Isohydric or anisohydric behaviour in grapevine…, a never-ending controversy?


In accordance to the type of stomatal response, many species have been classified as isohydric or anisohydric.
Isohydric plants are those that close their stomata when they sense a drop in soil water potential, or an
increase in the atmospheric demand. On the contrary, anisohydric plants continue to transpire even when soil
water content diminishes, because of a poor stomatal adjustment capacity. As consequence, their leaf water
potential (ΨL) falls, and the plant suffers increasing stress.
In general, grapevine is considered a water stress avoidant species, with a tight stomatal control. However,
some varieties have shown a more efficient stomatal control than others. This encouraged researchers to classify
grapevine varieties as isohydric or anisohydric. At present, this classification is under great controversy,
as many of the varieties that initially were classified under one behaviour, have shown opposite performances
under different climatic, edaphic and growth conditions. Consequently, many authors believe that this classification among grapevine varieties may not be completely clear and accurate.
Our study revises, once more, the varietal behaviour of four grapevine varieties, namely Syrah, Grenache,
Malbec and Chardonnay, under mild water stress conditions; elmo bounce house and tries to determine which behaviour confers
best stress tolerance. We intended to determine whether isohydric behaviour results in more tolerance to drought
than anisohydric behaviour, as assumed and tried to explain both types of behaviour giving attention to stomatal
conductance (gs); hydraulic conductance (kL) and vapour pressure deficit (vpd), as postulated by others.
Key words: isohydric, anisohydric, stomatal conductance, hydraulic conductance, vpd.

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