Classifying the fire‐response traits of plants: How reliable are species‐level classifications?

Plant species in fire‐prone environments possess specific traits which allow them to survive fire. Species are commonly classified according to whether they survive fire and resprout or whether they are killed by fire and regenerate from seed. However, different populations of the same species have been shown to vary in their responses. Therefore, the classification of a species into a single category based on fire‐response traits may not necessarily be representative of every population under every circumstance. This study examined the extent of within‐species variation in fire‐response traits of woody plants in south‐eastern Australia after the 2003 fires. Species were then classified using two approaches: (i) using data from a field survey of fire‐response traits, taking into account within‐species variation; and (ii) using species' fire responses listed in a pre‐existing fire‐response database compiled from a variety of primary sources. Field data showed that the majority of species in the study area resprouted after fire with around one in 10 species variable in their resprouting response. Almost half of all species varied from site to site according to whether they regenerated from seed, either solely or in addition to resprouting. The numbers of species classified as resprouters and seed regenerators varied according to the classification method used. Differences were also found between the classification method when calculating the mean proportion of resprouters and seed regenerators across sites. The fire‐response traits for some species from the database were found to differ from the observed field responses. This study demonstrated that the application of a fire‐response trait, reported in a trait database, to an entire species, may not adequately represent the actual fire responses of the populations of interest. Rather than considering the fire‐response traits of a species, accurate prediction may be better achieved by considering how different populations of plants will respond to fire.     

Do virus‐resistant plants pose a threat to non‐target ecosystems? I. Evidence from an Australian pathosystem based on glasshouse challenge experiments

One key environmental risk associated with the release of novel disease‐resistant plants is the potential for non‐target host populations to acquire resistance genes and undergo enemy release, leading to damage to associated native plant populations in high conservation‐value ecosystems. Unfortunately, the dynamics of most natural pathosystems are poorly understood, and risk assessment of disease‐resistant plants remains a challenge. Here we describe the first stage of a multi‐tiered risk assessment strategy aimed at quantifying potential ecological release in a model pathosystem (the weedy pasture species Trifolium repens infected with Clover yellow vein virus; ClYVV) in order to assess the level of risk posed by genetically modified and conventionally bred disease‐resistant host genotypes to non‐target plant communities in south‐eastern Australia. Glasshouse inoculation and growth experiments using 14 ClYVV isolates and 20 wild T. repens lines collected from high conservation‐value montane grassland and woodland communities show that viral infection reduces the survival and growth of host plants by on average 10–50%. However, T. repens lines exhibited variable levels of resistance and tolerance to virus infection and ClYVV isolates differed in infectivity and aggressiveness, with grassland isolates having a greater pathogenic effect on associated host plants than woodland isolates. We conclude that ClYVV potentially plays an important role in limiting the size of T. repens populations in some at‐risk non‐target ecosystems and that second‐tier field experiments are required to adequately quantify the risk associated with the commercial release of V‐R T. repens genotypes in Australia.     

Thermal de‐acclimation: how permanent are leaf phenotypes when cold‐acclimated plants experience warming?

We quantified a broad range of Arabidopsis thaliana (Col‐0) leaf phenotypes for initially warm‐grown (25/20 °C day/night) plants that were exposed to cold (5 °C) for periods of a few hours to 45 d before being transferred back to the warm, where leaves were allowed to mature. This allowed us to address the following questions: (1) For how long do warm‐grown plants have to experience cold before developing leaves become irreversibly cold acclimated? (2) To what extent is the de‐acclimation process associated with changes in leaf anatomy and physiology? We show that leaves that experience cold for extended periods during early development exhibit little plasticity in either photosynthesis or respiration, and they do not revert to a warm‐associated carbohydrate profile. The eventual expansion rate in the warm was inversely related to the duration of previous cold treatment. Moreover, cold exposure of immature/developing leaves for as little as 5 d resulted in irreversible changes in the morphology of leaves that subsequently matured in the warm, with 15 d cold being sufficient for a permanent alteration of leaf anatomy. Collectively, these results highlight the impact of transitory cold during early leaf development in determining the eventual phenotype of leaves that mature in the warm.     

