标题：Disequilibrium of terrestrial ecosystem CO2 budget caused by disturbance-induced emissions and non-CO2 carbon export flows a global model assessment
摘要：Abstract. The global carbon budget of terrestrial ecosystems ischiefly determined by major flows of carbon dioxide (CO2) such asphotosynthesis and respiration, but various minor flows exert considerableinfluence in determining carbon stocks and their turnover. This studyassessed the effects of eight minor carbon flows on the terrestrial carbonbudget using a process-based model, the Vegetation Integrative SImulator forTrace gases (VISIT), which included non-CO2 carbon flows, such asmethane and biogenic volatile organic compound (BVOC) emissions andsubsurface carbon exports and disturbances such as biomass burning, land-usechanges, and harvest activities. The range of model-associated uncertaintywas evaluated through parameter-ensemble simulations and the results werecompared with corresponding observational and modeling studies. In thehistorical period of 1901–2016, the VISIT simulation indicated that theminor flows substantially influenced terrestrial carbon stocks, flows, andbudgets. The simulations estimated mean net ecosystem production in 2000–2009 as 3.21±1.1 Pg C yr−1 without minor flows and 6.85±0.9 Pg C yr−1 with minor flows. Including minor carbon flowsyielded an estimated net biome production of 1.62±1.0 Pg C yr−1in the same period. Biomass burning, wood harvest, export of organic carbonby water erosion, and BVOC emissions had impacts on the global terrestrialcarbon budget amounting to around 1 Pg C yr−1 with specific interannual variabilities. After including the minor flows, ecosystem carbon storage wassuppressed by about 440 Pg C, and its mean residence time was shortened byabout 2.4 years. The minor flows occur heterogeneously over the land, such thatBVOC emission, subsurface export, and wood harvest occur mainly in thetropics, and biomass burning occurs extensively in boreal forests. They alsodiffer in their decadal trends, due to differences in their driving factors.Aggregating the simulation results by land-cover type, cropland fraction,and annual precipitation yielded more insight into the contributions ofthese minor flows to the terrestrial carbon budget. Considering theirsubstantial and unique roles, these minor flows should be taken into accountin the global carbon budget in an integrated manner.
