How does rising atmospheric CO2 affect marine organisms?

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Air Pollution (Non-Ozone - Effects on Plants) -- Summary
There is a strong movement afoot to have carbon dioxide declared a pollutant.  Unless the definition of the word is radically altered, however, this initiative would seem to be an exercise in futility, as noted in our answer to the question Is Carbon Dioxide a Pollutant?.  In the dictionary, for example, a pollutant is defined as something that makes things foul or unclean.  Thus, a pollutant taints, contaminates and defiles things.  But increasing levels of atmospheric CO2 nearly always do just the opposite, suggesting that Shakespeare's comment on the rose is as valid today as the day it was penned.

A superb example of this fact is described in the study of Idso et al. (1990), who doubled the atmospheric CO2 concentration over two of four stock tanks containing newly-planted water lily rhizomes and found that the putative pollutant stimulated just about everything the plants did.  The plants in the tanks exposed to the extra CO2 produced more leaves, bigger leaves, longer-lived leaves, and leaves with a higher percentage of dry matter.  They also produced more flowers with bigger blossoms that had more petals, longer petals, and petals with a greater concentration of dry matter.  Likewise, the stems that supported the flowers were longer in the CO2-polluted tanks; and they, too, had greater dry matter concentrations than the stems of the flowers in the ambient-treatment tanks.  The plants in the high CO2 tanks also had more and bigger basal rosette leaves that were attached to longer stems of greater percent dry matter content; and they had more unopened basal rosette leaves.  The plants "suffering" under the burden of the extra CO2 also produced more and bigger rhizomes, as well as more and bigger major roots with larger dry matter concentrations.  Altogether, the total amount of plant dry matter produced in the CO2-polluted tanks in a single season of growth was 270% greater than that produced in the tanks exposed to ambient air.

It's also interesting to observe what happens when CO2 confronts a real air pollutant.

Deepak and Agrawal (2001) grew two cultivars (PK472 and Bragg) of soybean (Glycine max L. Merr.) in open-top chambers maintained at atmospheric CO2 concentrations of 350 and 600 ppm alone and in combination with 60 ppb sulfur dioxide (SO2).  Exposure to elevated SO2 significantly reduced every growth parameter studied; total plant biomass and grain yield, for example, were both reduced by approximately 18% in both cultivars.  In contrast, elevated CO2 by itself significantly increased every growth parameter in both cultivars, boosting total plant biomass and grain yield by averages of 30 and 34%, respectively.  Moreover, when the plants were exposed simultaneously to elevated CO2 and SO2, the negative effects of SO2 were completely ameliorated, as is also often observed in studies where ozone-affected plants are exposed to elevated CO2 [see Ozone (Effects on Plants) in our Subject Index].  In fact, the growth responses observed under these conditions were not significantly different from those obtained under CO2-enriched conditions alone.

In an analogous study, Agrawal and Deepak (2003) grew two cultivars (Malviya 234 and HP1209) of wheat (Triticum aestivum L.) in open-top chambers maintained at atmospheric CO2 concentrations of 350 and 600 ppm alone and in combination with 60 ppb SO2.  Exposure to the extra CO2 significantly increased photosynthetic rates: by 58% in Malviya 234 and by 48% in HP1209.  In contrast, fumigation with elevated SO2 had no significant impact on the photosynthetic rates of either cultivar; but plants grown in the combined treatment of elevated CO2 plus elevated SO2 displayed photosynthetic rates that were 42% greater than those observed in control plants of Malviya 234 and 38% greater than those observed in control plants of HP1209.

The wheat plants grown in elevated CO2 also displayed a 20% reduction in stomatal conductance (which conserves water), while those grown in elevated SO2 exhibited a 15% increase in this plant property (which wastes water); and when simultaneously exposed to both gases, the plants displayed a favorable 11% reduction in stomatal conductance.  This phenomenon contributed to a 32% increase in water-use efficiency for plants simultaneously exposed to both gases, whereas those exposed to elevated SO2 alone displayed a 16% decrease in water-use efficiency.  Last of all, exposure to elevated SO2 caused a 13% decrease in foliar protein concentrations in both wheat cultivars; but when the plants were concomitantly exposed to elevated CO2, leaf protein levels only decreased by 3% in HP1209, while they actually increased by 4% in Malviya 234.

Before taking leave of agricultural crops, we note that considerably greater increases in the air's CO2 content than those employed in the preceding studies produce even greater positive impacts in the face of SO2 pollution.  Carlson (1983), for example, found that a 900-ppm increase in the air's CO2 concentration boosted photosynthetic rates of soybeans by 87% in unpolluted air but by whopping 715% in high-SO2 air.  Hence, it is clear that the ongoing rise in the air's CO2 content can do much to significantly alleviate or even totally prevent the adverse consequences of anthropogenic SO2 pollution in an agricultural setting.

In addition to crops, trees are also adversely affected by atmospheric SO2 pollution, as described in the study of Izrael et al. (2002), who note that 1.3 million hectares of Russian forest land have been adversely affected by this pollutant.  They further report that total forest destruction occurs on 2-5% of this area, and that heavy, moderate and slight damage occur on 10-15%, 30-40% and 40-50% of it, respectively.

We report these results to indicate the seriousness of SO2 pollution for forest health and as an introduction to the fact that atmospheric CO2 enrichment can significantly alleviate SO2's adverse impacts on trees.  Hallgren (1984), for example, demonstrated that a 300-ppm increase in the air's CO2 concentration stimulated the photosynthetic rates of Scots pines by 64% in unpolluted air and by 77% in air of abnormally high SO2 content, while a 600-ppm increase in atmospheric CO2 stimulated photosynthetic rates by 85% in unpolluted air and by 110% in air of high SO2 concentration.

