Soil Physicochemical Properties And Influencing Factors In Different Vegetation Type Zones In The Qilian Mountains,China

As an important ecological security barrier area in China,the Qilian Mountains play a crucial role in maintaining ecological balance,runoff recharge,and climatic regulation.Understanding the soil physicochemical properties of typical vegetation areas and identifying the influencing factors and mechanisms affecting soil physicochemical properties in the Qilian Mountains can provide data support and scientific references for further development of the National Park and important ecological security barrier area in China.In this study,we collected soil samples from0-60 cm depth in five typical vegetation zones:bareland,grassland,forest,shrub,and meadow.We analyzed various soil parameters including mechanical composition,fractal dimension,water-heat,organic carbon（SOC）,total nitrogen（TN）,and phosphorus contents（TP）,stoichiometric ratio,and soil quality index（SQI）.By considering topography,vegetation,and climate as influencing factors,we analyzed the main driving pathways and degree of contribution to changes in soil physicochemical properties in different vegetation zones.The results were as follows:（1）The composition of soil particles is dominated by clay and silt.The distribution of soil particle sizes was similar and distribution heterogeneity of soil particle was complex and variable in each vegetation type zone in the Qilian Mountains.The content of clay and silt varies among vegetation types and depths,with the lowest levels found in meadow and the highest levels in bareland and grassland.As soil depth increased,the clay and silt content tended to increase initially and then decrease.The degree of heterogeneity of soil particle distribution varies among vegetation types,with an overall trend of decreasing and then increasing with soil depth increasing.（2）Soil grain size fractal characteristics were similar in the different vegetation types of the Qilian Mountains.The single fractal dimension D_v of soil particle size distribution（PSD）did not differ significantly between vegetation types and soil depths.Similarly,the multifractal singularity spectra showed an inverse’S’-shaped decline,and the multiple fractal parameters D₁,D₁/D₀,and D₂ did not differ significantly by vegetation zone and soil depth.The multifractal singularity spectra functionΔf<0,with a"right hook"shape,Δαwas not significantly different between vegetation zones and had a large value.There was no significant fractal pattern of soil particles in each vegetation type.（3）Soil water-heat characteristics in each vegetation type zone showed little difference,with soil temperature（ST）showed more regularity compared to soil water content（SWC）in the Qilian Mountains.There was a certain interaction between the two,but the response degree was low.Specifically,there was no significant difference in soil water-heat overall（0-60 cm）,except that SWC was significantly higher in meadow than in forest and grassland at soil depth of 0-20 cm.ST showed no significant differences at different soil depths in each vegetation type zone.With increasing soil depth,SWC remained relatively constant while ST decreases significantly.The relationship between SWC and ST followed a logarithmic function represented by SWC=47.77-6.13ln（ST-1.12）（p<0.05,R²=0.24）.（4）SOC and TN were high and TP was lowe in each vegetation type zone in the Qilian Mountains.Specifically,SOC was significantly higher in shrub than in grassland overall（0-60 cm）,while TP was significantly higher in bareland than in grassland,forest,and meadow.TN showed no difference among vegetation types.Except for slight differences in SOC,TN,and TP at a depth of 0-20 cm in some vegetation zones,differences were small at depths of 20-40 cm and 40-60 cm.SOC and TN decreased with increasing soil depth,while TP varies complexly.（5）The C:N ratio was generally low,and the C:P ratio was high in each vegetation type zone in the Qilian Mountains,with N:P ratios between 10-20.The above three ratios were higher in good vegetation areas such as forest than in general vegetation areas such as bareland.C:N and C:P ratios showed similar differences between 0-20 cm and 0-60 cm,while there were no significant differences in each vegetation type zone at soil depths of 20-40 cm.At soil depth of 40-60 cm,the C:N ratio was significantly lower in grasslands than in bareland,forest,and shrub,while the C:P ratio was significantly higher in shrub than in bareland,grassland,and meadow,and significantly higher in meadow than in bareland.The N:P ratio was significantly higher in shrub than in meadow.There wereb no significant changes in C:N,C:P,and N:P ratios with increasing soil depth in each vegetation type zone.（6）The physicochemical properties of soils in the Qilian Mountains were largely influenced by vegetation.Both direct and indirect climatic influences are significant,but their effects were reversed.SQI showed that grassland and shrub were significantly higher than meadow,and there was little variation with changes in vegetation type and soil depth.The total effects of topography,climate,and vegetation on SQI were 0.26,0.18,and 0.49,respectively.Direct effects of topography and vegetation on SQI were positive,while the effect of climate was negative,with effect values of 0.26,0.49 and-0.35 respectively.Additionally,climate indirectly affected SQI through topography and vegetation,with an effect value of 0.53.Topography,climate,and vegetation collectively explained 66.55%of the variance in SQI,with vegetation alone explaining the largest portion（30.18%）,followed by a combination of vegetation and climate（19.20%）,and all three variables together（11.55%）.Based on soil physicochemical data and environmental element datasets,this study explored the characteristics of soil physicochemical properties and influencing factors in typical vegetation types in the Qilian Mountains,quantified the mediating pathways and contribution rates of environmental factors on soil physicochemical properties,and provides a theoretical basis and technological support for further construction of the Qilian Mountains National Park and enhancement of the ecological security barrier function of the Qilian Mountains.