Global pattern of plant utilization across different organisms: Does plant apparency or plant phylogeny matter?

The present study is the first to consider human and nonhuman consumers together to reveal several general patterns of plant utilization. We provide evidence that at a global scale, plant apparency and phylogenetic isolation can be important predictors of plant utilization and consumer diversity. Using the number of species or genera or the distribution area of each plant family as the island “area” and the minimum phylogenetic distance to common plant families as the island “distance”, we fitted presence–area relationships and presence–distance relationships with a binomial GLM (generalized linear model) with a logit link. The presence–absence of consumers among each plant family strongly depended on plant apparency (family size and distribution area); the diversity of consumers increased with plant apparency but decreased with phylogenetic isolation. When consumers extended their host breadth, unapparent plants became more likely to be used. Common uses occurred more often on common plants and their relatives, showing higher host phylogenetic clustering than uncommon uses. On the contrary, highly specialized uses might be related to the rarity of plant chemicals and were therefore very species‐specific. In summary, our results provide a global illustration of plant–consumer combinations and reveal several general patterns of plant utilization across humans, insects and microbes. First, plant apparency and plant phylogenetic isolation generally govern plant utilization value, with uncommon and isolated plants suffering fewer parasites. Second, extension of the breadth of utilized hosts helps explain the presence of consumers on unapparent plants. Finally, the phylogenetic clustering structure of host plants is different between common uses and uncommon uses. The strength of such consistent plant utilization patterns across a diverse set of usage types suggests that the persistence and accumulation of consumer diversity and use value for plant species are determined by similar ecological and evolutionary processes.     

Vegetation complexity—The influence of plant species diversity and plant structures on plant chemical complexity and arthropods

Vegetation complexity is characterized by two major traits, i.e., plant chemical and plant structural complexity. Plant species diversity strongly determines these traits. Furthermore, plant structures affect microclimatic conditions, which in turn influence the emission and dispersion of plant volatiles (e.g., chemical complexity). Plant volatile chemical complexity may significantly affect orientation of herbivorous and carnivorous arthropods. Therefore, the way in which plant chemical and plant structural complexity act “in concert” may influence foraging and mating success of arthropods, and thus, finally, community composition. This review emphasizes an integrative view on the relationship between plant species diversity, plant structural complexity, plant volatiles (chemical complexity) and their effects on arthropods. Three new hypotheses are raised, which predict possible relations between plant volatile complexity and plant species diversity: (1) saturation-, (2) step-by-step, (3) incoherence-hypothesis. We conclude that arthropod orientation in natural environments is strongly determined by the relationship between plant volatile diversity and plant species diversity. Furthermore, we emphasize that structural complexity of the vegetation affects plant volatile diversity and thus, arthropod orientation.We review available information on how insects actually respond to complexity during olfactory and visual search and ask for both laboratory and field studies to further unravel the mechanisms of interactions between vegetation traits and their impact on arthropod orientation.     

Invasive plant integration into native plant–pollinator networks across Europe

The structure of plant–pollinator networks has been claimed to be resilient to changes in species composition due to the weak degree of dependence among mutualistic partners. However, detailed empirical investigations of the consequences of introducing an alien plant species into mutualistic networks are lacking. We present the first cross-European analysis by using a standardized protocol to assess the degree to which a particular alien plant species (i.e. Carpobrotus affine acinaciformis, Impatiens glandulifera, Opuntia stricta, Rhododendron ponticum and Solanum elaeagnifolium) becomes integrated into existing native plant–pollinator networks, and how this translates to changes in network structure.Alien species were visited by almost half of the pollinator species present, accounting on average for 42 per cent of the visits and 24 per cent of the network interactions. Furthermore, in general, pollinators depended upon alien plants more than on native plants. However, despite the fact that invaded communities received more visits than uninvaded communities, the dominant role of alien species over natives did not translate into overall changes in network connectance, plant linkage level and nestedness. Our results imply that although supergeneralist alien plants can play a central role in the networks, the structure of the networks appears to be very permeable and robust to the introduction of invasive alien species into the network.     

