Chemical Traits that Predict Susceptibility of Pinus radiata to Marsupial Bark Stripping.

Bark stripping by mammals is a major problem in managed conifer forests worldwide. In Australia, bark stripping in the exotic plantations of Pinus radiata is mainly caused by native marsupials and results in reduced survival, growth, and in extreme cases death of trees. Herbivory is influenced by a balance between primary metabolites that are sources of nutrition and secondary metabolites that act as defences. Identifying the compounds that influence herbivory may be a useful tool in the management of forest systems. This study aimed to detect and identify both constitutive and induced compounds that are associated with genetic differences in susceptibility of two-year-old P. radiata trees to bark stripping by marsupials. An untargeted profiling of 83 primary and secondary compounds of the needles and bark samples from 21 susceptible and 21 resistant families was undertaken. These were among the most and least damaged families, respectively, screened in a trial of 74 families that were exposed to natural field bark stripping by marsupials. Experimental plants were in the same field trial but protected from bark stripping and a subset were subjected to artificial bark stripping to examine induced and constitutive chemistry differences between resistant and susceptible families. Machine learning (random forest), partial least squares plus discriminant analysis (PLS-DA), and principal components analysis with discriminant analysis (PCA-DA), as well as univariate methods were used to identify the most important totals by compound group and individual compounds differentiating the resistant and susceptible families. In the bark, the constitutive amount of two sesquiterpenoids - bicyclogermacrene and an unknown sesquiterpenoid alcohol -were shown to be of higher levels in the resistant families, whereas the constitutive sugars, fructose, and glucose, as well individual phenolics, were higher in the more susceptible families. The chemistry of the needles was not useful in differentiating the resistant and susceptible families to marsupial bark stripping. After artificial bark stripping, the terpenes, sugars, and phenolics responded in both the resistant and susceptible families by increasing or reducing amounts, which leveled the differences in the amounts of the compounds between the different resistant and susceptible classes observed at the constitutive level. Overall, based on the families with extreme values for less and more susceptibility, differences in the amounts of secondary compounds were subtle and susceptibility due to sugars may outweigh defence as the cause of the genetic variation in bark stripping observed in this non-native tree herbivory system.

Additive genetic variation in Pinus radiata bark chemistry and the chemical traits associated with variation in mammalian bark stripping.

Secondary metabolites are suggested as a major mechanism explaining genetic variation in herbivory levels in Pinus radiata. The potential to incorporate these chemical traits into breeding/deployment programmes partly depends on the presence of additive genetic variation for the relevant chemical traits. In this study, near-infrared spectroscopy was used to quantify the constitutive and induced levels of 54 compounds in the bark of trees from 74 P. radiata full-sib families. The trees sampled for chemistry were protected from browsing and induced levels were obtained by subjecting half of the trees to artificial bark stripping. The treatment effect on bark chemistry was assessed along with narrow-sense heritability, the significance of non-additive genetic effects and the additive genetic correlations of compounds with bark stripping by mammalian herbivores that was observed in unprotected replicates of the field trial. The results indicated: (i) significant additive genetic variation, with low-moderate narrow-sense heritability estimates for most compounds; (ii) while significant induced effects were detected for some chemicals, no significant genetic variation in inducibility was detected; and (iii) sugars, fatty acids and a diterpenoid positively genetically correlated while a sesquiterpenoid negatively genetically correlated with bark stripping by the mammalian herbivore, the Bennett's wallaby (Macropus rufogriseus). At the onset of browsing, a trade-off with height was detected for selecting higher amounts of this sesquiterpenoid. However, overall, results showed potential to incorporate chemical traits into breeding/deployment programmes. The quantitative genetic analyses of the near infrared predicted chemical traits produced associations with mammalian bark stripping that mostly conform with those obtained using standard wet chemistry.

Consistent community genetic effects in the context of strong environmental and temporal variation in Eucalyptus.

