106
Plant Structural C
(3y)
Plant Metabolic C
(.5y)
CO2
.55
Active Soil C
(1.5y)
G. Philip Robertson and Eldor A. Paul
FIGURE 7.1. Structural components
of the CENTURY soil organic matter
model. Values adjacent to arrows are
transfer coefficients for the noted
carbon pools; parenthetical values
are approximate turnover times.
(From Paustian et al. [1992].)
.85 -.68T
(25y)
SL Surface Litter
Passive Soil C
(1000y)
BL Belowground Litter
A
Lignin fraction
T
Soil Silt + Clay fraction
Schlesinger 1984; Jenkinson et al. 1991; IPCC
1996).
In the remainder of this chapter we present and
discuss appropriate methods for assessing plant litter decomposition and organic matter dynamics in
terrestrial ecosystems. Dozens of contributions in
the past decade have presented methods for assessing one or the other of these processes. We
concentrate on those methods that have ecological
relevance and that appear to be sufficiently well
standardized to be usable for cross-ecosystem
comparisons. This latter criterion is becoming increasingly important as the diversity of available
methods limits opportunities for a posteriori syntheses of independently collected data from multiple sites and studies. Our contribution is intended
to complement rather than complicate emerging
efforts to standardize current soil methods for ecological research (e.g., Robertson et al. 1999b).
Plant Litter Decomposition
Fine Litter Decomposition Rates
The decomposition of plant leaves and other relatively fine material is typically assayed by following mass and nutrient changes in litter placed in
mesh bags on the soil surface. As the organic material decomposes, changes in mass document the
decomposition rate, and changes in nutrient composition document rates of nutrient release, retention, and immobilization (e.g., Falconer et al. 1933;
Bocock et al. 1960; Gosz et al. 1973; Melillo et al.
1982; Heal et al. 1997).
Decomposition is carried out by a complex array
of heterotrophic organisms that vary widely in size
and function. Commonly these organisms are
grouped into size (body-width) classes that correspond to the groups microflora and -fauna, and
Plant Structural C
(3y)
Plant Metabolic C
(.5y)
CO2
.55
Active Soil C
(1.5y)
G. Philip Robertson and Eldor A. Paul
FIGURE 7.1. Structural components
of the CENTURY soil organic matter
model. Values adjacent to arrows are
transfer coefficients for the noted
carbon pools; parenthetical values
are approximate turnover times.
(From Paustian et al. [1992].)
.85 -.68T
(25y)
SL Surface Litter
Passive Soil C
(1000y)
BL Belowground Litter
A
Lignin fraction
T
Soil Silt + Clay fraction
Schlesinger 1984; Jenkinson et al. 1991; IPCC
1996).
In the remainder of this chapter we present and
discuss appropriate methods for assessing plant litter decomposition and organic matter dynamics in
terrestrial ecosystems. Dozens of contributions in
the past decade have presented methods for assessing one or the other of these processes. We
concentrate on those methods that have ecological
relevance and that appear to be sufficiently well
standardized to be usable for cross-ecosystem
comparisons. This latter criterion is becoming increasingly important as the diversity of available
methods limits opportunities for a posteriori syntheses of independently collected data from multiple sites and studies. Our contribution is intended
to complement rather than complicate emerging
efforts to standardize current soil methods for ecological research (e.g., Robertson et al. 1999b).
Plant Litter Decomposition
Fine Litter Decomposition Rates
The decomposition of plant leaves and other relatively fine material is typically assayed by following mass and nutrient changes in litter placed in
mesh bags on the soil surface. As the organic material decomposes, changes in mass document the
decomposition rate, and changes in nutrient composition document rates of nutrient release, retention, and immobilization (e.g., Falconer et al. 1933;
Bocock et al. 1960; Gosz et al. 1973; Melillo et al.
1982; Heal et al. 1997).
Decomposition is carried out by a complex array
of heterotrophic organisms that vary widely in size
and function. Commonly these organisms are
grouped into size (body-width) classes that correspond to the groups microflora and -fauna, and