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Home , Albatrellus, Amanita fulva, Auriscalpiaceae, Auriscalpium vulgare, Betula pendula, Cantharellus cibarius

Proc. Natl. Acad. Sci. USA Vol. 96, pp. 8534–8539, July 1999 Ecology

Natural 13C abundance reveals trophic status of fungi and -origin of carbon in mycorrhizal fungi in mixed

PETER HO¨GBERG*†,AGNETA H. PLAMBOECK*, ANDREW F. S. TAYLOR‡, AND PETRA M. A. FRANSSON‡

*Section of Soil Science, Department of Ecology, SLU (Swedish University of Agricultural Sciences), S-901 83 Umeå, Sweden; and ‡Department of Forest and Pathology, SLU, S-750 07 Uppsala, Sweden

Communicated by Harold Alfred Mooney, Stanford University, Stanford, CA, May 24, 1999 (received for review March 4, 1999)

ABSTRACT Fungi play crucial roles in the biogeochem- could differentiate between saprophytic and mycorrhizal istry of terrestrial ecosystems, most notably as saprophytes fungi. decomposing organic matter and as mycorrhizal fungi en- We also hypothesized (ii) that, because overstorey hancing nutrient uptake. However, a recurrent problem generally have a higher natural abundance of 13C than under- in fungal ecology is to establish the trophic status of storey trees (13), their associated ectomycorrhizal fungi should in the field. Our interpretations and conclusions are too often display similar differences. The higher 13C abundance of based on extrapolations from laboratory microcosm experi- overstorey trees is the result of less pronounced discrimination 13 ments or on anecdotal field evidence. Here, we used natural against CinCO2 during photosynthesis because of higher variations in stable carbon isotope ratios (␦13C) as an ap- illumination (and, therefore, higher rates of photosynthesis) proach to distinguish between fungal decomposers and sym- and also because of more exposure to drought stress in biotic mycorrhizal fungal species in the rich flora overstorey trees (13–15). Short in a closed forest may (our sample contains 135 species) of temperate forests. We obtain particularly low 13C abundance through assimilation of 13 also demonstrated that host-specific mycorrhizal fungi that C-depleted CO2 derived directly from soil respiration (13). receive C from overstorey or understorey species differ in We also hypothesized (iii) that most of the mycorrhizal fungi their ␦13C. The many promiscuous mycorrhizal fungi, asso- ought to receive their C from overstorey rather than from ciated with and connecting several tree hosts, were calculated understorey trees because rates of photosynthesis are higher in to receive 57–100% of their C from overstorey trees. Thus, overstorey trees. To test the three hypotheses (i–iii), we visited overstorey trees also support, partly or wholly, the nutrient- two two-storied, successional, temperate forests in Sweden and absorbing mycelia of their alleged competitors, the understo- sampled trees and a large number of fungi to analyze their 13C rey trees. abundance.

