Differential distribution of leaf chemistry in eucalypt seedlings due to variation in whole-plant nutrient availability

Site Classification of Eucalyptus urophylla × Eucalyptus grandis Plantations in China

Background and Objectives: It is important to match species needs with site conditions for sustainable forestry. In Eucalyptus urophylla × Eucalyptus grandis plantations in southern Yunnan, China, species-site mismatches have led to inappropriate expansion and management, which has degraded forests and decreased efficiency in plantation production. Further research is needed to understand the relationship between tree growth and site productivity. We empirically explored site features and classified site types within these plantations in southern Yunnan. Our objective was to develop a theoretical basis for improving site selection for afforestation, and to establish intensive management in that region. Materials and Methods: 130 standard plots were set up in 1−15-year-old eucalyptus plantations in Pu’er and Lincang. We used quantification theory to examine the relationship between dominant tree growth traits and site factors. Hierarchical cluster analysis and canonical correlation analysis were applied to classify sites and evaluate the growth potential of E. urophylla × E. grandis plantations, respectively. Results: The multiple correlation coefficient between eight site factors (altitude, slope, slope position, aspect, soil depth, texture, bulk density, and litter thickness) and the quantitative growth of the dominant tree was 0.834 (p < 0.05). Slope position, altitude, and soil depth were the main factors contributing to the variation in stand growth. Plantation growth was best on lower slopes at relatively low altitude, where thick and weathered red soil layers existed. Conversely, the poorest plantations were located on upper slopes at higher altitude, with a thin semi-weathered purple soil layer. The soil factors total nitrogen (N) and potassium (K), trace boron (B), copper (Cu), and zinc (Zn) content, available phosphorous (P), and organic matter content in the soil influenced plantation growth. Conclusions. The addition of N, P, and K fertilizer as well as trace elements such as B, Cu, and Zn can promote the productivity of these plantations.

Genetic and chemical diversity of the toxic herb Jacobaea vulgaris Gaertn. (syn. Senecio jacobaea L.) in Northern Germany

Tansy ragwort, Jacobaea vulgaris Gaertn. (syn. Senecio jacobaea L.), is a common Asteraceae in Europe and Asia and known to be an invasive pest in several regions in the world. Recently it is also spreading immensely in native regions like Northern Germany. Pyrrolizidine alkaloids (PAs), which are found in high amounts in Jacobaea vulgaris, are toxic for humans and potentially lethal for grazing animals. In this study we investigated 27 populations of tansy ragwort in Northern Germany for their PA concentration and composition using liquid chromatography coupled to high resolution mass spectrometry. Furthermore, we investigated the genetic structure of selected populations using amplified length polymorphism markers. We detected 98 different PAs in the samples and considerable differences of PA composition between populations. In contrast, PA content of populations did not differ significantly. Genetic (4%) differentiation among populations was low while average genetic diversity was high (0.35). There was no correlation between genetic and geographic distance. Neither genetic markers nor chemical composition revealed any connection to the geographic pattern. As we could not detect any pattern in genetic or chemical diversity, we suggest that the existence of this diversity is a result of a broad interaction with the environment rather than that of evolutionary constraints in the current selection process driving PA composition in J. vulgaris in certain chemotypes.

Ingestion and Absorption of Eucalypt Monoterpenes in the Specialist Feeder, the Koala (Phascolarctos cinereus)

The koala is a specialist feeder with a diet consisting almost exclusively of potentially toxic eucalypt leaves. Monoterpenes, an abundant class of plant secondary metabolites in eucalypts, are highly lipophilic. Chronic absorption and systemic exposure can be anticipated for the koala, causing health effects in various ways when consumed in high amounts, but particularly causing alterations in immune function in this species. Therefore, careful leaf selection, efficient detoxification pathways, and other specialist adaptations are required to protect animals from acute intoxication. This is the first paper providing insight into the systemic exposure of koalas to these compounds. Profiles of six selected major monoterpenes were investigated in the ingesta of deceased koalas from four different regions of NSW and South-East Queensland. Concentrations of the same compounds were measured in lymphoid tissues of deceased koalas and in the blood of live koalas from other regions of NSW. Analytical methods included liquid extraction and solid-phase micro-extraction, followed by gas-chromatography/ mass-spectrometry. Concentrations in the ingesta of individual animals vary remarkably, though the average proportions of individual monoterpenes in the ingesta of animals from the four different regions are highly comparable. Blood concentrations of the selected monoterpenes also varied considerably. The highest blood concentrations were found for 1,8-cineole, up to 971 ng/ml. There was similarity between circulating monoterpene profiles and ingesta profiles. Based on the observed lack of similarity between blood and lymph tissue concentrations, individual monoterpenes either exhibit different affinities for lymphatic tissue compared to blood or their accumulation in blood and lymph tissue differs temporally. In general, blood monoterpene concentrations found in koalas were low compared to those reported in other marsupial eucalypt feeders, but significant concentrations of monoterpenes were detected in all samples analysed. This data on blood and lymphatic tissue monoterpene concentrations builds the fundamental groundwork for future research into the effects of dietary monoterpenes on various biological processes of specialist herbivores and into the significance of these animals' metabolic and behavioural strategies for coping with these compounds. We have shown that the systemic exposure of koalas to potentially anti-inflammatory eucalypt monoterpenes is continuous, and we provide data on physiological concentrations which will allow realistic future studies of the effects of monoterpenes on immune cell function.

A review of climatic change as a determinant of the viability of koala populations

The koala (Phascolarctos cinereus) occupies a broad range of eastern and southern Australia, extending over tropical coastal, semiarid inland and temperate regions. In many areas koala populations are under threat, in particular from the direct and indirect effects of ongoing habitat destruction due to increased urbanisation and other anthropogenic processes. Climate change presents additional threats to the integrity of koala habitats because many species of food and non-food trees have narrow climate envelopes and are unable to adapt to altered temperatures and rainfall. Climate extremes also produce physiological stresses in koalas that may increase the likelihood of outbreaks of chlamydiosis and other diseases. Climate change–related increases in the relative content of toxic chemicals in leaves are further stresses to the koala after ingestion. In addition, populations that originated from a small number of founder individuals are at potential risk due to their relatively low genetic diversity. Strategies that maintain residual habitat fragments and promote the construction of new refugia are now being formulated. Modelling of the impact of habitat metrics on koala distribution is providing important information that can be used in the rehabilitation of koala refugia. In future these models could be augmented with metrics that describe koala homeostasis to inform local conservation strategies. These considerations are also relevant for the maintenance of other taxa in the wider ecosystem that are also at risk from habitat destruction and climate change.

Insect herbivory in a mature Eucalyptus woodland canopy depends on leaf phenology but not CO2 enrichment

Background

Climate change factors such as elevated atmospheric carbon dioxide concentrations (e[CO₂]) and altered rainfall patterns can alter leaf composition and phenology. This may subsequently impact insect herbivory. In sclerophyllous forests insects have developed strategies, such as preferentially feeding on new leaf growth, to overcome physical or foliar nitrogen constraints, and this may shift under climate change. Few studies of insect herbivory at elevated [CO₂] have occurred under field conditions and none on mature evergreen trees in a naturally established forest, yet estimates for leaf area loss due to herbivory are required in order to allow accurate predictions of plant productivity in future climates. Here, we assessed herbivory in the upper canopy of mature Eucalyptus tereticornis trees at the nutrient-limited Eucalyptus free-air CO₂ enrichment (EucFACE) experiment during the first 19 months of CO₂ enrichment. The assessment of herbivory extended over two consecutive spring—summer periods, with a first survey during four months of the [CO₂] ramp-up phase after which full [CO₂] operation was maintained, followed by a second survey period from months 13 to 19.

Results

Throughout the first 2 years of EucFACE, young, expanding leaves sustained significantly greater damage from insect herbivory (between 25 and 32 % leaf area loss) compared to old or fully expanded leaves (less than 2 % leaf area loss). This preference of insect herbivores for young expanding leaves combined with discontinuous production of new foliage, which occurred in response to rainfall, resulted in monthly variations in leaf herbivory. In contrast to the significant effects of rainfall-driven leaf phenology, elevated [CO₂] had no effect on leaf consumption or preference of insect herbivores for different leaf age classes.

Conclusions

In the studied nutrient-limited natural Eucalyptus woodland, herbivory contributes to a significant loss of young foliage. Leaf phenology is a significant factor that determines the level of herbivory experienced in this evergreen sclerophyllous woodland system, and may therefore also influence the population dynamics of insect herbivores. Furthermore, leaf phenology appears more strongly impacted by rainfall patterns than by e[CO₂]. e[CO₂] responses of herbivores on mature trees may only become apparent after extensive CO₂ fumigation periods.

Electronic supplementary material

The online version of this article (doi:10.1186/s12898-016-0102-z) contains supplementary material, which is available to authorized users.

Quantitative and qualitative shifts in defensive metabolites define chemical defense investment during leaf development in Inga, a genus of tropical trees

Selective pressures imposed by herbivores are often positively correlated with investments that plants make in defense. Research based on the framework of an evolutionary arms race has improved our understanding of why the amount and types of defenses differ between plant species. However, plant species are exposed to different selective pressures during the life of a leaf, such that expanding leaves suffer more damage from herbivores and pathogens than mature leaves. We hypothesize that this differential selective pressure may result in contrasting quantitative and qualitative defense investment in plants exposed to natural selective pressures in the field. To characterize shifts in chemical defenses, we chose six species of Inga, a speciose Neotropical tree genus. Focal species represent diverse chemical, morphological, and developmental defense traits and were collected from a single site in the Amazonian rainforest. Chemical defenses were measured gravimetrically and by characterizing the metabolome of expanding and mature leaves. Quantitative investment in phenolics plus saponins, the major classes of chemical defenses identified in Inga, was greater for expanding than mature leaves (46% and 24% of dry weight, respectively). This supports the theory that, because expanding leaves are under greater selective pressure from herbivores, they rely more upon chemical defense as an antiherbivore strategy than do mature leaves. Qualitatively, mature and expanding leaves were distinct and mature leaves contained more total and unique metabolites. Intraspecific variation was greater for mature leaves than expanding leaves, suggesting that leaf development is canalized. This study provides a snapshot of chemical defense investment in a speciose genus of tropical trees during the short, few-week period of leaf development. Exploring the metabolome through quantitative and qualitative profiling enables a more comprehensive examination of foliar chemical defense investment.

Specific polyphenols and tannins are associated with defense against insect herbivores in the tropical oak Quercus oleoides

The role of plant polyphenols as defenses against insect herbivores is controversial. We combined correlative field studies across three geographic regions (Northern Mexico, Southern Mexico, and Costa Rica) with induction experiments under controlled conditions to search for candidate compounds that might play a defensive role in the foliage of the tropical oak, Quercus oleoides. We quantified leaf damage caused by four herbivore guilds (chewers, skeletonizers, leaf miners, and gall forming insects) and analyzed the content of 18 polyphenols (including hydrolyzable tannins, flavan-3-ols, and flavonol glycosides) in the same set of leaves using high performance liquid chromatography and mass spectrometry. Foliar damage ranged from two to eight percent per region, and nearly 90% of all the damage was caused by chewing herbivores. Damage due to chewing herbivores was positively correlated with acutissimin B, catechin, and catechin dimer, and damage by mining herbivores was positively correlated with mongolinin A. By contrast, gall presence was negatively correlated with vescalagin and acutissimin B. By using redundancy analysis, we searched for the combinations of polyphenols that were associated to natural herbivory: the combination of mongolinin A and acutissimin B had the highest association to herbivory. In a common garden experiment with oak saplings, artificial damage increased the content of acutissimin B, mongolinin A, and vescalagin, whereas the content of catechin decreased. Specific polyphenols, either individually or in combination, rather than total polyphenols, were associated with standing leaf damage in this tropical oak. Future studies aimed at understanding the ecological role of polyphenols can use similar correlative studies to identify candidate compounds that could be used individually and in biologically meaningful combinations in tests with herbivores and pathogens.

Radical scavenging-linked antioxidant activities of commonly used herbs and spices in Korea

Herbs and spices not only variety and racy flavour to Korean foods, they also are the richest source for antioxidant power. The present study evaluates the radical scavenging-linked antioxidant activities of hot water extracts from commonly used herbs and spices in Korea. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical and superoxide anion scavenging activities of bay extract were 39.5% and 22.1%, respectively. The hydroxyl radical scavenging activity was in order of dill (50.0%) > bay (31.3%) > garlic (27.9%) > white pepper and black pepper (15.1-15.3%) > onion (10.1%) extracts. Bay extract had the highest total phenolic content (17.86 μg CE/g). High correlation coefficients were found between the total phenol content and DPPH radical scavenging activity (R = 0.9162). These results indicate that herbs and spices had high antioxidant activity that is partly due to the phenolic compounds and provide basic data for further development of processed food products.

Species by environment interactions affect pyrrolizidine alkaloid expression in Senecio jacobaea, Senecio aquaticus, and their hybrids

We examined the effects of water and nutrient availability on the expression of the defense pyrrolizidine alkaloids (PAs) in Senecio jacobaea and S. aquaticus. Senecio jacobaea, and S. aquaticus are adapted to different natural habitats, characterized by differing abiotic conditions and different selection pressures from natural enemies. We tested if PA concentration and diversity are plastic over a range of water and nutrient treatments, and also whether such plasticity is dependent on plant species. We also tested the hypothesis that hybridization may contribute to PA diversity within plants, by comparing PA expression in parental species to that in artificially generated F₁ hybrids, and also in later generation natural hybrids between S. jacobaea and S. aquaticus. We showed that total PA concentration in roots and shoots is not dependent on species, but that species determines the pattern of PA diversification. Pyrrolizidine alkaloid diversity and concentration are both dependent on environmental factors. Hybrids produce a putatively novel PA, and this PA is conserved in natural hybrids, that are backcrossed to S. jacobaea. Natural hybrids that are backcrossed several times to S. jacobaea are with regard to PA diversity significantly different from S. jacobaea but not from S. aquaticus, while F₁ hybrids are in all cases more similar to S. jacobaea. These results collectively suggest that PA diversity is under the influence of natural selection.

How do soil nutrients affect within-plant patterns of herbivory in seedlings of Eucalyptus nitens?

This study assessed how the palatability of leaves of different age classes (young, intermediate and older) of Eucalyptus nitens seedlings varied with plant nutrient status, based on captive feeding trials with two mammalian herbivores, red-bellied pademelons (Thylogale billardierii), and common brushtail possums (Trichosurus vulpecula). Seedlings were grown under three nutrient treatments (low, medium and high), and we determined how palatability was related to chemical and physical characteristics of the leaves. Pademelons ate more older leaves than young and intermediate leaves for all treatments. This pattern was best explained by sideroxylonals (formylated phloroglucinol compounds known to deter herbivory by other marsupials), and/or essential oil compounds that were present in lower concentrations in older leaves. In the low-nutrient treatment, possums also ate more of the older leaves. However, in the medium- and high-nutrient treatments, possums ate more intermediate leaves than older leaves and showed a behavioural preference for young leaves (consuming younger leaves first) over intermediate and older leaves, in spite of high levels of sideroxylonals and essential oils. The young leaves did, however, have the highest nitrogen concentration of all the leaf age classes. Thus, either sideroxylonals and essential oils provided little or no deterrent to possums, or the deterrent was outweighed by other factors such as high nitrogen. This study indicates that mammalian herbivores show different levels of relative use and damage to leaf age classes at varying levels of plant nutrient status and, therefore, their impact on plant fitness may vary with environment.