Ecophysiology of biocrusts at post-mining sites in Lower Lusatia

Stella Gypser, M.Sc., BTU Cottbus-Senftenberg, Soil Protection and Recultivation

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. Furthermore, they change hydrological properties of the soil surface and alternate sub-critical water hydrophobicity. The ecophysiological processes of the biocrusts organisms are highly dependent on water availability, differing in time and space. 

Biocrusts Lugteich

Biocrusts at the artificial sand dunes Neuer Lugteich in the post-mining area Welzow Süd, Brandenburg


Identification of spatial pattern of photosynthesis hotspots in biological soil crusts by combining chlorophyll fluorescence imaging and multispectral NDVI images

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. Five biological soil crust types were collected on an inland dune system in Lieberose, dominated by the moss Polytrichum piliferum and the lichens Cladonia fimbriata and C. coccifera. Five 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. NDVI (0.59-0.68) and Fv/Fm (0.724-0.751) were nearly in the same range for all biocrust samples, certainly, mosses showed a higher NDVI compared to lichens. F0 and Fm increased with species coverage and increasing biocrust development. The overlapping of NDVI with F0 and Fm showed that not all crustal organisms contribute to NDVI and chlorophyll fluorescence. The overlapping areas of NDVI and F0 ranged between 13 % and 29 %, while the overlapping of NDVI and Fm ranged between 17 % and 37 %. Generally, 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. Due to three-dimensional distortion, optical errors and alterations of the samples during transportation or watering, a perfect matching in two dimensions was not possible. Therefore, just a small portion of the biocrust image was used for matching. 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.

  • Kleefeld, A., Gypser, S., Herppich, W.B., Bader, G., Veste, M.: Identification of spatial pattern of photosynthesis hotspots in biological soil crusts by combining chlorophyll fluorescence imaging and multispectral NDVI images. submitted

Photosynthetic characteristics and their spatial variance of biological soil crusts covering initial soils in post-mining sites in Lower Lusatia, NE Germany

Following surface disturbance, quaternary sands are the basic substrate for soil development in the Lusatian reclamation area. These substrates mostly contain low organic matter and, hence, are nutrient poor. Accumulation of soil carbon is an important factor for ecosystem development, where biological soil crusts initially influence soil processes and promote ecosystem succession. The compositional structures of biological soil crusts at various developmental stages and their photosynthetic properties were investigated on two former open-cast lignite sites, currently under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). As development of biological soil crusts progressed, their contents of organic carbon and total chlorophyll increased. The ratio of these parameters, however, varied with the relative contribution of lichens and mosses in particular. Also maximum photochemical efficiency, net photosynthesis and respiration increased with crustal development. 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. During crustal succession, the rise of photosynthesis-related parameters is not necessarily linear as a result of the highly heterogenic distribution of the different crustal organisms between biocrusts of similar developmental stages as well as between those growing at the two study sites. Therefore, the evaluation of relevant ecophysiological parameters highlighted that not all biocrust-forming organisms similarly contribute to the ecophysiological behavior of biological soil crusts. Nevertheless, the occurrence of the biological soil crusts promoted soil formation and accumulation of soil carbon in initial soils.

Infiltration and water retention of biological soil crusts on reclaimed soils of former open-cast lignite mining sites in Brandenburg, north-east Germany

Investigations were done on two former open-cast lignite mining sites under reclamation, an artificial sand dune in Welzow Süd, and a forest plantation in Schlabendorf Süd (Brandenburg, Germany). The aim was to associate the topsoil hydrological characteristics of green algae dominated as well as moss and soil lichen dominated biological soil crusts during crustal succession with their water retention and the repellency index on sandy soils under temperate climate and different reliefs. The investigation of the repellency index showed on the one hand an increase due to the cross-linking of sand particles by green algae which resulted in clogging of pores. On the other hand, the occurrence of moss plants led to a decrease of the repellency index due to absorption caused by bryophytes. The determination of the water retention curves showed an increase of the water holding capacity, especially in conjunction with the growth of green algae layer. The pore-related van Genuchten parameter indicates a clay-like behaviour of the developed soil crusts. Because of the inhomogeneous distribution of lichens and mosses as well as the varying thickness of green algae layers, the water retention differed between the study sites and between samples of similar developmental stages. However, similar tendencies of water retention and water repellency related to the soil crust formation were observed. Biological soil crusts should be attended after disturbances in the context of reclamation measures, because of their small-scale succession and, hence, the promotion of soil and ecosystem development.

Formation of soil lichen crusts at reclaimed post-mining sites, Lower Lusatia, North-east Germany

Biological soil crusts were investigated at reclaimed post-mining sites near Welzow and Schlabendorf in Lower Lusatia (Brandenburg, Germany). Various development stages from initial biological soil crusts built up by green algae, to more developed soil crusts with mosses, as well as moss-soil lichen crusts, were classified. The spatial-temporal dynamics during the development resulted in a moss-lichens cover with discrete patches of pioneer organisms like green algae in between. At the study sites, 13 species of terricolous lichens were identified. The formation of the biological soil crust is important for the accumulation of soil organic matter in the first millimeters of the topsoil of these pioneer ecosystems. A correlation between cryptogamic biomass and soil carbon content were found.

Synergic hydraulic and nutritional feedback mechanisms control surface patchiness of biological soil crusts on tertiary sands at a post-mining site 

In a recultivation area located in Brandenburg, Germany, five types of biocrusts (initial BSC1, developed BSC2 and BSC3, mosses, lichens) and non-crusted mineral substrate were sampled on tertiary sand deposited in 1985 – 1986 to investigate hydrologic interactions between crust patches. Crust biomass was lowest in the non-crusted substrate, increased to the initial BSC1 and peaked in the developed BSC2, BSC3, the lichens and the mosses. Water infiltration was highest on the substrate, and decreased to BSC2, BSC1 and BSC3. Non-metric multidimensional scaling revealed that the lichens and BSC3 were associated with water soluble nutrients and with pyrite weathering products, thus representing a high nutrient low hydraulic feedback mode. The mosses and BSC2 represented a low nutrient high hydraulic feedback mode. These feedback mechanisms were considered as synergic, consisting of run-off generating (low hydraulic) and run-on receiving  (high hydraulic) BSC patches. Three scenarios for BSC succession were proposed. (1) Initial BSCs sealed the surface until they reached a successional stage (represented by BSC1) from which the development into either of the feedback modes was triggered, (2) initial heterogeneities of the mineral substrate controlled the development of the feedback mode, and (3) complex interactions between lichens and mosses occurred at later stages of system development. 

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