In terrestrial ecosystems, fungi are integral components of METHODS most biogeochemical cycles. Decomposer fungi degrade or- ganic macromolecules whereas mycorrhizal fungi, symbionts The study was conducted at Åheden in the Svartberget Re- of plant roots, actively forage for plant nutrients (1, 2). In the search Forest, 60 km northwest of Umeå, northern Sweden complex settings of forest ecosystems, even in those with few (64°14ЈN, 19°46ЈE, 175 m above sea level) and at Stadsskogen, plant species, there is often a diverse flora of sporocarps of an urban forest in Uppsala, central Sweden (59°52ЈN, 17°13ЈE, fungal decomposers and mycorrhizal fungi (3–5). However, the 35 m above sea level). Both forests had 150-year-old Scots trophic status of many fungal species remains unclear: that is, ( L.) in the overstorey, but with Norway whether they obtain their C by decomposing dead organic ( [L.] Karst.) approaching the role of codominant. material or from living plants by forming mycorrhizal root At Åheden, the dominant Scots pine were 25 m tall, and symbioses (6). The small size and cryptic growth of most ( Roth) was the only understorey species. At fungal mycelia effectively restricts in situ observations. Fur- Stadsskogen, the dominant Scots pine sometimes reached Ͼ30 thermore, the connection between mycorrhizal fungi and their m, and understorey deciduous tree species included aspen host trees cannot be easily established because many fungi are (Populus tremula L.), birch (B. pendula), (Salix caprea promiscuous and can receive C from several species of trees (2, L.), and (Alnus incana [L.] Moench). 7, 8). Such fungi form hyphal links transferring C and nutrients At each site, and current needles were sampled (Ͼ10 between plants and can thus influence plant competition (2, g dry weight͞sample) from branches on the south side, close 7–10). Recently, it was suggested, after feeding one seedling to the top of the tree, from up to 10 specimens per tree species. 14 13 with CO2 and one with CO2, that there was a net transfer Between one and eight fruit bodies from each fungal species of C from one seedling to another via mycorrhizal connections found at each site were sampled (Table 1). Sampling was (8). However, this type of tracer approach is highly elaborate conducted on an area of 1 hectare at Åheden in August 1997 and cannot easily be used to study a greater complexity: that and at 5 plots with an area of 0.25 hectare each at Stadsskogen is, flows of C to many fungal species simultaneously. in September 1997. Specificity between tree hosts and fungal Fungal decomposers break down complex C sources like symbionts was inferred from the literature relevant to the cellulose, hemicellulose, and lignin whereas mycorrhizal fungi region (16, 17). Because associations between fungi and po- receive simpler carbohydrates directly via the plant phloem (1, tential hosts are based primarily on repeated observations of 2). These C sources may differ significantly in their natural fruit bodies and not on establishing direct contacts between abundance of the heavy stable carbon isotope 13C (11, 12). the two symbionts, the question of specificity must be treated Accordingly, we speculated (i) that analysis of 13C abundance with some caution. In this study, fungal species were only regarded as specific to a single host when this was clearly The publication costs of this article were defrayed in part by page charge indicated in the literature. payment. This article must therefore be hereby marked ‘‘advertisement’’ in accordance with 18 U.S.C. §1734 solely to indicate this fact. †To whom reprint requests should be addressed. e-mail: Peter. PNAS is available online at www.pnas.org. [email protected].

