The document summarizes findings from a study conducted at 3 sites with a total of 9 stands of varying ages. At each site there were 2 stands, one mid-age and one mature. The 3 young, 3 mid-age and 3 mature stands were located at one of the sites. The study found that foliar N:P ratios indicated colimitation by nitrogen and phosphorus. Mature stands responded more to phosphorus additions while young stands responded more to nitrogen additions. Phosphorus additions decreased soil respiration and sap flow while calcium additions increased sap flow. Phosphorus additions also increased microbial phosphorus while nitrogen additions decreased microbial nitrogen. Both nitrogen and phosphorus additions also increased root biomass.

1. 3 sites:
•Jeffers Brook
•HBEF
•BEF
2 stands per site:
1 mid-age
1 mature
9 stands at BEF:
3 young
3 mid-age
3 mature
Multiple Element Limitation in Northern Hardwood Ecosystems

3. Five Years with MELNHE: What have we learned?
LIMITATION
Foliar N:P is in the colimitation range.
Mature stands respond to P, young to N, in aboveground growth. NP no better.
Adding N decreases soil respiration. No change with P addition.
P decreases sap flow, Ca increases sap flow.
Adding P increased microbial P, adding N decreased microbial N.
Root biomass is increased by both N and P addition.
INTERACTIONS
N uptake by plants and/or microbes increases in response to P addition.
Foliar N is reduced by P addition.
MECHANISMS
Foliar N and P resorption are increased by P and N additions, respectively.
Roots forage for P when P is not added, grow more when N is added.
Soil phosphatase is higher where N availability is high
…rooting depth? AM/EM dominance? …

4. NLIMITATION
PLIMITATION
CHALLENGES TO BALANCED NUTRITION
MECHANISMS FAVORING BALANCE
P binding
N fixation
N deposition
EM fungi
enzymes
shallow roots
N resorption
weathering
tree allometry
P fertilization
N losses
AM fungi
enzymes
deep roots
P resorption
N fertilization