Reduced chemical defence in ant‐plants? A critical re‐evaluation of a widely accepted hypothesis

Since its original formulation by Janzen in 1966, the hypothesis that obligate ant‐plants (myrmecophytes) defended effectively against herbivores by resident mutualistic ants have reduced their direct, chemical defence has been widely adopted. We tested this hypothesis by quantifying three classes of phenolic compounds (hydrolysable tannins, flavonoids, and condensed tannins) spectrophotometrically in the foliage of 20 ant‐plant and non‐ant‐plant species of the three unrelated genera Leonardoxa,Macaranga and Acacia (and three other closely related Mimosoideae from the genera Leucaena, Mimosa and Prosopis). We further determined biological activities of leaf extracts of the mimosoid species against fungal spore germination (as measure of pathogen resistance), seed germination (as measure of allelopathic activity), and caterpillar growth (as measure of anti‐herbivore defence).
Condensed tannin content in three of four populations of the non‐myrmecophytic Leonardoxa was significantly higher than in populations of the myrmecophyte. In contrast, we observed no consistent differences between ant‐plants and non‐ant‐plants in the Mimosoideae and in the genus Macaranga, though contents of phenolic compounds varied strongly among different species in each of these two plant groups. Similarly, among the investigated Mimosoideae, biological activity against spore or seed germination and caterpillar growth varied considerably but showed no clear relation with the existence of an obligate mutualism with ants. Our results did not support the hypothesis of ‘trade‐offs’ between indirect, biotic and direct, chemical defence in ant‐plants.
A critical re‐evaluation of the published data suggests that support for this hypothesis is more tenuous than is usually believed. The general and well‐established phenomenon that myrmecophytes are subject to severe attack by herbivores when deprived of their ants still lacks an explanation. It remains to be studied whether the trade‐off hypothesis holds true only for specific compounds (such as chitinases and amides whose cost may be the direct negative effects on plants’ ant mutualists), or whether the pattern of dramatically reduced direct defence of ant‐plants is caused by classes of defensive compounds not yet studied.     

Can biological control benefit from genetically‐modified crops? Tritrophic interactions on insect‐resistant transgenic plants

Abstract. The use of recombinant DNA technology to develop genetically‐modified crops is considered as a major breakthrough for agriculture by many scientists. However, some scientists, and an even larger proportion of the general public, are sceptical about the advantages and are even more concerned about the potential risk of this new technology. To evaluate this novel technology, cost‐benefit analyses are needed in which the real risks are measured and judged against the benefits. A tiered risk assessment scheme is described herein. This allows comparisons to be made with other insect‐control technologies (e.g. insecticides) and risks to be determined, rather than only hazards being identified. Recombinant DNA technology could allow plants to be designed that are well suited for use alongside biological control programmes. Unfortunately, plant breeders have continued to attempt to breed for total resistance, and biocontrol specialists have ignored the role of the plant in ensuring successful foraging behaviour by insect natural enemies. Although some scientists have highlighted the need to consider both the bottom‐up (plant defence) and top‐down (biocontrol) control of insect pests, there have been few serious attempts to combine these approaches. As more is understood about the proximate and ultimate causes of direct and indirect defences, the potential exists for engineering plants that combine both strategies. This new possibility for controlling insect pests, which will combine both ‘nature’s' own defences with man's ingenuity, may stack the odds in our favour in the continual struggle against insect pests.     

Are nurse‐protégé interactions more common among plants from arid environments?

