Effect Of Fallen Wood Decomposition Of Common Tree Species In Karst Forest On Soil Properties

As an important structural and functional element in the forest ecosystem,fallen wood is a carrier that connects the main functions of the ecosystem,such as nutrient cycling and community renewal,and plays an important role in maintaining the integrity and stability of the forest ecosystem.The Maolan Karst evergreen broad-leaved and deciduous mixed forest is currently a rare remaining subtropical karst karst forest in China and even the world.Studying the impact of the fallen wood decomposition of this community on the soil properties has the effect of revealing the existence of fallen wood on karst landforms.In this paper,the evergreen broad-leaved and deciduous mixed forest in Maolan Karst Forest Nature Reserve in China is used as the research area,and Machilus rehderi Allen.,Liquidambar formosana Hance.,and Cyclobalanopsis glauca(Thunb.)Oerst.,Platycarya longipes Wu.,four common tree species as the research object.Using field investigations and indoor experiments,preliminary study of different tree species and different decay levels of adjacent fellings(10cm,30 cm and 50cm)the distribution characteristics of soil chemical properties,humus and agglomerates and organic carbon of agglomerates aim to reveal the mechanism of the effect of the decomposition of fallen wood on the soil properties,and provide a theoretical basis for the scientific management and protection of karst forests.The results show that:(1)As the decay level increases,the moisture content of the fallen wood gradually increases and the density gradually decreases.Except for Platycarya longipes,the total nitrogen and total phosphorus of the fallen trees of other tree species are highest when they are heavily rotted.The nutrient content of fallen wood during heavy decay differs among tree species,and it is shown that total nitrogen,total phosphorus,and total potassium are the highest in fallen wood of Cyclobalanopsis glauca,which are 2.703 g/kg,0.156 g/kg,and 0.168 g/kg,respectively.The lowest of Machilus rehderi was 1.346 g/kg,0.063 g/kg and 0.007 g/kg,respectively.(2)Except for Machilus rehderi,other species of fallen wood have a significantly higher total nitrogen,hydrolyzed nitrogen,total phosphorus,available phosphorus and organic carbon in the adjacent soil than moderate decay.There is a significant difference in the distance of availablephosphorus between the soils of Liquidambar formosana and Cyclobalanopsis glauca.The higher the decay level,the greater the influence range of the tree species on the soil adjacent to the fallen wood,and the closer to the fallen wood,the higher the organic carbon content.The interaction of decay level and tree species had significant effects on soil total nitrogen,hydrolyzed nitrogen,total phosphorus,available phosphorus,available potassium,available potassium,organic carbon,and carbon-to-nitrogen ratio under fallen wood.(3)The deeper the degree of decay,the greater the influence range of tree species on the distance of each component of adjacent soil humus.Except for Machilus rehderi,the components of adjacent tree humus in moderate and severe decay were significantly higher than those in mild decay.The decay level,tree species and their interactions have extremely significant effects on the total carbon content of humus,humic acid,fulvic acid and humicin under the fallen wood.(4)The decay level had the greatest effect on the distribution of soil aggregates near the fallen wood of Cyclobalanopsis glauca,and had the least effect on Machilus rehderi.The deeper the decay,the more significant the influence of tree species on the distribution of soil aggregates closer to fallen wood.The decay level and tree species only have a significant effect on the destruction rate of aggregates at 10 cm near the fallen wood.The destruction rate of agglomerates at 10 cm near the severely decayed Liquidambar formosana and moderately decayed Platycarya longipes was significantly higher than 30 cm,50 cm and the control.The interaction between the decay level and tree species only had a significant effect on the aggregates and destruction rate of1-0.5 mm and <0.25 mm adjacent soils of fallen wood.(5)The organic carbon of neighboring soil aggregates in Liquidambar formosana,Cyclobalanopsis glauca and Platycarya longipes fallen woods in moderate or severe decay was significantly higher than that in mild decay.The higher the decay level of fallen wood,the greater the influence range of tree species on the distance of organic carbon of each particle size of soil aggregates.At moderate and severe decay,the organic carbon of each particle size of soil aggregates at various distances near the fallen wood was significantly higher than that of the control.The decay level,tree species and their interactions have a very significant effect on the organic carbon of each particle size aggregate in the soil.