Effect Of Simulated Warming On Soil Carbon And Nitrogen Processes In The Alpine Forests

With winter warming, extreme climate events and atmospheric CO2concentration elevated, climate change may change soil seasonal freeze-thaw characteristics at high latitude and altitudes. As one of the key ecological processes in forest ecological system, soil carbon and nitrogen processes are extremely sensitive to the change of environment. The change of freeze-thaw pattern could significantly influence on soil carbon and nitrogen processes under climate warming context. But so far, the reports of soil carbon and nitrogen process researches about simulated winter warming in high altitude forests have been seen rarely. Therefore, we chose apline forest soil of western Sichuan as the research object, which located in eastern margin of qinghai-tibet and the upper Yangtze river. With natural environment gradient experiment, apline forest (A1, altitude of3582m) soil columns were shifted to the altitude of3298m(A2, theoretical warming of2℃) and3023m (A3, theoretical warming of4℃)forests, which studied carbon and nitrogen processes under alpine forest soil organic layer (OL) and mineral soil layer (MS) in simulated warming. In order to provide certain scientific basis which deeply understand ecological system of alpine forests and the response to climate change.Simulated warming clearly influenced on organic carbon and dissolved organic carbon contents of soil organic layer and mineral soil layer in growing season and non-growing season. Simulated warming2℃and4℃obviously increased organic carbon and dissolved organic carbon contents of soil organic layer in the first early growing season, which significantly reduced organic carbon contents in the onset of freezing and the early of thawing and increased dissolved organic carbon contents in the early of thawing. As yet, simulated warming2℃and4℃decreased organic carbon contents of mineral soil layer in the first growing season and the onset of freezing, but dissolved organic carbon contents of mineral soil layer had no significant differences between simulated warming2℃and4℃in the total training period.Simulated warming treatment significantly affected total nitrogen and dissolved organic nitrogen contents of soil organic layer and mineral soil layer in growing season and non-growing season. Simulated warming2℃and4℃lowered total nitrogen contents of soil organic layer in the growing season, and significantly increased total nitrogen contents of soil organic layer in the second early growing season, but cut down total nitrogen contents of soil organic layer in the second early growing season. Among which, total nitrogen contents were more significant under simulated warming4℃; On the contrary, simulated warming2℃and4℃significantly increased dissolved organic nitrogen contents of soil organic layer and mineral soil layer in deep freezing period.The responses for the simulated warming of organic carbon variation amount, variation rate, net nitrogen mineralization amount and rate of soil organic layer and mineral soil layer were inconsistent. Simulated warming2℃and4℃had no significant influence on organic carbon variation amount and rate of soil organic layer and mineral soil layer in growing season, but strengthened organic carbon mineralization of soil organic layer and weakened organic carbon mineralization of mineral soil layer in seasonal freeze-thaw period. Meanwhile, simulated warming4℃significantly reduced nitrogen immobilization amount of soil organic layer and mineral soil layer in growing season, but simulated warming2℃and4℃significant increased net nitrogen mineralization amount and rate of soil organic layer and strengthened nitrogen immobilization action of mineral soil layer in seasonal freeze-thaw period.In addition, after a seasonal freeze-thaw period, compared with the two early of growing season, organic carbon, total nitrogen, dissolved organic carbon and nitrogen contents of soil organic layer and mineral soil layer were reduced. However, the responses to warming treatment were inconsistent. Simulated warming2℃and4℃significant decreased organic carbon, dissolved organic carbon and nitrogen of soil organic layer and total nitrogen, dissolved organic nitrogen of mineral soil layer. Meanwhile, simulated warming2℃and4℃lowered organic carbon immobilization amount of soil organic layer and mineral soil layer and declined nitrogen mineralization of mineral soil layer in the second early of growing season.In conclusion, simulated warming had significant effect on carbon and nitrogen processes of soil organic layer and mineral soil layer in subalpine/alpine forests of western Sichuan. And the responses of organic carbon, total nitrogen, dissolved organic carbon and nitrogen, organic carbon variation amount, variation rate, net nitrogen mineralization amount and rate to simulated warming treatment were inconsistent in growing season, freeze-thaw season and the early of growing season after a freeze-thaw season. These results indicated that increasing soil temperature in the future could not only significantly enhance soil carbon and nitrogen processes in the freeze-thaw season, but also improve soil carbon and nitrogen processes by increasing freeze-thaw cycle times and shortening freeze-thaw period to affect carbon and nitrogen cycle process in alpine forest ecosystem. Therefore, the results could be important significance for deeply understanding forest soil ecological process in cold regions and the responses for climate change.