Invasion potential and host shifts of Australian and African ectomycorrhizal fungi in mixed eucalypt plantations


Author for correspondence:
Leho Tedersoo
Tel: +372 7376222


  • Transportation of forestry materials results in unintended co-introduction of nonnative species that may cause enormous ecological or economic damage. While the invasion ecology of plants and animals is relatively well-known, that of microorganisms, except aboveground pathogens, remains poorly understood.
  • This work addresses host shifts and invasion potential of root symbiotic ectomycorrhizal fungi that were co-introduced with Australian eucalypts and planted in clear-cut miombo woodlands in Zambia, south-central Africa.
  • By use of rDNA and plastid intron sequence analysis for identification and phylogenetic techniques for inferring fungal origin, we demonstrated that host shifts were uncommon in the Australian fungi, but frequent in the African fungi, especially in mixed plantations where roots of different trees intermingle.
  • There was evidence for naturalization, but not for invasion by Australian ectomycorrhizal fungi. Nevertheless, the fungi introduced may pose an invasion risk along with further adaptation to local soil environment and host trees. Inoculation of eucalypts with native edible fungi may ameliorate the potential invasion risks of introduced fungi and provide an alternative source of nutrition.


Invasion of exotic plant and animal species has transformed many ecosystems and caused substantial losses in biodiversity (Lockwood et al., 2007). Of these microorganisms, the impact of aggressive pathogens, particularly fungi and oomycetes, is easily noticed because of the devastation of crops, abrupt changes in forest tree composition or disappearance of entire functional groups such as amphibians (Desprez-Lousteau et al., 2007). Infected animals, seeds, soil and forestry products are usually the main sources of accidental co-introduction of microbial pests. By contrast, introduction of soil pathogens and mutualistic microbes such as mycorrhizal fungi has received little attention as a potential biological hazard (Richardson et al., 2000a; Schwartz et al., 2006; van der Putten et al., 2007; Pringle et al., 2009b; Dickie et al., 2010; Litchman, 2010; Wolfe et al., 2010). Mycorrhizal fungi are usually unintentionally co-introduced along with forestry tree seedlings or potting medium rather than during inoculation programs (Schwartz et al., 2006; Vellinga et al., 2009).

Forestry plantations have become an increasingly important supply for wood during the era of rapid deforestation of primary habitats (Richardson, 1998). In 2010, forestry plantations covered c. 264 million ha in the world and contributed c. 7% to the world’s forested areas (FAO, 2010). Exotic trees are preferred over native ones because of their shorter rotation, well-studied biology and paucity of pests in new habitats. Among the hundreds of commercial tree species, Eucalyptus, Pinus and Acacia dominate in forestry plantations worldwide (Richardson, 1998; West, 2006).

The genus Eucalyptus (Myrtaceae) is native to Australia and the surrounding islands (Ladiges et al., 2003). In their native habitat, Eucalyptus spp. dominate the flora of mesic forest and sclerophyll vegetation. They prefer sandy and loamy soils with 600–1000 mm of annual precipitation (Doughty, 2000). More than 100 species of Eucalyptus have been used in plantation trials in tropical to temperate regions (as far north as Scotland) around the world. Eucalyptus species are used mainly for firewood and pulp, but also for timber. The first eucalypts were introduced to Mauritius in the early 1800s and subsequently to the African continent in the first half of the 19th century (c. 1828 in South Africa). They became widely distributed in the beginning of the 20th century (Doughty, 2000).

