Spatial Variability Of Soil Nutrients And The Influencing Factors In The Natural Spruce-fir Mixed Forest Of Northeast China

To study the spatial variability of soil nutrients and their response to cutting in the natural spruce-fir mixed forest,two 1-hm~2 plots of different cutting intensities(21.21%and 0%)were selected for soil sampling at depths of 0-20 cm and 20-40 cm in Jingouling Forest Farm of Wangqing Forestry Bureau,Jilin Province.A total of 400 soil samples were collected using“s”shaped sampling method for the determination of soil p H,organic matter content,total nitrogen,total phosphorus,total potassium,available phosphorus,and readily available potassium concentrations,and a total of 400 litter samples in semi-decomposed and complete decomposed horizons were collected using an equidistant grid point sampling method to determine litter nutrients concentration and to calculate nutrient return and use efficiency.The spatial distribution characteristics of soil nutrients were studied using classical statistics and geostatistics so as to provide a theoretical basis for the precise management of soil nutrients in natural forests and the protection of soil ecosystems.The results were showed as follows:(1)With the increase of soil depth,the soil p H,organic matter content,total nitrogen,total phosphorus,total potassium,available phosphorus,and readily available potassium concentrations decreased.The coefficients of variation of all soil nutrients at varied depths of the two plots ranged from4.34%to 66.99%,with the highest for total nitrogen,and the lowest for soil p H.The coefficients of variation of soil nutrients in the cutting plot were mostly higher than those in the non-cutting plot.(2)The soil was acid at varied soil depths and cutting enhanced soil acidity.Compared with the non-cutting plot,the soil nutrient concentrations decreased at 0-20 cm but increased at 20-40 cm.Therefore,cutting only affected the nutrient concentrations of the topsoil.There were varied degrees of correlation between soil nutrients,and soil organic matter content would significantly affect other nutrient concentrations.(3)The nugget effect of soil nutrient indicators in the cutting plot ranged 25%-75%at varied soil depths,with a moderate degree of spatial autocorrelation,indicating that structural factors and random factors worked jointly on spatial variability.However,the nugget effects of soil nutrient indicators in the non-cutting plot were mostly less than 25%with strong spatial autocorrelation,indicating that structural factors contributed significantly to their spatial variability.The high uniformity in all positions was illustrated by the fractal dimension close to 1.90 as for all soil nutrient indicators,indicative of their good spatial dependence.Preferential pattern appeared in different positions as for each soil nutrient judged by the coefficient of determination.(4)The spatial pattern of soil nutrients was diversified and had a clear directional trend at varied soil depths.In the cutting plot,soil nutrients had worse spatial continuity and more serious fragmentation.(5)Stand density,canopy density and litter properties changed due to cutting,but there was no obvious short-term effect of cutting on soil nutrients.