TreesTrees Feed Feed

Soil MicrobesSoil Microbes

a presentatio

n by Conor Flynn

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.

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

Materials + Methods

NutrientNutrient: homogenized with 0.5 M : homogenized with 0.5 M potassium sulfate (K2SO4), then vacuum-potassium sulfate (K2SO4), then vacuum-filtered and chemically analyzed for filtered and chemically analyzed for Carbon and Nitrogen.Carbon and Nitrogen.BiomassBiomass: chloroform fumigation, then as : chloroform fumigation, then as above. Subtract. above. Subtract. Extracellular EnzymeExtracellular Enzyme: homogenized in pH : homogenized in pH 5.0 buffer, incubated in fluorimetric 5.0 buffer, incubated in fluorimetric assays with their substrate; activities are assays with their substrate; activities are nmol of reaction product per hour per g nmol of reaction product per hour per g of dry soil.of dry soil.

Results: Extracellular Enzymes I

• Hydrolysis of chitin • Mineralizes organic P

Results: Extracellular Enzymes II

• BG: Cellobiose • AG: Starch

• BX: Xylans • BC: Degrades cellulose to Cellobiose

Results: Extracellular Enzymes III

•Peroxidase: can degrade lignin

Results: Microbial Carbon and Nitrogen

Results: Extracellular Enzymes IV

•LAP: hydrolysis of amino acids from peptides

Conclusions

•After girdling, roots begin to die After girdling, roots begin to die •First mycorrhizae decay, then labile starches, then cellulose, and finally First mycorrhizae decay, then labile starches, then cellulose, and finally lignin (~6 months).lignin (~6 months).

•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.

Discussion: Trees Feed Soil Microbes…

And Vice Versa!