Abstract
Heterogeneity in root-zone temperature both vertically and horizontally may contribute to the uneven vegetative and reproductive growth often observed across vineyards. An experiment was designed to assess whether the warmed half of a grapevine root zone could compensate for the cooled half in terms of vegetative growth and reproductive development. We divided the root system of potted Shiraz grapevines bilaterally and applied either a cool or a warm treatment to each half from budburst to fruit set. Shoot growth and inflorescence development were monitored over the season. Simultaneous cooling and warming of parts of the root system decreased shoot elongation, leaf emergence and leaf expansion below that of plants with a fully warmed root zone, but not to the same extent as those with a fully cooled root zone. Inflorescence rachis length, flower number and berry number after fertilization were smaller only in those vines exposed to fully cooled root zones. After terminating the treatments, berry enlargement and the onset of veraison were slowed in those vines that had been exposed to complete or partial root-zone cooling. Grapevines exposed to partial root-zone cooling were thus delayed in vegetative and reproductive development, but the inhibition was greater in those plants whose entire root system had been cooled.
Highlights
Plant roots can be exposed to a range of temperatures because root systems can explore large volumes of soil over great depths and distances
Using a split-pot method, we examined grapevine response to root zones 5 8C above and below the average vineyard soil temperature found at a depth of 15 cm in a warm grape-growing region of Australia
Similar to grapevines exposed to partial root-zone drying (PRD) (Dry et al 2000), a partial inhibition of shoot elongation under partial rootzone cooling may be a direct effect of decreased cytokinin levels
Summary
Plant roots can be exposed to a range of temperatures because root systems can explore large volumes of soil over great depths and distances. Once leaves become net exporters of carbon, cool root zones can have a direct effect on vegetative and reproductive growth by lowering net assimilation rates. This is a consequence of either alterations in photosynthetic reactions
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