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Volume 9, Issue 1
January 2017
EISSN 2041-2851
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Native and alien trees associate with a wide range of beneficial fungi, but the few studies of these interactions tend to focus only on a few plant species or locations at a time. Using extensive databases collected by mycologists in the United Kingdom and New Zealand, we show that, in the latter region, fungi on alien trees are less functionally diverse than those associated with natives. In both New Zealand and the United Kingdom, however, the structure of the interaction network is simplified and "nested". This suggests that beneficial fungi hosted by alien trees may help facilitate further tree invasion.

Research Article

Two speciose clades of Australian trees, Acacia and Eucalyptus, have shown differential invasive ability when exported, with introduced Acacia species more likely to become invasive. The evolutionary histories of Acacia and Eucalyptus clades do not contain underlying phylogenetic signals for invasiveness as individual component species progress along the introduction-naturalization-invasion (INI) continuum. Geographic and network analyses suggest that potentially invasive clades, like Acacia, may be identified because they contain invasive species with smoother and faster expanding native distributions and are located more to the edges of phylogenetic networks than less invasive clades.

This study provide a model-based calculating tool/software that can accurately calculate pollen-mediated gene flow (PMGF) frequencies of wind-pollinated plant species by including five biological and climatic parameters. The calculating tool can easily be used by any users who are not familiar with mathematical modeling. The required parameters can be measured directly in the field without conducting PMGF experiments, which makes this tool practical to estimate PMGF frequencies. This tool will be helpful to estimate transgene flow and its potential impacts, in addition to determining isolation distances between GE and non-GE crops.

The relationship between polyploidy in diploid and tetraploid Centaurea phrygia and seed production is mediated by a wide range of factors with opposing directions. Wider flower heads displayed higher above the ground suggested higher seed production in diploids while earlier flowering and a lower abundance of herbivores suggested higher seed production in tetraploids. The importance of different relationships varies between years. Knowledge of the patterns of interactions is thus more important than the specific values of the links and can be used to model the evolution of species traits and plant-herbivore and plant-pollinator interactions in diploid-polyploid systems.

Stipules are leaf structures common in many groups of plants that can take a variety of forms. In Gentianales, interpetiolar stipules are considered a synapomorphy of Rubiaceae but in this study we detected two lateral expansions at the base of the leaf primordia (stipules) that give rise to colleters in many genera of Apocynaceae, similarly to Rubiaceae species. Through ontogenetic study it was possible to prove for the first time that Apocynaceae is a stipulate family whose stipules are modified into colleters, and their absence might be a secondary loss, changing the interpretation of stipule evolution in Gentianales.

This paper reports the results of a multi-year manipulative common garden experiment that investigates the roles of variation in plant defense and growth in the competitive ability of an invasive tree in the native range and two introduced ranges. We found that plants from invasive populations had more rapid aboveground growth rates that contributed to their success in both introduced and native ranges independent of aboveground herbivory. However, strong variation among sites indicated that plants from invasive populations only have a strong advantage in a subset of sites in the introduced range.

The diversity of floral forms in angiosperms is frequently attributed to pollinators but herbivores can be just as important. Here we examine the role of a flower-feeding caterpillar, Mompha, in driving floral trait evolution and subsequent pollinator-shifts in a recently radiated clade of flowering plants, Oenothera sect. Calylophus (Onagraceae). Longer-tubed, hawkmoth flowers had substantially greater damage compared to smaller bee-pollinated flowers. Mompha's preference for longer-tubed flowers, which is evident even within populations of some species, may have played an important role in driving the morphological changes associated with shifts from hawkmoth to bee pollination.

Gynodioecy is a mating system where both hermaphrodite (pollen and seed producer) and female plants (seed producer) coexist within a population. We compared size-dependent sex allocation between hermaphrodites and females in a gynodioecious shrub, Daphne jezoensis. Hermaphrodites produced more flowers with size increment than females, while females produced 3.7 times more fruits than hermaphrodites. Despite the sexual difference in sex allocation, total reproductive investment did not differ between the sex morphs because of low pollination success. Severe pollen limitation under natural conditions resulted in the balanced resource investment in reproduction between the sex morphs in this species.

