Foliar Phenolic Concentrations Research Articles

Eucalyptus species maintain secondary metabolite production under water stress conditions at the expense of growth

AbstractPlants have evolved a vast array of secondary metabolites that help defend them against natural enemy attack. The production of these secondary metabolites is influenced by environmental factors, such as temperature, rainfall (soil water availability) and atmospheric [CO2], which may be altered under climate change. This study aimed to test how two of these environmental factors, namely soil water availability and [CO2], will affect secondary metabolite and biomass production in Eucalypts. To investigate this, we measured secondary metabolite and biomass production of three Eucalypt species (Eucalyptus grandis, E. moluccana, E. saligna) grown under ambient and elevated [CO2] (400 and 600 ppm, respectively) and water‐stressed and well‐watered conditions, in a fully factorial glasshouse experiment. The secondary metabolites measured were foliar phenolic concentration as well as terpene and green leaf volatile emissions. We found that water stress did not alter secondary metabolite production. Unsurprisingly, the water‐stressed plants maximised their water uptake potential by reducing shoot biomass but maintaining root biomass. The detrimental effects of water stress on shoot biomass production were not reduced under elevated [CO2] compared to ambient [CO2], despite all species experiencing significant reductions in stomatal conductance. Further, [CO2] as a single factor did not have a significant effect on species’ net carbon gain, with an increase in green leaf volatile emissions under elevated [CO2] being mitigated by a reduction in shoot biomass production. These results suggest that reductions in carbon gains due to water stress will affect the growth of Eucalypts rather than their chemical defence capabilities.

Still armed after domestication? Impacts of domestication and agronomic selection on silicon defences in cereals

Abstract Plant phenotypes reflect trade‐offs between competing resource‐intensive physiological processes. A shift in resource allocation, away from anti‐herbivore defences and towards growth and reproduction, is predicted through plant domestication, such that crops are faster growing and higher yielding than their wild ancestors. These changes are hypothesized to have come at the cost of defence investment, leaving crops “disarmed by domestication”. Silicon is the principal anti‐herbivore defence in grasses, including many of our most important staple cereal crops, but the impact of domestication on silicon‐based defences is unknown. We measured the effects of both domestication and modern agronomic selection on growth rate and a suite of anti‐herbivore defences, specifically leaf toughness, silicon and phenolic concentrations. Our comparison of wild, landrace and modern cultivated cereals spanned multiple cereal species, including wheat, barley and maize, sampling eight independent domestication events and five examples of modern agronomic selection. Leaf silicon concentration showed a small, but significant, 10% reduction through domestication, but there was no effect of modern agronomic selection, and phenolic concentration was not affected by either factor. Silicon concentration correlated positively with leaf tensile strength, but negatively with foliar phenolic concentrations, suggesting a trade‐off between chemical and physical defences. Size‐standardized growth rate was independent of domestication status, and did not trade‐off with silicon or phenolic defences. However, modelling showed that relative growth rate slowed more with increasing size in plants with higher silicon levels, so that they reached a smaller final size, implying a cost of silicon‐based defence. We found the opposite pattern for phenolic‐based defence, with increasing phenolic concentrations associated with a greater plant size at maturity, and faster maximum relative growth rates. Silicon‐based defences have been reduced in cereals through domestication, consistent with our predicted costs of these defences to growth. However, modern agronomic selection has not influenced silicon defences in cereal crops and the small decrease in silicon concentration associated with domestication is unlikely to have a major effect on the ability of cereals to withstand a range of abiotic and biotic stresses. These findings have broad implications for crop protection and our understanding of plant trade‐offs. A plain language summary is available for this article.

Effects of stand density on ecosystem properties of subalpine forests in the southern Rocky Mountains, USA

• Mixed coniferous, subalpine forest communities in the Rocky Mountains are historically dense and have experienced infrequent, high-severity fire. However, many of these high-elevation stands are thinned for a number of perceived benefits.• We explored the effects of forest stand density on ecosystem properties in subalpine forests in Colorado, USA, 17–18 y after forests were managed for timber.• Forest structure significantly altered the composition and chemical signature of plant communities. Previously managed stands contained lower density of overstory trees and higher ground cover compared to paired reference stands. Foliar phenolic concentration of several species was negatively related to basal area of overstory trees. Furthermore, reductions in stand density increased total foliar phenolic:nitrogen ratios in some species, suggesting that gap formation may drive long-term changes in litter quality. Despite significant changes in forest structure, reductions in stand density did not leave a strong legacy in surface soil properties, likely due to the integrity of soil organic matter reserves.• Changes in forest structure associated with past management has left a long-term impact on plant communities but has only subtly altered soil nutrient cycling, possibly due to trade offs between litter decomposability and microclimate associated with reductions in canopy cover.

