DFG Trilateral collaboration Deutschland-Israel-Palestine: "Biotic and abiotic factor affecting biological soil crust formation and recovery in a semiarid dune ecosystem : Gaza and NW Negev"
Zusammenfassung der Projektergebnisse
Cyanobacteria are crucial for the establishment and function of biological soil crusts (BSC) in arid and semiarid regions. The cyanobacterial population structure was characterized by molecular fingerprinting. The crusts were dominated by cyanobacteria of the subsection III, especially Microcoleus-like strains. Clear differences in the population structure were found among the three stations depending on the precipitation amount. In addition to control plots, we investigated the reappearance of BSCs over 4 years in mechanically disturbed plots. Whereas thickness estimated as chlorophyll content reached almost that of control plots, the biodiversty was still much less developed. Detailed investigations on the BSC structure showed a high complexity, which also suggested that the global contribution of the BSCs to global productivity is severely underestimated. One cyanobacterial strain, Leptolyngbya ohadii was isolated and purified from BSC of the Negev. We measured photosynthesis as CO 2 exchange and fluorescence in an artificial chamber that allows simulating the conditions that typically prevail in the crust and enabled extraction of RNA during desiccation, exactly mimicking the natural conditions and thereby we could identify sets of genes responding to the naturally occurring desiccation. The experiments showed that the performance of Leptolyngbya was clearly depending on the desiccation conditions. Currently, the performed sequence analyses using 454 and Illumina technologies is under evaluation to obtain more information on the molecular basis for the high light and desiccation tolerance of L. ohadii. Comparative genomics identified 52 genes found in desiccation tolerant cyanobacteria but not in those unable to recover from desiccation, often used as model organisms. Moreover, an axenic culture of the green alga Chlorella ohadii was isolated from the BSC, which shows unique characteristics including the fastest growth (generation time 2 h) rate ever reported for an algae and complete resistance to photodamage. Photosynthetic measurements indicate for alternative photosystem 2 routes allowing a non-radiative charge recombination pathway. Development and stability against mechanical disturbance of the biogenic crust as well as the vitality of crust organisms and the recovery potential are markedly a consequence of soil properties, which in turn are strongly influenced by the regional and local aridity and the dune age. The biogenic accumulation of total organic carbon and nitrogen, turnover of organic matter as well as deposition and accumulation of fines, carbonates and soluble salts and leaching of dissolvable elements are significantly related to depth, amount of annual rainfall, relief and shrub cover. Also the period of accumulation, limited by dune age and disturbance of the surface layer, plays an important role for local and regional differences in physico-chemical crust and soil properties. Crusts in an early stage of development, dominated by cyanobacteria and distributed within the arid part of the ecosystem are friable with and show a low penetration resistance. The recovery rate after mechanical disturbance as an indicator for the vitality of the crust organisms is distinctively lower than in the northern areas with higher rainfall. A subcritical water repellency and capillary barriers impede infiltration and favor interception and surface runoff. The physical functions of the biogenic crusts therefore limit the availability of water and nutrients for higher plants and influence the biogenic structure and the stability of the whole ecosystem. With increasing rainfall and the increasing abundance of lichen and mosses among the crust community the thickness, infiltrability, stability and recovery rate after mechanical disturbance increase. Nevertheless, the mechanical instability and low recovery rate of biological crusts allows only such a low carrying capacity of the semiarid dune ecosystem, that effective and sustainable land use by agriculture and grazing in the dune fields of the NW Negev is no realistic scenario.
Projektbezogene Publikationen (Auswahl)
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(2010): Light-Induced Changes within Photosystem II Protects Microcoleus sp. in Biological Desert Sand Crusts against Excess Light. PLoS ONE 5, e11000
Ohad, I., Raanan, H., Keren, N., Tchernov, D., Kaplan, A.
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(2012): An electronic micropenetrometer (EMP) for field measurements of biological soil crust stability. J. Plant Nutr. Soil Sci. 175, 519–520
Drahorad, S.L., Felix-Henningsen, P.
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(2013): A newly isolated Chlorella sp. from desert sand crusts exhibits a unique resistance to excess light intensity. FEMS Microbiol. Ecol. 86, 373–380
Treves, H., Raanan, H., Finkel, O.M., Berkowicz, S.M., Keren, N., Shotland, Y., Kaplan, A.
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(2013): Application of an electronic micropenetrometer to assess mechanical stability of biological soil crusts. J. Plant Nutr. Soil Sci. 176(6), 904- 909
Drahorad, S.L., Felix-Henningsen, P.
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(2013): Spatial carbon and nitrogen distribution and organic matter characteristics of biological soil crusts in the Negev desert (Israel) along a rainfall gradient. J. Arid Environ. 94, 18–26
Drahorad, S.L., Felix-Henningsen, P., Eckhardt, K.-U., Leinweber, P.
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(2014): Soil microstructure as an under-explored feature of biological soil crust hydrological properties: case study from the NW Negev Desert. Biodivers. Conserv. 23, 1687–1708
Felde, V.J.M.N.L., Peth, S., Uteau-Puschmann, D., Drahorad, S., Felix-Henningsen, P.
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(2015): Cyanobacterial Diversity in Biological Soil Crusts along a Precipitation Gradient, Northwest Negev Desert, Israel. Microb. Ecol. 70, 219–230
Hagemann, M., Henneberg, M., Felde, V.J.M.N.L., Drahorad, S.L., Berkowicz, S.M., Felix- Henningsen, P., Kaplan, A.
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(2015): Does 2- phosphoglycolate serve as an internal signal molecule of inorganic carbon deprivation in the cyanobacterium Synechocystis sp. PCC 6803? Environ. Microbiol. 17, 1794–1804
Haimovich-Dayan, M., Lieman-Hurwitz, J., Orf, I., Hagemann, M., Kaplan, A.
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(2015): Three-dimensional structure and cyanobacterial activity within a desert biological soil crust: Biological soil crust structure and activity. Environ. Microbiol.
Raanan, H., Felde, V.J.M.N.L., Peth, S., Drahorad, S., Ionescu, D., Eshkol, G., Treves, H., Felix-Henningsen, P., Berkowicz, S.M., Keren, N., Horn, R., Hagemann, M., Kaplan, A.
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Biological soil crusts cause subcritical water repellency in a sand dune ecosystem located along a rainfall gradient in the NW Negev desert, Israel. J. Hydrol. Hydromech., 2016
Keck, H., Felde, V.J.M.N.L., Drahorad, S.L., Felix-Henningsen, P.
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Simulated soil crust conditions in a chamber system provide new insights on cyanobacterial acclimation to desiccation: Simulation of BSC conditions and acclimation. Environ. Microbiol., 2016
Raanan, H., Oren, N., Treves, H., Berkowicz, S.M., Hagemann, M., Pade, N., Keren, N., Kaplan, A.
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The mechanisms whereby the green alga Chlorella ohadii, isolated from desert soil crust, exhibits unparalleled photodamage resistance. New Phytol. 210, Issue 4, June 2016, 1229-1243
Treves, H., Raanan, H., Kedem, H., Murik, O., Keren, N., Zer, H., Berkowicz, S.M., Giordano, M., Norici, A., Shotland, Y., Ohad, I., Kaplan, A.
