Optimality Principles in Earth System Models: More ...Silvia Caldararu. Tea Thum, Melanie Kern, Lin...
Transcript of Optimality Principles in Earth System Models: More ...Silvia Caldararu. Tea Thum, Melanie Kern, Lin...
Optimality Principles in Earth System Models: More
Complexity Without MoreParameters
Silvia CaldararuTea Thum, Melanie Kern, Lin Yu, Marleen Pallandt, Jan Engel, Sönke
Zaehle
Integrated C, N, and P cycles Improving process
representation
Plant – soil interaction New soil model including phosphorus dynamics
QUINCY: Quantifying the effects of interacting nutrient cycles on terrestrial biosphere dynamics and their climate feedbacks
Plant optimality
Experiments say plants are plastic
Decrease of leaf N concentration during the course of the Oak Ridge FACE experiment
Decrease of leaf to root ratio during the course of the Oak Ridge FACE experiment
Models fail to represent observed plasticity
ObservationsModel ensemble mean
Zaehle 2014, New Phytologist
Optimality: what is it and how can it help?
The plant evolutionary strategy that results in maximising survival and offspring fitness.
Can use processes that already exist
in the model
In the case of trees it reduces to maximising
growth
No pre-defined thresholds
Best use of resources
Optimality in practice
Leaf level:photosynthetic nitrogen fractions
Canopy level:leaf nitrogen content
Plant level:biomass allocation
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2
3
Study sites: 2 FACE experiments
Duke FACELoblolly pine evergreen plantationMaintained growth response until the end of the experiment
ORNL FACESweetgum deciduous plantationDecreased growth response towards the end of the experiment
Optimal photosynthetic nitrogen fractions
Amount of N allocated to each photosynthetic fraction changes dynamically to increase GPP
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Vcmax25Jmax25
Structural N Photosynthetic N
Rubisco
Electron transport
Chlorophyll
Observations❶ Optimal N fractions
Optimal fractions under elevated CO21Structural N Photosynthetic N
Rubisco
Electron transport
Chlorophyll
V cmax
25/ N
area
Year
DUKE
Data from D. Ellsworth and K. Crous
Optimal fractions seasonality1Structural N Photosynthetic N
Rubisco
Electron transport
Chlorophyll
Optimal leaf nitrogen content
• Higher leaf N –increased GPP
• Lower leaf N –decreased respiration
2Change in canopy C:N ratio if
CNC
N
Optimal leaf nitrogen content
CN
C N
Labile pool – biomass available for growth Only increase canopy
N if there is sufficient N available for plant growth
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Optimal leaf nitrogen under elevated CO22Observations❷ Optimal leaf N
Leaf nitrogen response relative to the start of the experiment
ORNL
DUKE
Optimal biomass allocation:nutrient response
C available for growth = N available for growth given specific tissue CN ratios
Labile pool – biomass available for growth
C
NC N
fleaf
froot
fwood
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Optimal biomass allocation:plant hydraulics response
• Hydraulics condition: maintain water column
• Optimal condition: build new tissue (roots or sapwood) with maximum benefit over its lifespan
Magnani et al, 2000, Plant, cell and environment
Ψleaf
Ψsoil
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Optimal allocation under elevated CO23
Observations❸ Optimal allocation
C
NC N
fleaf
froot
fwood
Leaf to root ratio response relative to the start of the experiment
ORNL
DUKE
Optimality: caveats
Mathematical optimality does
not mean it’s real
Don’t forget about structural constraints
Not every process is optimal
Optimality works at different timescales
Assumption: individual optimality scaled to the
ecosystem
There can always be missing processes
Data from manipulative experiments
Existing models
Optimality theory
Comparison with data
Hypothesis
New modelEvaluation
Summary
• Next generation land surface model: process-focused, explicitnutrient cycles, modular
• Optimality concepts are a way to include observed plant plastic responses in models
• Use of data from manipulative experiments to improve process understanding and representation
More info at:tinyurl.com/erc-quincy