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Improved estimates of global terrestrial photosynthesis using information on leaf chlorophyll content
Author(s) -
Luo Xiangzhong,
Croft Holly,
Chen Jing M.,
He Liming,
Keenan Trevor F.
Publication year - 2019
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.14624
Subject(s) - photosynthesis , evergreen , environmental science , biosphere , deciduous , atmospheric sciences , photosynthetic capacity , terrestrial plant , plant functional type , terrestrial ecosystem , chlorophyll fluorescence , ecosystem , botany , ecology , biology , physics
The terrestrial biosphere plays a critical role in mitigating climate change by absorbing anthropogenic CO 2 emissions through photosynthesis. The rate of photosynthesis is determined jointly by environmental variables and the intrinsic photosynthetic capacity of plants (i.e. maximum carboxylation rate;V c max 25 ). A lack of an effective means to derive spatially and temporally explicitV c max 25 has long hampered efforts towards estimating global photosynthesis accurately. Recent work suggests that leaf chlorophyll content (Chl leaf ) is strongly related toV c max 25 , since Chl leaf andV c max 25 are both correlated with photosynthetic nitrogen content. We used medium resolution satellite images to derive spatially and temporally explicit Chl leaf , which we then used to parameterizeV c max 25 within a terrestrial biosphere model. Modelled photosynthesis estimates were evaluated against measured photosynthesis at 124 eddy covariance sites. The inclusion of Chl leaf in a terrestrial biosphere model improved the spatial and temporal variability of photosynthesis estimates, reducing biases at eddy covariance sites by 8% on average, with the largest improvements occurring for croplands (21% bias reduction) and deciduous forests (15% bias reduction). At the global scale, the inclusion of Chl leaf reduced terrestrial photosynthesis estimates by 9 PgC/year and improved the correlations with a reconstructed solar‐induced fluorescence product and a gridded photosynthesis product upscaled from tower measurements. We found positive impacts of Chl leaf on modelled photosynthesis for deciduous forests, croplands, grasslands, savannas and wetlands, but mixed impacts for shrublands and evergreen broadleaf forests and negative impacts for evergreen needleleaf forests and mixed forests. Our results highlight the potential of Chl leaf to reduce the uncertainty of global photosynthesis but identify challenges for incorporating Chl leaf in future terrestrial biosphere models.