Provenance translocations of tree species are promoted in forestry, conservation, and restoration in response to global climate change. While this option is driven by adaptive considerations, less is known of the effects translocations can have on dependent communities. We investigated the relative importance and consistency of extended genetic effects in Eucalyptus using two species-E. globulus and E. pauciflora. In E. globulus, the dependent arthropod and pathogen canopy communities were quantified based on the abundance of 49 symptoms from 722 progeny from 13 geographic sub-races across 2 common gardens. For E. pauciflora, 6 symptoms were quantified over 2 years from 238 progeny from 16 provenances across 2 common gardens. Genetic effects significantly influenced communities in both species. However, site and year effects outweighed genetic effects with site explaining approximately 3 times the variation in community traits in E. globulus and site and year explaining approximately 6 times the variation in E. pauciflora. While the genetic effect interaction terms were significant in some community traits, broad trends in community traits associated with variation in home-site latitude for E. globulus and home-site altitude for E. pauciflora were evident. These broad-scale trends were consistent with patterns of adaptive differentiation within each species, suggesting there may be extended consequences of local adaptation. While small in comparison to site and year, the consistency of genetic effects highlights the importance of provenance choice in tree species, such as Eucalyptus, as adaptive divergence among provenances may have significant long-term effects on biotic communities.

A water availability gradient reveals the deficit level required to affect traits in potted juvenile Eucalyptus globulus.

Background and aims: Drought leading to soil water deficit can have severe impacts on plants. Water deficit may lead to plant water stress and affect growth and chemical traits. Plant secondary metabolite (PSM) responses to water deficit vary between compounds and studies, with inconsistent reports of changes to PSM concentrations even within a single species. This disparity may result from experimental water deficit variation among studies, and so multiple water deficit treatments are used to fully assess PSM responses in a single species. Methods: Juvenile Eucalyptus globulus were grown for 8 weeks at one of ten water deficit levels based on evapotranspiration from control plants (100 %). Treatments ranged from 90 % of control evapotranspiration (mild water deficit) to 0 % of control evapotranspiration (severe water deficit) in 10 % steps. Plant biomass, foliar abscisic acid (ABA) levels, Ψ leaf , leaf C/N, selected terpenes and phenolics were quantified to assess responses to each level of water deficit relative to a control. Key Results: Withholding ≥30 % water resulted in higher foliar ABA levels and withholding ≥40 % water reduced leaf water content. Ψ leaf became more negative when ≥60 % water was withheld. Plant biomass was lower when ≥80 % water was withheld, and no water for 8 weeks (0 % water) resulted in plant death. The total oil concentration was lower and C/N was higher in dead and desiccated juvenile E. globulus leaves (0 % water). Concentrations of individual phenolic and terpene compounds, along with condensed tannin and total phenolic concentrations, remained stable regardless of water deficit or plant stress level. Conclusions: These juvenile E. globulus became stressed with a moderate reduction in available water, and yet the persistent concentrations of most PSMs in highly stressed or dead plants suggests no PSM re-metabolization and continued ecological roles of foliar PSMs during drought.

The Extended Community-Level Effects of Genetic Variation in Foliar Wax Chemistry in the Forest Tree Eucalyptus globulus.

Genetic variation in foundation trees can influence dependent communities, but little is known about the mechanisms driving these extended genetic effects. We studied the potential chemical drivers of genetic variation in the dependent foliar community of the focal tree Eucalyptus globulus. We focus on the role of cuticular waxes and compare the effects to that of the terpenes, a well-studied group of secondary compounds known to be bioactive in eucalypts. The canopy community was quantified based on the abundance of thirty-nine distinctive arthropod and fungal symptoms on foliar samples collected from canopies of 246 progeny from 13 E. globulus sub-races grown in a common garden trial. Cuticular waxes and foliar terpenes were quantified using gas chromatography - mass spectrometry (GC-MC). A total of 4 of the 13 quantified waxes and 7 of the 16 quantified terpenes were significantly associated with the dependent foliar community. Variation in waxes explained 22.9% of the community variation among sub-races, which was equivalent to that explained by terpenes. In combination, waxes and terpenes explained 35% of the genetic variation among sub-races. Only a small proportion of wax and terpene compounds showing statistically significant differences among sub-races were implicated in community level effects. The few significant waxes have previously shown evidence of divergent selection in E. globulus, which signals that adaptive variation in phenotypic traits may have extended effects. While highlighting the role of the understudied cuticular waxes, this study demonstrates the complexity of factors likely to lead to community genetic effects in foundation trees.

