Ectomycorrhizal Fungal Communities of Oak Savanna Are Distinct from Forest Communities
Total Page：16
File Type：pdf, Size：1020Kb
Mycologia, 101(4), 2009, pp. 473–483. DOI: 10.3852/08-178 # 2009 by The Mycological Society of America, Lawrence, KS 66044-8897 Ectomycorrhizal fungal communities of oak savanna are distinct from forest communities I.A. Dickie1 remains (Nuzzo 1985). The oak savanna landscape Landcare Research, Box 40, Lincoln, (areas with continuous herbaceous cover dominated 7640 New Zealand by grass and with discontinuous tree coverage) is fire B.T.M. Dentinger2 dependent; frequent fires prevent woody dominance P.G. Avis3 and maintain an open park-like setting (Tester 1996, D.J. McLaughlin Peterson and Reich 2001). While most of the loss of Department of Plant Biology, University of Minnesota, oak savanna has been due to agricultural conversion, St Paul, Minnesota 55108 other large areas have been lost due to the suppres- sion of fire. In the absence of fire oak savanna P.B. Reich converts first to oak forests (here defined as closed- Department of Forest Resources, University of canopy oak-dominated forest) and eventually to more Minnesota, St Paul, Minnesota 55108 shade-tolerant tree species (Peterson and Reich 2001). The conversion of oak savanna to oak forest Abstract: Oak savanna is one of the most endan- is accompanied by a number of changes in soil gered ecosystems of North America, with less than fertility (White 1983, Reich et al 2001, McGill et al 0.02% of its original area remaining. Here we test 2007). whether oak savanna supports a unique community of Although the loss of any habitat is of conservation ectomycorrhizal fungi, a higher diversity of ectomy- concern, there is limited evidence of any negative corrhizal fungi or a greater proportional abundance effects of savanna conversion on particular taxonomic of ascomycete fungi compared with adjacent areas groups. A number of plant species, particularly shrubs where the absence of fire has resulted in oak savanna and forbs, reach their peak abundances in savanna, conversion to oak forest. The overall fungal commu- but most of these also are present in prairie (Bray nity was highly diverse and dominated by Cenococcum 1960). Individual plant functional groups tend to geophilum and other ascomycetes, Cortinarius, Rus- show lower or higher species richness in savannas sula, Lactarius and Thelephoraceae. Oak savanna than adjacent grasslands or forests but are not mycorrhizal communities were distinct from oak restricted to the savanna (Peterson and Reich 2001). forest communities both aboveground (sporocarp Similar limited fidelity for savanna habitat has been surveys) and belowground (RFLP identification of found for birds and arthropods, for which savanna ectomycorrhizal root tips); however total diversity was communities are a mixture of forest and grassland not higher in oak savanna than oak forests and there communities (Siemann et al 1997, Grundel and was no evidence of a greater abundance of ascomy- Pavlovic 2007). cetes. Despite not having a higher local diversity than The effect of savanna loss on fungal communities is oak forests, the presence of a unique fungal commu- unclear. Oak forests in general are dependent on and nity indicates that oak savanna plays an important role support a diverse community of ectomycorrhizal in maintaining regional ectomycorrhizal diversity. fungi (Walker et al 2005, Bergemann and Garbelotto Key words: Ascomycota, conservation, diversity, 2006, Avis et al 2008), but whether any ectomycor- fire, habitat loss, mycorrhizal ecology rhizal fungal species specifically require oak savanna is unclear. Fire, the driving ecological force in the INTRODUCTION persistence of savanna, has a number of known effects on fungal communities. Severe wildfire can kill fungal Oak savanna once dominated large areas of North ectomycorrhizal genets, reduce diversity (Bruns et al America, but less than 0.02% of its original area 2002) and result in an increased dominance by fungi Accepted for publication 19 February 2009. with resistant propagules (Taylor and Bruns 1999) 1 Corresponding author. Landcare Research, PO Box 40, Lincoln and facultatively mycorrhizal species capable of 7640, New Zealand. Tel: +64 3 321 9646; Fax: +64 3 321 9998. E- surviving as saprotrophs (Egger 1986). Fires in mail: [email protected] savanna however are typically low intensity; the stems 2 Current address: Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada M5S 3B2. of trees smaller than 5 cm diam are almost always 3 Current address: Biology Department, Indiana University North- killed but the individual almost always survives and west, Gary, Indiana 46408. resprouts while the stems of most larger trees 473 474 MYCOLOGIA generally survive. Similarly grasses quickly resprout fungi