R-3 Repository :: Browsing by Author "Siemann, Evan"

Browsing by Author "Siemann, Evan"

Now showing 1 - 20 of 42

A native plant competitor mediates the impact of above- and belowground damage on an invasive tree
(Wiley, 2016) Carrillo, Juli; Siemann, Evan
Plant competition may mediate the impacts of herbivory on invasive plant species through effects on plant growth and defense. This may predictably depend on whether herbivory occurs above or below ground and on relative plant competitive ability. We simulated the potential impact of above- or belowground damage by biocontrol agents on the growth of a woody invader (Chinese tallow tree,ﾠTriadica sebifera) through artificial herbivory, with or without competition with a native grass, little bluestem (Schizachyrium scoparium). We measured two defense responses ofﾠTriadicaﾠthrough quantifying constitutive and induced extrafloral nectar production and tolerance of above- and belowground damage (root and shoot biomass regrowth). We examined genetic variation in plant growth and defense across native (China) and invasive (United States)ﾠTriadicaﾠpopulations. Without competition, aboveground damage had a greater impact than belowground damage onﾠTriadicaﾠperformance, whereas with competition and above- and belowground damage impactedﾠTriadicaﾠsimilarly. Whole plant tolerance to damage below ground was negatively associated with tolerance to grass competitors indicating tradeoffs in the ability to tolerate herbivory vs. compete. Competition reduced investment in defensive extrafloral nectar (EFN) production. Aboveground damage inhibited rather than induced EFN production while belowground plant damage did not impact aboveground nectar production. We found some support for the evolution of increased competitive ability hypothesis for invasive plants as United States plants were larger than native China plants and were more plastic in their response to biotic stressors than China plants (they altered their root to shoot ratios dependent on herbivory and competition treatments). Our results indicate that habitat type and the presence of competitors may be a larger determinant of herbivory impact than feeding mode and suggest that integrated pest management strategies including competitive dynamics of recipient communities should be incorporated into biological control agent evaluation at earlier stages.
An investigation of the allelopathic potential of Chinese tallow tree (Sapium sebiferum [L.] Roxb.)
(2006) Johnson, Amy L.; Siemann, Evan
Invasive species can cause significant changes to their introduced environments. A set of experiments was conducted to determine whether Sapium sebiferum exhibits allelopathic effects on neighboring plants in its introduced range. Bioassays were performed on Sapium, Liquidambar styraciflua, Schizachyrium scoparium, Andropogon ischaemum, and Lolium perenne seeds using extracts from Sapium, Acer saccharinum, Platanus occidentalis and Liquidambar leaves. Germination and early growth comparisons were made using: (1) solutions treated with activated carbon to remove allelochemicals or left untreated, (2) solutions in a dilution series, and (3) solution mixtures prepared from rinsed leaves or soaked leaves using activated carbon to negate potential allelopathic effects of all but one leaf species in each mixture. In almost every analysis there were few significant predictors. The effects of Sapium extracts on germination or growth never differed from those of the three native tree species' extracts. Allelopathy does not appear to contribute to Sapium's invasive success.
Bacterial and fungal inhibitor interacted impacting growth of invasive Triadica sebifera and soil N2O emissions
(Frontiers Media S.A., 2023) Lai, Xiaoqin; Luo, Laicong; Fang, Haifu; Zhang, Ling; Shad, Nasir; Bai, Jian; Li, Aixin; Zhang, Xi; Yu, Yadi; Wang, Hao; Siemann, Evan
Plant invasions affect biodiversity and seriously endanger the stability of ecosystems. Invasive plants show strong adaptability and growth advantages but are influenced by various factors. Soil bacteria and fungi are critical to plant growth and are important factors affecting plant invasions. Plant invasions also affect soil N2O emissions, but the effects of invasive plants from different population origins on N2O emissions and their microbial mechanisms are not clear. In this experiment, we grew Triadica sebifera from native (China) and invasive (USA) populations with or without bacterial (streptomycin) and/or fungal (iprodione) inhibitors in a factorial experiment in which we measured plant growth and soil N2O emissions of T. sebifera. Plants from invasive populations had higher leaf masses than those from native populations when soil bacteria were not inhibited (with or without fungal inhibition) which might reflect that they are more dependent on soil bacteria. Cumulative N2O emissions were higher for soils with invasive T. sebifera than those with a plant from a native population. Bacterial inhibitor application reduced cumulative N2O emissions but reductions were larger with application of the fungal inhibitor either alone or in combination with the bacterial inhibitor. This suggests that fungi play a strong role in plant performance and soil N2O emissions. Therefore, it is important to further understand the effects of soil microorganisms on the growth of T. sebifera and soil N2O emissions to provide a more comprehensive scientific basis for understanding the causes and consequences of plant invasions.
Chinese Tallow Trees (Triadica sebifera) from the Invasive Range Outperform Those from the Native Range with an Active Soil Community or Phosphorus Fertilization
(Public Library of Science, 2013) Zhang, Ling; Zhang, Yaojun; Wang, Hong; Zou, Jianwen; Siemann, Evan
Two mechanisms that have been proposed to explain success of invasive plants are unusual biotic interactions, such as enemy release or enhanced mutualisms, and increased resource availability. However, while these mechanisms are usually considered separately, both may be involved in successful invasions. Biotic interactions may be positive or negative and may interact with nutritional resources in determining invasion success. In addition, the effects of different nutrients on invasions may vary. Finally, genetic variation in traits between populations located in introduced versus native ranges may be important for biotic interactions and/or resource use. Here, we investigated the roles of soil biota, resource availability, and plant genetic variation using seedlings of Triadica sebifera in an experiment in the native range (China). We manipulated nitrogen (control or 4 g/m2), phosphorus (control or 0.5 g/m2), soil biota (untreated or sterilized field soil), and plant origin (4 populations from the invasive range, 4 populations from the native range) in a full factorial experiment. Phosphorus addition increased root, stem, and leaf masses. Leaf mass and height growth depended on population origin and soil sterilization. Invasive populations had higher leaf mass and growth rates than native populations did in fresh soil but they had lower, comparable leaf mass and growth rates in sterilized soil. Invasive populations had higher growth rates with phosphorus addition but native ones did not. Soil sterilization decreased specific leaf area in both native and exotic populations. Negative effects of soil sterilization suggest that soil pathogens may not be as important as soil mutualists for T. sebifera performance. Moreover, interactive effects of sterilization and origin suggest that invasive T. sebifera may have evolved more beneficial relationships with the soil biota. Overall, seedlings from the invasive range outperformed those from the native range, however, an absence of soil biota or low phosphorus removed this advantage.
Chlorophyll fluorescence characteristics and H2O2 contents of Chinese tallow tree are dependent on population origin, nutrients and salinity
(Oxford University Press, 2024) He, Mengyue; Ge, Lihong; Hui, Xue; Li, Wenrao; Ding, Jianqing; Siemann, Evan
Plants from invasive populations often have higher growth rates than conspecifics from native populations due to better environmental adaptability. However, the roles of improved chlorophyll fluorescence or antioxidant defenses in helping them to grow better under adverse situations are insufficient, even though this is a key physiological question for elucidating mechanisms of plant invasion. Here, we conducted experiments with eight native (China) and eight introduced (USA) populations of Chinese tallow tree (Triadica sebifera). We tested how salinity, nutrients (overall amount or N:P in two separate experiments) and their interaction affected T. sebifera aboveground biomass, leaf area, chlorophyll fluorescence and antioxidant defenses. Plants from introduced populations were larger than those from native populations, but salinity and nutrient shortage (low nutrients or high N:P) reduced this advantage, possibly reflecting differences in chlorophyll fluorescence based on their higher PSII maximum photochemical efficiency (Fv/Fm) and PSI maximum photo-oxidizable P700 in higher nutrient conditions. Native population plants had lower Fv/Fm with saline. Except in high nutrients/N:P with salinity, introduced population plants had lower electron transfer rate and photochemical quantum yield. There were no differences in antioxidant defenses between introduced and native populations except accumulation of hydrogen peroxide (H2O2), which was lower for introduced populations. Low nutrients and higher N:P or salinity increased total antioxidant capacity and H2O2. Our results indicate that nutrients and salinity induce differences in H2O2 contents and chlorophyll fluorescence characteristics between introduced and native populations of an invasive plant, illuminating adaptive mechanisms using photosynthetic physiological descriptors in order to predict invasions.