The most important forestry trees, including Pinus and Eucalyptus, acquire mineral nutrition via root symbiosis with ectomycorrhizal (ECM) fungi. These ECM associations are widespread in temperate regions, but patchily distributed in tropical ecosystems (Alexander & Lee, 2005). Plantations of Pinus species fail in the absence of co-introduced symbiotic fungi in exotic habitats (Mikola, 1969), but the trees usually thrive when mycorrhizal (Nunez et al., 2009; Kohout et al., 2011). Pinus spp. cannot establish ECM symbiosis with native fungi in tropical habitats (Tedersoo et al., 2007; Nunez et al., 2009; Dickie et al., 2010; Walbert et al., 2010). By contrast, Eucalyptus spp. may associate with potentially native ECM fungi in tropical ecosystems outside Australia (Yazid et al., 1994; Tedersoo et al., 2007; Buyck, 2008), but not in Europe (Diez, 2005). Nevertheless, unnatural symbiotic associations are regarded as competitively inferior or less beneficial than interactions with native fungi (Malajczuk et al., 1982, 1984; Chen et al., 2007). Diez (2005) suggested that Laccaria fraterna, an Australian species, can colonize European Cistaceae in natural conditions, emphasizing the potential threats from Australian fungi.

Except for Amanita muscaria (Dunk, 2002; Orlovich & Cairney, 2004), there is no evidence for the invasion of ECM fungi from exotic Pinus plantations to native habitats in Australia and New Zealand, although some ‘cosmopolitan’ species are shared (Dickie et al., 2010; Walbert et al., 2010). Amanita phalloides is invading natural habitats in several plant communities in North America (Pringle et al., 2009a; Wolfe et al., 2010). Taken together, these studies suggest that host shifts and invasion are more likely to occur in similar habitats and/or among phylogenetically closely related (congeneric or con-familial) hosts (Wolfe et al., 2010). Ishida et al. (2007) hypothesized that greater host phylogenetic distance results in stronger host effects on communities of ECM fungi.

This study aims to distinguish the native and introduced ECM fungi in a Zambian miombo ecosystem, where eucalypt plantations have been commonly established on clear-cut woodlands of the native Caesalpinioideae. By use of plastid intron and rDNA sequence analysis for plant and fungal identification and building global phylogeographic patterns for ECM fungal taxa, we tested the hypothesis that African and Australian fungi are able to shift hosts, especially in mixed plantations where native trees form an understorey.

Materials and Methods

Study area and sampling

The study was carried out in two neighbouring plantations of Eucalyptus grandis W. Hill ex Maiden and Eucalyptus camaldulensis Dehnh. (13°28′ S; 24°25′ E, altitude 1077 m) near Tumbama village, Kabompo district, Northwestern Province of Zambia. The area receives mean annual rainfall of 1200 mm. Daily temperature ranges from 5–25°C during the coolest months in dry season to 21–32°C during the rest of the year. The rainy season lasts from mid-November until the end of March and peaks in January. The nutrient-poor soils rest on the highly weathered Kalahari sand parent material and comprise a thin humus layer that is subject to annual burning. The native vegetation belongs to Central Zambesian Miombo Woodlands type of dry tropical forests (Burgess et al., 2004). Domination of leguminous trees from the genera Brachystegia, Julbernardia or Isoberlinia (Caesalpinioideae) and a well-developed grass layer are characteristic of these ecosystems (Timberlake, 2000). In addition to the Caesalpinioideae, other common tree genera such as Monotes, Marquesia (Dipterocarpaceae) and Uapaca (Phyllanthaceae) are ectomycorrhizal (Högberg, 1986) and support a high diversity of symbiotic fungi that form an important food source for local tribes (Pegler & Piearce, 1980; Degreef et al., 1997; Härkönen et al., 2003).

