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| Titel |
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 |
| VerfasserIn |
O. Pérez-Priego, J. Guan, M. Rossini, F. Fava, T. Wutzler, G. Moreno, N. Carvalhais, A. Carrara, O. Kolle, T. Julitta, M. Schrumpf, M. Reichstein, M. Migliavacca |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 21 ; Nr. 12, no. 21 (2015-11-09), S.6351-6367 |
| Datensatznummer |
250118155
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| Publikation (Nr.) |
 copernicus.org/bg-12-6351-2015.pdf |
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| Zusammenfassung |
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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