You probably know what photosynthesis is, but do you know what really happens inside the grape vine during photosynthesis and why it is so important to expose your vine to enough sunlight?

Photosynthesis is one of the most important physiological processes that take place inside the vine. During photosynthesis, the energy for the salvation of the grape vine is created. This is quite a complex process where sunlight energy, absorbed by the chloroplast inside the mesophyl cells of the vine, is assimilated into CO2 and carbohydrates (mainly sucrose). Water is needed for this whole process to activate and stay active. The following formula explains photosynthesis:

CO2 + 2n H20 + sunlight energy –> chloroplast –> (CH2O)n + O2 + n H2O

All of these carbohydrates are then transferred to the endodermic cells of the vine and transported to the all the growing parts (growing points of shoots and roots), to the reproductive parts (buds and clusters) and some stored in the stems of the vine.

Which factors influence photosynthesis?

1. Environmental factors:

Light intensity: Maximum photosynthesis in a grape vine, takes place when the sunlight intensity is around 25 000 to 30 000 lux. When the canopy of the grape vine is too dense, the sunlight cannot penetrate the canopy enough for photosynthesis to take place. That is why we find yellow leaves inside these kinds of canopies. Photosynthesis can take place from reflected sunlight as well, but the intensity of this light is normally not high enough for optimum photosynthesis. Having a to dense or compact grape vine canopy will reduce the productivity of the vine, because of reasons mentioned above. Canopy control is therefore of utmost importance when growing your grape vine. There are several ways to control canopy growth, like topping of the shoots, removing water shoots, removing (suckering of unnecessary shoots) and the spacing of short bearers. The summer treatments of a grape vine are explained in depth in “The Complete Grape Growers Guide”.

Temperature: Normal photosynthesis takes place between 0 and 60*C (32 * F and 140 * F). The optimum temperature for photosynthesis is between 25 – 28 *C (77 – 82.5*F). During tests in a lab, with controlled environmental conditions, it was found that when the temperature decrease below 20 *C (68 *F) and above 30 * C (86 *F), the rate of photosynthesis drops dramatically. Outside, in nature, many factors influence photosynthesis, and it was found that optimal photosynthesis can take place at an optimum level of 16 *C, if the other factors are in favor of photosynthesis.

Moisture: A grape leaf must have at least 75 % to 85 % moisture to be biochemical active. In the formula of photosynthesis, you will notice that water is needed for the whole process to take place, in other words, the optimal soil moisture, where the grape vine grows, is very important for photosynthesis to take place. The humidity of the atmosphere around the vine influence the effects the rate of photosynthesis – a higher humidity at the same light intensity has a higher rate of photosynthesis.

CO2- and O2 concentration:
Normal CO2 concentration in the atmosphere is around 300 ppm. The rate at which photosynthesis takes place, increase as the CO2 concentration increases up to a point when it reaches 500 ppm, where it slows down and stops at a rate of +- 1000 ppm. Just as the opposite happens when the concentration of O2 (oxygen) increases above 21 %.

2. Internal factors:

The leaf of a grape vine starts to photosynthesize at a very early stage (when it is the size of a matchbox), but only until it is two-thirds of the size of a mature leaf, it is self-supporting. Now you may ask, how does a young grape vine grows with leaves that are self-supporting are non self-supporting? The secret lies in the energy that was stored inside the roots, and stems during the previous growing season. Therefore you MUST make sure that the leaves of the young grape vine reaches at least two-thirds of its mature size as quickly as possible, before the stored energy inside the vine are replenished. Using certain training methods explained in the Complete Grape Growers Guide, this stage of maturity of the leaf would be reached very early.

The need for photosynthetic products increase as the size of your crop increase, therefore you need to control the size of your crop according to the growth of your vine. A young vine with a small canopy and a large crop will not be able to produce enough carbohydrates to ripen or mature the harvest.

3. Genetic factors:

Different varieties react different to the exposure of sunlight from others; therefore, different varieties have different levels of photosynthesis than others. The opening and closing of the stomas of different grape vine cultivars are not the same, and this will influence how much moisture is available for photosynthesis – less moisture, less photosynthesis!

4. Cultivation practices:

As mentioned before; the more leaves exposed to direct sunlight, the better the photosynthesis will and therefore we need to design our trellis system in such a way. Row direction, summer treatments, pruning, planting distances and the irrigation or the vine will all play an important role in photosynthesis.

If we go through this whole process of photosynthesis, there is one thing that stands out – do not let your vine grow out of hand. A too dense vine is an unhappy vine and it will for sure not produce the grapes it should have.

For more information on how to increase the productivity and level of photosynthesis of your grape vine, go visit My-Grape-Vine.

Danie
“The Grape Guy”

http://www.my-grape-vine.com

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Filed under: growing grapes • how to grow grapes

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