Climate warming increases biological control agent impact on a non-target species
(Wiley, 2015) Lu, Xinmin; Siemann, Evan; He, Minyan; Wei, Hui; Shao, Xu; Ding, Jianqing
Climate change may shift interactions of invasive plants, herbivorous insects and native plants, potentially affecting biological control efficacy and non-target effects on native species. Here, we show how climate warming affects impacts of a multivoltine introduced biocontrol beetle on the non-target native plant Alternanthera sessilis in China. In field surveys across a latitudinal gradient covering their full distributions, we found beetle damage on A. sessilis increased with rising temperature and plant life history changed from perennial to annual. Experiments showed that elevated temperature changed plant life history and increased insect overwintering, damage and impacts on seedling recruitment. These results suggest that warming can shift phenologies, increase non-target effect magnitude and increase non-target effect occurrence by beetle range expansion to additional areas where A. sessilis occurs. This study highlights the importance of understanding how climate change affects species interactions for future biological control of invasive species and conservation of native species.
Conspecific Plasticity and Invasion: Invasive Populations of Chinese Tallow (Triadica sebifera)ﾠHave Performance Advantage over Native Populations Only in Low Soil Salinity
(Public Library of Science, 2013) Chen, Leiyi; Tiu, Candice J.; Peng, Shaolin; Siemann, Evan
Global climate change may increase biological invasions in part because invasive species may have greater phenotypic plasticity than native species. This may be especially important for abiotic stresses such as salt inundation related to increased hurricane activity or sea level rise. If invasive species indeed have greater plasticity, this may reflect genetic differences between populations in the native and introduced ranges. Here, we examined plasticity of functional and fitness-related traits of Chinese tallow (Triadica sebifera) populations from the introduced and native ranges that were grown along a gradient of soil salinity (control: 0 ppt; Low: 5 ppt; Medium: 10 ppt; High: 15 ppt) in a greenhouse. We used both norm reaction and plasticity index (PIv) to estimate the conspecific phenotypic plasticity variation between invasive and native populations. Overall, invasive populations had higher phenotypic plasticity of height growth rate (HGR), aboveground biomass, stem biomass and specific leaf area (SLA). The plasticity Index (PIv) of height growth rate (HGR) and SLA each were higher for plants from invasive populations. Absolute performance was always comparable or greater for plants from invasive populations versus native populations with the greatest differences at low stress levels. Our results were consistent with the ?Master-of-some? pattern for invasive plants in which the fitness of introduced populations was greater in more benign conditions. This suggests that the greater conspecific phenotypic plasticity of invasive populations compared to native populations may increase invasion success in benign conditions but would not provide a potential interspecific competitive advantage in higher salinity soils that may occur with global climate change in coastal areas.
Decomposition of Phragmites australis litter retarded by invasive Solidago canadensis in mixtures: an antagonistic non-additive effect
(Macmillan Publishers Limited, 2014) Zhang, Ling; Zhang, Yaojun; Zou, Jianwen; Siemann, Evan
Solidago canadensis is an aggressive invader in China. Solidago invasion success is partially attributed to allelopathic compounds release and more benefits fromAMfungi, which potentially makes the properties of Solidago litter different from co-occurring natives. These properties may comprehensively affect litter decomposition of co-occurring natives. We conducted a field experiment to examine litter mixing effects in a Phragmites australis dominated community invaded by Solidago in southeast China. Solidago had more rapid mass and N loss rate than Phragmites when they decomposed separately. Litter mixing decreased N loss rate in Phragmites litter and increased that of Solidago. Large decreases in Phragmites mass loss and smaller increases in Solidago mass loss caused negative non-additive effect. Solidago litter extracts reduced soil C decomposition and N processes, suggested an inhibitory effect of Solidago secondary compounds. These results are consistent with the idea that nutrient transfer and secondary compounds both affected litter mixtures decomposition.
Does phylogeny matter? Assessing the impact of phylogenetic information in ecological meta-analysis
(Blackwell Publishing Ltd/CNRS, 2012) Chamberlain, Scott A.; Hovick, Stephen M.; Dibble, Christopher J.; Rasmussen, Nick L.; Van Allen, Benjamin G.; Maitner, Brian S.; Ahern, Jeffrey R.; Bell-Dereske, Lukas P.; Roy, Christopher L.; Meza-Lopez, Maria; Carrillo, Juli; Siemann, Evan; Lajeunesse, Marc J.; Whitney, Kenneth D.
The Effect of Diet and Opponent Size on Aggressive Interactions Involving Caribbean Crazy Ants (Nylanderia fulva)
(Public Library of Science, 2013) Horn, Katherine C.; Eubanks, Micky D.; Siemann, Evan
Biotic interactions are often important in the establishment and spread of invasive species. In particular, competition between introduced and native species can strongly influence the distribution and spread of exotic species and in some cases competition among introduced species can be important. The Caribbean crazy ant, Nylanderia fulva, was recently introduced to the Gulf Coast of Texas, and appears to be spreading inland. It has been hypothesized that competition with the red imported fire ant, Solenopsis invicta, may be an important factor in the spread of crazy ants. We investigated the potential of interspecific competition among these two introduced ants by measuring interspecific aggression between Caribbean crazy ant workers and workers of Solenopsis invicta. Specifically, we examined the effect of body size and diet on individual-level aggressive interactions among crazy ant workers and fire ants. We found that differences in diet did not alter interactions between crazy ant workers from different nests, but carbohydrate level did play an important role in antagonistic interactions with fire ants: crazy ants on low sugar diets were more aggressive and less likely to be killed in aggressive encounters with fire ants. We found that large fire ants engaged in fewer fights with crazy ants than small fire ants, but fire ant size affected neither fire ant nor crazy ant mortality. Overall, crazy ants experienced higher mortality than fire ants after aggressive encounters. Our findings suggest that fire ant workers might outcompete crazy ant workers on an individual level, providing some biotic resistance to crazy ant range expansion. However, this resistance may be overcome by crazy ants that have a restricted sugar intake, which may occur when crazy ants are excluded from resources by fire ants.
Effects of nutrient pulses on exotic species shift from positive to neutral with decreasing water availability
(Wiley, 2024) Otieno, Evans O.; Shen, Changchao; Zhang, Kaoping; Wan, Jinlong; He, Minyan; Tao, Zhibin; Huang, Wei; Siemann, Evan
Temporal fluctuation in nutrient availability generally promotes the growth of exotic plant species and has been recognized as an important driver of exotic plant invasions. However, little is known about how the impact of fluctuating nutrients on exotic species is dependent on the availability of other resources, although most ecosystems are experiencing dramatic variations in a wide variety of resources due to global change and human disturbance. Here, we explored how water availability mediates the effect of nutrient pulses on the growth of six exotic and six native plant species. We subjected individual plants of exotic and native species to well watered or water stressed conditions. For each level of water availability, we added equivalent amounts of nutrients at a constant rate, as a single large pulse, or in multiple small pulses. Under well watered conditions, nutrient pulses promoted exotic plant growth relative to nutrients supplied constantly, while they had no significant effect on natives. In contrast, under water stressed conditions, water deficiency inhibited the growth of all exotic and native species. More importantly, nutrient pulses did not increase plant growth relative to nutrients supplied constantly and these phenomena were observed for both exotic and native species. Taken together, our study shows that the impact of fluctuating nutrient availability on the growth of exotic plant species strongly depends on the variation of other resources, and that the positive effect of nutrient pulses under well watered conditions disappears under water stressed conditions. Our findings suggest that the variation in multiple resources may have complex feedback on exotic plant invasions and, therefore, it is critical to encompass multiple resources for the evaluation of fluctuating resource availability effects on exotic plant species. This will allow us to project the invasive trajectory of exotic plant species more accurately under future global change and human disturbance.
Evolutionary dynamics of tree invasions: complementing the unified framework for biological invasions
(Oxford University Press, 2017) Zenni, Rafael D.; Dickie, Ian A.; Wingfield, Michael J.; Hirsch, Heidi; Crous, Casparus J.; Meyerson, Laura A.; Burgess, Treena I.; Zimmermann, Thalita G.; Klock, Metha M.; Siemann, Evan; Erfmeier, Alexandra; Aragon, Roxana; Montti, Lia; Le Roux, Johannes J.
Evolutionary processes greatly impact the outcomes of biological invasions. An extensive body of research suggests that invasive populations often undergo phenotypic and ecological divergence from their native sources. Evolution also operates at different and distinct stages during the invasion process. Thus, it is important to incorporate evolutionary change into frameworks of biological invasions because it allows us to conceptualize how these processes may facilitate or hinder invasion success. Here, we review such processes, with an emphasis on tree invasions, and place them in the context of the unified framework for biological invasions. The processes and mechanisms described are pre-introduction evolutionary history, sampling effect, founder effect, genotype-by-environment interactions, admixture, hybridization, polyploidization, rapid evolution, epigenetics and second-genomes. For the last, we propose that co-evolved symbionts, both beneficial and harmful, which are closely physiologically associated with invasive species, contain critical genetic traits that affect the evolutionary dynamics of biological invasions. By understanding the mechanisms underlying invasion success, researchers will be better equipped to predict, understand and manage biological invasions.
Examining competitive interaction between Rasberry crazy ants (Paratrechina sp.nr. pubens) and red imported fire ants (Solenopsis invicta) using laboratory and field studies
(2010) Horn, Katherine; Siemann, Evan
Studying nonnative species soon after their introduction is critical to understanding their risk of becoming widely invasive and determining effective methods of control. I conducted laboratory and field experiments on the Rasberry crazy ant (Paratrechina sp. nr. pubens), which was introduced to Pasadena, TX in 2002 and has since been spreading rapidly. These experiments focused on intraspecific aggression, as well as individual and colony-level interactions between crazy ants and red imported fire ants (Solenopsis invicta), which are dominant in the crazy ant's introduced range. Crazy ants displayed no intraspecific aggression. In individual aggressive encounters with fire ants, crazy ants had higher mortality than fire ants, but in colony-level clashes, crazy ants had less mortality and better control of food resources. These findings suggest that crazy ant abundance is key to their competitive success, and fire ants may provide biotic resistance to crazy ants in some areas.
Facilitation and Competition among Invasive Plants: A Field Experiment with Alligatorweed and Water Hyacinth
(Public Library of Science, 2012) Wundrow, Emily J.; Carrillo, Juli; Gabler, Christopher A.; Horn, Katherine C.; Siemann, Evan
Ecosystems that are heavily invaded by an exotic species often contain abundant populations of other invasive species. This may reflect shared responses to a common factor, but may also reflect positive interactions among these exotic species. Armand Bayou (Pasadena, TX) is one such ecosystem where multiple species of invasive aquatic plants are common. We used this system to investigate whether presence of one exotic species made subsequent invasions by other exotic species more likely, less likely, or if it had no effect. We performed an experiment in which we selectively removed exotic rooted and/or floating aquatic plant species and tracked subsequent colonization and growth of native and invasive species. This allowed us to quantify how presence or absence of one plant functional group influenced the likelihood of successful invasion by members of the other functional group. We found that presence of alligatorweed (rooted plant) decreased establishment of new water hyacinth (free-floating plant) patches but increased growth of hyacinth in established patches, with an overall net positive effect on success of water hyacinth. Water hyacinth presence had no effect on establishment of alligatorweed but decreased growth of existing alligatorweed patches, with an overall net negative effect on success of alligatorweed. Moreover, observational data showed positive correlations between hyacinth and alligatorweed with hyacinth, on average, more abundant. The negative effect of hyacinth on alligatorweed growth implies competition, not strong mutual facilitation (invasional meltdown), is occurring in this system. Removal of hyacinth may increase alligatorweed invasion through release from competition. However, removal of alligatorweed may have more complex effects on hyacinth patch dynamics because there were strong opposing effects on establishment versus growth. The mix of positive and negative interactions between floating and rooted aquatic plants may influence local population dynamics of each group and thus overall invasion pressure in this watershed.
