| As a clone plant,Phyllostachys edulis is an expansive species.With global warming,P.edulis expansion will become an inevitable trend.The Daiyun Mountain is located in the transitional zone of south subtropical and mid-subtropical areas.The P.edulis forest has spread to an altitude of 1500 m,and gradually formed a continuous trend,which attracted the attention of the management department.It can be known from the study of forest stand on the expansion of P.edulis into C.lanceolata in Daiyun Mountain Natural Reserve,that the P.edulis in the mixed forest can obtain more light and nutrients by increasing the height and increasing the diameter.At the same time,the species diversity of the shrub and herb layer was increased.The research has mainly focused on the expansion process of P.edulis to broad-leaved forest.Broad-leaved forest fertile soil promotes the expansion of P.edulis.It also reduces the soil quality and species diversity of broad-leaved forest.The forest stand on the expansion of P.edulis into C.lanceolata should meet the rapid growth needs of P.edulis and maintain more species diversity in the shrub and herb layer,soil quality was a major factor.Whether the P.edulis expand to C.lanceolata achieved by improving soil quality?How does the change of soil physical properties,chemical properties and aggregates stability affect each other in the improvement of the soil quality of P.edulis?And the litter as the important source of soil nutrients,how does the decomposition of mixed litter play a role in improving soil quality?At present,there is little research on these contents,which is the problem that needs to be solved in this thesis.In this study,three types of forest stands were studied in the expansion process of P.edulis to C.lanceolata forest,which are the P.edulis forest,the mixed forests of the P.edulis and the C.lanceolata forest,the C.lanceolata forest.We studied and analyzed the soil physical and chemical properties,soil agglomeration stability,and soil active organic carbon storage,litter decomposition and nutrient release,and discussed the change trend of soil quality during the expansion of P.edulis by using the method of mutation series.To reveal the influence factors of soil quality change during P.edulis spreading,and provide scientific basis for the management department to take control measures in the future.The main results are as follows.During the expansion of the P.edulis to the C.lanceolata,the P.edulis gets more nutrients and light by enlarging the diameter and increasing the height.At the same time,it can increase the species of shrub layer and herb layer,and the uniformity of species distribution in the herb layer was significantly changed.Changes of physical and chemical properties of the soil in the expansion of P.edulis forest:(1)The expansion of P.edulis can reduce the soil density,especially to the surface soil density;It can improved soil porosity mainly by improving the porosity of soil non-capillary and improve the water holding capacity of soil mainly by improving the surface and shallow soil moisture.(2)The expansion of P.edulis can increase soil organic carbon and total nitrogen content.Soil density mainly affects the change of soil organic carbon content through strong indirect negative effect.The maximum amount of water and the water content of the capillary are mainly affected the content of soil organic carbon by indirect promotion.Soil aeration and pH value mainly affect soil organic carbon content by direct promoting effect.(3)The physical properties of soil mainly affect the change of organic carbon,total N and P chemical properties.The stability of soil aggregate and its effect on the carbon and nitrogen storage in the expansion of P.edulis forest:(1)In the process of P.edulis expansion,soil agglomeration and stability are enhanced.Each particle size aggregates in the soil were positively correlated with the aggregates of adjacent grain diameters and negatively correlated with the large size difference.The soil fractal dimension and erosive K value of three types of forest were increased with the increase of soil depth,while the mean weight diameter and mean geometric dimneter were the opposite.Fractal dimension is the main factor that reflects the soil structure and stability and>5 mm and<0.25 mm aggregates are the leading factors affecting the fractal dimension of soil.(2)The expansion of P.edulis can increase the organic carbon,total nitrogen content and storage of soil aggregates,the effect on surface soil is particularly obvious.Three types of forest soil organic carbon and total nitrogen storage were mainly stored in>2 mm particle size soil aggregates.