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Volume 2 Number 16:  15 August 1999

Editorial
The Long, Long Reach of Atmospheric CO2 Enrichment: A newly recognized consequence of the aerial fertilization effect of atmospheric CO2 enrichment has been demonstrated to enhance the mass and stability of small aggregates in the soils of three intensively-studied natural ecosystems, thereby improving soil structure and lessening the potential for soil erosion via the negative effects of wind and rain.

Journal Reviews
Ecological Disturbance: A Contributor to the Atmosphere's Increasing Seasonal CO2 Amplitude?: A new study of the seasonal cycle of atmospheric CO2 finds that land disturbance and changes in plant composition may be responsible for a significant portion of the amplitude increase in the cycle that has been reported since the 1960s.

Atmospheric CO2 Concentrations in the Early Holocene: A proxy record of early Holocene atmospheric CO2 concentrations reveals century-scale fluctuations between 260 and 350 ppm at a time when there could have been little human contribution to this increase, thus calling into question the attribution of the 270-365 rise in CO2 since the Industrial Revolution to human activities.

CO2 Emissions from Soil: Measurements of soil carbon storage along a temperature gradient across the boreal forest zone in Finland reveal that soil carbon storage beneath both low-and high-productivity forests increases with temperature, contrary to assumptions typically used in modeling this phenomenon.

Vegetative Growth Trends in Northern Eurasia: Reconstructed estimates of carbon storage in Northern Eurasia for three extreme climatic periods reveal that vegetation thrived there under conditions warmer than the present.

Earth's Past Biospheric Productivity Inferred from Oxygen Isotopes in Greenland Ice Core: A study of oxygen isotopes of air bubbles trapped in a Greenland ice core suggests that biospheric productivity is at its highest level of the past 82,000 years.  This elevated productivity level is consistent with what would be expected from the aerial fertilization effect of atmospheric CO2 enrichment.

Response of Oats to Elevated CO2 and Disease: Elevated CO2 partially offset the negative effects of barley yellow dwarf virus in infected oats grown for two months at an atmospheric CO2 concentration of 700 ppm as evidenced by infected plants displaying greater CO2-induced increases in photosynthesis, water-use efficiency, and total biomass than did non-infected control plants.

Effects of Elevated CO2 and Water Stress on Soybean: Short-term atmospheric CO2 enrichment of 700 ppm for 18 days decreased transpirational water losses of well-watered and water-stressed soybeans relative to their controls grown at 360 ppm CO2.  Although water stress decreased rates of net photosynthesis, regardless of CO2 treatment, rates were consistently higher for plants exposed to elevated CO2.  In addition, atmospheric CO2 enrichment led to a significant 33% increase in the total dry weight of water-stressed plants, while little impact was observed on well-watered plants.

Effects of Elevated CO2 on Nitrogen Balance in Wheat: Wheat plants grown for 28 days in a controlled environment with an atmospheric CO2 concentration of 1000 ppm exhibited significantly greater biomass, both above-and belowground, than did plants grown at ambient CO2, regardless of soil nitrogen concentration.  In addition, even though CO2-enriched plants removed greater quantities of nitrate from the soil, compared to ambiently-grown plants, less of it was assimilated into organic nitrogen forms.  Thus, CO2-enriched plants contained less organic nitrogen per unit biomass than control plants, which is an observation consistent with photosynthetic acclimation resulting from atmospheric CO2 enrichment.

Root Responses of Spring Wheat to Elevated CO2: Spring wheat grown in a FACE experiment located in Arizona, USA, displayed greater root systems of more extensive branching, particularly when soil moisture was low, when subjected to an atmospheric CO2 concentration of 550 rather than 370 ppm.  This observation indicates the potential for atmospheric CO2 enrichment to alleviate the negative effects of water stress on growth by producing root systems that are better adept at finding water and removing it from the soil.

Seasonal Changes of Winter Wheat to Elevated CO2: Winter wheat grown in open-top chambers located in The Netherlands displayed increased photosynthesis, biomass, and yield when exposed to an atmospheric CO2 concentration of 700 ppm.  Over the course of the growing season, elevated CO2 was found to have the greatest stimulatory effect on photosynthesis and growth later, as opposed to earlier, in the year after irradiance and temperatures had increased.