Functional–structural plant models: a growing paradigm for plant studies

A number of research groups in various areas of plant biology as well as computer science and applied mathematics have addressed modelling the spatiotemporal dynamics of growth and development of plants. This has resulted in development of functional–structural plant models (FSPMs). In FSPMs, the plant structure is always explicitly represented in terms of a network of elementary units. In this respect, FSPMs are different from more abstract models in which a simplified representation of the plant structure is frequently used (e.g. spatial density of leaves, total biomass, etc.). This key feature makes it possible to build modular models and creates avenues for efficient exchange of model components and experimental data. They are being used to deal with the complex 3-D structure of plants and to simulate growth and development occurring at spatial scales from cells to forest areas, and temporal scales from seconds to decades and many plant generations. The plant types studied also cover a broad spectrum, from algae to trees. This special issue of Annals of Botany features selected papers on FSPM topics such as models of morphological development, models of physical and biological processes, integrated models predicting dynamics of plants and plant communities, modelling platforms, methods for acquiring the 3-D structures of plants using automated measurements, and practical applications for agronomic purposes.     

Denitrification by plant roots? New aspects of plant plasma membrane-bound nitrate reductase

A specific form of plasma membrane-bound nitrate reductase in plants is restricted to roots. Two peptides originated from plasma membrane integral proteins isolated from Hordeum vulgare have been assigned as homologues to the subunit NarH of respiratory nitrate reductase of Escherichia coli. Corresponding sequences have been detected for predicted proteins of Populus trichocarpa with high degree of identities for the subunits NarH (75%) and NarG (65%), however, with less accordance for the subunit NarI. These findings coincide with biochemical properties, particularly in regard to the electron donors menadione and succinate. Together with the root-specific and plasma membrane-bound nitrite/NO reductase, nitric oxide is produced under hypoxic conditions in the presence of nitrate. In this context, a possible function in nitrate respiration of plant roots and an involvement of plants in denitrification processes are discussed.     

Competition overwhelms the positive plant–soil feedback generated by an invasive plant

Invasive plant species can modify soils in a way that benefits their fitness more than the fitness of native species. However, it is unclear how competition among plant species alters the strength and direction of plant–soil feedbacks. We tested how community context altered plant–soil feedback between the non-native invasive forb Lespedeza cuneata and nine co-occurring native prairie species. In a series of greenhouse experiments, we grew plants individually and in communities with soils that differed in soil origin (invaded or uninvaded by L. cuneata) and in soils that were live vs. sterilized. In the absence of competition, L. cuneata produced over 60% more biomass in invaded than uninvaded soils, while native species performance was unaffected. The absence of a soil origin effect in sterile soil suggests that the positive plant–soil feedback was caused by differences in the soil biota. However, in the presence of competition, the positive effect of soil origin on L. cuneata growth disappeared. These results suggest that L. cuneata may benefit from positive plant–soil feedback when establishing populations in disturbed landscapes with few interspecific competitors, but does not support the hypothesis that plant–soil feedbacks influence competitive outcomes between L. cuneata and native plant species. These results highlight the importance of considering whether competition influences the outcome of interactions between plants and soils.     

Tissue culture and plant propagation of Gomphrena officinalis — a Brazilian medicinal plant

Leaf and stem segments of Gomphrena officinalis originated from aseptically grown seedlings were used to initiate cultures. Callus production was obtained on gelled Murashige & Skoog medium supplemented with 6-benzylaminopurine alone (1.0, 5.0 or 10.0 mgl^-1) or combined with -naphthalene acetic acid (0.1, 0.5 and 1.0 mgl^-1) after 10 to 15 days of culture, and can be transferred to fresh medium every 30 days. The combinations of 5.0 or 10.0 mgl^-1 of 6-benzylaminopurine with 0.1 mgl^-1 of -naphthalene acetic acid were found to be the best for shoot regeneration. Adventitious shoot formation occurred after 50 to 60 days of culture in leaf and internode stem explants. Nodal segments developed actively growing lateral buds after 30 days of culture. Gelled Murashige & Skoog medium containing 10 mgl^-1 of indole-3-butyric acid was considered optimal for the rooting of shoots. Rooted plants transferred to potting soil could be successfully established.Abbreviations BA 6-benzylaminopurine - IAA indole-3-acetic acid - IBA indole-3-butyric acid - MS Murashige & Skoog - NAA -naphthalene acetic acid     

