5th is a PDF [which because possible long loading time I generally skip for purpose of linking to it] but here it is anyhow:
Carbon dioxide enrichment in
greenhouse nurseries could be used as
a way to reduce propagation time,
improve sturdiness, and possibly favor
growth in the field after planting
during spring months in northern
latitudes, as little ventilation is
necessary, except on hot sunny days.
The almost entirely juvenile tissues of
seedlings are all expanding, and could
be utilizing and diluting the enhanced
photosynthate production in an enriched
CO2 atmosphere (Lindhout and
Pet, 1990). Hence, the greatest
advantage of CO2 enrichment would be
realized in the vegetative growth of
young plants (Kimball, 1983). As leaf
tissues formed early in seedling culture
begin to mature, starch accumulation
begins to slow photosynthetic rates and
relative growth rate (RGR) (Thomas et
al., 1975).
http://www.imok.ufl.edu/veghort/docs/physio_121202b.pdf
[anyways, it's only a couple pages and took about 30 secs for me to download]
6th:
CO2 Monitoring and control system for greenhouses.
One of the most important activities commonly being held in modern greenhouse is CO2 enrichment of internal atmosphere. Though this activity is well known as significally improving crops yields and quality, it can turn off to be very costly and wasteful if the CO2 enrichment process is inaccurately and inefficiently applied.

Waste of energy or CO2 gas can easily occur in case of CO2 overdosing or at underdosing as well, whereas the applied CO2 may be totally ineffective.

Eldar Shany Technologies, specializing many years in computerized control of greenhouses, has long ago developed an accurate and efficient CO2 controller detecting the air from one zone. The Multi-CO2 is a complementary development in which a simple, but sophisticated, system can sample, monitor and control CO2 enrichment from a large number of greenhouses using only a single CO2 sensor. By using Multi-CO2 you, the grower, gain twice: first by efficient application of CO2 for improvement of yields, and, secondly, by significantly save of unnecessary investments in expensive control equipment.
http://www.eldarshany.com/multico2.html

I'm done.