| Forests are rich in natural resources and are the largest ecosystem on earth,playing an important role in maintaining ecological balance.With the increasing area of plantation forest management,how to improve the quality of existing plantation forests in China has become an urgent issue that needs to be addressed.Soil is an important environmental factor for plant growth in the ecosystem.Scientific and reasonable use of soil resources can improve soil fertility,which is an important material basis for improving the quality of plantation forests.Therefore,four different plantation types: Robinia pseudoacacia,Robinia pseudoacacia-Quercus variabilis mixed,Platycladus orientalis,Quercus variabilis were selected as research objects in the rocky mountainous areas of North China.Soil samples of 0~10,10~20 and 20~30 cm depth were taken in 3 times(March,June,September).Determination of physical properties(Water content,Soil bulk density,Soil total porosity,Clay,Silt,Sand volume fraction),chemical properties(pH,Available potassium,Available nitrogen,Available phosphorus,Nitrate nitrogen,Ammonium nitrogen)and biological properties(Sucrase,Urease,Catalase)of each plantation type by field survey and in-laboratory analysis,exploring the distribution characteristics of different plantation forest types on soil physicochemical properties and the influence on biological properties,to evaluate soil quality based on the correlation among environmental factors,soil indicators and the weighted summation method based on principal component analysis.The specific findings of the study are as follows:(1)Different plantation types showed significant effects on soil bulk density,water content,soil porosity,clay,silt and sand volume fraction.The soil bulk density and soil water content of Robinia pseudoacacia plantation were significantly higher than those of other plantation types,The soil porosity,clay and powder volume fraction of Platyclus plantation was significantly higher than that of other plantation types,and the sand volume fraction of Robinia pseudoacacia-Quercus variabilis mixed forest was significantly higher than that of other plantation types.Seasonal variation only had a significant effect on water content,clay,silt,and sand volume fraction.Soil depth only had a significant effect on water content,soil bulk density,soil porosity,and clay volume fraction.Soil water content and porosity decreased gradually with the increase of soil depth,while soil bulk density and clay volume fraction increased gradually with the increase of soil depth.Both seasonal variation and soil depth had significant effects on soil bulk density and soil porosity.In contrast,the interaction of plantation type,season and soil layer had no significant effect.(2)Different plantation types showed significant effects on soil pH,AK,AN,AP,NO3--N,NH4+-N.The contents of pH,AK,AN and AP of Platycladus plantation were significantly higher than those of other plantation types.The contents of NO3--N and NH4+-N of Robinia pseudoacacia-Quercus variabilis mixed forest were significantly higher than those of other plantation types,while the contents of soil chemical properties of Quercus variabilis were significantly lower than those of other plantation types.Seasonal variation only had a significant effect on AN,AP.The contents of AN and AP were higher in June and lower in March,while the contents of pH,AK,NO3--N and NH4+-N had no obvious seasonal variation trend.Soil depth only had a significant effect on AN,AP,AK,NO3--N.The contents of AN,AP,AK and NO3--N decreased with the increase of soil depth.Both seasonal variation and soil depth had significant effects on AN.In contrast,the interaction of plantation type,season and soil layer had no significant effect.(3)Different plantation types showed significant effects on soil sucrase,urease,catalase.The activities of sucrase and urease in soil of Platycypress plantation were significantly higher than those of other plantation types.The catalase activities in Robinia pseudoacacia plantation were significantly higher than those in other plantation types,while the enzyme activities in soil of Quercus variabilis plantation were the lowest.Seasonal variation oshowed significant effects on soil sucrase,urease,catalase.The activities of soil urease and sucrase were higher in June and lower in March,Soil catalase activity was higher in March and lower in June.Soil depth only had a significant effect on soil sucrase,urease.Soil enzymatic activities decreased with the increase of soil depth.Both seasonal variation and soil depth had significant effects on soil sucrase.In contrast,the interaction of plantation type,season and soil layer had no significant effect.(4)In the correlation analysis of physical,chemical and biological indicators of soil,many reached significant or highly significant correlations.Therefore,the 15 soil quality evaluation indicators were used as correlations to extract principal components,and the minimum data set method was used to screen the indicators for evaluating soil quality,and the most representative 8 participating indicators were selected: water content,soil bulk density,soil total porosity,silt,AK,AP,NH4+-N and urease.The soil quality evaluation scores based on the weighted summation method,in descending order,they are: Platycladus orientalis>Robinia pseudoacacia>Robinia pseudoacacia-Quercus variabilis mixed>Quercus variabilis.In conclusion,there are significant differences in the physical,chemical and biological properties of soils in different plantation forest types in the rocky mountainous areas of North China,and both seasonal changes and soil depth can affect the changes in soil properties,Also there are also significant or highly significant correlations between soil indicators and a comprehensive evaluation of soil quality.Therefore,this study can improve the scientific and theoretical basis for the conservation of forest soil resources,the improvement of soil quality and the sustainable development of ecosystems in the rocky mountainous areas of North China. |
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