Performance and Secondary Chemistry of Two Hybrid Aspen (Populus tremula L. x Populus tremuloides Michx.) Clones in Long-Term Elevated Ozone Exposure

The effects of moderately elevated ozone (ca. 35 ppb) on the growth and secondary chemistry of the leaves of two soil-grown Finnish hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) clones with different ozone sensitivities were studied at an open-air exposure field in Kuopio, Finland. Stomatal conductance, photosynthetic rate, and chlorophyll fluorescence were measured during the third growing season. Foliar phenolic concentrations, ergosterol concentration of fine roots, and final dry mass of the trees were determined at the end of the third growing season. Elevated ozone increased the ectomycorrhizal status of the fine roots but had no effect on gas exchange or on the final biomass of either of the clones, indicating equal sensitivity to ozone and no effect of elevated ozone on the intraspecific competitive ability of the clones after three growing seasons. However, in agreement with the data from potted plants of the same clones after two growing seasons, significant differences between the clones were found in all parameters measured. A negative correlation between growth and high concentrations of foliar phenolics indicated that allocation to secondary chemistry also was costly in terms of growth under high resource availability.

Differences in leaf characteristics between ozone-sensitive and ozone-tolerant hybrid aspen (Populus tremula x Populus tremuloides) clones

The authors analyzed a suite of leaf characteristics that might help to explain the difference between ozone-sensitive and ozone-tolerant hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) clones. An open-field experiment comprising ambient ozone and 1.5x ambient ozone concentration (about 35 ppb) and two soil nitrogen regimes (60 and 140 kg N ha(-1) year(-1)) was conducted over two growing seasons on potted plants of eight hybrid aspen clones. Four of the clones had previously been determined to be ozone sensitive based on impaired growth in response to elevated ozone concentration. Photosynthetic rate, chlorophyll fluorescence, and concentrations of chlorophyll, protein and carbohydrates were analyzed three times during the second growing season, and foliar phenolic concentrations were measured at the end of the second growing season. Nitrogen amendment counteracted the effects of ozone, but had no effect on growth-related ozone sensitivity of the clones. Ozone-sensitive clones had higher photosynthetic capacity and higher concentrations of Rubisco and phenolics than ozone-tolerant clones, but the effects of ozone were similar in the sensitive and tolerant groups. Nitrogen addition had no effect on phenolic concentration, but elevated ozone concentration increased the concentrations of chlorogenic acid and (+)-catechin. This study suggests that condensed tannins and catechin, but not salicylates or flavonol glycosides, play a role in the ozone tolerance of hybrid aspen.

The Significance of Ectomycorrhizas in Chemical Quality of Silver Birch Foliage and Above-Ground Insect Herbivore Performance

We tested whether the ectomycorrhizal (ECM) infection level of roots of silver birch (Betula pendula) affects performance of above-ground insect herbivores by increasing available plant biomass, by enhancing availability of nutrients, or by modifying concentration of defense compounds, i.e., phenolics, in birch foliage. Insect performance was determined for a phloem-feeding generalist (Lygus rugulipennis, the European tarnished plant bug), a phloem-feeding specialist (Calaphis flava, the birch aphid), and a chewing generalist (Epirrita autumnata, the autumnal moth larva). Silver birch plantlets had either natural ECM infection level (on average 24% of short roots with ECM), reduced ECM infection level with fungicide (F-, 9% ECM), or enhanced ECM infection level after inoculation with the fungus Paxillus involutus (PI+, 45% ECM) or Leccinum versipelle (LV+, 42% ECM). In general, the most pronounced effect of ECM was observed on growth of plantlets, i.e., stem growth decreased. In PI+-treated plants, leaf biomass also decreased. The effect of mycorrhizal colonization on the host plant's nitrogen (N) and phosphorous (P) concentration was dependent on the mycorrhizal species and experiment. Fungicide treatment did not cause a consistent decrease in nutrients. Finally, defense of birch against herbivory, expressed as foliar phenolic concentration in plantlets, was not modified by ECM. However, E. autumnata had a significantly higher relative growth rate on PI+ plantlets with high leaf N concentration than on LV+ plantlets with low leaf N concentration. The birch aphid C. flava produced significantly less nymphs on birches with enhanced ECM infection levels (PI+ and LV+ plantlets) than on controls. In summary, our data show that the ECM infection level mainly affects the growth parameters of plantlets, whereas effects on leaf chemical quality are minor. Our data show that effects of ECM infection of birch roots on aboveground herbivores are multifaceted and depend on the fungal species forming ectomycorrhiza and also on the degree of specialization and feeding guild of insects.

