The occurrence of triterpenoids from Euphorbia gummifera inside the fairy circles of Garub in the southern Namibian pro-desert

Meyer, J.J.M.; Sénejoux, François; Heyman, Heino M.; Meyer, Nicole L.; Meyer, Marion

doi:10.1016/j.sajb.2015.01.019

Cited by 13 publications

(30 citation statements)

References 23 publications

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“…While many hypotheses have been proposed in attempts to explain the origin of Namib Desert fairy circles (2,4,8,10,11,(13)(14)(15), none take into account the presence of fairy circles in both the gravel plain and dune environments and the differences between them. Considering that almost all FC studies have focused exclusively on dune FCs, we compared microbial communities in dune and gravel plain FCs.…”

Section: Discussionmentioning

confidence: 99%

“…15 Fig. 5c), suggesting that differential assembly processes occur for fungal communities in each of the Namib Desert soil environments studied.…”

Section: Properties Of Namib Desert Soilsmentioning

confidence: 95%

“…Other published hypotheses implicate localized radioactivity hot spots (2), natural gas seepages (8), and the release of allelopathic compounds by dead Euphorbia damarana plants (5, 15). However, all previous studies testing these hypotheses have focused solely on FCs located in Namib Desert dunes (2,4,8,10,14,15), whereas FCs also occur, albeit more sparsely, in Namib Desert gravel plains (16). The latter distribution contradicts several of the extant hypotheses.…”

Section: Importancementioning

confidence: 99%

“…During times of drought, competition between plants for nutrients and water resources leads to the formation of barren patches (14), which in turn act as water traps, utilized by the peripheral grasses through extensive root systems and soil-water diffusion (13). Other published hypotheses implicate localized radioactivity hot spots (2), natural gas seepages (8), and the release of allelopathic compounds by dead Euphorbia damarana plants (5,15). However, all previous studies testing these hypotheses have focused solely on FCs located in Namib Desert dunes (2,4,8,10,14,15), whereas FCs also occur, albeit more sparsely, in Namib Desert gravel plains (16).…”

Section: Importancementioning

confidence: 99%

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Unique Microbial Phylotypes in Namib Desert Dune and Gravel Plain Fairy Circle Soils

Walt

Johnson

Cowan

et al. 2016

Appl Environ Microbiol

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Fairy circles (FCs) are barren circular patches of soil surrounded by grass species. Their origin is poorly understood. FCs feature in both the gravel plains and the dune fields of the Namib Desert. While a substantial number of hypotheses to explain the origin and/or maintenance of fairy circles have been presented, none are completely consistent with either their properties or their distribution. In this study, we investigated the hypothesis that FC formation in dunes and gravel plains is due to microbial phytopathogenesis. Surface soils from five gravel plain and five dune FCs, together with control soil samples, were analyzed using high-throughput sequencing of bacterial/archaeal (16S rRNA gene) and fungal (internal transcribed spacer [ITS] region) phylogenetic markers. Our analyses showed that gravel plain and dune FC microbial communities are phylogenetically distinct and that FC communities differ from those of adjacent vegetated soils. Furthermore, various soil physicochemical properties, particularly the pH, the Ca, P, Na, and SO 4 contents, the soil particle size, and the percentage of carbon, significantly influenced the compositions of dune and gravel plain FC microbial communities, but none were found to segregate FC and vegetated soil communities. Nevertheless, 9 bacterial, 1 archaeal, and 57 fungal phylotypes were identified as FC specific, since they were present within the gravel plain and dune FC soils only, not in the vegetated soils. Some of these FC-specific phylotypes were assigned to taxa known to harbor phytopathogenic microorganisms. This suggests that these FC-specific microbial taxa may be involved in the formation and/or maintenance of Namib Desert FCs. IMPORTANCEFairy circles (FCs) are mysterious barren circular patches of soil found within a grass matrix in the dune fields and gravel plains of the Namib Desert. Various hypotheses attempting to explain this phenomenon have been proposed. To date, however, none have been successful in fully explaining the etiology of FCs, particularly since gravel plain FCs have been largely ignored. In this study, we investigated the hypothesis that microorganisms could be involved in the FC phenomenon through phytopathogenesis. We show that the microbial communities in FC and control vegetated soil samples were significantly different. Furthermore, we detected 67 FC-specific microbial phylotypes, i.e., phylotypes present solely in both gravel plain and dune FC soils, some of which were closely related to known phytopathogens. Our results, therefore, demonstrate that microorganisms may play a role in the formation and/or maintenance of Namib Desert FCs, possibly via phytopathogenic activities. (1, 2). Common in the Namib Desert, and recently observed in the Australian outback (3), FCs are limited to arid areas that receive between 50 and 100 mm precipitation per annum. FCs are nonpermanent; they typically appear, enlarge, and disappear, with an estimated life span ranging from 22 to 60 years (4, 5).Although FCs were first reported in the 1970...