Abstract. Harsh conditions in arid and semi‐arid environments make seedling establishment rare. Plant recruitment in arid environments often occurs only in years with above average rainfall or in safe sites under the canopy of nurse plants that provide shelter from high temperatures and low moisture. Associations of establishing seedlings with adult plants are referred to as nurse‐protégé interactions and are thought to be commensalisms in which seedlings benefit from the micro‐environment created by adult plants with no effect for the latter. This phenomenon is thought to be more frequent in harsh than in mild environments and appears to occur frequently in deserts and arid and semi‐arid biomes. Here, we investigate whether nurse‐protégé interactions are more common in arid environments by searching the published literature from the previous 92 years using the terms nurse plants, protégé plants, facilitation, nucleation and facultative mutualism. We then quantitatively compared these reports from arid zones to other environments. A total of 296 papers were found which referred to nurse‐protégé interactions. More than half (158) focused on arid and semi‐arid zones. This information was also used to explore hypotheses of potential causative forces that might have selected for such interactions in the arid zones such as seed trapping, nutrient, moisture, protection from browsing or trampling and support availability. Because of the large number of different nurse species (147, from 98 genera and 40 families) and protégé species (429, from 273 genera and 84 families), described across a diversity of environments, we suggest that there may be more than one causative factor selecting for nurse‐protégé interactions in arid and semi‐arid environments.     

Is selection of host plants by Plagiodera versicolora based on plant‐related performance?

Plant-related performance may be one of the most important factors in the selection of host plants by insect herbivores. We investigated the importance of plant-related performance in host selection by the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), on four willow species: Salix chaenomeloides Kimura, Salix eriocarpa Fr. et Sav., Salix   integra Thunb., and Salix serissaefolia Kimura (Salicaceae). Bagging experiments in the field revealed that the performance of P. versicolora adults and larvae differed significantly among willow species under enemy-free conditions and at constant densities. Egg clutch and larval abundance were positively related to adult abundance. Plagiodera versicolora adults did not discriminate strongly among willow species for feeding and oviposition. Larval performance did not differ among willow species in the presence of natural enemies, suggesting that interspecific differences in host quality were overridden by mortality from natural enemies. Adult and egg clutch abundance of P. versicolora changed seasonally despite the temporal stability of adult and larval performance under enemy-free field conditions. Thus, plant-related performance of P. versicolora adults and larvae may contribute little to population growth and temporal dynamics of host use in P. versicolora . Potential factors that reduce discrimination of P. versicolora among host willow species are discussed.     

Biotic resistance to plant invasions? Native herbivores prefer non‐native plants

In contrast to expectations of the enemy release hypothesis, but consistent with the notion of biotic resistance, we found that native generalist crayfishes preferred exotic over native freshwater plants by a 3 : 1 ratio when plants were paired by taxonomic relatedness. Native crayfishes also preferred exotic over native plants when tested across 57 native and 15 exotic plants found growing sympatrically at 11 sites throughout the southeastern USA. Exotic grass carp that share little evolutionary history with most of these plants exhibited no preference for native vs. exotic species. Analyses of three terrestrial data sets showed similar patterns, with native herbivores generally preferring exotic plants, while exotic herbivores rarely exhibited a preference. Thus, exotic plants may escape their coevolved herbivores only to be preferentially consumed by the native generalist herbivores in their new ranges, suggesting that native herbivores may provide biotic resistance to plant invasions.     

Do cytokinins function as two‐way signals between plants and animals?

Cytokinins are plant hormones that have, among many other functions, senescence‐modulatory effects in plant tissue. This is evident not only from biochemical data, but is vividly illustrated in the “green island” phenotype in plant leaves caused by cytokinins released for example by leaf mining insects or microbial pathogens. It is beyond doubt that, in addition to their roles in plants, cytokinins also provoke physiological and developmental effects in animals. It is hypothesized that the recently much discussed modification of plant metabolism by insects and associated microbes via cytokinin signals has a counterpart in direct cytokinin signalling that interferes with the animals’ hormonal systems and impacts their population dynamics.     