Fluctuations in resource availability shape the competitive balance among non-native plant species
(Wiley, 2024) Tao, Zhibin; Shen, Changchao; Qin, Wenchao; Nie, Baoguo; Chen, Pengdong; Wan, Jinlong; Zhang, Kaoping; Huang, Wei; Siemann, Evan
Fluctuating resource availability plays a critical role in determining non-native plant invasions through mediating the competitive balance between non-native and native species. However, the impact of fluctuating resource availability on interactions among non-native species remains largely unknown. This represents a barrier to understanding invasion mechanisms, particularly in habitats that harbor multiple non-native species with different responses to fluctuating resource availability. To examine the responses of non-native plant species to nutrient fluctuations, we compared the growth of each of 12 non-native species found to be common in local natural areas to nutrients supplied at a constant rate or supplied as a single large pulse in a pot experiment. We found that seven species produced more biomass with pulsed nutrients compared to constant nutrients (hereafter “benefitting species”), while the other five species did not differ between nutrient enrichment treatments (hereafter “non-benefitting species”). To investigate how nutrient fluctuations influence the interactions among non-native plant species, we established experimental non-native communities in the field with two benefitting and two non-benefitting non-native species. Compared with constant nutrient supply, the single large pulse of nutrient did not influence community biomass, but strongly increased the biomass and cover of the benefitting species and decreased those of the non-benefitting species. Furthermore, the benefitting species had higher leaf N content and greater plant height when nutrients were supplied as a single large pulse than at a constant rate, whereas the non-benefitting species showed no differences in leaf N content and were shorter when nutrients were supplied as a single large pulse than at a constant rate. Our results add to the growing evidence that the individual responses of non-native species to nutrient fluctuation are species-specific. More importantly, benefitting species were favored by nutrients coming in a pulse, while non-benefitting ones were favored by nutrients coming constantly when they grew together. This suggests that nutrient fluctuations can mediate the competitive balance among non-native plants and may thus determine their invasion success in a community harboring multiple non-native plant species.
Genetic variation in anti-herbivore chemical defences in an invasive plant
(British Ecological Society, 2012) Wang, Yi; Siemann, Evan; Wheeler, Gregory S.; Zhu, Lin; Gu, Xue; Ding, Jianqing
Herbivore-specific induction of indirect and direct defensive responses in leaves and roots
(Oxford University Press, 2019) Xiao, Li; Carrillo, Juli; Siemann, Evan; Ding, Jianqing
Herbivory can induce both general and specific responses in plants that modify direct and indirect defence against subsequent herbivory. The type of induction (local versus systemic induction, single versus multiple defence induction) likely depends both on herbivore identity and relationships among different responses. We examined the effects of two above-ground chewing herbivores (caterpillar, weevil) and one sucking herbivore (aphid) on indirect defence responses in leaves and direct defence responses in both leaves and roots of tallow tree, Triadica sebifera. We also included foliar applications of methyl jasmonate (MeJA) and salicylic acid (SA). We found that chewing herbivores and MeJA increased above-ground defence chemicals but SA only increased below-ground total flavonoids. Herbivory or MeJA increased above-ground indirect defence response (extrafloral nectar) but SA decreased it. Principal component analysis showed there was a trade-off between increasing total root phenolics and tannins (MeJA, chewing) versus latex and total root flavonoids (aphid, SA). For individual flavonoids, there was evidence for systemic induction (quercetin), trade-offs between compounds (quercetin versus kaempferitrin) and trade-offs between above-ground versus below-ground production (isoquercetin). Our results suggest that direct and indirect defence responses in leaves and roots depend on herbivore host range and specificity along with feeding mode. We detected relationships among some defence response types, while others were independent. Including multiple types of insects to examine defence inductions in leaves and roots may better elucidate the complexity and specificity of defence responses of plants.
Home range, habitat use and pup attendance of red wolves ( Canis rufus) during the pup rearing season
(2006) Hinton, Joseph William; Siemann, Evan
Despite a 20 year reintroduction effort into northeastern North Carolina, little is known about the natural history and ecology of red wolves (Canis rufus). In 2005, I studied home ranges, habitat use and pup attendance of red wolves during the pup rearing season. Data indicated that red wolves have home range sizes intermediate between those of coyotes (Canis latrans) and gray wolves (Canis lupus). Similar to other canids in the eastern United States, red wolves preferred to use extensive agricultural fields during the summer months rather than adjacent wooded areas. Red wolves abandoned dens early to move pups into adjacent agricultural fields. Consistent with pup rearing studies done on gray wolves, red wolf pups were rarely left alone indicating that red wolves share duties of pup rearing and that males play a significant role in the rearing of red wolf pups.
