Recently, the prestigious journal in the field of agricultural and forestry science, Agricultural and Forest Meteorology, published an academic paper “Light use efficiency models incorporating diffuse radiation impacts for simulating terrestrial ecosystem gross primary productivity: A global comparison” online by Professor Zhiqiang Zhang's research team from the School of Soil and Water Conservation at Beijing Forestry university. Dr. Hang Xu, a young faculty from the School of Soil and Water Conservation, is the paper's first author, while Prof. Zhiqiang Zhang serves as the corresponding author.
Terrestrial ecosystem Gross Primary Productivity (GPP) reflects the ability of plants to fix CO2 through photosynthesis and is a key component of the global carbon cycle and an important foundation for ecosystem service functions. Accurately simulating the spatiotemporal variability of terrestrial ecosystem GPP is an essential prerequisite for properly assessing the carbon sequestration function of terrestrial ecosystems and provides crucial support for understanding the impacts of climate change on terrestrial ecosystems.
The Light Use Efficiency (LUE) models based on the "Big-leaf" and "Two-leaf" theories have been widely applied in global GPP simulations due to their solid theoretical foundation, simple model structure, and limited driving data requirements. However, it is still unclear which type of model performs better in simulating global terrestrial ecosystem GPP.
To address this issue, the research team utilized multi-source data (e.g., carbon flux, meteorological, and vegetation information) from 102 global terrestrial ecosystems and 950 site-years to conduct a global assessment of the simulation results from ten widely-used LUE models (CFLUX, DIFFUSE, CI-LUE, Wang's Model, CI-EF, TL-LUE, TL-LUEn, DTEC, and RTL-LUE).
Figure 1 Global distribution of research sites
The study found that the improved "Big-leaf" and "Two-leaf" models can explain 46.7% to 63.6% of terrestrial ecosystem GPP dynamics, and they perform better in simulating deciduous broadleaf forests but poorly in evergreen broadleaf forests and croplands. In the context of rapidly changing global diffuse radiation, although the "Two-leaf" models have greater potential in capturing terrestrial ecosystem GPP, the current two types of models do not show significant differences. This is mainly due to the errors in the leaf area index data from remote sensing on which the "Two-leaf" models rely. The study emphasizes that producing vegetation remote sensing products with higher spatial-temporal resolution and accuracy is crucial for the reliability and stability of the "Two-leaf" models.
Figure 2 Performance of the improved "Big-leaf" and "Two-leaf" models in simulating terrestrial ecosystem GPP
Figure 3 Sensitivity of GPP simulated by "Two-leaf" models to Leaf Area Index (LAI)
This study was supported by the National Natural Science Foundation of China (Grant No. 31872711), the Fundamental Research Funds for the Central Universities (Grant No. BLX202108), the China Postdoctoral Science Foundation (Grant No. 2022M710407), and the National Key Research and Development Program of China (Grant No. 2022YFF1302501).