Browsing by Author "Theron, Hanle"

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    Impact of changing climatic factors on physiological and vegetative growth parameters of young grafted grapevines
    (Stellenbosch : Stellenbosch University, 2020-03) Theron, Hanle; Hunter, Jacobus Johannes; Stellenbosch University. Faculty of AgriSciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: The establishment of a new vineyard is expensive and a high survival rate of the young vines is important to prevent re-planting and ensure that the vines come into full production as early as possible. The initial growth of the young vines is very sensitive to the environment and this has a direct effect on the performance and longevity of the vineyard. It is expected that future climatic scenarios will put additional strain on young vine growth. In this study the physiological functioning and growth of the vine during the first few months after planting were measured in simulated future conditions. Newly potted vines were investigated during their first 12 weeks of growth in a glasshouse. The same rootstock (101-14 Mgt) was used throughout with Shiraz (SH 470) and Merlot noir (MO 348) as scion cultivars. The treatment factors comprised three climatic variables with two levels each: temperature, CO2 and water. Measurements were taken at 4, 8 and 12 weeks after planting. The physiological activity, vegetative growth response, mineral uptake and translocation as well as the synthesis and allocation of metabolites to the various vine parts were investigated. High CO2 levels increased the photosynthetic activity of the young vines and improved the efficiency of water and nitrogen use, provided that water stress did not increase to severe levels. The negative effect of water deficit on physiological activity was to a certain extent mitigated by elevated CO2. Inherent phenology-linked patterns in the grapevine pertaining to shoot and root growth, nutrient uptake, metabolite synthesis, translocation and accumulation, and reserve storage were similar in the various treatments. Merlot performance and growth seemed more sensitive to water deficit than Shiraz, but Merlot was more stimulated by elevated CO2 levels. The effects of the treatment factors on macro- and micro-nutrient levels in vine tissues depended on the particular nutrient, the tissue type concerned, as well as the scion/rootstock genotype. Stronger vegetative growth was associated with lower nutrient concentrations in the tissues, but a similar (or higher) content. The results showed that the choice of the scion-rootstock combination per terroir would become increasingly important. Soil preparation depth should be maximised to enhance depth penetration of roots and improve the buffer capacity of the vines against unfavourable conditions. Irrigation strategies for young vines should be aimed at increased root growth and distribution. Any cultivation should be done with circumspection in young vineyards and restrictive growth environments to avoid competition for water and nutrients. Higher CO2 levels increased (and sustained) physiological activity and metabolism and induced stronger vegetative growth. These positive effects were further enhanced by water supply. It is suggested that irrigation and fertilisation programmes be re-evaluated, especially for young vines in the context of a changing climate where water would become less available and vegetative growth would increase as result of a higher atmospheric CO2.