Soil Carbon And Nitrogen Stock's Response To Warming And Increase Precipitation And Its Changes In Tibetan Plateau From 1980s To 2010s

The soil carbon and nitrogen play an important role in terrestrial ecosystem.With the global climate warming in recent years,the Tibetan Plateau due to its special geographic location and altitude has experience the strong regional warming,and also has the biggest uncertainty to response global climate change in the future.In spite of the regional scale,estimation of soil carbon and nitrogen density and storage has carried out related researches,but because of the limited field observation and the larger spatial heterogeneity of the Tibetan Plateau,the soil carbon and nitrogen density and storage of the top 30 cm in Tibetan Plateau area scale were still exists a lot of uncertainty.By artificially increasing temperature and precipitation control experiments,we observed the response of soil carbon and nitrogen to climate change during the short term on the alpine meadow ecosystem.And combined with the sampling site data field survey and NDVI data separately calculated the three periods of the Tibetan Plateau surface soil carbon and nitrogen density sequentially,analysis how soil carbon and nitrogen response to global climate change of the long time scale and large regional scale of the Tibetan Plateau.The conclusion shows as listed:1.Two years of open top chamber?OTC?experiment has no significant effect on soil carbon and nitrogen,and three years of multi-gradient increase water experiment has not caused significant changes in soil carbon and nitrogen.However,the soil carbon has increased not significantly under the warming treatment of T1,T3?p=0.58?and increasing water treatment by 40%and 80%?p=0.47?.The liner regression showed that soil carbon and nitrogen were more sensitive to soil moisture?p<0.05?.2.The soil carbon density?SCD?of the surface soil of Tibetan Plateau terrestrial ecosystem in the 1980s was estimated about 8.73 kg C m^-2,and soil carbon storage?SCS?was 20.99 Pg C.soil nitrogen density?SND?is 0.75 kg N m^-2and soil nitrogen storage SNS is 1.80 Pg N.The SCD of the surface soil of Tibetan Plateau terrestrial ecosystem in the 2000s was estimated about 6.19 kg C m^-2,and SCS is 14.88 Pg C.SND is 0.94 kg N m^-2 and SNS is 2.69 Pg N.The SCD of the surface soil of Tibetan Plateau terrestrial ecosystem in the 2010s was estimated about 5.21 kg C m^-2,and SCS was 12.53 Pg.SND is 0.38 kg N m^-2,SNS is 0.91 Pg N.Based on normalized difference vegetation index?NDVI?dataset,the soil carbon and nitrogen density of the 2000s was evaluated about 5.10 kg C m^-2 and 0.90 kg N m^-2.In 2010s,soil carbon and nitrogen density was evaluated about 9.20 kg C m^-2and 0.68 kg N m^-2.3.In 1980s-2000s,the carbon density of the surface soil of the Tibetan Plateau has increased in forest,decreased in the grassland,but all of this change has not reached a significant value?p=0.47,p=0.21?.The increasing trend of soil carbon density in forest was slow in 2000s-2010s,and it in grassland has increased?p=0.21?.It is shown that climate change has positive effect on the accumulation of soil carbon in ecosystem.Although the trend of the Tibetan Plateau is decreasing?p=0.07?,but due to the increase of forest and grassland,the soil carbon stock of Tibetan Plateau may be plays the role of carbon sink.In the past 30 years,the nitrogen density has been reduced in the surface soil of the Tibetan Plateau?p<0.01?,and it has increased in the 1980s and 2000s.But after the 2000s,it has decreased?p<0.01?.The nitrogen density of the forest has been decreasing?p=0.87?,indicating that more and more nitrogen has been lost from soil to the atmosphere or water,and the nitrogen stock in the Tibetan Plateau plays the role of nitrogen source.4.Many researches have reported that climate warming contributes to soil carbon accumulation in terrestrial ecosystems.However,in the case of global warming,the precipitation change has great spatial heterogeneity on Tibetan Plateau.It is reported that the precipitation in arid area is a not obviously decreasing trend,so it is believed that the reduction of precipitation caused drought stress and then caused the decrease of carbon density in the soil of the 1980s and 2000s.The decrease of soil nitrogen density may be due to the warming has increased the rate of nitrogen mineralization.And due to the increasing rate of biological nitrogen fixation and the artificial fertilization,too much nitrogen has input into the soil,leading the original nature of nitrogen fixation and nitrogen balance,nitrogen cycle were severely disturbed,more and more“activation of nitrogen”was lose from soil to the atmosphere and aquatic ecosystem.