Photo: Sagebrush habitat, Yellowstone NP. © 2016 Delena Norris-Tull
Resource allocation: Its role in invasive plant success or failure
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Funk (2013) conducted a thorough review of the literature on resource utilization in native and invasive plants, focusing on low-resource environments. She specifically looked at research on plant efficiency in using limited soil nutrients, water, and light. She defined low-resource environments as “those where plant productivity is severely limited by light, water, or soil nutrient availability, such as forest understories, deserts, and ancient landscapes. In many of these ecosystems, native plants have evolved mechanisms to tolerate stress and to facilitate the extraction of limiting resources. These adaptations have resulted in a high degree of species richness and functional diversity in many low-resource ecosystems.”
Funk, 2013, found that “native species appear to have a competitive advantage over invasive species in low-resource systems…, and communities become more susceptible to invasion when resource availability is increased.” However, “many invasive species do occur in low-resource ecosystems.” Funk found that, “It is difficult to identify a suite of general traits explaining invasiveness, because traits of invaders depend on characteristics of the invaded habitats.”
She stated that “research… suggests that plants in high-resource ecosystems succeed through high rates of resource acquisition, while species adapted to low-resource ecosystems largely display traits associated with resource conservation.”
In examining research on species’ use of soil nutrients, Funk, 2013, found that “plant species may be differentially limited by N [nitrogen] and P [phosphorus] in many systems…. Plant growth in species with special adaptations for N (e.g. fixation) or P acquisition (e.g. cluster roots) may not be limited by the same nutrient as are neighbouring species… Species also vary in their nutrient requirements. For example, grasses require lower amounts of P than forbs… Grasses with a C4 photosynthetic pathway can also operate at a lower N concentration.” In low-resource environments where non-native species have invaded successfully, “invasive species appear to use nutrients more efficiently than natives in low-nutrient soils.” However, she found that there is limited research on the mechanisms of nutrient-use efficiency in invasive plants.
In studies conducted in arid and semi-arid environments, Funk, 2013, concluded that the “results suggest that water availability most strongly limits plant growth in normal precipitation years, while N availability limits plant growth in wet years…. There is evidence that some invasive species possess drought-tolerant traits, while others do not.”
Funk, 2013, found that “data suggest that LMA [leaf mass per unit area] is lower in invasive species than native species occurring in arid environments…. Thin leaves generally have low quantities of structural carbohydrates, which results in low energetic or construction cost of the leaf… Low construction cost is often associated with higher plant growth rates… However, while cheap structures may provide an initial growth advantage, more leaf area leads to higher plant-level transpiration rates, and this may render these exotic species more prone to water stress in low-precipitation years. Nevertheless, many annual species (particularly invasive annuals) may employ this strategy, where the production of cheap structures facilitates a rapid response to unpredictable precipitation events… This mechanism may explain why exotic species can spread in wet years and remain in the soil bank during dry years.” Research indicates that “invasive species may favour drier microsites within habitats, deplete soil moisture levels more than natives, or have higher nocturnal transpiration.” Funk, 2013, found no research on the factor of root depth on invasive success in arid systems.
Funk, 2013, found research that “exotic species generally develop leaves earlier in the year than natives, which may allow them to pre-empt resources.” And while “evergreen species may be more constrained in their ability to respond morphologically to precipitation events than deciduous perennials or annual species,… long-lived leaves may provide evergreens with an advantage over those that must produce new leaves following a precipitation event.”
In low-light forest environments, “Shade-intolerant species grow rapidly in order to reach higher light levels at the top of the canopy… Some shade-tolerant exotic species can take advantage of disturbances that create high-light gaps… Higher leaf area ratios and low R:S [root to shoot biomass ratio], characteristics of many species invading forests… suggest that these species are able to take advantage of high-light conditions and grow rapidly in response to human-induced canopy gaps.” Again, Funk found limited research on the conditions that contribute to the success of forest invaders.
Funk, 2013, concluded that, “Community-level restoration approaches will be most effective when native and invasive species differ in the timing and magnitude of resource use.” However, much more research is needed to determine where these differences occur. In particular, we know little about the impact of global climate change on invasive and native species.
Reference:
Next Sections on research on the success of invasive species:
Resource allocation: Its role in invasive plant success or failure
Summaries of the research and commentary by Dr. Delena Norris-Tull, Professor Emerita of Science Education, University of Montana Western, July 2020.
