Effects Of Vegetation Restoration On Soil Aggregate Stability In Karst Slope Land In Eastern Yunnan

This paper aims to study the particle size of soil aggregates,the characteristics of nutrient distribution and accumulation,and the influencing factors of stability under different vegetation restoration types of Pinus yunnanensis in rocky desertification slope of karst rift basin in eastern Yunnan.In January 2019,pinus yunnanensis pure forest,pinus yunnanensis artificial mixed forest,pinus yunnanensis natural mixed forest,shrub and primeval forest were selected in Haifeng area of Zhanyi County,Yunnan Province.The particle size distribution,nutrient content,stoichiometric ratio,stability characteristics and soil physical and chemical properties of soil aggregates in0-10 cm,10-20 cm,20-40 cm and 40-60 cm soil layers under different vegetation types were analyzed by field survey and laboratory analysis,and the influencing factors of soil aggregate stability under different vegetation restoration types were explored.The results are as follows:(1)The proportion of clay content(<0.002 mm)in different vegetation types showed:Pinus yunnanensis artificial mixed forest(48.52%)>Pinus yunnanensis natural mixed forest(45.58%)>Pinus yunnanensis pure forest(43.00%)>shrub(25.24%)>native forest(20.77%).Soil water content and bulk density of three Pinus yunnanensis forests were higher than those of native forests.The mass fraction of soil aggregates with particle sizes of>5 mm,2-5,0.25-0.5 mm and<0.25 mm in pure Pinus yunnanensis forest was high in surface layer and low in deep layer,and the mass fraction of soil aggregates with particle sizes of 1-2 mm and 0.5-1 mm was the highest.(2)The contents of organic carbon and total nitrogen of soil aggregates with six particle sizes in three pinus yunnanensis forests were lower than those in shrub and native forests,and decreased with the deepening of soil layer,showing surface aggregation.>5 mm,<0.25 mm soil aggregate organic carbon,total nitrogen content showed native forest>shrub>Pinus yunnanensis artificial mixed forest>Pinus yunnanensis natural mixed forest>Pinus yunnanensis pure forest,may small size soil aggregate organic carbon and nitrogen from large size transfer.The total phosphorus content of soil aggregates of different vegetation types did not change significantly in the four layers of soil,and there was no significant difference among the particle sizes.The contribution rate of carbon,nitrogen and phosphorus of soil aggregates in pure Pinus yunnanensis forest was mainly 1-2 mm particle size.The contribution rate of carbon,nitrogen and phosphorus of Pinus yunnanensis artificial mixed forest and natural mixed forest was mainly 2-5 mm.The contribution rate of carbon,nitrogen and phosphorus of soil aggregates in primary forest was mainly<0.25 mm,which was mainly related to the high mass fraction of soil aggregates with related particle size.(3)The stoichiometry was:shrub soil aggregate C/N(13.08-17.79)>native forest and natural mixed forest of Pinus yunnanensis(10.17-12.28)>pure forest and artificial mixed forest of Pinus yunnanensis(5.69-11.75).Soil aggregate C/P and N/P(22.00-39.75,1.78-2.39)of shrub and native forest>Pinus yunnanensis pure forest(5.88-7.21,0.56-0.75)>Pinus yunnanensis artificial mixed forest and natural mixed forest(3.11-6.98,0.45-0.65).C/N and C/P of>5 mm,2-5 mm and 1-2 mm soil aggregates increased with soil depth,while C/N and C/P of microaggregates(<0.25 mm)decreased with soil depth,and C/N,C/P and N/P of small size soil aggregates(<0.25 mm)were slightly higher than those of large size aggregates(>5mm),in Three Pinus yunnanensis forests.(4)Surface soil aggregate stability of Pinus yunnanensis artificial mixed forest,natural mixed forest and shrub is better.The stability of surface soil aggregates in pure Pinus yunnanensis forest is poor.On the whole,the soil structure stability of Pinus yunnanensis artificial mixed forest was the best,followed by native forest and natural mixed forest,and pure forest and shrub were the worst.The mass fractions of soil aggregates with>5 mm and 2-5 mm particle sizes were positively correlated with GMD,MWD and R_0.25(p<0.01),and negatively correlated with D,while those with 0.25-0.5 mm and<0.25 mm particle sizes were opposite.Total phosphorus content,clay content,soil water content were positively correlated with GMD,MWD,R_0.25 and 2-5 mm particle size.Total nitrogen content,organic carbon content,N/P,C/P and C/N were positively correlated with 0.25-0.5 mm and<0.25 mm soil aggregates.Clay content,organic carbon content,N/P and C/P are the key factors affecting the stability of soil aggregates under different vegetation restoration types in Haifeng karst mountain area of eastern Yunnan plateau.Higher clay content can promote the formation of aggregates and increase soil compaction.Studies have shown that the clay content in the soil in the karst mountain area of the sea peak in the eastern Yunnan Plateau is an important factor affecting the stability of aggregates.The accumulation of organic carbon and total nitrogen in soil aggregates of three kinds of Pinus yunnanensis forests was relatively slow.In the growth process of Pinus yunnanensis,the P content of soil aggregates is sufficient,and the total nitrogen content is the constraint factor.Organic fertilizer and nitrogen fertilizer should be applied in the growth process of Pinus yunnanensis,and the return level of nitrogen and carbon should be paid attention to so as to achieve a good balance of nutrients,or to mix nitrogen-fixing associated tree species to promote the growth of Pinus yunnanensis.The natural mixed forest of Pinus yunnanensis has achieved certain results compared with the pure forest of Pinus yunnanensis,which plays an important role in the fixation of soil nutrients and can be used as the main vegetation type of vegetation restoration in the region.