Study On Soil Nutrient Content Characteristics And Influencing Factors Of Economic Forest Tree Species In Gangu County

Economic forests,with their renewable nature,have the potential to alleviate poverty and conserve nature around the world,but their productivity and quality are influenced by soil nutrients and other factors.Therefore,understanding the drivers and spatial distribution patterns of soil nutrients is essential for the efficient management of economic forests.Soil organic carbon(SOC),soil total nitrogen(STN)and soil total phosphorus(STP)are important indicators of soil nutrients and are essential for maintaining ecosystem function and preventing land degradation.In this paper,soil samples were collected in layers from 0-100 cm depth from different economic forest vegetation in Gangu County,Tianshui City,Gansu Province.The distribution characteristics of SOC,STN and STP contents of apple(Malus pumila),walnut(Juglans regia),pepper(Zanthoxylum bungeanum),apricot(Prunus armeniaca),peach(Prunus persica)and wasteland were analysed under different tree species and soil layers.The distribution of SOC,STN and STP contents in forest type and soil depth was investigated in relation to soil microbial population(soil bacterial population,soil fungal population,soil actinomycete population),soil pondus hydrogenii(p H),soil bulk density(SBD),soil water content(SWC)and soil electrical conductivity(EC).and modelled with the help of structural equation model(SEM).The results of the study showed that:(1)The SOC,STN and STP contents of different economic forest soils in Gangu County ranged from 9.17±0.15-17.20±0.13 g/kg,0.808±0.03-2.190±0.05g/kg and 0.207±0.11-0.971±0.55 g/kg,respectively.In terms of economic forest types,the SOC contents at 0-100 cm depth were,in descending order,Malus pumila,Juglans regia,Zanthoxylum bungeanum,Prunus armeniaca,Prunus persica,and wasteland;the TN contents were,in descending order,Malus pumila,Juglans regia,Prunus persica,Zanthoxylum bungeanum,Prunus armeniaca,and wasteland;and the TP contents were,in descending order,Malus pumila,Zanthoxylum bungeanum,Juglans regia,Prunus persica,Prunus armeniaca,and wasteland.In terms of vertical distribution,the SOC contents of all five forest types and wasteland showed obvious surface aggregation;the STN contents of all five forest types and wasteland decreased in the 80-100 cm soil layer compared with their contents in the0-10 cm soil layer;the STP contents of all five forest types decreased in the 80-100 cm soil layer compared with their contents in the 0-10 cm soil layer,and the STP contents of wasteland in the 80-100 cm soil layer were the same as their contents in the 0-10 cm soil layer.The STP content in the 80-100 cm soil layer was 1.41 times higher than that in the 0-10 cm soil layer.The SOC content of the sampling sites was generally in the middle to upper level;the STN content was generally in the middle to upper level,but there were also some sampling sites where the soil total nitrogen content was deficient;the STN content was generally in the middle deficient level.(2)The analysis of soil factors revealed that the mean values of SWC from high to low at 0-100 cm depth were: Prunus persica,Zanthoxylum bungeanum,Juglans regia,Malus pumila,wasteland,Prunus armeniaca;the mean values of SBD from high to low were: wasteland,Prunus armeniaca,Malus pumila,Prunus persica,Zanthoxylum bungeanum,Juglans regia;the mean values of p H from high to low were: wasteland,Juglans regia,Malus pumila,Zanthoxylum bungeanum,Prunus armeniaca,Prunus persica;the mean values of EC from high to low:Zanthoxylum bungeanum,Malus pumila,Prunus armeniaca,Prunus persica,wasteland,Juglans regia.The SWC in the surface layer of the same economic forest species was higher than that in the bottom layer of the soil;the EC fluctuated in the 0-100 cm soil layer;SBD and p H showed a trend of gradually increasing with the depth of the soil.(3)The analysis of soil microbial numbers revealed that the numbers of soil microorganisms in all five forest types and wastelands were bacteria >actinomycetes > fungi,and the numbers of all three microorganisms showed a decreasing trend in the 0-100 cm soil layer.Overall,the average number of soil microorganisms was higher in Juglans regia and Malus pumila,and the lowest in wasteland.(4)The Pearson correlation results showed that the SOC,STN and STP contents of the five economic forests and wastelands showed positive correlations;the SOC,STN and STP contents of the five economic forests were positively correlated with SWC,soil bacterial count,soil fungal count and soil actinomycete count;and significantly negatively correlated with SBD and p H.The SOC,STN and STP contents of Malus pumila and wasteland were negatively correlated with EC,while the SOC,STN and STP contents of Prunus persica,Juglans regia and Prunus armeniaca were positively correlated with EC.(5)The results of the structural equation model indicate that soil factors have both direct and indirect effects on soil nutrients.SWC has a direct impact on the content of SOC,and can also affect the content of SOC,STN,and STP by directly affecting SBD and p H.SWC has a direct impact on the number of soil microorganisms,with a path coefficient of 0.347.The content of SOC has a direct impact on the number of soil microorganisms,with a path coefficient of 0.637.The direct impact of p H on SOC content and STN content is-0.408 and-0.458,respectively.SBD has a direct impact on SOC content,with a path coefficient of-0.695.EC has a direct impact on STP content,with a path coefficient of 0.367.