The Eucalyptus plantations were established on a clear-cut miombo woodland in 1979. The native miombo trees have, however, effectively and continuously resprouted from stumps. Thus, the plantations comprise an overstorey of either E. camaldulensis or E. grandis and the second layer of native trees Isoberlinia angolensis (Welw. ex Benth.) Hoyle & Brenan, Julbernardia paniculata (Benth.) Troupin, Brachystegia spiciformis Benth., Brachystegia longifolia Benth., Colophospermum mopane (J. Kirk ex Benth.; non-EcM) J. Léonard (all Caesalpinioideae), and Marquesia macroura Gilg. (Dipterocarpaceae). The plantations are heavily disturbed by cutting of firewood and annual burning. In January 2008, two 2-ha plots were established in these plantations. The plots were located > 10 m away from patches of corn fields and relatively undisturbed native vegetation. In each plot, 20 root samples (15 × 15 cm) were taken to 10 cm depth. To ensure the occurrence of roots of various trees in samples, the samples were collected from randomly selected spots in areas where both the eucalypts and native trees were < 2 m distant. In addition, roots were collected from several solitary trees of c. 50-yr old E. grandis in the nearby villages of Manyinga (13°25.0′ S; 24°19.9′ E) and Kabompo (13°35.9′ S; 24°12.5′ E). Unfortunately, there is no information whether the trees were solitary during planting and where the seedlings originated.

The ECM roots were cleaned from soil by soaking in water. Root tips from four largest root fragments were separated into morphotypes under a stereomicroscope at ×50 magnification. Care was taken to ensure sampling of roots with different morphology, because the roots of Eucalyptus spp. and I. angolensis had distinct characters; roots of J. paniculata and Brachystegia spp. were indistinguishable under the stereomicroscope and were identified based solely on molecular techniques (see later). Clusters of each ECM morphotype per root fragment per sample were stored in CTAB buffer (1% cetyltrimethylammonium bromide, 100 mM Tris–HCl (pH 8.0), 1.4M NaCl, and 20 mM EDTA) for shipping to a molecular laboratory.

Molecular analyses

The DNA was extracted from 1 to 6 root tips per morphotype per sample using either a Qiagen MagAttract 96 DNA Plant Kit, which performed poorly, or Qiagen Dneasy 96 Plant Kit according to manufacturer’s recommendations.

To improve sequence quality, tomentelloid and other morphotypes were initially amplified by use of primer pairs ITSOF-T (5′-acttggtcatttagaggaagt-3′) + LR5-Tom (5′-ctaccgtagaaccgtctcc-3′), and ITSOF-T + LB-W (5′-cttttcatctttccctcacgg-3′), respectively. DNA yielding no PCR product was reamplified with the primer ITSOF-T combined with universal primers ITS4 (5′-tcctccgcttattgatatgc-3′) or ITS2 (5′-gctgcgttcttcatcgatgc-3′). Sequencing was performed with primers ITS5 (5′-ggaagtaaaagtcgtaacaagg-3′), LF340 (5′-tacttgtkcgctatcgg-3′) and/or ITS4. The PCR and product purification were as described in Tedersoo et al. (2006, 2008), respectively. Sequences were edited using sequencher 4.7 software (GeneCodes Corp., Ann Arbor, MI, USA) and assigned to molecular species based on 97.0% sequence similarity threshold of the internal transcribed spacer (ITS) region. Plant hosts were confirmed for all root fragments per sample based on the sequence of plastid trnL intron as described in Tedersoo et al. (2010b). Both host and mycobiont were sequenced from additional replicate root tips in cases where Australian fungi that were detected on roots of Caesalpinioideae to avoid false positive results. Fungal species were identified based on queries against the International Sequence Database (INSD) using a bulk BLASTN search tool as implemented in PlutoF workbench of the UNITE database (Abarenkov et al., 2010a,b). One or two representative sequences from each species per site were submitted to the UNITE and INSD (accession numbers FR731162FR731964) public sequence repositories.

Statistical analyses

Species accumulation curves with 95% confidence intervals and 1000 permutations were computed to compare species beta diversity between eucalypts and native trees by use of estimates ver. 7.5.2 (Colwell, 2006). Species accumulation curves were calculated separately for each host species, or data from host species were pooled within a family. To address the influence of host tree and plot on community composition of EcM fungi, the ADONIS routine of the Vegan package of R (R Core Development Team, 2007) was used with Bray–Curtis (Sørensen) dissimilarity metric, presence/absence of species, exclusion of singletons and 1000 permutations. Using the same options, nonmetric multidimensional scaling (NMS) ordination was calculated to provide a visual approximation for the results of ADONIS. For fungi inhabiting at least three samples, Fisher’s exact tests were performed to address biases in host association at the host family level.

Phylogenetic analyses were conducted to address the potential biogeographic origin of EcM fungi, assuming that the closest relatives are likely to originate from the same continent or closely related hosts (Martin et al., 2002; Hosaka et al., 2008; Matheny et al., 2009). These analyses used ITS sequences obtained from four sources: ECM root tips and fruit-body specimens at Tumbama; other eucalypt plantations and native forests in Zambia, Cameroon, São Tomé and Principe, Madagascar, Ecuador and Scotland (L. Tedersoo et al., unpublished); native woodlands and rain forests in Zambia, Cameroon, Gabon, Benin, São Tomé and Principe and Madagascar (L. Tedersoo et al., unpublished); and INSD. All relevant INSD and UNITE sequences were downloaded by lineages of EcM fungi (cf. Tedersoo et al., 2010a) as implemented in the PlutoF workbench, and subjected to separate phylogenetic analyses. The phylogenetic analyses of the /tomentella-thelephora and /russula-lactarius lineages were restricted to tropical and Southern Hemisphere isolates, because of the unmanageable size of the all-inclusive data sets and strong distinction of the northern boreal and tropical clades as seen from the other lineages. The alignments of ITS sequences were constructed by use of mafft ver. 6 (Katoh & Toh, 2008) and corrected manually. Unrooted maximum likelihood phylograms were constructed by use of RAxML with 200 bootstrap (BS) replicates and default options (Stamatakis et al., 2008). Rapid bootstrap values were used to estimate the robustness of branches and the potential origin of isolates. Isolates were considered to be native African if the same species were found in natural African habitats or they clustered with other African and/or SE Asian isolates with strong support (> 70% BS). Conversely, taxa were regarded as Australian if they belonged to EcM lineages absent from the native vegetation of Sub-Saharan Africa, occurred in other eucalypt plantations, and/or belonged to the strongly supported Austral (including Australia, New Zealand, New Caledonia and Argentina) clades. Isolates that matched none of these criteria were conservatively assigned to uncertain origin.


Sequence analysis of 268 root tips revealed 63 species of ECM fungi, including 60 species in the Tumbama plantations. In these plots, 28 species were associated with the introduced Eucalyptus spp., whereas 46 species were associated with the native Caesalpinioideae. Eucalyptus grandis and E. camaldulensis hosted 13 spp. and 19 spp., respectively. Twenty-five species were associated with J. paniculata, 17 species with B. longifolia and nine species with I. angolensis (Fig. 1; Table 1; see the Supporting Information, Table S1). Eucalyptus spp. and Caesalpinioideae shared 14 spp. of EcM fungi, whereas another 14 spp. were found solely on roots of Eucalyptus and 32 spp. exclusively on roots of the native trees combined.

Figure 1.

Rarefied species accumulation curves (solid lines) and their 95% confidence intervals (dotted lines) of ectomycorrhizal fungi on root systems as based on (a) host species; and (b) host families. Circles, Eucalyptus spp.; triangles, Caesalpinioideae spp. Open circles, Eucalyptus grandis; closed circles, Eucalyptus camalduensis; open triangles, Julbernardia paniculata; tinted triangles, Isoberlinia angloensis; closed triangles, Brachystegia longifolia.

Table 1.   Distribution of ectomycorrhizal fungi among host plants
Brachystegia longifolia (= 9)Isoberlinia angolensis (= 3)Julbernardia paniculata (= 15)Eucalyptus camaldulensis (= 14)Eucalyptus grandis (= 10)Eucalyptus grandis (= 8)
  1. Details on identification are given in the Supporting Information Table S1.

  2. 1Present on unidentified Caesalpinioideae.

  3. 2Present in other Eucalyptus plantations throughout Africa, Ecuador and/or Scotland (LT, unpublished).

