Kennedy F. Rubert-Nason

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.

Rapid phytochemical analysis of birch (Betula) and poplar (Populus) foliage by near-infrared reflectance spectroscopy

AbstractPoplar (Populus) and birch (Betula) species are widely distributed throughout the northern hemisphere, where they are foundation species in forest ecosystems and serve as important sources of pulpwood. The ecology of these species is strongly linked to their foliar chemistry, creating demand for a rapid, inexpensive method to analyze phytochemistry. Our study demonstrates the feasibility of using near-infrared reflectance spectroscopy (NIRS) as an inexpensive, high-throughput tool for determining primary (e.g., nitrogen, sugars, starch) and secondary (e.g., tannins, phenolic glycosides) foliar chemistry of Populus and Betula species, and identifies conditions necessary for obtaining reliable quantitative data. We developed calibrations with high predictive power (residual predictive deviations ≤ 7.4) by relating phytochemical concentrations determined with classical analytical methods (e.g., spectrophotometric assays, liquid chromatography) to NIR spectra, using modified partial least squares regression. We determine that NIRS, although less sensitive and precise than classical methods for some compounds, provides useful predictions in a much faster, less expensive manner than do classical methods. Graphical abstractNear-infrared reflectance spectroscopy with calibrations based on modified partial least squares regression can provide quantitative measurements of foliar nitrogen, carbohydrate, tannin, and phenolic glycoside content in poplar and birch

Phytochemical traits underlie genotypic variation in susceptibility of quaking aspen (Populus tremuloides) to browsing by a keystone forest ungulate

Summary 1.Overbrowsing by ungulates is a major cause of poor aspen stand regeneration across North America and Eurasia. In general, factors driving ungulate browser preferences include concentrations of plant secondary compounds and the nutritional composition (non-structural carbohydrates, protein, and minerals) of foliage. While each of these phytochemical factors has been shown to independently influence ungulate preference, the relative impact of each factor is unknown, as no study to date has examined them simultaneously. 2.Plant fitness depends not only on the capacity of plants to resist browsing, but also on their capacity to tolerate browsing once it has occurred. Little is known of aspen tolerance to browsing, which inflicts a different form of damage than insect herbivory. 3.We employed multiple aspen genotypes, replicate trees of which were subjected to different soil nutrient treatments, to investigate: 1) the effects of aspen genotype, nutrient treatment, and genotype x nutrient interactions on susceptibility to browsing by white-tailed deer, 2) the phytochemical basis for the patterns observed in (1), and 3) the effects of genotype, soil nutrients, and their interaction on short-term tolerance to deer browsing. 4.Aspen genotypes varied markedly in their vernal susceptibility to deer browsing. Genetic variation in early season levels of non-structural carbohydrates (sugars), protein, and multiple macro- and trace minerals had the strongest influence on tree susceptibility to browsing. In contrast, levels of phytochemical defenses had minimal effects, although the range of levels expressed in this study was small. Soil nutrient availability did not significantly influence deer preference. 5.The extent of browsing affected post-browse tolerance across genotypes. Soil nutrient treatment had little differential effect on tolerance, and, for the most part, genotypes did not display differential tolerance to browsing, regardless of which soil nutrient treatment they experienced. 6.Synthesis: Genetic variation for susceptibility to browsing indicates that ungulate browsers have the potential to be agents of selection in aspen populations. In contrast with previous studies in aspen highlighting the importance of phytochemical defenses in shaping preferences of browsing mammals, our results indicate that the nutritional composition of foliage (sugars, protein, and mineral concentrations) can have sizable effects on preference. The observed lack of influence of soil nutrient availability on tree browsing tolerance contrasts with predictions of the limiting resource model, the prevailing model for plant tolerance. This article is protected by copyright. All rights reserved.

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.

Effects of Elevated Atmospheric Carbon Dioxide and Tropospheric Ozone on Phytochemical Composition of Trembling Aspen (Populus tremuloides) and Paper Birch (Betula papyrifera)

Anthropogenic activities are altering levels of atmospheric carbon dioxide (CO2) and tropospheric ozone (O3). These changes can alter phytochemistry, and in turn, influence ecosystem processes. We assessed the individual and combined effects of elevated CO2 and O3 on the phytochemical composition of two tree species common to early successional, northern temperate forests. Trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera) were grown at the Aspen FACE (Free-Air Carbon dioxide and ozone Enrichment) facility under four combinations of ambient and elevated CO2 and O3. We measured, over three years (2006–08), the effects of CO2 and O3 on a suite of foliar traits known to influence forest functioning. Elevated CO2 had minimal effect on foliar nitrogen and carbohydrate levels in either tree species, and increased synthesis of condensed tannins and fiber in aspen, but not birch. Elevated O3 decreased nitrogen levels in both tree species and increased production of sugar, condensed tannins, fiber, and lignin in aspen, but not birch. The magnitude of responses to elevated CO2 and O3 varied seasonally for both tree species. When co-occurring, CO2 offset most of the changes in foliar chemistry expressed under elevated O3 alone. Our results suggest that levels of CO2 and O3 predicted for the mid-twenty-first century will alter the foliar chemistry of northern temperate forests with likely consequences for forest community and ecosystem dynamics.

Photosynthetic acclimation of an evergreen broadleaved shrub ( Ammopiptanthus mongolicus ) to seasonal climate extremes on the Alxa Plateau, a cold desert ecosystem

Key messageSurvival of Ammopiptanthus mongolicus in a cold desert environment is facilitated by high photosynthesis rates in spring and summer, and efficient photoprotective strategies in winter cold.AbstractWoody evergreen plants inhabiting cold desert ecosystems must retain their foliage amidst chronically dry conditions and large seasonal temperature variations. To understand the strategies enabling survival of evergreens in these environments, we monitored seasonal changes in foliar gas exchange and photosynthetic traits of Ammopiptanthus mongolicus, an evergreen broadleaved shrub native to the cold desert of northwestern China. We found that photosynthesis was relatively higher in spring and summer and lower in fall and winter. Transitioning from spring to summer, A. mongolicus maintained high photosynthetic capacity (Amax). Transitioning into fall, the Amax and maximum stomatal conductance (gsmax) decreased, while the relative stomatal limitation to photosynthesis (Ls) increased. In winter, A. mongolicus decreased Amax, maximum quantum efficiency of photosystem II (Fv/Fm), maximum RuBisCo carboxylation rates (Vcmax), maximum RuBP regeneration rates (Jmax), and photosynthetic nitrogen-use efficiency (PNUEmax) relative to other seasons. Collectively, these results suggest that A. mongolicus adapts physiologically to maximize carbon assimilation during spring and summer, and to maximize foliar resistance to cold stress at the expense of photosynthesis in winter. Foliage was protected against photo-oxidative damage during temperature extremes in winter by dark-sustained thermal energy dissipation. Overall, our study reveals that multiple photosynthetic adjustments, varying among the seasons, enable the survival of cold desert evergreens.

Purification and Analysis of Salicinoids

DOI: 10.2174/1573411014666171221131933 Abstract: Background: Salicinoids (a type of phenolic glycoside) are plant secondary metabolites with chemical structures based on salicyl alcohol conjugated to b-D-glucopyranose, with demonstrated antiherbivore activity. These compounds have been purified and quantified in a variety of contexts. Validation of published methods is often incomplete, and there is no broadly-applicable reference procedure.