This study investigated the combined effect of drought and heat wave on physiological responses of tomato seedlings. We found that the negative impacts of drought stress were exacerbated by heat wave through stomatal and biochemical limitations. Additionally, the recovery of leaf gas exchange in the combination of drought and heat wave was delayed more than in other treatments. Our results suggest that future climates characterized by drought and extreme heat may have substantial impacts on tomato productivity and survival.

We studied the fitness of an endemic and vulnerable violet species along its altitudinal range (2,400 m - 3,500 m), and we found it to be mainly affected by inter-annual and microhabitat variability along the gradient, especially at the lowest edge. Despite the increasingly adverse environmental conditions, the plant showed no pollen limitation with elevation, which is attributed to the increase in selfing and decrease in competition for pollinators at higher elevations. Plant fitness was extremely reduced owing to the presence of non-native rabbits, which changed plant trait-environment interactions along the gradient, threatening the survival of this violet.

Under rising temperature, the rate of any developmental process increased with temperature more rapidly than that of CO2 assimilation. We found that this discrepancy, summarised by the CO2 assimilation rate per unit of plant development, could explain the observed reductions in biomass accumulation in leaves and grain under high temperatures. This simple model describes the effects of night and day temperature equally well, and offers a simple framework for describing the effects of temperature on plant growth, without any supplementary effect of rising night temperatures.

Small and peripheral populations often contain low levels of genetic variation. This may limit their ability to adapt to environmental change, including climate warming. In a recent study published in AoB PLANTS, Birkeland, Skjetne and colleagues show that many rare and threatened plant species in the High Arctic archipelago Svalbard harbour low levels of genetic variation. Most of them are probably relicts from the early Holocene warmer period. They have likely experienced strong genetic founder/bottleneck effects due to climatic limitations. Even though temperatures now are rising, it is highly uncertain whether this will be beneficial for these warmth-demanding species.

We performed a glasshouse experiment to test whether degree of phylogenetic relatedness between Aquilegia canadensis and six co-occurring heterospecifics affects A. canadensis biomass through soil legacy effects. We found that A. canadensis performed significantly better in distant relatives' soils than in close relatives' soils, and this effect disappeared with soil sterilization. The greater performance of A. canadensis in soils of more versus less distant relatives is consistent with a hypothesis of phylogenetically-constrained pathogen escape, a phenomenon expected to promote coexistence of phylogenetically distant species.

Review

Bamboos are one of the most economically important plant groups globally, but this world-wide trade creates risks of invasions. Here we identified 1662 species of bamboo, of which almost a seventh (232) have been introduced outside their native range, with Asiatic and larger species preferred. Only 12 species were found to have become invasive. However, invasiveness was found to be more a function of human-usage than specific species traits, suggesting the recent upsurge in bamboo cultivation could pose future invasion risks.

Hybridization can generate additional genetic diversity and create invasive plant species. Invasive tree species are a growing ecological concern worldwide, and some of these invasions involve hybridization events. Here we review 1) abundance of hybrid trees compared to parental taxa in an invasion; 2) hybrid phenotypes that may enhance invasions; 3) the presence of first generation vs further hybrid generations and introgression; 4) the role of native genetic material in invasive tree hybridization; 5) how important intentional hybridization is in contributing to tree invasion and 6) how often hybrid tree invasions are preceded by intentional vs. accidental introduction.

Non-native plant invasions represent ecological disequilibrium situations, that is, the immediate breakdown of historically co-evolved interactions once introduced into novel environments. Globalization has led to increased transfer in organisms between countries. Native enemies also undergo host expansions onto non-native plants. Ecological disequilibrium conditions can thus be expected to change unpredictably over time. By retrospectively analysing the insect pest and pathogen accumulation on established non-native trees in South Africa, we review the eco-evolutionary background that may help to explain and predict variation in ecological disequilibrium conditions in non-native trees.

Evolution greatly impacts the outcomes of biological invasions. In our review, we review such evolutionary processes, with an emphasis on tree invasions, and place them in the context of a unified framework for biological invasions. The processes and mechanisms described are pre-introduction evolutionary history, sampling effect, founder effect, genotype-by-environment interactions, admixture, hybridization, polyploidization, rapid evolution, epigenetics, and second-genomes. By understanding the mechanisms underlying invasion success, researchers will be better equipped to predict, understand, and manage biological invasions.

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