For an "Earth Scientist" you are somewhat limited in you understanding of how this planets ecosystem functions.
Normally i would not bother giving references, but since you seem incapable of your own research, i will give you some help..
Denman, K.L., G. Brasseur, A. Chidthaisong, P. Ciais, P.M. Cox, R.E. Dickinson, D. Hauglustaine, C. Heinze, E. Holland, D. Jacob, U. Lohmann, S Ramachandran, P.L. da Silva Dias, S.C. Wofsy and X. Zhang. Couplings Between Changes in the Climate System and Biogeochemistry. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 2007.
the most relevant summary being ..
The largest natural source of carbon dioxide emissions is from ocean-atmosphere exchange. This produces 42.84% of natural carbon dioxide emissions. The oceans contain dissolved carbon dioxide, which is released into the air at the sea surface. Annually this process creates about 330 billion tonnes of carbon dioxide emissions
and yes, plants do take up more than they emit, but remember the scale of their emissions.... 220 bT compared to 33 bT for human input !.
....so just maybe there is potential for them to take up some of that human emissions as well ??