• Abstract and Figures
• Public Full-text

Lectures 19 and 20: Mycorrhizas – Reading: Text, Chapter 17. ALSO great website from CSIRO in Austalia http://www.ffp.csiro.au/research/mycorrhiza/index.html http://mycorrhizas.info/index.html Rodriguez R and Redman R. 2008. More than 400 years of evolution and some plants still canʼt make it on their own. Journal of Experimental Botany 59: 1109-1114. Parniske M. 2008. Arbuscular mycorrhiza: the mother of plant root endosymbioses. Nature Reviews Microbiology 6: 763-773. Stinson, K.A. et al. 2006. Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms. PLOS Biology Objectives: Understand the importance of mycorrhizas. Know how to recognize ectomycorrhizas, and the types of endomycorrhizas. Know how to prove that a mycorrhizal symbiosis has been formed (differentiating between what you expect with ecto- vs. endomycorrhizas). Know which groups of fungi (phyla, orders, families) form ectomycorrhizas, which form endomycorrhizas. Keywords: ectomycorrhiza, mantle, Hartig net, endomycorrhiza, vesicle, arbuscule, spore, Glomeromycota. Study questions: 1) What are the soil and root-associated structures found with VAM? With orchid mycorrhizas? Compare and contrast the structures of VAM, orchid mycorrhizas, and ECMs. Which fungal phyla form each of the three types of mycorrhizas that we have discussed? 2) Are VAM common in plant roots? Explain. 3) VAM appears to be a balanced mutualism – is this true? 4) You wish to prove that Russula mississaugii is a mycorrhizal fungus. How could you convince our class? Use your naked eye, a dissecting microscope, a compound microscope, and radio-isotope study of tree seedlings to prove your point! What are the controls? 5) What are the benefits to the plant and to the ecosystem of mycorrhizas? 6) Why do plant species that depend on mycorrhizas tend to lack root hairs? 7) Garlic mustard is very common around Mississauga and on this campus. Despite the wet weather this year, mushroom biomass and diversity was not high on campus. Also, young tree seedlings may not be competing well to restore the tree canopy as older trees die. Explain a possible role for garlic mustard and speculate on additional factors behind these observations. 8) What are myco-heterotrophs and why are they “cheaters”? 9) What do we mean when we say that mycorrhizas are “dynamic” and form “nutrient networks”? 10) What is Parniskeʼs theory about VAM as the “mother of plant root endosymbioses”? There are two types of evidence – what are they? PLoS BIOLOGY Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Belowground Mutualisms Kristina A. Stinson1, Stuart A. Campbell2, Jeff R. Powell2, Benjamin E. Wolfe2, Ragan M. Callaway3, Giles C. Thelen3, Steven G. Hallett4, Daniel Prati5, John N. Klironomos2* 1 Harvard Forest, Harvard University, Petersham, Massachusetts, United States of America, 2 Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada, 3 Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America, 4 Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana, United States of America, 5 Department of Community Ecology, UFZ Centre for Environmental Research, Halle, Germany The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat. Citation: Stinson KA, Campbell SA, Powell JR, Wolfe BE, Callaway RM, et al. (2006) Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms. PLoS Biol 4(5): e140. DOI: 10.1371/journal.pbio.0040140 Introduction plants, can be negatively affected by AMF [14–16]. Natural- ized exotic plants have been found to be poorer hosts and Widespread anthropogenic dispersal of exotic organisms depend less on native AMF than native plants [17]. They often has raised growing concern over their devastating ecological colonize areas that have been disturbed [2], and disturbances impacts, and has prompted decades of research on the to soil have been shown to negatively impact AMF function- ecology of invasive species [1–3]. Exotic plants may become ing [18]. Furthermore, it has been proposed that the aggressive invaders outside their home ranges for a number proliferation of plants with low mycorrhizal dependency of reasons, including release from native, specialized antag- may degrade AMF densities in the soil [17]. However, a few onists [4], higher relative performance in a new site [5], direct invasive plants proliferate in the understory of mature chemical (allelopathic) interference with native plant per- temperate forests [2], where AMF density is typically high formance [6], and variability in the responses and resistance [19]. The existing mycelial network in mature forest soils may of native systems to invasion [7,8]. Thus, successful invasion in facilitate the establishment of exotic, mycorrhizal-dependent, many cases appears to involve the fact that invasive species recruits [20,21], but this should not be the case for non- are not at equilibrium, and are either freed of long-standing mycorrhizal invaders. If non-mycorrhizal invasive plants biotic interactions with their enemies in the home range, and/ establish and degrade AMF in mature forests, then the effects or disrupt interactions among the suite of native organisms on certain resident native plants could be substantial. they encounter in a new range [9]. Nevertheless, experimental One of the most problematic invaders of mesic temperate data on species-level impacts of exotic plants are still limited forests in North America is Alliaria petiolata (garlic mustard; [10]. One particularly understudied area is the potential for Brassicaceae), a non-mycorrhizal, shade-tolerant, Eurasian invasive plants to disrupt existing ecological associations biennial herb which, like most other mustards, primarily occupies disturbed areas. Garlic mustard is abundant in within native communities [6,10]. Many exotic and native forest edges, semishaded floodplains, and other disturbed plants alike depend upon mutualisms with native insects, sites in its home range [22]. However, this species has recently birds, or mammals for pollination and seed dispersal [11], and become an aggressive and widespread invader of both with soil microbes for symbiotic nutrient exchange [12]. Thus, when an introduced species encounters a new suite of resident organisms, it is likely to alter closely interlinked Academic Editor: Michel Loreau, McGill University, Canada ecological relationships, many of which have co-evolved Received December 5, 2005; Accepted March 1, 2006; Published April 25, 2006 within native systems [6,11]. DOI: 10.1371/journal.pbio.0040140 One such relationship is that between plants and mycor- Copyright: Ó 2006 Stinson et al. This is an open-access article distributed under rhizal fungi [12]. Most vascular plants form mycorrhizal the terms of the Creative Commons Attribution License, which permits unrestricted associations with arbuscular mycorrhizal fungi (AMF) [12], use, distribution, and reproduction in any medium, provided the original author and many plants are highly dependent on this association for and source are credited. their growth and survival [12], particularly woody perennials Abbreviations: AMF, arbuscular mycorrhizal fungi; ANOVA, analysis of variance; and others found in late-successional communities [13]. In REGW, Ryan-Einot-Gabriel-Welsch contrast, many weedy plants, in particular non-mycotrophic * To whom correspondence should be addressed. E-mail: [email protected] PLoS Biology | www.plosbiology.org 0727 May 2006 | Volume 4 | Issue 5 | e140 Invasive Plant Disrupts Mycorrhizas disturbed areas and closed-canopy forest understory across much of the United States and Canada [23], where it apparently suppresses native understory plants, including the seedlings of dominant canopy trees [22,24]. The mecha- nism underlying garlic mustard’s unusual capacity to enter and proliferate within intact North American forest com- munity has not yet been established. As shown in recent greenhouse experiments, garlic mustard’s impact on native understory flora may involve competitive [25] or allelopathic effects on native plants [26], but it has also been hypothesized that this species interferes with plant–AMF interactions in its invaded range [27]. Members of the Brassicaceae, including garlic mustard, produce various combinations of glucosinolate products [28], organic plant chemicals with known anti-herbivore, anti-pathogenic and allelopathic [29] properties, that may also prevent this non-mycorrhizal plant family from associat- ing with AMF [30]. These phytochemicals may be released into soils as root exudates, as a result of damaged root tissue, or in the form of leaf litter. High densities of garlic mustard in the field correlate with low inoculum potential of AMF, and extracts of garlic

Load more

  26

Copy Link