Genetic control of cuticular wax compounds in Eucalyptus globulus.

Plant cuticular wax compounds perform functions that are essential for the survival of terrestrial plants. Despite their importance, the genetic control of these compounds is poorly understood outside of model taxa. Here we investigate the genetic basis of variation in cuticular compounds in Eucalyptus globulus using quantitative genetic and quantitative trait loci (QTL) analyses. Quantitative genetic analysis was conducted using 246 open-pollinated progeny from 13 native sub-races throughout the geographic range. QTL analysis was conducted using 112 clonally replicated progeny from an outcross F2 population. Nine compounds exhibited significant genetic variation among sub-races with three exhibiting signals of diversifying selection. Fifty-two QTL were found with co-location of QTL for related compounds commonly observed. Notable among these was the QTL for five wax esters, which co-located with a gene from the KCS family, previously implicated in the biosynthesis of cuticular waxes in Arabidopsis. In combination, the QTL and quantitative genetic analyses suggest the variation and differentiation in cuticular wax compounds within E. globulus has a complex genetic origin. Sub-races exhibited independent latitudinal and longitudinal differentiation in cuticular wax compounds, likely reflecting processes such as historic gene flow and diversifying selection acting upon genes that have diverse functions in distinct biochemical pathways.

Phylogeny Explains Variation in The Root Chemistry of Eucalyptus Species.

Plants are dependent on their root systems for survival, and thus are defended from belowground enemies by a range of strategies, including plant secondary metabolites (PSMs). These compounds vary among species, and an understanding of this variation may provide generality in predicting the susceptibility of forest trees to belowground enemies and the quality of their organic matter input to soil. Here, we investigated phylogenetic patterns in the root chemistry of species within the genus Eucalyptus. Given the known diversity of PSMs in eucalypt foliage, we hypothesized that (i) the range and concentrations of PSMs and carbohydrates in roots vary among Eucalyptus species, and (ii) that phylogenetic relationships explain a significant component of this variation. To test for interspecific variation in root chemistry and the influence of tree phylogeny, we grew 24 Eucalyptus species representing two subgenera (Eucalyptus and Symphyomyrtus) in a common garden for two years. Fine root samples were collected from each species and analyzed for total phenolics, condensed tannins, carbohydrates, terpenes, and formylated phloroglucinol compounds. Compounds displaying significant interspecific variation were mapped onto a molecular phylogeny and tested for phylogenetic signal. Although all targeted groups of compounds were present, we found that phenolics dominated root defenses and that all phenolic traits displayed significant interspecific variation. Further, these compounds displayed a significant phylogenetic signal. Overall, our results suggest that within these representatives of genus Eucalyptus, more closely related species have more similar root chemistry, which may influence their susceptibility to belowground enemies and soil organic matter accrual.

Population divergence in the ontogenetic trajectories of foliar terpenes of a Eucalyptus species.

BACKGROUND AND AIMS: The development of plant secondary metabolites during early life stages can have significant ecological and evolutionary implications for plant-herbivore interactions. Foliar terpenes influence a broad range of ecological interactions, including plant defence, and their expression may be influenced by ontogenetic and genetic factors. This study investigates the role of these factors in the expression of foliar terpene compounds in Eucalyptus globulus seedlings. METHODS: Seedlings were sourced from ten families each from three genetically distinct populations, representing relatively high and low chemical resistance to mammalian herbivory. Cotyledon-stage seedlings and consecutive leaf pairs of true leaves were harvested separately across an 8-month period, and analysed for eight monoterpene compounds and six sesquiterpene compounds. KEY RESULTS: Foliar terpenes showed a series of dynamic changes with ontogenetic trajectories differing between populations and families, as well as between and within the two major terpene classes. Sesquiterpenes changed rapidly through ontogeny and expressed opposing trajectories between compounds, but showed consistency in pattern between populations. Conversely, changed expression in monoterpene trajectories was population- and compound-specific. CONCLUSIONS: The results suggest that adaptive opportunities exist for changing levels of terpene content through ontogeny, and evolution may exploit the ontogenetic patterns of change in these compounds to create a diverse ontogenetic chemical mosaic with which to defend the plant. It is hypothesized that the observed genetically based patterns in terpene ontogenetic trajectories reflect multiple changes in the regulation of genes throughout different terpene biosynthetic pathways.

Evolution of rarity and phylogeny determine above- and belowground biomass in plant-plant interactions.

Rare species are often considered inferior competitors due to occupancy of small ranges, specific habitats, and small local populations. However, the phylogenetic relatedness and rarity level (level 1-7 and common) of interacting species in plant-plant interactions are not often considered when predicting the response of rare plants in a biotic context. We used a common garden of 25 species of Tasmanian Eucalyptus, to differentiate non-additive patterns in the biomass of rare versus common species when grown in mixtures varying in phylogenetic relatedness and rarity. We demonstrate that rare species maintain progressively positive non-additive responses in biomass when interacting with phylogenetically intermediate, less rare and common species. This trend is not reflected in common species that out-performed in monocultures compared to mixtures. These results offer predictability as to how rare species' productivity will respond within various plant-plant interactions. However, species-specific interactions, such as those involving E. globulus, yielded a 97% increase in biomass compared to other species-specific interaction outcomes. These results are important because they suggest that plant rarity may also be shaped by biotic interactions, in addition to the known environmental and population factors normally used to describe rarity. Rare species may utilize potentially facilitative interactions with phylogenetically intermediate and common species to escape the effects of limiting similarity. Biotically mediated increases in rare plant biomass may have subsequent effects on the competitive ability and geographic occurrence of rare species, allowing rare species to persist at low abundance across plant communities. Through the consideration of species rarity and evolutionary history, we can more accurately predict plant-plant interaction dynamics to preserve unique ecosystem functions and fundamentally challenge what it means to be "rare".

An evolutionary case for plant rarity: Eucalyptus as a model system.

Species rarity is a common phenomenon across global ecosystems that is becoming increasingly more common under climate change. Although species rarity is often considered to be a stochastic response to environmental and ecological constraints, we examined the hypothesis that plant rarity is a consequence of natural selection acting on performance traits that affect a species range size, habitat specificity, and population aggregation; three primary descriptors of rarity. Using a common garden of 25 species of Tasmanian Eucalyptus, we find that the rarest species have 70% lower biomass than common species. Although rare species demonstrate lower biomass, rare species allocated proportionally more biomass aboveground than common species. There is also a negative phylogenetic autocorrelation underlying the biomass of rare and common species, indicating that traits associated with rarity have diverged within subgenera as a result of environmental factors to reach different associated optima. In support of our hypothesis, we found significant positive relationships between species biomass, range size and habitat specificity, but not population aggregation. These results demonstrate repeated convergent evolution of the trait-based determinants of rarity across the phylogeny in Tasmanian eucalypts. Furthermore, the phylogenetically driven patterns in biomass and biomass allocation seen in rare species may be representative of a larger plant strategy, not yet considered, but offering a mechanism as to how rare species continue to persist despite inherent constraints of small, specialized ranges and populations. These results suggest that if rarity can evolve and is related to plant traits such as biomass, rather than a random outcome of environmental constraints, we may need to revise conservation efforts in these and other rare species to reconsider the abiotic and biotic factors that underlie the distributions of rare plant species.

Stability of plant defensive traits among populations in two Eucalyptus species under elevated carbon dioxide.

Plant secondary metabolites (PSMs) mediate a wide range of ecological interactions. Investigating the effect of environment on PSM production is important for our understanding of how plants will adapt to large scale environmental change, and the extended effects on communities and ecosystems. We explored the production of PSMs under elevated atmospheric carbon dioxide ([CO(2)]) in the species rich, ecologically and commercially important genus Eucalyptus. Seedlings from multiple Eucalyptus globulus and E. pauciflora populations were grown in common glasshouse gardens under elevated or ambient [CO(2)]. Variation in primary and secondary chemistry was determined as a function of genotype and treatment. There were clear population differences in PSM expression in each species. Elevated [CO(2)] did not affect concentrations of individual PSMs, total phenolics, condensed tannins or the total oil yield, and there was no population by [CO(2)] treatment interaction for any traits. Multivariate analysis revealed similar results with significant variation in concentrations of E. pauciflora oil components between populations. A [CO(2)] treatment effect was detected within populations but no interactions were found between elevated [CO(2)] and population. These eucalypt seedlings appear to be largely unresponsive to elevated [CO(2)], indicating stronger genetic than environmental (elevated [CO(2)]) control of expression of PSMs.

