Distribution Of Carbon And Nitrogen Storage Under Different Soil Types And Its Response To Climate Change In Bailong River Basin

Soil is one of the most important elements of a terrestrial ecosystem that provides indispensable,fundamental natural resources and factor of production for life activities.Different types of soil embrace considerably broad spatial heterogeneity,with each soil type featuring distinct development,unique properties,and varying fertility.Soil organic carbon（SOC）and soil total nitrogen（STN）are core indicators for assessment of soil quality,soil fertility,and sustainable land use.However,it is not clearly understood how SOC and STN in different types of soils respond to climate change,especially in a vulnerable ecosystem like Bailong River Basin.This study used De Nitrification-De Composition（DNDC）,in combination with long-term spot tests and field surveys,for simulation analysis of spatiotemporal changes in soil carbon and nitrogen in Bailong River Basin under current and future climate scenarios,as well as distribution of carbon and nitrogen stocks in different types of soils in Bailong River Basin and soil carbon and nitrogen dynamics in response to climate change,thereby providing a theoretical basis to promote the formation of major ecological shields,cope with future climate change,continue to improve the quality of the environment and support green and sustainable development.The study results are described as follows:（1）Long-term spot test results revealed that SOC levels were between 6.32 g·kg^-1and 12.90 g·kg^-1 and STN levels between 0.93 g·kg^-1 and 2.54 g·kg^-1,representing an annual growth trend.DNDC was shown to be applicable to Bailong River Basin,with a root-mean-square error（RMSE）of between 1.1%and 2.1%,a coefficient of correlation（r）of between 97.5%and 99.5%,a model efficiency coefficient（ME）of between 86.8%and 98.5%,and a fit index（d）of between 95.6%and 99.7%.（2）SOC and STN stocks in Bailong River Basin were 156.06 Tg and 15.61 Tg,respectively.In Bailong River Basin,variations in SOC and STN levels in the topsoil（0-20 cm）were 3-105 g·kg^-1 and 0-5 g·kg^-1,respectively.In different types of soils,there were significant differences in SOC and STN levels.Dark-brown earths contained the highest levels of SOC and STN were 80.82 g·kg^-1 and 8.63 g·kg^-1.Cinnamon soils had the lowest levels of SOC and STN were 11.72 g·kg^-1 and 1.25 g·kg^-1.（3）During the 1980-2019 period,the average annual change rates of SOC density（SOCD）in Bailong River Basin ranged from 10 kg·hm^-2·a^-1 to 50 kg·hm^-2·a^-1,while the average annual change rates of STN density（STND）in Bailong River Basin varied between 5 kg·hm^-2·a^-1 and 20 kg·hm^-2·a^-1.Under the 2020-2100 future climate scenario,the average annual SOCD and STND change rates declined slightly;however,the decrease rates varied under three different emission scenarios.The climate change scenario RCP 8.5 yielded the most significant changes in SOCD and STND,with the average annual SOCD and STND change rates of 0-450 kg·hm^-2·a^-1 and 0-40 kg·hm^-2·a^-1,respectively.Under the RCP 2.6 scenario,the average annual SOCD and STND change rates were 0-150 kg·hm^-2·a^-1 and 0-10 kg·hm^-2·a^-1,respectively,representing the slightest changes.（4）Under the 2020-2100 future climate scenario,SOC and STN both exhibited a downward trend.SOC and STN stocks fell by 31.87 Tg and 2.73 Tg under the RCP 8.5scenario,denoting the sharpest decline.The RCP 2.6 scenario had the smallest decreases in SOC and STN stocks,with the SOC stock being reduced by 10.20 Tg and the STN stock by 1.07 Tg.（5）Different types of soils showed significant differences in SOC and STN stocks under future climate scenarios.Dark-brown earths underwent subtle changes in SOC and STN stocks under different climate scenarios.Significant changes in SOC and STN stocks were observed in yellow-brown earths under the RCP 2.6 scenario and in cinnamon soils under the RCP 4.5 scenario.The RCP 8.5 scenario brought drastic changes to both yellow-brown earths and cinnamon soils in SOC and STN stocks.