How does rising atmospheric CO2 affect marine organisms?

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Effects of Elevated CO2 on a Tropical Orchid
Li, C.R., Gan, L.J., Xia, K., Zhou, X. and Hew, C.S.  2002.  Responses of carboxylating enzymes, sucrose metabolizing enzymes and plant hormones in a tropical epiphytic CAM orchid to CO2 enrichment.  Plant, Cell and Environment 25: 369-377.

What was done
The authors grew the epiphytic CAM orchid Mokara Yellow in controlled environment chambers receiving atmospheric CO2 concentrations of 380 and 760 ppm for two months to study the effects of elevated CO2 on plant growth and enzyme functioning.

What was learned
The elevated CO2 concentration increased the relative growth rate of the orchids by 25%.  As a result, the CO2-enriched plants produced 31 and 98% more shoot and aerial-root dry mass, respectively, than their ambiently-grown counterparts.  At the biochemical level, elevated CO2 reduced rubisco activity during the light period, but significantly stimulated PEPcarboxylase activity during the dark period.  Also, the activities of SPS (sucrose-phosphate synthase, a key regulatory enzyme involved in partitioning carbon between sucrose and starch in leaves) and SS (sucrose synthase) were significantly increased by atmospheric CO2 enrichment.  Finally, elevated CO2 increased the concentrations of several plant hormones in leaf and aerial root tips by as much as 21-fold.

What it means
As the CO2 content of the air increases, this particular orchid, and perhaps other plants that utilize CAM metabolism, will likely exhibit significant increases in growth and dry matter production as a result of optimization of resources at the enzymatic level within plant organs.  Indeed, the nocturnal CO2-induced increase in PEPcarboxylase should significantly increase carbon uptake, while the similarly-induced increases in SPS and SS should enhance the mobilization and utilization of photosynthetically-derived sugars, preventing or reducing their accumulation in leaves and, therefore, eliminating or reducing feedback inhibition of carbon assimilation.  Thus, one can anticipate greater and more robust growth by Mokara Yellow orchids, and perhaps other CAM plants as well, as the air's CO2 content continues to rise.

Reviewed 12 June 2002