CO sub(2) and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study

• Published in: Oecologia 2006-06, Vol.148 (3), p.517-525
• Main Authors: Phillips, Donald L, Johnson, Mark G, Tingey, David T, Storm, Marjorie J, Ball, JTimothy, Johnson, Dale W
• Format: Article
• Language: English
• Subjects: Pinus ponderosa
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-006-0392-5

We conducted a 4-year study of juvenile Pinus ponderosa fine root ( less than or equal to 2 mm) responses to atmospheric CO sub(2) and N-fertilization. Seedlings were grown in open-top chambers at three CO sub(2) levels (ambient, ambient+175 mu mol/mol, ambient+350 mu mol/mol) and three N-fertilization levels (0, 10, 20 g m super(-2) year super(-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 CO sub(2) nor N-fertilization treatments affected the seasonal patterns of root production or mortality. Yearly values of fine-root length standing crop (m m super(-2)), production (m m super(-2) year super(-1)), and mortality (m m super(-2) year super(-1)) were consistently higher in elevated CO sub(2) treatments throughout the study, except for mortality in the first year; however, the only statistically significant CO sub(2) effects were in the fine-root length standing crop (m m super(-2)) in the second and third years, and production and mortality (m m super(-2) year super(-1)) in the third year. Higher mortality (m m super(-2) year super(-1)) in elevated CO sub(2) was due to greater standing crop rather than shorter life span, as fine roots lived longer in elevated CO sub(2). 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 CO sub(2). Multi-year studies at all life stages of trees are important to characterize belowground responses to factors such as atmospheric CO sub(2) 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 CO sub(2).