8534 Downloaded by guest on September 25, 2021 Ecology: Ho¨gberg et al. Proc. Natl. Acad. Sci. USA 96 (1999) 8535

Table 1. Natural 13C abundance (␦13C) of fungal fruit bodies sampled in mixed temperate forests at two sites, Åheden and Stadsskogen, in Sweden Host n ␦13C value SD ÅÅheden site Mycorrhizal species molle (Bon) Bon Betula 1 Ϫ27.6 (Bull. Ex Fr.) S.F. Gray Betula 4 Ϫ27.5 0.4 Leccinum variicolor Watl. Betula 4 Ϫ27.6 0.8 Leccinum versipelle (Fr.) Snell Betula 4 Ϫ27.5 0.6 variegatus (Swartz ex Fr.) O. Kuntze Pinus 6 Ϫ25.0 0.4 rutilus (Schff. ex Fr.) O.K. Miller Pinus 4 Ϫ26.0 0.6 flavovirens (Pers. ex Fr.) Promiscuous 4 Ϫ25.4 0.8 Tricholoma virgatum (Fr.:Fr.) Kumm. Promiscuous 1 Ϫ25.2 Laccaria bicolor (Maire) Orton Promiscuous 2 Ϫ25.3 0.6 muscaria (L.) Hook Promiscuous 5 Ϫ26.6 1.0 armeniacus (Schaeff.:Fr.) Fr. 5 Ϫ24.5 0.6 (Fr.) Fr. Betula 5 Ϫ26.9 1.3 Cortinarius bataillei (Moser) Hiøland Conifers 1 Ϫ25.3 Cortinarius biformis Fr. Conifers 4 Ϫ25.2 0.6 (Fr.:Fr.) Fr. Conifers 1 Ϫ25.6 Cortinarius evernuis (Fr.:Fr.) Fr. Picea 1 Ϫ24.8 (Pers.:Fr.) Fr. Betula 1 Ϫ27.8 Cortinarius laniger Fr. Picea 6 Ϫ26.4 1.7 Cortinarius malachius Fr. Conifers 2 Ϫ24.8 0.2 (Fr.:Fr.) Fr. Betula 6 Ϫ27.6 1.0 Cortinarius scaurus (Fr.:Fr.) Fr. Promiscuous 1 Ϫ25.2 Cortinarius semisanguineus (Fr.) Gill. Conifers 3 Ϫ24.9 0.7 Cortinarius strobilaceus Mos. Conifers 1 Ϫ27.0 Fr. (Pinus) 2 Ϫ25.2 0.5 Rozites caperata (Pers. ex Fr.) Karst. Promiscuous 4 Ϫ25.8 0.4 rufus (Scop.) Fr. Promiscuous 6 Ϫ24.9 0.7 paludosa Britz. Conifers 1 Ϫ25.0 Aphyllophorales Thelphoraceae Phelloden tomentosa (L.:Fr.) Baker Promiscuous 1 Ϫ24.1 Saprophytic species Boletales Boletaceae piperatus (Bull. ex Fr.) Bat. na 1 Ϫ22.3 Tricholomataceae Armillaria borealis Marx. & K. Korh. na 2 Ϫ23.8 0.1 Strophariaceae Stropharia hornemanii (Fr.:Fr.) Lund. na 1 Ϫ23.1 Cortinariaceae penetrans (Fr.) Murr. 1 Ϫ22.4 Aphyllophorales Polyporaceae Trametes hirsuta (Wulfen:Fr.) Pil. na 1 Ϫ24.0 Stadsskogen site Mycorrhizal species Boletales Boletaceae edulis Bull. ex Fr. Promiscuous 5 Ϫ24.6 0.5 Boletus pinophilus Pil. & Dermek Pinus 1 Ϫ24.7 (Bull. ex St. Am.) S.F. Gray Populus 3 Ϫ27.3 0.9 Leccinum holopus (Rostk.) Watl. Betula 1 Ϫ29.2 Leccinum scabrum (Bull. ex Fr.) S.F. Gray Betula 6 Ϫ26.4 1.9 Leccinum variicolor Watl. Betula 1 Ϫ26.1 Leccinum versipelle (Fr.) Snell Betula 2 Ϫ27.1 1.1 Leccinum vulpinum Watl. Pinus 5 Ϫ25.0 0.7 (Table continues on the next page.) Downloaded by guest on September 25, 2021 8536 Ecology: Ho¨gberg et al. Proc. Natl. Acad. Sci. USA 96 (1999)