In another pertinent study, Grill et al. (2004) analyzed various properties of leaves and acorns produced on two species of oak tree (Quercus ilex L. and Quercus pubescens L.) growing at double-to-triple normal atmospheric CO2 concentrations near natural CO2 springs in Italy that emit higher-than-normal concentrations of both SO2 and H2S, another phytotoxic air pollutant (Schulte et al., 1999), as well as the same characteristics of leaves and acorns growing on similar trees located some distance away in ambient-CO2 air.  In addition, they analyzed several characteristics of seedlings they sprouted from acorns produced by the CO2-enriched and ambient-CO2 trees; and they used chromosome stress tests "to investigate whether alterations in sulphur-regime have negative consequences for seedlings."

The scientists found that "acorns from CO2 springs contained significantly higher sulphur concentrations than controls (0.67 vs. 0.47 mg g-1 dry weight in Q. ilex cotyledons and 1.10 vs. 0.80 in Q. pubescens)," indicative of the fact that the trees were indeed significantly affected by the H2S- and SO2-enriched air in the vicinity of the CO2-emitting springs.  They also report that Q. ilix seedlings grown from CO2 spring acorns showed elevated rates of chromosomal aberrations in root tips, suggestive of the presence of a permanent stress.  Nevertheless, as demonstrated by the results of several studies conducted on mature trees from these sites, the CO2-enriched air - even in the presence of significantly elevated concentrations of phytotoxic H2S and SO2 - tremendously enhances the trees' photosynthetic prowess: by 26-69% (Blaschke et al., 2001), 36-77% (Stylinski et al., 2000), and a whopping 175-510% (Tognetti et al., 1998).

In light of these many diverse observations, it should be clear to all that we very much need the help provided by the ongoing rise in the air's CO2 concentration to combat the deleterious biological effects of the still-rampant air pollution that plagues much of the planet.  And since Wilkening et al. (2000) and Satheesh and Ramanathan (2000) have described how air pollutants can be transported thousands of miles from one continent to another, the ability of elevated levels of atmospheric CO2 to combat the deleterious effects of those pollutants will likely become ever more important in the years and decades ahead, as humanity struggles to feed, clothe and house a burgeoning global population, and as nature struggles to survive the problems created by man in doing so.

Agrawal, M. and Deepak, S.S.  2003.  Physiological and biochemical responses of two cultivars of wheat to elevated levels of CO2 and SO2, singly and in combination.  Environmental Pollution 121: 189-197.

Blaschke, L., Schulte, M., Raschi, A., Slee, N., Rennenberg, H. and Polle, A.  2001.  Photosynthesis, soluble and structural carbon compounds in two Mediterranean oak species (Quercus pubescens and Q. ilex) after lifetime growth at naturally elevated CO2 concentrations.  Plant Biology 3: 288-297.

Carlson, R.W.  1983.  The effect of SO2 on photosynthesis and leaf resistance at varying concentrations of CO2Environmental Pollution Series A 30: 309-321.

Deepak, S.S. and Agrawal, M.  2001.  Influence of elevated CO2 on the sensitivity of two soybean cultivars to sulphur dioxide.  Environmental and Experimental Botany 46: 81-91.

Grill, D., Muller, M., Tausz, M. Strnad, B., Wonisch, A. and Raschi, A.  2004.  Effects of sulphurous gases in two CO2 springs on total sulphur and thiols in acorns and oak seedlings.  Atmospheric Environment 38: 3775-3780.

Hallgren, J.-E.  1984.  Photosynthetic gas exchange in leaves affected by air pollutants.  In: Koziol, M.J. and Whatley, F.R. (Eds.).  Gaseous Air Pollutants and Plant Metabolism.  Butterworths, London, UK, pp. 147-159.

Idso, S.B., Allen, S.G. and Kimball, B.A.  1990.  Growth response of water lily to atmospheric CO2 enrichment.  Aquatic Botany 37: 87-92.

Izrael, Yu.A., Gytarsky, M.L., Karaban, R.T., Lelyakin, A.L. and Nazarov, I.M.  2002.  Consequences of climate change for forestry and carbon dioxide sink in Russian forests.  Isvestiya, Atmospheric and Oceanic Physics 38: S84-S98.

Satheesh, S.K. and Ramanathan, V.  2000.  Large differences in tropical aerosol forcing at the top of the atmosphere and Earth's surface.  Nature 405: 60-63.

Schulte, M., Raiesi, F.G., Papke, H., Butterbach-Bahl, K., van Breemen, N. and Rennenberg, H.  1999.  CO2 concentration and atmospheric trace gas mixing ratio around natural CO2 vents in different Mediterranean forests in central Italy.  In: Raschi, A., Vaccori, F.P. and Miglietta, F. (Eds.).  Ecosystem Response to CO2: The Maple Project Results.  European Communities, Brussels, Belgium, pp. 168-188.

Stylinski, C.D., Oechel, W.C., Gamon, J.A., Tissue, D.T., Miglietta, F. and Raschi, A.  2000.  Effects of lifelong [CO2] enrichment on carboxylation and light utilization of Quercus pubescens Willd. examined with gas exchange, biochemistry and optical techniques.  Plant, Cell and Environment 23: 1353-1362.

Tognetti,R., Johnson, J.D., Michelozzi, M. and Raschi, A.  1998.  Response of foliar metabolism in mature trees of Quercus pubescens and Quercus ilex to long-term elevated CO2Environmental and Experimental Botany 39: 233-245.

Wilkening, K.E., Barrie, L.A. and Engle, M.  2000.  Trans-Pacific air pollution.  Science 290: 65-67.

Last updated 2 February 2005