Phenolic-rich leaf carbon fractions differentially influence microbial respiration and plant growth

Phenolics can reduce soil nutrient availability, either indirectly by stimulating microbial nitrogen (N) immobilization or directly by enhancing physical protection within soil. Phenolic-rich plants may therefore negatively affect neighboring plant growth by restricting the N supply. We used a slow-growing, phenolic-rich alpine forb, Acomastylis rossii, to test the hypothesis that phenolic-rich carbon (C) fractions stimulate microbial population growth and reduce plant growth. We generated low-molecular-weight (LMW) fractions, tannin fractions, and total soluble C fractions from A. rossii and measured their effects on soil respiration and growth of Deschampsia caespitosa, a fast-growing, co-dominant grass. Fraction effects fell into two distinct categories: (1) fractions did not increase soil respiration and killed D. caespitosa plants, or (2) fractions stimulated soil respiration and reduced plant growth and plant N concentration while simultaneously inhibiting root growth. The LMW phenolic-rich fractions increased soil respiration and reduced plant growth more than tannins. These results suggest that phenolic compounds can inhibit root growth directly as well as indirectly affect growth by reducing pools of plant available N by stimulating soil microbes. Both mechanisms illustrate how below-ground phenolic effects may influence the growth of neighboring plants. We also examined patterns of foliar phenolic concentrations among populations of A. rossii across a natural productivity gradient (productivity was used as a proxy for competition intensity). Concentrations of some LMW phenolics increased significantly in more productive sites where A. rossii is a competitive equal with the faster growing D. caespitosa. Taken together, our results contribute important information to the growing body of evidence indicating that the quality of C moving from plants to soils can have significant effects on neighboring plant performance, potentially associated with phytoxic effects, and indirect effects on soil biogeochemistry.

Willow genotype, but not drought treatment, affects foliar phenolic concentrations and leaf‐beetle resistance

AbstractIn a greenhouse experiment we examined the effect of willow genotype and irrigation regime (moderate drought and well‐watered) on plant growth parameters, foliar nitrogen, and phenolic concentrations, as well as on the preference and performance of the blue leaf beetle, Phratora vulgatissima (L.) (Coleoptera: Chrysomelidae). The 10 vegetatively propagated willow genotypes in the experiments were F2 full‐sibling hybrids, originated from a cross between Salix viminalis (L.) (Salicaceae) (high in condensed tannins) and Salix dasyclados (L.) (Salicaceae) (rich in phenolic glycosides). Insect bioassays were conducted on detached leaves in Petri dishes as well as with free‐living insects on intact potted plants. The 10‐week long irrigation treatments caused statistically significant phenotypic differences in the potted willow saplings. Total biomass was somewhat higher in the well‐watered treatment. The root to total biomass ratio was higher in the drought‐treatment plants. There was significant genotypic variation in foliar nitrogen concentrations, and they were higher in the drought‐treatment plants. There was also a strong genotypic variation in each of the phenolic substances analyzed. Condensed tannins, which accounted for the greatest proportion of total phenolic mass, were higher in the well‐watered treatment. There was, however, no difference in levels of the other phenolics (salicylates, cinnamic acid, flavonoids, and chlorogenic acid) between irrigation treatments. The sum of these phenolics was higher in the well‐watered treatment. There was a strong variation in P. vulgatissima larval development on different willow genotypes, and larval performance was negatively correlated with levels of salicylates and cinnamic acid. There was, however, no effect of irrigation treatment on larval performance. Phratora vulgatissima preferred to feed on well‐watered plants, and we found a preference for oviposition there, but neither feeding nor oviposition site preference was affected by willow genotype. Adult feeding and oviposition preferences were not correlated with larval performance.

Ultraviolet-B radiation alters phenolic salicylate and flavonoid composition of Populus trichocarpa leaves.

