Interactive effects of atmospheric CO2 enrichment and soil N on growth and ectomycorrhizal colonization of ponderosa pine seedlings.
Walker R.F. | Geisinger D.R. | Johnson D.W. | Ball J.T.
Interactive effects of elevated atmospheric CO2 and soil N fertility on above- and belowground development of juvenile ponderosa pine (Pinus ponderosa Dougl. ex Laws.) were examined. Seedlings were grown from seed in atmospheres containing 700 microliters l-1, 525 microliters l-1, or ambient CO2. Medium and high soil N treatments were created by adding sufficient (NH4)2SO4 to the potting mixA to increase total N by 100 micrograms g-1 and 200 micrograms g-1, respectively, while unamended mix, which had a total N concentration of approximately 300 micrograms g-1, served as the low N treatment. Three whole-seedling harvests at 4-month intervals permitted assessment of shoot and root growth and ectomycorrhizal formation resulting from inoculation with Pisolithus tinctorius (Pers.) Coker and Couch. After 4 months, CO2 enrichment increased shoot volume and dry weight of seedlings grown in high soil N, but this result was not evident in the other N treatments and did not persist to the second harvest. Root weight, however, increased, and shoot/root ratio decreased as the CO2 concentration increased within all three N treatments at the first harvest. At the second harvest, root weights within the high and intermediate N treatments were lowest in seedlings grown in ambient CO2 and shoot/root ratios decreased as CO2 increased in these two N treatments as well. Although the ectomycorrhizal infection percentage of seedlings grown in 700 microliters l-1 CO2 was highest among the seedlings grown in high N after 4 months, mycorrhizal colonization was variable overall at the first and second harvests. After 1 yr, the 525 microliters l-1 CO2 concentration stimulated above- and belowground growth more than the high CO2 atmosphere in both high and medium soil N. These seedlings also had relatively extensive ectomycorrhizal formation, but colonization was again variable. Results presented here suggest the response of juvenile ponderosa pine to CO2 enrichment is ephemeral.
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