Genomic selection for resistance to mammalian bark stripping and associated chemical compounds in radiata pine.

The integration of genomic data into genetic evaluations can facilitate the rapid selection of superior genotypes and accelerate the breeding cycle in trees. In this study, 390 trees from 74 control-pollinated families were genotyped using a 36K Axiom SNP array. A total of 15,624 high-quality SNPs were used to develop genomic prediction models for mammalian bark stripping, tree height, and selected primary and secondary chemical compounds in the bark. Genetic parameters from different genomic prediction methods-single-trait best linear unbiased prediction based on a marker-based relationship matrix (genomic best linear unbiased prediction), multitrait single-step genomic best linear unbiased prediction, which integrated the marker-based and pedigree-based relationship matrices (single-step genomic best linear unbiased prediction) and the single-trait generalized ridge regression-were compared to equivalent single- or multitrait pedigree-based approaches (ABLUP). The influence of the statistical distribution of data on the genetic parameters was assessed. Results indicated that the heritability estimates were increased nearly 2-fold with genomic models compared to the equivalent pedigree-based models. Predictive accuracy of the single-step genomic best linear unbiased prediction was higher than the ABLUP for most traits. Allowing for heterogeneity in marker effects through the use of generalized ridge regression did not markedly improve predictive ability over genomic best linear unbiased prediction, arguing that most of the chemical traits are modulated by many genes with small effects. Overall, the traits with low pedigree-based heritability benefited more from genomic models compared to the traits with high pedigree-based heritability. There was no evidence that data skewness or the presence of outliers affected the genomic or pedigree-based genetic estimates.

A geographic mosaic of genetic variation within a foundation tree species and its community-level consequences.

Knowledge of the manner in which genetic variation within a tree species affects associated communities and ecosystem processes across its entire range is important for understanding how geographic mosaics of genetic interactions might develop and support different communities. While numerous studies have investigated the community and ecosystem consequences of genetic variation at the hybrid cross type or genotype level within a species, none has investigated the community-level effects of intraspecific genetic variation across the geographic range of a widespread species. This is the scale at which geographic mosaics of coevolution are hypothesized to exist. Studies at this level are particularly important for foundation tree species, which typically support numerous microbial, fungal, plant, and animal communities. We studied genetic variation across eight geographical races of the forest tree Eucalyptus globulus representing its natural distribution across southeastern Australia. The study was conducted in a 15-year-old common garden trial based on families derived from single-tree open-pollinated seed collections from the wild. Neutral molecular genetic variation within E. globulus was also assessed and compared with genetic divergence in the phenotypic and community traits. Three major findings emerged. First, we found significant genetically based, hierarchical variation in associated communities corresponding to geographical races of E. globulus and families within races. Second, divergence in foliar communities at the racial level was associated with genetically based divergence in specific leaf morphological and chemical traits that have known defensive functions. Third, significant positive correlations between canopy community dissimilarity and both neutral molecular genetic and leaf quantitative genetic dissimilarity at the race level supported a genetic similarity rule. Our results argue that genetic variation within foundation tree species has the potential to be a significant driver of the geographical mosaics of variation typical of forest communities, which could have important ecological and evolutionary implications.

Genetic stability of physiological responses to defoliation in a eucalypt and altered chemical defence in regrowth foliage.