Is nitrogen transfer among plants enhanced by contrasting nutrient‐acquisition strategies?

Nitrogen (N) transfer among plants has been found where at least one plant can fix N₂. In nutrient‐poor soils, where plants with contrasting nutrient‐acquisition strategies (without N₂ fixation) co‐occur, it is unclear if N transfer exists and what promotes it. A novel multi‐species microcosm pot experiment was conducted to quantify N transfer between arbuscular mycorrhizal (AM), ectomycorrhizal (EM), dual AM/EM, and non‐mycorrhizal cluster‐rooted plants in nutrient‐poor soils with mycorrhizal mesh barriers. We foliar‐fed plants with a K¹⁵NO₃ solution to quantify one‐way N transfer from ‘donor’ to ‘receiver’ plants. We also quantified mycorrhizal colonization and root intermingling. Transfer of N between plants with contrasting nutrient‐acquisition strategies occurred at both low and high soil nutrient levels with or without root intermingling. The magnitude of N transfer was relatively high (representing 4% of donor plant N) given the lack of N₂ fixation. Receiver plants forming ectomycorrhizas or cluster roots were more enriched compared with AM‐only plants. We demonstrate N transfer between plants of contrasting nutrient‐acquisition strategies, and a preferential enrichment of cluster‐rooted and EM plants compared with AM plants. Nutrient exchanges among plants are potentially important in promoting plant coexistence in nutrient‐poor soils.     

Cloning and functional analysis of chicory root fructan1‐exohydrolase I (1‐FEH I): a vacuolar enzyme derivedfrom a cell‐wall invertase ancestor? Mass fingerprint of the 1‐FEH I enzyme

This paper describes the cloning and functional analysis of chicory (Cichorium intybus L.) fructan 1-exohydrolase I cDNA (1-FEH I). To our knowledge it is the first plant FEH cloned. Full-length cDNA was obtained by a combination of RT-PCR, 5' and 3' RACE using primers based on N-terminal and conserved amino acid sequences. Electrophoretically purified 1-FEH I enzyme was further analyzed by in-gel trypsin digestion followed by matrix-assisted laser desorption ionization and electrospray time-of-flight tandem mass spectrometry. Functionality of the cDNA was demonstrated by heterologous expression in potato tubers. 1-FEH I takes a new, distinct position in the phylogenetic tree of plant glycosyl hydrolases being more homologous to cell-wall invertases (44-53%) than to vacuolar invertases (38-41%) and fructosyl transferases (33-38%). The 1-FEH I enzyme could not be purified from the apoplastic fluid at significantly higher levels than can be explained by cellular leakage. These and other data suggest a vacuolar localization for 1-FEH I. Also, the pI of the enzyme (6.5) is lower than expected from a typical cell-wall invertase. Unlike plant fructosyl transferases that are believed to have evolved from a vacuolar invertase, 1-FEH I might have evolved from a cell-wall invertase-like ancestor gene that later obtained a vacuolar targeting signal. 1-FEH I mRNA quantities increase in the roots throughout autumn, and especially when roots are stored at low temperature.     

Do virus‐resistant plants pose a threat to non‐target ecosystems? II. Risk assessment of an Australian pathosystem using multi‐scale field experiments

