Mycorrhiza (2003) 13:143–149 DOI 10.1007/s00572-002-0210-9 ORIGINAL PAPER M.-A. Selosse Founder effect in a young Leccinum duriusculum (Schultzer) Singer population Received: 6 May 2002 / Accepted: 15 October 2002 / Published online: 15 November 2002 Springer-Verlag 2002 Abstract The genetic diversity of a Leccinum duriuscu- mainly responsible (Watkinson 1998), by interfering with lum population growing under <20-year-old Populus alba plant/plant competition and plant/soil interface. Recipro- on former farming soil was analysed from 1998 to 2001 cally, successional appearances and extinctions in the and compared in 2000 to the two nearest populations plant community drive evolution of the soil microbial found under >70-year-old P. alba. Genets were recog- communities. The settlement of ectomycorrhizal fungi, nized using RAPD amplifications with three different which symbiotically colonize the roots of trees and shrubs primers, while their conspecificity was assessed by (Smith and Read 1997), requires the presence of the host sequencing the nuclear ITS and mitochondrial large species. Ectomycorrhizal fungi are lacking in former ribosomal subunit. The young population was colonized farmed soils and their arrival occurs with the planting of by a large genet that persisted from 1998 to 2001 (most trees (Last et al. 1987; Selosse 2001), with a progressive distal sporophores were 10.4 m apart in 2001) and a recruitment of the ectomycorrhizal community. This has second genetically related genet appeared in 2001. Five been well documented thanks to sporophore surveys, e.g. and six genets, respectively, of smaller size were found in under Betula (Ford et al. 1980; Mason et al. 1982, 1983; the two other populations, while the investigated area was Last et al. 1983), Eucalyptus (Lu et al. 1999) and conifers slightly smaller (72.25 m2) and the three populations were (Dighton et al. 1986; Richter and Bruhn 1993). Sporo- strongly divergent genetically (>33%). The genetic uni- phore patches were reported to enlarge and move formity, as well as the high speed of radial growth of the outwards from the tree from one year to the next (Ford lasting genet under <20-year-old P. alba (radial growth: et al. 1980; Mason et al. 1982; Last et al. 1987; de la 1 m/year), are interpreted in the framework of a founder Bastide et al. 1994). This progressive colonization was effect. The slow recruitment of genets is proposed to also documented underground by analysing ectomycor- lower the intraspecific competition and to entail large, rhizal diversity directly on roots (e.g. Deacon et al. 1983; fast-growing genets. The differences from ectomycor- Natarajan et al. 1992). rhizal populations due to secondary colonization, which Studies on ectomycorrhizal populations have focused have been investigated often, are also emphasized. up to now on populations from forest stands. Populations were analysed at old forest sites with long-established Keywords Founder effect · Leccinum duriusculum fungal populations (Selosse 2001), for example for (Schultzer) Singer species of Amanita (Redecker et al. 2001; Sawyer et al. 2001), Laccaria (Gherbi et al. 1999; Fiore-Donno and Martin 2001), and Suillus (Dahlberg and Stenlid 1994; Introduction Zhou et al. 2000). In some cases, populations were investigated on younger tree stands (de la Bastide et al. The dynamics of plant communities are tightly linked to 1994; Selosse et al. 1998a, b, 1999), sometimes allowing the diversity of the soil microflora (Bever et al. 1997). In a comparison with older stands (Dahlberg and Stenlid the successional process occurring during colonization of 1994; Dahlberg 1997; Gryta et al. 1997). In every case, new areas in terrestrial ecosystems, changes in soil these ectomycorrhizal populations were growing in or microbial communities induce modifications in the plant close to an already established forest, after a disturbance community. Here, soil pathogens and symbionts are (e.g. fire or clearcut) that gave rise to a new tree generation. These data thus reflect populations from M.-A. Selosse secondary successions (the so-called “second generation” Institut de Systmatique (IFR CNRS 1541), in Last et al. 1987). Little is known of the genetic Musum National d’Histoire Naturelle, 43 rue Cuvier, 75005 Paris, structure and diversity of the pioneer ectomycorrhizal France 144 populations observed during primary succession. In several cases, early-stage species still occur under older trees (Newton 1992; de la Bastide et al. 1994; Kranabetter and Wylie 1997), allowing for comparisons. Hebeloma cylindrosporum in French coastal dunes provide popula- tions in colonization zones, at the forest border, as well as in mature forests (Gryta et al. 1997, Guidot et al. 2002). As H. cylindrosporum recolonizes sandy patches resulting from anthropic perturbations in mature forests, it is unsure whether this provides ectomycorrhizal populations of typical mature forests. Here I considered a specific ectomycorrhizal