We investigated foliar phenolic composition of field- and greenhouse-grown Populus trichocarpa Torr. & A. Gray (black cottonwood) ramets subjected to near zero (0x), ambient (1x) or twice ambient (2x) concentrations of biologically effective ultraviolet-B (UV-B) radiation. After a 3-month treatment period, several age classes of foliage samples were harvested and the phenolic compounds extracted, separated by high performance liquid chromatography and identified and quantified by diode-array spectrometry and mass spectrometry. Foliar phenolic concentration was greater in 1x- and 2x-treated tissue than in 0x-treated tissue. Phenolic compounds that increased in response to UV-B radiation were predominantly flavonoids, primarily quercetin and kaempferol glycosides. Enhancement of UV-B radiation from 1x to 2x ambient concentration did not result in further flavonoid accumulation in either greenhouse or field ramets; however, a non-flavonoid phenolic glycoside, salicortin, increased in response to an increase in UV-B radiation from 1x to 2x ambient concentration. Increased salicortin concentrations accounted for at least 30-40% of the total (5%) increase in UV-absorption potential of 2x-treated tissue. Because salicortin and other salicylates are important in plant-herbivore-predator relationships, these increases are discussed in the context of collateral feeding studies. We conclude that enhanced solar UV-B radiation may significantly alter trophic structure in some ecosystems by stimulating specific phenolic compounds.

Effects of nutrient availability on biomass allocation as well as constitutive and rapid induced herbivore resistance in poplar

Many studies have examined effects of nutrient availability on constitutive herbivore resistance of plants, but few have addressed effects on expression of rapid induced resistance (RIR). We quantified effects of two levels of nutrient availability on growth, biomass allocation, photosynthesis, and constitutive secondary metabolism of black poplar (Populus nigra). We also examined effects of nutrient availability on expression of constitutive resistance of poplar to gypsy moth (Lymantria dispar) and whitemarked tussock moth (Orgyia leucostigma), as well as RIR to both folivores in response to localized herbivory by gypsy moth.The high nutrient treatment had no effect on photosynthetic rate of poplar, but dramatically increased relative growth rate, total biomass, and total leaf area, while foliar phenolic concentrations and root:shoot ratio decreased. Plant growth was negatively correlated with foliar phenolic concentrations, which is consistent with predictions of the Growth/Differentiation Balance Hypothesis when increased nutrient availability increases growth without affecting photosynthesis. These responses of root:shoot ratio and constitutive secondary metabolism to nutrient availability are consistent with those proposed by models of adaptive phenotypic plasticity in resource allocation patterns.Nutrient availability affected constitutive resistance of poplar to first and fifth instar gypsy moth larvae, which grew much faster on high fertility plants. However, nutrient availability had no effect on constitutive resistance to whitemarked tussock moth. Localized herbivory elicited systemic RIR in poplar within 72 hours. However, the magnitude of RIR was dependent on nutrient availability, with differing effects on the two insect species. Expression of RIR to gypsy moth was most dramatic in the high fertility treatment. In contrast, RIR to whitemarked tussock moth was expressed only in the low fertility treatment. The idiosyncratic nature of effects of nutrient availability on constitutive and induced resistance challenges the value of using insect bioassays as surrogate measures of secondary metabolism for testing allocation models of plant defense, as well as the value of generalized plant defense models for predicting effects of environmental variation on resistance to specific herbivores. These results also suggest that the effects of nutrient availability on the expression of RIR may represent a largely over‐looked source of variation in plant/herbivore interactions.

Effects of elevated atmospheric carbon dioxide on insect–plant interactions

Effects of elevated atmospheric carbon dioxide on insect–plant interactions

Responses of Pinus sylvestris branches to simulated herbivory are modified by tree sink/source dynamics and by external resources

