Browsing by Author "Vardien, Waafeka"

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    Management history determines gene flow in a prominent invader
    (Nordic Society Oikos, 2013) Vardien, Waafeka; Richardson, David M.; Foxcroft, Llewellyn C.; Wilson, John R. U.; Le Roux, Johannes J.
    Invasive plants pose substantial threats to protected areas globally. Although management can limit impacts, spread and reinvasion from neighbouring areas into protected areas are a major and an ongoing problem for land managers. However, identifying the main sources of propagules and the dimensions of invasion pathways is challenging. Th is study used population genetic markers [inter simple sequence repeats (ISSRs) and amplified fragment length polymorphisms (AFLPs)] to infer the source(s) of re-colonization and dispersal patterns for a typical invader of riparian and terrestrial habitats (Lantana camara) along the Sabie-Sand catchment, one of the most important river systems flowing into and across South Africa ’ s flagship protected area, the Kruger National Park (KNP). Results indicate that populations located along the lower reaches of the Sabie and Sand tributaries harboured substantially higher genetic diversity than those in the upper Sabie catchment. Bayesian assignments indicated that the upper Sabie tributary contributed far fewer propagules than the Sand tributary to the lower Sabie River. Current invasion patterns are due to a combination of a major flood event in 2000 and differences in the degree to which the upstream reaches were managed after the flooding. The major flood of 2000 effectively cleared lantana from the riparian areas. However, whereas on-going management efforts against riparian species in the KNP have been effective, rendering the upper Sabie relatively clear of lantana, only a small part of the Sand tributary falls under jurisdiction of the KNP and has received consistent management attention. The reinvasion of the lower Sabie in the KNP was therefore almost entirely by propagules from the Sand tributary. The study highlights the important role that molecular tools can play in determining dispersal dynamics and directing invasive species management. For invasive plant species that invade both riparian habitats and landscapes away from rivers in protected areas, such as lantana, management must focus on all major sources of propagules to limit reinvasion.
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    Phosphorus mobilization and localisation in the roots and nodules of a Cape Floristic Region legume, and its impact on nitrogen fixation
    (Stellenbosch : Stellenbosch University, 2015-12) Vardien, Waafeka; Valentine, Alexander Joseph; Steenkamp, Emma; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    ENGLISH ABSTRACT: During phosphorus (P) deficiency, plants can exhibit a wide array of morphological, physiological and biochemical responses. Legume plants are vulnerable to P deficiency, because it affects their ability to fix atmospheric nitrogen (N2) via their symbiotic interaction with rhizobial bacteria. In particular, legumes from nutrient poor ecosystems, such as the fynbos in the Cape Floristic Region (CFR) would have evolved on P deficient soils and may therefore display unique modifications. Moreover, since P distribution in soils is heterogenous, even less is known about the recovery from P deficiency responses in nodules. The aim of this research was to investigate P recycling and distribution in the nodules of the fynbos legume Virgilia divaricata, during low P supply and its recovery from P deficiency. The legume species was inoculated with a locally compatible N2 fixing bacterial strain, Burkholderia, isolated from V. divaricata nodules grown in fynbos soil. Plants were grown under glasshouse conditions, using a modified Long Ashton Nutrient Solution (LANS) to simulate the low nutrient conditions of the fynbos ecosystem. Plants were subsequently analysed for growth kinetics, nutrient acquisition and distribution, nodule anatomy, P recycling and P metabolite composition. The results indicated that V. divaricata can experience P deficiency during exposure to low P supply. Under low P conditions, plants experienced lower biomass and nodule production. Although biological N2 fixation (BNF) was lower during P deficiency as compared to during conditions of optimal P supply, the nodules of plants grown under P deficient conditions had a greater BNF per nodule mass and unit P. In addition, low P nodules also showed homogenous P tissue localisation and a greater concentration of Fe. The total P level was lower in nodule tissues, and the activities of phosphohydrolases (APase, RNase and phytase) higher. In addition, there was also a possible remobilization of membrane phospholipids, in order to release additional Pi. Although V. divaricata experiences P deficiency in its biomass and P nutrition, it also has a remarkable physiological ability to recover from P deficiency during P resupply. In contrast to the observed perturbations in biomass and nutrition during P stress, the impact on the nodules was different to that of the roots. The underlying mechanisms for functional maintenance of the nodules during low P seems to be associated with an internal mechanism, related to P mobilization from organic sources, metabolic bypass mechanisms to conserve P and a re-allocation of Fe to the infected cells. The higher enzyme activity of the internal phosphohydrolases (APase, RNase and phytase) favours the liberation of cellular P for metabolic reactions and internal P turnover. This research has generated knowledge regarding the physiological impact and flexibility of mechanisms involving below-ground P recycling in legumes. It has demonstrated that a legume from a nutrient poor ecosystem, favours internal mechanisms of P recycling and conservation, in order to maintain the efficient functioning of nodules under P stress rather than improve acquisition from external sources.