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A path forward to improve the
representation of fine roots in
terrestrial biosphere models
Colleen M. Iversen
Climate Change Science Institute and
Environmental Sciences Division
Oak Ridge National Laboratory
13 August 2014
Co-conspirators:
Luke McCormack (CAS)
Jeff Warren (ORNL)
Anthony Walker (ORNL)
Xiaojuan Yang (ORNL)
Dali Wang (ORNL)
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A continuing goal is to LINK
empirical data with model
structure and process.
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Models may help pinpoint mechanisms and
explain dynamic responses
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Iversen, 2010 (New Phytologist)
a. G’DAY
2.0
7 m
Models may help pinpoint mechanisms and
explain dynamic responses
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a. G’DAY b. LPJ
2.07
m
1.5
m
Iversen, 2010 (New Phytologist)
Models may help pinpoint mechanisms and
explain dynamic responses
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a. G’DAY b. LPJ c. CLM-CN
2.07
m
1.5
m
3.43
m
Iversen, 2010 (New Phytologist)
Models may help pinpoint mechanisms and
explain dynamic responses
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Warren et al., 2014 (New Phytologist)
Continuing issue is appropriate representation
of root form & function at multiple scales
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At the global scale, plant
functional types (PFTs) are
groups of traits that represent,
or relate to, PLANT FUNCTION in
large-scale models.
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‘Tree Roots’, Vincent van Gogh, 1890
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Most plants are grouped into PFTs
according to ABOVEGROUND traits.
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How can we inform the
representation of BELOWGROUND
PROCESSES in large-scale
models through PFTs?
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We (empirical scientists) need
to PROACTIVELY provide the
information needed for model
parameters and processes.
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Improve the representation of
roots in the next-generation
TERRESTRIAL BIOSPHERE
MODELS.
WORKSHOP GOAL:
*Workshop support from Office of Biological
and Environmental Sciences in the Department
of Energy’s Office of Science
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It was important to bring
together an interdisciplinary
team of ROOT AND RHIZOSPHERE
ECOLOGISTS, MODELERS, and
DATABASE MANAGERS.
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Workshop continued a historical focus on
fine roots and their representation in models
1980 1985 1990 1995 2000 2005 2010 2015
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1980 1985 1990 1995 2000 2005 2010 2015
…UM, WHAT
ABOUT
MYCORRHIZAE?
YES, ROOTS ARE
IMPORTANT
ROOTS SHOULD PROBABLY
BE BETTER REPRESENTED
IN LARGE-SCALE MODELS
LET’S DO IT!
*
HOW CAN THIS
BE DONE?
ARE ROOTS
IMPORTANT?
THE INCLUSION OF
BELOWGROUND
PROCESSES AFFECTS
MODEL OUTCOMES
Workshop continued a historical focus on
fine roots and their representation in models
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What are the gaps between current
MODEL REPRESENTATION of roots and
EMPIRICAL UNDERSTANDING of roots
based on current measurements?
WORKSHOP DISCUSSION:
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PF
T p
ara
mete
r va
lue
s
0.0
0.5
1.0
1.5
2.0
Plant functional type
1 2 3 4 5 6 7 8 9 10 11 12 13 14
30
35
40
45
PF
T p
ara
me
ter
va
lue
s
0.0
0.5
1.0
1.5
2.0
Plant functional type
1 2 3 4 5 6 7 8 9 10 11 12 13 14
30
35
40
45
PF
T p
ara
mete
r valu
es
0.0
0.5
1.0
1.5
2.0
Plant functional type
1 2 3 4 5 6 7 8 9 10 11 12 13 14
30
35
40
45
Root C/N ratio
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PF
T p
ara
mete
r va
lue
s
0.0
0.5
1.0
1.5
2.0
Plant functional type
1 2 3 4 5 6 7 8 9 10 11 12 13 14
30
35
40
45
PF
T p
ara
me
ter
va
lue
s
0.0
0.5
1.0
1.5
2.0
Plant functional type
1 2 3 4 5 6 7 8 9 10 11 12 13 14
30
35
40
45
PF
T p
ara
mete
r valu
es
0.0
0.5
1.0
1.5
2.0
Plant functional type
1 2 3 4 5 6 7 8 9 10 11 12 13 14
30
35
40
45
Root C/N ratio = 42
New roots / new leaves = 1 (or 2)
Cellulose fraction = 0.5
Labile and lignin fractions = 0.25
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Do we agree on an IDEAL
CONCEPTUAL REPRESENTATION of root
processes that could be made
numerical in a model? What are the
PRIORITIES for the next steps in the
evolution of model representation?
WORKSHOP DISCUSSION:
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What are the BEST ROOT DATA
AVAILABLE across the globe for
model use?
WORKSHOP DISCUSSION:
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Number of entries
0 100000 200000 300000 400000
Y D
ata
1
2
3
4
5
Plant traits
Leaf traits
Seed traits
Stem traits
Root traits
Root traits underrepresented in TRY
J. Kattge, MPI
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Do we have continuous
measurements of the relationships
between ROOT PROCESSES AND
ENVIRONMENTAL CONDITIONS for
representation in models?