Defoliation may initiate physiological recovery and chemical defence mechanisms that allow a plant to improve fitness after damage. Such responses may result in changes in plant resource allocation that influence growth and foliar chemistry. In this study, we investigated the nature and stability of the defoliation response of juvenile plants from three divergent populations of Eucalyptus globulus Labill. A partial defoliation treatment that removed all upper crown leaves and the apical buds was applied to plants sourced from eight families from each of three populations representing contrasting chemical resistance to mammalian herbivory. Growth, photosynthetic rate and chlorophyll content were assessed pre-defoliation and periodically up to 12 weeks post-defoliation. The content of key plant primary and secondary metabolites was assessed pre-defoliation, at 12 weeks post-defoliation in the old foliage (positioned below the point of defoliation) and in the new foliage of the control plants and regrowth (from axillary buds) on the defoliated plants. There were clear treatment impacts on physiological responses, growth and foliar chemical traits, but despite significant constitutive differences in physiology, growth and chemistry the three E. globulus populations did not vary in their response to foliage loss. Distinct physiological responses to defoliation were observed with treatment plants showing significant up-regulation of photosynthetic rate and increased chlorophyll content in the old foliage remaining in the lower crown. There was a significant increase in the concentrations of a number of foliar chemical compounds in the regrowth arising from previously dormant axillary buds compared with new growth derived from apical meristems. There were changes in biomass allocation; defoliated plants had increased branching and leaf biomass, with changes in regrowth morphology to increase light capture. This study argues for multiple responses of E. globulus juveniles to defoliation involving apical bud loss, including elevated chemical defences matched with increased growth. From a chemical defence perspective, these responses create an enhanced chemical mosaic to the herbivore, with leaves remaining after partial browsing potentially being more palatable than the regrowth. This study demonstrates the multiple independent strategies plants may use to respond to partial defoliation and emphasizes the dynamic interplay between growth and defence in the recovery response.

Responses to mild water deficit and rewatering differ among secondary metabolites but are similar among provenances within Eucalyptus species.

Water deficit associated with drought can severely affect plants and influence ecological interactions involving plant secondary metabolites. We tested the effect of mild water deficit and rewatering on physiological, morphological and chemical traits of juvenile Eucalyptus globulus Labill. and Eucalyptus viminalis Labill. We also tested if responses of juvenile eucalypts to water deficit and rewatering varied within species using provenances across a rainfall gradient. Both species and all provenances were similarly affected by mild water deficit and rewatering, as only foliar abscisic acid levels differed among provenances during water deficit. Across species and provenances, water deficit decreased leaf water potential, above-ground biomass and formylated phloroglucinol compound concentrations, and increased condensed tannin concentrations. Rewatering reduced leaf carbon : nitrogen, and total phenolic and chlorogenic acid concentrations. Water deficit and rewatering had no effect on total oil or individual terpene concentrations. Levels of trait plasticity due to water deficit and rewatering were less than levels of constitutive trait variation among provenances. The overall uniformity of responses to the treatments regardless of native provenance indicates limited diversification of plastic responses when compared with the larger quantitative variation of constitutive traits within these species. These responses to mild water deficit may differ from responses to more extreme water deficit or to responses of juvenile/mature eucalypts growing at each locality.

Genetic variation in resistance of Eucalyptus globulus to marsupial browsers.

The evolution of plant defensive traits in response to selection pressures imposed by herbivores is central to co-evolutionary theory. To demonstrate the role of herbivores as selective agents on plant resistance there must be variability in plant resistance to herbivores within a plant population. This variability must be under genetic control, and the variability in plant resistant traits and consequently herbivore damage to plants must reflect variability in plant fitness. We used a common eucalypt species, Eucalyptus globulus, and two major mammalian herbivores, the common brushtail possum (Trichosurus vulpecula) and the red-bellied pademelon (Thylogale billardierii), as a system to investigate intraspecific variation in plant resistance to mammalian herbivores and to investigate if this variation has a genetic basis. We measured mammalian browsing damage on 2,302 individual trees of E. globulus, from 563 families derived from range-wide native stand seed collections of known pedigree and grown in a common environment field trial. Using a selection of trees from the field trial we then conducted a feeding trial with captive herbivores to assess if the genetic variation in plant resistance in the field was reflected in feeding preferences of captive animals, as measured by relative intake. Results from the field trial showed significant genetic variation in plant resistance amongst races, localities and amongst different families. These results were consolidated in the captive trial with similar trends in genetic variation among E. globulus localities. Dry matter intake of foliage by Trichosurus vulpecula was consistently greater than that by Thylogale billardierii; however, the intraspecific preferences of the two herbivores were significantly correlated.

Evolutionary history and novel biotic interactions determine plant responses to elevated CO2 and nitrogen fertilization.

