|Kustas, William - Bill|
|Russ, Andrew - Andy|
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2009
Publication Date: 7/5/2009
Citation: Middleton, E.M., Cheng, Y., Corp, L.A., Huemmrich, F.K., Campbell, P., Zhang, Q., Kustas, W.P., Russ, A.L. 2009. Diurnal and seasonal dynamics of canopy-level solar-induced chlorophyll fluorescence and spectral reflectance indices in a cornfield. In: Proceedings of the 6th EARSeL SIG Workshop on Imaging Spectroscopy, March 16-19, 2009, Tel Aviv, Isreal. 2009 CDROM. Interpretive Summary:
Technical Abstract: A collaborative field campaign was undertaken to examine the temporal dynamics of canopy-level solar-induced fluorescence (SIF) and the Photochemical Reflectance Index (PRI) in conjunction with photosynthetic light use efficiency (LUE) obtained from fluxes measured at an instrumented tower. We conducted intensive diurnal measurements weekly from June-August (6 dates) in 2007, and from mid-July through early October 2008 (14 dates), using high resolution (0.2 - 3.0 nm) field spectroradiometers and collecting supporting leaf-level and canopy biophysical data. At the canopy level, we used a Fraunhofer Line Depth (FLD) retrieval approach to obtain SIF in the two atmospheric oxygen bands (O2-B and O'2-A) centered on 688 and 760 nm. We found that canopy-level SIF, fluorescence yield (Fyield), and the PRI varied significantly throughout each field day. In addition, daily averages for PRI, SIF, and Fyield declined across the growing season as the cornfield progressed through vegetative and reproductive stages, and senescence. The greatest seasonal change was captured by SIF expressed in energy units (W m-2 sr-1 um-1) in the O2-B band (r'2 = 0.93) and the O2-A band (r2 = 0.87), and by the PRI (r2 = 0.88), all determined from 1 nm spectral resolution data (with Ocean Optics spectroradiometer). The PRI determined at 3 nm resolution (with an ASD-FR spectroradiometer) from both years was related to LUE (r2 = 0.67), obtaining PRI values of +0.02 (indicating little stress) in the early growth stage but late stage values of -0.075 (indicating substantial stress), as LUE declined from 0.048 mol C/mol Qa to near zero LUE. The PRI (@1 nm): LUE relationship (r2 = 0.61) was similar, but enabled detection of a slightly greater range in LUE. The PRI (@1 nm) and Fyield were strongly correlated for daily values examined over the season: PRI: F688yield (r = 0.88) and PRI: F760yield (r=0.86). Daily trends for leaf-level photosynthesis were similar to those obtained from tower measurements, but knowledge of the green canopy fraction was necessary to model the canopy net production from leaf-level data inputs.