On the relationship between ecosystem-scale hyperspectral reflectance and CO2 exchange in European mountain grasslands

[摘要] In this paper we explore the skill of hyperspectral reflectance measurementsand vegetation indices (VIs) derived from these in estimating carbon dioxide(CO₂) fluxes of grasslands. Hyperspectral reflectance data, CO₂fluxes and biophysical parameters were measured at three grassland siteslocated in European mountain regions using standardized protocols. Therelationships between CO₂ fluxes, ecophysiological variables,traditional VIs and VIs derived using all two-band combinations ofwavelengths available from the whole hyperspectral data space were analysed.We found that VIs derived from hyperspectral data generally explained a largefraction of the variability in the investigated dependent variables butdiffered in their ability to estimate midday and daily average CO₂fluxes and various derived ecophysiological parameters. Relationships betweenVIs and CO₂ fluxes and ecophysiological parameters were site-specific,likely due to differences in soils, vegetation parameters and environmentalconditions. Chlorophyll and water-content-related VIs explained the largestfraction of variability in most of the dependent variables. Band selectionbased on a combination of a genetic algorithm with random forests (GA–rF)confirmed that it is difficult to select a universal band region suitableacross the investigated ecosystems. Our findings have major implications forupscaling terrestrial CO₂ fluxes to larger regions and for remote- andproximal-sensing sampling and analysis strategies and call for morecross-site synthesis studies linking ground-based spectral reflectance withecosystem-scale CO₂ fluxes.

[学科分类] 地球化学与岩石