## 2 Materials and Methods  
### Data  
We collected 2632 records of observed specific leaf area (SLA) data for 1056 species from published papers during 2005-2020 by searching for keywords (i.e., leaf traits, specific leaf area, leaf mass per area, China) in the Web of Science and the China National Knowledge Infrastructure. SLA values estimated from models were excluded. These SLA data were distributed in different climates zones (Figure 1). According to the plant functional types setting in the CLM4.5 model and observations in China, we statistically analyzed the SLA data for 15 plant functional types (PFTs), including temperate and boreal needleleaf evergreen tree (temperate and boreal NET), boreal needleleaf deciduous tree (boreal NDT), tropical and temperate broadleaf evergreen tree (tropical and temperate BET), tropical and temperate and boreal broadleaf deciduous tree (tropical and temperate and boreal BDT), temperate broadleaf evergreen shrub (temperate BES), temperate and boreal broadleaf deciduous shrub (temperate and boreal BDS), C3 grass, C4 grass, and rainfed crop (Table S1). Here, we combined C3 arctic grass and C3 grass with the same default SLA value in the CLM4.5 model into one plant functional type. We used the coefficient of variation (CV) to quantify the variation in SLA among species within the same plant functional type. The default SLA parameter values for plant functional types were collected from seven state-of-the-art terrestrial biosphere models, including Boreal Ecosystems Productivity Simulator (BEPS), the Joint UK Land Environment Simulator (JULES), Hybrid model, Biome Biogeochemical model (BIOME-BGC), Simple Biosphere and Carnegie-Ames-Stanford Approach model (SiBCASA), Community Land Model (CLM4.5), and Integrated Biosphere Simulator (IBIS) [18; 22; 23; 24; 25; 26]. Considering the differences in FFT assignment among the seven models, we just compared the differences in default SLA values among the models for eight plant functional types, i.e., NET, NDT, BDT, BET, BES, BDS, grass, and crop). For the models with subgroups for each of the eight PFTs, we used the average default SLA values of all subgroups. Half-hourly climate data (i.e., downwelling short-wave radiation (W m\({}^{-2}\)), downwelling long-wave radiation (W m\({}^{-2}\)), air temperature (K), precipitation (mm s\({}^{-1}\)), surface pressure (Pa), relative humidity (%), and wind speed (m s\({}^{-1}\))) at four ChinaFLUX sites ([[http://www.nesdc.org.cn/](http://www.nesdc.org.cn/)]([http://www.nesdc.org.cn/](http://www.nesdc.org.cn/)) accessed on 15 June 2022) were collected to drive the CLM4.5 model. The four sites included Qianyanzhou subtropical coniferous forest (QYZ), Changbaishan temperate broadleaved Korean pine mixed forest (CBS), Dinghushan subtropical evergreen coniferous forest (DHS), and Haibei alpine shrub-meadow (HBG). The CBS temperate broadleaf deciduous forest is an old growth forest in northeastern China. The HBG is a typical grassland site in the Qinghai-Tibet Plateau. QYZ and DHS are two evergreen forests in southern China. A brief description of the sites' characteristics is listed in Table 1.  
Missing climate data were filled in using observations from meteorological stations at the same site in the Chinese Ecosystem Research Network (CERN) ([[http://www.chern.org.cn/](http://www.chern.org.cn/)]([http://www.chern.org.cn/](http://www.chern.org.cn/)) accessed on 25 June 2022). A seven-day running mean diurnal cycle was used under \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Site Name** & **QYZ** & **CBS** & **DHS** & **HBG** \\ \hline latitude (E) & 26.74 & 42.40 & 23.17 & 37.67 \\ longitude (N) & 115.06 & 128.10 & 112.57 & 101.33 \\ elevation (m) & 102 & 738 & 300 & 3327 \\ plant functional type & temperate NET & temperate BDT & temperate BET & C3 grass \\ simulated years & 2003–2008 & 2003–2008 & 2003–2008 & 2003–2008 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Site information of four ChinaFLUX sites. Figure 1: Distribution of observed specific leaf area (SLA) data in China.