Abstract Island biogeography has classically focused on abiotic drivers of species distributions. However, recent work has highlighted the importance of mutualistic biotic interactions in structuring island floras. The limited occurrence of specialist pollinators and mycorrhizal fungi have been found to restrict plant colonization on oceanic islands. Another important mutualistic association occurs between nearly 15,000 plant species and nitrogen-fixing (N-fixing) bacteria. Here, we look for evidence that N-fixing bacteria limit establishment of plants that associate with them. Globally, we find that plants associating with N-fixing bacteria are disproportionately underrepresented on islands, with a 22% decline. Further, the probability of N-fixing plants occurring on islands decreases with island isolation and, where present, the proportion of N-fixing plant species decreases with distance for large, but not small islands. These findings suggest that N-fixing bacteria serve as a filter to plant establishment on islands, altering global plant biogeography, with implications for ecosystem development and introduction risks.
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Mycorrhizal types influence island biogeography of plants
Abstract Plant colonization of islands may be limited by the availability of symbionts, particularly arbuscular mycorrhizal (AM) fungi, which have limited dispersal ability compared to ectomycorrhizal and ericoid (EEM) as well as orchid mycorrhizal (ORC) fungi. We tested for such differential island colonization within contemporary angiosperm floras worldwide. We found evidence that AM plants experience a stronger mycorrhizal filter than other mycorrhizal or non-mycorrhizal (NM) plant species, with decreased proportions of native AM plant species on islands relative to mainlands. This effect intensified with island isolation, particularly for non-endemic plant species. The proportion of endemic AM plant species increased with island isolation, consistent with diversification filling niches left open by the mycorrhizal filter. We further found evidence of humans overcoming the initial mycorrhizal filter. Naturalized floras showed higher proportions of AM plant species than native floras, a pattern that increased with increasing isolation and land-use intensity. This work provides evidence that mycorrhizal fungal symbionts shape plant colonization of islands and subsequent diversification.
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- Award ID(s):
- 1656006
- NSF-PAR ID:
- 10322355
- Date Published:
- Journal Name:
- Communications Biology
- Volume:
- 4
- Issue:
- 1
- ISSN:
- 2399-3642
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The latitudinal diversity gradient (LDG) dominates global patterns of diversity1,2, but the factors that underlie the LDG remain elusive. Here we use a unique global dataset3to show that vascular plants on oceanic islands exhibit a weakened LDG and explore potential mechanisms for this effect. Our results show that traditional physical drivers of island biogeography4—namely area and isolation—contribute to the difference between island and mainland diversity at a given latitude (that is, the island species deficit), as smaller and more distant islands experience reduced colonization. However, plant species with mutualists are underrepresented on islands, and we find that this plant mutualism filter explains more variation in the island species deficit than abiotic factors. In particular, plant species that require animal pollinators or microbial mutualists such as arbuscular mycorrhizal fungi contribute disproportionately to the island species deficit near the Equator, with contributions decreasing with distance from the Equator. Plant mutualist filters on species richness are particularly strong at low absolute latitudes where mainland richness is highest, weakening the LDG of oceanic islands. These results provide empirical evidence that mutualisms, habitat heterogeneity and dispersal are key to the maintenance of high tropical plant diversity and mediate the biogeographic patterns of plant diversity on Earth.
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Abstract Non-native, invasive plants are increasingly common in Eastern North American forests, but their impact on soil fungi remains unclear. We used DNA metabarcoding to investigate the effects of nativity, plant mycorrhizal type and soil factors on root-associated fungal communities. We focused on understory woody plants in a deciduous forest tract in central New York state, and included three plant types, invasive arbuscular mycorrhizal (AM), native AM, and native ectomycorrhizal (EM), each represented by 3–5 species. We found lower fungal operational taxonomic unit (OTU) diversity in EM than AM plants, but no OTU diversity difference between native and invasive AM species. Pathogen OTU richness and relative abundance were not distinct between plant types. OTU composition was influenced by host mycorrhizal type and by AM plant nativity, with mycorrhizal fungi being important drivers in both cases. The relationships of soil characteristics (e.g., pH) with OTU composition were independent of plant nativity and mycorrhizal type. Specific root length of native AM species was lower than that of invasive AM plants, while EM plants were intermediate. Irrespective of plant type, OTU composition was distinct among plant species, particularly in fungal communities associated with the invader
Rhamnus cathartica . These results suggest that invasive AM plants may shift fungal composition relative to native AM and EM plants, with potential long-term consequences for soil biodiversity. -
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Abstract Arbuscular mycorrhizal (AM) fungi are root symbionts that can facilitate plant growth and influence plant communities by altering plant interactions with herbivores. Therefore, AM fungi could be critical for the conservation of certain rare plants and herbivores. For example, North American milkweed species are crucial hosts for monarch butterflies (
Danaus plexippus ). Understanding how mycorrhizal composition affects milkweeds will have direct impacts on the conservation and restoration of both increasingly threatened guilds. We present data from three studies on the effect of AM fungal composition on milkweed growth, latex production, and establishment. First, we grew seven milkweed species with and without a mixture of native mycorrhizal fungi. We assessed how important fungal composition is to milkweed growth and latex production by growing four milkweed species with seven fungal compositions, as single‐species inoculations with four native fungi, a mixture of native fungi, a single commercial fungus of presumably non‐native origin, and noninoculated controls. Finally, we assessed the field establishment of two milkweed species with and without native mycorrhizal inoculation. Milkweed species grew 98% larger and produced 82% more latex after inoculation with native mycorrhizae. Milkweeds were strongly affected by fungal composition; milkweeds were inhibited by commercial fungi (average of −14% growth) and showed variable but positive responses to native fungal species (average of +3% to +38% biomass). Finally, we found that restoration establishment was dependent on inoculation with native fungi and milkweed species. Overall, our findings indicate that some milkweed species (i.e.,Asclepias syriaca andA. incarnata ) are not responsive to mycorrhizal fungal presence or sensitive to mycorrhizal composition while others are, including endangered species (A. meadii ) and species of high conservation value (A. tuberosa ). We conclude that the reintroduction of native AM fungi could improve the establishment of desirable milkweed species and should be considered within strategies for plantings for monarch conservation. -
null (Ed.)Abstract In a globalized world, plant invasions are common challenges for native ecosystems. Although a considerable number of invasive plants form arbuscular mycorrhizae, interactions between arbuscular mycorrhizal (AM) fungi and invasive and native plants are not well understood. In this study, we conducted a greenhouse experiment examining how AM fungi affect interactions of co-occurring plant species in the family Asteracea, invasive Echinops sphaerocephalus and native forb of central Europe Inula conyzae . The effects of initial soil disturbance, including the effect of intact or disturbed arbuscular mycorrhizal networks (CMNs), were examined. AM fungi supported the success of invasive E. sphaerocephalus in competition with native I. conyzae , regardless of the initial disturbance of CMNs. The presence of invasive E. sphaerocephalus decreased mycorrhizal colonization in I. conyzae , with a concomitant loss in mycorrhizal benefits. Our results confirm AM fungi represent one important mechanism of plant invasion for E. sphaerocephalus in semi-natural European grasslands.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s42003-021-02649-2
