References

1
On Predicting Root Decomposition
Kim H. Ludovici USDA Forest Service, SRS-4160
Abstract Quantification of root decomposition
remains controversial because researchers can not
control the process. The literature provides
examples in which researchers have limited the
size, age and species of roots used in studies,
or controlled the onset of decomposition. Others
have controlled ambient and/or soil conditions
during root growth and decomposition. Still,
there is not one quintessential root
decomposition methodology that can be utilized
across species or ecotomes. Using data from
available publications, decay curves will be
generated with consideration given to tree
species, stand age, root size, temperature and
methodology.
Discussion Research studies have been conducted
on every continent, and on many of the most
economically important species. The 2 phase
pattern of decomposition, often reported for fine
roots, supports the idea that root structure and
complexity control nutrient release rates from
roots, however, most studies include only roots lt
5mm in diameter, and last only a year or two
(approximately the duration of a Masters
project). Consideration that most decomposition
work is conducted on a small percentage of the
root system (just 5 15 of the total tree
biomass), and has a duration far shorter than the
lifespan of a fine root, is necessary. Root
decomposition and nutrient release are also
traditionally estimated from dried root tissues,
and while it is unlikely that roots dehydrate
prior to decomposition in-situ, the limited
studies disagree on the cause and effect.

• Results
• Summarization across species, ecotomes and
  methodologies suggest
• Root decomposition rate does not differ by soil
  depth
• Soil temperature may, or may not be positively
  related to
• decomposition rate
• Root decomposition is affected by soil texture
• Site fertility is not a predictor of
  decomposition rate
• Soil biota are always important for root
  decomposition
• Ambient temperature and CO2 level do not strongly
  impact root
• decomposition rates
• Decomposition is negatively related to root
  diameter
• Nutrient concentrations in roots may or may not
  be related to
• decomposition rate
• Decomposition is negatively related to root
  lignin and carbohydrate
• concentrations
• Root decomposition rates vary widely between
  species

Table 1. Summary of literature review including
root size and species, and decomposition rate
constants (k-values) when published.
PC2
Scores All Soils 0-20 cm
PC1
Conclusions We are seriously over estimating the
amount of root decomposition that occurs over a
forest rotation. Additional studies are required
to test the mechanisms of nutrient loss, and the
long-term decomposition rates of larger roots.
Table 2. Summary of root decomposition rate
response to within-species manipulations and/or
direct tests of site effects.

• References
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  and nutrient changes of decaying woody roots in
  lodgepole pine forests, southeastern Wyoming.
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• McClaugherty, C.A., J.D. Aber and J.M. Melillo.
  1984. Decomposition dynamics of fine roots in
  forested ecosystems. Oikos 42378-386
• Fahey, T.J., J.W. Hughes, Mou Pu and M.A. Arthur.
  1988. Root Decomposition and Nutrient Flux
  Following Whole-Tree Harvest of Northern Hardwood
  Forest. For. Sci. 34(3)744-768
• Bloomfield, J., K.A. Vogt and D.J. Vogt. 1993.
  Decay rate and substrate quality of fine roots
  and foliage of two tropical tree species in the
  Luquillo Experimental Forest, Puerto Rico. Plant
  and Soil 150233-245
• Ruark, G.A. 1993. Modeling Soil Temperature
  Effects on In Situ Decomposition Rates for Fine
  Roots of Loblolly Pine. For. Sci. 39(1)118-129
• Silver, W.L. and K.A. Vogt. 1993. Fine root
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  disturbances in a subtropical wet forest
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• Scheu, S. and J. Schauermann. 1994.Decomposition
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  and ash), diameter, site of exposure and
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• Lohmus,K. and M. Ivask. 1995.Decomposition and
  nitrogen dynamics of fine roots of Norway spruce
  (Picea abies (L.) Karst.) at different sites.
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• King, J.S.. H.L. Allen, P.M. Dougherty and B.R.
  Strain. 1997. Decomposition of roots in loblolly
  pine Effects of nutrient and water availability
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• Mun, H.T. and W.G. Whitford. 1998. Changes in
  mass and chemistry of plant roots during
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• Ostertag, R. and S.E. Hobbie 1999. Early stages
  of root and leaf decomposition in Hawaiian
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• Chen, Hua, M.E. Harmon, R.P. Griffiths and W.
  Hicks. 2000. Effects of temperature and moisture
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• Usman, S., S.P. Singh, Y.S. Rawat and S.S.
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• Dilustro, J.J, F.P. Day and B.G. Drake. 2001.
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Fig. 1 Photograph of recovered root material from
55 to 70-year-old loblolly pine stumps that had
been decomposing for (A) 5 years, (B) 20 years,
(C) 10 years, and (D) 55 years, on a Kanhapludult
in the Piedmont region of North Carolina.
Reproduced from Ludovici et al. 2002

Introduction and Methods Determining what we
know about root decomposition means going back
through the literature, to see what has really
been done, what assumptions have been made, what
species and environmental conditions are
included, and how the work was implemented. A
literature search for peer-reviewed publications
reguarding tree and root and decomposition
identified only 58 articles published in the past
40 years (Table 1). Of those 58, only 24
publications included within-species
manipulations and/or direct tests of site effects
on root decomposition rate (Table 2).
Post-harvest decomposition (Fig. 1) is virtually
unstudied, even though large roots persist for
many years (Fig. 2), and contribute a sizable
pool of C to the developing forest (Fig. 3)
Methodologies have varied widely, but most often
utilize live, excised roots that are washed and
dried prior to decomposition (Fig. 4). Studies
incorporating season and root hydration (Fig. 5)
suggest additional sources of variability in root
decomposition rates.
A
B
Fig. 2. Biomass of mature loblolly pine root
systems recovered along a time chronosequence,
Durham, NC
Fig. 3. Carbon pools in decomposing roots and the
soil volume surrounding them, measured along a
time chronosequence, Durham, NC 2000
Fig. 5. Graph of biomass loss (A) and carbon
concentrations (B) in fine roots of Pinus taeda
decomposing in-situ.
Fig. 4. Photograph of a controlled environment
chamber used in root incubations.