Solidago Altissima Research Articles

Modification of plant‐induced responses by an insect ecosystem engineer influences the colonization behaviour of subsequent shelter‐users

Summary Herbivores that modify plant morphology, such as gall‐forming insects, can disproportionately impact arthropod community on their host plants by providing novel habitats and shelters from biotic and abiotic stresses. These ecosystem engineers could also modify plant chemical properties, but how such changes in plant quality affect the behaviour of subsequent colonizers has rarely been investigated. We explored how an initial infestation of the tall goldenrod (Solidago altissima) by an ecosystem engineer, the rosette gall‐midge (Rhopalomyia solidaginis), affects colonization behaviour of a shelter‐using beetle (Microrhopala vittata) through plant‐induced responses in the field. Beetles preferentially colonized plants with galls and exhibited a clumped distribution on those plants, which suggested a possible advantage for aggregating on galled plants. Accordingly, we found that beetles remained longer on galled plants with previous beetle damage than those without beetle damage. No such effect of beetle damage was found on plants without a gall. Similar interactions between galler infestation and beetle damage were found in beetle's feeding choice, leaf diterpene and serine protease inhibitor production, and volatile organic compound (VOC) emission. These plant metabolic induction and herbivore response patterns indicated that the gall‐midge can alter how plants respond to the beetle damage and that gall presence coupled with beetle damage improves leaf palatability for the beetle. Finally, we found reciprocal effects of beetles on gall‐midge performance to be neutral to slightly positive, suggesting that the observed field association of the two herbivores could be formed by plant‐mediated facilitation. Synthesis. Our study suggests that an ecosystem engineer could have significant impact on herbivore community not only by changing plant morphology, but also by altering host quality and modifying plant‐induced responses to subsequent herbivory. As such, R. solidaginis also functions as a keystone herbivore that has disproportionate effects on community dynamics and composition meditated by induced plant growth and metabolic responses.

Herbivore release drives parallel patterns of evolutionary divergence in invasive plant phenotypes

Summary Herbivory can drive rapid evolution of plant chemical traits mediating defensive and competitive ability. At a geographic scale, plant populations that escape selection from their ancestral herbivores may evolve decreased defence and increased competitiveness. While contrasts between native and invasive populations of plants lend support to this hypothesis, such experiments cannot establish causal links between herbivory and evolved invasive phenotypes. Here, we conducted geographic contrasts, and coupled these with long‐term selection experiments that directly test for evolutionary responses to herbivore exclusion. In common gardens, we contrasted Solidago altissima genotypes that were historically exposed or protected from herbivory across two experimental time‐scales: (i) a natural experiment where plant populations evolved either with native herbivory (in Minnesota and New York) or evolved relatively free from herbivory for ˜100 years in Japan, and (ii) a 12‐year manipulative experiment where plants were either exposed to ambient herbivory or treated with insecticide. In both experiments, plant populations responded to herbivore release by evolving increased production of root allelochemicals and interspecific competitive ability against Poa pratensis. While plant resistance to a beetle herbivore did not diverge between plant origins, we still observed parallel evolutionary shifts in leaf secondary metabolite and protease inhibitor production, which may confer resistance to diverse herbivore species. Synthesis. Observed evolutionary convergence for multiple plant traits, between the natural and manipulative experiments, emphasizes the role of insect herbivores as key drivers of plant adaptation and geographic differentiation.

Synthesis of nanoparticles composed of silver and silver chloride for a plasmonic photocatalyst using an extract from a weed Solidago altissima (goldenrod)

Phytosynthesis of nanomaterials is advantageous since it is economical, ecofriendly, and simple, and, what is more, in the synthetic protocols, nontoxic chemicals and biocompatible materials are used. Here, a green synthetic methodology of nanoparticles (NPs) composed of silver (Ag) and silver chloride (AgCl) NPs is developed using a leaf extract of Solidago altissima as a reducing agent for the first time. Utilization of a terrestrial weed for the synthesis of Ag and AgCl NPs is a novel environmentally friendly approach considering that no toxic chemicals, external halide source, or elaborate experimental procedures are included in the process. The optical properties and elemental compositions of as-synthesized Ag and AgCl NPs are well characterized, and the degradation of an organic dye, i.e., rhodamine B (RhB), is investigated using the Ag and AgCl NPs. We find that degradation of RhB is effectively achieved thanks to both surface plasmon resonance and semiconductor properties of Ag and AgCl NPs. The surface-enhanced Raman scattering and antibacterial activities are also examined. The present approach to the synthesis of NPs using a weed may encourage the utilization of hazardous plants for the creation of novel nanomaterials.

「河川における生物多様性に配慮した堤防植生管理」 チガヤ型植物多様性ホットスポットに侵入したセイタカアワダチソウの影響評価

利根川中流域の堤防法面には前報で山田らが指摘したように築堤履歴や種類組成からチガヤーツリガネニンジン型群落9) と認められる草地が点在している。チガヤーツリガネニンジン型群落は 1960年頃から全国的に進められた農地の大規模整備による表土の攪乱を免れた場所に残存する草地で，通常の管理では外来種は侵入しにくいと考えられている 9) 。ところが利根川中流域には，築堤履歴からチガヤーツリガネニンジン型群落と言える草地内の全面にセイタカアワダチソウ Solidago altissima L.が分布する場所がある。当該場所のセイタカアワダチソウは個体サイズにばらつきがあり，またセイタカアワダチソウ個体が集中する箇所が認められた。本報では上記のチガヤ型植物多様性ホットスポット (以下，チガヤ型ホットスポット) に出現したセイタカアワダチソウの生育を抑制し，在来種多様性を維持・管理する視点から，その代表的な堤防法面で，全面 (長さ 20 m × 幅 15 m) を 1 mメッシュで細分化し植生調査を行った。また同じ場所のセイタカアワダチソウ個体の生活史についても解析した。さらにチガヤ型ホットスポットを構成している優占種のタイプ別に，構成種の草高と被度に基づく群落構造図を作成，セイタカアワダチソウが当該チガヤ型ホットスポットの植物多様性に及ぼす影響程度を評価した。

Solidago altissima differs with respect to ploidy frequency and clinal variation across the prairie-forest biome border in Minnesota.

Although our awareness of ploidy diversity has expanded with the application of flow cytometry, we still know little about the extent to which cytotypes within mixed-ploidy populations are genetically differentiated across environmental gradients. To address this issue, we reared 14 populations of Solidago altissima spanning the prairie-forest ecotone in Minnesota in a common garden with a watering treatment. We assessed ploidy frequencies and measured survival, flowering phenology, and plant architectural traits for 4 years. All populations harbored multiple cytotypes; prairie populations were dominated by tetraploids, forest populations by hexaploids. Diploids and polyploids differed significantly for 84% of the traits. Beyond average differences, the slope of trait values covaried with latitude and longitude, but this relationship was stronger for diploids than the other two polyploid cytotypes as indicated by numerous ploidy × latitude and ploidy × longitude interactions. For example, the timing of flowering of the cytotypes overlapped in populations sampled from the northeastern hemiboreal forest but differed significantly between cytotypes sampled from populations in the southwestern prairie. The watering treatments had weak effects, and there were no ploidy differences for phenotypic plasticity. Our data show that diploids have diverged genetically to a greater extent than polyploids along the environmental clines sampled in this study. Moreover, different environments favor phenotypic convergence over divergence among cytotypes for some traits. Differences in ploidy frequency and phenotypic divergence among cytotypes across gradients of temperature and precipitation are important considerations for restoration in an age of climate change.

Interactions between alien goldenrods (Solidago and Euthamia species) and comparison with native species in Central Europe

Competitive interactions are among the crucial determinants of plant invasion. Most invasive species are more competitive than native species, with the strongest competition expected between species that share similar niches and/or those that are closely related. Because many habitats can be invaded by several non-native species, the competition between alien plants has an increasing importance. The American-origin goldenrods (Solidago and Euthamia) are exceptionally successful invaders in Europe. A replacement series experiment was performed, to identify the interactions between goldenrods in their invasive range. We determined what type of interferences dominated between the examined taxa by comparing the total yield of plants in mixtures and as a monoculture. Four alien goldenrods [Solidago altissima L., Solidago canadensis L., Solidago gigantea Aiton and Euthamia graminifolia (L.) Nutt] were studied and compared with native species (Solidago virgaurea L. and Tanacetum vulgare L.) that co-occur with them in natural conditions. The results show that the invasive Solidago species had similar competitive abilities. The invasive species that were examined, out-competed the native taxa. These results highlight the high competitiveness of E. graminifolia, which reduced the biomass of the other species. Such competitive abilities were related to underground competition. These results suggest the necessity to monitor this species as a potentially invasive taxon.

Inhibitory Effects of the Flower of Canadian Goldenrod (Solidago altissima L.) on Tumour Promotion Induced by 12-O-tetradecanoylphorbol-13-actete

Cancer prevention is an important issue in various healthcare fields; thus, we continue searching for potential useful compounds. This study focuses on the utilization of Canadian goldenrod, which is commonly seen growing on vacant land. Methanol extracts of the flower of Canadian goldenrod inhibited inflammation by 12-O-tetradecanoylphorbol-13-acetate (TPA) and inhibited promotion in the mouse skin two-stage carcinogenesis model. Five inhibitory compounds were isolated from the active fraction, and these compounds were identified as flavonoids; kaempferol (1), quercetin (2), kaempferol-3-O-rutinoside (3), querectin-3-O-rutinoside (4), and isorhamnetin-3-O-rutinoside (5). These compounds inhibited the inflammation induced by TPA, and the inhibitory effects were similar to indomethacin.

Seed Predators, not Herbivores, Exert Natural Selection on Solidago spp. in an Urban Archipelago.

The effects of urbanization on biodiversity are well established, as a growing city will reduce the size and diversity of patches of native plants. Recolonization of old patches and discovery of new ones by arthropod herbivores should occur as predicted by island biogeography theory. Although colonization represents an increase in biodiversity, such arrivals may exert new forms of natural selection on plants through herbivory and seed predation. Using a single species of old-field aster (Solidago altissima L.), we found that the level of natural selection by seed predators and herbivores follows patterns of island biogeography, with lower amounts of damage on smaller islands, where there are fewer species, and hypothetically smaller populations of arthropods. We also found that in an urban system, levels of herbivory are far below the tolerance levels of Solidago, and that seed predators are likely to be the only arthropod to cause reduced fitness. The pattern seen also implies that as a patch of Solidago grows through clonal expansion, it will come under higher selective pressure.

Multiple and mass introductions from limited origins: genetic diversity and structure of Solidago altissima in the native and invaded range.

Understanding the origins and diversity of invasive species can reveal introduction and invasion pathways, and inform an effective management of invasive species. Tall goldenrod, Solidago altissima, is a herbaceous perennial plant native to North America and it has become a widespread invasive weed in East Asian countries. We used microsatellite and chloroplast DNA markers to obtain information on neutral processes and on genetic diversity in native and invaded populations of S. altissima and to infer how it invaded and spread in Japan. We found that introduced (n = 12) and native (n = 20) populations had similar levels of genetic diversity at nuclear SSR loci. Genetic structure analysis indicated that at least two independent colonization events gave rise to current S. altissima populations in Japan. The majority (68%) of the Japanese S. altissima were genetically similar and likely shared a common origin from a single or a small number of populations from the southern USA populations, while the populations in Hokkaido were suggested to arise from a different source. Our results suggest that multiple and mass introductions have contributed to the persistence and rapid adaptation of S. altissima promoting its widespread establishment throughout Japan.

Prey aphid inhibits development and reproduction of Coccinella septempunctata bruckii and Propylea japonica (Coleoptera: Coccinellidae) but maintains adults

We compared the development and survival of Coccinella septempunctata bruckii Mulsant and Propylea japonica (Thunberg) raised on Uroleucon nigrotuberculatum (Olive) with those of the same species raised on Megoura crassicauda Mordvilko. Uroleucon nigrotuberculatum significantly prolonged the development time and drastically reduced the survival of the larval stages of both predators. Adult body weight of C. septempunctata and females of P. japonica raised on M. crassicauda was substantially heavier. No females of C. septempunctata raised on U. nigrotuberculatum laid eggs. Only 15 % of C. septempunctata females collected from Solidago altissima L. patch laid eggs for 48 h when fed on U. nigrotuberculatum. In contrast, females fed on M. crassicauda were highly fecund. Some P. japonica females raised on U. nigrotuberculatum laid a few eggs discontinuously for a short period. Approximately 90 % of P. japonica adult females collected from the solidago patch and fed on U. nigrotuberculatum laid a few eggs, but females fed on M. crassicauda laid substantially more eggs. These results suggest that patches of the introduced plant solidago, a natural host of the introduced aphid, U. nigrotuberculatum, are not adequate habitats for reproduction but may provide lady beetle adults with alternative prey on which to survive when suitable prey are scarce.

Selective manipulation of a non-dominant plant and its herbivores affects an old-field plant community

Competition and herbivory can interact to influence the recovery of plant communities from disturbance. Previous attention has focused on the roles of dominant plant species in structuring plant communities, leaving the roles of subordinate species often overlooked. In this study, we examined how manipulating the density of a subordinate plant species, Solanum carolinense, and its insect herbivores influenced an old-field plant community in northern Florida following a disturbance. Five years following the disturbance, the initial densities of S. carolinense planted at the start of the experiment negatively influenced total plant cover and species diversity, and the cover of some grasses (e.g., Paspalum urvillei) and forbs (e.g., Rubus trivalis). Selectively removing herbivores from S. carolinense increased S. carolinense abundance (both stem densities and cover), increased the total cover of plants in the surrounding plant community, and affected plant community composition. Some plant species increased (e.g., Digitaria ciliaris, Solidago altissima) and others decreased (e.g., Paspalum notatum, Cynodon dactylon) in cover in response to herbivore removal. Herbivore effects on plant community metrics did not depend on S. carolinense density (no significant herbivory by density interaction), suggesting that even at low densities, a reduction of S. carolinense herbivores can influence the rest of the plant community. The recovery of the plant community was context dependent, depending on site- and plot-level differences in underlying environmental conditions and pre-disturbance plant community composition. We demonstrate that the density of and herbivory on a single subordinate plant species can affect the structure of an entire plant community.

Plant neighborhood effects on herbivory: damage is both density and frequency dependent.

Neighboring plants can affect the likelihood that a focal plant is attacked by herbivores. Both the density of conspecific neighbors (resource concentration or dilution effects) and the relative density of heterospecific neighbors (associational effects or effects of neighbor frequency) within the local neighborhood can affect herbivore load and plant damage. Understanding how these neighborhood effects influence processes such as plant competition or natural selection on plant resistance traits will require knowing how both plant density and frequency affect damage, but previous studies have generally confounded density and frequency effects. In this study, we independently manipulated the absolute density and frequency (i.e., relative density) of two plant species (Solanum carolinense and Solidago altissima) to characterize neighborhood composition effects on S. carolinense damage by herbivores, providing the first picture of how both density and frequency of neighbors influence damage in a single system. We found both a positive effect of S. carolinense density on S. carolinense damage (a resource concentration effect) and a nonlinear effect of S. altissima frequency on S. carolinense damage (associational susceptibility). If these types of patterns are common in nature, future studies seeking to understand neighborhood effects on damage need to incorporate both density and frequency effects and capture any nonlinear effects by selecting a range of values rather than focusing on only a pair of densities or frequencies. This type of data on neighborhood effects will allow us to understand the contribution of neighborhood effects to population-level processes such as competition, the evolution of plant resistance to herbivores, and yield gains in agricultural crop mixtures.

Evidence For Plant-mediated Competition Between Defoliating and Gall-forming Specialists Attacking Solidago altissima

Abstract Phytophagous insects from different feeding guilds may compete indirectly via altering the chemical defenses or nutritional quality of their shared host plants. Gall-formers are understudied in this context but may be susceptible to this mode of competition early in their life history, when they may be particularly sensitive to changes to the specific reactive tissue needed for gall development. Here, we conducted a natural experiment to investigate the effect of folivory of Canada goldenrod, Solidago altissima, by Trirhabda beetles on gall induction success for the goldenrod gall fly, Eurosta solidaginis. We monitored oviposition events and gall development on individual Solidago ramets at sites differing in their levels of Trirhabda folivory. We found a strong inverse relationship between Trirhabda leaf damage and successful gall induction rates. These results suggest Trirhabda beetles may negatively impact Eurosta demographics and highlight the need for further study on how factors affecting g...

Colonization of Solidago altissima by the specialist aphid Uroleucon nigrotuberculatum: effects of genetic identity and leaf chemistry.

In dominant old-field plant species, genotypic variation in traits important for herbivorous insects may explain variation in insect species abundance. While the importance of plant genetic identity on arthropod abundance has been demonstrated, specific factors that drive genotype choice by insects remain largely unknown. Sixteen genotypes of the widely distributed plant species Solidago altissima were used to investigate the possible role of nutrients and terpene secondary metabolites in shaping the abundance of a common specialist aphid, Uroleucon nigrotuberculatum. Ramets were propagated in a greenhouse and then transferred to a natural field setting. After 76 days, aphid abundance was quantified and leaf tissue assayed for nutrients and terpenes. Aphids/g plant biomass significantly differed among genotypes, with a 30-fold difference observed among plant genotypes. Leaf nitrogen, C:N ratio and water did not vary among genotypes. Of eight terpenes quantified, five were influenced by plant genotype. Aphid abundance increased marginally with the concentration of the monoterpene β-pinene in leaf tissue (P = 0.056). A partial least squares analysis determined that nutritional chemicals did not explain aphid responses, while 49% of the variation in aphid colonization among genotypes was explained by terpenes. This study is one of the first to demonstrate that variation in allelochemicals may be related to differences in the abundance of a key herbivore among genotypes of a plant species that exhibits large intraspecific genetic variation.

Love thy neighbor? reciprocal impacts between plant community structure and insect herbivory in co‐occurring Asteraceae

Patterns of herbivory may vary with fine‐scale plant community structure: the degree of damage plants experience may depend on their neighbors (i.e., associational resistance or susceptibility). Differential herbivory, in turn, may facilitate a shift in plant community structure. We investigated these reciprocal effects of plant community structure and insect herbivory in a field mesocosm experiment with closely related, native Asteraceae that co‐occur in early‐successional habitats (old fields). After one year of establishment, we excluded or augmented insect herbivores for two years in equal‐density communities of three types: goldenrod‐dominated (Solidago spp.) or aster‐dominated (Symphyotrichum spp.) congeneric communities and mixtures of the two genera. In manipulated outbreaks, overall and species‐specific patterns of herbivory by the main herbivore, the leaf beetle Trirhabda virgata, varied dramatically with community composition. In both years, the preferred goldenrods suffered 25−70% higher defoliation in mixtures with the less‐preferred asters (i.e., associational susceptibility), compared to when growing with congeners; in contrast, asters experienced lower damage in mixtures (i.e., associational resistance). Insect herbivory consistently reduced overall plant productivity, and promoted colonization by other old‐field species. Importantly, herbivory also initiated a shift in the structure of the plant communities, and this effect depended on the starting community composition, implying potential reciprocal effects. For instance, only in mixtures did elevated herbivory reduce the proportional abundance of the preferred host, and the old‐field dominant, Solidago altissima. Our findings underscore the importance of plant community composition for variation in and impacts of herbivory and suggest the possibility of feedbacks between herbivory and local community structure as one of the mechanisms contributing to the maintenance of vegetation heterogeneity.

외래 관상식물의 국내 귀화 현황

Numerous cases have been reported of naturalization by exotic ornamental plants. To obtain basic data about how those plants affect the ecosystems of Korea, we compiled a list of 78 species categorized as ornamentals from 309 naturalized species in Korea and analyzed their life forms, origin, and their current global status of naturalization and regulation. Plants belonging to Compositae comprised the largest group, with 23 species. In all, 75 species were considered herbaceous, and perennial species out-numbered annuals and biennials. Most species originated from Europe and North America. Except for Houttuynia cordata, the other 77 species were naturalized in other countries as well. Furthermore, 34 species, including Aster pilosus and Solidago altissima, have been subject to legal restrictions or classified as alert species in Korea or other countries. Therefore, monitoring may be required to prevent spread of those species, especially for species which have not been managed under domestic law up to now.

An exotic herbivorous insect drives the evolution of resistance in the exotic perennial herb Solidago altissima

Invasive plants often experience rapid changes in biological interactions by escaping from their original herbivores at their new habitats, and sometimes re‐associating with those herbivores afterwards. However, little is known about whether the temporal changes in herbivorous impact work as a selective agent for defensive traits of invaded plants. Solidago altissima (goldenrod) is a North American perennial that has widely invaded abandoned fields in Japan. Recently, an herbivorous insect Corythucha marmorata (lace bug), an exotic insect also from North America, which was first recorded in 2000 in Japan, has been expanding its habitat on S. altissima populations in Japan. In this study, we investigated whether the invasion of C. marmorata had a selective impact on the defensive traits of S. altissima, by conducting a field survey, a common garden experiment and microsatellite analysis. We compared quantitative genetic differentiation of traits (resistance, growth, and reproduction) and neutral molecular differentiation among 16 S. altissima populations with different establishment years of C. marmorata.The common garden experiment, in which plants were grown in a greenhouse and treated to either C. marmorata herbivory or no herbivory, revealed the presence of higher resistance, sexual reproduction, and asexual (rhizome) reproduction in populations subjected to a longer history of C. marmorata pressure. Such phenotypic variability among establishment years of lace bugs was likely driven by natural selection rather than stochastic events such as genetic drift and founder effects. In addition, when plants were exposed to lace bug herbivory, resistance had a positive relationship with sexual and asexual reproduction, although no relationship was found when plants were free from herbivory. These findings suggest that defensive traits in S. altissima have evolved locally in the last decade in response to the selective pressure of C. marmorata.

Growth, phenology, and biomass allocation of alien Solidago species in central Europe

AbstractPlant invasion is a major threat to the integrity of an ecosystem. Exceptionally successful invaders in Europe are the American species of Solidago genus. In this study we examined growth, reproduction, and phenology of Solidago species, of American origin, growing in central Europe (S. altissima, S. canadensis, S. gigantea, S. graminifolia). These taxa were compared with two native species: Solidago virgaurea and Tanacetum vulgare. We observed high differentiation in height, number of shoots, and biomass production between individuals within taxa. Generally, the invasive species produced substantially (two to five times) more biomass than the native ones, being statistically significant in the comparison of alien Solidago graminifolia and S. gigantea versus native S. virgaurea and T. vulgare. The ratio of biomass of reproductive parts to overall biomass varied considerably among years, but generally the lowest one was for Solidago altissima, and the highest for S. graminifolia. It shows a lack of a clear pattern of differentiation between alien and native species in terms of biomass investment in reproduction. We observed a general tendency of allocation of a major part of biomass in rhizomes by phalanx species (S. graminifolia and S. gigantea), while species with guerrilla strategy (S. altissima and S. canadensis) invested more biomass in stems and leaves. However, because of the high variability there was no clear, stable pattern of statistically significant differences between these two groups. The results suggest that S. graminifolia reveals a strong potential of invasion, in spite of its, so far limited, distribution in Europe.

The volatile emission of Eurosta solidaginis primes herbivore-induced volatile production in Solidago altissima and does not directly deter insect feeding.

BackgroundThe induction of plant defenses in response to herbivory is well documented. In addition, many plants prime their anti-herbivore defenses following exposure to environmental cues associated with increased risk of subsequent attack, including induced volatile emissions from herbivore-damaged plant tissues. Recently, we showed in both field and laboratory settings that tall goldenrod plants (Solidago altissima) exposed to the putative sex attractant of a specialist gall-inducing fly (Eurosta solidaginis) experienced less herbivory than unexposed plants. Furthermore, we observed stronger induction of the defense phytohormone jasmonic acid in exposed plants compared to controls. These findings document a novel class of plant-insect interactions mediated by the direct perception, by plants, of insect-derived olfactory cues. However, our previous study did not exclude the possibility that the fly emission (or its residue) might also deter insect feeding via direct effects on the herbivores.ResultsHere we show that the E. solidaginis emission does not (directly) deter herbivore feeding on Cucurbita pepo or Symphyotrichum lateriflorum plants—which have no co-evolutionary relationship with E. solidaginis and thus are not expected to exhibit priming responses to the fly emission. We also document stronger induction of herbivore-induced plant volatiles (HIPV) in S. altissima plants given previous exposure to the fly emission relative to unexposed controls. No similar effect was observed in maize plants (Zea mays), which have no co-evolutionary relationship with E. solidaginis.ConclusionsTogether with our previous findings, these results provide compelling evidence that reduced herbivory on S. altissima plants exposed to the emission of male E. solidaginis reflects an evolved plant response to olfactory cues associated with its specialist herbivore and does not involve direct effects of the fly emission on herbivore feeding behavior. We further discuss mechanisms by which the priming of HIPV responses documented here might contribute to enhanced S. altissima defense against galling.

Exploring plant defense theory in tall goldenrod, Solidago altissima

Understanding the evolutionary reasons for patterns of chemical defense in plants is an ongoing theoretical and empirical challenge. The goal is to develop a model that can reliably predict how defenses are distributed within the plant over space and time. This is difficult given that evolutionary, ecological, and physiological processes and tradeoffs can operate over different spatial and temporal scales. We evaluated the major predictions of two leading defense theories, the growth-differentiation balance hypothesis (GDBH) and optimal defense theory (ODT). To achieve this, enemies, fitness components, terpenoids, and protease inhibitors were measured in Solidago altissima and used to construct conventional univariate and structural equation models (SEMs). Leaf-tissue value indices extracted from an SEM revealed a strong correlation between tissue value and terpenoid defense that supports ODT. A tradeoff between serine protease inhibition and growth as well as an indirect tradeoff between growth and terpenoids manifested through galling insects supported the GDBH. Interestingly, there was a strong direct effect of terpenoids on rhizome mass, suggesting service to both storage and defense. The results support established theories but unknown genotypic traits explained much of the variation in defense, confirming the need to integrate emerging theories such as pollination constraints, defense syndromes, tolerance, mutualisms, and facilitation.