16. Ecosystem Nutrient Balance and Dynamics
regimes. Nadelhoffer et al. (1998a) added 15N to
both reference and chronically fertilized stands at
the Harvard Forest, Massachusetts, and found that
tree uptake increased with fertilization; this pattern
was not, however, observed by Tietema et al.
(1998) in a series of lightly (3 to 6 kg N ha -I yr- I )
to more heavily (20 to 91 kg N ha -I yr- I ) fertilized NITREX sites. In this latter study, the percentage of 15N applied that was taken up by trees
(10 to 42%) after 1 year did not appear to be related
to total fertilizer addition, although the efficiency
of retention by organic soil horizons (11 to 47%)
decreased with N addition as loss to leaching (0 to
50%) increased with N additions.
Labeled tracers have the advantage of allowing
the researcher to trace the movement of an element
through a plot-level ecosystem. However, there are
several disadvantages to these techniques. Most
studies have added tracer directly to the forest floor,
thus ignoring canopy interactions. The size of the
plots that can be used is necessarily small, as tracers
tend to be expensive and, in the case of radioactive
tracers, dangerous to use in levels that can leach out
of the system. Another problem is the time course
of study. Most studies can follow added label for a
year or two at most due to the decreasing recovery
of the tracer. Preston and Mead (1995) followed
labeled litter for 7.5 years and found stabilization
of the label after 3 years, but also found a low recovery (under 20%) with time. In contrast, White
and Howes (1994) found 40% of added label remaining after 7 years in a salt marsh. Yet because
so much of added N is immobilized in soil organic
matter, this N could become available for uptake
by vegetation or else lost from the system via leaching or denitrification at a later date, and thus these
processes will be underestimated in short-term
studies. Because there is continuous exchange between mineral and organic bound N-forms in soils,
the label will begin to behave like the bulk of soil
N (Knicker et al. 1997). However, with further refinement and perhaps through the use of models to
track the further fate of label, these techniques will
certainly add to the arsenal of methods that can be
used in the calculation of ecosystem-level elemental budgets.
Acknowledgments This review benefited greatly
from discussions with and reviews by Linda Pardo,
Dan Binkley, Steve Perakis, C. Wayne Martin,
259
Knute Nadelhoffer, and Charley Driscoll, who generously offered advice, references, data, and
criticism.
References
Aber, J.D. Nitrogen cycling and nitrogen saturation in
temperate forest ecosystems. Trends Ecol. Evolut.
7:220--223; 1992.
Aber, J.D.; Magill, A; Boone, R.; Melillo, J.M.; Steudler,
P.; Bowden, R. Plant and soil responses to chronic
nitrogen additions at the Harvard Forest, Massachusetts. Ecol. Applic. 3:156-166; 1993.
Aber, lD.; Ollinger, S.V.; Federer, C.A; Reich, P.B.;
Goulden, M.L.; Kicklighter, D.W.; Melillo, lM.; Lathrop, RG., Jr. Predicting the effects of climate change
on water yield and forest production in the northeastern United States. Clim. Res. 5:207-222; 1995.
Adams, M.B.; Angradi, T.R; Kochenderfer, IN. Stream
water and soil solution response to 5 years of nitrogen
and sulfur additions at the Fernow Experimental Forest, West Virginia. For. Ecol. Manage. 95:79-91;
1997.
Anderson, D.W. The effect of parent material and soil
development on nutrient cycling in temperate ecosystems. Biogeochemistry 5:71-97; 1988.
Baron, lS.; Ojima, D.S.; Holland, E.A.; Parton, w.J.
Analysis of nitrogen saturation potential in Rocky
Mountain tundra and forest: Implications for aquatic
systems. Biogeochemistry 27:61-82; 1994.
Bayley, S.E.; Schindler, D.W. The role of fire in determining stream water chemistry in northern coniferous
forests. In: Mooney, H.A; Medina, E.; Schindler,
D.W.; Schulze, E.D.; Walker, B.H., eds. Ecosystem
Experiments. SCOPE 45. New York: Wiley;
1991:141-165.
Billen, G.; Lancelot, c.; Meybeck, M. N, P, and Si retention along the aquatic continuum from land to
ocean. In: Mantoura, R.F.C.; Martin, J.-M.; Wollast,
R, eds. Ocean Margin Processes in Global Change.
New York: Wiley; 1991:19-44.
Binkley, D. The influence of tree species on forest soils:
Processes and patterns. In: Mead, D.J.; Cornforth, I.S.,
eds. Proceedings of the Trees and Soil Workshop.
Agronomy Society of New Zealand Special Publication 10. Canterbury, NZ: Lincoln Univ Pr.; 1996:133.
Binkley, D.; Kimmins, lP.; Feller, M.C. Water chemistry
profiles in an early- and mid-successional forest in
coastal British Columbia. Can. 1 For. Res. 12:240-248; 1982.
Binkley, D.; Sollins, P.; Bell, R.; Sachs, D.; Myrold, D.