(3)There was a significant linear correlation between the organic carbon content and the total nitrogen content of aggregates.The aggregate organic carbon content for the size of 1-2 mm,0.5-1 mm,0.25-0.5 mm is strongly influenced by soil total nitrogen content,the proportion of the observed value variation can be explained by the total nitrogen were more than 90%.However,the organic carbon content of>2 mm was less affected by the total nitrogen content,and the observed value variation could be accounted for 54.6%by the total nitrogen content of aggregates.The total nitrogen content of aggregates has the similar results influenced by soil organic carbon content.The effect of P.edulis spreading on soil active organic carbon storage:(1)the expansion of P.edulis can increase soil organic carbon and total nitrogen content,and also can increase the soil organic carbon reserves and total nitrogen reserves,but the accumulation path is mainly the increase of the corresponding reserves of the lower soil.The soil organic carbon content,total nitrogen content and C/N ratio were higher in January than in August.The linear regression between the total nitrogen content and organic carbon content of each forest was significant.If the soil organic carbon was increased,the increasing of total nitrogen of the P.edulis was the largest,and the increasing of C.lanceolata was the smallest.The higher the proportion of large size aggregates,the softer the soil,the better the water holding performance,the higher are the soil organic carbon and total nitrogen content.(2)The expansion of P.edulis can increase soil readily oxidized carbon content,and also can increase the soil water soluble organic carbon reserves and readily oxidized carbon reserves.There is obvious surface enrichment of soil active organic carbon in three kinds of forests.The soil microbial biomass carbon content in August was higher than that in January,while the readily oxidized carbon was the opposite.Soil organic carbon and total nitrogen are the main influencing factors of soil readily oxidation carbon.The content of organic carbon in soil was increased,and the increasing of soil readily oxidation carbon in P.edulis forest was the most.In addition,the total nitrogen content of the soil was increased,the increasing of soil readily oxidation carbon in C.lanceolata forest was the most.(3)On average,the Carbon Management Index of three kinds of forest in the 0-60cm soil layer is the P.edulis forest>mixed forest>C.lanceolata forest.(4)The higher the mass fraction of the large aggregates,and the better structure and stability of the soil,the more the readily oxidation carbon and microbial biomass accumulate in the soil.The main physical properties have great influence on the soil water soluble organic carbon and the readily oxidation carbon.Soil density,maximum water capacity,total porosity,capillary water retention and soil ventilation are the main factors affecting active organic carbon.The chemical properties have a great influence on the soil readily oxidation carbon.The soil quality with the expansion of P.edulis forest:(1)the change of soil quality was studied from soil physical and chemical properties,aggregates stability,organic carbon nitrogen and soil active organic carbon.The results showed the soil quality of each soil layer was PP1>PPCL1>CL1>PP2>PPCL2>CL2>PP3>PPCL3>CL3.The soil quality of PP1 and PPCL1 reached the better level,and the soil quality of CL1 reached a good level,and PPCL2,PP2,CL2 and PP3 were the general level,and PPCL3 and CL3 were relatively poor.The expansion of P.edulis forest can improve soil quality,especially to the surface soil.The decomposition dynamics and nutrient release mode with the expansion of P.edulis forest:(1)The higher the content of P.edulis in litters,the faster the decomposition rate of litters.The trig function model is more accurate than the Olson index model.The biomass ratio hypothesis was not supported by the mixed litter decomposition process.In PP6CL9,the litter of P.edulis and C.lanceolata is likely to interfere with each other,while in PP9CL6 two kinds of litters are likely to promote each other.(2)The initial nutrient content of mixed litter was significantly different from that of single species.The higher the content of P.edulis leaves in litter,the faster the release of litters C and N.The initial C,N,P concentration of litters and the residual mass fraction of the corresponding elements in the litters after a year of decomposition have significant binomial,power law function and exponential function relationship.(3)The decomposition of litters has obvious seasonal regularity,in which temperature is the most direct and main factor.The period release rate of C and P were also obviously seasonal.In low temperature and low precipitation stage,C shows slow release or even enrichment,and P is mainly manifested as enrichment effect.When temperature and precipitation gradually increase,both C and P are converted to net release.In summary the expansion process of P.edulis to C.lanceolata mainly improves the soil physical properties and aggregates stability through a large number of whipping root growth.The soil organic carbon and total nitrogen generation and accumulation were promoted by the decomposition of whipping root.In this way,the active carbon components such as carbon and microbial biomass are improved.At the same time,the expansion of P.edulis to C.lanceolata can accelerate the decomposition rate of litter.The soil organic carbon and total nitrogen content were improved by accelerating the returning of the nutrient to soil,to achieve the goal of improving soil quality and meeting the need for nutrients of the increasing of the diameter and height in the process of P.edulis expansion,and to satisfy the growth of more species.In addition,the long-term effects on the inhibition of growth of C.lanceolata,the species diversity of shrub and herb layers after the succession of pure forest and soil quality were further studied. |
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