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Volume 2 Number 21:  1 November 1999

Editorial
Climate Change Science: Is Bigger Better?: In an enlightening Forum article in the 31 August 1999 issue of the American Geophysical Union's weekly EOS publication, Dr. Gerald Stanhill of The Volcani Centre's Institute of Soil, Water, and Environmental Sciences in Bet-Dagan, Israel raises a number of disturbing issues related to the historical development of climate change science (or CCS for short), beginning with a graph that shows that the cumulative scientific literature on this topic has grown exponentially since 1950, with a doubling time of eleven years...

Journal Reviews
Carbon Budgets of Two Grasslands as Affected by Elevated CO2: A two-year atmospheric CO2 enrichment study of soil monoliths of two contrasting grasslands native to the United Kingdom revealed root growth to be dramatically stimulated, even though above-ground growth was essentially unaffected; and the authors report that the increase in soil organic matter due to the CO2-induced increase in root growth is "likely to persist" under continued CO2 fertilization, thus helping to slow the rate of rise of the air's CO2 concentration.

Effects of Elevated CO2 on Below-Ground Carbon Allocation in Three Grasses: In a two-month study of three grass species conducted at two different soil nitrogen levels, a doubling of the atmospheric CO2 concentration increased whole-plant biomass, root growth more than shoot growth, and soil microbial biomass, causing the authors of the study to conclude that "elevated CO2 could result in greater soil carbon stores due to increased carbon-input into soils," which would clearly slow the rate at which the atmospheric CO2 content would rise in the absence of this phenomenon.

Effects of Atmospheric CO2 Enrichment on Soil Organic Carbon Content in Southwestern United States: Analyses of stable carbon isotopes in the air, plants and soil over the third year of a three-year free-air CO2 enrichment (FACE) study of cotton has revealed that 10% of the soil carbon in the FACE plots was replaced with "fresh" carbon over the three-year period, with some of it going into a very recalcitrant portion of the soil organic matter, suggestive of the likelihood that it will gradually build up there over time, lowering the CO2 content of the air below what it would be in the absence of this effect.

Effects of Atmospheric CO2 Enrichment on Soil Organic Carbon Content in Switzerland: A free-air CO2 enrichment (FACE) study of white clover near Zurich, Switzerland revealed a 71% increase in atmospheric CO2 concentration to produce a 146% increase in above-ground growth, a 50% increase in soil carbon input, and a 24% decrease in root decomposition.  The greater soil carbon input and lesser root decomposition produced by the elevated CO2 resulted in an increase in soil carbon storage that would be expected to have a significant braking effect on the ongoing rise in the air's CO2 content.

Decomposition of Grass Roots as Affected by Elevated CO2: A two-year study of the effects of a 350 to 700 ppm doubling of the atmospheric CO2 concentration on perennial ryegrass plants produced a 92% increase in root growth, along with significant increases in soil microbial biomass and significant decreases in root decomposition rates, leading to a longer residence time and greater storage of soil carbon.  These facts, according to the authors of the report, "should be taken into account in models predicting the fate of carbon under different scenarios for climatic change."

Response of Soybean to Elevated CO2 and Ozone: Soybeans grown in open-top chambers fumigated with ambient CO2 and elevated atmospheric ozone concentrations exhibited less rubisco and starch contents per unit leaf area than did plants grown at elevated CO2 and ambient ozone concentrations.  However, when plants were grown at elevated CO2 and ozone concentrations, leaf rubisco and starch contents were similar to those exhibited by plants grown under conditions of elevated CO2 and ambient atmospheric ozone, demonstrating the complete amelioration of the deleterious effects of ozone on these and other important leaf properties by atmospheric CO2 enrichment.

Soil Biota Responses to Long-Term Atmospheric CO2 Enrichment: Long-term atmospheric CO2-enrichment of grassland ecosystems for six years led to increased root colonization by arbuscular mycorrhizal fungi.  In addition, elevated CO2 increased soil fungal populations and the populations of soil microarthropods, which often consume fungal colonies to meet their energy demands.  Thus, this paper demonstrates that atmospheric CO2 enrichment stimulates the soil fungal food chain beneath grassland ecosystems.

Responses of Wild C4 and C3 Grass Species to Elevated CO2: An extensive literature review revealed that C4 grasses are much more responsive to elevated CO2 than previously thought by some researchers.  On average, C4 grasses exhibited CO2-induced increases in photosynthesis and total biomass of 25 and 33%, respectively, in response to a doubling of the air's CO2 content.

Responses of Pineapple to Elevated CO2 and Temperature: Pineapple plants grown at an atmospheric CO2 concentration of 700 ppm for six months exhibited significantly greater rates of carbon assimilation than plants grown at 350 ppm CO2 at three different day/night temperature regimes characteristic of computer-predicted global warming scenarios.  Moreover, assimilation rates were so robust under the interactive treatments of elevated CO2 and temperature, they caused the authors to suggest that the primary carboxylating enzyme used by C4 and CAM plants during photosynthesis is "not CO2 saturated at ambient CO2 and a night temperature of 25C."  Thus, the CO2-responsiveness of C4 and CAM plants needs to be re-examined under the interactive conditions of elevated CO2 and temperature, as it may be more robust than it is under conditions of elevated CO2 alone.

Forest Carbon Sinks Should Increase with Increasing Atmospheric CO2 Concentrations: A review of the peer-reviewed scientific literature shows that a doubling of the current atmospheric CO2 concentration will reduce plant respiratory carbon losses by an average of 17% on a biomass basis.  Within the next century, this phenomenon will thus increase the size of earth's terrestrial carbon sink, which can actually help reduce the amount of CO2 in the atmosphere.