Funk (2013) conducted a thorough review of the literature on resource utilization in native and invasive plants, focusing on low-resource environments. She specifically looked at research on plant efficiency in using limited soil nutrients, water, and light. She defined low-resource environments as “those where plant productivity is severely limited by light, water, or soil nutrient availability, such as forest understories, deserts, and ancient landscapes. In many of these ecosystems, native plants have evolved mechanisms to tolerate stress and to facilitate the extraction of limiting resources. These adaptations have resulted in a high degree of species richness and functional diversity in many low-resource ecosystems.”
Funk, 2013, found that “native species appear to have a competitive advantage over invasive species in low-resource systems…, and communities become more susceptible to invasion when resource availability is increased.” However, “many invasive species do occur in low-resource ecosystems.” Funk found that, “It is difficult to identify a suite of general traits explaining invasiveness, because traits of invaders depend on characteristics of the invaded habitats.”
She stated that “research… suggests that plants in high-resource ecosystems succeed through high rates of resource acquisition, while species adapted to low-resource ecosystems largely display traits associated with resource conservation.”
In examining research on species’ use of soil nutrients, Funk, 2013, found that “plant species may be differentially limited by N [nitrogen] and P [phosphorus] in many systems…. Plant growth in species with special adaptations for N (e.g. fixation) or P acquisition (e.g. cluster roots) may not be limited by the same nutrient as are neighbouring species… Species also vary in their nutrient requirements. For example, grasses require lower amounts of P than forbs… Grasses with a C4 photosynthetic pathway can also operate at a lower N concentration.” In low-resource environments where non-native species have invaded successfully, “invasive species appear to use nutrients more efficiently than natives in low-nutrient soils.” However, she found that there is limited research on the mechanisms of nutrient-use efficiency in invasive plants.
In studies conducted in arid and semi-arid environments, Funk, 2013, concluded that the “results suggest that water availability most strongly limits plant growth in normal precipitation years, while N availability limits plant growth in wet years…. There is evidence that some invasive species possess drought-tolerant traits, while others do not.”
Funk, 2013, found that “data suggest that LMA [leaf mass per unit area] is lower in invasive species than native species occurring in arid environments…. Thin leaves generally have low quantities of structural carbohydrates, which results in low energetic or construction cost of the leaf… Low construction cost is often associated with higher plant growth rates… However, while cheap structures may provide an initial growth advantage, more leaf area leads to higher plant-level transpiration rates, and this may render these exotic species more prone to water stress in low-precipitation years. Nevertheless, many annual species (particularly invasive annuals) may employ this strategy, where the production of cheap structures facilitates a rapid response to unpredictable precipitation events… This mechanism may explain why exotic species can spread in wet years and remain in the soil bank during dry years.” Research indicates that “invasive species may favour drier microsites within habitats, deplete soil moisture levels more than natives, or have higher nocturnal transpiration.” Funk, 2013, found no research on the factor of root depth on invasive success in arid systems.
Funk, 2013, found research that “exotic species generally develop leaves earlier in the year than natives, which may allow them to pre-empt resources.” And while “evergreen species may be more constrained in their ability to respond morphologically to precipitation events than deciduous perennials or annual species,… long-lived leaves may provide evergreens with an advantage over those that must produce new leaves following a precipitation event.”
In low-light forest environments, “Shade-intolerant species grow rapidly in order to reach higher light levels at the top of the canopy… Some shade-tolerant exotic species can take advantage of disturbances that create high-light gaps… Higher leaf area ratios and low R:S [root to shoot biomass ratio], characteristics of many species invading forests… suggest that these species are able to take advantage of high-light conditions and grow rapidly in response to human-induced canopy gaps.” Again, Funk found limited research on the conditions that contribute to the success of forest invaders.
Funk, 2013, concluded that, “Community-level restoration approaches will be most effective when native and invasive species differ in the timing and magnitude of resource use.” However, much more research is needed to determine where these differences occur. In particular, we know little about the impact of global climate change on invasive and native species.
Reference:
- Funk, J.L. (Nov. 5, 2013). The physiology of invasive plants in low-resource environments. Conservation Physiology,1. doi:10.1093/conphys/cot026
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