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The Problem Non-indigenous invasive plants have become one of the greatest threats to biodiversity in natural ecosystems around the world. As a result, enormous amounts of finances and resources are expended annually to combat invasive species. For example, in the U.S. it is estimated that a minimum of $34 billion annually is spent to combat invasive plants on agricultural lands. The estimated costs of combating invasive plants on public lands and natural ecosystems is much greater than the amount currently spent on agricultural lands. Although only a small percentage of introduced non-indigenous plant species become invasive, it is not yet possible to predict the invasiveness of a species or the impacts of introductions on native habitats. Currently, control strategies for non-indigenous plants include chemical herbicides, biological agents, and physical removal, all of which have had limited success or are costly. These control strategies reflect short-term fixes and do not represent management solutions based on understanding processes that promote or inhibit colonization of valued landscapes.
Although mechanisms of non-indigenous plant invasiveness have not been defined, it has been theorized that invasiveness is predominantly related to the reduction or absence of herbivorous and/or pathogenic organisms. However, there are few published accounts that substantiate this theory. Until mechanisms that control plant invasiveness in non-native and native habitats are characterized and understood, it may not be possible to design practical and long lasting management strategies. One of the least studied but critical aspects of plant community structure and dynamics involves symbiotic interactions with endophytic and mycorrhizal fungi. Few, if any, plants in natural ecosystems exist independent of symbiotic associations with mycorrhizal and/or endophytic fungi. In the last several decades it has become apparent that symbiotic fungi and their interactions are important to the structure, function, and health of plant communities. Without these symbiotic associations, it is possible that plant communities may not survive many environmental stresses. A novel aspect of mutualistic symbioses has recently been discovered at the Western Fisheries Research Center (WFRC). Symbionts isolated from plants growing in habitats that impose high adaptive pressures (e.g. geothermal soils, salt marshes) appear to allow the host plants to tolerate the stresses. This suggests that symbionts are responsible for the adaptation of at least some plants to specific selective pressures and that without symbiosis those plants do not survive environmental stresses. More importantly, "habitat-adapted symbionts" can transfer the ability to survive specific selective pressure to unrelated plants that evolved in completely different habitats. Objectives The 5-year research goals within the Invasive Species and Emerging Diseases Program are to: improve capabilities for inventory and multi-scale monitoring of established invaders; and expand research to support prevention and control of invasive species. The objective of this research is to determine if symbiotic fungi are responsible for the invasiveness of plants in non-native habitats. Specifically, we will test the following three hypotheses:
The null hypothesis (H0) for all three hypotheses is that symbiotic fungi are not involved in the invasiveness of introduced plants. Methodology Fungi are isolated from surface sterilized plant tissues and grown on standard medium. Plants and seeds will be collected from North Cascades, Olympic, Mt Rainier, Yellowstone and/or Wind Cave National Parks. Plant seeds will be surface sterilized and germinated to produce non-symbiotic (NS) plants. Some of the NS-plants will be colonized with the same fungi isolated from field samples to generate symbiotic (S) plants. Competition studies will be performed between NS- and S-plants to determine if the symbiotic fungi are responsible for invasiveness. In addition, the symbionts will be tested for the ability to confer drought tolerance and enhance growth rates.
Highlights and Key Findings The proposed research is based on the following observations made at the WFRC (Redman et al., 2001):
Where Are We Headed In 2003 This study will involve isolating fungi from internal tissues of several non-indigenous plant species that have been identified as serious problems by the U.S. NPS (Leafy spurge, St. Johns wort, Ox-eye daisy, and Reed canarygrass). Plants and seeds will be collected from North Cascades, Olympic, Mt Rainier, and/or Wind Cave National Parks. Plant seeds will be surface sterilized and germinated to produce non-symbiotic (NS) plants. Some of the NS-plants will be colonized with the same fungi isolated from field samples to generate symbiotic (S) plants. Competition studies will be performed between NS- and S-plants to determine if the symbiotic fungi are responsible for invasiveness. If symbiotic fungi are found to contribute to plant invasiveness then new control strategies will be developed based on symbiotic interactions.
Project Contact Rusty Rodriguez Email: rusty_rodriguez@usgs.gov Publications | ||||||||||||||||||||||
