Spatial analysis of ground-based sun induced fluorescence data and canopy pigment content in a dry grassland

Monitoring of canopy photosynthetic performance in optimal and stress conditions has major importance in carbon budget estimates or in precision agriculture. Photosynthesis responds very rapidly to the environmental conditions balancing photochemical processes with different other processes through which excitation energy is lost from the system, including photo-protective heat loss and fluorescent light emission. Although the ratio of photosynthesis to fluorescence in optimal and stress conditions differ, it is not an easy task to assess their actual share, because of the quick adjustment of the pigment-protein complexes or the changing intensity of light re-absorption by chlorophylls.

Sun induced fluorescence (SIF) measured by ground-based instrument provided direct data of the photosynthetic capacity of the canopy. The O₂ absorptions bands filled with fluorescence served to calculate actual fluorescence intensity within the total upwelling signal. Furthermore, field leaf samples were collected and laboratory analysis was performed to determine photosynthetic pigment contents (both chlorophylls and carotenoids).

The sampling, both for SIF and pigment data collection followed spatial grid arrangements with different resolutions, 10 × 10 m and 30 × 30 m. Spatial analysis lays on a relatively large number of samples, collected within a very short time period. Our aim was to link the spatial distribution of one target phenomenon to the distribution or intensity of different driving forces, such as terrain features, soil moisture content, soil temperature etc., which were also simultaneously collected in the field work. One measuring occasion at both spatial scales were selected for detailed spatial data processing with geostatistics and kriging.