Meyer, Marion2025-12-082025-12-082019-042018-07*A2019http://hdl.handle.net/2263/107107Dissertation (MSc (Medical Plan Science))--University of Pretoria, 2018.Circular barren patches, also known as fairy circles (FCs), occur throughout Namibia, devoid of vegetation and surrounded by a matrix of grasses. Several hypotheses regarding the origin and maintenance of FCs have been proposed, none widely accepted. Soil physical properties and chemical constituents were investigated to determine whether differences in properties are present and to what extent they differ. Results obtained from physical property analyses indicated greater hydrophobicity in soil collected from FCs than matrix soil as well as a higher infiltration rate. Extracts prepared from FCs and matrix soil, and from locations where Euphorbia damarana are decomposing (DP), were analysed by GC-MS and NMR to determine the cause of the increased infiltration rate and the FC soil’s hydrophobicity. To identify discriminative signals from GC-MS and NMR data, PCA-plots, OPLS-plots, and S-plots were created to aid compound identification. The PCA-plot created from GC-MS results displayed clear discrimination, segregating matrix (M) sample observations from DP and FC sample observations, simultaneously grouping DP and FC observations. This indicates greater similarity between DP and FC soil, than between DP and M or FC and M observations. Specific compounds were present in both FC and DP soil samples and not in matrix soil. NMR based metabolomics indicated similar concentrations of ester, phenol, alkene and aromatic functional groups within FC and DP soil, while differences between FC and matrix soil were greater. From these results, it is deduced that there’s a definite difference in physical properties and chemical constituents of FC and matrix soil. Causes of these differences can be concluded to be initiated by decomposing Euphorbiaceae species, as indicated by specific compounds such as 1-(4-acetamidoanilino)-3,7-dimethylbenzo[4,5]imidazo[1,2-a]pyridine-4-carbonitrile present in FC and DP soil samples, previously identified in a variety of plants’ non-polar latex. It is thus proposed that the formation of FCs in northern Namibia are indirectly caused by decomposing E. damarana, which alters the soil physical properties at the decomposition site, increasing hydrophobicity and infiltration rates in soil upon decomposition which It is thus proposed that the formation of FCs in northern Namibia are indirectly caused by decomposing E. damarana, which alters the soil physical properties at the decomposition site, increasing hydrophobicity and infiltration rates in soil upon decomposition which decreases the amount of plant available soil water content and leads to the formation of barren patches, devoid of any vegetation, in the same circular shape as the E. damarana plants which once grew at that location. This mechanism of formation is proposed as the most likely cause in other areas of Namibia, where succulent Euphorbia spp. are present.en© 2024 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.UCTDSustainable Development Goals (SDGs)Soil hydrophobicityEuphorbiaFairy CirclesNamibiaEuphurternitrileDissertationu11247152