Microorganisms in the Namib Desert
Microorganisms include viruses, prokaryotes (bacteria and archaea), and microscopic single- and multi-cellular eukaryotes including fungi, algae and protozoa. Some would also include micro-animals, such as nematodes and microarthropods, although these are not studied by typical microbiologists.
Despite the extreme aridity of the Namib, a diverse array of microorganisms have been found across the landscape. All over the desert, hypolithic cyanobacteria and other algae colonize the underside and interior of translucent rocks such as quartz, giving the rocks an obvious greenish tint1. The rocks protect the cyanobacteria from the full force of the sun’s radiation but still allow enough light through for them to perform photosynthesis – and the soil helps trap water, especially in the zone immediately around the algae, which cement the soil.
A diverse array of lichens (symbioses of fungi, algae and cyanobacteria), also colonize rocks and soil substrates in the Namib2,3. Lichens and soil crusts18 are important primary producers in the nearly barren gravel plains of the fog belt where rain is very infrequent. Here they serve as critical regulators of temperature, soil moisture and stability of the soil.
Mycorrhizal fungi are associated with the roots of many plants in the Namib, including grasses on the gravel plains and in the dunes, as well as with Welwitschia mirabilis4-7. Above ground, fungal pathogens, particularly members of the black Aspergillus group, severely limit seed recruitment of this iconic Namib Desert plant 8-10. In addition, six large macro-fungi (all mushroom-related Basidiomycetes) decompose buried plant material and dung in the dunes and gravel plains in response to minimal rains (10-20 mm)11.
Ephemeral rivers such as the Kuiseb are also sites of high fungal and myxomycete diversity (54 species documented to date, including three myxomyetes) and long-term subterranean decomposition after flooding12,13. Soil microarthropods, including mites and collembolans, have also been found in all three habitats, in close association with perennial vegetation14. In addition, scattered aquatic habitats, including saline and mineral springs, host a fascinating array of microbes and other organisms15-17. These were almost completely unstudied until recently.
Studies done in the 1970s and early 1980s suggested that microbial communities in the Namib Desert were of minimal importance in desert foodwebs18,19. Recent studies
suggest that fungal communities in the Namib Desert may be activated by rain events of only 10mm, to decomposer buried material20. Molecular tools are now being deployed to fully characterize the diverse communities of prokaryotes and fungi that occur in the Namib Desert gravel plains, dunes and ephemeral rivers, and respond to these moisture pulses1,21,22.
Current investigations of microorganisms at Gobabeb:
1. Soil prokaryote and potentially fungal communities associated with grasses on the gravel plains
2. Bacteriophage and other viral and alga and bacterial diversity in dune, gravel plain, salt spring and hypolithic habitats.
3. Fungal decomposition of senescent grasses in response to fog
4. Fungal pathogen diversity of Welwitschia mirabilis
5. The diversity and functioning of subterranean fungal decomposers in the Namib dune field
There is obviously still much to be discovered about microorganisms in the Namib, and future research on this theme is rich with possibilities. An important ultimate goal of this work should be to more accurately assess the role that microorganisms play in Namib Desert ecosystem processes, as this information is essential for accurate modeling of soil carbon flows, and the effects of climate change and mineral exploration on Namib Desert biota.
1. Stomeo, F., A. Valverde, S.B. Pointing, C.P. McKay, K.A. Warren-Rhodes, M.I. Tuffin, M.K. Seely, & D.A. Cowan. 2013. Hypolithic and soil microbial community assembly along an aridity gradient in the Namib Desert. Extremophiles 17:329-337.
2. Lalley, J.S., H.A.Viles, N. Copeman and C. Cowley. 2006. The influence of multi-scale environmental variables on the distribution of terricolous lichens in a fog desert. Journal of Vegetation Science 17: 831-838
3. Wirth, V. 2010. Lichens of the Namib Desert – A guide to their identification. Klaus Hess Verlag/Publishers: Göttingen. 96 pages.
