Effects Of Nitrogen Deposition On Litterfall Decomposition And Nutrient Release Of Quercus Acutissima Forest Along Urban And Rural Gradient

With the advancement of science and technology and social development,the impact of human activities on the natural ecological environment has become more and more significant.The nitrogen cycle of the global ecosystem is affected by human industrial and agricultural production activities,and the nitrogen deposition in the terrestrial ecosystem is increasing rapidly,which leads to the restriction of the nutrient cycle of the ecosystem.Litter is the main source of material and energy for decomposers in the ecosystem.The decomposition process of litter is the key and central link of the material and energy cycle in the forest ecosystem.It is of great significance for enhancing soil productivity,regulating energy flow and nutrient balance.The study of forest litter decomposition and its nutrient release dynamics has extremely important theoretical and practical significance in the global climate change environment.In the context of increasing global atmospheric nitrogen deposition,studying the response mechanism of litter decomposition and nutrient release to nitrogen deposition can provide a more in-depth understanding of the environmental impact of increased atmospheric nitrogen deposition.In this study,pure oak forests were taken as the research object,along the urban and rural environmental gradients,experimental plots were established in Hefei(Dashu Mountain,Zipeng Mountain)and Luan Shucheng(Wanfo Mountain),and simulated nitrogen deposition experiments were conducted.The nitrogen deposition gradients were respectively.They are: 0 kg N ha-1yr-1(CK control),50 kg N ha-1yr-1(LN low nitrogen),and 100 kg N ha-1yr-1(HN high nitrogen).Litter decomposition bag method is used to study the response mechanism of litter decomposition and its nutrient release to nitrogen deposition,analyze the difference of litter decomposition and its nutrient release and influencing factors in different urban and rural environmental gradients,and formulate it to understand the response of forest ecosystems to nitrogen deposition.Relevant environmental protection policies and countermeasures provide scientific reference.The research results are as follows:(1)The dry matter residue rate of the litter in the oak forests showed a downward trend during the whole decomposition process,and the decomposition rate of the litter in the three urban-rural oak forests under the three urban-rural gradients showed that the decomposition rate was faster in the early stage,and the decomposition rate tended to be slow in the later stage.The decomposition rate of litter under different urban-rural gradients is significantly different(p < 0.05).The decomposition rate of litter under the three urban-rural gradients is as follows: rural forest > urban forest >urban forest.The reason for the faster decomposition rate of litter in rural forests may be due to less human disturbance in rural forests,richer biodiversity,and good soil and water conservation.Sawtooth oak forests accumulate more nutrients in litter,and rich nutrients are conducive to the growth of microorganisms.Thereby promoting the decomposition of litter.(2)Nitrogen addition can promote the decomposition of litter in the suburban forest(Zipeng Mountain)Quercus acutissima forest.Nitrogen addition experiment increased the available nitrogen in the leaves of Sawtooth oak forest,promoted its growth and reproduction,thereby promoting nutrient cycling and the decomposition rate of leaf litter.At the same time,nitrogen addition experiment promoted the change of microbial community composition in Sawtooth oak forest in the suburbs.High-efficiency but higher demand for N development.The response of urban forest(Dashu Mountain)and rural forest(Wanfoshan)to nitrogen addition is different from that of suburban forests.The Olson index model fitting results show that low-concentration nitrogen addition shortens the decomposition of urban forest and rural forest.Period,but when the nitrogen concentration increases,it will inhibit the decomposition of litter.This may be because the N element is not the main limiting factor for the decomposition of litter in the oak forests in this area.(3)The change of C content in leaf litter of Quercus acutissima forest under different urban and rural gradients showed different forms.The C content of leaf litter in rural forests showed a downward-increasing trend under the treatment of nitrogen addition,while the C content of leaf litter in urban forests and suburban forests It showed a slow downward trend under the treatment of nitrogen addition.The C content of the three urban-rural gradient leaf litter under the treatment of nitrogen addition was significantly higher than that of the control stand,and the C content of the litter generally showed a trend of first decline and then increase.Under different urban-rural gradients,the N content in the litter of the oak forests showed an upward trend and then a downward trend,that is,an enrichment-release pattern.The change of N content during the decomposition of litter is affected by the combined effect of biological decomposition and decomposition of other non-biological factors.The P element of litter leaves mainly showed an enrichment mode during the decomposition process.The average C/P ratio of litter leaf litter in the three urban-rural gradients was greater than the critical value,and the P content showed an increasing trend during the decomposition process.Since the P ratio of litter leaves in rural forests is much higher than that in urban forests,the P-enrichment of leaves in the decomposition process is also more obvious.During the decomposition process of litter,the K element increased first and then stabilized;the Ca element showed a fluctuating decline,and the Mg element showed a fluctuating rise.The higher C/N and C/P of litter under the three urban-rural gradients reflect the higher nutrient utilization efficiency of plants,and also reflect the slower growth of litter under the three urban-rural gradients.(4)The effect of N addition on the release of litter nutrients not only depends on the type and activity of the decomposers in the ecosystem,but also by many factors such as region,climate,and tree species.N application has no significant effect on the release of element C.N addition significantly promoted the release of N and P nutrients during the decomposition of rural and suburban forests,but had no significant effect on the release of N and P in urban forests.The decomposition environment of litter leaves under the three urban-rural gradients is quite different.The C/P ratio of litter in urban forests is lower than that in rural forests.Nitrogen application will improve the surrounding nitrogen deficiency,thereby promoting the growth and reproduction of microbial communities and speeding up its N,P element release.