The existing level of CO2 is sufficient for the crop requirements, this is teh reason why the atmospheric CO2 is increasing. If you mean that with increased oceanic CO2 sequestration, then yes it will lead to increased productivity in oceans and this will inturn acidify oceans. so the answer is No for terrestrial and Yes for oceanic.

Kenneth thanks for your input, can i have some of the papers which document the Eocene and Oligocene CO2 concentration.

Thanks Kenneth this is interesting so what is the explanation to blame CO2 increase to anthropogenic activity since this natural changes can be much severe than what the humans have been adding.

Plant response to high carbon dioxide is species dependent and can be influenced by biotic and abiotic factors. For example physiological and molecular analyses suggest that cold-acclimated winter wheat is more tolerant to elevated carbon dioxide than non-acclimated wheat during long-term exposure to elevated carbon dioxide. This increased tolerance could be provided by their ability to maintain higher expression of biotic and abiotic defense-related genes and their efficient way to adapt their physiology to improve CO2 fixation while protecting their photosynthetic machinery.

Please find attached our recent findings on the subject

Best regards

Article Long-Term Growth Under Elevated CO2 Suppresses Biotic Stress...

Dear Katharina Bastl

Your Opinion is right. I agree with you. Emigration of plants and ecosystems is one of the major consequences of global warming and climate change.It is predicted that at the end of this century there will be large scale shifts in the global distribution of vegetation in response to anthropogenic climate change.With man doubling the amount of carbon dioxide entering into the atmosphere the climate is changing more rapidly then plant migration can keep up. Therefore some plants will face extinction because habitat will become too small.

Mohammad Kazemi

Dear Kenneth Towe

I greatly appreciate your support and contributions allowing us to continue our discusstion.

Mohammad Kazemi

Dear Saif Uddin

Increasing carbon dioxide in the atmosphere is expected to enhance plant growth in some crops such as C3 crops, but studies suggest that this effect declines with increasing concentrations.

However I would like to have your opinion about total productivity of plants at the global level when CO2 will be increased by human activities.

Thank you

Mohammad Kazemi

Dear Khalil Kane

Thank you very much. Relation between physiology, ecology and genetic is very interesting and I think that a holistic approach is needed to understand this matter properly.

Mohammad Kazemi

Mohammad just to understand your point better. "Increasing CO2 in atmosphere is expected to enhance plant growth in some crops" so is the thought behind this is that current CO2 concentrations are not high enough for optimal growth?

Atmospheric CO2 for September 2013 was about 393.31 ppm( http://co2now.org/) and it's concentrations in the atmosphere are increasing from month to month. it is well established that higher CO2 levels can have a fertilizing effect on C3 plants, but some plants already have mechanisms for concentrating CO2 in their tissues, known as C4, so higher CO2 will not boost the growth of them.

However with increasing atmospheric CO2, there are limiting factors such as high temperature and water stress, can adversely affect growth of the plants.

So co2 concentration may be suboptimal for C3 and Optimal for C4 plants.

It is not quite clear to me.

Mohammad Kazemi

interesting so your point of view is that C3 plants will flourish, but synergies with temp and water content is not considered.

Dear Saif

Thank You

What are the c3 plants?

Dear Saif Uddin

Source of this difinition is http://en.wikipedia.org/wiki/C3_plant

C3 carbon fixation is a metabolic pathway for carbon fixation in photosynthesis, along with C4 and CAM metabolic pathways. This process converts carbon dioxide and ribulose bisphosphate (RuBP, a 5-carbon sugar) into 3-phosphoglycerate through the following reaction:

CO2 + RuBP → (2) 3-phosphoglycerate

This reaction occurs in all plants as the first step of the Calvin-Benson cycle. In C4 plants, carbon dioxide is drawn out of malate and into this reaction rather than directly from the air.

Plants that survive solely on C3 fixation (C3 plants) tend to thrive in areas where sunlight intensity is moderate, temperatures are moderate, carbon dioxide concentrations are around 200 ppm or higher, and ground water is plentiful. The C3 plants, originating during Mesozoic and Paleozoic eras, predate the C4 plants and still represent approximately 95% of Earth's plant biomass. C3 plants lose 97% of the water taken up through their roots to transpiration. Examples include rice and barley.

C3 plants cannot grow in hot areas because RuBisCO incorporates more oxygen into RuBP as temperatures increase. This leads to photorespiration, which leads to a net loss of carbon and nitrogen from the plant and can, therefore, limit growth. In dry areas, C3 plants shut their stomata to reduce water loss, but this stops CO2 from entering the leaves and, therefore, reduces the concentration of CO2 in the leaves. This lowers the CO2:O2 ratio and, therefore, also increases photorespiration. C4 and CAM plants have adaptations that allow them to survive in hot and dry areas, and they can, therefore, out-compete C3 plants.

Thank you

Mohammad Kazemi

Dear Mohammed thank you very much for such a nice and detailed description.