Assessing the vegetation and soil microbial ecology of renosterveld rangelands around Nieuwoudtville, Northern Cape Province Gabrielle Marie Solomon A thesis submitted in fulfilment of the requirements for the degree Magister Scientiae, in the Department of Biodiversity and Conservation Biology, Faculty of Natural Science, University of the Western Cape. May 2015 Supervisor: Mr. Frans M. Weitz, Department of Biodiversity and Conservation Biology, University of the Western Cape Co-supervisors: Mr. C.F. Cupido, Animal Production Institute, Agricultural Research Council Prof. W.J. Swart, Department of Plant Sciences, University of the Free State Keywords Rhizosphere, microbial ecology, plant species richness, rangelands, renosterveld, Northern Cape i Abstract The Bokkeveld Plateau, a region hosting high plant endemism, is home to two arid mountain centre renosterveld types. One, Nieuwoudtville Shale Renosterveld, has partially been transformed into croplands and pastures, with about 40 % remaining as non-contiguous fragments on privately owned land, and is used as natural rangelands for sheep grazing. The vegetation, soil chemical parameters, and rhizosphere soil microbial ecology of a dominant plant, Eriocephalus purpureus, were assessed. A combination of field sampling and recording, laboratory analyses of soil samples, and interviews were used to glean data. Data were statistically analysed using multivariate techniques. Overall plant species richness did not differ among the study sites, though plant species richness and cover of the different plant growth form categories varied among the sites. Soil chemical parameters varied among sites. Soil chemical and rhizosphere soil microbial parameters co-varied, and showed different profiles among the study sites. High cover of E. purpureus was associated with high microbial enzyme activity, while high cover of (other, non-dominant) non-succulent shrubs was associated with high bacterial functional diversity. Cover of geophytes, Asparagus capensis and perennial grass was associated with high microbial biomass. The findings indicate that E. purpureus-dominated Niewoudtville Shale Renosterveld is heterogeneous not only in terms of vegetation, but also in terms of soil chemical and microbial parameters. The results support the conservation of all fragments of remaining renosterveld, as they may serve as valuable resources of not only plant genetic material but also of soil microbial communities. ii Declaration I declare that ‘Assessing the vegetation and soil microbial ecology of renosterveld rangelands around Nieuwoudtville, Northern Cape Province’ is my own work, that it has not been submitted for any degree or examination at any other university, and that all the sources which I have used or quoted have been indicated and acknowledged by complete references. …………………………. ………………….. Gabrielle Marie Solomon Date iii Acknowledgements Without my supervisors, who provided academic, financial, and logistical support, this project would have remained an idle idea. I was fortunate to receive a Scarce Skills bursary (number 79795) from the National Research Foundation which made pursuing this project possible. I was helped in official, and un-official, ways by the following people, who unstintingly gave of their time and expertise. I call them my all-star cast: Lilburne Cyster and the laboratory of the Department of Biodiversity and Conservation Biology. Marieta Van der Rijst, ARC Biometry for statistical analyses. Igshaan Samuels, Melvin Swarts and Grant Birch for much advice and help in the field. In Nieuwoudtville, resident researchers and field-experts: Eugene Marinus and Colleen Rust (Hantam National Botanical Garden, SANBI), Simon Todd, Christy Bragg, and Mandy Schumann. And, most importantly, the farmers and their families who allowed me on their land, answered my questions and pointed out the questions I hadn’t asked. Without you there would have been no project. This is for you. iv Contents Keywords i Abstract i Declaration ii Acknowledgements iii Table of contents iv List of figures vii List of tables viii Chapter 1 General Introduction .......................................................................... 1 1.1 Background and motivation for research ............................................................................ 1 1.2 Objectives ........................................................................................................................... 3 1.2.1 Project aim................................................................................................................. 3 1.2.2 Targeted outcomes ..................................................................................................... 3 1.2.3 Research questions .................................................................................................... 3 1.3 Thesis structure ................................................................................................................... 4 Chapter 2 Literature review ................................................................................. 6 2.1 Drylands ................................................................................................................................. 6 2.2 Agro-ecosystems, biodiversity and ecosystem services........................................................ 10 2.3 Rangeland ecology ............................................................................................................... 15 2.4 Renosterveld ......................................................................................................................... 23 2.5 Soil ecology .......................................................................................................................... 30 2.6 Links between vegetation and soil biota ............................................................................... 38 Chapter 3 Study area - The Bokkeveld Plateau and Nieuwoudtville ............. 45 v 3.1 Study area ............................................................................................................................. 45 3.2 Study sites ................................................................ ............................................................ 52 3.3 Stocking data ................................................................ ........................................................ 53 Chapter 4 Renosterveld rangeland vegetation cover and diversity ................ 57 4.1 Introduction .......................................................................................................................... 57 4.2 Materials and methods .......................................................................................................... 59 4.2.1 Study area ..................................................................................................................... 59 4.2.2 Rapid Renosterveld Assessment Method ...................................................................... 60 4.2.2.1 Plant surveys ........................................................................................................................ 60 4.2.2.2 Geographical data ................................................................................................................ 61 4.2.2.3 Farmer/land manager interviews .......................................................................................... 61 4.2.3 Statistical analyses ........................................................................................................ 62 4.3 Results .................................................................................................................................. 62 4.4 Discussion ............................................................................................................................ 66 4.5 Conclusion ............................................................................................................................ 75 Chapter 5 Rhizosphere ecology of Eriocephalus purpureus, a dominant shrub in renosterveld rangelands ................................................................................. 77 5.1 Introduction .......................................................................................................................... 77 5.2 Materials and methods .......................................................................................................... 80 5.2.1 Study area ..................................................................................................................... 80 5.2.2 Soil sampling ................................................................................................................ 80 5.2.2.1 Soil chemical sampling ........................................................................................................ 80 5.2.2.2 Soil microbial sampling, dry season .................................................................................... 81 5.2.2.3 Soil microbial sampling, rainy season .................................................................................. 81 5.2.3 Soil chemical analyses .................................................................................................. 82 5.2.3.1 Soil digestion ....................................................................................................................... 82 5.2.3.2 Cation analyses ...................................................................................................................