1. Stoichiometry of Forest Nutrient LimitationStoichiometry of Forest Nutrient Limitation
Melany Fisk, Miami University

2. Bormann et al. 1977
Stoichiometry of Forest Nutrient LimitationStoichiometry of Forest Nutrient Limitation
Dynamic context:
Interacting elements
Resource
optimization by
organisms
Species traits
Disturbance and
ecosystem
development
Heterogeneous
landscape

3. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
− Theory predicts N limitation
− Has N deposition induced P limitation?
− Recent syntheses predict co-limitation
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
 At what time scales can
resource allocation
processes operate to
minimize single-element
limitation?

4. Rethinking limitationRethinking limitation
 Regional approach incorporates forest succession, soil variation

5. Rethinking limitationRethinking limitation
 Regional approach incorporates forest succession, soil variation
parent material, succession

6. Rethinking limitationRethinking limitation
 Regional approach incorporates forest succession, soil variation
 Short-term experimental responses evaluated in context of
longer-term pattern
parent material, succession

7. Rethinking limitationRethinking limitation
 Regional approach incorporates forest succession, soil variation
 Short-term experimental responses evaluated in context of
longer-term pattern
N x P fertilization
experiment:
13 sites
30 kg N/ha/yr
10 kg P/ha/yr parent material, succession

8. Examples of Resource Allocation Across SitesExamples of Resource Allocation Across Sites
 Above vs belowground
• Total soil respiration is negatively
related to N availability (Bae et al.
submitted)
 Belowground: N vs P
• N and P availability are coupled by
phosphatase activity (Ratliff 2012)

9. Examples of Resource Allocation Across SitesExamples of Resource Allocation Across Sites
 Above vs belowground
• Total soil respiration is negatively
related to N availability (Bae et al.
submitted)
 Belowground: N vs P
• N and P availability are coupled by
phosphatase activity (Ratliff 2012)
• Fine root allocation to acquire N vs
P depends on N availability (Naples
and Fisk 2010)
• P enhances C mineralization, while
N depresses it (Santangelo et al, in prep)

10. Rastetter et al. 2013
Predictions of the multiple-element limitation modelPredictions of the multiple-element limitation model
• Allocation shifts between N and P after large-scale disturbance
• Colimitation occurs when allocation to N and P equilibrates

11. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae

12. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae

13. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Allocation
feedbacks

14. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Allocation
feedbacks

15. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Allocation
feedbacks

16. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Allocation
feedbacks
Maintain
consistent
N:P

17. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Allocation
feedbacks
Maintain
consistent
N:P

18. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Community or
ecosystem
level?
Allocation
feedbacks
Maintain
consistent
N:P

19. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
 Is co-limitation a long-term outcome of ecosystem development?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Community or
ecosystem
level?
Allocation
feedbacks
Maintain
consistent
N:P

20. Rethinking limitationRethinking limitation
 What limits productivity in northern hardwood forests?
 Does a resource allocation framework explain patterns of
limitation or co-limitation?
 Is co-limitation a long-term outcome of ecosystem development?
 Or, is it a transient part of long-term, ultimate limitation, mediated
by shifting resource allocation?
Geohydrologic template
Available nutrients
Decomposer
microbes
mycorrhizae
Enzymatic
feedbacks
Community or
ecosystem
level?
Allocation
feedbacks
Maintain
consistent
N:P