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Appendix 1. Fractionation (Δ) of 15N upon Uptake of Inorganic and Organic Forms of Nitrogen by Plants, Fungi, Bacteria, and Algae
Conc. Δ

Organism N compound (mM N) (‰) Reference

Plants

Eriophorum ammonium 1.4 8 Emmerton and others

vaginatum nitrate 1.4 6 to 8 (2001a)

glycine 1.4 0

glutamic acid 1.4 0

Betula nana ammonium 1.4 15 Emmerton and others

nitrate 1.4 10 (2001a)

glycine 1.4 0 to 5

glutamic acid 1.4 0



Hakea actites ammonium 0.5, 4.5 -2.8 to 0.9 Schmidt and others

glutathione 0.5, 4.5 -7.7 to -2.9 (2006)

nitrate 0.5, 4.5 2.5 to 4.4

glutamine 0.5, 4.5 1.1 to 5.3

protein (BSA) 0.5, 4.5 3.3 to 4.1

Fungi

Leccinum scabrum ammonium 1.4 4 Emmerton and others

nitrate 1.4 8 (2001b)

glycine 1.4 1

glutamic acid 1.4 1

Ericoid mycorrhizal ammonium 1.4 15 Emmerton and others

fungi nitrate 1.4 0 (2001b)

glycine 1.4 1

glutamic acid 1.4 0



Marasmius androsaceus ammonium 3.6 17.3 Henn and Chapela

Cryptoporus volvatus ammonium 3.6 16.5±1.5 (2004)

Saprotrophic fungi (grown on agar) Hobbie and others (2004)



Agaricus subrutilescens ammonium 3.6 4.3±0.3

Six other species1 ammonium 3.6 -0.1±0.43

Ectomycorrhizal fungi (grown on agar) Hobbie and others (2004)

Lactarius deliciosus ammonium 3.6 8.7±0.4

Russula adusta ammonium 3.6 11.3±0.2

Russula sororia ammonium 3.6 6.0±0.2

Six other species3 ammonium 3.6 -0.1±0.32

Four ectomycorrhizal nitrate 4.5 5.4±0.54 a Schmidt and others

fungi ammonium 4.5 2.8±0.9 b (2006)

glutathione 4.5 -3.7±0.7 c

glutamine 4.5 2.1±0.6 b

protein (BSA) 4.5 3.8±0.6 ab

Bacteria

Anabaena sp. nitrate 24 13.3±0.4 Macko and others (1987)

59 11.4±0.6



Anabaena sp. ammonium 18 13.6

Vibrio harveyi glutamic acid 14 -12.8

alanine 22 9.4



Vibrio harveyi ammonium 0.013 3.8 Hoch and others (1992)

0.026 13.9

0.044 15.7

0.073 16.7

0.159 26.5

1.48 17.5

21.2 14.3

natural assemblages ammonium 0.005 10±1.7 Hoch and others (1994)

Algae

Skeletonema costatus ammonium 0 0 Pennock and others


0.005 1 (1996)

0.010 5


0.050 12

0.100 10


diatom assemblage ammonium 0.025-3 0-14 Waser and others (1999)

natural community ammonium 0.007 9 Peterson and others

(1993)

BSA = bovine serum albumin. 1Agaricus albolutescens, Clitocybe nebularis, Leucopaxillus gentianeus, Lycoperdon perlatum, Panellus serotinus, Stropharia ambigua. 2represents the average standard error for the six species. 3Amanita gemmata, A. muscaria, Paxillus involutus, Rhizopogon occidentalis, Suillus brevipes, S. fuscotomentosus (2 strains). 4Values followed by different letters differ statistically at p = 0.05 by ANOVA.



Appendix 2. Estimates of Carbon Use Efficiency in Biomass Production with Mycorrhizal Fungi or with Mycorrhizal (Plant-Fungal) Systems
System Efficiency Reference

Pure culture

3 fungal species1 54-62% Henn and Chapela (2000)

ectomycorrhizal species2 35-40% Lindeberg and Lindeberg (1977)
Symbiotic culture

Betula pendula-Paxillus involutus 34%, 36%, 57% Ek (1997)

Eucalyptus coccifera (nonmycorrhizal) 43%2.2%3 Jones and others (1998)

E. coccifera-Thelephora terrestris 55.71.73 Jones and others (1998)

Pinus sylvestris (3 fungi, 8 treatments) 40-48% Colpaert and others (1996)

Pinus muricata-Rhizopogon (3 strains) 31%4, 54%4, 64%4 Bidartondo and others (2001)

Pinus muricata-Suillus pungens 41%4 Bidartondo and others (2001)

P. ponderosa-Hebeloma crustuliniforme 39% (48% roots) Rygiewicz and Andersen (1994)

Pinus contorta (unknown isolate) 41% (pH 3.8) Erland and others (1991)

P. contorta (unknown isolate) 51% (pH 5.2) Erland and others (1991)

Salix viminalis-Thelephora terrestris 43%3 Durall and others (1994)
1Grown on 9:1 sucrose: malt extract; species were Coprinus volvatus (saprotrophic), Marasmius androsaceus (saprotrophic), and Suillus granulatus (ectomycorrhizal). 2Grown on glucose. 39-day pulse 14C labeling1.4efficiency for mycorrhizal fungi only. 5Aboveground only.

