期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2014
卷号：111
期号：44
页码：15774-15779
DOI：10.1073/pnas.1418075111
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceUnderstanding and accurately predicting how global terrestrial primary production responds to rising atmospheric CO2 concentrations is a prerequisite for reliably assessing the long-term climate impact of anthropogenic fossil CO2 emissions. Here we demonstrate that current carbon cycle models underestimate the long-term responsiveness of global terrestrial productivity to CO2 fertilization. This underestimation of CO2 fertilization is caused by an inherent model structural deficiency related to lack of explicit representation of CO2 diffusion inside leaves, which results in an overestimation of CO2 available at the carboxylation site. The magnitude of CO2 fertilization underestimation matches the long-term positive growth bias in the historical atmospheric CO2 predicted by Earth system models. Our study will lead to improved understanding and modeling of carbon-climate feedbacks. In C3 plants, CO2 concentrations drop considerably along mesophyll diffusion pathways from substomatal cavities to chloroplasts where CO2 assimilation occurs. Global carbon cycle models have not explicitly represented this internal drawdown and therefore overestimate CO2 available for carboxylation and underestimate photosynthetic responsiveness to atmospheric CO2. An explicit consideration of mesophyll diffusion increases the modeled cumulative CO2 fertilization effect (CFE) for global gross primary production (GPP) from 915 to 1,057 PgC for the period of 1901-2010. This increase represents a 16% correction, which is large enough to explain the persistent overestimation of growth rates of historical atmospheric CO2 by Earth system models. Without this correction, the CFE for global GPP is underestimated by 0.05 PgC/y/ppm. This finding implies that the contemporary terrestrial biosphere is more CO2 limited than previously thought.
关键词：mesophyll conductance ; CO2 fertilization ; carbon cycle ; gross primary production ; photosynthetic model
