CO2 and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study |
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Authors: | Donald L. Phillips Mark G. Johnson David T. Tingey Marjorie J. Storm J. Timothy Ball Dale W. Johnson |
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Affiliation: | (1) U.S. Environmental Protection Agency, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Western Ecology Division, 200 SW 35th St., Corvallis, OR 97333, USA;(2) Dynamac International Inc., 200 SW 35th St., Corvallis, OR 97333, USA;(3) Fireball Information Technologies, 1240 Fairfield Ave., Reno, NV 89509, USA;(4) Environmental and Resource Sciences, University of Nevada, Reno, NV 89557, USA |
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Abstract: | We conducted a 4-year study of juvenile Pinus ponderosa fine root (≤2 mm) responses to atmospheric CO2 and N-fertilization. Seedlings were grown in open-top chambers at three CO2 levels (ambient, ambient+175 μmol/mol, ambient+350 μmol/mol) and three N-fertilization levels (0, 10, 20 g m−2 year−1). Length and width of individual roots were measured from minirhizotron video images bimonthly over 4 years starting when the seedlings were 1.5 years old. Neither CO2 nor N-fertilization treatments affected the seasonal patterns of root production or mortality. Yearly values of fine-root length standing crop (m m−2), production (m m−2 year−1), and mortality (m m−2 year−1) were consistently higher in elevated CO2 treatments throughout the study, except for mortality in the first year; however, the only statistically significant CO2 effects were in the fine-root length standing crop (m m−2) in the second and third years, and production and mortality (m m−2 year−1) in the third year. Higher mortality (m m−2 year−1) in elevated CO2 was due to greater standing crop rather than shorter life span, as fine roots lived longer in elevated CO2. No significant N effects were noted for annual cumulative production, cumulative mortality, or mean standing crop. N availability did not significantly affect responses of fine-root standing crop, production, or mortality to elevated CO2. Multi-year studies at all life stages of trees are important to characterize belowground responses to factors such as atmospheric CO2 and N-fertilization. This study showed the potential for juvenile ponderosa pine to increase fine-root C pools and C fluxes through root mortality in response to elevated CO2. |
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Keywords: | Fine-root dynamics Pinus ponderosa Carbon dioxide Nitrogen fertilization |
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