Concentrations Of Phenolic Glycosides Research Articles

Genomic and transcriptomic analyses reveal polygenic architecture for ecologically important traits in aspen (Populustremuloides Michx.).

Intraspecific genetic variation in foundation species such as aspen (Populus tremuloides Michx.) shapes their impact on forest structure and function. Identifying genes underlying ecologically important traits is key to understanding that impact. Previous studies, using single-locus genome-wide association (GWA) analyses to identify candidate genes, have identified fewer genes than anticipated for highly heritable quantitative traits. Mounting evidence suggests that polygenic control of quantitative traits is largely responsible for this "missing heritability" phenomenon. Our research characterized the genetic architecture of 30 ecologically important traits using a common garden of aspen through genomic and transcriptomic analyses. A multilocus association model revealed that most traits displayed a highly polygenic architecture, with most variation explained by loci with small effects (likely below the detection levels of single-locus GWA methods). Consistent with a polygenic architecture, our single-locus GWA analyses found only 38 significant SNPs in 22 genes across 15 traits. Next, we used differential expression analysis on a subset of aspen genets with divergent concentrations of salicinoid phenolic glycosides (key defense traits). This complementary method to traditional GWA discovered 1243 differentially expressed genes for a polygenic trait. Soft clustering analysis revealed three gene clusters (241 candidate genes) involved in secondary metabolite biosynthesis and regulation. Our work reveals that ecologically important traits governing higher-order community- and ecosystem-level attributes of a foundation forest tree species have complex underlying genetic structures and will require methods beyond traditional GWA analyses to unravel.

Consumer response to wine made from smoke-affected grapes

When vineyards and grapes are exposed to smoke from wildfires or controlled burns, this can result in wines with smoky, burnt or ashy attributes that have been linked to the presence of elevated concentrations of volatile phenols and phenolic glycosides. These smoky flavours are considered undesirable by winemakers, but there is little information about how consumers respond to smoke-affected wines. To investigate whether consumers respond negatively to smoky attributes when wine is tasted blind, three studies assessing sets of Pinot noir rosé, Chardonnay and unoaked Shiraz wines with varied smoke flavour were conducted. Overall, wines rated high in smoke flavour were less liked compared to non-smoke-affected wines. Independent of wine type, there was a strong negative correlation between smoky flavour and overall consumer liking. Detailed data analysis revealed that consumers who are wine drinkers fell into one of three categories: highly responsive to smoke, moderately responsive, or a smaller group of non-responders. This consumer-based information is essential for guiding the assessment of risk from smoke exposure of grapes and potential for quality defects in wine, as well as identifying and benchmarking management options for wine producers, not only in Australia, but globally.

Modelling Smoke Flavour in Wine from Chemical Composition of Smoke-Exposed Grapes and Wine

Wine grapes exposed to smoke and wine made from grapes exposed to smoke can robustly be identified through their elevated concentrations of volatile phenols and phenolic glycosides serving as smoke markers, compared to concentrations typically found in non-smoke-exposed samples. Smoke-affected wines with high concentrations of volatile phenols and glycosides can have smoky flavours, but the relationship between concentrations of specific smoke markers in grapes and the intensity of smoky sensory attributes in the resulting wine has not been established. This study sought to determine whether volatile phenols and glycoside concentration in grapes and wine are suited to predict smoke flavour, to identify the key drivers of smoke flavour in both matrices. The study aimed to determine what concentrations of volatiles and glycosides in grapes impart an unacceptable smoke flavour in the resulting wine, to provide a guide for producers assessing suitability of smoke-exposed grapes for wine production. During vintage 2020, a total of 65 grape samples were collected from vineyards exposed to bushfire smoke, as well as unaffected vineyards. Chardonnay, Pinot Noir, and Shiraz grapes were harvested from vineyards in New South Wales, South Australia, and Victoria. Unoaked wines (50 kg scale) were produced under controlled conditions. The wines had a wide range of smoke flavour intensities rated by a trained sensory panel. Statistical models based on guaiacol, o-cresol, m-cresol, p-cresol, and some glycosides gave good predictions of smoke flavour intensity, with a slightly different optimal model for each cultivar. Subsequently, critical concentrations for quality defects were estimated to provide a guide for producers. A subset of smoke exposure markers in wine grapes affected by smoke from bushfires can be used to predict the degree of smoke flavour in wine. This information provides a first guide for assessing the risk of producing smoke tainted wine from smoke-exposed grapes.

Temporal patterns of ungulate herbivory and phenology of aspen regeneration and defense.

Ungulate herbivory can create strong top-down effects on forest recruitment, especially after fire. Defense strategies of tree species against ungulate herbivory include escape through vertical growth and resistance through the production of defense compounds. Using afour-way fence design and camera traps we characterized the differential impacts of ungulate herbivores (deer, elk, cattle) on aspen forest recruitment and plant defense responses and how they vary depending on the timing of herbivory. Aspen height growth was greatest between June and August and ungulate use of aspen was highest in July and August. Threeyears after fire, height of aspendiffered among fence treatments with full ungulate exclusion > deer-only plots > native ungulate plots > fenceless plots: 108 ± 4cm, 94 ± 4cm, 89 ± 4cm, and 65 ± 4cm, respectively. Fenceless plots had the highest rates of removal of apical meristems by the end of 2014 and 2015 (61% and 53%, respectively). Native ungulate plots, and deer-only plots both had similar removal of apical meristems in 2014 (37% and 39%, respectively). The highest phenolic glycoside concentrations were associated with an 80% reduction in meristem removal and four-fold greater aspen height by the end of summer. Low nitrogen was associated with an 86% reduction in apical meristem removal and threefold greater aspen height. In conclusion, our study suggests that high ungulate abundance can have detrimental impacts on forest recruitment and that high aspen defense chemistry and lower leaf N deters ungulate herbivory, especially in the late summer.

Nutritional state and secondary compounds influence trembling aspen (Populus tremuloides) intake by lambs

The foraging ecology of mammalian herbivores is determined by plant secondary compounds (PSC) that defend plants against herbivory, by nutrients that are required for maintenance, growth, and reproduction, and by the interaction between these variables. In this study, we explored the influence of an herbivore’s nutritional state and experience on intake of aspen (Populus tremuloides) leaves with contrasting concentrations of a PSC, phenolic glycosides (PG). Thirty-two lambs were randomly assigned to two groups (N = 16). Each group received aspen leaves with either higher (21.2%) or lower (16.3%) concentrations of PG throughout the study. In Experiment 1, half of the lambs within each group received rations with a high (22.2% crude protein [CP]; 3.13 Mcals/kg) or low (11.9% CP; 3.13 Mcals/kg) concentration of CP. During Experiment 2, half of the lambs within each group received rations with a high (3.45 Mcals/kg; 16.1% CP) or low (2.52 Mcals/kg; 18.5% CP) concentration of energy. During Experiment 3, all lambs received a simultaneous offer of aspen leaves containing higher (20.6%) and lower (14.8%) concentrations of PG. Aspen intake was greater when lambs received the high-protein or the low-energy rations (P < 0.05), and when they received aspen leaves with lower concentrations of PG (P = 0.009). During Experiment 3 (choice of high- or low-PG aspen), aspen intake was not affected by PG, but intake increased when nutrients were present in aspen in a combination of low concentrations of Cu, P, K, S, crude protein, and an intermediate concentration of condensed tannins. In summary, nutritional state and aspen chemical composition modulated the extent to which aspen was consumed by lambs. Herbivores grazing plant communities with high concentrations of protein or low concentrations of energy may be more likely to consume greater amounts of aspen than those animals grazing forages with low concentrations of protein or high concentrations of energy. This knowledge can be applied at the landscape level to identify potential “at-risk areas” of aspen regeneration and recruitment, allowing for the development of supplementation programs that reduce aspen herbivory.

Genetic variation in aspen phytochemical patterns structures windows of opportunity for gypsy moth larvae.

Empirical studies indicate that host-tree bud break will likely advance faster than spring-folivore egg hatch in response to predicted increases in temperature. How these phenological shifts will affect herbivory will depend on temporal patterns of foliar traits that occur during leaf expansion, and their effects on folivore performance. Through fine-scale time series sampling of newly flushed trembling aspen (Populus tremuloides) foliage, we observed a previously unknown peak in phenolic glycoside concentrations that coincides with the emergence of sensitive neonates of gypsy moths and rapidly declines soon after bud break. The magnitude and duration of the initial post-bud break peak in phenolic glycosides varied substantially among genotypes. In contrast, foliar nitrogen concentrations declined at a more uniform rate among genotypes throughout leaf expansion. In addition, leaf toughness remained uniformly low throughout these periods of phytochemical change, and did not rise or vary substantially among genotypes until after anticipated windows of climate change-induced shifts between bud break and egg hatch had elapsed. Controlled manipulation of intervals between gypsy moth egg hatch and aspen bud break generated differences in larval performance among hatch cohorts and host genotypes that corresponded with changes in foliar phenolic glycoside and nitrogen concentrations. These findings indicate that the effects of climate change-induced phenological shifts on herbivory will differ among host plant genotypes, and that genetic variation in foliar chemical patterns will strongly influence this heterogeneity.

Outbreak of Drepanopeziza fungus in aspen forests and variation in stand susceptibility: leaf functional traits, compensatory growth and phenology.

In the spring of 2015, a severe outbreak of the necrotrophic pathogen Drepanopeziza (also known as Marssonina) spread across large portions of aspen (Populus tremuloides Michx.) forests in the western United States. Among adjacent stands, some were diseased and others were not. Drepanopeziza infection in diseased aspen stands stimulated compensatory growth of second-flush leaves at the top of the canopy. These patterns of infection provided an opportunity to characterize associations of pathogen infection and leaf functional traits. Eight pairs of adjacent healthy and diseased aspen stands were identified across a forest landscape in northern Utah. Average leaf surface area, specific leaf area (SLA), photosynthesis, starch concentration and defense chemistry expression (phenolic glycosides and condensed tannins) were measured on original, first-flush leaves in the lower portion of the tree canopy of healthy and diseased stands and compensatory, second-flush leaves produced in the canopy top of diseased stands. Only first-flush leaves of diseased stands showed high levels of Drepanopeziza infection. Leaf area of second-flush leaves of diseased stands was threefold larger than all other leaf types in healthy or diseased stands. Lower canopy leaves of healthy stands had the highest SLA. Photosynthesis was lowest in infected first-flush leaves, highest in second-flush leaves of diseased stands and intermediate in leaves of healthy stands. Foliar starch concentrations were lower in leaves of diseased stands than leaves from healthy stands. Condensed tannins were greater in second-flush leaves than first-flush leaves in both healthy and diseased stands. Phenolic glycoside concentrations were lowest in infected leaves of diseased stands. Diseased stands leafed out a week earlier in the spring than healthy stands, which may have exposed their emerging leaves to rainy conditions that promote Drepanopeziza infection. Compensatory leaf regrowth of diseased stands appears to offset some of the functional loss (i.e., photosynthetic capacity) of infected leaves.

Plant Community Chemical Composition Influences Trembling Aspen (Populus tremuloides) Intake by Sheep.

Nutrients and plant secondary compounds in aspen (Populus tremuloides) may interact with nutrients in the surrounding vegetation to influence aspen use by herbivores. Thus, this study aimed to determine aspen intake and preference by sheep in response to supplementary nutrients or plant secondary compounds (PSC) present in aspen trees. Thirty-two lambs were randomly assigned to one of four molasses-based supplementary feeds to a basal diet of tall fescue hay (N=8) during three experiments. The supplements were as follows: (1) high-protein (60% canola meal), (2) a PSC (6% quebracho tannins), (3) 25% aspen bark, and (4) control (100% molasses). Supplements were fed from 0700 to 0900, then lambs were fed fresh aspen leaves collected from stands containing high (Experiment 1, 2) or low (Experiment 3) concentrations of phenolic glycosides (PG). In Experiment 2, lambs were simultaneously offered aspen, a forb (Lathyrus pauciflorus), and a grass (Bromus inermis) collected from the aspen understory. Animals supplemented with high protein or tannins showed greater intake of aspen leaves than animals supplemented with bark or the control diet (P<0.05), likely because some condensed tannins have a positive effect on protein nutrition and protein aids in PSC detoxification. Overall, animals supplemented with bark showed the lowest aspen intake, suggesting PSC in bark and aspen leaves had additive inhibitory effects on intake. In summary, these results suggest that not only the concentration but also the types and proportions of nutrients and chemical defenses available in the plant community influence aspen use by herbivores.

Interactions between Bacteria And Aspen Defense Chemicals at the Phyllosphere - Herbivore Interface.

Plant- and insect-associated microorganisms encounter a diversity of allelochemicals, and require mechanisms for contending with these often deleterious and broadly-acting compounds. Trembling aspen, Populus tremuloides, contains two principal groups of defenses, phenolic glycosides (salicinoids) and condensed tannins, which differentially affect the folivorous gypsy moth, Lymantria dispar, and its gut symbionts. The bacteria genus Acinetobacter is frequently associated with both aspen foliage and gypsy moth consuming that tissue, and one isolate, Acinetobacter sp. R7-1, previously has been shown to metabolize phenolic glycosides. In this study, we aimed to characterize further interactions between this Acinetobacter isolate and aspen secondary metabolites. We assessed bacterial carbon utilization and growth in response to different concentrations of phenolic glycosides and condensed tannins. We also tested if enzyme inhibitors reduce bacterial growth and catabolism of phenolic glycosides. Acinetobacter sp. R7-1 utilized condensed tannins but not phenolic glycosides or glucose as carbon sources. Growth in nutrient-rich medium was increased by condensed tannins, but reduced by phenolic glycosides. Addition of the P450 enzyme inhibitor piperonyl butoxide increased the effects of phenolic glycosides on Acinetobacter sp. R7-1. In contrast, the esterase inhibitor S,S,S,-tributyl-phosphorotrithioate did not affect phenolic glycoside inhibition of bacterial growth. Degradation of phenolic glycosides by Acinetobacter sp. R7-1 appears to alleviate the cytotoxicity of these compounds, rather than provide an energy source. Our results further suggest this bacterium utilizes additional, complementary mechanisms to degrade antimicrobial phytochemicals. Collectively, these results provide insight into mechanisms by which microorganisms contend with their environment within the context of plant-herbivore interactions.

Heterozygosity, gender, and the growth-defense trade-off in quaking aspen.

Although plant growth is generally recognized to be influenced by allocation to defense, genetic background (e.g., inbreeding), and gender, rarely have those factors been addressed collectively. In quaking aspen (Populus tremuloides Michx.), phenolic glycosides (PGs) and condensed tannins (CTs) constitute up to 30% of leaf dry weight. To quantify the allocation cost of this chemical defense, we measured growth, defense chemistry, and individual heterozygosity (H obs at 16 microsatellite loci) for male and female trees in both controlled and natural environments. The controlled environment consisted of 12 juvenile genets grown for 3years in a common garden, with replication. The natural environment consisted of 51 mature genets in wild populations, from which we sampled multiple ramets (trees) per genet. Concentrations of PGs and CTs were negatively correlated. PGs were uncorrelated with growth, but CT production represented a major cost. Across the range of CT levels found in wild-grown trees, growth rates varied by 2.6-fold, such that a 10% increase in CT concentration occurred with a 38.5% decrease in growth. H obs had a marked effect on aspen growth: for wild trees, a 10% increase in H obs corresponded to a 12.5% increase in growth. In wild trees, this CT effect was significant only in females, in which reproduction seems to exacerbate the cost of defense, while the H obs effect was significant only in males. Despite the lower growth rate of low-H obs trees, their higher CT levels may improve survival, which could account for the deficit of heterozygotes repeatedly found in natural aspen populations.

Nutrient and plant secondary compound composition and iron-binding capacity in leaves and green stems of commonly used plant browse (Carolina willow; Salix caroliniana) fed to zoo-managed browsing herbivores.

Plant secondary compounds are diverse structurally, and associated biological effects can vary depending on multiple factors including chemical structure and reaction conditions. Phenolic compounds such as tannins can chelate dietary iron, and supplementation of animal species sensitive to iron overload with tannins may prevent/treat iron overload disorder. We assessed the nutrient and phenolic composition and iron-binding capacity of Carolina willow (Salix caroliniana), a plant fed to zoo-managed browsing herbivores. Based on studies in other plant species and the chemical structures of phenolic compounds, we hypothesized that the concentration of condensed tannins in willow would be inversely related to the concentration of phenolic glycosides and directly related to iron-binding capacity. Our results indicated that willow nutrient composition varied by year, season, and plant part, which could be taken into consideration when formulating animal diets. We also found that the predominant plant secondary compounds were condensed tannins with minimal phenolic glycosides. Instead of binding to iron, the willow leaf extracts reduced iron from the ferric to ferrous form, which may have prooxidative effects and increase the bioavailability of iron depending on animal species, gastrointestinal conditions, and whole animal processes. We recommend identifying alternative compounds that effectively chelate iron in vitro and conducting chelation therapy trials in vivo to assess potential effects on iron balance and overall animal health.

Aspen defense chemicals influence midgut bacterial community composition of gypsy moth.

Microbial symbionts are becoming increasingly recognized as mediators of many aspects of plant - herbivore interactions. However, the influence of plant chemical defenses on gut associates of insect herbivores is less well understood. We used gypsy moth (Lymantria dispar L.), and differing trembling aspen (Populus tremuloides Michx.) genotypes that vary in chemical defenses, to assess the influence of foliar chemistry on bacterial communities of larval midguts. We evaluated the bacterial community composition of foliage, and of midguts of larvae feeding on those leaves, using next-generation high-throughput sequencing. Plant defense chemicals did not influence the composition of foliar communities. In contrast, both phenolic glycosides and condensed tannins affected the bacterial consortia of gypsy moth midguts. The two most abundant operational taxonomic units were classified as Ralstonia and Acinetobacter. The relative abundance of Ralstonia was higher in midguts than in foliage when phenolic glycoside concentrations were low, but lower in midguts when phenolic glycosides were high. In contrast, the relative abundance of Ralstonia was lower in midguts than in foliage when condensed tannin concentrations were low, but higher in midguts when condensed tannins were high. Acinetobacter showed a different relationship with host chemistry, being relatively more abundant in midguts than with foliage when condensed tannin concentrations were low, but lower in midguts when condensed tannins were high. Acinetobacter tended to have a greater relative abundance in midguts of insects feeding on genotypes with high phenolic glycoside concentrations. These results show that plant defense chemicals influence herbivore midgut communities, which may in turn influence host utilization.

Aspen (Populus tremuloides Michx.) intake and preference by mammalian herbivores: the role of plant secondary compounds and nutritional context.

Aspen (Populus tremuloides Michx.) has evolved a chemical defense system comprised of phenolic glycosides (PG), which effectively deter insect herbivory. However, much less is known about the role of PG and the nutritional quality of the associated plant community on aspen browse susceptibility to mammalian herbivores. In three successive periods during the growing season, we conducted experiments with sheep by offering leaves from two aspen stands with different concentrations of PG (LOW, HIGH) or aspen leaves vs. leaves from a forb (Utah pea, Lathyrus pauciflorus) or a grass (smooth brome, Bromus inermis Leyss.) growing in an aspen understory. Intake of aspen (19 to 35% PG) was low in all periods (1 to 6g/Kg(0.75) in 2hr) supporting the notion that aspen's defense system may contribute to its ecological success. However, lambs ate larger amounts of LOW than of HIGH suggesting that sheep could discriminate between aspen stands with different concentrations of PG, even when both stands were relatively well defended. Concentration of nutrients and chemical defenses in aspen leaves remained fairly stable across the growing season, and preference for aspen increased over the growing season. In contrast, preference for the forb and the grass decreased across the growing season in concert with a decline in the nutritional quality of these plants. The data suggest that nutritional context of aspen and associated forage species drove preference more than contrasts in defense chemistry of aspen. There may be periods of "susceptibility" of aspen use by mammalian herbivores, despite high concentrations of chemical defenses, which can potentially be targeted by management to reduce aspen herbivory.

Fire severity alters plant regeneration patterns and defense against herbivores in mixed aspen forests

Fire and herbivory are primary disturbances that often overlap and strongly influence plant community development, but it is unclear how herbivory changes in relation to variability in burn severity. With climate change expected to alter fire regimes globally there is a critical need to understand how heterogeneity in post‐fire habitat conditions modifies plant–herbivore interactions. We examined herbivory patterns, growth responses and defense chemistry expression (phenolic glycoside, condensed tannins) of regenerating aspen Populus tremuloides that experienced variable burn severity in the 2010 Twitchell Canyon Fire, Utah, USA. Browse damage was approximately 60% lower in moderate and high burn severity plots compared to low severity and unburned plots. Aspen regeneration density was 2.3 and 3.1 fold greater in high and moderate severity burn plots than in low severity and unburned plots. High burn severity stimulated photosynthesis, vertical growth and biomass accumulation. Defense chemistry expression responded dynamically over time depending on burn severity. From June to August, phenolic glycoside concentrations showed no significant change in unburned and low severity fire conditions but increased 79% and 139% in moderate and high severity burn environments. By the end of summer, condensed tannins increased six‐fold in high severity burn plots, with increases of 50% or less in the lower burn severity plots. Deer activity, as defined by pellet counts, was inversely related to fire severity and positively related to browse damage. Elk and cattle activity showed no significant relationship with browse activity. Greater light availability in higher severity burn environments appears to enhance tolerance and resistance of aspen against herbivory by increasing growth potential and defense chemistry expression of aspen. These results suggest that burn severity influences plant–herbivore interactions through bottom–up and top–down mechanisms, and that higher fire severity increases post‐disturbance vegetation recruitment potential by increasing resilience to herbivory.

Root Chemistry in Populus tremuloides: Effects of Soil Nutrients, Defoliation, and Genotype

Although genetic, environmental, and G x E effects on aboveground phytochemistry have been well documented in trembling aspen (Populus tremuloides), little work has focused on the same factors affecting tissues underground. Belowground plant defenses are likely important mediators of root-feeding herbivores that can strongly influence plant fitness. We used a common garden of potted aspen trees to explore the individual and interactive effects of soil nutrient availability, foliar damage, genotype, and their interactions, on concentrations of phytochemicals in aspen roots. Our common garden experiment employed 12 aspen genotypes that were planted into either low- or high-nutrient soil environments. Half of the trees were subjected to defoliation for two successive years, while the others were protected from damage. At the end of the growing season after the second defoliation, we harvested the trees to obtain root samples for which we assessed levels of phenolic glycosides, condensed tannins, nitrogen, and starch. Phenolic glycosides were most affected by genotype, while the other root phytochemicals were most responsive to soil nutrient conditions. The effects of defoliation were observed in interaction with soil nutrient environment and/or genotype. Interestingly, the effect of defoliation on phenolic glycosides was mediated by soil nutrients, whereas the effect of defoliation on condensed tannins was observed in concert with effects of both soil nutrients and genotype. Comparison of data from this study with an earlier, related study revealed that concentrations of phenolic glycosides and condensed tannins are lower in roots than leaves, and less responsive to defoliation. That soil nutrient environment affects root phytochemical concentrations is not unexpected given the intimate association of roots and soil, but the complex interactions between soil nutrients, aboveground damage, and genotype, and their effects on root phytochemistry, are intriguing. Variation in root chemistry could have wide-reaching effects on soil microbial communities, nutrient cycling, and herbivores. Additionally, the response of phytochemicals to damage across organs can link different, spatially separated herbivores as they use different parts of the same plant resource.

Reserves Accumulated in Non-Photosynthetic Organs during the Previous Growing Season Drive Plant Defenses and Growth in Aspen in the Subsequent Growing Season

Plants store non-structural carbohydrates (NSC), nitrogen (N), as well as other macro and micronutrients, in their stems and roots; the role of these stored reserves in plant growth and defense under herbivory pressure is poorly understood, particularly in trees. Trembling aspen (Populus tremuloides) seedlings with different NSC and N reserves accumulated during the previous growing season were generated in the greenhouse. Based on NSC and N contents, seedlings were assigned to one of three reserve statuses: Low N-Low NSC, High N-Medium NSC, or High N-High NSC. In the subsequent growing season, half of the seedlings in each reserve status was subjected to defoliation by forest tent caterpillar (Malacosoma disstria) while the other half was left untreated. Following defoliation, the effect of reserves was measured on foliar chemistry (N, NSC) and caterpillar performance (larval development). Due to their importance in herbivore feeding, we also quantified concentrations of phenolic glycoside compounds in foliage. Seedlings in Low N-Low NSC reserve status contained higher amounts of induced phenolic glycosides, grew little, and supported fewer caterpillars. In contrast, aspen seedlings in High N-Medium or High NSC reserve statuses contained lower amounts of induced phenolic glycosides, grew faster, and some of the caterpillars which fed on these seedlings developed up to their fourth instar. Furthermore, multiple regression analysis indicated that foliar phenolic glycoside concentration was related to reserve chemistry (NSC, N). Overall, these results demonstrate that reserves accumulated during the previous growing season can influence tree defense and growth in the subsequent growing season. Additionally, our study concluded that the NSC/N ratio of reserves in the previous growing season represents a better measure of resources available for use in defense and growth than the foliar NSC/N ratios.

Assessing the Impact of Smoke Exposure in Grapes: Development and Validation of a HPLC-MS/MS Method for the Quantitative Analysis of Smoke-Derived Phenolic Glycosides in Grapes and Wine

Bushfires occur frequently in the vicinity of grape growing regions, resulting in smoke drifting over the vineyards. Wine made from smoked grapes is often downgraded or unfit for sale due to negative sensory characters. To manage or avoid the risk of producing smoke-affected wine, a diagnostic assay was developed for assessing the extent of smoke exposure in grapes and the resulting wines. The method relies on the quantitation of the glycosidic grape metabolites that are formed from major volatile phenols present in smoke. Using HPLC-MS/MS with APCI, a quantitation method for phenolic glycosides as smoke marker compounds was developed and validated. The method was confirmed to be of sufficient sensitivity and reliability to use as a diagnostic assay. On the basis of phenolic glycoside concentrations, grapes or wine can be assessed as smoke exposed or not, and the relative intensity of smoke exposure can be determined.

Re-evaluating the role of ascorbic acid and phenolic glycosides in ozone scavenging in the leaf apoplast of Arabidopsis thaliana L.

Phenolic glycosides are effective reactive oxygen scavengers and peroxidase substrates, suggesting that compounds in addition to ascorbate may have functional importance in defence responses against ozone (O(3)), especially in the leaf apoplast. The apoplastic concentrations of ascorbic acid (AA) and phenolic glycosides in Arabidopsis thaliana L. Col-0 wild-type plants were determined following exposure to a range of O(3) concentrations (5, 125 or 175 nL L(-1)) in controlled environment chambers. AA in leaf apoplast extracts was almost entirely oxidized in all treatments, suggesting that O(3) scavenging by direct reactions with reduced AA was very limited. In regard to phenolics, O(3) stimulated transcription of numerous phenylpropanoid pathway genes and increased the apoplastic concentration of sinapoyl malate. However, modelling of O(3) scavenging in the apoplast indicated that sinapoyl malate concentrations were too low to be effective protectants. Furthermore, null mutants for sinapoyl esters (fah1-7), kaempferol glycosides (tt4-1) and the double mutant (tt4-1/fah1-7) were equally sensitive to chronic O(3) as Ler-0 wild-type plants. These results indicate that current understanding of O(3) defence schemes deserves reassessment as mechanisms other than direct scavenging of O(3) by extracellular AA and antioxidant activity of some phenolics may predominate in some plant species.

Tree competition and defense against herbivores: currency matters when counting the cost

Browsing by herbivores profoundly affects the nature and extent of woody plant communities through a variety of mechanisms, including alterations to disturbance regimes (such as fire frequency), indirect effects on nutrient cycling and soil fertility, and changes to net primary production (Hobbs 1996). Plants have evolved myriad ways to avoid being eaten, ranging from the development of spiny, unpalatable foliage to the production of secondary metabolites as defense compounds (Bennett and Wallsgrove 1994). In analyzing the responses of plants to herbivory and the consequences of these responses for plant–plant competition, there has often been an implicit assumption that such defense strategies come at a cost to the individual (more defense means less growth or reproduction), thereby providing the basis for fundamental ecological and evolutionary hypotheses about allocation of limited resources (Strauss et al. 2002). Several hypotheses have been used as a framework for investigating the patterns and trade-offs of plant defense against herbivores (Stamp 2003), especially in the ecological literature. These hypotheses have been used singularly, or even in combination, to try and produce a unifying theory of plant– herbivore ecology and evolution. All of these hypotheses have been criticized in the literature. Although there are many instances when hypotheses have predicted empirical observations correctly, there are also many instances when either they have not, or they have been misinterpreted (Stamp 2003). One of these hypotheses, the carbon/nutrient balance (CNB) hypothesis, was originally developed to explain the influence of soil nutrients and shade on plant defense chemistry (Bryant et al. 1983). The CNB hypothesis suggests that species adapted to fertile sites (such as early-successional species) will respond to herbivory by utilizing stored resources for compensatory growth, while slower-growing species adapted to relatively infertile soils will instead protect their leaves by investing more carbon in anti-herbivory defense compounds. Such a hypothesis is appealing, as it makes specific predictions about patterns of allocation to plant secondary metabolite production, which have often been confirmed by empirical observation (reviewed by Stamp 2003). However, the CNB hypothesis has also been criticized, as there are many instances when predictions do not match observations (e.g., Hamilton et al. 2001, Koricheva 2002). In this issue, Calder et al. (2011) report that conifer expansion reduces the competitive ability of Populus tremuloides (trembling aspen). The transition from aspen to conifer forests in western North America often coincides with a transition to soils with lower pH and lower nitrogen concentrations (Jerabkova et al. 2006), at least partly mediated by the chemical composition of conifer needles being added to the litter. The loss of early-successional species, such as aspen, in these systems over time has been attributed to their physiological preference for nitrogen uptake as NO3, which may become less available in soils as conifer dominance increases (Kronzucker et al. 1997, Min et al. 1998, Kronzucker et al. 2003). While changes in nutrient availability may partly explain this successional trajectory, the canopies of evergreen conifers and deciduous broad-leaf trees also provide very different light environments for seedlings. Calder et al. (2011) show that by reducing light availability and altering soil characteristics, a conifer species (Abies lasiocarpa, subalpine fir) inhibited the growth of competing aspen trees. However, these abiotic changes induced by conifer dominance had another effect: they led to lower concentrations of phenolic glycosides (PGs) and condensed tannins (CTs) in aspen leaves, two groups of Commentary

Conifer expansion reduces the competitive ability and herbivore defense of aspen by modifying light environment and soil chemistry

Disturbance patterns strongly influence plant community structure. What remains less clear, particularly at a mechanistic level, is how changes in disturbance cycles alter successional outcomes in plant communities. There is evidence that fire suppression is resulting in longer fire return intervals in subalpine forests and that these lengthened intervals increase competitive interactions between aspen and conifer species. We conducted a field and greenhouse study to compare photosynthesis, growth and defense responses of quaking aspen and subalpine fir regeneration under light reductions and shifts in soil chemistry that occur as conifers increase in dominance. The studies demonstrated that aspen regeneration was substantially more sensitive to light and soil resource limitations than that of subalpine fir. For aspen, light reductions and/or shifts in soil chemistry limited height growth, biomass gain, photosynthesis and the production of defense compounds (phenolic glycosides and condensed tannins). Biomass gain and phenolic glycoside concentrations were co-limited by light reduction and changes in soil chemistry. In contrast, subalpine fir seedlings tended to be more tolerant of low light conditions and showed no sensitivity to changes in soil chemistry. Unlike aspen, subalpine fir increased its root to shoot ratio on conifer soils, which may partially explain its maintenance of growth and defense. The results suggest that increasing dominance of conifers in subalpine forests alters light conditions and soil chemistry in a way that places greater physiological and growth constraints on aspen than subalpine fir, with a likely outcome being more successful recruitment of conifers and losses in aspen cover.