This document summarizes a study that investigated whether soil nitrogen controls phosphorus resorption in a nitrogen and phosphorus co-limited forest system. The study found that phosphorus resorption efficiency was not correlated with soil phosphorus levels for the tree species studied. However, phosphorus resorption efficiency was positively correlated with soil nitrogen levels in 4 out of the 6 tree species, providing evidence that soil nitrogen availability may control phosphorus resorption under co-limitation by nitrogen and phosphorus. The document concludes that more nitrogen may be required to produce enzymes involved in resorbing phosphorus from leaves before abscission.

1. Does soil nitrogen control phosphorus
resorption in a co-limited system?
Craig See
SUNY-ESF
Photo: USFS

2. Before the leaves fall. . .
•Nutrients move from leaves to stem
tissues
•Resorption Efficiency = percent of leaf
nutrients resorbed before abscission
•Resorption efficiencies vary
•Critical for plant nutrient
conservation

3. Ryan and Bormann 1982
NITROGEN PHOSPHORUS

4. Single element hypothesis:
The resorption of a nutrient should be higher
when that nutrient is in low supply
Soil phosphorus
phosphorusresorption
phosphorusresorptionphosphorusresorption
Soil phosphorus
Soil phosphorus

5. Multiple element hypothesis:
In a co-limited system, the resorption of an
element should depend on the relative availability
of all limiting elements.
Soil Nitrogen
phosphorusresorption

6. METHODS
• 18 30x30m plots in 6
stands at BEF
• 1 quantitative soil pit
per plot
• 5 litter baskets
• Resorption data for up
to 5 trees/species/plot
Bartlett Experimental Forest

7. Methods
• Stands Sampled 2009, 2010
• Fresh leaves sampled
August, litter sampled in
October
RE=(G-L)/G
RE=Resorption Efficiency
G=Green leaf nutrient concentration
L=Litter nutrient concentration

8. Soil Phosphorus (mg/m2
)
0 10 20 30 40 50 60
PhosphorusResorptionEfficiency
0.0
0.2
0.4
0.6
0.8
1.0
No detectable
correlation
between soil P
and P resorption
for any of the
species studied.

9. Total soil N was
positively correlated
with P resorption
efficiency in 4 of 6
species:
American beech (p<0.01)
yellow birch(p=0.04)
white birch (p=0.05)
sugar maple (p=0.07)

10. Soil Nitrogen (mg/m2
)
)
100 200 300 400 500 600
PhosporusResorptionEfficiency
0.3
0.4
0.5
0.6
0.7
0.8
0.9
BEFC1
BEFC2
BEFC4
BEFC6
BEFC8
BEFC9

11. Soil N (mg/m2
)
200 250 300 350 400 450 500
PhosphorusResorptionEffeciency
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
R2= 0.89
P<0.01

12. Possible mechanism
Phospholipases, nucleases cost N
(and C) to produce…

13. Conclusions
• P resorption correlates positively with soil
N, but not with P.
• Relationship is stronger at the community
level, when weighted by the species
composition of litterfall.
Future research: Post-fertilization resampling

14. Thank you!
Ruth Yanai
Melany Fisk
Matt Vadebonceour
Shoestring Crew