Biocrust succession on temperate sand dunes

Succession of N cycling processes in biological soil crusts on a central European inland dune. 

Biological soil crusts (BSCs) are microbial assemblages that occur worldwide and facilitate ecosystem development by nitrogen (N) and carbon accumulation. N turnover within BSC ecosystems has been intensively studied in the past; however, shifts in the N cycle during BSC development have not been previously investigated. Our aim was to characterise N cycle development first by the abundance of the corresponding functional genes (in brackets) and second by potential enzyme activities; we focussed on the four processes: N fixation (nifH), mineralisation as proteolysis and chitinolysis (chiA), nitrification (amoA) and denitrification (nosZ). We sampled from four phases of BSC development and from a reference located in the rooting zone of Corynephorus canescens, on an inland dune in Germany. BSC development was associated with increasing amounts of chlorophyll, organic carbon and N. Potential activities increased and were highest in developed BSCs. Similarly, the abundance of functional genes increased. We propose and discuss three stages of N process succession. First, the heterotrophic stage (mobile sand without BSCs) is dominated by mineralisation activity. Second, during the transition stage (initial BSCs), N accumulates, and potential nitrification and denitrification activity increases. Third, the developed stage (established BSCs and reference) is characterised by the dominance of nitrification.

Brankatschk, R., Fischer, T., Veste, M., Zeyer, J. FEMS Microbiology Ecology 83 (1),149-160, 2013. (more…)

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Biological soil crusts on temperate dunes near Lieberose, Brandenburg 

Biological soil crusts on initial soils: organic carbon dynamics and chemistry under temperate climatic conditions

Numerous studies have been carried out on the community structure and diversity of biological soil crusts (BSCs) as well as their important functions on ecosystem processes. However, the amount of BSC-derived organic carbon (OC) input into soils and its chemical composition under natural conditions has rarely been investigated. In this study, different development stages of algae- and moss-dominated BSCs were investigated on a~natural (<17 yr old BSCs) and experimental sand dune (<4 yr old BSCs) in northeastern Germany. We determined the OC accumulation in BSC-layers and the BSC-derived OC input into the underlying substrates for bulk materials and fractions <63 μm. The chemical composition of OC was characterized by applying solid-state 13C NMR spectroscopy and analysis of the carbohydrate-C signature.14C contents were used to assess the origin and dynamic of OC in BSCs and underlying substrates. Our results indicated a rapid BSC establishment and development from algae- to moss-dominated BSCs within only 4 yr under this temperate climate. The distribution of BSC types was presumably controlled by the surface stability according to the position in the slope. We found no evidence that soil properties influenced the BSC distribution on both sand dunes. 14C contents clearly indicated the existence of two OC pools in BSCs and substrates, recent BSC-derived OC and lignite-derived "old" OC (biologically refractory). The input of recent BSC-derived OC strongly decreased the mean residence time of total OC. The downward translocation of OC into the underlying substrates was only found for moss-dominated BSCs at the natural sand dune which may accelerate soil formation at these spots. BSC-derived OC mainly comprised O-alkyl C (carbohydrate-C) and to a lesser extent also alkyl C and N-alkyl C in varying compositions. Accumulation of alkyl C was only detected in BSCs at the experimental dune which may induce a~lower water solubility of BSC-derived extracellular polymeric substances when compared to BSCs at the natural sand dune indicating that hydrological effects of BSCs on soils depend on the chemical composition of the extracellular polymeric substances.

Dümig, A., Veste, M., Hagedorn, Fischer, T., Lange, P., Spröte, R., Kögel-Knabner, I., Biogeosciences Discussions 10, 851-894, 2013  (more..)


Biological soil crust covering temperate sand dunes in Lieberose, Brandenburg

Water repellency and pore clogging at early successional stages of microbiotic crusts on inland dunes, Brandenburg, NE Germany

Biological soil crusts play a key role for hydrological processes in many open landscapes. They seal the topsoil and generate surface run-off. Utilization of the mineral substrate at early stages of microbiotic crusts was investigated using scanning electron microscopy (SEM), water repellency indices were measured using the ethanol/water microinfiltrometer method, and steady state water flow was determined on the dry crusts and after 300, 600, 1200 and 1800 s of wetting, thus allowing to follow pore clogging through swelling of extracellular polymeric substances (EPS). It was found that water repellency increases with initial crust development where filamentous cyanobacteria and filamentous green algae were dominating, but decreases as coccal algae, bryophytes and fungi associated with bryophytes emerged. Swelling of EPS took place immediately after wetting, and its influence on steady state water flow was most pronounced when filamentous cyanobacteria and algae partially filled in the matrix pores and enmeshed sand grains, still leaving micropore channels available for free water infiltration, but prior to appearance of coccal algae, bryophytes and associated fungi which formed a dense cover on the surface. It was concluded that a new phase of crust succession was accompanied by easier wettability but slower infiltration. Transition from hydrophobicity to pore clogging as ruling mechanisms causing water run-off may occur during wetting of individual biological crusts, but also during crust succession over time.

