Browsing by Author "Valentine, A. J."

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    Mycorrhizal-associated nutrient dynamics in key ecosystems and their response to a changing environment
    (Guizhou Academy of Agricultural Sciences, 2016-04-27) Heng, G.; Hyde, K. D.; Jianchu, X.; Valentine, A. J.; Mortimer, P. E.
    Environmental change incorporates the full range of natural and anthropogenic changes currently affecting the planet. These changes include fluxes within the carbon and nutrient cycles, resulting in disturbances at the ecosystem level, which may affect plant species distribution as well as soil systems. Mycorrhizal fungi form an important link between plants and soil systems, functioning at the root-soil interface, contributing towards nutrient cycling processes, and, ultimately, influencing the plant composition of terrestrial ecosystems. A more integrated and systemic understanding of these mycorrhizal associations can help us predict, and thus mitigate, the impact of environmental change on biotic communities. In this review we present the latest research on how the carbon, nitrogen and phosphorus dynamics of arbuscular and ectomycorrhiza vary in their representative ecosystems. Furthermore, we also demonstrate how they respond to environmental change, which relates to both biotic and abiotic factors, such as CO2-enrichment, nitrogen-depletion, and the impact of invasive species. This review provides insight on the role of mycorrhiza in offsetting the negative effects of environmental change.
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    The occurrence and infectivity of arbuscular mycorrhizal fungi in inoculated and uninoculated rhizosphere soils of two-year-old commercial grapevines
    (South African Society for Enology and Viticulture, 2005) Meyer, A. H.; Botha, A.; Valentine, A. J.; Archer, E.; Louw, P. J. E.
    Arbuscular mycorrhizal (AM) fungal populations present in the rhizosphere of vine roots in the vineyards of a commercial farm in the Stellenbosch Region were investigated using microscopic analyses. AM root colonisation levels of between 70% and 90% were found in both grapevine roots that were previously artificially inoculated with commercial AM inocula, and in uninoculated (control) grapevine roots. The AM fungal isolates in the rhizosphere soil, identified using morphological criteria, belonged to the genera Acaulospora, Gigaspora, Glomus, Sclerocystis and Scutellospora. The majority of species found was not present in the commercial inocula and was either indigenous to the vineyard or originated from the nursery where the vines were obtained. Isolates of Glomus and Acaulospora appeared to be the most abundant. The AM fungal species occurred at a soil phosphorus (P) concentration of up to 80 mg/kg P and a soil pH (KCl) that ranged between 5.63 and 6.10. Total spore counts ranged between 1 000 and 3 779 spores/100 g dry soil. In accordance with literature, lower spore concentrations were recorded for the heavier soil types with no cover crop system, compared with the sandy soil type on which cover crops were sown annually.
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    Young grapevine response and root colonisation following inoculation with arbuscular mycorrhizal fungi
    (South African Society for Enology and Viticulture, 2004) Meyer, A. H.; Valentine, A. J.; Botha, A.; Archer, E.; Louw, P. J. E.
    The host plant response following inoculation with commercially available arbuscular mycorrhizal (AM) fungi was determined in young grapevines under field conditions which would prevail on a typical farm. Measurements regarding growth improvement, nutrition and water relations were made in a field trial carried out on a commercial farm in the Stellenbosch region. Merlot noir grafted onto 101-14 Mgt and 110 Richter (110 R) in a Westleigh soil form and 99 Richter (99 R) in a Fernwood soil form was planted in December 1998. Vine roots were inoculated during planting with Biocult, Vaminoc and Glomus sp. 1054. Inoculation generally had little effect on xylem sap and leaf nutrient concentrations, water relations or growth responses. This was mainly ascribed to indigenous AM fungi, which seemed to have masked the effects of inoculation. A high soil P concentration was also implicated as a possible contributing factor to the general lack of grapevine response to AM inoculation.