Hotspot Biocrusts

Combining chlorophyll  fluorescence and NDVI to analyze spatial and temporal variations of photosynthesis


Biological soil crusts can be found in open landscapes worldwide, whereupon their species composition depends on microclimate and their developmental stage. Beside microclimatic conditions, also water holding capacity or soil chemical properties led to the formation of spatial patterns and different biocrust types on the landscape level. For evaluation of biocrust functions, the connection of photosynthetic activity in relation to various spatial distribution pattern and biocrust types is necessary. Therefore, an image processing approach was used to combine chlorophyll fluorescence imaging and multispectral NDVI images for the identification of spatial pattern of photosynthetic hotspots in biological soil crusts. Photosynthetic activity and community respiration were measured in relation to successional stage and species composition. As photoautotroph microbiotic communities they contribute to carbon accumulation and soil formation of initial soils. The ecophysiological processes of the biocrusts organisms are highly dependent on water availability, differing in time and space. 


BSC2 (1)Ecohydro_biocrustsSpatial analysis of photosynthesis using Imaging-Chlorophyll FluoresenceNDVIBiocrust wetness probes for monitoring crust wetness


An additional evaluation of NDVI and chlorophyll fluorescence images showed that especially moss-dominated biocrusts had higher photosynthetic capacity compared to green algae-dominated biocrusts or soil lichens, so the photosynthetic capacity showed to be highly species-specific. The ratio of gross photosynthesis to respiration indicated a higher ecological efficiency of biocrusts dominated by green algae than of biocrusts. The occurrence of soil lichens reduced net CO2 fixation and increased CO2 release due to the enhanced mycobiontic respiration.

Biocrust samples with different ratios of bare substrate, mosses and lichens were chosen for the image analysis. RGB-images of the biocrusts were taken by using a standard consumer camera Nikon 5200, NDVI images were taken by using a modified Canon S110 NIR camera and a FluorCAM 700MF open modular system was used for chlorophyll fluorescence imaging, respectively. The matching of the RGB-, NDVI and chlorophyll fluorescence images showed that the photosynthetic performance of mosses was higher compared to lichens, and hence, these species represented the hotspots of photosynthesis of the biocrust.  In general, the ecophysiological performance of biocrusts can be related to their specific community composition and a saturation of the photosynthetic performance of developed biocrusts should be considered in the analysis of carbon cycles and accumulation during ecosystem development.


Publications


Funding

Development of biocrusts on temperate sand dunes and post-mining sites and their application in restoration ecology funded by Geschwister-Stauder-Stiftung, University of Hohenheim, 2016-2017.


  © Maik Veste 2017-2020 Last update: APRIL 2020