2015 Hubbard Brook Annual Meeting—W. Thornton, NH—July 8, 2015

1. Co-limitation in BEF: N affects P
resorption and P affects N
resorption
Kara Phelps
SUNY ESF

2. Why should we
study?
• Unintentional fertilization
of ecosystems over last 150
years
▫ Doubling in atmospheric
nitrogen concentrations
▫ About 400% increase in
global phosphorus cycle
• Realization that ecosystems are
often co-limited
▫ Not limited by single least
available nutrient
▫ Result = synergistic
ecosystem response to
addition of multiple nutrients
Justus von Liebig
http://todayinsci.com/L/Liebig_Ju
stus/LiebigJustus-Quotations.htm

3. How can we
study?
• Foliar resorption
▫ Translocation of foliar
nutrients prior to leaf
senescence
▫ Result = nutrient
conservation and
recycling within the
plant

4. How do we measure resorption?
Efficiency Proficiency
• The percent difference
between nutrient
concentrations of litterfall and
green leaves
• The concentration to which
nutrients have been reduced in
litter

5. Previous studies
• Elements in isolation
▫ Attempts to link P resorption
to soil P and green leaf P
▫ Ditto for N

6. What do we expect?
• Single element limitation:
▫ Resorption of an element
is more efficient when
that element is in low
supply
▫ Low P efficiency with
high soil P

7. What do we expect?
• Multiple element
limitation:
▫ Resorption of an element
is driven by supply of
other elements
▫ High P efficiency with
high soil N

8. What have we seen so
far?
Pre-Treatment: See et al., 2014
• P efficiency and
proficiency improved
with increasing soil N
content across six
stands
• No detectable
correlation between soil
P and P resorption!
Whoa…

9. See, Yanai, Fisk, Vadeboncoeur,
Quintero, and Fahey 2014
• Strong positive
correlation between total
soil N and P resorption
efficiency
▫ Across six sites
▫ Among 4 of 6 species
studied

10. What did we do?
In the field
• Three young stands in Bartlett
Experimental Forest
▫ C1, C2, and C3
▫ 25-35 years old
▫ Four plots in each stand
 N, P, NP, Control
• Green leaves collected in C2 in
August 2014
▫ American beech, pin cherry,
white birch, yellow birch, red
maple
• Litter collected in C1, C2, C3 in
October 2014

11. What did we do?
In the lab:
• All leaves were:
▫ Dried
▫ Ground
▫ Analyzed for C and N (CN analyzer)
▫ Ashed and digested
▫ Analyzed for Al, Ca, Mg, Mn, P, K,
Na, Sr, and S (ICP-OES)

12. C:N ratios
Green Leaves – C2

13. • Green leaf N content
and green leaf N
concentration
▫ Highest in N-
fertilized plot of C2
▫ Soil N highest in NP
plot

14. • P efficiency highest in N fertilized plot
• N efficiency highest in P-fertilized plot

15. October P resorption proficiency

16. N efficiency correlation with green leaf P

17. N efficiency correlated with green leaf P concentrations, but not
with green leaf N
P efficiency did not depend upon green leaf P concentrations,
but was correlated with green leaf N concentrations
Resorption Efficiency
Green Leaf
Concentrations
Nitrogen Phosphorus
Nitrogen
ρ = 0.19
p = 0.43
ρ = 0.54
p = 0.02
Phosphorus
ρ = 0.48
p = 0.03
ρ = -0.14
p = 0.56

18. N efficiency correlated with green leaf P concentrations, but not
with green leaf N
P efficiency did not depend upon green leaf P concentrations,
but was correlated with green leaf N concentrations
Resorption Efficiency
Green Leaf
Concentrations
Nitrogen Phosphorus
Nitrogen
ρ = 0.19
p = 0.43
ρ = 0.54
p = 0.02
Phosphorus
ρ = 0.48
p = 0.03
ρ = -0.14
p = 0.56

19. N efficiency correlated with green leaf P concentrations, but not
with green leaf N
P efficiency did not depend upon green leaf P concentrations,
but was correlated with green leaf N concentrations
Resorption Efficiency
Green Leaf
Concentrations
Nitrogen Phosphorus
Nitrogen
ρ = 0.19
p = 0.43
ρ = 0.54
p = 0.02
Phosphorus
ρ = 0.48
p = 0.03
ρ = -0.14
p = 0.56

20. Next steps…
• Compare with pretreatment
data
• Same methods, more stands to
compare:
▫ Age
▫ Treatment, including Ca plots

21. Thank you to: