Transcription-mediated tissue-specific lignification of vascular bundle causes trade-offs between growth and defence capacity during invasion of Solidago canadensis.

Allocation of more resources to growth but less to defense causing growth vigor of invasive alien plant populations contributes to successful invasion. However, few studies has addressed to relationship between vascular development variation and this mechanism. In this study, a common garden experimentwas established to compare the growth and vascular bundle development between native and introduced populations of Solidago canadensis, which is a wide-distributed invasive species in China. Our results suggested that the rapid growth of introduced populations could be explained by the well-developed and highly lignified xylem; while native populations present more developed and highly lignified phloem, which contributed more resistance to the infection of Sclerotiun rofsii compared with introduced populations. This difference was resulted from tissue-specific tradeoff distribution of lignification related gene expression between xylem and phloem, which is regulated by upstream MYB transcription factors. Our study gives a novel insight of mechanism that explain invasion success: lignin-related gene transcription-mediated tissue-specific lignification of vascular bundle contributes tradeoffs in resource allocation between growth and defence capacity during successful invasion of S. canadensis.

Synergistic Effects of Soil Microbes on Solidago canadensis Depend on Water and Nutrient Availability.

Soil microbes may greatly affect plant growth. While plants are commonly associated with diverse communities of soil microbes, complementary roles of different microbial communities that may stimulate synergistic effects on plant growth are not adequately tested. Also, such synergistic effects may vary with environmental conditions such as soil nutrient and water availability. We conducted a greenhouse experiment with a widespread clonal plant Solidago canadensis. The experiment was a factorial design with four levels of soil microbial inoculation (fresh soil inocula from grasslands in northern and southern China that were expected to differ in soil microbial composition, a mixture of the two fresh soil inocula, and a sterilized mixed inoculum control), two levels of nutrient availability (low vs. high), and two levels of water supply (low vs. high, i.e., 1376 vs. 352 mm per year). Irrespective of water supply and nutrient availability, total, aboveground, and belowground mass of S. canadensis were generally higher when the plant grew in soil inoculated with a mixture of soil microbes from the south and north of China (in the mixed inoculum treatment) than when it grew in soil inoculated with soil microbes from only the north or the south or the sterilized control. Such effects of soil microbes on total and aboveground mass were stronger under high than under low nutrient availability and also under high than under low water supply. Our results suggest that interactions of different soil microbial communities can result in a synergistic effect on plant growth and such a synergistic effect depends on environmental conditions. The findings shed light on the importance of plant-microbe interactions during the spreading of some plant species in face of increased atmospheric nutrient deposition coupled with altered rainfall pattern due to global change.

Genetic consequences of being a dwarf: do evolutionary changes in life-history traits influence gene flow patterns in populations of the world's smallest goldenrod?

BACKGROUND AND AIMS: Contrasting life-history traits can evolve through generations of dwarf plant ecotypes, yet such phenotypic changes often involve decreased plant size and reproductive allocation, which can configure seed dispersal patterns and, subsequently, population demography. Therefore, evolutionary transitions to dwarfism can represent good study systems to test the roles of life-history traits in population demography by comparing genetic structure between related but phenotypically divergent ecotypes. METHODS: In this study, we examined an ecotypic taxon pair of the world's smallest goldenrod (stem height 2.6 cm) in alpine habitats and its closely related lowland taxon (30-40 cm) found on Yakushima Island, Japan. Genetic variation in chloroplast DNA sequences, nuclear microsatellites and genome-wide single-nucleotide polymorphisms were used to investigate 197 samples from 16 populations, to infer the population genetic demography and compare local genetic structure of the ecotypes. KEY RESULTS: We found a pronounced level of genetic differentiation among alpine dwarf populations, which were much less geographically isolated than their lowland counterparts. In particular, several neighbouring dwarf populations (located ~500 m apart) harboured completely different sets of chloroplast haplotypes and nuclear genetic clusters. Demographic modelling revealed that the dwarf populations have not exchanged genes at significant levels after population divergence. CONCLUSIONS: These lines of evidence suggest that substantial effects of genetic drift have operated on these dwarf populations. The low-growing stature and reduced fecundity (only 3.1 heads per plant) of the dwarf plants may have reduced gene flow and rare long-distance seed dispersal among habitat patches, although the effects of life-history traits require further evaluation using ecological approaches.

Evaluation of connected clonal growth of Solidago chilensis as an avoidance mechanism in copper-polluted soils.

Plant resistance to metals can be achieved by two strategies, tolerance and avoidance. Although metal tolerance has been broadly studied in terrestrial plants, avoidance has been less considered as a strategy to cope with soil metal pollution. Avoidance may be an effective alternative in herbaceous plants with connected clonal growth in environments having high heterogeneity in soil micro-spatial distribution of available metals and other soil conditions (i.e. organic matter). In this study, we performed a laboratory experiment on clonal growth of Solidago chilensis when exposed to copper-spiked soils (800 mg kg-1) at different depths (0, 2, 5 and 8 cm depth), with (20%) and without addition of organic matter to mimic contrasting microhabitats found at smelter hinterlands (i.e. open bare ground and microhabitats below shrubs). Results showed that plants grown in the 2 cm-depth Cu-spiked soils were able to growth and produce ramets and rhizomes. However, increased Cu uptake of plants determined phytotoxic effects and a reduction in clonal spread in the 5 cm- and 8 cm-depth Cu-spiked soils. Addition of organic matter to the Cu-spiked soil layers allowed clonal spread. Considering that ramet and rhizome production is decreased but not inhibited when copper pollution is restricted to the uppermost soil layer (2 cm depth) and that organic matter eliminated soil copper toxicity allowing normal clonal spread, connected clonal growth may be an effective avoidance mechanism of Solidago chilensis, particularly in environments with high heterogeneity in micro-spatial distribution of metals and organic matter in the soil profile and between microhabitats.

Costs of plant defense priming: exposure to volatile cues from a specialist herbivore increases short-term growth but reduces rhizome production in tall goldenrod (Solidago altissima).

BACKGROUND: By sensing environmental cues indicative of pathogens or herbivores, plants can "prime" appropriate defenses and deploy faster, stronger responses to subsequent attack. Such priming presumably entails costs-else the primed state should be constitutively expressed-yet those costs remain poorly documented, in part due to a lack of studies conducted under realistic ecological conditions. We explored how defence priming in goldenrod (Solidago altissima) influenced growth and reproduction under semi-natural field conditions by manipulating exposure to priming cues (volatile emissions of a specialist herbivore, Eurosta solidaginis), competition between neighbouring plants, and herbivory (via insecticide application). RESULTS: We found that primed plants grew faster than unprimed plants, but produced fewer rhizomes, suggesting reduced capacity for clonal reproduction. Unexpectedly, this effect was apparent only in the absence of insecticide, prompting a follow-up experiment that revealed direct effects of the pesticide esfenvalerate on plant growth (contrary to previous reports from goldenrod). Meanwhile, even in the absence of pesticide, priming had little effect on herbivore damage levels, likely because herbivores susceptible to the primed defences were rare or absent due to seasonality. CONCLUSIONS: Reduced clonal reproduction in primed plants suggest that priming can entail significant costs for plants. These costs, however, may only become apparent when priming cues fail to provide accurate information about prevailing threats, as was the case in this study. Additionally, our insecticide data indicate that pesticides or their carrier compounds can subtly, but significantly, affect plant physiology and may interact with plant defences.

Simulated warming enhances biological invasion of Solidago canadensis and Bidens frondosa by increasing reproductive investment and altering flowering phenology pattern.

Phenological and reproductive shifts of plants due to climate change may have important influences on population dynamics. Climate change may also affect invasive species by changing their phenology and reproduction, but few studies have explored this possibility. Here, we investigated the impact of climate change on the phenology, reproduction and invasion potential of two alien Solidago canadensis and Bidens frondosa and one native weed, Pterocypsela laciniata, all of which are in the Asteraceae family. The three species responded to simulated climate change by increasing reproductive investments and root/leaf ratio, prolonging flowering duration, and while the two alien species also displayed a mass-flowering pattern. Moreover, our experimental results indicated that the alien invasive species may have greater phenological plasticity in response to simulated warming than that of the native species (P. laciniata). As such, climate change may enhance the invasion and accelerate the invasive process of these alien plant species.

Local root growth and death are mediated by contrasts in nutrient availability and root quantity between soil patches.

Plants are thought to be able to regulate local root growth according to its overall nutrient status as well as nutrient contents in a local substrate patch. Therefore, root plastic responses to environmental changes are probably co-determined by local responses of root modules and systematic control of the whole plant. Recent studies showed that the contrast in nutrient availability between different patches could significantly influence the growth and death of local roots. In this study, we further explored, beside nutrient contrast, whether root growth and death in a local patch are also affected by relative root quantity in the patch. We conducted a split-root experiment with different splitting ratios of roots of Canada goldenrod (Solidago canadensis) individuals, as well as high- (5× Hoagland solution versus water) or low- (1× Hoagland solution versus water) contrast nutrient conditions for the split roots. The results showed that root growth decreased in nutrient-rich patches but increased in nutrient-poor patches when more roots co-occurred in the same patches, irrespective of nutrient contrast condition. Root mortality depended on contrasts in both root quantity and nutrients: in the high-nutrient-contrast condition, it increased in nutrient-rich patches but decreased in nutrient-poor patches with increasing root proportion; while in the low-nutrient-contrast condition, it showed the opposite trend. These results demonstrated that root growth and death dynamics were affected by the contrast in both nutrient availability and root quantity between patches. Our study provided ecological evidence that local root growth and death are mediated by both the responses of root modules to a nutrient patch and the whole-plant nutrient status, suggesting that future work investigating root production and turnover should take into account the degree of heterogeneity in nutrient and root distribution.

Solidago canadensis invasion affects soil N-fixing bacterial communities in heterogeneous landscapes in urban ecosystems in East China.

Soil nitrogen-fixing bacterial communities (SNB) can increase the level of available soil N via biological N-fixation to facilitate successful invasion of several invasive plant species (IPS). Meanwhile, landscape heterogeneity can greatly enhance regional invasibility and increase the chances of successful invasion of IPS. Thus, it is important to understand the soil micro-ecological mechanisms driving the successful invasion of IPS in heterogeneous landscapes. This study performed cross-site comparisons, via metagenomics, to comprehensively analyze the effects of Solidago canadensis invasion on SNB in heterogeneous landscapes in urban ecosystems. Rhizospheric soil samples of S. canadensis were obtained from nine urban ecosystems [Three replicate quadrats (including uninvaded sites and invaded sites) for each type of urban ecosystem]. S. canadensis invasion did not significantly affect soil physicochemical properties, the taxonomic diversity of plant communities, or the diversity and richness of SNB. However, some SNB taxa (i.e., f_Micromonosporaceae, f_Oscillatoriaceae, and f_Bacillaceae) changed significantly with S. canadensis invasion. Thus, S. canadensis invasion may alter the community structure, rather than the diversity and richness of SNB, to facilitate its invasion process. Of the nine urban ecosystems, the diversity and richness of SNB was highest in farmland wasteland. Accordingly, the community invasibility of farmland wasteland may be higher than that of the other types of urban ecosystem. In brief, landscape heterogeneity, rather than S. canadensis invasion, was the strongest controlling factor for the diversity and richness of SNB. One possible reason may be the differences in soil electrical conductivity and the taxonomic diversity of plant communities in the nine urban ecosystems, which can cause notable shifts in the diversity and richness of SNB.

Population genetics and adaptation to climate along elevation gradients in invasive Solidago canadensis.

Gene flow between populations may either support local adaptation by supplying genetic variation on which selection may act, or counteract it if maladapted alleles arrive faster than can be purged by selection. Although both such effects have been documented within plant species' native ranges, how the balance of these forces influences local adaptation in invasive plant populations is less clear, in part because introduced species often have lower genetic variation initially but also tend to have good dispersal abilities. To evaluate the extent of gene flow and adaptation to local climate in invasive populations of Solidago canadensis, and the implications of this for range expansion, we compared population differentiation at microsatellite and chloroplast loci for populations across Switzerland and assessed the effect of environmental transfer distance using common gardens. We found that while patterns of differentiation at neutral genetic markers suggested that populations are connected through extensive pollen and seed movement, common-garden plants nonetheless exhibited modest adaptation to local climate conditions. Growth rate and flower production declined with climatic distance from a plant's home site, with clones from colder home sites performing better at or above the range limit. Such adaptation in invasive species is likely to promote further spread, particularly under climate change, as the genotypes positioned near the range edge may be best able to take advantage of lengthening growing seasons to expand the range.

No evidence for local adaptation to salt stress in the existing populations of invasive Solidago canadensis in China.

Local adaptation is an important mechanism underlying the adaptation of plants to environmental heterogeneity, and the toxicity of salt results in strong selection pressure on salt tolerance in plants and different ecotypes. Solidago canadensis, which is invasive in China, has spread widely and has recently colonized alkali sandy loams with a significant salt content. A common greenhouse experiment was conducted to test the role of local adaptation in the successful invasion of S. canadensis into salty habitats. Salt treatment significantly decreased the growth of S. canadensis, including rates of increase in the number of leaves and plant height; the root, shoot, and total biomass. Furthermore, salt stress significantly reduced the net photosynthetic rate, stomatal conductance, transpiration rate and relative chlorophyll content but significantly increased peroxidase activity and the proline content of S. canadensis and the root/shoot ratio. Two-way analysis of variance showed that salt treatment had a significant effect on the physiological traits of S. canadensis, except for the intercellular CO2 concentration, whereas the population and the salt × population interaction had no significant effect on any physiological traits. Most of the variation in plasticity existed within and not among populations, excep for the root/shoot ratio. S. canadensis populations from soil with moderate/high salt levels grew similarly to S. canadensis populations from soils with low salt levels. No significant correlation between salt tolerance indices and soil salinity levels was observed. The plasticity of the proline content, intercellular CO2 concentration and chlorophyll content had significant correlations with the salt tolerance index. These findings indicate a lack of evidence for local adaption in the existing populations of invasive S. canadensis in China; instead, plasticity might be more important than local adaptation in influencing the physiological traits and salt tolerance ability across the S. canadensis distribution.

Individual Plasticity of the Shade Response of the Invasive Solidago canadensis in China.

To evaluate the population variation, individual plasticity, and local adaptability of Solidago canadensis in response to shade treatment, we conducted a common pots experiment with a total of 150 ramets (5 genets, 15 populations, and 2 treatments) subjected to both control (natural light) and shady treatment (10% of natural light). Shade treatment significantly reduced growth and content of defense metabolites in S. canadensis. Compared to control, shading led to increased height, decreased basal diameter, increased leaf width, increased leaf length, increased chlorophyll content, stronger photosynthetic rate (Pn), stronger stomatal conductance (gs), and lower root to shoot ratio. Three-way analysis of variance revealed geographical origin to significantly affect the basal diameter of S. canadensis, while genotype significantly affected plant height, intercelluar CO2 concentration (Ci), transpiration rate (Tr), and proline content. Significant interactive effects between shade and geographic origin were prevalent for most traits. The phenotypic differentiation coefficient of the plasticity of all traits was below 0.4, indicating that most of all variations can be found among individuals within populations. Phenotypic selection analysis revealed that fitness was significantly positively related to plant height, basal diameter, Ci, total flavonoid content, as well as the plasticity of plant height, leaf length, leaf width, gs, Ci, total flavonoid content, and malondialdehyde content under the control condition. However, subjected to shade, fitness was only significantly positively related to plant height, basal diameter, and the plasticity of basal diameter. Rather than local adaption, these results suggest that individual plasticity played a more prominent role in the shade response of the invasive S. canadensis.

Few effects of invasive plants Reynoutria japonica, Rudbeckia laciniata and Solidago gigantea on soil physical and chemical properties.

Biological invasions are an important problem of human-induced changes at a global scale. Invasive plants can modify soil nutrient pools and element cycling, creating feedbacks that potentially stabilize current or accelerate further invasion, and prevent re-establishment of native species. The aim of this study was to compare the effects of Reynoutria japonica, Rudbeckia laciniata and Solidago gigantea, invading non-forest areas located within or outside river valleys, on soil physical and chemical parameters, including soil moisture, element concentrations, organic matter content and pH. Additionally, invasion effects on plant species number and total plant cover were assessed. The concentrations of elements in shoots and roots of invasive and native plants were also measured. Split-plot ANOVA revealed that the invasions significantly reduced plant species number, but did not affect most soil physical and chemical properties. The invasions decreased total P concentration and increased N-NO3 concentration in soil in comparison to native vegetation, though the latter only in the case of R. japonica. The influence of invasion on soil properties did not depend on location (within- or outside valleys). The lack of invasion effects on most soil properties does not necessarily imply the lack of influence of invasive plants, but may suggest that the direction of the changes varies among replicate sites and there are no general patterns of invasion-induced alterations for these parameters. Tissue element concentrations, with the exception of Mg, did not differ between invasive and native plants, and were not related to soil element concentrations.

The growth and phosphorus acquisition of invasive plants Rudbeckia laciniata and Solidago gigantea are enhanced by arbuscular mycorrhizal fungi.

While a number of recent studies have revealed that arbuscular mycorrhizal fungi (AMF) can mediate invasive plant success, the influence of these symbionts on the most successful and high-impact invaders is largely unexplored. Two perennial herbs of this category of invasive plants, Rudbeckia laciniata and Solidago gigantea (Asteraceae), were thus tested in a pot experiment to determine whether AMF influence their growth, the concentration of phosphorus in biomass, and photosynthesis. The following treatments, including three common AMF species, were prepared on soils representative of two habitats that are frequently invaded by both plants, namely fallow and river valley: (1) control-soil without AMF, (2) Rhizophagus irregularis, (3) Funneliformis mosseae, and (4) Claroideoglomus claroideum. The invaders were strongly dependent on AMF for their growth. The mycorrhizal dependency of R. laciniata was 88 and 63 % and of S. gigantea 90 and 82 % for valley and fallow soils, respectively. The fungi also increased P concentration in their biomass. However, we found different effects of the fungal species in the stimulation of plant growth and P acquisition, with R. irregularis and C. claroideum being the most and least effective symbionts, respectively. None of AMF species had an impact on the photosynthetic performance indexes of both plants. Our findings indicate that AMF have a direct effect on the early stages of R. laciniata and S. gigantea growth. The magnitude of the response of both plant species to AMF was dependent on the fungal and soil identities. Therefore, the presence of particular AMF species in a site may determine the success of their invasion.

Characterization of cold-associated microRNAs in the freeze-tolerant gall fly Eurosta solidaginis using high-throughput sequencing.

Significant physiological and biochemical changes are observed in freeze-tolerant insects when confronted with cold temperatures. These insects have adapted to winter by retreating into a hypometabolic state of diapause and implementing cryoprotective mechanisms that allow them to survive whole body freezing. MicroRNAs (miRNAs), a family of short ribonucleic acids, are emerging as likely molecular players underlying the process of cold adaptation. Unfortunately, the data is sparse concerning the signature of miRNAs that are modulated following cold exposure in the freeze-tolerant goldenrod gall fly Eurosta solidaginis. Leveraging for the first time a next-generation sequencing approach, differentially expressed miRNAs were evaluated in 5°C and -15°C-exposed E. solidaginis larvae. Next-generation sequencing expression data was subsequently validated by qRT-PCR for selected miRNA targets. Results demonstrate 24 differentially expressed freeze-responsive miRNAs. Notable, miR-1-3p, a miRNA modulated at low temperature in another cold-hardy insect, and miR-14-3p, a miRNA associated with stress response in the fruit fly, were shown to be significantly up-regulated in -15°C-exposed larvae. Overall, this work identifies, for the first time in a high-throughput manner, differentially expressed miRNAs in cold-exposed E. solidaginis larvae and further clarifies an emerging signature of miRNAs modulated at low temperatures in cold-hardy insects.

Host-parasitoid evolution in a metacommunity.

Patch size and isolation are predicted to alter both species diversity and evolution; yet, there are few empirical examples of eco-evolutionary feedback in metacommunities. We tested three hypotheses about eco-evolutionary feedback in a gall-forming fly, Eurosta solidaginis and two of its natural enemies that select for opposite traits: (i) specialization and poor dispersal ability constrain a subset of natural enemies from occupying small and isolated patches, (ii) this constraint alters selection on the gall fly, causing phenotypic shifts towards traits resistant to generalist and dispersive enemies in small and isolated patches, and (iii) reduced dispersal evolves in small, isolated populations. We sampled patches in a natural metacommunity and found support for all hypotheses; Eurosta's specialist wasp parasitoid attacked fewer galls in small and isolated patches, generating a selection gradient that favoured small galls resistant to predation by a dispersive and generalist bird predator. Phenotype distributions matched this selection gradient, and these phenotypic differences were maintained in a common garden experiment. Finally, we found lower dispersal abilities in small and isolated patches, a phenotypic shift that aids in the maintenance of local adaptation. We suggest that the trophic rank and the species traits of consumers are central to evolution in metacommunities.

What determines positive, neutral, and negative impacts of Solidago canadensis invasion on native plant species richness?

Whether plant invasions pose a great threat to native plant diversity is still hotly debated due to conflicting findings. More importantly, we know little about the mechanisms of invasion impacts on native plant richness. We examined how Solidago canadensis invasion influenced native plants using data from 291 pairs of invaded and uninvaded plots covering an entire invaded range, and quantified the relative contributions of climate, recipient communities, and S. canadensis to invasion impacts. There were three types of invasion consequences for native plant species richness (i.e., positive, neutral, and negative impacts). Overall, the relative contributions of recipient communities, S. canadensis and climate to invasion impacts were 71.39%, 21.46% and 7.15%, respectively; furthermore, the roles of recipient communities, S. canadensis and climate were largely ascribed to plant diversity, density and cover, and precipitation. In terms of direct effects, invasion impacts were negatively linked to temperature and native plant communities, and positively to precipitation and soil microbes. Soil microbes were crucial in the network of indirect effects on invasion impacts. These findings suggest that the characteristics of recipient communities are the most important determinants of invasion impacts and that invasion impacts may be a continuum across an entire invaded range.

Rapid plant evolution in the presence of an introduced species alters community composition.

Because introduced species may strongly interact with native species and thus affect their fitness, it is important to examine how these interactions can cascade to have ecological and evolutionary consequences for whole communities. Here, we examine the interactions among introduced Rocky Mountain elk, Cervus canadensis nelsoni, a common native plant, Solidago velutina, and the diverse plant-associated community of arthropods. While introduced species are recognized as one of the biggest threats to native ecosystems, relatively few studies have investigated an evolutionary mechanism by which introduced species alter native communities. Here, we use a common garden design that addresses and supports two hypotheses. First, native S. velutina has rapidly evolved in the presence of introduced elk. We found that plants originating from sites with introduced elk flowered nearly 3 weeks before plants originating from sites without elk. Second, evolution of S. velutina results in a change to the plant-associated arthropod community. We found that plants originating from sites with introduced elk supported an arthropod community that had ~35 % fewer total individuals and a different species composition. Our results show that the impacts of introduced species can have both ecological and evolutionary consequences for strongly interacting species that subsequently cascade to affect a much larger community. Such evolutionary consequences are likely to be long-term and difficult to remediate.

Informed herbivore movement and interplant communication determine the effects of induced resistance in an individual-based model.

