Photo: Chihuahuan Desert, Big Bend National Park. © 2018 Delena Norris-Tull
The role of native plant neighbors in biological invasions
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020, updated November 2024.
Sun, Müller-Scharer, and Schaffner (2014) conducted experiments to test the impact of neighboring communities of native plant species on the invasive species, spotted knapweed (Centaurea stoebe), and they also tested whether soil biota contribute to invasive success. Previous studies have focused on those two possible factors as contributors to the success of invasive species. They collected field soil from both European and North American ranges, in areas where native plants and C. stoebe grew, but at a distance from the knapweed plants (to avoid possible negative effects of plant-soil history).
Sun, et al., 2014, germinated seeds from European populations of spotted knapweed and seeds from invaded North American knapweed populations, in a greenhouse setting. They planted germinated knapweed in pots, with the following pairings/groupings:
Sun, at al., 2014, used relative plant biomass as the measure of invasive species success. They found that, in pots with native species without the presence of C. stoebe, there was no biomass difference between pots with EU native species and pots with NA native species, in both un-sterilized EU and NA soils.
In competition pots with C. stoebe, the biomass of the plants in the EU neighboring community was larger than the biomass of plants in the NA neighboring community. Thus, the impact of C. stoebe on native plants from its native range was less than the impact of C. stoebe on native plants from North American communities, regardless of the origin of the soil. Soil origin had no effect on the biomass of neighboring plant communities.
“Biomass of both EU and NA C. stoebe was significantly larger (on average 25%) when they competed with NA than with EU neighboring community,” regardless of the origin of the soil. “Similarly, the biomass of both EU and NA C. stoebe was more strongly reduced when they competed with EU than NA neighbors,” regardless of soil origin. “Interestingly, the biomass of C. stoebe was 25% higher when grown in NA soil than in EU soil…, but soil origin did not affect the reduction in biomass of C. stoebe” (Sun, at al., 2014).
“In the competition pots, soil sterilization significantly increased the biomass of neighboring communities… As in non-sterilized soil, biomass of the EU neighboring community was significantly higher… than that of NA neighboring community,” regardless of soil origin. “Soil sterilization also lead to an overall increase in biomass of EU and NA C. stoebe… Yet, while the effect of soil sterilization on biomass of C. stoebe was significant when C. stoebe competed with NA neighboring community in NA soil…, it was non-significant when C. stoebe competed with EU neighboring community in EU soil… As in non-sterilized soil, the biomass of EU and NA C. stoebe was significantly higher (on average 22%) when they competed with NA than with the EU neighboring community in both sterilized EU and NA soils” (Sun, at al., 2014).
“The reduction in biomass of neighbouring communities was significantly lower in sterilized soil, compared to non-sterilized soil… As in non-sterilized soil, NA neighbours had stronger reduction in biomass than EU neighbours in both sterilized EU and NA soils when competing with C. stoebe” (Sun, at al., 2014).
Sun, et al., 2014, concluded that the success of C. stoebe in the invaded grasslands ecosystems, “strongly resulted from release from highly competitive plant neighbouring species at home.” And they concluded that “altered biotic soil conditions in the introduced range and evolutionary changes in the plant invader were of less importance.” They believe that their study “provides evidence that the high impact of C. stoebe is not an inherent species trait,… but is strongly driven by the origin of its neighbouring competitor(s).”
“Release from competition with co-evolved neighbours appears to be more important than release from soil biota or post-introduction evolution. It is likely, though, that other factors, especially release from root herbivores…, may also contribute to the high impact of C. stoebe in the introduced range, and that the relative importance of factors affecting the competitive ability of and impact by C. stoebe shifts during the invasion process” (Sun, at al., 2014).
Reference:
Next Sections on research on the success of invasive species:
The role of native plant neighbors in biological invasions
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020, updated November 2024.