Table 1. (Continued) Host n ␦13C value SD (L.) Kuntze Pinus 6 Ϫ25.2 0.5 (L. ex Fr.) S.F. Gray Pinus 6 Ϫ24.6 0.4 Suillus variegatus (Swartz ex Fr.) O. Kuntze Pinus 7 Ϫ24.3 0.9 Tylopilus felleus (Bull.:Fr.) Karst. Promiscuous 5 Ϫ25.0 0.5 Xerocomus badius (Fr.:Fr.) Gilb. Promiscuous 4 Ϫ25.3 0.8 Xerocomus lanatus (Rostk.) Gilb. Promiscuous 1 Ϫ25.9 Gomphidiaceae (Schff. ex Fr.) O.K. Miller Pinus 6 Ϫ25.3 0.7 glutinosus (Schff.) Fr. Picea 3 Ϫ26.4 0.6 L.:Fr. Pinus 5 Ϫ24.9 0.7 involutus (Batsch) Fr. Promiscuous 3 Ϫ26.6 0.4 obtextus (Spreng) S. Rauschert Pinus 2 Ϫ25.0 0.2 agathosmus (Fr.) Fr. Picea 1 Ϫ28.1 Hygrophorus camarophyllus (Alb. & Schw.:Fr.), Dume´e et al. Conifers 5 Ϫ24.6 1.4 Hygrophorus olivaceoalbus (Fr. ex Fr.) Fr. Picea 5 Ϫ26.0 1.1 Tricholomataceae Laccaria laccata (Scop. ex Fr.) Bk. & Br. Promiscuous 3 Ϫ25.3 1.0 Tricholoma flavovirens (Pers. ex Fr.) Promiscuous 2 Ϫ26.1 0.8 Tricholoma fracticum (Britz.) Kreisel Pinus 1 Ϫ24.3 Tricholoma fucatum (Fr.) Kummer Conifers 2 Ϫ25.8 0.6 Tricholoma fulvum (DC:Fr.) Sacc. Betula 5 Ϫ26.6 0.6 (Pers.:Fr) Kumm. Picea 1 Ϫ26.9 Tricholoma virgatum (Fr.:Fr.) Kumm. Promiscuous 2 Ϫ24.3 0.2 Amanitaceae Amanita fulva (Sch:Fr) Fr. (Betula) 6 Ϫ26.3 1.1 (L.) Hook Promiscuous 4 Ϫ26.3 0.7 Amanita porphyria (Alb & Schw:Fr) Mlady Conifers 8 Ϫ24.8 0.7 Amanita rubescens (Pers:Fr.) SF Gray Promiscuous 5 Ϫ25.3 0.5 Amanita virosa (Kamarck) Bertillon Promiscuous 7 Ϫ25.1 0.9 Cortinariaceae Cortinarius albo-violaceus (Pers:Fr.) Fr. Betula 1 Ϫ28.4 Cortinarius armeniacus (Schaeff.: Fr.) Fr. Conifers 1 Ϫ25.1 Cortinarius armillatus (Fr.) Fr. Betula 3 Ϫ27.5 0.9 Cortinarius bolaris (Pers:Fr.) Fr. (Betula) 3 Ϫ27.0 0.8 Cortinarius brunneus Fr. (Conifers) 2 Ϫ26.1 0.2 Cortinarius camphoratus (Fr.:Fr.) Fr. Conifers 1 Ϫ23.7 Cortinarius crocea (Schff.) Big. & Guill. Promiscuous 1 Ϫ29.2 (Fr.) Fr. (Picea) 4 Ϫ25.6 0.6 Cortinarius laniger Fr. (Picea) 2 Ϫ25.9 1.5 Cortinarius limonius (Fr. ex Fr.) Fr. Conifers 2 Ϫ25.9 2.6 Cortinarius malachius Fr. Conifers 3 Ϫ25.5 1.4 Cortinarius muscigenus Peck Picea 3 Ϫ26.1 0.8 Cortinarius paleaceus (Weinm.) Fr. Conifers 7 Ϫ25.7 1.3 Cortinarius pholideus (Fr.:Fr.) Fr. Betula 1 Ϫ26.3 Cortinarius semisanguineus (Fr.) Gill. Conifers 7 Ϫ25.2 0.3 Cortinarius speciosissimus Ku¨hner & Rom. Conifers 1 Ϫ25.8 Cortinarius stillatitius Fr. Conifers 3 Ϫ24.2 1.1 Cortinarius strobilaceus Mos. Conifers 3 Ϫ25.5 0.8 Cortinarius traganus Fr. (Pinus) 2 Ϫ25.6 1.4 Cortinarius uliginosus Berk. Salix 3 Ϫ28.0 1.3 Cortinarius vibratilis (Fr.:Fr.) Fr. Conifers 7 Ϫ25.1 1.1 crustuliniforme (Bull:Fr.) Que´l. Promiscuous 4 Ϫ27.1 2.1 Hebeloma mesophaeum (Pers) Que´l. Promiscuous 2 Ϫ26.8 0.5 acuta Boud. Promiscuous 1 Ϫ26.2 Inocybe cincinnata (Fr.) Que´l. Promiscuous 1 Ϫ26.5 Inocybe friesii Heim. Conifers 1 Ϫ27.0 Inocybe geophylla (Sow. ex Fr.) Kummer Promiscuous 3 Ϫ25.0 0.5 Inocybe pseudodestricta Stangl. & Veselsky Promiscuous 1 Ϫ26.5 Inocybe tigrina Heim Conifers 1 Ϫ26.9 Rozites caperata (Pers. ex Fr.) Karst. Promiscuous 5 Ϫ24.7 0.7 (Table continues on opposite page.) Downloaded by guest on September 25, 2021 Ecology: Ho¨gberg et al. Proc. Natl. Acad. Sci. USA 96 (1999) 8537