Impact of disturbance on arthropod community structure: Nutrient enrichment, fire and the invasive Chinese tallow tree (Sapium sebiferum)
(2006) Hartley, Maria Kate; Siemann, Evan
Invasive species, fire suppression and nutrient deposition, as distinct disturbance factors, have altered Texas prairie communities. Arthropod diversity, abundance, and community composition may be modified by these factors either directly or by changes in plant community structure. Because arthropods provide essential ecosystem services and represent a large proportion of terrestrial biodiversity, understanding the responses of arthropod communities to disturbance is the central theme of this doctoral thesis. Land managers commonly utilize fire to control woody species encroachment into prairies and anthropogenic nutrient deposition increases plant productivity. The responses of arthropods to fire and fertilizer manipulations were examined. Fire maintained arthropod diversity by limiting woody plant cover. Path analysis indicated fertilization decreased arthropod diversity by promoting woody plant invasion. Direct negative effects of fire on the arthropod community were small compared to the indirect, positive effects. Arthropod abundance and species richness on the invasive species Chinese Tallow Tree (Sapium sebiferum) were compared to arthropods on three native tree species: Silver Maple (Acer saccharinum), Sycamore (Platanus occidentalis), and Sweetgum ( Liquidambar styraciflua). Although arthropod community composition differed on Sapium, species richness and abundance were similar to levels on native trees. Sapium experienced less chewing, fungal, and mining damage and supported relatively abundant predators and detritivores whilst there were relatively fewer herbivores. These observations are in accord with the Enemies Release Hypothesis that predicts low herbivore loads may contribute to Sapium's invasive success. When Sapium was compared to native plant dominated habitats, predators and detritivores were again relatively abundant while total arthropod diversity was comparatively low. This implies that Sapium has not acquired an insect fauna comparable to native plants in Texas. Insect assemblages on Sapium were examined along a geographical gradient, representing time since introduction. Sapium trees in Florida and Georgia (present longer) had higher insect loads compared to those in Louisiana and Texas (more recently introduced), but species richness did not differ. Herbivore and omnivore abundance and species richness were higher where Sapium has been present longer. This suggests that time since introduction is an important factor constraining herbivore diversity and abundance. Accumulation of herbivores may limit Sapium populations in the future.
Increasing flavonoid concentrations in root exudates enhance associations between arbuscular mycorrhizal fungi and an invasive plant
(Springer Nature, 2021) Tian, Baoliang; Pei, Yingchun; Huang, Wei; Ding, Jianqing; Siemann, Evan
Many invasive plants have enhanced mutualistic arbuscular mycorrhizal (AM) fungal associations, however, mechanisms underlying differences in AM fungal associations between introduced and native populations of invasive plants have not been explored. Here we test the hypothesis that variation in root exudate chemicals in invasive populations affects AM fungal colonization and then impacts plant performance. We examined flavonoids (quercetin and quercitrin) in root exudates of native and introduced populations of the invasive plant Triadica sebifera and tested their effects on AM fungi and plant performance. We found that plants from introduced populations had higher concentrations of quercetin in root exudates, greater AM fungal colonization and higher biomass. Applying root exudates more strongly increased AM fungal colonization of target plants and AM fungal spore germination when exudate donors were from introduced populations. The role of root exudate chemicals was further confirmed by decreased AM fungal colonization when activated charcoal was added into soil. Moreover, addition of quercetin into soil increased AM fungal colonization, indicating quercetin might be a key chemical signal stimulating AM fungal associations. Together these results suggest genetic differences in root exudate flavonoids play an important role in enhancing AM fungal associations and invasive plants’ performance, thus considering root exudate chemicals is critical to unveiling mechanisms governing shifting plant-soil microbe interactions during plant invasions.

Browsing by Author "Siemann, Evan"

Results Per Page

Sort Options