Near-distance imaging spectroscopy investigating chlorophyll fluorescence and photosynthetic activity of grassland in the daily course

Detection of grassland canopy chlorophyll fluorescence (Chl-F) conducted with an imaging spectroradiometer provided evidence of potential remote sensing estimation of steady-state Chl-F(Chl-F-s). Daily near-nadir views of extremely high spatial resolution hyperspectral images were acquired from a distance of 4m for temperate montane grassland in the Czech Republic. Simultaneously, measurements of Chl-F and total chlorophyll content (Chl(a+b)) were made on a single leaf at ground level were collected. A specifically designed 'shade removal' experiment revealed the influence of dynamic physiological plant processes on hyperspectral reflectance of three wavelengths: 532, 686 and 740 nm. Based on this information, the vegetation indexes R-686/R-630, R-740/R-800 and PRI calculated as (R-532-R-570)/(R-532+R-570) were tested for statistical significance with directly measured Chl-F parameters (maximum fluorescence yield, F-v/F-m; steady-state chlorophyll fluorescence, Chl-F-s and actual quantum yield, phi(II)). The grassland species under investigation were: Festuca rubra agg. (L.), Hieracium sp., Plantago sp., Nardus stricta (L.) and Jacea pseudophrygia (C. A. Meyer). The coefficients of determination (R-2) for best-fit relationships between PRI-phi(II) and PRI-Chl-F-s, measured in the daily course, show a high variability of 0.23-0.78 and 0.20-0.65, respectively. Similarly, R-2 for the R-686/R-630-phi(II) and R-686/R-630-Chl-F-s relationships varied between 0.20-0.73 and 0.41-0.70, respectively. The highest average R2 values were found between PRI and Chl(a+b) (0.63) and R-686/R-630 and Chl(a+b) (0.72). The ratio R-740/R-800 did not yield a statistically significant relation with Chl-F parameters.