Table 1. (Continued) Host n ␦13C value SD Russulales Russulaceae Lactarius badiosanguinea Kuehn. & Rom. Picea 2 Ϫ26.2 0.0 Lactarius camphoratus (Bull.) ex Fr. Promiscuous 5 Ϫ26.8 0.8 Fr. Pinus 6 Ϫ24.9 0.6 Lactarius deterrimus Groeger Picea 8 Ϫ26.6 0.8 Lactarius fuliginosus Fr. Betula 2 Ϫ24.9 0.4 Fr. Betula 4 Ϫ27.0 0.5 Lactarius helvus Fr. Promiscuous 4 Ϫ23.8 0.4 Lactarius mitissimus Fr. Promiscuous 1 Ϫ25.1 Lactarius musteus Fr. Pinus 1 Ϫ24.9 Lactarius necator (Bull. em Pers. ex Fr.) Karst. Promiscuous 5 Ϫ26.0 1.1 Lactarius obscuratus (Lasch) Fr. Alnus 3 Ϫ27.1 0.6 Lactarius repraesentaneus Britz. Promiscuous 1 Ϫ26.5 (Scop.) Fr. Promiscuous 3 Ϫ25.3 0.5 (Scop. ex Fr.) Fr. Picea 2 Ϫ27.3 0.6 Lactarius theiogalus (Bull:Fr.) SF Gray Promiscuous 3 Ϫ27.1 0.8 (Schff. ex Fr.) S.F. Gray Betula 3 Ϫ25.8 1.4 Lactarius trivialis Fr. Promiscuous 1 Ϫ23.5 Fr. Betula (Salix) 2 Ϫ26.0 0.2 Fr. Betula (Salix) 5 Ϫ26.2 0.7 Russula atrorubens Que´l. Conifers 5 Ϫ25.5 0.7 Hora Betula 1 Ϫ25.1 Russula coerulea Fr. Pinus 2 Ϫ24.1 0.3 Russula decolorans Fr. Conifers 5 Ϫ25.4 0.3 Fr. Pinus (Picea) 2 Ϫ24.9 0.0 Russula foetens Fr. Promiscuous 1 Ϫ24.8 Schaeff. Betula 1 Ϫ27.7 Russula griseascens (Bon & Gaugue´) L. Marti Conifers 1 Ϫ26.4 L. ex Fr. (Picea) 1 Ϫ25.4 Britz. Conifers 2 Ϫ25.2 0.4 Russula puellaris Fr. Promiscuous 1 Ϫ25.5 Fr. Picea 1 Ϫ27.5 Russula rhodopoda Zv. Picea 1 Ϫ26.0 Russula sanguinea (Bull. ex St. am.) Fr. Pinus (Picea) 3 Ϫ24.5 0.4 Fr. ex Rom. Pinus 2 Ϫ26.3 1.7 Russula vinosa Lindbl. Conifers 2 Ϫ25.3 0.4 (Schff. ex Secr.) Fr. Pinus (Picea) 1 Ϫ26.3 Aphyllophorales Polyporaceae ovinus (Fr.) Kotl. & Pouz. Conifers 2 Ϫ25.9 0.8 Thelephoraceae ferrugineum (Fr.:Fr.) Karst. Conifers 2 Ϫ22.5 0.5 Banker apud Peck Conifers 1 Ϫ23.3 Phelloden niger (Fr.:Fr.) Karst. Promiscuous 1 Ϫ22.7 repandum L.:Fr. Promiscuous 3 Ϫ25.4 0.5 Hydnum rufescens Fr. Promiscuous 6 Ϫ25.4 1.3 cibarius Fr. Promiscuous 3 Ϫ26.3 0.3 Cantharellus lutescens Fr. Picea & Betula 2 Ϫ25.0 0.0 Cantharellus tubaeformis Fr. (Picea) 4 Ϫ25.2 0.6 Saprophytic species Boletales Boletaceae (Bull. ex Fr.) Bat. na 2 Ϫ22.0 0.9 Agaricales Paxillaceae aurantiaca (Wulf.:Fr.) Mre. na 2 Ϫ21.6 1.1 Paxillus atromentarius (Batsch: Fr.) Fr. na 1 Ϫ23.0 Agaricales Tricholomataceae clavipes (Pers. ex Fr.) Kummer na 3 Ϫ25.6 1.1 Mycena pura (Pers. ex Fr.) Kummer na 1 Ϫ22.9 Mycena rosella (Fr.) Kummer na 1 Ϫ23.3 (Table continues on next page.) Downloaded by guest on September 25, 2021 8538 Ecology: Ho¨gberg et al. Proc. Natl. Acad. Sci. USA 96 (1999)