  4. 3Present in pristine Zambian woodlands or elsewhere in Africa with no Eucalyptus nearby.

  5. 4Based on phylogenetic analyses.

/sordariales Z01Australian2766
/clavulina Z01African3,41
/clavulina Z02African41
/clavulina Z03African4122
/clavulina Z04African4121
/clavulina Z05Uncertain411
/clavulina Z06Uncertain411
/clavulina Z07African411
/clavulina Z09African41
/russula-lactarius Z01African3,411
/russula-lactarius Z04African31
/russula-lactarius Z07African31
/russula-lactarius Z08African412
/russula-lactarius Z09African3,41
/russula-lactarius Z10African3,41
/russula-lactarius Z11African42
/russula-lactarius Z25African3,41
/russula-lactarius Z29African41
/russula-lactarius Z30African41
/russula-lactarius Z31Uncertain41
/russula-lactarius Z32African41
/russula-lactarius Z50African41
/tomentella-thelephora Z01African3,411
/tomentella-thelephora Z05Uncertain41
/tomentella-thelephora Z06African3,411
/tomentella-thelephora Z07African3,43341
/tomentella-thelephora Z09African3,41
/tomentella-thelephora Z12African411
/tomentella-thelephora Z13Australian42
/tomentella-thelephora Z14African3,41
/tomentella-thelephora Z15African41
/tomentella-thelephora Z16African41
/tomentella-thelephora Z18African41
/tomentella-thelephora Z19African3,41
/tomentella-thelephora Z231African4
/tomentella-thelephora Z24African41
/ceratobasidium1 Z01African3,411
/ceratobasidium1 Z03African421
/marcelleina-peziza gerardii Z01African42
/marcelleina-peziza gerardii Z03African41
/marcelleina-peziza gerardii Z04African3,41111
/terfezia-peziza depressa Z01Australian411
/terfezia-peziza depressa Z02Australian45
/coltricia Z01African41
/amanita Z02African3,41
/inocybe Z02African32
/inocybe Z10African41
/inocybe Z12African41
/sebacina Z03African41
/sebacina Z04Uncertain411
/sebacina Z05African3,412
/sebacina Z121African3,4
/sebacina Z15African41
/sebacina Z16African41
/amanita Z01Uncertain41
/tomentellopsis Z01Australian411
/amanita Z06Uncertain41
/hysterangium Z01Australian234
/hysterangium Z02Uncertain11
/hysterangium Z04Australian21
/amanita Z07African41
/pisolithus-scleroderma Z01Australian214
/pisolithus-scleroderma Z02Australian2,41

Phylogenetic analyses revealed potential Australian origin in nine species of ECM fungi, whereas African origin was assigned to 46 spp. (Table 1; Fig. S1). The origin of eight species remained unclear, but these taxa are probably native given their colonization of native trees and the relatively large number of Australian ITS sequences available in INSD. While African species were equally distributed among the Caesalpinioideae and Eucalyptus hosts, Australian species were predominately restricted to their original host. Two Australian species (/terfezia-peziza depressa Z01, /tomentellopsis Z01) colonized both the introduced and native African trees (sharing identical ITS sequences), whereas the third putatively Australian species (/hysterangium Z04) was found only once on B. longifolia. All three Australian species were found on native trees on a single occasion, which was confirmed with sequence analysis of replicate root tips.

In Tumbama, the accumulating species richness (beta diversity) did not differ significantly among host genera or families (Fig. 1a,b). At other sites, the eight 50-yr-old solitary eucalypt trees hosted seven fungal species of which three were unique and three were shared with 29-yr-old eucalypts in Tumbama. Only one of these species (/terfezia-peziza depressa Z01) was shared with the native Caesalpinioideae in Tumbama. Although the solitary eucalypts supported similar amount of species per sample (one-way ANOVA: F1,29 = 2.94; = 0.097), they hosted less African species (F1,29 = 10.34; = 0.003) and had a lower proportion of root tips converted to ectomycorrhizas (F1,29 = 4.79; = 0.037) compared with eucalypts in the plantation. There were no differences in species richness and composition, and EcM colonization between the two Eucalyptus species in Tumbama.

