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Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright FUN GAL E COL 0 G Y 5 (20 I 2) 430 -442 available at www.sciencedirect.com SciVerse ScienceDirect j ou rna I h 0 mepage: www.elsevier.com/l ocate/fu neco Twenty years of research on fungal-plant interactions on Lyman Glacier forefront - lessons learned and questions yet unanswered Ari JUMPPONENQ,*, Shawn P. BROWNQ, James M. TRAPPEb, Efren CAZARESb, Rauni STROMMERc aDivision of Biology, Kansas State University, Manhattan, KS 66506, USA bDepartment of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA CDepartment of Environmental Sciences, University of Helsinki, Lahti 15140, Finland ARTI CLE INFO AB STRACT Article history: Retreating glaciers and the periglacial areas that they vacate produce a harsh environment Received 19 July 2011 of extreme radiation, nutrient limitations and temperature oscillations. They provide Revision received 2 November 2011 a model system for studying mechanisms that drive the establishment and early assembly Accepted 4 January 2012 of communities. Here, we synthesize more than 20 yr of research at the Lyman Glacier Available online 13 March 2012 forefront in the North Cascades Mountains, comparing the results and conclusions for Corresponding editor Kevin Newsham: plant and fungal communities. Compared to plant communities, the trajectories and processes of fungal community development are difficult to deduce. However, a combina Keywords: tion of high throughput sequencing, more revealing experimental designs, and phyloge Community assembly netic community analyses provide insights into mechanisms that shape early microbial Community convergence communities. While the inoculum is likely to be randomly drawn from regional pools and Community divergence accumulates over time, our data provide no support for increases in richness over time Community trajectory since deglaciation, as is commonly observed for plant communities. Re- analyses of exist Establishment ing datasets suggest that microbial, and particularly fungal, communities are insensitive to Glacier forefront time since substrate exposure from underneath the retreating glacier, but are responsive to Mycorrhiza plant establishment both in biomass and community composition. Further research on Propagule functional aspects, organismal activity, or ecosystem services in early successional envi ronments will provide deeper appreciation of the dynamics of these communities. © 2012 Elsevier Ltd and The British Mycological Society. All rights reserved. Introduction nitrogen (Matthews 1992; Tscherko et al. 2003; Strauss et al. 2009), factors that globally limit ecosystem productivity Many alpine glaciers reached their glacial maximum during (Vitousek et al. 1997). These nutrient limitations are often the Little Ice Age in the mid-19th century (Egli et al. 2001) and combined with extreme fluctuations of daily temperatures, have been retreating over the past century and a half at limited barriers against wind damage, poor water retention increasing rates (Hodge et al. 1998; Dyurgerov & Meier 2000; and high irradiation, all of which may limit plant establish Pelto 2006). Glacial retreat exposes a mineral substrate that ment and survival (Stocklin & Baumler 1996; Jumpponen et al. is devoid of organic legacies and often deficient in mineral 1999b; Lichter 2000; Jones & del Moral 2009). Additionally, * Corresponding author. Tel.: +1 785 5326 751; fax: +1 785 5326653. E-mail address: [email protected] (A. Jumpponen). 1754 -5048/$ - see front matter © 2012 Elsevier Ltd and The British Mycological Society. All rights reserved. doi:10.1016/j .funeco.2012.01.002 Twenty years of research on community dynamics on Lyman Glacier forefront 431 glaciers and their forefronts most often occur at high latitudes Many of our studies test hypotheses about the establish and altitudes, characterized by short growing seasons and ment and succession of communities. We have focused on the substantial winter snow cover. Together, these abiotic role of mycorrhizal fungi in primary plant succession and stressors make primary successional forefronts challenging subsequent secondary succession. Early studies by Reeves environments to research, but they also provide unique et al. (1979) showed that in a desert ecosystem with opportunities to study the early assembly of communities a severely disturbed, secondary successional habitat, the early (Cazares et al. 2005). plant invaders were nonmycorrhizal species, whereas plants Many mechanisms controlling primary succession in plant that dominated the adjacent nondisturbed system mostly communities have been recently clarified (Walker & del Moral formed associations with AM fungi. Reeves et al. (1979) also 2003; Pickett et al. 2009) and older theories reevaluated reviewed literature on primary succession of volcanic islands (Clements 1916; Connell & Slatyer 1977). Some of these that showed early plant communities to be nonmycorrhizal. insights have shifted views on community assembly They hypothesized that the early nonmycorrhizal invaders processes in terrestrial ecosystems. For example, early were poor competitors and were therefore rapidly replaced successional community development seems not to depend when mycorrhizal hosts could establish after AM inoculum on deterministic colonization by pioneering species but rather had entered the disturbed site. These AMhosts were argued to combines stochastic dispersal and establishment controls be better competitors and produced additional AM inoculum (Fastie 1995; del Moral 2009) that are later amended by deter in the soil to enable other myco.rrhizal plants to establish. ministic processes such as biotic, competitive and facilitative Allen et al. (2005) reached similar conclusions on primary controls (del Moral 2009). successional tephra resulting from the Mount St. Helens Long-term studies in glacier forefronts are rare because of eruption. One of our early driving questions was whether or their remote locations and short accessible seasons, dictated not a glacier forefront would exhibit similar primary and by high altitudes and latitudes. Instead, glacier forefronts have secondary successions. often been subjected to a chronosequence approach (space While glacier systems differ in numerous characteristics for-time substitution), in which distance from the glacier and the conclusions may be context dependent, many general terminus is considered as a proxy for time since exposure trends and patterns have proved consistent (Tscherko et al. (Pickett 1989; Cazares et al. 2005; Walker et al. 2010). While 2003; Orwin et al. 2006). Here, we use our research on the suffering from potential correlations between position in the Lyman Glacier forefront, which spans more than 20 yr, as chronosequence and substrate chemistry, fluctuations in a model. We first briefly review patterns of plant community weather or climatic conditions, distance to propagule sources, establishment and trajectories, then compare plant and or other environmental parameters (Fastie 1995; Walker et al. fungal communities. Finally, we identify critical areas that 2010), the forefronts benefit from providing a single location have received little attention and propose approaches to wherein substrates of different ages can be observed in a rela address them in fungal and/or microbial systems. tively homogeneous environment (Matthews 1992; Jumpponen et al. 1998; Cazares et al. 2005; Raffl et al. 2006). In this contribution, we reflect on and synthesize more than Community assembly and ecological filtering 20 yr of research at a glacier forefront in Washington State's North Cascades Mountains, which contain more than 700 As a general framework, we rely on assembly rules used in glaciers (Post et al. 1971). Similarly to glaciers globally (Hodge community ecology (Cole 1983; Hunt 1991). This community et al. 1998; Dyurgerov & Meier 2000), glaciers in the North assembly model integrates traits and life histories and their Cascades have been receding in recent decades (Pelto 2006, contribution to organismal environmental tolerances 2011). To optimize our choice of a forefront environment, we Oumpponen & Egerton-Warburton 2005). Factors deter explored several glaciers to find one that would best serve as mining successful establishment are considered as abiotic the long-term study site. Our criteria included (1) reasonable and biotic filters that select community components from accessibility, (2) a forefront with relatively little elevational local, regional and ecologically suited species pools (Weiher change, (3) a subalpine habitat to allow establishment of & Keddy 1995, 2001; Booth & Swanton 2002). Local and ectomycorrhizal (EcM), ericoid mycorrhizal (ErM) and arbus regional propagule pools determine candidate species with cular mycorrhizal