Estimated Impacts Of Extreme Temperature Events On Gross Primary Productivity Of Ecosystems In Northern Asi

Terrestrial ecosystem in Northern Asia plays an important part in global carbon cycle,fixing carbon and reducing atmospheric CO₂concentrations.Change of ecosystem productivity and its response to climate extremes in the context of global warming are of great interest and particular concern for ecosystem management and adaptation.Using the simulations with and without the CO₂fertilization effect from the Yale Interactive Biosphere（YIBs）model driven by seven CMIP5 climate models,this article investigates the future change in the gross primary productivity（GPP）of the Northern Asia ecosystem as well as the impacts from extreme heat events under the RCP2.6 and RCP8.5 scenarios,respectively.The differences brought about by geographical location,vegetation type,different time periods and time scales are analyzed.Main conclusions are as follows:1.The results show an overall increase of GPP in Northern Asia during the growing season（May-September）under both scenarios,in which the CO₂fertilization effect plays a dominant role.The increases in GPP under RCP8.5 scenario are larger than that under RCP2.6scenario,and the greatest projected increases occur in Western Siberia and Northeast China.2.Future extreme heat events exhibit spatiotemporaly heterogenous impacts on the Northern Asian ecosystem GPP.Under the RCP2.6 scenario,the positive and adverse effects from the extreme heat events coexist in Northern Asia during the middle of the 21st century.During the end of the 21st century,the areas dominated by positive effects are expected to expand particularly in Northeast China and Central-Western Siberia.For the RCP8.5 scenario,the facilitation effects of the extreme heat events are widely distributed in Northern Asia during the middle of the 21st century,which tends to decline in both intensity and extent during the end of the 21st century.In most regions of Northern Asia,extreme low temperature events lead to GPP loss under each warming scenario and time period,which is greater under RCP8.5 scenario.3.The influences of high temperature months,which have little difference between each month,are similar to that of extreme heat events at daily scale.However,the influences of low temperature months have significant seasonal differences.In May,September and October,low temperatures lead to the decrease of ecosystem GPP in most regions and scenarios.In March and April,stimulative effects with larger area and higher strength will appear.At the same time,those areas dominated by inhibition will suffer greater GPP losses.4.In most cases,CO₂fertilization would not reverse the positive and negative effects of extreme high and low temperature events on GPP,but only promote the increase of GPP.In a few regions where the CO₂contribution is absent,GPP will decrease rather than increase during extreme heat events.5.Evergreen coniferous forest occupies a dominant position in the vegetation types of Northern Asia,whose GPP anomalies under climate extrems are similar to that of the whole ecosystem in Northern Asia under each scenario.Tundra GPP contributes little to the Northern Asian ecosystem,but has much greater anomalies than evergreen coniferous forest during extreme temperature events,regardless of positive and negative.