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Allen & Kitajima, 2013 (New Phytologist)
Continuous sensor and observation systems are needed
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We developed a PATH FORWARD to
improve the representation of fine
roots in terrestrial biosphere models.
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Develop a ROOT TRAIT DATABASE,
and let it guide our priorities for
future data collection.
*PLEASE SEND US DATA!*
1. A ROOT TRAIT DATABASE:
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http://www.try-db.org/TryWeb/Home.php
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Root
diameter (mm)
Specific
root length (m g-1)
Root tissue
density (g cm-1)
Branching
intensity (# roots per higher
order root)
Branching
architecture (root length per
higher order root)
Type of
mycorrhizae (AM or EM)
EM
colonization (% tips colonized)
% AM
colonization (% length colonized)
Survivorship (roots year-1)
Lifespan (days)
Turnover rate (% growing season-1)
Respiration
rate (nmol O2 g
-1 s-1)
Respiration
rate by mass (nmol s-1 m-2)
Stele
diameter (µm)
Cortex
diameter (µm)
Root
porosity (area)
Vessel
diameter (µm)
Absolute
biomass (g m-2)
Total root
biomass (%)
Annual
production (g m-2)
Annual
mortality (g m-2 year-1)
Biomass
turnover (g m-2 year-1)
Root C, N, K, P,
Al, Ca, Mg (mg g-1)
Root Cr, Ni, Cu,
Zn, As, Cd, Pb (mg kg-1)
C:N ratio
Ion
concentration
(Na+ and Cl-) (mg g d.wt-1)
Carbohydrates
(TNC) (mg g-1)
Mean root
stable δ15N (%)
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Develop a MODULARIZED VERSION
OF THE COMMUNITY LAND MODEL to
test effects of environmental drivers
on root and rhizosphere dynamics,
and effects of changing model
parameters on ecosystem
processes.
2. IMPROVED MODEL INTERFACE:
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“Root Window”
Function
• Allocation
• Phenology
• Mortality
• Water uptake
• Nutrient uptake
• Respiration
Structure
• Vertical dist.
• Horizontal dist.
• Size classes
• C:N:P
Wang et al., 2014 (EMS)
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Add an ADDITIONAL FINE-ROOT POOL
to the Community Land Model
representing ephemeral,
ABSORPTIVE ROOTS, and
parameterize PFTs with data
compiled in the root trait database.
3. MODIFIED MODEL STRUCTURE:
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Where global data are unavailable,
begin with phylogeny
Species
Root
dia
mete
r (
m)
0
200
400
600
800
1000Euphorbiaceae
Magnoliaceae
Lauraceae
Fagaceae
Other families
Kong et al. 2014. (New Phytologist)
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Gain a CONSENSUS FROM THE
BROADER COMMUNITY on the relative
importance of different root traits.
4. CONTINUE TO SOLICIT COMMUNITY INPUT:
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There are some things that WE
DON’T UNDERSTAND well enough to
represent in terrestrial biosphere
models.
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The NEXT STEPS in our
understanding of roots and their
role in the ecosystem involve NEW
QUESTIONS, NEW METHODS, NEW
TECHNOLOGY, and IMPROVED
REPRESENTATION of root
processes in models of all scales.
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Henning, Weston, Schadt; ORNL
Taylor et al. 2013 (Ecology Letters)
De Graaff et al., 2014 (SBB)
Yang et al., 2014 (Biogeosciences)
Wei et al., 2014 (DAAC)
Warren et al., 2013 (Plant and Soil)
RhizoSystems, LLC
Iversen, Childs, 2014
www.rhizonetscience.com
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Fine roots are where I START
thinking about ecosystem
processes, but not where I stop,
and models need the bigger
picture too.
WHAT IF MY RESEARCH ISN’T ON FINE ROOTS?
WHOLE-PLANT C ALLOCATION · SOIL NUTRIENT AVAILABILITY · SOIL C STORAGE
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To track our progress, and LEND
YOUR VOICE (and your data) to the
effort, following us at:
http://web.ornl.gov/~ciz/Roots_in_Models.html
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Funding:
Office of Biological and Environmental Research in the DOE Office of
Science supported the Roots in Models Workshop and continuing
work.
Workshop attendees:
Mike Allen, Allison Boyer, Eddie Brzostek, Joanne Childs, Bob Cook,
Marie-Anne De Graaff, Dave Eissenstat, Adrien Finzi, Josh Fisher,
Lianhong Gu, Paul Hanson, Colleen Iversen, Andy Jones, Shujiang
Kang, Jens Kattge, Tong King, Jitu Kumar, Hans Lambers, Roser
Matamala, Melanie Mayes, Rich Norby, Rich Phillips, Shafer Powell,
Seth Pritchard, Dan Ricciuto, H. Jochen Schenk, Ingrid Slette, Jens-
Arne Subke, Peter Thornton, Collin Timm, Anthony Walker,
Gangsheng Wang, Jeff Warren, Dave Weston, Stan Wullschleger,
Xiaojuan Yang
Acknowledgements http://web.ornl.gov/~ciz/Roots_in_Models.html