Table 1. (Continued) Host n ␦13C value SD Entolomataceae Clitopilus prunulus (Scop. ex Fr.) Kummer na 2 Ϫ22.9 0.1 Entoloma nitidum Que´l. na 3 Ϫ23.5 0.4 Rhodocybe nitellina (Fr.) Sing. na 1 Ϫ20.8 haemorrhoideus Kalchbr. & Schulz. na 2 Ϫ22.0 0.4 carcharias (Pers. ex Secr.) Fay. na 1 Ϫ23.8 Cortinariaceae Gymnopilus spectabilis (Fr.) Sing. na 2 Ϫ24.0 3.1 Aphyllophorales vulgare S.F. Gray na 2 Ϫ22.2 0.8 Lycoperdaceae Lycoperdon foetidum Bonord. na 1 Ϫ24.5 Nomenclature and host-specificity (in case of ectomycorrhizal species) of fungal species follows Hansen and Knutsen (16, 17). Brackets around proposed host genera indicate an unknown degree of specificity and the fungi are not included in the specificity groups in Fig. 1. na, not applicable.

The fungal fruit bodies and foliar samples from plants were fungi, i.e., host-specific and non-host-specific fungi, had a ␦13C dried (70°C, 24 h) and then were ground in a ball mill. Samples significantly different from that of saprophytic fungi (Tukey’s were analyzed for 13C abundance by using an online continuous test, P Ͻ 0.05; Fig. 1). The difference between saprophytic and flow CN analyzer coupled to an isotope mass spectrometer (18, mycorrhizal fungi was found at both sites and is large enough 19). Results are expressed in the standard notation (␦13C) in to be developed as a tool to separate the two groups of fungi. parts per thousand (‰) relative to the international standard For example, Chalciporus piperatus has been suspected to be ␦13 ϭ ͞ Vienna Pee Dee Belemnite, where C [(Rsample mycorrhizal, but this has not been confirmed in experiments in Ϫ ϫ 13 ͞12 Rstandard) 1] 1,000, and R is the molar ratio C C. The which mycorrhizal syntheses have been attempted (20, 21). Its standard deviation based on analysis of replicated samples was high 13C abundance at both sites (Table 1) would place this 0.15‰. Linear two-source isotopic mixing models were used fungal species amongst the saprophytes. The difference in ␦13C to calculate the fractional contribution of two C sources (plant between tree foliage C and C in saprophytic fungi was Ϸ4‰ hosts) to the C in -specific and promiscuous fungi. For (Fig. 1), which was the difference between wood and fungal this, mean values of ␦13C for host-specific fungi were used as decomposers observed by Gleixner et al. (11). isotopic endpoints. However, despite the significant differences between the mean ␦13C values of saprophytic and mycorrhizal fungi, several ␦13 RESULTS AND DISCUSSION. ectomycorrhizal fungi had high C (Table 1). These latter include , Hydnellum peckii, and Phell- A total of 135 fungal species were sampled; 117 of these are odon niger, all of which are known to be ectomycorrhizal (22). ectomycorrhizal (Table 1). All groups of ectomycorrhizal The fruit bodies of these three species are unique among the

FIG. 1. Natural abundance of 13C(␦13C) of fungal fruit bodies and of the host trees of ectomycorrhizal fungi (as indicated by connecting lines) in mixed temperate forests at two sites, Åheden and Stadsskogen, in Sweden. Promiscuous fungi are non-host-specific ectomycorrhizal fungi. Pine (P. sylvestris) is the dominant tree at both sites, most closely followed by spruce (P. abies) and birch (B. pendula). Other trees are A. incana, P. tremula, and S. caprea. Ectomycorrhizal fungi are arranged in groups according to their host specificity (compare with Table 1). Bars show SD of single observations. Replicates are individuals in case of host trees; in case of fungi, replicates are species (Table 1). Downloaded by guest on September 25, 2021 Ecology: Ho¨gberg et al. Proc. Natl. Acad. Sci. USA 96 (1999) 8539

ectomycorrhizal fungi we sampled because they exist and grow corrhizal could act as a subsidy against the cost of the for a much longer period than any of the other ectomycorrhizal symbioses (2, 25, 26) in connected shaded understorey plants fungi in our study. The mycorrhizal roots associated with fruit and could help them to survive a long period of shading. bodies of these three species are, as far as we know, also unique in that they appear to be degraded and moribund [carbonized We thank M. Sandstro¨m for preparing samples, H. Wallmark for sensu Agerer (22)]. The partly decomposed state of the mass spectrometric analysis, and R. Finlay, M. Ho¨gberg, and A. mycorrhizal roots and the high 13C values of the fungal fruit Jumpponen for comments. This research was supported by grants from bodies may suggest that the mutualistic balance between the the Swedish Natural Sciences Research Council and the Swedish host roots and the fungi may be weighed in favor of the fungi. Council for and Agricultural Research. In both forests, the overstorey Scots pine (P. sylvestris L.) ␦13 1. Hudson, H. J. (1986) Fungal Biology (Edward Arnold, London). had, as predicted, the highest C found among the tree 2. Smith, S. E. & Read, D. J. (1997) Mycorrhizal (Aca- species (Fig. 1) but was more or less closely followed by the demic, San Diego). other conifer, Norway spruce (Picea abies [L.] Karst.), which 3. Gulden, G., Hoiland, K., Bendiksen, K. & Brandrud, T. E. (1992) is the likely climax species at both sites. Understorey broad- Bibl. Mycol. 144, 1–81. leaved species had up to 2–3‰ lower ␦13C than the . 4. Molina, R., Massicotte, H. & Trappe, J. M. (1992) in Mycorrhizal Some of the ectomycorrhizal fungi collected are specific to one Functioning, ed. Allen, M. F. (Chapman & Hall, London), pp. host species (Table 1), as shown by connecting lines in Fig. 1. 357–423. Their ␦13C was between 1.2 and 2.9‰ higher than that of their 5. Va¨re,H., Ohenoja, E. & Ohtonen, R. (1996) Karstenia 36, 1–18. host species (Fig. 1). This isotopic shift may relate to fraction- 6. Trojanowski, J., Haider, K. & Hu¨ttermann, A. (1984) Arch. ation during biochemical processes involved in the transfer of Microbiol. 139, 202–206. 7. Read, D. J., Francis, R. & Finlay, R. D. (1985) in Ecological C from the host to the , or it may suggest that such Interactions in Soil, eds. Fitter, A. H., Atkinson D., Read, D. J. transfer occurs under conditions of higher rates of photosyn- & Usher, M. B. (Blackwell, Oxford), pp. 193–217. thesis than the average (23). The isotopic shift between tree 8. Simard, S. W., Perry, D. A., Jones, M. D., Myrold, D. D., Durall, and fungus has to be taken into consideration but does not D. M. & Molina, R. (1997) (London) 388, 579–582. seriously confound the pattern of higher ␦13C in fungi associ- 9. Perry, D. A., Margolis, H., Choquette, C., Molina, R. & Trappe, ated with overstorey trees. J. M. (1989) New Phytol. 