(1) Fine roots of plants in mature northern hardwood forests were found to forage for patches of apatite, a primary mineral source of phosphorus, when phosphorus was limiting. (2) When phosphorus was added to the soil, fine root foraging for apatite decreased, since phosphorus availability was no longer limiting. (3) Addition of nitrogen to the soil increased overall fine root growth but did not change foraging for apatite, indicating that nitrogen increases plant demand for phosphorus.

1. Root Foraging for Apatite is
Influenced by N and P Availability
Shan Shan1, Hannah Devens1, Melany
Fisk1, Joel Blum2, Timothy Fahey3, Ruth
Yanai4
1Department of Biology, Miami University; 2Ecology and Evolutionary Biology,
University of Michigan; 3Department of Natural Resource, Cornell University;
4Forest and Natural Resource Management, SUNY ESF

2. Background
• Roots can respond to a limiting nutrient by
proliferating in localized patches of that nutrient,
defined as “foraging”.
control
core
non-limiting
nutrient
limiting
nutrient

3. • Aboveground productivity of BEF mature stands
increased in response to P addition.
• High P availability can decrease plant demand for P.
• High N availability can increase plant demand for P.
– P resorption (See et. al., 2015)
– Soil phosphatase activity (Ratliff et. al., 2016)
– Mycorrhizal association
Background

4. (a) Fine roots forage for P.
(b) High P availability reduces P foraging.
(c) High N availability increases P foraging.
Hypotheses

5. • 3 mature stands: C7, C8, C9
• Installed ingrowth cores in 2013
– Non-apatite cores: root-free soil
– Apatite cores: root-free soil + apatite
– Apatite: primary mineral P source, Joel Blum
measured apatite-derived P uptake (data not shown)
• 4 fertilization treatment plots, each with 8 pairs of non-
apatite and apatite cores
• Incubated in situ for 2 years
Methods

6. Control N
P NP

7. • Cores were extracted after 2 years of incubation.
• Roots were sorted into <2 mm (fine) and >2 mm (coarse), and
scanned.
Methods

8. • Cores were extracted after 2 years of incubation.
• Roots were sorted into <2 mm (fine) and >2 mm (coarse), and
scanned.
• Fine root length was measured with ImageJ.
Methods

9. Results
• Roots foraged for P in control plots.
• Roots did not forage for P where P was added.
• N increased fine root length.

10. • P limitation of aboveground productivity in
northern hardwood forests drives fine roots to
forage for P.
• Elevated P reduces apatite foraging.
• Elevated N increases total root growth, but not
foraging.
Conclusion
We gratefully acknowledge Shinjini Goswami, Jerome Barner,
Jenna Tiller, Bradley Wells and other crews for their help in
sample collection and process.