Modelling The Response Of ANPP And SOC To Climate Change In Zhunge'er Desert Steppe

For a long time,climate change dominated by the global warming has a strong impact on grassland ecosystem.Grassland ecosystem plays an important role in evaluating the effects of global climate change on carbon biogeochemical cycle and global carbon balance due to its sensitivity.Clarifying the interaction between grassland ecosystem and climate change is of great significance for understanding the structure and function of grassland ecosystem and evaluating grassland ecological security.In this study,the temperate desert steppe in Zhunge'er Banner of Inner Mongolia was selected as the research area,the CENTURY model was adopted to simulate the dynamic changes of aboveground net primary productivity(ANPP)and soil organic carbon(SOC),and also their responses to climate change in the temperate desert steppe during the past two decades,in addition,we also studied the effects of elevated atmospheric CO₂ concentration on ANPP and SOC in desert grasslands under different future climate scenarios.The main conclusions are as follows:(1)The CENTURY model was parameterized,calibrated using the observed data including ANPP and SOC,the results showed that the model had good applicability for ANPP and SOC simulation in Zhunge'er Banner desert steppe grassland ecosystem.The correlation analysis between the simulated values and the observed values of ANPP showed that the coefficient was 0.881,and the root mean square error(RMSE)was 8.44.The SOC model simulation value ranged from 3418.83 g/m² to 3457.449 g/m²,which is consistent with observed historical data.(2)From 2000 to 2019,the annual average temperature,the average temperature in the growing season,the annual average precipitation and the average precipitation in the growing season of the desert steppe in Zhunge'er County all showed an increasing trend,among which the annual average precipitation showed significant(P<0.05),and the others were not significant.The rising rates of temperature and precipitation were 0.048?/a?0.006?/a and9.136 mm/a?4.065 mm/a,respectively.In the past two decades,ANPP in the desert steppe of Zhunge'er Banner showed an increasing trend of volatility,with the growth rate of 1.419g/m²,a,which was not significant.SOC showed a certain fluctuation trend as a whole.The rising rates of total SOC,active SOC and slow SOC were 1.481 g/m²,a?0.831 g/m²,a?0.823g/m²,a,respectively,and the total SOC and active SOC showed significant differences.Passive SOC showed a downward trend,but the difference was not statistically significant.Annual fluctuation of SOC was Active SOC>Slow SOC>Total SOC>Passive SOC.(3)The results of partial correlation analysis between ANPP and SOC and meteorological factors show that ANPP in the desert steppe of Zhunge'er showed a significantly positive correlation with precipitation in growing season and annual average precipitation(P<0.01),but no significant correlation was found with temperature.The results showed that the Pearson correlation coefficient of total SOC and annual average precipitation was 0.553,showing a significantly positive correlation(P<0.05),but no significant correlation with other climatic factors.The Pearson correlation coefficients of active SOC with precipitation in growing season and annual average precipitation were 0.707 and 0.778,respectively,showing a very significant positive correlation(P<0.01).The Pearson correlation coefficient of active SOC with annual low temperature extreme value was 0.489,showing a significant positive correlation(P<0.05),but no significant correlation with other climatic factors.However,there was no significant correlation between slow SOC and passive SOC and temperature,precipitation and other related climatic factors.ANPP was positively correlated with total SOC and active SOC(P<0.05).Pearson correlation coefficients were 0.459 and 0.647,respectively.ANPP was not significantly correlated with slow SOC and passive SOC.(4)Compared with the baseline period,the temperature and precipitation of SSP1-2.6and SSP2-4.5 climate scenarios increased in different degrees in the next three periods.Regardless of CO₂ concentration gain,the average ANPP of desert steppe in Zhunge'er banner remained unchanged in 2050s and 2070s under SSP1-2.6 scenario,but decreased by 3.9%in2030s.Under the SSP2-4.5 scenario,the next 2030s,2050s and 2070s will increase by 2.6%,3.1%and 6.1%respectively.Under SSP1-2.6 and SSP2-4.5 scenarios,the average SOC of desert steppe in Zhunge'er r banner will increase by 0.5%,1.2%,1.6%and 0.87%,2.2%,2.4%in 2030s,2050s and 2070s,respectively.Compared with the SSP1-2.6 scenario,the increase of ANPP and SOC in SSP2-4.5 mode is larger.Considering the CO₂ concentration gain,the average ANPP of desert steppe in Zhunge'er banner will increase by 1.8%,4.6%,6.7%and4.4%,5.4%and 13.1%respectively in 2030s,2050s and 2070s under SSP1-2.6 and SSP2-4.5scenarios.Under the scenarios of SSP1-2.6 and SSP2-4.5,the average SOC of desert steppe in Zhunge'er banner will increase by 0.73%,1.6%,2.3%and 1.9%,3.9%,5.3%in 2030s,2050s and 2070s,respectively.Compared with the SSP1-2.6 scenario,the increase of ANPP and SOC in SSP2-4.5 mode is larger.(5)In the future SSP1-2.6 climate scenario model and considering the increase of CO₂concentration(compared with the current atmospheric CO₂ concentration),ANPP in desert steppe will increase significantly in the next three periods of 2030s,2050s and 2070s(P<0.05),while SOC will increase in the next three periods,but it does not show significance.In the future SSP2-4.5 climate scenario,considering the elevated CO₂ concentration,ANPP and SOC in desert steppe did not show significant increase in 2030s and 2050s,but increased significantly in 2070s.(P<0.05).In summary,the CENTURY model has good applicability for the simulation of ANPP and SOC in Zhunge'er Banner desert steppe.In the long-term series,ANPP and SOC of desert steppe in Zhunge'er Banner showed significant positive correlation with precipitation(P<0.05),but had little correlation with temperature.The increase of atmospheric CO₂concentration will promote the increase of ANPP and SOC in Zhunge'er Banner desert steppe,showing a certain lag.According to the SSP2-4.5 scenario,the desert steppe in Zhungeer Banner will develop towards“warm and humid”in the future.