112, 501–511. Conifer-specific and promiscuous fungi, known to form 10. Arnebrant, K., Ek, H., Finlay, R. D. & So¨derstro¨m, B. (1993) New ectomycorrhizal symbioses with a wide range of both conif- Phytol. 124, 231–242. erous and broadleaved species, had a ␦13C, which indicated a 11. Gleixner, G., Danier, H.-J., Werner, R. A. & Schmidt, H.-L. large C flux from the overstorey pine. At the Åheden site (Fig. (1993) Plant Physiol. 102, 1287–1290. ␦13 12. Schmidt, H.-L., Kexel, H., Butzenlechner, M., Schwarz, S., Gleix- 1), there was no difference in C between promiscuous fungi ner, G., Thimet, S., Werner, R. A. & Gensler, M. (1995) in Stable (eight species), conifer-specific fungi (eight species), and those Isotopes in the Biosphere (Kyoto Univ. Press, Kyoto), pp. 17–35. specific for pine and spruce; that is, all (100%) of their C came 13. Brooks, J. R., Flanagan, L. B., Buchmann, N. & Ehleringer, J. R. from either of those two hosts or from both of them. At the (1997) Oecologia 110, 301–311. Stadsskogen site (Fig. 1), simple isotopic mixing-model calcu- 14. Ehleringer, J. R., Field, C. B., Lin, Z. & Kuo, C. (1986) Oecologia lations indicated that pine contributed on average 57% of the 70, 520–526. C in promiscuous fungi (33 species) and 81% of the C in 15. Farquhar, G. D., Ehleringer, J. R. & Hubick, H. T. (1989) Annu. conifer-specific fungi (23 species). These calculations were Rev. Physiol. Plant Mol. Biol. 40, 503–537. based on the assumption that C comes from pine and spruce 16. Hansen, L. & Knutsen, H. (1992) Nordic Macromycetes, Vol. 2: only in both cases; a contribution of C from understorey , Boletales, Agaricales, Russulales (Nordsvamp, Copen- hagen). species other than spruce would increase the percent C from 17. Hansen, L. & Knutsen, H. (1997) Nordic Macromycetes, Vol. 3: pine in promiscuous fungi! At Stadsskogen, three species of Heterobasidioid, Aphyllophoroid and Gasteromycetoid Basidio- the commercially valuable genus Cantharellus (24) were sam- mycetes (Nordsvamp, Copenhagen). pled. Their ␦13C values (Table 1) indicated that Cantharellus 18. Barrie, A. & Lemley, M. (1989) Int. Lab. Techniques 19, 82–91. lutescens and Cantharellus tubaeformis received C from over- 19. Ohlsson, K. E. A. & Wallmark, P. H. (1999) Analyst 124, 571–577. storey pine whereas , the famous golden 20. Alexander, I. J. & Watling, R. (1987) Proc. R. Soc. Edinburgh 93B, chantarelle, also received C from understorey trees. 107–115. In conclusion, analysis of ␦13C of fungi reveals whether they 21. Godbout, C. & Fortin, J. A. (1983) New Phytol. 94, 349–262. are saprophytic or ectomycorrhizal and, in the latter case, 22. Agerer, R. (1987–1993) Color Atlas of Ectomycorrhizae (Einhorn- whether they receive C from overstorey or from understorey Verlag, Schwa¨bisch Gmu¨nd, Germany). 23. Pate, J. & Arthur, D. (1998) Oecologia 117, 301–311. trees. It is interesting from an ecological perspective that the 24. Watling, R. (1997) Nature (London) 385, 299–300. many promiscuous fungi (Table 1), which can associate with 25. Finlay, R. D. & So¨derstro¨m, B. (1992) in Mycorrhizal Functioning, and connect both overstorey and understorey tree species, had ed. Allen M. F. (Chapman & Hall, London), pp. 134–160. a ␦13C indicating a large C flux from overstorey trees. Such a 26. Rygiewicz, P. T. & Anderson, C. P. (1996) Nature (London) 369, flow of C from sunlit overstorey trees to a common ectomy- 58–60. Downloaded by guest on September 25, 2021