It has been widely argued that the acquisition of novel disease resistance genes by wild host populations following the release of novel pathogen‐resistant plants into agricultural systems could pose a significant threat to non‐target plant communities. However, predicting the magnitude of ecological release in wild plant populations following the removal of disease remains a major challenge. In this paper we report on the second phase of a tiered risk assessment designed to investigate the role of disease on host growth, survival, fecundity and fitness in a model pathosystem (the pasture species Trifolium repens infected with Clover yellow vein virus, ClYVV) and to assess the level of risk posed to at‐risk native plant communities in southeast Australia by newly developed genetically modified and conventionally bred virus‐resistant T. repens genotypes. Multi‐year field experiments conducted in woodland and grassland environments using host‐pathogen arrays derived from 14 ClYVV isolates and 21 T. repens genotypes indicate that viral infection reduces fecundity, growth and survival of wild T. repens plants but that the severity of these effects depends on host tolerance to infection, isolate aggressiveness and specific spatial and temporal environmental conditions. Demographic modelling showed that by reducing host survival and growth, ClYVV also limits the intrinsic population growth rate and niche size of wild T. repens populations. Given the significant fitness cost associated with viral infection we conclude that virus‐resistant T. repens genotypes may pose a threat to some high conservation‐value non‐target ecosystems in SE Australia. We also argue that long‐term, multi‐tiered experiments conducted in a range of controlled and non‐controlled environments are necessary to detect and accurately quantify risks associated with the release of disease‐resistant plants in general.     

Latitudinal trends in plant‐pollinator interactions: are tropical plants more specialised?

The increase in richness of species and higher taxa going from higher to lower latitudes is one of the most studied global biogeographical patterns. Latitudinal trends in the interactions between species have, in contrast, hardly been studied at all, probably because recording interactions is much less straightforward than counting species. We have assembled two independent data sets which suggest that plant-pollinator interactions are not more ecologically specialised in the tropics compared to temperate latitudes. This is in contrast to a prevailing view that tropical ecological interactions tend towards higher specificity than their temperate counterparts.     

Does the growth response of woody plants to elevated CO2 increase with temperature? A model‐oriented meta‐analysis

The temperature dependence of the reaction kinetics of the Rubisco enzyme implies that, at the level of a chloroplast, the response of photosynthesis to rising atmospheric CO₂ concentration (C_a) will increase with increasing air temperature. Vegetation models incorporating this interaction predict that the response of net primary productivity (NPP) to elevated CO₂ (eC_a) will increase with rising temperature and will be substantially larger in warm tropical forests than in cold boreal forests. We tested these model predictions against evidence from eC_a experiments by carrying out two meta‐analyses. Firstly, we tested for an interaction effect on growth responses in factorial eC_a × temperature experiments. This analysis showed a positive, but nonsignificant interaction effect (95% CI for above‐ground biomass response = ?0.8, 18.0%) between eC_a and temperature. Secondly, we tested field‐based eC_a experiments on woody plants across the globe for a relationship between the eC_a effect on plant biomass and mean annual temperature (MAT). This second analysis showed a positive but nonsignificant correlation between the eC_a response and MAT. The magnitude of the interactions between CO₂ and temperature found in both meta‐analyses were consistent with model predictions, even though both analyses gave nonsignificant results. Thus, we conclude that it is not possible to distinguish between the competing hypotheses of no interaction vs. an interaction based on Rubisco kinetics from the available experimental database. Experiments in a wider range of temperature zones are required. Until such experimental data are available, model predictions should aim to incorporate uncertainty about this interaction.     

Molecular pharming — VLPs made in plants

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Host plants and butterfly biology. Do host‐plant strategies drive butterfly status?

Abstract. 1. To determine whether rarity and decline is linked to organism ecology, associations have been examined between butterfly larval host‐plant competitive, stress‐tolerant, ruderal (C‐S‐R) strategies and butterfly biology. 2. Associations have been sought between mean C‐S‐R scores for larval host plants with butterfly life history, morphology and physiology variables, resource use, population attributes, geography, and conservation status. Comparisons are carried out across species and controlled for phylogenetic patterning. 3. Butterfly biology is linked to host‐plant strategies. An increasing tendency of a butterfly's host plants to a particular strategy biases that butterfly species to functionally linked life‐history attributes and resource breadth and type. In turn, population attributes and geography are significantly and substantially affected by host choice and the strategies of these host plants. 4. The greatest contrast is between butterfly species whose host plants are labelled C and R strategists and those whose host plants are labelled S strategists. Increasingly high host‐plant C and R strategy scores bias butterflies to rapid development, short early stages, multivoltinism, long flight periods, early seasonal emergence, higher mobility, polyphagy, wide resource availability and biotope occupancy, open, areally expansive, patchy population structures, denser distributions, wider geographical ranges, resistance to range retractions as well as to increasing rarity in the face of environmental changes. Increasing host‐plant S strategy scores have reversed tendencies, biasing those butterfly species to extended development times, fewer broods, short flight periods, smaller wing expanse and lower mobility, monophagy, restricted resource exploitation and biotope occupancy, closed, areally limited populations with typical metapopulation structures, sparse distributions, and limited geographical ranges, range retractions, and increased rarity. 5. Species with S strategy host plants are species vulnerable to current environmental changes and species of conservation concern.     

