Green Alert

September 18, 2001 Vol. 1, No. 7

As the atmosphere’s carbon dioxide concentration rises, earth’s plants are becoming increasingly productive due to CO2’s aerial fertilization effect. With more CO2 available, the plants’ photosynthetic prowess increases. This helps drive the great "greening of the earth" that is documented by satellite observations (Myneni et al., 1997; Zhou et al., 2001). Plant growth rates get a boost of 30 to 50 percent in response to a doubling of the ambient CO2 concentration (Idso and Idso, 1994). This, in turn, enables earth’s plants to remove greater quantities of CO2 from the atmosphere. For plants, CO2 is a most highly-prized resource, one that ultimately allows them to sequester more of the trace gas’ valuable carbon in their tissues and in the soils in which they grow.

How different humans are than plants! In a somewhat comparable situation, when we get access to more of something we highly prize (money, for example), often we become less efficient (or more wasteful) in our use of it. Plants, however, once on the receiving end of enhanced acquisition of CO2 (and able to "bank" more through sequestration) seem engendered with greater appreciation. They expend an even smaller proportion of the resource to maintain their lifestyle. Case-in-point, in a review of the pertinent literature, Drake et al. (1999) found that a doubling of the atmospheric CO2 concentration (about a 350 ppm increase) reduces by approximately 17 percent the mean respiration rate of the plants studied. This reduction in the rate at which stored carbon is used to drive growth processes and maintain tissue viability – which is measured by the rate of CO2 emissions from plant foliage, stems and roots – is quite substantial. The twelve researchers involved calculate this equates to an extra six to seven gigatons (six to seven billion tons) of carbon annually sequestered over the entire planet.

Such frugality in the vegetative carbon economy likely is ubiquitous. It has been observed in plants ranging from trees to peat moss. Karnosky et al. (1999), for example, measured a 24 percent decrease in the dark respiration rate of deciduous trembling aspen leaves exposed to a 200 ppm increase in atmospheric CO2 concentration over a period of one year. Jach and Cuelemans (2000) measured a 33 percent decrease in the dark respiration rate of evergreen Scots pine needles exposed to a 400 ppm CO2 increase over a similar time frame. In the case of hydroponically-grown peat moss, Van der Heijden et al. (2000) measured dark respiration rate reductions ranging from 40 to 60 percent (depending upon solution nitrogen concentration) in response to an atmospheric CO2 increase of 350 ppm maintained over a period of six months.

In each of these situations, plant carbon storage was increased at both ends of the CO2 exchange process. As the air’s CO2 content rose, more carbon was captured via photosynthesis. At the same time, less was lost via respiration. This is another example of the many ways in which atmospheric CO2 enrichment enhances biological carbon sequestration, offering some assurance that, as global CO₂ emissions rise in the future, so too will the carbon sequestering prowess of the biosphere, thereby helping reduce the rate at which the air’s CO2 content would otherwise increase.

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This is part of a series of "greening alerts" that Greening Earth Society intends to periodically publish online in response to research concerning the impact of carbon dioxide emissions on earth’s biosphere, especially as it relates to plant life’s ability to sequester carbon. Beginning with the seventh edition, these alerts are prepared by Drs. Sherwood B. Idso and Keith E. Idso of the Center for the Study of Carbon Dioxide and Global Change in Tempe, Arizona (www.co2science.org).

References

Drake, B.G., Azcon-Bieto, J., Berry, J., Bunce, J., Dijkstra, P., Farrar, J., Gifford, R.M., Gonzalez-Meler, M.A., Koch, G., Lambers, H., Siedow, J. and Wullschleger, S. 1999. Does elevated atmospheric CO2 inhibit mitochondrial respiration in green plants? Plant, Cell and Environment 22:649-657.

Idso, K.E. and Idso, S.B. 1994. Plant responses to atmospheric CO2 enrichment in the face of environmental constraints: A review of the past 10 years’ research. Agricultural and Forest Meteorology 69:153-203.

Jach, M.E. and Ceulemans, R. 2000. Short- versus long-term effects of elevated CO2 on night-time respiration of needles of Scots pine (Pinus sylvestris L.). Photosynthetica 38:57-67.

Karnosky, D.F., Mankovska, B., Percy, K., Dickson, R.E., Podila, G.K., Sober, J., Noormets, A., Hendrey, G., Coleman, M.D., Kubiske, M., Pregitzer, K.S. and Isebrands, J.G. 1999. Effects of tropospheric O₃ on trembling aspen and interaction with CO2: results from an O3-gradient and a FACE experiment. Water, Air, and Soil Pollution 116:311-322.

Myneni, R.C., Keeling, C.D., Tucker, C.J., Asrar, G. and Nemani, R.R. 1997. Increased plant growth in the northern high latitudes from 1981 to 1991. Nature 386:698-702.

Van der Heijden, E., Verbeek, S.K. and Kuiper, P.J.C. 2000. Elevated atmospheric CO2 and increased nitrogen deposition: effects on C and N metabolism and growth of the peat moss Sphagnum recurvum P. Beauv. Var. mucronatum (Russ.) Warnst. Global Change Biology 6:201-212.

Zhou, L., Tucker, C.J., Kaufmann, R.K., Slayback, D., Shabanov, N.V. and Myneni, R.B. 2001. Variations in northern vegetation activity inferred from satellite data of vegetation index during 1981 to 1999. Journal of Geophysical Research 106:20,069-20,083.