Stoichiometric Characteristics Of Carbon,nitrogen And Phosphorus Of Reclaimed Soil Aggregate In Coal Mining Subsidence Area

The subsidence in coal mining area resulted in destruction of a large number of farmland and deterioration of the physical and chemical properties of the soil.Farmland cultivation could not be continued in subsidence,and it needs to be improved by vegetation reclamation to increase the fertility.Shrubs or small trees were optimal to plant in the early stage of reclamation for improving land production capacity,especially the well-growing local tree species.Three types of reclaimed forests,Amygdalus pedunculata,Cerasus humilis,and Xanthoceras sorbifolia,were set up in the subsidence of Shenfu Dongsheng Mining Area.The composition and stability of soil aggregates,the contents of carbon,nitrogen and phosphorus in soil aggregates,as well as their stoichiometric characteristics and enzyme activity were analyzed in 0～20 cm and 20～40cm soil layer respectively of different types of reclaimed forests.The aim of this study was to explore the mechanisms of different types of reclaimed forests in improving soil aggregate stability,carbon,nitrogen and phosphorus nutrients,and enzyme activity,in order to provide theoretical basis of vegetation reclamation for this area or other similar area of mining subsidence.The main results were as follows:（1）The contents of soil mechanical stable and water-stable aggregates,that particle size>2 mm and 2～0.25mm,in 0～20 cm and 20～40 cm soil layers were increased by the reclamation of A.pedunculata,C.humilis and X.sorbifolia,and the contents of aggregates,particle size of 0.25～0.053 mm and<0.053 mm,were decreased.The aggregates content that particle size>2 mm in reclamation of X.sorbifolia was higher,whereas<0.053 mm was lower than other reclaimed forests significantly.（2）Compared with the control,the mechanical stable aggregates(DR_>0.25)and water-stable aggregates(WR_>0.25)in each soil layers of different reclaimed forests were increased by 17.86%～33.36%and 12.94%～21.69%,respectively,and the weight diameter（MWD）and geometric mean diameter（GMD）were increased significantly,while the fractal dimension（D）was reduced.The MWD and GMD values of soil aggregates in the X.sorbifolia reclaimed forest were the largest,and the D value was the smallest notably.（3）Contents of organic carbon（SOC）,total nitrogen（TN）and total phosphorus（TP）of soil aggregates in the soil layers of 0～20 cm and 20～40 cm were increased in each reclaimed forests.The biggest increase of contents of SOC,TN and TP were in X.sorbifolia,and the contents of SOC and TN were higher than other reclaimed forests significantly.The contents of SOC,TN and TP of soil aggregates,particle size<0.053mm,were the largest in reclaimed forests,while particle size>2 mm and 2～0.25 mm had the greatest contribution to soil SOC,TN,and TP.（4）The C/N,C/P,and N/P of soil aggregates of reclaimed forests were higher than that of control.C/N,C/P and N/P of soil aggregate in each forest type were 10.46～15.53,14.10～20.52 and 1.01～1.72 respectively,which were lower than the national and global average levels.Nitrogen was the limiting factor in the area.（5）Activities of alkaline phosphatase（S-ALP）,invertase（S-SC）,urease（S-UE）and catalase（S-CAT）of soil aggregate in each soil layer were increased in reclaimed forests.The soil enzyme activities in reclaimed forests of A.pedunculata and X.sorbifolia were higher than C.humilis,and the highest was observed in the aggregates particle size<0.053 mm.The activity of S-ALP,S-SC,S-UE and S-CAT in soil aggregates were positively correlated with contents of SOC,TN,and TP.Xanthoceras sorbifolia was better in improvement of soil fertility,so it is an optimal tree for reclamation of coal mining subsidence area.