| Litter decomposition is a key process to maintain nutrient balance in ecosystems,and is of great significance in ecosystem nutrient cycling.Litter decomposition is affected by various biotic and abiotic factors.Numerous studies have proved that atmospheric nitrogen addition may affect forest litter decomposition and related biological processes through direct or indirect pathways.In this study,the main tree species Quercus acutissima and Pinus thunbergii forest in the arid and barren mountains of Yimeng Mountains were used as the research objects.We used control(0 kg N·hm-2·yr-1,CK),low nitrogen addition(50 kg N hm-2·yr-1,LN),medium nitrogen addition(100 kg N hm-2·yr-1,MN),high nitrogen addition(200 kg N hm-2·yr-1,HN))four levels of nitrogen addition experiments.Experiments were conducted to analyze the effects of mass remaining,decomposition rate,main nutrient residual rate,and soil physicochemical properties and soil enzyme activities in response to simulated nitrogen addition in these two forest stands.Management provides data support and theoretical basis,and then provides sci-entific basis for the management and management of plantation.The results show:(1)There is a significant difference in the decomposition of the litter of the Quercus acutis-sima and Pinus thunbergii.The k value of the Quercus acutissima is in descending order of MN(0.484)>HN(0.46)>LN(0.421)>CK(0.386).The k value of the Pinus thunbergii litter is the order of the values from large to small is LN(0.4164)>CK(0.367)>MN(0.34)>HN(0.315),it can be concluded that nitrogen addition promotes the decomposition of the litter of the Quer-cus acutissima litter,while for the litter of Pinus thunbergii in leaves,LN promoted decompo-sition,while MN and HN treatments inhibited decomposition.(2)The effect of nitrogen addition on the element release of litter varies with different types of litter.During the decomposition process,the residues of C in the leaf litter of the two tree species decreased gradually with the increase of decomposition time,and the residues of C in the Pinus thunbergii were higher than those in the Quercus acutissima at different periods.The residual rates of N and?in the litter of Quercus acutissima and Pinus thunbergii were first enriched and then released.After one year of decomposition,the residual rates of C,N,and P in Quercus acutissima were 38.04-50.09%,71.83-87.06%,and 59.82-76.69%,respectively,and the residual amounts of C,N,and P in Pinus thunbergii were 55.28-69.79%,63.56-79.63%and61.89-71.63%,respectively.Nitrogen addition had a significant effect on cellulose content of litter,especially HN treatment significantly promoted cellulose degradation.The average cellulose content of the leaves of the Quercus acutissima and Pinus thunbergii under the HN treatment was 12.02%and 13.75%lower than that of the control,respectively.(3)The chemical properties of soil vary with decomposition time and nitrogen application.The general rule is that p H decreases with the increase of nitrogen application,while the inor-ganic nitrogen content increases gradually with the increase of nitrogen application.The index regularity has different responses with different species.Nitrogen application and decomposi-tion time significantly affected soil enzyme activities,and were greatly affected by seasons.Generally,enzyme activities were relatively low in January and relatively high in April-July,except for cellulase,sucrase and Urease was not significantly affected by nitrogen application except that the other enzyme activities responded significantly to nitrogen addition.(4)The stoichiometric ratio of the leaf litter largely reflects the speed of the decomposition rate of the leaf litter.The lower the C:N,the faster the decomposition rate.The average C:N size of Quercus acutissima under different nitrogen addition treatment was:HN(43.62) |
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