Role of a cyanobacterial cover on structural stability of sandy soils in the Sahelian part of western Niger

Microbiotic soil crusts, mostly formed by cyanobacteria, are widespread on the surface of fallow land in western Niger. They lie adjacent to completely bare soils. We have investigated the structural stability of these soils by testing aggregate breakdown under fast-wetting, slow-wetting and mechanical breakdown. The tests were effected on aggregates ranging from 3 to 5 mm in size. These experiments were completed by micromorphological examinations under light and scanning electron microscope. For all tests, the fragment size distribution and the mean weight diameter (MWD) revealed the great stability of aggregates from soils with a cyanobacterial cover (MWD 1.82 to 3.10 mm), compared to those from soils devoid of cyanobacterial cover (MWD 0.25 to 1.26 mm). Fast- and slow-wetting of microbiotic soil crust material induced a lesser disaggregation of aggregates compared to mechanical breakdown. On the contrary, fast-wetting and mechanical breakdown of aggregates from soils devoid of cyanobacterial cover induced a greater disaggregation than slow-wetting. Microscopic examination of microbiotic crusts revealed an intricate network of filamentous cyanobacteria and extracellular polymer secretions, which binds and entraps mineral particles on the soil surface. Organo-mineral aggregates ranging from 0.10 to 0.12 mm were observed. Below the superficial crusts, filaments and residual organic matter bind tightly soil particles, thus giving a compact structure. The great stability of aggregates of soil with cyanobacterial cover is likely related to the binding and gluing effect of cyanobacteria and derived organic matter. This is consistent with the positive correlation between MWD values and organic carbon content. The present results thereby confirm the resistance to erosion of soil with microbial cover as indicated by field measurements.

[1]  J. Sprent,et al.  Nitrogen Cycling in West African Ecosystems. , 1982 .

[2]  A. O. Isichei.  Nitrogen fixation by blue-green algal soil crusts in Nigerian savanna. , 1980 .

[3]  J. Belnap,et al.  Vulnerability of desert biological soil crusts to wind erosion: the influences of crust development, soil texture, and disturbance , 1998 .

[4]  O. Lange,et al.  Photosynthesis and water relations of lichen soil crusts: field measurements in the coastal fog zone of the Namib Desert , 1994 .

[5]  A. P. Mazurak,et al.  AGGREGATION OF SOIL PARTICLES BY ALGAE 1 , 1973 .

[6]  J. Lynch,et al.  Microorganisms and Soil Aggregate Stability , 1985 .

[7]  M. Shilo,et al.  The role of cell‐bound flocculants in coflocculation of benthic cyanobacteria with clay particles , 1988 .

[8]  Christian Défarge,et al.  Morphology and microstructure of microbiotic soil crusts on a tiger bush sequence (Niger, Sahel) , 1999 .

[9]  Cheryl McKenna Neuman,et al.  Wind transport of sand surfaces crusted with photoautotrophic microorganisms , 1996 .

[10]  Y. Bissonnais,et al.  Effect of clay content and silt—clay fabric on stability of artificial aggregates , 1998 .

[11]  Otto L. Lange,et al.  Taxonomic composition and photosynthetic characteristics of the biological soil crusts covering sand dunes in the western Negev Desert , 1992 .

[12]  Y. Le Bissonnais,et al.  Aggregate stability and assessment of soil crustability and erodibility: I. Theory and methodology , 1996 .

[13]  K. Harper,et al.  Soil Properties in Relation to Cryptogamic Groundcover in Canyonlands National Park , 1977 .

[14]  J. Belnap,et al.  Soil microstructure in soils of the Colorado Plateau: the role of the cyanobacterium Microcoleus vaginatus , 1993 .

[15]  Dominique Arrouays,et al.  Organic Matter Influence on Clay Wettability and Soil Aggregate Stability , 2000 .

[16]  Jayne Belnap,et al.  DISTURBANCE OF BIOLOGICAL SOIL CRUSTS: IMPACTS ON POTENTIAL WIND ERODIBILITY OF SANDY DESERT SOILS IN SOUTHEASTERN UTAH , 1997 .

[17]  J. Dobrowolski,et al.  Microphytic Crust Influence on Interrill Erosion and Infiltration Capacity , 1995 .

[18]  A. Danin,et al.  The role of cyanobacteria in stabilization of sand dunes in Southern Israel , 1989 .

[19]  Christian Défarge,et al.  Nitrogen fixation by microbial crusts from desiccated Sahelian soils (Niger) , 2001 .

[20]  B. A. Stewart,et al.  Advances in Soil Science , 1986, Advances in Soil Science.

[21]  D. Eldridge,et al.  Assessment of sediment yield by splash erosion on a semi-arid soil with varying cryptogam cover , 1994 .

[22]  S. O. Link,et al.  Acetylene reduction by cryptogamic crusts from a blackbrush community as related to resaturation and dehydration , 1992 .

[23]  Paul T. Tueller,et al.  Vegetation science applications for rangeland analysis and management , 1988, Handbook of vegetation science.

[24]  D. H. Yaalon,et al.  Two Causes for Runoff Initiation on Microbiotic Crusts: Hydrophobicity and Pore Clogging , 1999 .

[25]  J. Oades,et al.  Organic Matter in Water-stable Aggregates , 2003 .

[26]  Y. Bissonnais,et al.  Seal Formation, Runoff, and Interrill Erosion from Seventeen California Soils , 1993 .

[27]  Francisco L. Pérez,et al.  Microbiotic crusts in the high equatorial Andes, and their influence on paramo soils , 1997 .

[28]  P. Kinnell,et al.  Assessment of erosion rates from microphyte-dominated calcareous soils under rain-impacted flow , 1997 .

[29]  J. Tisdall,et al.  Organic matter and water‐stable aggregates in soils , 1982 .

[30]  P. Groffman,et al.  Nitrogen fixation in macro- and microphytic patches in the Negev desert , 1998 .

[31]  L. Stal.  Physiological ecology of cyanobacteria in microbial mats and other communities. , 1995, The New phytologist.

[32]  N. West,et al.  Structure and Function of Microphytic Soil Crusts in Wildland Ecosystems of Arid to Semi-arid Regions , 1990 .

[33]  J. Current,et al.  Theory and methodology , 1991 .

[34]  C. Valentin,et al.  Micromorphology of microbiotic crusts from Niger soils : influence on soil-water dynamics , 1998 .

[35]  R. Bond,et al.  The influence of the microflora on the physical properties of soils. I. Effects associated with filamentous algae and fungi , 1964 .