CO₂ and N-Fertilization Effects on Fine-Root Length, Production, and Mortality: A 4-Year Ponderosa Pine Study

• Published in: Oecologia Vol. 148; no. 3; pp. 517 - 525
• Main Authors: Phillips, Donald L., Johnson, Mark G., Tingey, David T., Storm, Marjorie J., Ball, J. Timothy, Johnson, Dale W.
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01-06-2006; Springer Nature B.V
• Subjects: Agrology; Animal, plant and microbial ecology; Applied ecology; Atmosphere; Atmospherics; Biological and medical sciences; Carbon dioxide; Carbon Dioxide - physiology; Crops; Ecotoxicology, biological effects of pollution; Evergreen trees; Fertilizers; Forest soils; Fundamental and applied biological sciences. Psychology; Global Change Ecology; Mortality; Nitrogen; Nitrogen - physiology; Pine trees; Pinus ponderosa - growth & development; Plant roots; Plant Roots - growth & development; Plants; Roots; Seedlings; Seedlings - growth & development; Soil air; Terrestrial environment, soil, air; Trees; Nitrogen fertilization; Energy flow; Root; Mortality; Carbon dioxide; Environmental factor; Fine-root dynamics; Medium enrichment; Pinus ponderosa; Gymnospermae; Global change; Air pollution; Coniferales; Spermatophyta; Biological effect; Rooting
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-006-0392-5

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.