A remotely sensed pigment index reveals photosynthetic phenology in evergreen conifers

Authors

John A. Gamon, University of Nebraska-LincolnFollow
K. Fred Huemmrich, University of Maryland
Christopher Y.S. Wong, University of Toronto
Ingo Ensminger, University of Toronto
Steven Garrity, Decagon Devices, Inc.
David Y. Hollinger, U.S. Forest Service
Asko Noormets, North Carolina State University
Josep Peñuelas, Consejo Superior de Investigaciones Cientificas

Date of this Version

2016

Citation

PNAS vol. 113, no. 46, 13087–13092

Comments

Open Access Article

Abstract

In evergreen conifers, where the foliage amount changes little with season, accurate detection of the underlying “photosynthetic phenology” from satellite remote sensing has been difficult, presenting challenges for global models of ecosystem carbon uptake. Here, we report a close correspondence between seasonally changing foliar pigment levels, expressed as chlorophyll/carotenoid ratios, and evergreen photosynthetic activity, leading to a “chlorophyll/carotenoid index” (CCI) that tracks evergreen photosynthesis at multiple spatial scales. When calculated from NASA’s Moderate Resolution Imaging Spectroradiometer satellite sensor, the CCI closely follows the seasonal patterns of daily gross primary productivity of evergreen conifer stands measured by eddy covariance. This discovery provides a way of monitoring evergreen photosynthetic activity from optical remote sensing, and indicates an important regulatory role for carotenoid pigments in evergreen photosynthesis. Improved methods of monitoring photosynthesis from space can improve our understanding of the global carbon budget in a warming world of changing vegetation phenology.