Mechanisms Of Carbon And Nitrogen Concentrations And Stable Isotope Variations In Terrestrial Mosses

Since the industrial revolution,the increase of anthropogenic reactive nitrogen(N)emissions lead to a rapid increase of atmospheric N deposition,and a series of ecological environment problems.The study of the flux and chemical composition of atmospheric N deposition can provide scientific basis for making decision for emission reduction and the assessment of N pollutant effect.Due to the complex chemical compositions and high spatio-temporal variations of atmospheric N deposition,the sampling and monitoring of atmospheric N deposition in a large area with high spatiotemporal resolution are costly and difficult.The major N source for mosses is considered as atmospheric N deposition,and the N concentrations and?¹⁵N values in mosses are widely used to assess the changes of atmospheric N deposition and environmental conditions due to their unique morphological structure and wide distribution.Although there have been a lot of studies using moss N concentrations and?¹⁵N values to evaluate atmospheric N deposition in different space scales.However,the biological and the abiological mechanisms behind the changes of moss N concentrations and?¹⁵N values have not been systematically researched and remained unclear.Which is the bottleneck of using moss N parameters to assess the levels and effects of atmospheric N deposition accurately.In this thesis,the changes of moss N concentrations and?¹⁵N values in terrestrial mosses and their responses to atmospheric N deposition were analyzed.Then,combined with the analysis of C concentrations,N concentrations,?¹³C and?¹⁵N values in mosses and their substrates,different moss species and terrestrial systems were selected to explore the key mechanisms affecting the changes of moss N concentrations and?¹⁵N values.The main conclusions are as follows:(1)By integrating the published data of N concentrations and?¹⁵N values in terrestrial mosses in different regions and combining the corresponding atmospheric N deposition,whether and how moss N concentrations response to atmospheric N deposition vary with the levels and the forms of atmospheric N deposition,and the proportional contributions of atmospheric N deposition to moss N(relative to the contributions of soil N to moss N)were discussed.(2)By analyzing the concentrations and isotopic signatures of C and N in four moss species collected in thirteen consecutive months,the variation mechanisms of the concentrations and isotopic signatures of C and N in mosses were revealed.(3)By analyzing the concentrations and isotopic signatures of C and N in epilithic mosses and their substrates on limestones and sandstones,combined with the nitrate reductase activity of mosses,the moisture of substrates,p H values of substrates,the rate of net mineralization and the rate of net nitrification in substrates,the differences and these mechanisms of the parameters of C and N in epilithic mosses and organic substrates(EM-OS)on limestones and sandstones were explored.(4)By analyzing the concentrations and isotopic signatures of C and N in mosses grown for 14 years(38 cm high)and in mosses grown in eight peatlands and combining the principles of biogeochemistry and isotope geochemistry methods,the spatial and temporal variations the concentrations and isotopic signatures of C and N in living mosses in peatland were discussed.This study would provide basic data for the evaluation of N availability changes and their effects in terrestrial ecosystems and provide scientific basis for the protection of moss diversity,environmental protection,and ecosystem management.