Project Funding: 2017 - 2020

NRA: 2016 NASA: Carbon Cycle Science   

Funded by NASA

Abstract:
Remotely sensed Solar Induced Chlorophyll Fluorescence (SIF) can be a very effective proxy for gross primary production in agricultural environments. Agricultural systems exhibit the largest peak carbon fluxes and are playing an increasingly important role in the global carbon cycle. CO2 drawdown in summer can result in boundary layer CO2 concentrations close to pre-industrial levels, potentially limiting growth for C3 crops and natural landscapes. Intensification of agriculture also impacts changes in CO2 seasonal amplitudes as are related to cooling of US Midwest summer temperature extremes (Mueller et al, Nature CC, 2015). In summary, crops, esp. in the Midwest, alter the regional and global carbon cycle as well as latent and sensible heat fluxes, affecting summer temperatures, regional climate and precipitation. SIF can provide unique insights in the carbon cycle of agricultural systems and forest canopies. For crops, both remote sensing indices for greenness as well as carbon cycle models, that are largely calibrated in forest systems, fail to reproduce the observed large carbon uptake rates. However, SIF clearly identifies the higher carbon fluxes (Guanter et al PNAS, 2014) and carbon use efficiency (Guan et al, GBC, 2015) of crop systems. Initial comparisons with OCO-2 have already shown strong local features of CO2 drawdown associated with high fluorescence values in the Midwest crop areas, strongly contrasting forested systems. Despite this potential, many up-scaling approaches using SIF are still empirical and lack validation and mechanistic understanding. We posit that agricultural systems are an ideal study area to address this as I) traditional vegetation indices fail to reproduce high carbon uptakes, II) canopy structure is well defined and can be treated in 1-Dimensional radiative transfer models, and III) provide a wealth of additional information via harvest statistics. The goal of this proposal is to provide a solid framework for using SIF to estimate gross and net carbon fluxes in agricultural systems. We will leverage recent developments for measuring chlorophyll fluorescence and carbon exchange from the leaf to the canopy and landscape scale. This includes a modified Fluorescence and Gas Exchange system (Walz), a set of novel high-resolution ground- based SIF spectrometers (PhotoSpec, UCLA/Caltech/JPL) enabling independent measurements of SIF at 680 and 740nm as well as surface reflectance (300-900nm) with full 2D scanning capabilities, air-borne observation already acquired with the Chlorophyll Fluorescence Imaging Spectrometer (CFIS, JPL) as well as space-based data from OCO-2 and TROPOMI, to be launched in October 2016 (ESUSPI proposal for SIF retrievals is funded). We will deploy three ground-based PhotoSpec systems at selected Fluxtower sites in different agricultural systems to measure SIF and reflectance (bi-directional) at <10min temporal resolution over the full growing cycle in parallel with direct carbon exchange measurements (NEE, GPP) from the FluxTower at 30min resolution. SIF directionality and impact of spatial averaging, which has thus far been poorly defined, will be assessed using the 2D scanning capability of PhotoSpec. In addition, leaf-level measurements of gas exchange and the full fluorescence spectral shape will be performed at different growing stages. This full set of observations, in conjunction with SIF/GPP modeling (Soil-Canopy Observation of Photosynthesis and Energy, SCOPE), will enable us to derive a robust scaling approach from the leaf to the canopy and landscape scale. Ultimately, we will use satellite data to determine carbon uptake at the county level (bi- weekly) and compare annual totals against available yield statistics. Ground-based measurements in irrigated vs. rainfed will also be used to evaluate the relationship of SIF with latent heat fluxes and the impact of water stress (both in terms of soil moisture as well as atmospheric evaporative demand).'

Publications:

Magney, T. S., Bowling, D. R., Logan, B. A., Grossmann, K., Stutz, J., Blanken, P. D., Burns, S. P., Cheng, R., Garcia, M. A., Kohler, P., Lopez, S., Parazoo, N. C., Raczka, B., Schimel, D., Frankenberg, C. 2019. Mechanistic evidence for tracking the seasonality of photosynthesis with solar-induced fluorescence. Proceedings of the National Academy of Sciences. 116(24), 11640-11645. DOI: 10.1073/pnas.1900278116

Wang, C., Guan, K., Peng, B., Chen, M., Jiang, C., Zeng, Y., Wu, G., Wang, S., Wu, J., Yang, X., Frankenberg, C., Kohler, P., Berry, J., Bernacchi, C., Zhu, K., Alden, C., Miao, G. 2020. Satellite footprint data from OCO-2 and TROPOMI reveal significant spatio-temporal and inter-vegetation type variabilities of solar-induced fluorescence yield in the U.S. Midwest. Remote Sensing of Environment. 241, 111728. DOI: 10.1016/j.rse.2020.111728

Yin, Y., Byrne, B., Liu, J., Wennberg, P. O., Davis, K. J., Magney, T., Kohler, P., He, L., Jeyaram, R., Humphrey, V., Gerken, T., Feng, S., Digangi, J. P., Frankenberg, C. 2020. Cropland Carbon Uptake Delayed and Reduced by 2019 Midwest Floods. AGU Advances. 1(1). DOI: 10.1029/2019AV000140

Yu, L., Wen, J., Chang, C. Y., Frankenberg, C., Sun, Y. 2019. High-Resolution Global Contiguous SIF of OCO-2. Geophysical Research Letters. 46(3), 1449-1458. DOI: 10.1029/2018GL081109

More details may be found in the following project profile(s):

• NASA Terrestrial Ecology (TE) Project Profile
• North American Carbon Program (NACP) Project Profile