Balzarolo M., Peñuelas J., Filella I., Portillo-Estrada M., Ceulemans R. (2018) Assessing ecosystem isoprene emissions by hyperspectral remote sensing. Remote Sensing. 10: 0-0.LinkDoi: 10.3390/rs10071086
This study examined the relationship between foliar isoprene emissions, light use efficiency and photochemical reflectance index (PRI) throughout the canopy profile and explored the contribution of xanthophyll cycle pigments versus other carotenoid pigments to the isoprene/PRI relationship. Foliar isoprene emissions within the canopy profile were measured in a high-density poplar plantation in Flanders (Belgium) during the 2016 growing season. The results confirmed that PRI was a promising estimator of isoprene emissions at canopy level. Interestingly, xanthophyll cycle pigments contributed more to isoprene biosynthesis than chlorophyll and drove the isoprene/PRI relationship. The simple independent pigment index and novel defined indices, such as the hyperspectral isoprene index and simple hyperspectral isoprene index, showed promising results and could be suitable estimators of isoprene emissions due to their strong relationship with the xanthophyll pool. © 2018 by the authors.
Filella I., Zhang C., Seco R., Potosnak M., Guenther A., Karl T., Gamon J., Pallardy S., Gu L., Kim S., Balzarolo M., Fernandez-Martinez M., Penuelas J. (2018) A MODIS photochemical reflectance index (PRI) as an estimator of isoprene emissions in a temperate deciduous forest. Remote Sensing. 10: 0-0.LinkDoi: 10.3390/rs10040557
The quantification of isoprene and monoterpene emissions at the ecosystem level with available models and field measurements is not entirely satisfactory. Remote-sensing techniques can extend the spatial and temporal assessment of isoprenoid fluxes. Detecting the exchange of biogenic volatile organic compounds (BVOCs) using these techniques is, however, a very challenging goal. Recent evidence suggests that a simple remotely sensed index, the photochemical reflectance index (PRI), which is indicative of light-use efficiency, relative pigment levels and excess reducing power, is a good indirect estimator of foliar isoprenoid emissions. We tested the ability of PRI to assess isoprenoid fluxes in a temperate deciduous forest in central USA throughout the entire growing season and under moderate and extreme drought conditions. We compared PRI time series calculated with MODIS bands to isoprene emissions measured with eddy covariance. MODIS PRI was correlated with isoprene emissions for most of the season, until emissions peaked. MODIS PRI was also able to detect the timing of the annual peak of emissions, even when it was advanced in response to drought conditions. PRI is thus a promising index to estimate isoprene emissions when it is complemented by information on potential emission. It may also be used to further improve models of isoprene emission under drought and other stress conditions. Direct estimation of isoprene emission by PRI is, however, limited, because PRI estimates LUE, and the relationship between LUE and isoprene emissions can be modified by severe stress conditions. © 2018 by the authors.
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