would comprise a greater proportion of from roots and crowns and soil heating is minimal ectomycorrhizal fungi in oak savanna compared with over large areas. Further the three major ectomycor- oak forest. rhizal hosts in Minnesota oak savanna are Quercus macrocarpa, Q. ellipsoidalis and Corylus americana, all MATERIALS AND METHODS three of which are also present in oak forests, while the one host plant that does decline with fire We used a combined belowground and aboveground suppression, Helianthemum bicknelii, is relatively rare sampling of fungal structures. Sampling ectomycorrhizal and appears to support largely the same fungal roots belowground, with a combined morphotyping and RFLP approach, let us detect species such as hypogeous community as Quercus (Tester 1996, Dickie et al ascomycetes that were not detectable aboveground (Smith 2004). Oak savannas are highly spatially heteroge- et al 2007). Including aboveground sporocarp collections neous, creating a potentially greater number of let us build a species list based on robust identifications with spatial niches for fungi that preferentially occur sporocarp vouchers, and permitted a much greater total distant from trees (Last et al 1984, Dickie and Reich area to be sampled. 2005); this might be expected to increase fungal diversity in savanna. On the other hand oak savannas Sites.—Cedar Creek Science Ecosystem Reserve and Long harbor fewer trees (i.e. smaller islands of habitat) Term Ecological Research site in Minnesota, including burn history, has been described by Tester (1996) and Reich et al compared with forests and because ectomycorrhizal (2001). We sampled ectomycorrhizal fungi from six sites, species richness is known to relate to the size of three of which have had frequent controlled burns (plots habitat (Peay et al 2007) this might be expected to 103, 104, 106), which we will refer to as savanna, and three result in fewer species in savanna than in forest. of which have had no fire history during that period (plots Higher level taxonomic groups might also be 109, 110, 309), which we will refer to as forests. The sites expected to occur preferentially in oak savanna. differed markedly in soil parameters, including pH and One fungal group that might be particularly expected nitrogen availability (TABLE I), both of which are likely to preferentially to occur in oak savannas is the influence fungal communities (Lilleskov et al 2002, Avis et ectomycorrhizal ascomycetes (Tedersoo et al 2006). al 2008). A portion of plot 106 had been included in a In extreme pinyon pine scrub ascomycetes are nutrient addition experiment; we avoided this portion of abundant (Gehring et al 1998), perhaps suggesting the plot in belowground sampling (TABLE II). a higher abundance in savanna, which also can be Belowground sampling.—We sampled ectomycorrhizal fungi more extreme than oak forests. We also have found from individual roots collected in soil cores 2.8 cm diam ascomycetes to be more common on seedlings and 20 cm deep. A common approach to sampling planted in abandoned agricultural fields than in ectomycorrhizal communities is to use tree-centered soil adjacent oak forests (Dickie and Reich 2005), which cores (Gehring et al 1998, Avis et al 2003). This technique suggests they might prefer open, disturbed habitat. would be inappropriate for our sites because distance from Warcup (1991) found that ascomycetes dominated trees is an important factor structuring fungal communities ectomycorrhizal communities on Eucalyptus after fire (Dickie and Reich 2005) and savanna sites have a highly heterogeneous spatial pattern of tree occurrence. We and Fujimura et al (2005) showed 15% of ectomycor- therefore established six, parallel, 100 m transects spaced rhiza on roots of Pinus ponderosa in a postfire site 10 m apart in each plot, with 20 sampling points identified were ascomycetes but in neither case was a direct by flags every 5 m along these transects, and sampled cores comparison made with sites without fire. Ectomycor- randomly from these 120 points (80 in plot 106) until a rhizal ascomycetes may be facultatively saprotrophic, minimum of 30 cores were obtained that contained permitting survival in the absence of host roots ectomycorrhizal roots. In forests 100% of cores taken (Egger 1986). Increased soil pH in savanna might contained ectomycorrhizal roots; the final sample size was also favor ascomycetes because it has been suggested 31–32 cores (TABLE II). In savanna 61% of cores contained that higher soil pH favors sporocarp production of ectomycorrhizal roots, requiring 40–64 cores to obtain the the ascomycetous genus Tuber (Hall et al 2008). desired sample size of a minimum of 30 cores with roots; the We studied the belowground and aboveground final sample size was 30–33 cores (TABLE II). Sampling was