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

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_Justus/LiebigJustus-Quotations.htm

How can we study?

• Foliar resorption ▫ Translocation of

foliar nutrients prior to leaf senescence

▫ Result = nutrient conservation and recycling within the plant

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

Previous studies • Elements in isolation

▫ Attempts to link P resorption to soil P and green leaf P

▫ Ditto for N

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

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

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…

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

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

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)

C:N ratios

Green Leaves – C2

• Green leaf N content and green leaf N concentration ▫ Highest in N-

fertilized plot of C2

▫ Soil N highest in NP plot

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

October P resorption proficiency

N efficiency correlation with green leaf P

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

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

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

Next steps…• Compare with

pretreatment data • Same methods, more

stands to compare: ▫ Age ▫ Treatment, including Ca

plots

Ruth Yanai Adam Wild Craig See B9 Bunch

Thank you to: