Herbivory: effects on plant abundance, distribution and population growth

Plants are attacked by many different consumers. A critical question is how often, and under what conditions, common reductions in growth, fecundity or even survival that occur due to herbivory translate to meaningful impacts on abundance, distribution or dynamics of plant populations. Here, we review population-level studies of the effects of consumers on plant dynamics and evaluate: (i) whether particular consumers have predictably more or less influence on plant abundance, (ii) whether particular plant life-history types are predictably more vulnerable to herbivory at the population level, (iii) whether the strength of plant-consumer interactions shifts predictably across environmental gradients and (iv) the role of consumers in influencing plant distributional limits. Existing studies demonstrate numerous examples of consumers limiting local plant abundance and distribution. We found larger effects of consumers on grassland than woodland forbs, stronger effects of herbivory in areas with high versus low disturbance, but no systematic or unambiguous differences in the impact of consumers based on plant life-history or herbivore feeding mode. However, our ability to evaluate these and other patterns is limited by the small (but growing) number of studies in this area. As an impetus for further study, we review strengths and challenges of population-level studies, such as interpreting net impacts of consumers in the presence of density dependence and seed bank dynamics.     

Plant proteome changes under abiotic stress--contribution of proteomics studies to understanding plant stress response

Plant acclimation to stress is associated with profound changes in proteome composition. Since proteins are directly involved in plant stress response, proteomics studies can significantly contribute to unravel the possible relationships between protein abundance and plant stress acclimation. In this review, proteomics studies dealing with plant response to a broad range of abiotic stress factors--cold, heat, drought, waterlogging, salinity, ozone treatment, hypoxia and anoxia, herbicide treatments, inadequate or excessive light conditions, disbalances in mineral nutrition, enhanced concentrations of heavy metals, radioactivity and mechanical wounding are discussed. Most studies have been carried out on model plants Arabidopsis thaliana and rice due to large protein sequence databases available; however, the variety of plant species used for proteomics analyses is rapidly increasing. Protein response pathways shared by different plant species under various stress conditions (glycolytic pathway, enzymes of ascorbate-glutathione cycle, accumulation of LEA proteins) as well as pathways unique to a given stress are discussed. Results from proteomics studies are interpreted with respect to physiological factors determining plant stress response. In conclusion, examples of application of proteomics studies in search for protein markers underlying phenotypic variation in physiological parameters associated with plant stress tolerance are given.     

Plant antigens cross-react with rat polyclonal antibodies against KLH-conjugated peptides

Keyhole limpet hemocyanin (KLH)-conjugated peptides are routinely used to raise polyclonal antibodies for biochemical or immunolocalization studies. Rats are suitable for producing antisera against plant antigens as they often lack non-specific response towards plant materials. We attempted to obtain rat antisera against peptides derived from several plant proteins. However, most antisera recognized the same background KLH-related plant antigen (KRAP) in Arabidopsis and tobacco. We characterized KRAP with respect to size and cellular localization and examined possible antigen-specific reasons for the failure of most immunizations. We also found no reports of successful use of rat anti-KLH-peptide antibodies in plant studies. We thus believe that the rat-KLH:peptide system is poorly suited for production of antibodies, especially against plant antigens, and should be used with caution, if at all.     

Radiation measurement for plant ecophysiology

The principles of radiation physics for plant ecophysiological studies are outlined with an emphasis on choosing appropriate sensors for specific purposes such as for studies of photosynthesis, UV-B damage or canopy energy balance. Remote sensing, both from the ground and from aircraft or satellites, is increasingly being used as a tool for the study of plant canopies. Therefore, relevant terminology and applications are discussed, including the use of remote sensing for the determination of canopy structural properties and the use of thermal remote sensing for the measurement of canopy temperature, for example, in energy balance studies.     

Geminivirus-based shuttle vectors capable of replication in Escherichia coli and monocotyledonous plant cells

Shuttle vectors have been constructed that are able to replicate in either Escherichia coli or plant cells. They contain the ColE1 origin of replication and parts of the wheat dwarf virus genome, a geminivirus infecting a variety of species of monocotyledonous plants. Such plasmids are able to replicate in E. coli and wheat cells. The plasmids can be rescued in E. coli and show no changes during their passage through plant cells. Such an E. coli/plant cell shuttle vector system could be used for the amplification of foreign genes in plant cells, for studies on DNA rearrangement or the isolation of plant transposons.     

Using nuclear gene data for plant phylogenetics: Progress and prospects

The paper reviews the current state of low and single copy nuclear markers that have been applied successfully in plant phylogenetics to date, and discusses case studies highlighting the potential of massively parallel high throughput or next-generation sequencing (NGS) approaches for molecular phylogenetic and evolutionary investigations. The current state, prospects and challenges of specific single- or low-copy plant nuclear markers as well as phylogenomic case studies are presented and evaluated.     

Reprint of: Using nuclear gene data for plant phylogenetics: Progress and prospects

The paper reviews the current state of low and single copy nuclear markers that have been applied successfully in plant phylogenetics to date, and discusses case studies highlighting the potential of massively parallel high throughput or next-generation sequencing (NGS) approaches for molecular phylogenetic and evolutionary investigations. The current state, prospects and challenges of specific single- or low-copy plant nuclear markers as well as phylogenomic case studies are presented and evaluated.     

Cytoskeleton and plant organogenesis

The functions of microtubules and actin filaments during various processes that are essential for the growth, reproduction and survival of single plant cells have been well characterized. A large number of plant structural cytoskeletal or cytoskeleton-associated proteins, as well as genes encoding such proteins, have been identified. Although many of these genes and proteins have been partially characterized with respect to their functions, a coherent picture of how they interact to execute cytoskeletal functions in plant cells has yet to emerge. Cytoskeleton-controlled cellular processes are expected to play crucial roles during plant cell differentiation and organogenesis, but what exactly these roles are has only been investigated in a limited number of studies in the whole plant context. The intent of this review is to discuss the results of these studies in the light of what is known about the cellular functions of the plant cytoskeleton, and about the proteins and genes that are required for them. Directions are outlined for future work to advance our understanding of how the cytoskeleton contributes to plant organogenesis and development.     

Molecular population genetics and the search for adaptive evolution in plants

The first papers on plant molecular population genetics were published approximately 10 years ago. Since that time, well over 50 additional studies of plant nucleotide polymorphism have been published, and many of these studies focused on detecting the signature of balancing or positive selection at a locus. In this review, we discuss some of the theoretical and statistical issues surrounding the detection of selection, with focus on plant populations, and we also summarize the empirical plant molecular population genetics literature. At face value, the literature suggests that a history of balancing or positive selection in plant genes is rampant. In two well-studied taxa (maize and Arabidopsis) over 20% of studied genes have been interpreted as containing the signature of selection. We argue that this is probably an overstatement of the prevalence of natural selection in plant genomes, for two reasons. First, demographic effects are difficult to incorporate and have generally not been well integrated into the plant population genetics literature. Second, the genes studied to date are not a random sample, so selected genes may be overrepresented. The next generation of studies in plant molecular population genetics requires additional sampling of local populations, explicit comparisons among loci, and improved theoretical methods to control for demography. Eventually, candidate loci should be confirmed by explicit consideration of phenotypic effects.     

Monitoring plant and soil water status: established and novel methods revisited and their relevance to studies of drought tolerance

In all studies of the effects of water deficits on plant functioning there is a need for an accurate and comprehensive definition of treatments and their effects on plant water status. The various measures of water status used in plant and soil science are reviewed and their appropriateness for different purposes such as for studies of mechanistic effects of water deficits on plants, for breeding of drought-tolerant plants, or for management of irrigation systems are reviewed. An important conclusion is that the frequent emphasis on water potential rather than on cell turgor can be shown to be misleading, as can be measurements in the leaf. The disadvantages of the current trend towards the omission of necessary water-status measurements, especially common in more molecular studies, are outlined, and recommendations made for minimal sets of measurements for specific types of experiments.     

Are herbivore-induced plant volatiles reliable indicators of herbivore identity to foraging carnivorous arthropods?

Plants that are damaged by herbivorous arthropods provide carnivorous enemies of the herbivores with important information. They emit an induced volatile blend that is highly detectable to the carnivores from a distance. Such detectable signals that indicate herbivore presence are important for the carnivores because herbivores themselves are under strong selection not to expose themselves. In addition, carnivores would benefit from a specificity of the induced plant volatiles. Whether herbivore-induced plant volatiles are reliable indicators of herbivore identity, however, has not been resolved unambiguously. Some studies support the reliability of herbivore-induced plant volatiles, while others do not. Different approaches have been used such as chemical analysis, behavioural analysis or a combination of the two. Based on the total of chemical studies one might conclude that in most cases herbivore-induced plant volatiles are not very specific for the herbivore that damages the plant. However, arthropod chemosensors are much more sensitive than the detectors of analytical instruments. Therefore, chemical analyses are not suitable to demonstrate whether or not herbivore-induced plant volatiles are reliable indicators of herbivore identity to carnivores. Behavioural studies should provide this information. In analysing carnivore behaviour it should be realised, however, that arthropod behaviour can be highly variable. Arthropod foraging decisions are affected by external and internal factors such as (a) abiotic environmental factors, (b) presence of competitors or enemies, (c) deprivation of food or oviposition sites, (d) specific deprivation of certain nutrients or (e) learning. In this paper their effect on discrimination of carnivores between volatile blends emitted by plants infested by different herbivores is reviewed. This provides testable hypotheses of why discrimination was not found in some studies. The ability of carnivores to discriminate is likely to be more common than is clear to date, which should invoke functional studies of the conditions that influence the occurrence of this discrimination.     

On quantifying tolerance of herbivory for comparative analyses

As the evolutionary importance of plant tolerance of herbivory is increasingly appreciated, more and more studies are not just measuring a plant's tolerance, but are comparing tolerance among plant genotypes, populations, species, and environments. Here, we suggest that caution must be taken in such comparative studies in the choice of measurement scales (and data transformations) for damage levels and plant performance. We demonstrate with a simple scenario of two plant groups of equal tolerance how the choice of scales can lead one to infer that the first group is more tolerant, the second group is more tolerant, or the two groups are equally tolerant-using the identical dataset. We conclude that to make reliable, logically consistent inferences when comparing tolerances among groups of plants, damage and performance should both be on an additive scale or both on a multiplicative scale.     

Female Salix viminalis are more severely infected by Melampsora spp. but neither sex experiences associational effects

Associational effects of plant genotype or species on plant biotic interactions are common, not least for disease spread, but associational effects of plant sex on interactions have largely been ignored. Sex in dioecious plants can affect biotic interactions with herbivores and pollinators; however, its effects on plant–pathogen interactions are understudied and associational effects are unknown. In a replicated field experiment, we assessed Melampsora spp. leaf rust infection in monosexual and mixed sex plots of dioecious Salix viminalis L. to determine whether plant sex has either direct or associational effects on infection severity. We found no differences in Melampsora spp. infection severity among sexual monocultures and mixtures in our field experiment. However, female plants were overall more severely infected. In addition, we surveyed previous studies of infection in S. viminalis clones and reevaluated the studies after we assigned sex to the clones. We found that females were generally more severely infected, as in our field study. Similarly, in a survey of studies on sex‐biased infection in dioecious plants, we found more female‐biased infections in plant–pathogen pairs. We conclude that there was no evidence for associational plant sex effects of neighboring conspecifics for either females or males on infection severity. Instead, plant sex effects on infection act at an individual plant level. Our findings also suggest that female plants may in general be more severely affected by fungal pathogens than males.     

植物茎秆性状形成与发育的分子基础

株型是作物品种改良的重要目标性状, 其中茎秆是最重要的株型性状。植物发育分子生物学研究表明, 茎秆性状的形成和发育受多个重要基因的严格调控。本文从茎秆的发生、形状和分枝的形成等方面对茎秆发育的分子机理进行概述, 以期为植物株型的改良提供理论依据。     

植物茎秆性状形成与发育的分子基础

株型是作物品种改良的重要目标性状,其中茎秆是最重要的株型性状。植物发育分子生物学研究表明,茎秆性状的形成和发育受多个重要基因的严格调控。本文从茎秆的发生、形状和分枝的形成等方面对茎秆发育的分子机理进行概述,以期为植物株型的改良提供理论依据。     

The Banker Plant Method in Biological Control

In the banker plant method, long-lasting rearing units for beneficials are created in the crop by distributing plants infested with herbivores or carrying other food items, such as pollen. The method has been widely investigated over many years and used to aid establishment, development and dispersal of beneficial organisms employed in biological control. In this review, we refine the definition of the banker plant method based on previous concepts and studies and offer the term “banker plant system” to describe the unit that is purposefully added to or established in a crop for control of pests in greenhouses or open field. The three basic elements of a banker plant system (banker plant, food source, beneficials) are discussed and illustrated with examples, and the diversity of banker plant systems (classified by target pest) used or investigated is documented. The benefits of using banker plant systems, such as low cost, increased freshness of beneficials, possibility for preventive control and for integration within IPM frameworks, make the method an interesting plant protection option with potential to enhance adoption of biological control in pest management programs.     

Interpreting phenotypic variation in plant allelochemistry: problems with the use of concentrations

Ecologists often use concentrations of defensive compounds as measures of plant allocation to defence and/or allelochemical production. I demonstrate that this practice may lead to erroneous conclusions because plants produce and allocate molecules (quantities) of compounds whereas concentrations reflect the distribution of these quantities in plant tissues and are, therefore, functions of plant biomass. As a tool for distinguishing between shifts in allelochemical production versus changes in plant biomass in determining allelochemical concentrations, I suggest using a technique known as graphical vector analysis (GVA) which has been developed for diagnosing nutrient limitations in forest stands, but has seldom been applied by researchers studying plant allelochemicals. I used data from several published studies to demonstrate how GVA can be applied to interpret ontogenetic and environmental effects on allelochemical levels and to compare the results obtained for different allelochemical types, plant species, treatments and experiments. These examples show that changes in plant biomass per se are an important source of variation in allelochemical concentrations and, therefore, concentration data can be easily misinterpreted if changes in absolute content and plant biomass are not considered simultaneously. Because studies reporting variation in allelochemical concentrations have been considered as tests for general theories of plant chemical defence, evidence in support of or against these theories should be re-examined using multivariate techniques such as analysis of covariance, allometric analysis and GVA. Received: 16 September 1998 / Accepted: 4 March 1999     

Plant–plant interactions,environmental gradients and plant diversity: A global synthesis of community-level studies

Previous syntheses on the effects of environmental conditions on the outcome of plant–plant interactions summarize results from pairwise studies. However, the upscaling to the community-level of such studies is problematic because of the existence of multiple species assemblages and species-specific responses to both the environmental conditions and the presence of neighbors. We conducted the first global synthesis of community-level studies from harsh environments, which included data from 71 alpine and 137 dryland communities to: (i) test how important are facilitative interactions as a driver of community structure, (ii) evaluate whether we can predict the frequency of positive plant–plant interactions across differing environmental conditions and habitats, and (iii) assess whether thresholds in the response of plant–plant interactions to environmental gradients exists between “moderate” and “extreme” environments. We also used those community-level studies performed across gradients of at least three points to evaluate how the average environmental conditions, the length of the gradient studied, and the number of points sampled across such gradient affect the form and strength of the facilitation-environmental conditions relationship. Over 25% of the species present were more spatially associated to nurse plants than expected by chance in both alpine and dryland areas, illustrating the high importance of positive plant–plant interactions for the maintenance of plant diversity in these environments. Facilitative interactions were more frequent, and more related to environmental conditions, in alpine than in dryland areas, perhaps because drylands are generally characterized by a larger variety of environmental stress factors and plant functional traits. The frequency of facilitative interactions in alpine communities peaked at 1000 mm of annual rainfall, and globally decreased with elevation. The frequency of positive interactions in dryland communities decreased globally with water scarcity or temperature annual range. Positive facilitation-drought stress relationships are more likely in shorter regional gradients, but these relationships are obscured in regions with a greater species turnover or with complex environmental gradients. By showing the different climatic drivers and behaviors of plant–plant interactions in dryland and alpine areas, our results will improve predictions regarding the effect of facilitation on the assembly of plant communities and their response to changes in environmental conditions.     

Mechanisms underlying the impacts of exotic plant invasions

Although the impacts of exotic plant invasions on community structure and ecosystem processes are well appreciated, the pathways or mechanisms that underlie these impacts are poorly understood. Better exploration of these processes is essential to understanding why exotic plants impact only certain systems, and why only some invaders have large impacts. Here, we review over 150 studies to evaluate the mechanisms underlying the impacts of exotic plant invasions on plant and animal community structure, nutrient cycling, hydrology and fire regimes. We find that, while numerous studies have examined the impacts of invasions on plant diversity and composition, less than 5% test whether these effects arise through competition, allelopathy, alteration of ecosystem variables or other processes. Nonetheless, competition was often hypothesized, and nearly all studies competing native and alien plants against each other found strong competitive effects of exotic species. In contrast to studies of the impacts on plant community structure and higher trophic levels, research examining impacts on nitrogen cycling, hydrology and fire regimes is generally highly mechanistic, often motivated by specific invader traits. We encourage future studies that link impacts on community structure to ecosystem processes, and relate the controls over invasibility to the controls over impact.