| Soil aggregates is the basic constituent unit of soil,which affects the function and stability of soil.To explore the changing characteristics and influencing mechanism of soil aggregate structure in the restoration Robinia Pseudoacacia forest,the restoration age from 10 a,18a,28 a and 43 a in Loess Hilly Area was selected as the object,and the cultivated land was used as the control.Combined the field sampling and indoor analysis,we studied the distribution and stability variation characteristics of different particle size aggregates in 0-20 cm and 20-40 cm soil layer.And we used the correlation analysis about the content of carbon(C),nitrogen(N),phosphorus(P)and its stoichiometric characteristic in soil,aggregates,microbial and leaves,litter,as well as the distribution characteristics of clay minerals and soil texture was included.The main results are as follows.1.The soil structure of Robinia Pseudoacacia forest was improved and tended to be stable.In the soil,the aggregate content with particle size of 0.053-0.25 mm is the highest,followed by 5 mm,and the rest is small.The content of large aggregates(> 0.25mm)increased with the increase of recovery years,and the range of changes in soil layers of 0-20 cm and 20-40 cm were: 13.37%-52.47%,10.93%-40.68%,respectively,>5 mm increased the most.Microaggregate(<0.25 mm)decreased with the increase of recovery years,and 0.053-0.25 mm decreased the most.The stability coefficient GMD and MWD increased,K decreased,while the stability of soil aggregates increased.2.The content of C and N in Robinia Pseudoacacia forest is increased,they were Mainly affected by leaf P,litter P,MBC,MBN and MBPSoil and aggregate C,N and its stoichiometric ratio were affected by the restoration years and particle size.P content changes little.The content of C,N and C: P,N: P in soil and soil aggregates increased with the recovery years.The content of C,N and C: N,C: P,N: P increased first and then decreased as the particle size decreases,and the 0.5-1 mm is the highest.The content of C and N in soil and agglomerates of 0-20 cm was higher than that in 20-40 cm.And soil C,N were affected by > 5 mm,1-2 mm and 0.5-1 mm with the fastest rate of change.leaves,litters,and microbial C,N,and P was affected by restoration years.The content of C in the leaves changed little,and its value was stable around the mean value of 453.35 g·kg-1.The content of N,P and N: P first increased and then decreased with the increase ofrecovery years.The content of MBC,MBN and MBC: MBP,MBN: MBP first increased and then decreased with the increase of recovery years,MBP was increased with the age of recovery.There was an extremely significant correlation between MBC,MBN,MBP with leaf N,P and litter P.Soil aggregates C,N was Significantly relevant with MBC,MBN,MBP,only 1-2 mm particle size aggregate P was significantly correlated with litters P.3.Robinia pseudoacacia plantation had no significant effect on soil texture and clay minerals.There was no significant difference in the content of soil particles and clay minerals in Robinia Pseudoacacia forest between different years and soil layers.The mean content of clay,silt and sand was 17.76%?47.03%?35.22%.The main clay minerals are hydromica,chlorite,kaolinite,vermiculite and montmorillonite,and the content of them was 64.01%?15.43%?9.17%?7.41%?3.98%.The mass of clay,silt and clay minerals in surface soil was slightly higher than that in deep soil.The mass of clay and silt was increased with the age of recovery.4.The key factors of soil aggregates structure in Robinia Pseudoacacia forest were preliminarily clarified.In our study,microorganisms and leaf,litter P affectd the aggregates C,N and P.the content of C,N,P of aggregates made up the content of soil C,N and P.they affectd the change of soil aggregates structure.RDA analysis showed that the content of soil C,N,P,C:P,N:P,C:P,soil bulk density and clay were positively correlated with aggregates.Of these,P is more sensitive than C and N.In addition,a number of other factors also have an important impact on a particular particle size agglomerates.for example,Kaolinite was affected in >5 mm,2-5 mm particle size aggregates;Soil moisture content was affected in 1-2 mm,0.5-1,0.25-0.5 mm particle size aggregates.sand was affected in 0.053-0.25 mm particle size aggregates,soil p H was affected in <0.053 mm particle size aggregates.In conclude,the soil structure improved and the stability increased during the recovery of Robinia Pseudoacacia forest in loess hilly area,which is closely related to the increase of the content of large agglomerates.The key influencing factors of soil aggregates structure were soil and microbial nutrient bank,bulk weight and clay content,and the influence of litter and leaf was small.The results of this study have reference value for the study of soil structure improvement and erosion resistance in Loess Hilly Area,and provide theoretical basis for the study of soil aggregate structure in restoration region. |
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