Sun, Müller-Scharer, and Schaffner (2014) conducted experiments to test the impact of neighboring communities of native plant species on the invasive species, spotted knapweed (Centaurea stoebe), and they also tested whether soil biota contribute to invasive success. Previous studies have focused on those two possible factors as contributors to the success of invasive species. They collected field soil from both European and North American ranges, in areas where native plants and C. stoebe grew, but at a distance from the knapweed plants (to avoid possible negative effects of plant-soil history).
Sun, et al., 2014, germinated seeds from European populations of spotted knapweed and seeds from invaded North American knapweed populations, in a greenhouse setting. They planted germinated knapweed in pots, with the following pairings/groupings:
- European knapweed with European field soil, and with sterilized soil.
- EU knapweed with North American field soil.
- North American knapweed with North American field soil, and with sterilized soil.
- North American knapweed with EU field soil.
- In pots, they planted European germinated knapweed with germinated seedlings from five native European plant neighbors (grasses and perennial herbs).
- And they planted EU knapweed with five native North American germinated species.
- And they planted North American knapweed with germinated seedlings from five North American native plant neighbors (grasses and perennial herbs and shrubs).
- And they planted NA knapweed with five EU seedlings.
Sun, at al., 2014, used relative plant biomass as the measure of invasive species success. They found that, in pots with native species without the presence of C. stoebe, there was no biomass difference between pots with EU native species and pots with NA native species, in both un-sterilized EU and NA soils.
In competition pots with C. stoebe, the biomass of the plants in the EU neighboring community was larger than the biomass of plants in the NA neighboring community. Thus, the impact of C. stoebe on native plants from its native range was less than the impact of C. stoebe on native plants from North American communities, regardless of the origin of the soil. Soil origin had no effect on the biomass of neighboring plant communities.
“Biomass of both EU and NA C. stoebe was significantly larger (on average 25%) when they competed with NA than with EU neighboring community,” regardless of the origin of the soil. “Similarly, the biomass of both EU and NA C. stoebe was more strongly reduced when they competed with EU than NA neighbors,” regardless of soil origin. “Interestingly, the biomass of C. stoebe was 25% higher when grown in NA soil than in EU soil…, but soil origin did not affect the reduction in biomass of C. stoebe” (Sun, at al., 2014).
“In the competition pots, soil sterilization significantly increased the biomass of neighboring communities… As in non-sterilized soil, biomass of the EU neighboring community was significantly higher… than that of NA neighboring community,” regardless of soil origin. “Soil sterilization also lead to an overall increase in biomass of EU and NA C. stoebe… Yet, while the effect of soil sterilization on biomass of C. stoebe was significant when C. stoebe competed with NA neighboring community in NA soil…, it was non-significant when C. stoebe competed with EU neighboring community in EU soil… As in non-sterilized soil, the biomass of EU and NA C. stoebe was significantly higher (on average 22%) when they competed with NA than with the EU neighboring community in both sterilized EU and NA soils” (Sun, at al., 2014).
“The reduction in biomass of neighbouring communities was significantly lower in sterilized soil, compared to non-sterilized soil… As in non-sterilized soil, NA neighbours had stronger reduction in biomass than EU neighbours in both sterilized EU and NA soils when competing with C. stoebe” (Sun, at al., 2014).
Sun, et al., 2014, concluded that the success of C. stoebe in the invaded grasslands ecosystems, “strongly resulted from release from highly competitive plant neighbouring species at home.” And they concluded that “altered biotic soil conditions in the introduced range and evolutionary changes in the plant invader were of less importance.” They believe that their study “provides evidence that the high impact of C. stoebe is not an inherent species trait,… but is strongly driven by the origin of its neighbouring competitor(s).”
“Release from competition with co-evolved neighbours appears to be more important than release from soil biota or post-introduction evolution. It is likely, though, that other factors, especially release from root herbivores…, may also contribute to the high impact of C. stoebe in the introduced range, and that the relative importance of factors affecting the competitive ability of and impact by C. stoebe shifts during the invasion process” (Sun, at al., 2014).
Reference:
- Sun, Y., Müller-Scharer, H., & Schaffner, U. (2014). Plant neighbours rather than soil biota determine impact of an alien plant invader. Functional Ecology, 28, 1545-1555.
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