Dear Hicham.

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I found a really interesting question, including the originality of it.

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However, when you discover something unprecedented I think we should see why it was not done before! Perhaps the reason that prevents this type of study is the difficulty of separating influences another control area. Do not forget that the roadside there are effects that may be far more important than light cars, for example, the generation of the exhaust gases as CO2, CO, lead or other gases.

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Also do not forget that the same light that could influence photosynthesis can attract or repel species (insects or their predators) as well as kills them by the influence of traffic. Would be difficult to separate all these effects and be restricted to the effect of light on photosynthesis. Maybe if you did the research verifying the global influence of plant species on the road to later find out the influence of each item would be less ambitious, but much more secure.

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Most likely, due to rather low photosynthetic flux density and almost impulse regime of lighting from passing traffic, the effect on actual photosynthetic productivity could be negligible. However, the light from traffic can act as signal to affect plant development processes where photoperiodicty is involved

Dear Ģederts.

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As my knowledge on the subject is extremely limited, ask?

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It is easy to detect the influence on plant physiology from the weak light effect, separating it from other stronger effects as I mentioned above? Ie, it is possible to separate the variables?

Dear Rogerio,

First of all I would like to thank you for your interest for my question. Second like you my knowledge about photosynthesis are limited and I posted this question only for curiosity. On other hand, I think that all natural systems are complex and we found always a way to study it. For example in vitro (at the laboratory scale) we try to find a method which allows us to study those systems, for example by fixing all the factors and parameters except one which we want to study. In the case of the effect of car light on tree on the road as a first step, maybe we can start by fixing in vitro all the others factors and parameters and try to change the frequency and intensity of the light and see what will happen.

For the presence of more important issues than light cars on roadside I think the effect of car light is also an important issue for example why not use these trees to fight against CO2 generated by cars?

Finally another issue which I think is very important. The curiosity of humans has no limit and sometimes we study some systems and phenomenon only for this curiosity even if it hasn’t any economic importance.

This is not my topic, but from my experience in growing plants in inddor conditions, it is well known that classical lamps - which might be the case for cars - are not suited at all for growing plants. If you are not using sodium or metal halid lamps or equivalent, you won't grow anything. Moreover, considering the distance from car lights to the canopy, you will find that the energy received by the latter is very low in comparison to what is provided by the sun (approx. 100000lux/m²). So considering that the wavelength of lamps is not adapted for photosynthesis (maybe 10 to 30% of the wavelength can be used in photosynthesis, against 90-100% for specific lamps) and that the distance from the light source to the canopy is quite big (few meters), we can assume that cars lights have no significant effects on photosynthesis. However car lights may have effects on photodegradable molecules in plants, such as hormones.