Mycorrhiza re-establishment on post-mined rehabilitated areas of the Brand se Baai Succulent Karoo vegetation.
Parts of the West Coast Strandveld and adjacent Succulent Karoo on the arid coast of Namakwaland in the Western Cape of South Africa are subject to surface mining. An understanding of mycorrhizal association of plants in the natural vegetation of this area could contribute to the improvement of post-mining re-vegetation of the area. This study investigated mycorrhizal association of plants in the West Coast Strandveld, and compared mycorrhizal infection rates of soils taken from natural vegetation to soils from post-mined rehabilitated vegetations. The study was divided into two components. In the first component a pot experiment was conducted in the greenhouse to assess vesicular-arbuscular mycorrhiza (AM) infectivity of post-mined rehabilitated areas of Brand se Baai in Namakwa Sands mining areas. Rehabilitated areas used in this study included sites that has been strip mined for heavy minerals and then progressively backfilled with sub-soil sand remaining after mineral extraction (tailings), topsoil and translocated plants in an effort to restore the structure and functional aspects of the mined site to its original (pre-mining) ecosystem. Rehabilitated sites 1 assessed in this study included sites backfilled with: tailings + translocated plants (TP); tailing + topsoil + translocated plants (TSP) and tailings + topsoil only (TS). Natural sites (N) were also assessed to serve as reference points. AM infection was evaluated as percent root colonization on wheat planted as bioassay on sterilised sand and inoculum from rehabilitated sites in the ratio of 3:1 respectively. Results of this study component showed that mycorrhiza infectivity of rehabilitated soils was high on TSP and TS because mining disturbance has been remedied by topsoil with or without translocated plant replacement. The structural and chemical components of topsoil used as rehabilitation material favoured re-establishment of microbial activities. Infectivity was however low on soils rehabilitated with tailings and translocated plants (TP) because this treatment lacked topsoil which is a major source of infective mycorrhizal propagules. Infectivity was also low in soils from undisturbed sites (N) probably high phosphorus concentration or presence of perennial vegetation led to low mycorrhiza infection. Results showed that there was no significant effect of mycorrhiza on plant growth rate, nutrient uptake or carbon cost of mycorrhizal plants when related to non-mycorrhizal plants, instead the biomass production and nutrient contents of plants were determined by chemical properties of treatment soils. The second component of the study investigated presence of mycorrhiza on randomly selected common indigenous species of Aizoaceae, Asparagaceae, Asteraceae, Chenopodiaceae, Fabaceae, Lamiaceae, Mesembryanthemaceae, Restionaceae, families growing on unmined areas of the study site. Total mycorrhiza infection was recorded on 85% of the assessed species with percent infection level ranging from 8% in Atriplex lindleyi and Drosanthemum hispidum to 98% in Salvia lanceolata. Functional mycorrhizal association with arbuscule structures were however only observed on 15% of all species assessed. Low arbuscules infection observed in indigenous species assessed in this study could be associated with the timing of mycorrhiza infection assessment and root competition in the soil. There was no infection observed on four species belonging to Chenopodiaceae, Zygophyllaceae, Sterculiaceae, and Asteraceae families, which represented 15% of all species assessed. Most species belonging to Chenopodiaceae and Zygophyllaceae have been reported as non-mycorrhizal in other studies, absence of mycorrhiza on the remaining three families species observed in this study require further confirmation.