| With the global natural forest resources disappearing at a rate of 11.45 million hm2 per year,the total forest volume in the world has drastically decreased.Therefore,the development of artificial forest has become one of the important means to reduce the contradiction between wood supply and demand.After China introduced the giant clam successfully in the 1960 s,the giant clam was widely promoted throughout the country.Due to the large-scale planting of giant clams for a long time,a series of problems such as soil degradation and declining forest productivity have emerged in the planting areas,which has become a major issue that hinders the development of giant clams.Based on this,this study selected the 6-year-old I,II,and III generations of E.grandis plantations with the same site conditions in Qingshen County of Sichuan Province as the research object,and used the time-series method(space-for-time)to study The effects of soil microbe number,microbial biomass and enzyme activity on soil depth in-10 cm and10-20 cm soil layers provide basic data for revealing the effects of continuous planting of Eucalyptus grandis on soil fertility.The main findings are as follows:(1)The total amount of microorganisms,bacteria,fungi,and actinomycetes in the0-10 cm soil layer of each generation of giant oyster plantations in Qingshen County is greater than 10-20 cm.The number of soil actinomycetes decreased from generation to generation in the 0-10 cm and 10-20 cm soil layers with the increase of the succession time of giant oysters,showing the characteristics of I-generation forest>II-generation forest>III-generation forest.The total amount of fungi decreased from generation to generation in 0-10 cm and 10-20 cm soil layers,but the difference was not significant.The total amount of soil microorganisms and total bacteria decreased from generation to generation in the 0-10 cm soil layer,and the difference was not significant;it decreased significantly from generation to generation in the 10-20 cm soil layer,showing the characteristics of I-generation forest> II-generation forest> III-generation forest.(2)The soil microbial biomass carbon(MBC)and nitrogen(MBN)content in the0-10 cm soil layer of each generation of Eucalyptus grandis in Qingshen County is greater than 10-20 cm.With the increase of continuous planting times,the contents of MBC and MBN in the 0-10 cm and 10-20 cm soil layers decreased significantly from generation to generation,showing I-generation forest>II-generation forest>III-generation forest.The range of soil microbial biomass C/N fluctuating between 0-10 cm and 10-20 cm soil layers was 9.39-10.64 and 9.95-12.26,respectively.There was no significant difference in soil microbial biomass C/N between different soil layers.It indicated that the soil microbial community in giant planting plantation was dominated by fungi,and soil fertility was weak.(3)The activities of sucrase,cellulase,urease,acid phosphatase,peroxidase,and polyphenol oxidase in 0-10 cm soil layer of giant oyster plantations in Qingshen County were all greater than 10-20 cm.(4)The urease activity decreased from generation to generation in the 0-10 cm soil layer,and decreased from generation to generation in the 10-20 cm soil layer,but the difference was not significant.The activity of sucrase and acid phosphatase decreased significantly from generation to generation in 0-10 cm and 10-20 cm soil layers,showing the behavior of I-generation forest>II-generation forest>III-generation forest.The activity of polyphenol oxidase and catalase decreased significantly from generation to generation in 0-10 cm and 10-20 cm soil layers,showing the characteristics of I-generation forest>II-generation forest>III-generation forest.The activity of peroxidase in the 10-20 cm soil layer decreased significantly from generation to generation,showing the behavior of I-generation forest>II-generation forest>III-generation forest;the peroxidase activity in the 0-10 cm soil layer decreased from generation to generation but the difference was not significant.(5)Correlation analysis showed that the total amount of microorganisms,the number of bacteria,the number of actinomyces and the number of fungi and invertase activity,catalase activity,peroxidase activity,polyphenol oxidase activity,acid phosphatase activity and urease Activity was positively correlated.In summary,as the giant locust is a fast-growing species,it grows fast and grows for a long time,resulting in acidification of the soil.The decrease of litter in the forest leads to a decrease in soil organic matter,which leads to a decrease in forest soil microbes and enzyme activity.Therefore,in the process of continuous planting of giant oysters,management measures such as fertilizing,keeping cuttings,and building mixed forests should be adopted in order to improve soil microbial and enzyme activities,thereby improving soil fertility and improving the productivity of Eucalyptus grandis plantations. |
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