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.
Phillips
Donald L
DL
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
Johnson
Mark G
MG
Tingey
David T
DT
Storm
Marjorie J
MJ
Ball
J Timothy
JT
Johnson
Dale W
DW
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