| As one of the main characteristics of global climate change,global warming has changed and will continue to change the structure and function of the global ecosystem.Litter decomposition is an important process of nutrient cycling in terrestrial ecosystems.In order to predict the C storage potential of forest ecosystems under future global change,it is necessary to understand the impact of temperature change on litter decomposition of trees.In the past,studies on the effects of temperature rise on litter decomposition have been carried all over the world.With high annual average temperature and abundant plant groups in subtropical region,what kind of response will happen to litter decomposition in mid subtropical forest under the background of global change?Therefore,in order to explore the litter decomposition and its internal mechanism in the mid subtropical forest ecosystem under the background of global warming,the natural forest of Castanopsis kawakamii in Sanming Nature Reserve(26°10?N,117°27?E)and mature Cunninghamia lanceolata plantation around the reserve were selected to establish warming sample plots,and the C.kawakamii litter,C.lanceolata litter and C.lanceolata green leaves were arranged It is a common tree species in this area,and the difference of litter leaf matrix is significant.In order to explore the effect of warming on litter decomposition,two treatments of warming(+4?)and control were set in two plots,and litter bag decomposition method was used to carry in-situ decomposition experiment for two years.The main results are as follows:(1)During the two-year decomposition period,the soil temperature at 10 cm in the surface layer of C.kawakamii natural forest increased significantly(the average annual temperature of control was19.15?,and that of warming was 23.35?),and the water content of litter leaves decreased significantly.Soil warming decreased the decomposition rate of C.kawakamii and C.lanceolata litter,and increased the decomposition rate of C.lanceolata green leaves.At the end of one year,the decomposition rate of C.kawakamii and C.lanceolata litter was significantly reduced by soil warming treatment.At the end of two years,the mass residue rate of three kinds of litter was between27-35%.During the two-year decomposition period,the C,N and P residue rates of the three kinds of leaves changed little under the warming treatment.The lignin residue rate of C.lanceolata green leaves(125.45%)in the first year of decomposition was significantly higher than that of C.kawakamii(47.57%)and C.lanceolata leaves(53.03%).At the end of the first year of decomposition,soil warming significantly increased the lignin residue rate of C.kawakamii and C.lanceolata leaves.Warming treatment significantly reduced the activities of four kinds of enzymes in the litter of C.kawakamii and C.lanceolata at the end of the first year,and significantly reduced the activities of AP,?G and NAG in the three kinds of litter.Soil warming significantly changed the microbial community structure of three kinds of litter,significantly increased the abundance of actinobacteria and Ascomycota of C.kawakamii and C.lanceolata.However,Ascomycota of C.lanceolata green leaves showed the opposite result,and Basidiomycota,the dominant fungus of C.lanceolata green leaves,significantly increased under warming treatment.(2)During the two-year decomposition period,the soil temperature at 10 cm of the top layer of C.lanceolata plantation was significantly increased by soil warming(the average annual temperature of control was 18.73?,and that of warming was 22.04?),and the water content of litter leaves was significantly decreased.The decomposition rates of C.kawakamii,C.lanceolata litter and C.lanceolata green leaves were decreased by soil warming treatment,and there was significant difference among C.lanceolata litter treatments.At the end of two years,the mass residue rates of three kinds of litter were between 23%and 38%.Soil warming also increased the residual rate of extractable matter at the end of two years,and the microbial community structure on the surface of C.lanceolata litter also changed significantly under warming treatment.Warming treatment significantly reduced the bacterial abundance of C.lanceolata litter and C.lanceolata green leaves,and significantly increased the abundance of C.lanceolata litter and Basidiomycota,and the contents of Ascomycota and actinobacteria also increased It decreased significantly under warming treatment.(3)Through the interactive transplanting experiment of C.kawakamii and C.lanceolata litter,it was found that the main effect in the process of decomposition was different due to the difference of decomposition environment and the difference of litter quality.The average home field effect of mass loss in the decomposition process of C.kawakamii litter control and warming treatment and C.lanceolata litter warming treatment were negative.Warming treatment significantly reduced the average home field effect of C.lanceolata litter,mainly because when the C.lanceolata litter with higher lignin content was transplanted to C.kawakamii natural forest,the specialized microorganisms for decomposing refractory compounds in natural forest were relatively low In addition,the decomposition rate of the main and away fields of C.lanceolata leaves decreased under the warming treatment,and the decomposition rate of the main and away fields was higher than that of the away fields,showing a negative home effect,leading to significant difference in home effect among the treatments.In conclusion,the decomposition of three kinds of litter leaves under soil temperature increasing treatment was studied.The results showed that the decomposition rate of three kinds of litter leaves was reduced by the temperature increasing treatment,and the difference between the treatments was significant(control 0.68a-1,increasing temperature 0.50a-1).During the decomposition process,the decomposition rate of litter was reduced by inhibiting the degradation of lignin,cellulose and extractable substances.The leaching effect caused by rainfall promoted the decomposition of the leaves of C.kawakamii.However,as coniferous leaves,the leaves of C.lanceolata had a layer of hydrophobic cuticle,so it was less affected by rainfall;the decrease of moisture content of litter resulted in the decrease of microbial secretory enzyme efficiency.Although the temperature increasing treatment increased the abundance and diversity of fungi in the three kinds of litter leaves,it did not decompose more litter.The main reason is that fungi are more resistant to stress,and turned to seek more urgently needed water resources due to the decrease of water,and more used to maintain the metabolism of the living,rather than energy consumption and decomposition function,and the effect on decomposition was very small. |
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