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

Abstract

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 (f APAR) -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 (r 2 = 0.86, p < 0.01), it was poorly related to GPP (r 2 = 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 (AIC cv = 127, ME cv = 0.879) outperformed RSM (AIC cv = 140, ME cv = 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.

Analysis of Red and Far-Red Sun-Induced Chlorophyll Fluorescence and Their Ratio in Different Canopies Based on Observed and Modeled Data

“…Whilst the feasibility to detect the F FR signal was demonstrated at different scales [7][8][9][10], only few studies successfully retrieved canopy F R [11,12]. This is because the majority of available instruments have a coarse spectral resolution combined with a low signal-to-noise ratio that make it difficult to resolve the width of the narrow O 2 -B band and properly retrieve the faint F R signal.…”

Dependence of spectral characteristics on parameters describing CO2 exchange between crop species and the atmosphere

“…Studies on the relationships of the spectral characteristics of the vegetation cover with CO 2 fluxes measured using the chamber technique have been conducted relatively rarely till now (Boelman et al, 2003;Dagg and Lafleur, 2010;Perez-Priego et al, 2015). However, considering that both chamber and spectral measurements can be performed at a small scale of crop fields where the EC technique cannot be applied, our aim was to demonstrate how these two methods can be successfully combined to develop simple empirical models which allow estimation of the GEP and NEP of different crops with remote sensing.…”

Fate of N additions in a multiple resource‐limited Mediterranean oak savanna

“…This was not the case for microbial biomass, which did not differ between nutrient addition treatments except for the last sampling campaign where the N + P treatment had higher biomass N. The treatment effect in plant tissues is possibly a result of the form of fertilizer applied, which was dominated to a greater extent by NO 3 À in the N-only plots. It is known that the herbaceous layer of the Majadas dehesa is more productive with N addition and shows an additional increase with N + P fertilization (Perez-Priego et al 2015. Alternatively, it is possible that the many different species that make up the dehesa herbaceous layer on average prefer NO 3 À (Britto and Kronzucker 2013).…”

“…This is due to the relatively nutrient-poor parent material of the soil and the extremely dry summer conditions typical of the Mediterranean climate (Olea and San Miguel-Ayanz 2006, Moreno 2008, Vitousek et al 2010. Previous work has highlighted the vulnerability of dehesas to N deposition due to differing responses of individual vegetative components (Ochoa-Hueso et al 2013, Perez-Priego et al 2015 and the possibility of exacerbated fire-cycles due to increased biomass, such as that seen in the equivalent Californian ecosystem (Ochoa-Hueso et al 2011, Rivest et al 2011. Previous work has highlighted the vulnerability of dehesas to N deposition due to differing responses of individual vegetative components (Ochoa-Hueso et al 2013, Perez-Priego et al 2015 and the possibility of exacerbated fire-cycles due to increased biomass, such as that seen in the equivalent Californian ecosystem (Ochoa-Hueso et al 2011, Rivest et al 2011.…”