Soil nutrition is not a passive or one-way interaction. Instead, plants actively communicate their needs with soil microorganisms, and the soil community responds by making nutrients available to the rhizosphere.

1. TTrreeeess
FFeeeedd
SSooiill MMiiccrroobbeess
a
presentatio
n by
Conor Flynn

2. General Idea: Linking above- and
below-ground processes
•Phloem and xylem
•Rhizodeposition and Litterfall
•Priming Effect
•Girdling
•Girdling severs phloem, eliminates
rhizodeposition, tests Priming Effect
•Weintraub MN, Scott-Denton LE, Schmidt SK, Monson
RK. The effects of tree rhizodeposition on soil exoenzyme
activity, dissolved organic carbon, and nutrient
availability in a subalpine forest ecosystem. Oecologia.
2007;154(2):327–338.

3. Site Description
• W of Denver, CO
• 3,000 meters above sea level
• Lodgepole Pine (Pinus contorta)
• Sandy Inceptisol w/ thin organic
layer
• Girdled in July 2004
• Photosynthesis begins mid-April
2005

4. Materials + Methods
NNuuttrriieenntt:: hhoommooggeenniizzeedd wwiitthh 00..55 MM
ppoottaassssiiuumm ssuullffaattee ((KK22SSOO44)),, tthheenn vvaaccuuuumm--
ffiilltteerreedd aanndd cchheemmiiccaallllyy aannaallyyzzeedd ffoorr
CCaarrbboonn aanndd NNiittrrooggeenn..
BBiioommaassss:: cchhlloorrooffoorrmm ffuummiiggaattiioonn,, tthheenn aass
aabboovvee.. SSuubbttrraacctt..
EExxttrraacceelllluullaarr EEnnzzyymmee:: hhoommooggeenniizzeedd iinn ppHH
55..00 bbuuffffeerr,, iinnccuubbaatteedd iinn fflluuoorriimmeettrriicc
aassssaayyss wwiitthh tthheeiirr ssuubbssttrraattee;; aaccttiivviittiieess aarree
nnmmooll ooff rreeaaccttiioonn pprroodduucctt ppeerr hhoouurr ppeerr gg
ooff ddrryy ssooiill..

5. Results: Extracellular Enzymes I
• Hydrolysis of chitin • Mineralizes organic P

6. Results: Extracellular Enzymes II
• BG: Cellobiose
• AG: Starch
• BX: Xylans
• BC: Degrades cellulose to Cellobiose

7. Results: Extracellular Enzymes III
•Peroxidase: can degrade
lignin

8. Results: Microbial Carbon and Nitrogen

9. Results: Extracellular Enzymes IV
•LAP: hydrolysis of amino
acids from peptides

10. Conclusions
•After ggiirrddlliinngg,, rroooottss bbeeggiinn ttoo ddiiee
•FFiirrsstt mmyyccoorrrrhhiizzaaee ddeeccaayy,, tthheenn llaabbiillee ssttaarrcchheess,, tthheenn cceelllluulloossee,, aanndd ffiinnaallllyy
lliiggnniinn ((~~66 mmoonntthhss))..
•In healthy forests….
•Microbes benefit from rhizodeposition in spring, (while soil still covered in
snow) and increase in microbial biomass.
•Rhizodeposits are probably sugars, low in N.
•Microbes must immobilize N from proteins in soil.
•When this labile microbial N is mineralized it will result in increased N
availability for the trees.

11. Discussion: Trees Feed Soil Microbes…
And Vice Versa!