frankzappatistas said:
Wikipedia refers to
light intensity, that means that the photo period is irrelevant? There is an article somewhere in
http://www.aquajournal.net that refers that photosynthesis starts after 4-5 hours from the moment the lights switched on.
Err..no, that's absolutely incorrect, however, higher plants take longer to "spool up" their machinery of photosynthesis than do algae, which have much simpler mechanisms. The first light dependent reactions begin immediately but there are thousands of reactions in total.
frankzappatistas said:
Considering all the above mentioned, can someone conclude, that extended photo period to 8-10 hours could not encourage algae growth considering that the intensity of light is in line with compensation point and enough nutrients and Co2 are provided?
No, this is an incorrect conclusion. Firstly, the LCP of each plant is different. Plants we call 'low light" such as mosses, ferns and so forth, have a lower LCP than stem plants, for example. Secondly, the photo reactions have a limited time span in higher plants. 8-10 hours is about the limit. After that the plants start to shut down. Algae on the other hand are opportunists and they can happily continue all day, so algae will continue to produce food while the plants have closed up shop. Extended lighting periods therefore have an impact by encouraging algae.
The way we think about light is the reason we have so much difficulty understanding it's impact. When we see light it appears to us as a continuous ray or stream of brightness, but this is not the truth of light. light is actually a series of individual pulses, in a way, like raindrops. A low intensity light is like a light rain falling gently on a leaf. A high intensity light is like a torrent, and just like a storm, high intensity light does damage to the plant photo cells as they collide with the cells.
So intensity is much more important than duration because the intensity determines the number of collisions the light particles make with the the photo receptors in the leaf. If the intensity is too weak, i.e. the number of collisions is too low, the receptors cannot make enough use of the energy. if the intensity is too high then the receptors are bombarded and actually are destroyed by the bombardment. So now, within this context, think about duration. The photoperiod will only have relevance depending on the intensity. With insufficient intensity the photoperiod has no meaning because the plant cannot make use of the weak energy and at the same time it is respiring (using energy). If the intensity is too high then the damage to the cells is occurring for a longer time, but whether short duration or long duration, damage is being incurred.
There is a phenomenon called "photoinhibition" which is a stalling of photosynthesis, and which occurs all the time that the light is on, simply because the light particles raining down on the plant inevitably damages some of the chlorophyll cells. If the rate at which collisions occur (intensity) is modest, then the plant is able to manufacture and release enzymes that repair the cells. If the collision rate is too high then more damage occurs than can be repaired by the plant in a given time period. It's entirely possible that the colors we see in plants under high lighting are a direct result of the plants attempt to minimize the rate of photoinhibition by reflecting (or fluorescing) some of the light energy it is being pummeled with.
Cheers,