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Section: Discussionmentioning

confidence: 99%

“…15 Fig. 5c), suggesting that differential assembly processes occur for fungal communities in each of the Namib Desert soil environments studied.…”

Section: Properties Of Namib Desert Soilsmentioning

confidence: 95%

Section: Importancementioning

confidence: 99%

Section: Importancementioning

confidence: 99%

See 2 more Smart Citations

Unique Microbial Phylotypes in Namib Desert Dune and Gravel Plain Fairy Circle Soils

Walt

Johnson

Cowan

et al. 2016

Appl Environ Microbiol

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“…, b), and plant toxicity (Meyer et al. ) have investigated these mysterious FCs. With such varying disciplines and approaches, the origin of FCs is still unclear.…”

Section: Introductionmentioning

confidence: 99%

A multi‐scale study of Australian fairy circles using soil excavations and drone‐based image analysis

et al. 2019

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Fairy circles (FCs) are extremely ordered round patches of bare soil within arid grasslands of southwestern Africa and northwestern Australia. Their origin is disputed because biotic factors such as insects or abiotic factors such as edaphic and eco‐hydrological feedback mechanisms have been suggested to be causal. In this research, we used a multi‐scale approach to shed light on the origin of Australian FCs. At a local scale, we investigated the potential cause of FCs using analyses of soil compaction and texture within FCs, the surrounding matrix vegetation, and in nearby large bare‐soil areas. We found that soil hardness and clay content were similarly higher inside the FCs and in the large bare‐soil areas. When compared to the matrix soils with protective grass cover, the 2.6–2.8 times higher clay content in FCs and large bare‐soil areas is likely sourced via multiple abiotic weathering processes. Intense rainfall events, particle dispersion, surface heat, evaporation, and mechanical crust building inhibit plant growth in both areas. At the landscape scale, a systematic survey of 154 soil excavations within FCs was undertaken to evaluate the presence of pavement termitaria that could inhibit plant growth. We show that in up to 100% and most of the excavations per plot, no hard pavement termitaria were present in the FCs. This fact is substantiated by the observation that small, newly forming FCs are initiated on soft sand without evidence of termite activity. At the regional scale, we investigated the spatial properties of FCs and common termite‐created gaps in Western Australia, using spatially explicit statistics. We mapped three 25‐ha FC plots with a drone and compared them with three aerial images of typical vegetation gaps created by harvester and spinifex termites. We demonstrate that the small diameters, the lower ordering, and the heterogeneous patterns of these common termite gaps strongly differ from the unique spatial signature of FCs. Our multi‐scale approach emphasizes that FCs are not trivial termite gaps and that partial correlation with termites at some sites does not imply causation. Instead, we highlight the need to study the edaphic and eco‐hydrological drivers of vegetation‐pattern formation in water‐limited environments.

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Unusual Namibian fairy circle patterns in heterogeneous and atypical environments

Getzin

Yizhaq

2019

Journal of Arid Environments

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The occurrence of triterpenoids from Euphorbia gummifera inside the fairy circles of Garub in the southern Namibian pro-desert

Cited by 13 publications

References 23 publications

Unique Microbial Phylotypes in Namib Desert Dune and Gravel Plain Fairy Circle Soils

Unique Microbial Phylotypes in Namib Desert Dune and Gravel Plain Fairy Circle Soils

A multi‐scale study of Australian fairy circles using soil excavations and drone‐based image analysis

Unusual Namibian fairy circle patterns in heterogeneous and atypical environments

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