1. Plant induced resistance to herbivory affects the spatial distribution of herbivores, as well as their performance. In recent years, theories regarding the benefit to plants of induced resistance have shifted from ideas of optimal resource allocation towards a more eclectic set of theories that consider spatial and temporal plant variability and the spatial distribution of herbivores among plants. However, consensus is lacking on whether induced resistance causes increased herbivore aggregation or increased evenness, as both trends have been experimentally documented. 2. We created a spatial individual-based model that can describe many plant-herbivore systems with induced resistance, in order to analyse how different aspects of induced resistance might affect herbivore distribution, and the total damage to a plant population, during a growing season. 3. We analyse the specific effects on herbivore aggregation of informed herbivore movement (preferential movement to less-damaged plants) and of information transfer between plants about herbivore attacks, in order to identify mechanisms driving both aggregation and evenness. We also investigate how the resulting herbivore distributions affect the total damage to plants and aggregation of damage. 4. Even, random and aggregated herbivore distributions can all occur in our model with induced resistance. Highest levels of aggregation occurred in the models with informed herbivore movement, and the most even distributions occurred when the average number of herbivores per plant was low. With constitutive resistance, only random distributions occur. Damage to plants was spatially correlated, unless plants recover very quickly from damage; herbivore spatial autocorrelation was always weak. 5. Our model and results provide a simple explanation for the apparent conflict between experimental results, indicating that both increased aggregation and increased evenness of herbivores can result from induced resistance. We demonstrate that information transfer from plants to herbivores, and from plants to neighbouring plants, can both be major factors in determining non-random herbivore distributions.

[Effects of Cuscuta australis parasitism on the growth, reproduction and defense of Solidago canadensis].

In order to find out how parasitic Cuscuta australis influences the growth and reproduction of Solidago canadensis, the effects of the parasitism of C. australis on the morphological, growth and reproductive traits of S. canadensis were examined and the relationships between the biomass and the contents of the secondary metabolites were analyzed. The results showed that the parasitism significantly reduced the plant height, basal diameter, root length, root diameter, root biomass, stem biomass, leaf biomass, total biomass, number of inflorescences branches, axis length of inflorescence, and number of inflorescence. In particular, plant height, number of inflorescence and the stem biomass of parasitized S. canadensis were only 1/2, 1/5 and 1/8 of non-parasitized plants, respectively. There was no significant difference of plant height, root length, stem biomass and total biomass between plants parasitized with high and low intensities. But the basal diameter, root volume, leaf biomass, root biomass, the number of inflorescences branches, axis length of inflorescence and number of inflorescence of S. canadensis parasitized with high intensity were significantly lower than those of plants parasitized with low intensity. The parasitism of C. australis significantly increased the tannins content in the root and the flavonoids content in the stem of S. canadensis. The biomass of S. canadensis was significantly negatively correlated with the tannin content in the root and the flavonoids content in the stem. These results indicated that the parasitism of C. australis could inhibit the growth of S. canadensis by changing the resources allocation patterns as well as reducing the resources obtained by S. canadensis.

Complex effects of fertilization on plant and herbivore performance in the presence of a plant competitor and activated carbon.

Plant-herbivore interactions are influenced by host plant quality which in turn is affected by plant growth conditions. Competition is the major biotic and nutrient availability a major abiotic component of a plant's growth environment. Yet, surprisingly few studies have investigated impacts of competition and nutrient availability on herbivore performance and reciprocal herbivore effects on plants. We studied growth of the specialist aphid, Macrosiphoniella tanacetaria, and its host plant tansy, Tanacetum vulgare, under experimental addition of inorganic and organic fertilizer crossed with competition by goldenrod, Solidago canadensis. Because of evidence that competition by goldenrod is mediated by allelopathic compounds, we also added a treatment with activated carbon. Results showed that fertilization increased, and competition with goldenrod decreased, plant biomass, but this was likely mediated by resource competition. There was no evidence from the activated carbon treatment that allelopathy played a role which instead had a fertilizing effect. Aphid performance increased with higher plant biomass and depended on plant growth conditions, with fertilization and AC increasing, and plant competition decreasing aphid numbers. Feedbacks of aphids on plant performance interacted with plant growth conditions in complex ways depending on the relative magnitude of the effects on plant biomass and aphid numbers. In the basic fertilization treatment, tansy plants profited from increased nutrient availability by accumulating more biomass than they lost due to an increased number of aphids under fertilization. When adding additional fertilizer, aphid numbers increased so high that tansy plants suffered and showed reduced biomass compared with controls without aphids. Thus, the ecological cost of an infestation with aphids depends on the balance of effects of growth conditions on plant and herbivore performance. These results emphasize the importance to investigate both perspectives in plant herbivore interactions and characterize the effects of growth conditions on plant and herbivore performance and their respective feedbacks.