A remotely sensed pigment index reveals photosynthetic phenology in evergreen conifers

Boreal forest
Boreal forest, researchers find a close correspondence between seasonally changing foliar pigment level and evergreen photosynthetic activity Photo by ŠtefanŠtefančík

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, causing errors in terrestrial photosynthetic carbon uptake models. This represents a challenge for global models of ecosystem carbon uptake.

In a new study in the journal Proceedings of the National Academy of Sciences researchers find 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. “This methodology could improve the assessment of the evergreen component of the terrestrial carbon budget, which has been elusive” said Prof. Josep Peñuelas.

“Improved methods of monitoring photosynthesis from space can improve our understanding of the global carbon budget in a warming world of changing vegetation phenology”, said Prof. John Gamon.

 

Citation: Gamon, J., Huemmrich, J.K.F., Wong, C.Y.F., Ensminger, I., Garrity, S., Hollinger, D.Y., Noormets, A., Peñuelas, J. 2016. A remotely sensed pigment index reveals photosynthetic Q:1 phenology in evergreen conifers. Proceedings of the National Academy of Sciences, 2016. In press