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Improving Simulation of the Terrestrial Carbon Cycle of China in Version 4.5 of the Community Land Model Using a Revised Vcmax Scheme |
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| Authors: | WANG Yuan-Yuan XIE Zheng-Hui JIA Bing-Hao YU Yan |
| Affiliation: | 1. State Key Laboratory of Numerical Modeling, for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China;University of Chinese Academy of Sciences, Beijing 100049, China 2. State Key Laboratory of Numerical Modeling, for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China 3. Zhejiang Institute of Meteorological Sciences, Hangzhou 310017, China |
| Abstract: | The maximum rate of carboxylation(Vcmax) is a key photosynthetic parameter for gross primary production(GPP) estimation in terrestrial biosphere models. A set of observation-based Vcmax values, which take the nitrogen limitation on photosynthetic rates into consideration, are used in version 4.5 of the Community Land Model(CLM4.5). However, CLM4.5 with carbon-nitrogen(CN) biogeochemistry(CLM4.5-CN) still uses an independent decay coefficient for nitrogen after the photosynthesis calculation. This means that the nitrogen limitation on the carbon cycle is accounted for twice when CN biogeochemistry is active. Therefore, to avoid this double nitrogen down-regulation in CLM4.5-CN, the original Vcmax scheme is revised with a new one that only accounts for the transition between Vcmax and its potential value(without nitrogen limitation). Compared to flux towerbased observations, the new Vcmax scheme reduces the root-mean-square error(RMSE) in GPP for mainland China by 13.7 g C m-2 yr-1, with a larger decrease over humid areas(39.2 g C m-2 yr-1). Moreover, net primary production and leaf area index are also improved, with reductions in RMSE by 0.8% and 11.5%, respectively. |
| Keywords: | CLM4.5 Vcmax gross primary production net primary production leaf area index |
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