How does rising atmospheric CO2 affect marine organisms?

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Cash-Crop Halophytes in a CO2-Enriched World
Geissler, N., Hussin, S. and Koyro, H.-W. 2009. Interactive effects of NaCl salinity and elevated atmospheric CO2 concentration on growth, photosynthesis, water relations and chemical composition of the potential cash crop halophyte Aster tripolium L. Environmental and Experimental Botany 65: 220-231.

The authors write that halophytes are "naturally salt tolerant plants which are able to complete their life cycle on a substrate rich in NaCl," and that cash-crop halophytes "can be used for various economical and ecological purposes, e.g. for food, fodder, for obtaining timber, fibers, reed or chemicals, as ornamental plants, for coastal protection, land reclamation or greenification of deserts," noting that Aster tripolium, in particular, "can be used for food (the leaves have a high nutritional value and can be eaten as salad or vegetable), for fodder and as an ornamental plant."

What was done
Geissler et al. grew adequately fertilized two-month-old A. tripolium plants for an additional month within open-top chambers (maintained at atmospheric CO2 concentrations of either 370 or 520 ppm) inside a controlled-environment greenhouse, where they were irrigated with water having a salt (NaCl) content equivalent to 0, 50 or 100% Sea Water Salinity (SWS), while monitoring a number of plant properties and processes.

What was learned
This work revealed, first of all, that the 40% increase in the air's CO2 content increased the light-saturated rate of net photosynthesis by 56%, 82% and 71%, respectively, in the plants irrigated with water of 0, 50 and 100% SWS, while it increased their water use efficiencies by 14, 26 and 61% at the same respective SWS percentages. Other positive impacts of the CO2-enriched air were "an enhanced synthesis of proline, carbohydrates and proteins," and the three researchers say that "these mechanisms led to a higher survival rate under saline conditions, i.e. to an improved salt tolerance."

What it means
Geissler et al. conclude their paper by stating that "from the results one can infer that A. tripolium is a promising cash crop halophyte which will probably benefit from rising atmospheric CO2 concentrations in the future," and that "its sustainable use can help feeding the growing world population and counteracting the greenhouse effect."

Reviewed 18 March 2009