4. Jacobson K.M., P.J. Jacobson & O.K. Miller Jr. 1993. The mycorrhizal status of Welwitschia mirabilis. Mycorrhiza 3:13-17.
5. Jacobson K.M. 1997. Moisture and substrate stability determine VA-mycorrhizal fungal community distribution and structure in an arid grassland. Journal of Arid Environments 35:59-76.
6. Stutz JC; R. Copeman, C.A. Martin; J.B. Morton 2000. Patterns of species composition and distribution of arbuscular mycorrhizal fungi in arid regions of southwestern North America and Namibia, Africa. Canadian Journal of Botany 78(2):237-245.
7. Uhlmann, E., C. Gorke, A. Petersen & F. Oberwinkler 2006. Arbuscular mycorrhizae from arid parts of Namibia. Journal of Arid Environments 64(2):221-237.
8. Cooper-Driver GAC, C Wagner & H Kolberg. 2000. Patterns of Aspergillus niger var. phoenicis (Corda) Al-Musallam infection in Namibian populations of Welwitschia mirabilis Hook.f. Journal of Arid Environments 46: 181-98.
9. Pekarek E, K Jacobson & A Donovan, 2006. High levels of genetic variation exist in Aspergillus niger populations infecting Welwitschia mirabilis Hook. Journal of Heredity 97, 270-278.
10. Whitaker,C., P. Berjak,, H. Kolberg, NW Pammenter. 2004. Responses to various manipulations, and storage potential, of seeds of the unique desert gymnosperm,Welwitschia mirabilis Hook. fil. South African Journal of Botany 70(4): 622–630
11. Jacobson, K.M. 1996. Macrofungal ecology in the Namib Desert: a fruitful or futile study? McIlvainea 12(2):21-32.
12. Jacobson, K.M., P.J. Jacobson, O.K. Miller Jr. 1999. The autecology of Battarrea stevenii (Liboshitz) Fr. in ephemeral rivers of southwestern Africa. Mycological Research 103: 9-17.
13. Jacobson, P.J. & K.M. Jacobson. 2012. Hydrologic controls of physical and ecological processes in Namib Desert ephemeral rivers: implications for conservation and management. Journal of Arid Environments 93: 1-14.
14. Andre, H.M., M.-I. Noti, K.M. Jacobson. 1998. The soil microarthropods of the Namib Desert: a patchy mosaic. Journal of African Zoology 111:499-517.
15. Day, J.A. 1990. Environmental correlates of aquatic faunal distribution in the Namib Desert. In: Seely, M.K., ed., Namib Ecology: 25 years of Namib research, pp. 99-107. Transvaal Museum Monograph No. 7, Transvaal Museum, Pretoria.
16. Brain, C.K. and Adams, C.G. 1984. Observations on Foraminifera living in a Namib spring. South African Journal of Science 80: 194.
17. Brain, C.K. and Koste, W. 1993. Rotifers of the genus Proales from saline springs in the Namib desert, with the description of a new species. Hydrobiologia 255/256: 449-454.
18. le Roux, G.J. 1970. The microbiology of sand-dune ecosystems in the Namib Desert. M.Sc. Thesis, University of Stellenbosch, Stellenbosch.
19. Seely, M.K. & G.N. Louw. 1980. First approximation of the effects of rainfall on the ecology and energetic of a Namib Desert ecosystem. Journal of Arid Environments 3:25-54.
20. Jacobson, K.M. & P.J. Jacobson. 1998. Rainfall regulates decomposition of buried cellulose in the Namib Desert. Journal of Arid Environments 38(4):571-83.
21. Budel, B., T. Darienko, K. Deutschewitz, S. Dojani, T. Friedl, K. Mohr, M. Salisch, W. Reisser, B. Weber. 2009. Southern African biological soil crusts are ubiquitous and highly diverse in drylands, being restricted by rainfall frequency. Soil Microbiology 57:229-247.
22. Prestel, E., S. Salamitou, M.S. DuBow. 2008. An examination of the bacteriophages and bacteria of the Namib Desert. The Journal of Microbiology 46(4):364-372.