Appendix 3. Estimating Carbon Allocation to Mycorrhizal Fungi from Nitrogen Isotope Measurements
Belowground carbon flux to mycorrhizal fungi has been difficult to estimate because of the rapid turnover of mycorrhizal root tips and hyphae, and difficulties in translating any static measurement of hyphal mass into a carbon flux. The close coupling between nitrogen and carbon cycling in plants (Ågren and Bosatta 1996) suggests that a theoretical treatment of plant-mycorrhizal carbon and nitrogen cycles may prove useful in determining carbon flux to mycorrhizal fungi. We start from the basic premise that uptake of available soil nitrogen by fungi (and plants) is proportional to the growth of hyphae (and roots) into previously unexploited areas (Clarkson 1985; Ingestad and Ågren 1988). In other words, because of the limited mobility of available nitrogen in the soil, the flux of nitrogen to the hyphal or root surface is proportional to growth and not mass. Below we have outlined the mathematical framework by which this approach could be used to estimate carbon allocation to mycorrhizal fungi.
Carbon allocation to mycorrhizal fungi can be estimated by the below equation:
Cfungal = (1/Tr -1) • Np • c/n •1/e (1)
Derivation of equation (1)
Definitions:

Tr = transfer ratio (unitless)

Np = nitrogen passed to plant (kg ha-1 yr-1)

Ntu = nitrogen taken up by fungus (kg ha-1 yr-1)

Nk = nitrogen retained by fungus (kg ha-1 yr-1)

G = growth of fungus (kg biomass ha-1 yr-1)

n = %N of fungus

Cfungal = kg ha-1 yr-1 to fungus from plant

e = fungal growth efficiency

c = %C of fungus
Equations:
The fungal carbon demand can be expressed as fungal growth times the fungal carbon concentration divided by the efficiency with which carbon received from the host plant can be converted to fungal carbon.
Cfungal = G • c • 1/e (2)
The mycorrhizal transfer ratio is defined as the fraction of nitrogen taken up by the fungus (Ntu) that is transferred to the host plant (Np).

Tr = Np/Ntu (3)

Ntu = Np/Tr (4)


The amount of nitrogen retained in the fungus (Nk) can be defined in two ways. One way is to define Nk relative to the partitioning of nitrogen between plants and fungi:
Nk = (1- Tr ) • Ntu (5)
Alternatively, Nk can be defined as simply the fungal growth times the nitrogen concentration.
Nk = G • nitrogen (6)
Setting (5) and (6) equal to each other:
G • nitrogen = (1- Tr) • Ntu (7)
Substituting (4) into (7) and dividing by n:
G = (1/Tr -1) • Np/n (8)
Substituting (8) into (2) gives the final expression for fungal carbon demand:
Cfungal = (1/Tr -1) • Np • c/n • 1/e (1)
Because the transfer ratio (Tr) can be estimated from nitrogen isotope measurements (Equation 7 in the text), it is possible to relate nitrogen isotope patterns to carbon demand of mycorrhizal fungi.

References for Appendices not in Main Text Bibliography


Bidartondo MI, Ek H, Wallander H, Söderström B. 2001. Do nutrient additions alter carbon sink strength of ectomycorrhizal fungi? New Phytologist 151:543-550.

Colpaert J, van Laere A, van Assche JA. 1996. Carbon and nitrogen allocation in ectomycorrhizal and non-mycorrhizal Pinus sylvestris L. seedlings. Tree Physiology 16:787-793.

1Durall DM, Jones MD, Tinker PB. 1994. Allocation of 14C-carbon in ectomycorrhizal willow. New Phytologist 128:109-114.

Ek H. 1997. The influence of nitrogen fertilization on the carbon economy of Paxillus involutus in ectomycorrizal association with Betula pendula. New Phytologist 135:133-142.

1Erland S, Finlay, R, Söderström B. 1991. The influence of substrate pH on carbon translocation in ectomycorrhizal and non-mycorrhizal pine seedlings. New Phytologist 119:235-242.

1Henn MR, Chapela IH. 2000. Differential C isotope discrimination by fungi during decomposition of C3- and C4-derived sucrose. Applied and Environmental Microbiology 66:4180-4186.

Hoch MP, Fogel ML, Kirchman DL. 1992. Isotopic fractionation associated with ammonium uptake by a marine bacterium. Limnology and Oceanography 37:1447-1459.

Hoch MP, Fogel ML, Kirchman DL. 1994. Isotope fractionation during ammonium uptake by marine microbial assemblages. Geomicrobiology Journal 12:113-127.

Jones MD, Durall DM, Tinker PB. 1998. A comparison of arbuscular and ectomycorrhizal Eucalyptus coccifera: growth response, phosphorus uptake efficiency and external hyphal production. New Phytologist, 140:125-134.

Lindeberg G, Lindeberg M. 1977. Pectinolytic ability of some mycorrhizal and saprophytic hymenomycetes. Archives of Microbiology 115:9-12.

Macko SA, Fogel ML, Hare PE, Hoering TC. 1987. Isotopic fractionation of nitrogen and carbon in the synthesis of amino acids by microorganisms. Chemical Geology 65:79-92.

Pennock JR, Velinsky DJ, Ludlam JM, Sharp JH, Fogel ML. 1996. Isotopic fractionation of ammonium and nitrate during uptake by Skeletonema costatum: Implications for δ15N dynamics under bloom conditions. Limnology and Oceanography 41:451-459.

Peterson B, Fry B, Deegan L. 1993. The trophic significance of epilithic algal production in a fertilized tundra river ecosystem. Limnology and Oceanography 38:872-878.

Rygiewicz PT, Andersen CP. 1994. Mycorrhizae alter quality and quantity of carbon allocated below ground. Nature 369:58-60.



Waser NA, Yu ZM, Yin KD, Nielsen B, Harrison PJ, Turpin DH, Calvert SE. 1999. Nitrogen isotopic fractionation during a simulated diatom spring bloom: importance of N-starvation in controlling fractionation. Marine Ecology Progress Series 179:291-296.




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