Study On Modeling The Response Of Soil Heterotrophic Respiration To Climate Scenario Using Process-based Model

Soil heterotrophic respiration?RH?is a key links of global change,Earth System Model?ESMs?is a tool to predict the response of RH to climate change.Soil temperature and soil microbial physiology are two key factors in ESMs model,most studies focus the effect of soil temperature on RH,However,little study consider soil microbial physiology influence on RH and the response of this effect to climate scenario.Firstly,the STM model was calibrated with level₄ data at AmeriFulx sites,which provided soil temperature to TEM model as a driving data.Natural ecosystems were divided into six vegetational types.This study examined the spatiotemporal trends of soil temperature at depths of 10cm,20cm,and 50cm in the conterminous U.S.during 1948-2008.After that,this study revised the classic Q10-based heterotrophic respiration?RH?algorithms of TEM model by incorporating the algorithms of Dual Arrhenius and Michaelis-Menten kinetics and microbial-enz.And then applied the revised model to the forest ecosystems of the conterminous United States for the 21st century under the future climate scenarios of the Intergovernmental Panel on Climate Change?IPCC?Special Report on Representative Concentration Pathways?RCP?2.6 and 8.5.?1?The warming trend was 0.2?at 10cm depth;0.3?at 20cm depth;1.2?at 50cm depth.There was the highest warming trend at 50cm depth.And soil temperature at 20cm depth was lowest.Actually,the lowest soil temperatures were in Colorado and the area where Wyoming,Idaho,and Montana meet.The coastal areas,such as Texas,Florida,and California,experienced the highest soil temperature.In addition,such as Texas,Florida,and California,experienced the highest soil temperature.The coastal areas,such as Texas,Florida,and California,experienced the highest soil temperature.In addition,areas that experienced weak cooling in summer soil temperature include Texas,Oklahoma,and Arkansas.Warming was recorded in Arizona,Nevada,and Oregon.In winter,Mississippi,Alabama,and Georgia showed a cooling trend,and Montana,North Dakota,and South Dakota have been warming over the 61-year period.This study is among the first to analyze the spatiotemporal distribution characteristics of soil temperature in the conterminous U.S by using multiple site observational data.Meanwhile,it also improved the accuracy of STM and herein provided the basic scientific data to TEM assessment.In natural ecosystem,Shrubland had the highest soil temperature and Deciduous had the lowest soil temperature.In shrubland and grassland ecosystem,soil temperature at 50cm depth was higher than that at 10cm and 20cm depth.In savanna ecosystem,soil temperature at 10cm depth was higher 1.5?than that at 20cm and 50cm depth.In deciduous ecosystem,soil temperature at 10cm,20cm and 50cm varied soomthly.In Forest ecosystem,the annual mean soil temperature at three soil depths in evergreen forest was higher that in deciduous forest.?2?MIC-TEM is able to capture carbon fluxes dynamics.MIC-TEM is compareble to other studies during the same period and area.Under RCP 2.6 scenario,GPP and NPP increased slowly firstly,and decreased sharply after 2090s.NEP had the same trend;however,NEP decreased slowly after 2090s.Under RCP 8.5 scenario,GPP,NPP and NEP showed the increasing trend.There was a significance correlation between RH and air temperature.In sum,the carbon dynamics simulated by TEM under RCP 8.5 scenario was higher than that under RCP 2.6.Meanwhile,the carbon pools were assessed,soil carbon pools and vegetation carbon pools increased steady under both scenarios.Under both TEM and MIC-TEM,the magnitude was different with carbon dynamics and carbon pools.For example,the simulated GPP,NPP and NEP by MIC-TEM was 0.98,0.42 and 0.34PgC yr-1 higher than that by TEM.The simulated RH from MIC-TEM is 0.07PgC yr-1 higher than that from TEM.Under RCP 2.6 scenario,The RH with MIC-TEM was 0.05PgC yr-1 lower than that from TEM.Due to similar microbial biomass pools,RH under both scenarios was the same.In summer,soil temperature would cause higher RH, and meanwhile soil microbial biomass was also decreased by higher soil temperature.Under both RCP 2.6 and 8.5,there were significant differences between the estimates of carbon fluxes from the previous and revised models.The largest differences occured under the RCP 2.6 scenario,in which the model that considers soil microbial activities predicted that the region would act as a carbon sink,and the cumulative carbon sink in the 21st century would be 17.1PgC higher than the estimates from the model that does not explicitly consider soil microbial activities.This study further indicated that the revised TEM could capture and simulate the seasonal trends of RH and soil microbial biomass scientifically and suggested that terrestrial ecosystem models should explicitly consider the effects of seasonal soil microbial biomass on ecosystem carbon fluxes at regional scales.