At species level, three out of 12 fungal taxa tested (species that were present in three or more samples) displayed statistically significant host-biased distribution at the host family level in Tumbama. All these species (/sordariales Z01, /terfezia-peziza depressa Z02 and /hysterangium Z01) exclusively colonized roots of Eucalyptus spp. and were the most frequent mycobionts on these introduced hosts (Table 1). The NMS ordination and multivariate ANOVA suggested that the community composition of EcM fungi is significantly affected by host tree species (R2 = 0.143; F4,44 = 1.88; P =0.006), but not plot (R2 = 0.051; F1,44 = 1.60; P = 0.504; Fig. 2a). When Australian fungi were excluded, the effect of host remained nonsignificant (R2 = 0.077; F4,41 = 1.24; P =0.523; Fig. 2b).

Figure 2.

Relative effects of hosts and plot (arrows) on placement of samples in the nonmetric multidimensional scaling (NMS) ordination space as based on the community structure of ectomycorrhizal fungi: (a) all fungal species included; (b) fungi of Australian origin excluded. Open triangles, Julbernardia paniculata; tinted triangles, Isoberlinia angolensis; closed triangles, Brachystegia longifolia; open circles, Eucalyptus grandis; closed circles, Eucalyptus camaldulensis.


Tracking the potential origin of mycobionts relies on extensive reference data that has been deposited in INSD and UNITE databases, and has been annotated for taxonomy and metadata (Abarenkov et al., 2010b). Phylogenetic analyses revealed that several species of EcM fungi associated with eucalypts and/or native trees have conspecific or close congeneric relatives in other African sites, particularly in undisturbed woodlands of Zambia and eucalypt plantations throughout Africa, including Madagascar (Fig. S1). Two lineages of EcM fungi (/terfezia-peziza depressa and /tomentellopsis) that are common in Australia, but have never been recorded in Africa above- or below-ground (Tedersoo et al., 2010a; unpublished data from > 2000 root tips and > 1000 fruit-bodies) are obviously new introductions to the African mycota.

Ectomycorrhizal symbionts of the native Caesalpinioideae and introduced Eucalyptus spp. overlapped in the degraded eucalypt plantations, confirming the implications from a previous pure culture synthesis trial (Garbaye et al., 1988) and a fruit-body survey in Madagascar (Buyck, 2008). Here we show for the first time that identical ITS genotypes of ECM fungi are shared between the co-occurring native and introduced tree roots in field conditions. Compared with the solitary trees, eucalypts in mixed plantations were relatively more frequently colonized by African ECM fungi (χ2 = 9.258; df = 1; = 0.002). This suggests that intermingling of root systems and a reliable carbon source may be of particular importance for host shifting for native fungi and potentially so for the co-introduced, alien ECM mycobionts. In nitrogen-fixing bacterial symbioses, the introduced plants often associate with native rhizobia and Frankia (reviewed in Litchman, 2010). In all these cases, the functional compatibility of such unnatural associations remains unknown, but opens opportunities for exploitative relationships (Finlay, 1989; Schwartz et al., 2006).