1. It is claimed that the quality of foliage following defoliation depends on carbon/nutrient balance of the tree. To study the importance of sink/source regulation for the quality of foliage, as well as for its quantity, Pinus sylvestris trees were defoliated and fertilized both in southern Finland and at the tree line in northern Finland. 2. The pattern of defoliation in a shoot was more decisive for quantitative changes in new foliage than its extent: removal of similar amounts of foliage from different branch parts led to different outcomes. 3. Defoliation of 50% spread evenly within a shoot, or applied to the basal part of a shoot only, did not alter production of new foliage, whereas defoliation applied to the apical part of a shoot decreased the mass and length of needles in the new shoot. Defoliation of apically located 1‐year‐old needles of the branch leader shoot, but not of 2‐year‐old ones, significantly reduced the mass and length of needles in new shoots. 4. These results are consistent with the explanation that damage alters the ability of shoots and branches to form strong meristematic sinks and that sink strength determines the ability of these meristems to draw resources from the common pool of the tree. 5. Defoliation of the main photosynthate source lowered concentrations of the fructose and glucose, indicating shortage of carbon. However, whole‐tree defoliation did not affect the concentrations of individual foliar sugars. 6. Traits describing pine shoot growth correlated negatively with foliar phenolic concentrations but not with concentrations of other secondary compounds. Concentrations of foliage phenolics consistently increased after defoliation, while terpenoids, putatively the main class of defensive compounds in Scots Pine, did not respond to defoliation. Defoliation of a branch or a whole tree had only slight effects on the concentrations of fibre, mono‐ and sesquiterpenes, resin acids or nitrogen. 7. Likewise, fertilization significantly increased the concentration of some sesquiterpenes only in pine foliage. Whole‐branch defoliation and fertilization together had no effect on the concentration of fibre or nitrogen in pine foliage. 8. Altogether, the amount of foliar biomass removed, nutrients or carbon did not explain in any consistent way the qualitative changes in the pine foliage. Instead, results were consistent with simple physiological dependence of foliar traits on sink strength. Production of terpenoids reflected increased sink strength, but the production of phenolics was negatively correlated with sink strength. 9. The difference between shoot growth characteristics and foliage concentrations of phenolics and, on the other hand, terpenoids, may have a biosynthetic, instead of an ecological or evolutionary explanation. Protein synthesis, and thereby possibilities for growth, competes with phenolic synthesis (via phenylalanine) but not with terpenoid synthesis. 10. These results indicate that in Scots Pine the predicted trade‐off between growth and production of pooled carbon‐rich secondary compounds was found in phenolics but presumably for reasons external to the carbon/nutrient balance and growth/differentiation balance hypotheses. Instead, terpenoids did not behave as predicted by these theories.

The effect of elevated atmospheric CO2 concentration and nutrient supply on gas exchange, carbohydrates and foliar phenolic concentration in live oak (Quercus virginiana Mill.) seedlings

We determined the direct effects of atmospheric CO, concentration ((CO,)) on leaf gas exchange, phenolic and carbohy- drate allocation in live oak seedlings (Quercus virginiana Mill.) grown at present (370 μmol·molor elevated (520 μmol·mol (CO,) for 6 months in open-top chambers. Two soil nitrogen (N) treatments (20 and 90 μmol·mol total N, low N and high N treat- ments, respectively) were imposed by watering the plants every 5 d with modified water soluble fertilizer. Enhanced rates of leaf- level photosynthesis were maintained in plants subjected to elevated (COover the 6-month treatment period in both N treatments. A combination of increased rates of photosynthesis and decreased stomatal conductance was responsible for nearly doubling water use efficiency under elevated (COThe sustained increase in photosynthetic rate was accompanied by decreased dark respiration in elevated (COElevated (CO led to increased growth rates, while total non-structural carbohydrate (sugars and starch) concentra- tions were not significantly affected by elevated (CO,) treatment. The concentration of phenolic compounds increased significantly under elevated (CO,). (© Inra/Elsevier, Paris.)

Growth Responses of Tropical Shrubs to Treefall Gap Environments

To investigate the effects of differences in light and nutrient availability on growth, we planted seven species of shrubs in two genera, Miconia (Melastomataceae) and Piper (Piperaceae), into the centers, edges, and adjacent forest understory of four natural treefall gaps (275—3355 m2) in the tropical premontane rain forest of Costa Rica. We used rooted cutting of species typical of forest understory environments on the one hand and large clearings or disturbed areas on the other. We also compared growth rates of three Miconia species grown in shade houses under 2, 20, and 40% full sunlight. Both light and nutrient availability in newly formed gaps of these sizes were strongly buffered by the canopy and root systems of the surrounding forest. Total incident radiation was higher in gap centers (9—23% full sunlight) than in gap—forest edges (3—11%) or under intact forest canopy (.04—2%), but varied among similar microhabitats from different sites. Relative stem growth rates (RGRs) of all field—grown plants were significantly greater in gap centers than at edges or beneath forest understories. Fertilization did not significantly affect growth rate in any light environment. Light appears to be the most critical resource limiting growth at these gap sizes. In general, shade—tolerant species were less plastic than light—demanding species, but at these gap sizes grew as fast or faster in the gap centers. In shade—houses, the shade—tolerant species grew faster at 20% full sunlight and light—demanding species grew faster at 40% full sunlight. We found no evident of a trade—off between growth and foliar phenolic concentration in these species.