A major frontier in global change research is predicting how multiple agents of global change will alter plant productivity, a critical component of the carbon cycle. Recent research has shown that plant responses to climate change are phylogenetically conserved such that species within some lineages are more productive than those within other lineages in changing environments. However, it remains unclear how phylogenetic patterns in plant responses to changing abiotic conditions may be altered by another agent of global change, the introduction of non-native species. Using a system of 28 native Tasmanian Eucalyptus species belonging to two subgenera, Symphyomyrtus and Eucalyptus, we hypothesized that productivity responses to abiotic agents of global change (elevated CO2 and increased soil N) are unique to lineages, but that novel interactions with a non-native species mediate these responses. We tested this hypothesis by examining productivity of 1) native species monocultures and 2) mixtures of native species with an introduced hardwood plantation species, Eucalyptus nitens, to experimentally manipulated soil N and atmospheric CO2. Consistent with past research, we found that N limits productivity overall, especially in elevated CO2 conditions. However, monocultures of species within the Symphyomyrtus subgenus showed the strongest response to N (gained 127% more total biomass) in elevated CO2 conditions, whereas those within the Eucalyptus subgenus did not respond to N. Root:shoot ratio (an indicator of resource use) was on average greater in species pairs containing Symphyomyrtus species, suggesting that functional traits important for resource uptake are phylogenetically conserved and explaining the phylogenetic pattern in plant response to changing environmental conditions. Yet, native species mixtures with E. nitens exhibited responses to CO2 and N that differed from those of monocultures, supporting our hypothesis and highlighting that both plant evolutionary history and introduced species will shape community productivity in a changing world.

Genetic and ontogenetic variation in an endangered tree structures dependent arthropod and fungal communities.

Plant genetic and ontogenetic variation can significantly impact dependent fungal and arthropod communities. However, little is known of the relative importance of these extended genetic and ontogenetic effects within a species. Using a common garden trial, we compared the dependent arthropod and fungal community on 222 progeny from two highly differentiated populations of the endangered heteroblastic tree species, Eucalyptus morrisbyi. We assessed arthropod and fungal communities on both juvenile and adult foliage. The community variation was related to previous levels of marsupial browsing, as well as the variation in the physicochemical properties of leaves using near-infrared spectroscopy. We found highly significant differences in community composition, abundance and diversity parameters between eucalypt source populations in the common garden, and these were comparable to differences between the distinctive juvenile and adult foliage. The physicochemical properties assessed accounted for a significant percentage of the community variation but did not explain fully the community differences between populations and foliage types. Similarly, while differences in population susceptibility to a major marsupial herbivore may result in diffuse genetic effects on the dependent community, this still did not account for the large genetic-based differences in dependent communities between populations. Our results emphasize the importance of maintaining the populations of this rare species as separate management units, as not only are the populations highly genetically structured, this variation may alter the trajectory of biotic colonization of conservation plantings.

Chemical variation in a dominant tree species: population divergence, selection and genetic stability across environments.

Understanding among and within population genetic variation of ecologically important plant traits provides insight into the potential evolutionary processes affecting those traits. The strength and consistency of selection driving variability in traits would be affected by plasticity in differences among genotypes across environments (G×E). We investigated population divergence, selection and environmental plasticity of foliar plant secondary metabolites (PSMs) in a dominant tree species, Eucalyptus globulus. Using two common garden trials we examined variation in PSMs at multiple genetic scales; among 12 populations covering the full geographic range of the species and among up to 60 families within populations. Significant genetic variation in the expression of many PSMs resides both among and within populations of E. globulus with moderate (e.g., sideroxylonal A h(2)op = 0.24) to high (e.g., macrocarpal G h(2)op = 0.48) narrow sense heritabilities and high coefficients of additive genetic variation estimated for some compounds. A comparison of Qst and Fst estimates suggest that variability in some of these traits may be due to selection. Importantly, there was no genetic by environment interaction in the expression of any of the quantitative chemical traits despite often significant site effects. These results provide evidence that natural selection has contributed to population divergence in PSMs in E. globulus, and identifies the formylated phloroglucinol compounds (particularly sideroxylonal) and a dominant oil, 1,8-cineole, as candidates for traits whose genetic architecture has been shaped by divergent selection. Additionally, as the genetic differences in these PSMs that influence community phenotypes is stable across environments, the role of plant genotype in structuring communities is strengthened and these genotypic differences may be relatively stable under global environmental changes.