Diurnal and seasonal dynamics in vegetation fluorescence associated with photosynthetic function and CO2 dynamics

Authors: CAMPBELL, P.K.E. - The Community College Of Baltimore County; HUEMMERICH, K.F. - The Community College Of Baltimore County; MIDDLETON, E.M. - Goddard Space Flight Center; WARD, L.A. - University Of Hawaii; Daughtry, Craig; BURKART, A. - University Of Dusseldorf; Russ, Andrew - Andy; Kustas, William - Bill

Submitted to: Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2019
Publication Date: 2/27/2019
Citation: Campbell, P., Huemmerich, K., Middleton, E., Ward, L., Daughtry, C.S., Burkart, A., Russ, A.L., Kustas, W.P. 2019. Diurnal and seasonal dynamics in vegetation fluorescence associated with photosynthetic function and CO2 dynamics. Remote Sensing. https://doi.org/10.3390/rs11050488.
DOI: https://doi.org/10.3390/rs11050488

Interpretive Summary: Solar light absorbed by leaf chlorophyll drives photosynthesis in plants. Chlorophyll is the key indicator of plant function and productivity. Chlorophyll levels vary with foliage maturity, nutrient levels, environmental conditions, and light availability. Plants continuously regulate photosynthetic processes in response to changing environmental conditions on diurnal and seasonal time scales. Two remotely sensed indices, photochemical reflectance index (PRI) and chlorophyll fluorescence (F), together show potential for assessing vegetation photosynthesis at local and regional scales. The goals of this study were to better understand how these remotely sensed indices predict leaf level photosynthesis and canopy-level productivity. During the summer of 2017, we collected complementary diurnal leaf and canopy measurements capturing the seasonal dynamics in photosynthesis, reflectance, and fluorescence of a corn canopy at the USDA-ARS Beltsville Agricultural Research Center near Beltsville, MD. This research emphasizes the importance of consistent observation timing for scaling from leaf to canopy level photosynthetic rates. Our results also demonstrated that canopy-level fluorescence measurements captured the dynamics in leaf level photosynthetic efficiency which facilitated scaling photosynthetic rates canopy levels for monitoring plant productivity at field to regional scales.

Technical Abstract: To accurately monitor vegetation function there is a critical need for sensitive remote sensing approaches capturing the parameters governing photosynthesis at the temporal and spatial scales relevant to their dynamics. The photochemical reflectance index (PRI) and chlorophyll fluorescence (F) offer a strong potential to assess vegetation photosynthesis at local and regional scales. The goals of this study are to better understand how the fine spatial and temporal scale solar induced F (SIF red and far-red) measurements relate to: leaf level photosynthetic efficiency and F, and to canopy PRI and gross ecosystem productivity (GEP), and thus contribute to understanding of how SIF can be used for monitoring vegetation function. During the summer of 2017 we collected complementary diurnal leaf and canopy measurements capturing the seasonal dynamics in photosynthesis, reflectance, F and SIF of a corn canopy. Positive diurnal linear relationships of SIF to leaf photochemical efficiency of photosystem II (e.g. YII) and to canopy GEP were established, which differed significantly among growth stages. On a diurnal and seasonal scale total SIF (SIF A+B) traced best GEP. Yield of SIF B (SIF By) traced best LUE at diurnal scale across growth stages, while midday SIF Ay did so on the seasonal scale. We offer an important seasonal and diurnal demonstration from field observations on the importance of including SIF B for measurements related to photosynthetic function. This research emphasizes the importance of consistent observation timing for scaling from leaf to canopy level photosynthetic function based on SIF. Our results demonstrate that canopy total SIF A+B, SIF A and SIF B are able to capture the dynamics in leaf level photosynthetic efficiency, and therefore can facilitate scaling photosynthetic functionality from leaf to canopy level.