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Cross-Ecosystem Comparisons of In Situ Plant Uptake of Amino Acid-N and NH4 +

TitleCross-Ecosystem Comparisons of In Situ Plant Uptake of Amino Acid-N and NH4 +
Publication TypeJournal Article
Year of Publication2010
AuthorsMcFarland, JW, Ruess, RW, Kielland, K, Pregitzer, K, Hendrick, R, Allen, M
JournalEcosystems
Volume11
Pagination177–193
Abstract

Plant and microbial use of nitrogen (N) can besimultaneously mutualistic and competitive, particularlyin ecosystems dominated by mycorrhizalfungi. Our goal was to quantify plant uptake oforganic and inorganic N across a broad latitudinalgradient of forest ecosystems that varied with respectto overstory taxon, edaphic characteristics,and dominant mycorrhizal association. Using 13Cand 15N, we observed in situ the cycling dynamicsof NH4+ and glycine through various soil pools andfine roots over 14 days. Recovery of 15N as soil Nvaried with respect to N form, forest type, andsampling period; however, there were similaritiesin the cycling dynamics of glycine and NH4+ amongall forest types. Microbial immobilization of 15Nwas immediately apparent for both treatments andrepresented the largest sink (25%) for 15N amongextractable soil N pools during the first 24 h. Incontrast, fine roots were a relatively small sink(<10%) for both N forms, but fine root 13Cenrichment indicated that plants in all forest typesabsorbed glycine intact, suggesting that plants andmicrobes effectively target the same labile soil Npools. Relative uptake of amino acid-N versus NH4+varied significantly among sites and approximatelyhalf of this variation was explained by mycorrhizalassociation. Estimates of plant uptake of aminoacid-N relative to NH4+ were 39 higher in ectomycorrhizal-dominated stands (1.6 ± 0.2) thanarbuscular mycorrhizae-dominated stands (0.5 ±0.1). We conclude that free amino acids are animportant component of the N economy in allstands studied; however, in these natural environmentsplant uptake of organic N relative toinorganic N is explained as much by mycorrhizalassociation as by the availability of N forms per se.

DOI10.1007/s10021-009-9309-6