Optimality modeling and fitness trade‐offs: when should plants become pollinator specialists?

The assumption that flowers readily evolve specializations for pollination by particular animals has been central to a standard view of pollinator-mediated adaptive divergence in angiosperms. Stebbins' Most Effective Pollinator Principle (MEPP) formalized this assumption in proposing that a plant should always evolve specializations to its most effective pollinator. I argue that the MEPP and its corollaries are unsupported by basic models of phenotypic selection which predict that a plant should evolve greater specialization to a particular pollinator when the marginal fitness gain exceeds the marginal fitness loss from becoming less adapted to all other pollinators. Differences in pollinator effectiveness are neither necessary nor sufficient to predict specialization. Differences in effectiveness certainly can foster floral specialization to the most effective pollinator in some cases, but when adaptation to a relatively ineffective pollinator requires little loss in the fitness contribution of a more effective pollinator, plants may exhibit striking specializations for the less effective pollinator. Recognizing that the effectiveness of pollinators is not tightly coupled to their importance in selecting for phenotypic novelty may resolve the mismatch between floral features that appear to represent clear evolutionary responses to specific pollinators and patterns of flower visitation that often seem generalized. To shed light on agents of selection and the adaptive value of floral traits I argue that we must go beyond measures of pollinator effectiveness to investigate pollinator-mediated fitness trade-offs over a range of floral phenotypes.     

How do plants know when other plants are flowering? Resource depletion,pollen limitation and mast‐seeding in a perennial wildflower

Mast-seeding is the synchronous and periodic reproduction by plant populations. This phenomenon has been widely studied from a community-level perspective, but we know extremely little about how plants are able to synchronize reproduction. Here, we present the first experimental test of proximate mechanisms of mast-seeding, by preventing reproduction in an iteroparous, mast-seeding wildflower. Through a series of experiments, we show that mobile carbohydrate stores (NSC) control alternate-year flowering by individual plants; seed set depletes NSC which prevents flowering the following year. Plants are synchronized by density-dependent pollen limitation; when plants flower asynchronously, they set fewer seeds, which prevents NSC depletion. Therefore, these individual plants flower in subsequent years and become synchronized. Because mast-seeding is a consequence of physiological controls of reproduction, differences in plant resource acquisition and allocation could dramatically change patterns of seed production, and changes in plant consumers and pollinators could change selection on physiological and developmental pathways.     

Mapitjakuna—Shall I Go Away From Myself Towards You? Being‐with and Looking‐at Across Cultural Divides

Anthropologists increasingly express links between individuals or collectivities through the discursively convenient prefix ‘‐inter’; inter‐personal, inter‐subjective, inter‐cultural, inter‐textual. However, attempts to describe the psychodynamics that effect the linkings that are integral to human social experience have not held pace. I want to suggest that a regard for the ontogenetic primary forms of encounter—looking, eating, playing—can substantiate the analysis of being a self among other selves within and across the boundaries of social worlds. Engaging a phenomenological and psychoanalytic perspective, this paper examines how We‐relationships have been variously structured by Pitjantjatjara Aborigines in encountering others at home and in Germany.