Editorial
In Search of the Second "Green Revolution": In the 2 December 1999 Supplement to Nature titled "Impacts of Foreseeable Science," the Rockefeller Foundation's Conway and Toenniessen (1999) discuss the task of feeding the world in the twenty-first century.  They note that "the Green Revolution was one of the great technological success stories of the second half of the twentieth century," but that its benefits are dropping and a number of arguments "point to the need for a second Green Revolution."  We explore the role that the ongoing rise in the air's CO2 content may play in this regard.

Subject Index Summaries

Journal Reviews
Climate Intrigue at the Mid-Holocene: A brief review of mid-Holocene climatic history reveals a period of slowly rising atmospheric CO2 concentrations and significantly declining global air temperatures.

Climate Instability During the Penultimate Glacial Age: A climate record derived by grain-size analysis of soil cores obtained on the Chinese Loess Plateau suggests that glacial periods experience much more climate variability than do intervening interglacials.

The El Niño - Hurricane Connection: A study of the relationship between El Niño-type weather and the number of intense Atlantic basin hurricanes occurring in a given year reveals that these two phenomena are inversely related to each other.

Is the Sky Falling?: Challenges associated with measuring a lowering of the ionospheric F2 layer that has been predicted to occur as a consequence of rising concentrations of atmospheric CO2 and methane are discussed by the man who first proposed the idea.

Bird and Mammal Range Expansions Courtesy of Increasing Temperatures: In the face of regional warming, a portion of the Canadian Northwest Territories was found to be experiencing significant increases in bird and mammal species richness.

Gas-Exchange Responses of a Chaparral Shrub to Atmospheric CO2 Enrichment: Adenostoma fassciculatum shrubs exposed to an atmospheric CO2 concentration of 550 ppm for six weeks in a FACE experiment displayed reduced photosynthetic rates indicative of CO2-induced acclimation.  In addition, CO2-enriched shrubs maintained higher (less stressful) leaf water potentials than control plants, suggesting that atmospheric CO2 enrichment caused reductions in their stomatal conductance and transpirational water loss.  These data suggest that as the CO2 content of the air rises, this shrub may reallocate excess resources away from photosynthesis and into other more-limiting processes to growth.  They also suggest that this shrub will be more adept at dealing with drought conditions in the future.

Effects of Elevated CO2 on Grass Root Decomposition: Atmospheric CO2 enrichment stimulated the above- and belowground biomass of ryegrass by 28 and 42%, respectively, regardless of soil nitrogen content.  This phenomenon led to enhanced soil carbon inputs, as indicated by significantly greater amounts of ¹⁴C-labeled soil carbon and microbial biomass.  In addition, because elevated CO2 reduced the decomposition of soil organic matter by about 13%, greater amounts of carbon were sequestered in CO2-enriched plant-soil systems than in ambient CO2 systems.

Effects of Elevated CO2 and O3 on Leaf Nitrogen and Decomposition of Yellow-Poplar and Eastern White Pine: After four years of growth in open-top chambers receiving various concentrations of atmospheric O3 and CO2, seedlings of yellow-poplar and eastern white pine displayed 8 to 28% reductions in foliar nitrogen content, but only when exposed to an elevated O3 and CO2 treatment combination.  Elevated O3, alone, had no effects on litter decomposition, while the elevated O3 and CO2 combination reduced decomposition rates in yellow-poplar, but not eastern white pine seedlings.  Thus, yellow-poplar trees may sequester greater amounts of carbon in their litter in a future world characterized by elevated levels of atmospheric O3 and CO2.

Effects of Elevated CO2 on Soil Bacterial Communities as Influenced by Plant Type: Swards of ryegrass and white clover were exposed to differential atmospheric CO2 concentrations for two growing seasons in a FACE experiment located in Switzerland.  Elevated CO2 tended to increase the total number of bacteria in the rhizosphere beneath each plant species.  In addition, it changed bacterial community structure by favoring bacterial species most adept at facilitating plant nutrient acquisition in a plant species-dependent manner.

Effects of Elevated CO2, High Temperature, and Fertilization on Root Nitrogen Exudation in Black Locust Seedlings: Black locust seedlings did not exhibit any significant change in the amount of organic nitrogen exudation from their root systems after 100 days of growth in elevated CO2.  However, nitrogen exudation was increased in this nitrogen-fixing tree by nearly 40% when exposed to a growth temperature of 30, instead of 26°C.  Overall, the amount of exuded nitrogen was between 1 and 2% of that symbiotically fixed by this species.  Thus, as the CO2 content of the air rises, nitrogen-fixing species should continue to exude small but significant amounts of nitrogen into the soil, where it can become available for uptake by neighboring species.  In addition, if air temperatures rise, regardless of the cause, even greater amounts of nitrogen should become available to such species.  This phenomenon will likely result in greater CO2-induced growth enhancements for plants growing next to nitrogen-fixing species, as it reduces the limitation of nitrogen on growth.