Fischer, Veste, M., Wiehe, W., Lange, P., Catena 80 (1), 47-52, 2010. (more...)


Biological soil crusts on temperate dunes near Lieberose, Brandenburg 

Microstructure and hydraulic properties of biological soil crusts on sand dunes: a comparison between arid and temperate climates

We studied the relationships between crust microstructure, infiltration and water holding capacity under arid and temperate conditions (Factor A: Climate) on biological soil crusts (BSCs) sampled along a~catena on mobile sand dunes (Factor B: Catena). The arid study site was located near Nizzana, Israel (precipitation: 86 mm a−1, PET: ~2500 mm a−1) and the temperate site near Lieberose, Germany (precipitation: 569 mm a−1, PET: ~780 mm a−1). BSCs were sampled near the dune crest, at the centre of the dune slope and at the dune base at each site. Scanning electron microscopy (SEM) was used to characterize BSC morphology and microstructure. Infiltration was determined using microinfiltrometry under controlled moisture conditions in the lab. Water holding capacities were determined after water saturation of the dry BSCs. Wettability of the crusts was characterized using a "repellency index", which was calculated from water and ethanol sorptivities. Irrespective of the climate, an accumulation of fine particles in the BSCs was found, increasing along the catena from dune crest to dune base. Texture was finer and water holding capacities of the underlying substrate were higher at the arid site, whereas surface wettability was reduced at the temperate site. At both sites, BSCs caused extra water holding capacity compared to the substrate. Infiltration rates decreased along the catena and were generally lower at the dune slope and base of the arid site. A mechanism of crust stabilization is proposed where BSCs benefit from increased texture and biomass mediated water supply, and where the water supply to higher plants was limited due to alteration of physico-chemical surface properties under temperate conditions.

Fischer, T., Yair, A., Veste, M.,  Biogeosciences Discuss., 9, 12711-12734, 2012. (more…)

Biological soil crust sand dunes Lieberose, Brandenburg, NE Germany

Biological soil crusts on temperate dunes near Lieberose, Brandenburg 

Small scale spatial heterogeneity of Normalized Difference Vegetation Indices (NDVIs) and hot spots of photosynthesis in biological soil crusts 

Normalized Difference Vegetation Indices (NDVIs) are typically determined using satellite or airborne remote sensing, or field portable spectrometers, which give an averaged signal on centimetre to metre scale plots. Biological soil crust (BSC) patches may have smaller sizes, and ecophysiological, hydrological as well as pedological processes may be heterogeneously distributed within this level of resolution. A ground-based NDVI imaging procedure using low-cost equipment (Olympus Camedia 5000z digital camera equipped with a Hoya R72 infrared filter) was developed in this study to fill this gap at the level of field research, where carrying costly and bulky equipment to remote locations is often the limiting factor for data collection. Method principle and field data are presented, and the field experiment was deepened comparing NDVI measurements and CO2 turnover of soil crust samples in the laboratory, backing the reliability of the approach.

A commercially available colour rendition chart with known red (600–700 nm) and NIR (800–900 nm) reflectances was placed into each scene and used for calibration purposes on a per-image basis. Generation of NDVI images involved (i) determination of red and NIR reflectances from the pixel values of the red and NIR channels, respectively, and (ii) calculation and imaging of the NDVI, where NDVI values of −1 to +1 were mapped to grey values of 0 to 255. The correlation between NDVI values retrieved from these images and NDVI values determined using field spectrometry was close (r2 = 0.91), the 95% confidence interval amounted to 0.10 NDVI units. The pixel resolution was 0.8 mm in the field and 0.2 mm in the laboratory, but can still be improved significantly with closer distance to the crust or with higher camera resolution. NDVI values obtained using the new method were related to the net CO2 uptake of BSCs, where both slope and correlation coefficient of the respective regression function conformed with literature data. Geostatistical analysis revealed that both spatial variability of net CO2 uptake as well as size of individual hot spots of this parameter increased with crust development. The latter never exceeded 4 mm in the investigated crusts, which points to the necessity of high resolution imaging for linking remote sensing with ecophysiology. Perspectively, the new method could be used for field monitoring of both biological soil crusts and vascular vegetation.

Fischer, T., Veste, M., Eisele, A., Bens, O., Spyra, W.,  Hüttl, R.F., Flora 207 (3), 159-167, 2012 (more…)

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