A Novel Diffuse Fraction-Based Two-Leaf Light Use Efficiency Model: An Application Quantifying Photosynthetic Seasonality Across 20 AmeriFlux Flux Tower Sites

Authors

Hao Yan, University of VirginiaFollow
Shao-Qiang Wang, Chinese Academy of Sciences
Kai-Liang Yu, University of Virginia
Bin Wang, University of Virginia
Qin Yu, The George Washington University
Gil Bohrer, The Ohio State University
Dave P. Billesbach, University of Nebraska - LincolnFollow
Rosvel Bracho, University of Florida
Faiz Rahman, Indiana University - Bloomington

Document Type

Article

Date of this Version

2017

Citation

Journal of Advances in Modeling Earth Systems, 9, 2317–2332.

Comments

Copyright 2017. The Authors.

This is an open access article

https://doi.org/10.1002/2016MS000886

Abstract

.

Diffuse radiation can increase canopy light use efficiency (LUE). This creates the need to differentiate the effects of direct and diffuse radiation when simulating terrestrial gross primary production (GPP). Here, we present a novel GPP model, the diffuse-fraction-based two-leaf model (DTEC), which includes the leaf response to direct and diffuse radiation, and treats maximum LUE for shaded leaves (ε_msh defined as a power function of the diffuse fraction (D_f)) and sunlit leaves (ε_msu defined as a constant) separately. An Amazonian rainforest site (KM67) was used to calibrate the model by simulating the linear relationship between monthly canopy LUE and D_f. This showed a positive response of forest GPP to atmospheric diffuse radiation, and suggested that diffuse radiation was more limiting than global radiation and water availability for Amazon rainforest GPP on a monthly scale. Further evaluation at 20 independent AmeriFlux sites showed that the DTEC model, when driven by monthly meteorological data and MODIS leaf area index (LAI) products, explained 70% of the variability observed in monthly flux tower GPP. This exceeded the 51% accounted for by the MODIS 17A2 big-leaf GPP product. The DTEC model’s explicit accounting for the impacts of diffuse radiation and soil water stress along with its parameterization for C4 and C3 plants was responsible for this difference. The evaluation of DTEC at Amazon rainforest sites demonstrated its potential to capture the unique seasonality of higher GPP during the diffuse radiation-dominated wet season. Our results highlight the importance of diffuse radiation in seasonal GPP simulation.