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CO2 AND N-FERTILIZATION EFFECTS ON FINE ROOT LENGTH, PRODUCTION, AND MORTALITY: A 4-YEAR PONDEROSA PINE STUDY
Phillips, D L., M G. Johnson, D T. Tingey, M. J. Storm, J. T. Ball, AND D. W. Johnson. CO2 AND N-FERTILIZATION EFFECTS ON FINE ROOT LENGTH, PRODUCTION, AND MORTALITY: A 4-YEAR PONDEROSA PINE STUDY. OECOLOGIA. Springer, New York, NY, 148(3):517-525, (2006).
To evaluate responses to atmospheric CO2 and N-fertilization in the ponderosa pine
We conducted a 4-year study of Pinus ponderosa fine root (<2 mm) responses to atmospheric CO2 and N-fertilization. Seedlings were grown in open-top chambers at 3 CO2 levels (ambient, ambient+175 mol/mol, ambient+350 mol/mol) and 3 N-fertilization levels (0, 10, 20 g?m-2?yr-1). Length and width of individual roots were measured from minirhizotron video images bimonthly over 4 years. Biomass estimates were made by cross-calibrating with soil core root biomass.
Neither CO2 nor N-fertilization treatments affected seasonal root production or turnover patterns. Elevated CO2 resulted in significantly higher biomass (g?m-2) in the first 3 years and higher turnover (g?m-2?yr-1) in the last 2 years. No significant N effects were noted for annual root biomass, production, or turnover. Fine root nutrient cycling rates varied from 74-362 g?m-2?yr-1 for C and 0.9-4.6 g?m-2?yr-1 for N. Higher turnover in elevated CO2 was due to greater biomass rather than shorter life-span. Fine roots lived longer in elevated CO2, and turnover relative to biomass was generally < that in ambient CO2, emphasizing the importance of root turnover definitions.