The many roles of water in grape vine growth and development

Water is a key player in the development and growth of the grape vine.  In this post I highlight its many roles.

Soil Component

Soil is comprised of air, water, mineral particles (a mix of clay, silt, and sand), organic matter (decomposing plant material), and organisms (bacteria, algae, fungi, earthworms, insects, etc.).  Half of the overall soil content is pore space, a 50-50 mix of air and water. Organic matter is, in addition, a reservoir of nutrients and water.

Soil-based nutrients are resident either in the soil solution (water and dissolved minerals in the soil pores) or in the soil matrix (mineral particles and organic matter).

Raw Material for Photosynthesis

Along with carbon dioxide and sunlight, water is a key raw material in photosynthesis, the process by which the grape vine produces its needed energy.  In photosynthesis the hydrogen and oxygen molecules are split apart by light energy and the hydrogen combines with the carbon, leaving the oxygen as the waste matter in the process.

Chloroplasts, the sub-cellular structures within which the process occurs, is found primarily in the leaf of the vine but is also contained in the stems and reproductive organs. With the largest surface area of the vine, leaves are its most significant producers of carbohydrates.

Photosynthesis can be slowed or stopped in the event of a water deficit.  Such slowing or stoppage will have a negative effect on vine vigor.

Transport Vehicle

Through the process of transpiration, water serves as a vehicle for moving material into, within, and out of the vine plant.  Water enters a vineyard through precipitation or irrigation and that water either runs off, flows to levels beyond which it can be accessed by the vine plant, or remains in the rooting zone where it is available for the plant's use. The plant uses water as an internal distribution vehicle (in addition to other functions) and facilitates this by expelling water through pores (stomata) in the leaves.  As water is transpired from the leaves, replacement water is drawn in at the roots.

Source: talktalk.co.uk

Water attracted to the vine root by transpiration moves undiluted nutrients to the root surface (bulk flow) but also carries dissolved nutrients into the roots as a part of its transit. Nitrogen is the nutrient most frequently acquired by the roots in this manner.  Nutrients are moved up from the roots to needed areas through the phloem by transpiration.

Photosynthates, the products of photosynthesis, are used to fuel vine growth and maintain plant functions and are allocated to various parts of the vine based on need.  A net producer of photosynthates is referred to as a "source" while a net consumer is called a "sink."  According to Lebon et al., there are two phases to the annual cycle of grapevine physiology.  In Phase 1 starch is mobilized from the woody parts of the plant to supply the annual organs with carbohydrates to sustain their growth.  In this case, the majority of food material is first sent to actively growing areas (shoot tips, developing fruit, root tips). Phase 2 is initiated when photosynthate production exceeds the needs of the vine. The excess production is routed to the woody (roots, trunks) parts of the vine for storage.  The berry cluster is the main sink for photosynthates during ripening while the woody tissues are the primary sinks post-harvest.  The process of moving photosynthates between sources and sinks through the xylem is called translocation and is enabled by the previously described transpiration process.

Solvent

Nutrients and sucrose are in solution for carriage through the vine.

Air Conditioner

Ninety percent of the water drawn into the plants through the roots is transpired with the remainder used in photosynthesis and cell growth.  The expiry of this much water through the leaves serves a cooling function both for the plant and humans in its vicinity.

Stiffening Agent

Water within the plant cells exerts an outward pressure (turgor pressure) which, like the air in a ballon, serves to give form to the non-wood parts of the plant pressure.  Turgidity is important in helping the plant compete for light energy as well as providing the force which pushes the roots through the soil.

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In vine growth and development, water is the ultimate multi-tasker.

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