to the impact of global change and human activities,the ecological function of the Inner Mongolia grassland has decreased sharply.Grazing is the main way to use the typical grassland in Inner Mongolia.The grazing animals directly or indirectly affect the grassland vegetation and soil through trampling,feeding and excretion.However,the mechanism of soil structure change caused by grazing is still unclear.At the same time,the conclusion of the effect of grazing on grassland soil organic carbon is controversial,and it is urgent to use new technology and new means to do further research.In view of this,this study of xilingol league area in Inner Mongolia typical grassland,ga flag as the research object,taking soil in the pasture under different grazing intensity,the X-ray computer tomography(CT)method is adopted,the combustion oxidation-non-dispersive infrared spectrometry,wet screening method to obtain the soil aggregate and soil organic carbon data,analysis the characteristics of both,To reveal the response of soil aggregates and organic carbon to grazing intensity.The main results and conclusions are as follows:(1)Soil organic carbon had different characteristics with the change of grazing intensity.With the increase of grazing intensity,the total organic carbon and the organic carbon of aggregates larger than 5 mm,2-1 mm and1-0.5 mm increased gradually.The characteristics of 0.5-0.25mm,0.25-0.053mm and less than 0.053mm were increased first and then decreased.Among the correlations among different organic carbon,the correlation between medium and heavy forage was the strongest,and the correlation between heavy forage and heavy forage was the weakest.Total organic carbon is most sensitive to the change of 1-0.5 mm aggregate organic carbon.(2)The particle size,stability and structural parameters of soil aggregates varied with grazing intensity.With the increase of grazing intensity,the soil macroaggregates decreased and the soil microaggregates increased.The aggregates larger than 5 mm and 1-0.5 mm decreased gradually.The aggregates content of 0.5-0.25 mm,0.25-0.053 mm and less than 0.053 mm increased gradually.The stability of soil aggregates decreased gradually.The results showed that the proportion of aggregates larger than 0.25 mm(R_0.25)decreased in medium grazing,fractal dimension(D)increased first and then decreased,average weight diameter(MWD)and geometric mean diameter(GWD)decreased gradually,and unstable aggregate index(IUA)increased gradually.The aggregates destruction rate(PAD)decreased with the increase of grazing intensity,while the macropores gradually decreased,the regular pores first decreased and then increased,the slender pores and irregular pores first increased and then decreased.Large aggregates mainly affect MWD and GWD.The structural parameters are mainly restricted by the stability of aggregates.The pore structure of 30-70?m has significant positive correlation with R_0.25,MWD and GWD(P<0.05),and significant negative correlation with D and IUA(P<0.05).The regular pores had a significant positive correlation with GWD(P<0.05),and a significant negative correlation with D(P<0.05).There was a significant negative correlation between irregular pores and MWD and GWD(P<0.05),and a significant positive correlation between irregular pores and D(P<0.05).It is worth noting that the soil pore parameters have the highest fitting strength with R_0.25and IUA,the soil regular pore shape parameters have the highest fitting strength with D,and the irregular pore parameters have the highest fitting strength with GWD.(3)The correlation between soil aggregate size and SOC was weak in no-grazing and light forage fields,and significant correlation was found between large aggregate size and SOC size under medium forage fields,while significant correlation was found between microaggregate size and SOC size in heavy forage fields.With the increase of grazing intensity,the relationship between stability and organic carbon gradually strengthened.The relationship between the structure parameters of soil aggregates and soil organic carbon was significant,the porosity under forbidden grazing and soil organic carbon had a significant correlation,and the pore shape under medium pasture had a significant correlation with soil organic carbon,but the correlation between the structure parameters of soil aggregates and soil organic carbon was weak in light grazing and heavy pasture fields.