The diversity of mycobionts was similar on root tips of the introduced and native hosts in mixed plantations. In particular, all common (n > 2) African EcM fungal species also colonized the eucalypts. These results indicate that Eucalyptus spp. do not choose their mycobionts among the local species pool. However, all African species of EcM fungi are unable to colonize eucalypts in pure culture synthesis experiments (et al., 2010), but this may reflect properties of individual strains or unsuitability of experimental conditions for particular fungi. By contrast, Australian fungi constituted the three most common ECM species on the roots of Eucalyptus spp., but failed to infect Caesalpinioideae hosts in the field. This suggests that both the physiological compatibility between symbionts and adaptation to local soil conditions are important for competition below ground. In non-native soil, Australian fungi are more competitive with African fungi for niches on roots of their historical hosts (eucalypts), whereas the better soil-adapted African fungi are able to compete for root niches in both their natural and alien hosts. Experimental work confirms that Eucalyptus spp. perform better with their co-introduced fungi than with locally available mycobionts, emphasizing the importance of a long-term coevolution and enhancement of histological and functional compatibility (Malajczuk et al., 1984; Chen et al., 2007). The low specificity for EcM fungi in both the Caesalpinioideae and Eucalyptus spp. in their natural environments (Tedersoo et al., 2008; Diedhiou et al., 2010) may further facilitate host shifts. Naturalization and invasion potential of EcM fungi may be enhanced with phylogenetically closely related hosts (Selosse et al., 1998; Pringle et al., 2009a). Amanita muscaria, a mycobiont of Pinaceae and Fagaceae, has only recently become invasive in Australia and New Zealand despite two centuries of known introduction history (Dunk, 2002; Orlovich & Cairney, 2004). Many invasive plants and animals require a naturalization period to adapt to local conditions or alter their environment for the invasion step (Richardson et al., 2000b). Eucalypts and many other invasive trees modify soil properties by exuding allelochemicals and accumulating recalcitrant litter (Ehrenfeld, 2003), both of which may alter the competitive balance among fungi (Jonsson et al., 2006).

Only three potentially co-introduced Australian fungi were found to colonize the root tips of the native Caesalpinioideae trees. Nevertheless, at least some alien fungi (/hysterangiales sp Z01 and /pisolithus-scleroderma Z01) were able to complete their life cycle by producing fruit-bodies and spores, which indicates that they are adapting to the native conditions. Such adaptation leads to naturalization that probably occurs independently in thousands of small plantations, road sides and yards, where the native and introduced trees and their microbes interact. We speculate that some of the naturalized fungi may gain the capacity to invade when fungal populations coevolve to improve the physiological compatibility with native hosts or encounter highly suitable soils (Richardson et al., 2000b; Wolfe et al., 2010).

While little is known about the functional diversity of EcM fungi in different ecosystems (Courty et al., 2010), we cannot predict the potential threats from invasive EcM fungi other than on local fungal biodiversity. It is interesting to note that two of the three host shifts from Australian to African plants were performed by members of fungal lineages that are not known to occur naturally in Africa. Different evolutionary origins and soil adaptations are likely to result in differential functions. In novel habitats, EcM fungi may transform soil carbon cycling (Gadgil & Gadgil, 1975; Chapela et al., 2001), affect mineral nutrient dynamics (Phillips & Fahey, 2006) and alter surrounding vegetation (Richardson & Rejmanek, 2004). In addition to potential threats to African biota, host shifts and subsequent establishment of African ECM fungi may similarly threaten Australian biodiversity if cheap, African-produced eucalypt wood with attached soil particles is exported to Australia (Wingfield et al., 2001).

To conclude, intermingling root systems of the introduced and native host trees facilitate host shifting among the Australian and particularly native African ECM fungi. Further adaptation to local hosts and soil environment poses a risk of naturalization and further invasion of the introduced Australian fungi (Richardson et al., 2000a). Therefore, it is recommended that exotic forestry plantations are kept separate from native woodlands and native trees are used for shelter in villages. Exotic forestry plantations could ideally be established by use of seeds of seedlings preinoculated with native edible mushrooms to reduce the potential for microbial invasion and encourage utilization of forestry ‘byproducts’ (Degreef et al., 1997; Buyck, 2008).


We thank the Chief of Manyinga for permission for this research, K. Abarenkov and I. Saar for bioinformatics advice, M.-A. Selosse and six anonymous referees for their comments on previous versions of the manuscript. This work was supported from ESF grants 7434, 8235, JD-0092, and FIBIR. Special thanks to Kaleva Travel for logistic support to TJ.