Primary estimation of Chinese terrestrial carbon sequestration during 2001–2010

Abstract

Quantifying the carbon budgets of terrestrial ecosystems is the foundation on which to understand the role of these ecosystems as carbon sinks and to mitigate global climate change. Through a re-examination of the conceptual framework of ecosystem productivity and the integration of multi-source data, we assumed that the entire terrestrial ecosystems in China to be a large-scale regional biome-society system. We approximated the carbon fluxes of key natural and anthropogenic processes at a regional scale, including fluxes of emissions from reactive carbon and creature ingestion, and fluxes of emissions from anthropogenic and natural disturbances. The gross primary productivity, ecosystem respiration and net ecosystem productivity (NEP) in China were 7.78, 5.89 and 1.89 PgC a -1 , respectively, during the period from 2001 to 2010. After accounting for the consumption of reactive carbon and creature ingestion (0.078 PgC a -1 ), fires (0.002 PgC a -1 ), water erosion (0.038 PgC a -1 ) and agricultural and forestry utilization (0.806 PgC a -1 ), the final carbon sink in China was about 0.966 PgC a -1 ; this was considered as the climate-based potential terrestrial ecosystem carbon sink for the current climate conditions in China. The carbon emissions caused by anthropogenic disturbances accounted for more than 42 % of the NEP, which indicated that humans can play an important role in increasing terrestrial carbon sequestration and mitigating global climate change. This role can be fulfilled by reducing the carbon emissions caused by human activities and by prolonging the residence time of fixed organic carbon in the large-scale regional biome-society system through the improvement of ecosystem management.

Optimizing photosynthetic and respiratory parameters based on the seasonal variation pattern in regional net ecosystem productivity obtained from atmospheric inversion

“…The multi-timescale optimization scheme described above is first applied to flux data at the CA-Obs site to demonstrate the methodology for optimizing V max 25 and Q 10 at the site level. The scheme is then used for optimizing V max 25 and Q 10 to the regional NEP obtained from AI for the purpose of exploring the feasibility of using atmospheric CO 2 concentration measurements for optimizing ecosystem parameters.…”

“…Therefore, as an alternative, it is assumed that the V max,j 25 of all PFTs change with the same proportion. V max,j 25 can be expressed as follows:…”

“…b is a multiplier and kept constant in optimization process. In this study, we optimize the base maximum carboxylation rate (V max 25 ) for all PFTs.…”

“…In the last step, optimized V max 25 and Q 10 are compared to the prior parameters in the model. If the difference between prior and optimized parameter values is less than 1 for V max 25 and 0.1 for Q 10 , the process of optimization is completed. If not, steps 2 and 3 will be repeated using optimized parameters as prior parameters.…”

“…Since atmospheric CO 2 measurements are intrinsically influenced by regional ecosystem carbon fluxes, carbon fluxes derived from AI systems can allow us to obtain parameters of ecological models applicable at the regional scale [20][21][22][23][24]. Because photosynthetic and respiratory processes simultaneously contribute to the net ecosystem carbon flux [25], it is generally perceived to be difficult to separate the net flux into photosynthesis and respiration components without any additional information [26,27]. However, this perception may be challenged by utilizing a data assimilation technique.…”