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Volume 3 Number 7:  1 April 2000

The Future of Forests: Trees, it seems, are growing much more profusely now than they did one and two centuries ago; yet some people want to turn back the clock and recreate the biological paucity of the past.  Do they not know progress when they see it?

Journal Reviews
CO2 and Temperature: What Drives What?: A highly data-constrained model is developed to explain the synchrony between Antarctic temperature and atmospheric CO2 concentration over glacial-interglacial cycles.  It reveals that atmospheric CO2 responds to air temperature variations and not vice versa.

Shortcomings of GCM Cloud and Radiation Parameterizations: A diagnostic study reveals that present-generation GCMs perform poorly in terms of simulating cloud-radiation interactions in the atmosphere as a consequence of insufficient vertical resolution.

Adaptation of Reef Corals to Reduce Susceptibility to Bleaching: Experimental observations reveal increased adaptation to the combined stress of temperature and solar radiation in certain G. aspera colonies among the reef corals at Phuket, Thailand.  If this adaptive mechanism is operational in other coral species, a decline in the severity of the temperature-induced bleaching episodes that have plagued many reefs over the past two decades may follow as corals begin to better tolerate such events.

Gallery Forest Expansion in Kansas: Gallery forest and total forest area in a Kansas preserve have increased dramatically since the mid-1800s in tandem with the historical rise in the air's CO2 content.

Does Grazing Favor Woody Species Expansion?: Reductions in biomass and density of herbaceous vegetation had no influence on the emergence, growth, or survival of honey mesquite seedlings in this controlled study, suggesting that livestock grazing is a minimal factor in explaining the recent range expansion of this woody species in the southwestern United States.

Effects of Elevated CO2 on Soil Microbiota: After nearly 1.5 years of differential CO2 exposure, artificial tropical ecosystems fumigated with air containing 610 ppm CO2 exhibited a significantly greater proportion of humic substances in their soil compared to those fumigated with air containing 340 ppm CO2.  In addition, elevated CO2 significantly increased total mycorrhizal fungal and bacterial populations within ecosystem soils, which were characterized as being nutrient-poor.  Thus, it is likely that the increasing CO2 content of the air will impact nutrient-poor tropical soils in ways that tend to favor increased plant growth and development.

Elevated CO2 Stimulates Soil Microbial Activities Beneath a Calcareous Grassland: Grassland monoliths grown for 18 months at elevated CO2 concentrations of 600 ppm displayed 10 to 20% more soil moisture than monoliths grown at 350 ppm CO2.  In turn, soil microbial activities increased in response to increased soil moisture.  Thus, atmospheric CO2 enrichment stimulated soil microbial activities in grassland communities.

Elevated CO2 Stimulates Cell Division in Dactylis glomerata: Elevated CO2 shortened the cell cycle in shoot and root meristems of the grass Dactylis glomerata.  Additionally, elevated CO2 increased the proportion of meristematic cells that were rapidly dividing.  Together, these two phenomena increased the growth rate of this grass and led to greater biomass accumulation in plants grown at 700 ppm CO2 than it did for plants grown at 400 ppm CO2.

Effects of Elevated CO2 and Simulated Herbivory on a Tropical Tree: Over a short 50-day experiment, seedlings of the tropical tree Copaifera aromatica that were grown in an atmospheric CO2 concentration of 860 ppm maintained rates of net photosynthesis that were 50 to 100% greater than their ambiently-grown counterparts, even after a defoliation treatment that removed 40% of their leaf area.  Although the removed leaf area was never fully compensated for at either CO2 level, defoliated seedlings exposed to elevated CO2 attained final leaf areas and total plant dry weights that were 20 and 15% greater, respectively, than those of defoliated control plants grown at 390 ppm CO2.  Thus, atmospheric CO2 enrichment better prepared CO2-enriched seedlings of this species to cope with the stresses induced by simulated herbivory.

Genotypic Responses of Ponderosa Pine to Elevated CO2: After 28 months of differential CO2 exposure in open-top chambers, 15 genotypes of ponderosa pine seedlings grown at 525 and 700 ppm displayed average photosynthetic rates that were 19 and 49% greater, respectively, than those of seedlings grown at 350 ppm CO2.  In addition, seedlings grown at an atmospheric CO2 concentration of 700 ppm exhibited values of stomatal conductance that were 18% lower than those of ambiently-grown seedlings.  Thus, elevated CO2 facilitated an increase in plant water-use efficiency in all seedlings.