Biogeochemistry of adjacent conifer and alder-conifer
stands. Ecology 73:2022-2033; 1992.
regimes. Nadelhoffer et al. (1998a) added 15N to
both reference and chronically fertilized stands at
the Harvard Forest, Massachusetts, and found that
tree uptake increased with fertilization; this pattern
was not, however, observed by Tietema et al.
(1998) in a series of lightly (3 to 6 kg N ha -I yr- I )
to more heavily (20 to 91 kg N ha -I yr- I ) fertilized NITREX sites. In this latter study, the percentage of 15N applied that was taken up by trees
(10 to 42%) after 1 year did not appear to be related
to total fertilizer addition, although the efficiency
of retention by organic soil horizons (11 to 47%)
decreased with N addition as loss to leaching (0 to
50%) increased with N additions.
Labeled tracers have the advantage of allowing
the researcher to trace the movement of an element
through a plot-level ecosystem. However, there are
several disadvantages to these techniques. Most
studies have added tracer directly to the forest floor,
thus ignoring canopy interactions. The size of the
plots that can be used is necessarily small, as tracers
tend to be expensive and, in the case of radioactive
tracers, dangerous to use in levels that can leach out
of the system. Another problem is the time course
of study. Most studies can follow added label for a
year or two at most due to the decreasing recovery
of the tracer. Preston and Mead (1995) followed
labeled litter for 7.5 years and found stabilization
of the label after 3 years, but also found a low recovery (under 20%) with time. In contrast, White
and Howes (1994) found 40% of added label remaining after 7 years in a salt marsh. Yet because
so much of added N is immobilized in soil organic
matter, this N could become available for uptake
by vegetation or else lost from the system via leaching or denitrification at a later date, and thus these
processes will be underestimated in short-term
studies. Because there is continuous exchange between mineral and organic bound N-forms in soils,
the label will begin to behave like the bulk of soil
N (Knicker et al. 1997). However, with further refinement and perhaps through the use of models to
track the further fate of label, these techniques will
certainly add to the arsenal of methods that can be
used in the calculation of ecosystem-level elemental budgets.
Acknowledgments This review benefited greatly
from discussions with and reviews by Linda Pardo,
Dan Binkley, Steve Perakis, C. Wayne Martin,
259
Knute Nadelhoffer, and Charley Driscoll, who generously offered advice, references, data, and
criticism.
References
Aber, J.D. Nitrogen cycling and nitrogen saturation in
temperate forest ecosystems. Trends Ecol. Evolut.
7:220--223; 1992.
Aber, J.D.; Magill, A; Boone, R.; Melillo, J.M.; Steudler,
P.; Bowden, R. Plant and soil responses to chronic
nitrogen additions at the Harvard Forest, Massachusetts. Ecol. Applic. 3:156-166; 1993.
Aber, lD.; Ollinger, S.V.; Federer, C.A; Reich, P.B.;
Goulden, M.L.; Kicklighter, D.W.; Melillo, lM.; Lathrop, RG., Jr. Predicting the effects of climate change
on water yield and forest production in the northeastern United States. Clim. Res. 5:207-222; 1995.
Adams, M.B.; Angradi, T.R; Kochenderfer, IN. Stream
water and soil solution response to 5 years of nitrogen
and sulfur additions at the Fernow Experimental Forest, West Virginia. For. Ecol. Manage. 95:79-91;
1997.
Anderson, D.W. The effect of parent material and soil
development on nutrient cycling in temperate ecosystems. Biogeochemistry 5:71-97; 1988.
Baron, lS.; Ojima, D.S.; Holland, E.A.; Parton, w.J.
Analysis of nitrogen saturation potential in Rocky
Mountain tundra and forest: Implications for aquatic
systems. Biogeochemistry 27:61-82; 1994.
Bayley, S.E.; Schindler, D.W. The role of fire in determining stream water chemistry in northern coniferous
forests. In: Mooney, H.A; Medina, E.; Schindler,
D.W.; Schulze, E.D.; Walker, B.H., eds. Ecosystem
Experiments. SCOPE 45. New York: Wiley;
1991:141-165.
Billen, G.; Lancelot, c.; Meybeck, M. N, P, and Si retention along the aquatic continuum from land to
ocean. In: Mantoura, R.F.C.; Martin, J.-M.; Wollast,
R, eds. Ocean Margin Processes in Global Change.
New York: Wiley; 1991:19-44.
Binkley, D. The influence of tree species on forest soils:
Processes and patterns. In: Mead, D.J.; Cornforth, I.S.,
eds. Proceedings of the Trees and Soil Workshop.
Agronomy Society of New Zealand Special Publication 10. Canterbury, NZ: Lincoln Univ Pr.; 1996:133.
Binkley, D.; Kimmins, lP.; Feller, M.C. Water chemistry
profiles in an early- and mid-successional forest in
coastal British Columbia. Can. 1 For. Res. 12:240-248; 1982.
Binkley, D.; Sollins, P.; Bell, R.; Sachs, D.; Myrold, D.
Biogeochemistry of adjacent conifer and alder-conifer
stands. Ecology 73:2022-2033; 1992.