species, Leccinum duriusculum under Populus alba, which is unlikely to exist before planting of its host (Last et al. 1987) because of its specificity (Lannoy and Estads 1995). I followed its appearance in a small garden plantation of P. alba growing on former farmed soil. I propose it here as a model for studying an ectomycor- rhizal population at the time of its establishment. The Fig. 1 Map of population A, with positions of the Leccinum structure of the population was assessed by RAPD, a duriusculum sporophores found in 1998, 2000 and 2001 (symbols method providing polymorphic, dominant markers, which indicating the year of collection and genet of origin, B1 or B2, are explained in the box at the right). Trees are located by black dots have been used already in studies of ectomycorrhizal with sizes reflecting tree diameter; several closely growing populations (e.g. de la Bastide et al. 1994; Selosse et al. sporophores are represented by a single symbol 1998a, b, 1999). The genetic structure was followed over 4 years and revealed an unexpectedly lower genetic diversity than in populations on the nearest old P. alba sporophores in population B and 31 sporophores in population C. The ground location of the sporophores was mapped in every case stands. with a precision of 5 cm. Sporophores were dried for transport and frozen at –80C before DNA extraction. Materials and methods DNA extraction Sampling sites Total DNA from frozen sporophores was extracted following the protocol of Henrion et al. (1994) for the 1998 and 2000 sampling Three L. duriusculum populations under P. alba were surveyed in and using the DNeasy Plant Mini Kits (Qiagen S.A., Courtaboeuf, Belle-Ile-en-Mer, an island off Brittany in France (4720’N and France), according to the manufacturer’s instructions, for the 2001 530’W, 50 m above sea level). The average annual precipitation is sampling. In both cases, the DNA was resuspended in distilled 1,100 mm, evenly distributed over the year, with a mean annual water and kept at –80C. temperature of 12.3C (less than 9 days of freezing per year; data since 1950). The forest cover of the island was totally clearcut for farming purposes and there have been no forest stands at least since RAPD analysis the 19th century (Chasle de la Touche 1852). However, Salix and spp. and Populus spp. hedgerows still grow at the borders of wet RAPD reactions were carried out twice using primers 152C (5’- fields. Population A was found in my family garden in the town of CGCACCGCAC-3’), 155 (5’-CGTGCGGCTG-3’) and 156 (5’- Borgrouaguer, on a soil that was previously farmed, where six 5- GCCTGGTTGC-3’) that were previously selected for their ability year-old poplar trees were outplanted in 1983 near two perpendic- to generate reproducible and polymorphic patterns on this sample ular hedgerows of non-ectomycorrhizal shrubs, one planted with set (data not shown). RAPD amplification was performed using the Eleagnus sp. (hedgerow 1) and the second with Spartium junceum enhanced protocol of Selosse et al. (1998a), followed by electro- (hedgerow 2) (Fig. 1). The outplanted poplar trees were grown in a phoretic separation on 8% acrylamide gels in 1 Tris-borate-EDTA nursery situated 3 km away. Due to the plateau nature of the site, buffer, as described in Selosse et al. (1998a). To compare the this stand is unlikely to have harboured any spontaneous poplar various RAPD patterns found, comigrations and side-by-side trees in the past. Leccinum duriusculum sporophores were found migrations were performed in every permutation for all genets. here for the first time in 1997 (M.-A. Selosse, unpublished data). The presence/absence of each RAPD fragment was recorded, This population was surveyed daily during the fruiting period (May excluding the fragments of low intensity and of a size greater than to November) in 1998, 2000 and 2001, allowing an extensive 1,400 bp that are less reproducible. A matrix of the number of sporophore survey during those 3 years (9, 34, and 14 sporophores, differences between genets was established using the Mega respectively, were collected; no sampling was performed in 1997 programme (Kumar et al. 2000). This was then used to build a and 1999). Populations B (Dout de Borgrouaguer) and C (Kerland) phenetic tree using the Neighbour-Joining method, with the same were found under P. alba trees at least 70 years old and where L. software. The percentage differences within or among populations duriusculum has been fruiting yearly at least since 1983 (M.-A. were calculated as the mean percent of fragments by which genets Selosse, unpublished data). Population B grows under the poplar differed from each other, considering every permutation. stand nearest to population A (200 m away). Populations A and B are situated 1.35 km away from population C. In populations B and C, a 8.5 m 8.5 m area (i.e. an area slightly smaller than that of population A in 2001) was arbitrarily chosen and surveyed daily during the fruiting period in 2000.