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Volume 12, issue 21
Biogeosciences, 12, 6351–6367, 2015
https://doi.org/10.5194/bg-12-6351-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: EUROSPEC – spectral sampling tools for vegetation biophysical...

Biogeosciences, 12, 6351–6367, 2015
https://doi.org/10.5194/bg-12-6351-2015
© Author(s) 2015. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 09 Nov 2015

Research article | 09 Nov 2015

Sun-induced chlorophyll fluorescence and photochemical reflectance index improve remote-sensing gross primary production estimates under varying nutrient availability in a typical Mediterranean savanna ecosystem

O. Perez-Priego1, J. Guan1,2, M. Rossini3, F. Fava3, T. Wutzler1, G. Moreno4, N. Carvalhais1,5, A. Carrara6, O. Kolle1, T. Julitta3, M. Schrumpf1, M. Reichstein1, and M. Migliavacca1 O. Perez-Priego et al.
  • 1Max Planck Institute for Biogeochemistry, Jena, Germany
  • 2Chinese Academy of Sciences and Ministry of Water Resources, State Key Laboratory of Soil Erosion and Dryland Farming on Loess Plateau, Institute of Soil and Water Conservation, Yangling, Shaanxi, China
  • 3Università degli Studi Milano-Bicocca, Remote Sensing of Environmental Dynamics Laboratory, DISAT, Milan, Italy
  • 4Universidad de Extremadura, Forest Research Group, Plasencia, Spain
  • 5Departamento de Ciencias e Engenharia do Ambiente, DCEA, Faculdade de Ciencias e Tecnologia, FCT, Universidade Nova de Lisboa, Caparica, Portugal
  • 6Fundación Centro de Estudios Ambientales del Mediterráneo (CEAM), Valencia, Spain

Abstract. This study investigates the performances of different optical indices to estimate gross primary production (GPP) of herbaceous stratum in a Mediterranean savanna with different nitrogen (N) and phosphorous (P) availability. Sun-induced chlorophyll fluorescence yield computed at 760 nm (Fy760), scaled photochemical reflectance index (sPRI), MERIS terrestrial-chlorophyll index (MTCI) and normalized difference vegetation index (NDVI) were computed from near-surface field spectroscopy measurements collected using high spectral resolution spectrometers covering the visible near-infrared regions. GPP was measured using canopy chambers on the same locations sampled by the spectrometers. We tested whether light-use efficiency (LUE) models driven by remote-sensing quantities (RSMs) can better track changes in GPP caused by nutrient supplies compared to those driven exclusively by meteorological data (MM). Particularly, we compared the performances of different RSM formulations – relying on the use of Fy760 or sPRI as a proxy for LUE and NDVI or MTCI as a fraction of absorbed photosynthetically active radiation (fAPAR) – with those of classical MM.

Results showed higher GPP in the N-fertilized experimental plots during the growing period. These differences in GPP disappeared in the drying period when senescence effects masked out potential differences due to plant N content. Consequently, although MTCI was closely related to the mean of plant N content across treatments (r2 = 0.86, p < 0.01), it was poorly related to GPP (r2 = 0.45, p < 0.05). On the contrary sPRI and Fy760 correlated well with GPP during the whole measurement period. Results revealed that the relationship between GPP and Fy760 is not unique across treatments, but it is affected by N availability. Results from a cross-validation analysis showed that MM (AICcv = 127, MEcv = 0.879) outperformed RSM (AICcv =140, MEcv = 0.8737) when soil moisture was used to constrain the seasonal dynamic of LUE. However, residual analyses demonstrated that GPP predictions with MM are inaccurate whenever no climatic variable explicitly reveals nutrient-related changes in the LUE parameter. These results suggest that RSM is a valuable means to diagnose nutrient-induced effects on the photosynthetic activity.

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Sun-induced chlorophyll fluorescence and photochemical reflectance index revealed controls of climate and nutrient availability on photosynthesis (gross primary production, GPP). Meteo-driven models (MMs) were unable to describe nutrient-induced effects on GPP. Important implications can be derived from these results, and uncertainties in the prediction of global GPP still remain when MMs do not account for plant nutrient availability.
Sun-induced chlorophyll fluorescence and photochemical reflectance index revealed controls of...
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