Distribution Characteristics Of Nutrients And Microbial Activity In Soil Aggregates Of Pure And Mixed Stands Of Cunninghamia Lanceolata

Exploring the microscopic characterization of organic carbon and nutrients in surface soil of different Cunninghamia lanceolata stands at aggregate scale can lay a theoretical foundation for promoting the sustainable use of soil resources in Cunninghamia lanceolata plantations,thus improving soil health and fertility.Soil nutrients and microbial activity were analyzed in aggregate fractions that were collected from 0-10 cm and 10-20 cm depth in three different stands,mixed stand of Cunninghamia lanceolata and Michelia macclurei,Cunninghamia lanceolata and Mytilaria laosensis and pure stand of Cunninghamia lanceolata respectively,the soil aggregates were classified into>2,2-0.25,and<0.25 mm fractions.The main results are as follows:(1)The soil aggregate of different stand types were dominated by macro-aggregate(>0.25 mm),while the distribution of micro-aggregates(<0.25mm)was less.The MWD were ranked as?>?>?,indicating that the mixed stands soil aggregate structure were more stable than the pure stand,and the MWD decreased with the increase of soil depth in different stand types.(2)Most of the nutrients and microbial activities in the mixed stands soil were higher than those of pue stand,and stand?was better than stand?,while the K,AK,exchangeable K⁺content and ACP in the pure stand soil were higher than those of mixed stands.The distribution of different stands soil nutrients and microbial activities in the vertical structure was mainly decreased with the deepening of soil depth.(3)The main distribution of different stands soil aggregates nutrient and microbial activity was increased with the aggregate size decreased,and the secondary distribution trend was decreased first and then increased as the aggregate size decreased.(4)The composition of soil aggregate fractions was mainly(>2mm)>(0.25-2 mm)>(<0.25 mm)in the 0-10 cm soil layer,while it was(>2mm)>(<0.25 mm)>(0.25-2 mm)in the 10-20 cm soil layer.The soil aggregates organic carbon and nutrient storage were highly correlated with the distribution of different aggregate sizes.(5)The results showed that soil C,Na⁺,K⁺,EB were the main nutrient factors influencing microbial activity in stand I,soil AK,Na⁺,AP were the main nutrient factors influencing microbial activity in stand II,and soil C,N,Mg²⁺,EB,CEC,AP,AK were the main nutrient factors influencing microbial activity in stand III.(6)The correlation between different stands soil aggregates nutrients and microbial activity decreased with deepening soil depth,and the correlation decreased as the size of soil aggregates decreased.The correlations between soil C,N and microbial activity were strong in different stands.In addition,the correlations between soil exchangeable cations and microbial activity were strong in stand?,the correlations between soil EOC,AN,AP,AK and microbial activity were strong in stand?,the correlations between soil EB,K⁺,Na⁺in0-10 cm layer and soil P,EOC,AP,AK in 10-20 cm layer of stand?was strong.In conclusion,compared with pure stand,the soil aggregate structure of mixed stands were more stable,because mixed stands with large litter has more macro-aggregates,and stand?was better than stand?.Therefore,the mixed stand of Cunninghamia lanceolata and Michelia macclurei can effectively promote the formation and stability of soil aggregates,and alleviating the problems of decomposition of soil organic matter and nutrient loss in pure stand of Cunninghamia lanceolate.