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Effects of Elevated CO2, Soil Nitrogen and Phosphorus on Growth and Fungal Colonization of Pine Trees
Walker, R.F., Johnson, D.W., Geisinger, D.R. and Ball, J.T.  1998.  Growth and ectomycorrhizal colonization of ponderosa pine seedlings supplied different levels of atmospheric CO2 and soil N and P.  Forest Ecology and Management 109: 9-20.

What was done
The authors grew ponderosa pine seedlings for an entire year in controlled environment chambers with atmospheric CO2 concentrations of ambient, 525 or 700 ppm.  In addition, low or high levels of nitrogen and phosphorus were supplied to determine the main and interactive effects of atmospheric CO2 enrichment and soil nutrition on seedling growth and fungal colonization of their roots.

What was learned
After twelve months, the authors determined that phosphorus supply had little impact on overall seedling growth, while high nitrogen increased nearly every parameter measured, including root, shoot and total biomass, as did atmospheric CO2 enrichment.  Averaged across all nitrogen and phosphate treatments, total root dry weights at 525 and 700 ppm CO2 were 92 and 49% greater, respectively, than those observed at ambient CO2, while shoot dry weights were 83 and 26% greater.  Consequently, seedlings grown at 525 and 700 ppm CO2 had total dry weights that were 86 and 35% greater, respectively, than those measured at ambient CO2.  In addition, elevated CO2 increased the total number of ectomycorrhizal fungi on roots by 170% at 525 ppm CO2 and 85% at 700 ppm CO2 relative to the number observed at ambient CO2.

What it means
As the CO2 content of the air continues to rise, ponderosa pine seedlings will likely increase their biomass regardless of soil nitrogen and phosphorus supply.  However, if excess nitrogen is available in the soil, ponderosa pine should exhibit even greater growth increases with increases in the CO2 content of the air.  Moreover, as the atmospheric CO2 concentration rises, the number of ectomycorrhizal fungi associated with ponderosa pine roots should also rise, thereby increasing the availability of soil nutrients to seedlings, which can also cause greater CO2-induced increases in plant growth.

Reviewed 1 February 1999