CO2 and N-fertilization effects on fine-root length, production, and mortality: a 4-year ponderosa pine study.
We conducted a 4-year study of juvenile Pinus ponderosa fine root (< or =2 mm) responses to atmospheric CO2 and N-fertilization. Seedlings were grown in open-top chambers at three CO2 levels (ambient, ambient+175 mumol/mol, ambient+350 mumol/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.
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. Phillips.Donald@epa.gov
Donald L
DL
Phillips
Mark G
MG
Johnson
David T
DT
Tingey
Marjorie J
MJ
Storm
J Timothy
JT
Ball
Dale W
DW
Johnson
D001272:Atmosphere; D002245:Carbon Dioxide / Q000502:physiology*; D005308:Fertilizers; D009584:Nitrogen / Q000502:physiology*; D041604:Pinus ponderosa / Q000254:growth & development*; D018517:Plant Roots / Q000254:growth & development*; D036226:Seedlings / Q000254:growth & development*
D005308:Fertilizers; D002245:Carbon Dioxide; D009584:Nitrogen