The effect of host mycorrhizal status on host plant–parasitic plant interactions

Two pot experiments were conducted to examine three-level interactions between host plants, mycorrhizal fungi and parasitic plants. In a greenhouse experiment, Poa annua plants were grown in the presence or absence of an AM fungus (either Glomus lamellosum V43a or G. mosseae BEG29) and in the presence or absence of a root hemiparasitic plant (Odontites vulgaris). In a laboratory experiment, mycorrhizal infection (Glomus claroideum BEG31) of Trifolium pratense host plants (mycorrhizal versus non-mycorrhizal) was combined with hemiparasite infection (Rhinanthus serotinus) of the host (parasitized versus non-parasitized). Infection with the two species of Glomus had no significant effect on the growth of P. annua, while hemiparasite infection caused a significant reduction in host biomass. Mycorrhizal status of P. annua hosts (i.e. presence/absence of AM fungus) affected neither the biomass nor the number of flowers produced by the attached O. vulgaris plants. Infection with G. claroideum BEG31 greatly increased the biomass of T. pratense, but hemiparasite infection had no effect. The hemiparasitic R. serotinus plants attached to mycorrhizal hosts had higher biomass and produced more flowers than plants growing with non-mycorrhizal hosts. Roots of T. pratense were colonized by the AM fungus to an extent independent of the presence or absence of the hemiparasite. Our results confirm earlier findings that the mycorrhizal status of a host plant can affect the performance of an attached root hemiparasite. However, improvement of the performance of the parasitic plant following attachment to a mycorrhizal host depends on the extent to which the AM fungi is able to enhance the growth of the host. Accepted: 23 February 2001     

Additive effects of exotic plant abundance and land-use intensity on plant–pollinator interactions

The continuing spread of exotic plants and increasing human land-use are two major drivers of global change threatening ecosystems, species and their interactions. Separate effects of these two drivers on plant–pollinator interactions have been thoroughly studied, but we still lack an understanding of combined and potential interactive effects. In a subtropical South African landscape, we studied 17 plant–pollinator networks along two gradients of relative abundance of exotics and land-use intensity. In general, pollinator visitation rates were lower on exotic plants than on native ones. Surprisingly, while visitation rates on native plants increased with relative abundance of exotics and land-use intensity, pollinator visitation on exotic plants decreased along the same gradients. There was a decrease in the specialization of plants on pollinators and vice versa with both drivers, regardless of plant origin. Decreases in pollinator specialization thereby seemed to be mediated by a species turnover towards habitat generalists. However, contrary to expectations, we detected no interactive effects between the two drivers. Our results suggest that exotic plants and land-use promote generalist plants and pollinators, while negatively affecting specialized plant–pollinator interactions. Weak integration and high specialization of exotic plants may have prevented interactive effects between exotic plants and land-use. Still, the additive effects of exotic plants and land-use on specialized plant–pollinator interactions would have been overlooked in a single-factor study. We therefore highlight the need to consider multiple drivers of global change in ecological research and conservation management.     

Individual flowering phenology shapes plant–pollinator interactions across ecological scales affecting plant reproduction

The balance of pollination competition and facilitation among co-flowering plants and abiotic resource availability can modify plant species and individual reproduction. Floral resource succession and spatial heterogeneity modulate plant–pollinator interactions across ecological scales (individual plant, local assemblage, and interaction network of agroecological infrastructure across the farm). Intraspecific variation in flowering phenology can modulate the precise level of spatio-temporal heterogeneity in floral resources, pollen donor density, and pollinator interactions that a plant individual is exposed to, thereby affecting reproduction. We tested how abiotic resources and multi-scale plant–pollinator interactions affected individual plant seed set modulated by intraspecific variation in flowering phenology and spatio-temporal floral heterogeneity arising from agroecological infrastructure. We transplanted two focal insect-pollinated plant species (Cyanus segetum and Centaurea jacea, n = 288) into agroecological infrastructure (10 sown wildflower and six legume–grass strips) across a farm-scale experiment (125 ha). We applied an individual-based phenologically explicit approach to match precisely the flowering period of plant individuals to the concomitant level of spatio-temporal heterogeneity in plant–pollinator interactions, potential pollen donors, floral resources, and abiotic conditions (temperature, water, and nitrogen). Individual plant attractiveness, assemblage floral density, and conspecific pollen donor density (C. jacea) improved seed set. Network linkage density increased focal species seed set and modified the effect of local assemblage richness and abundance on C. segetum. Mutual dependence on pollinators in networks increased C. segetum seed set, while C. jacea seed set was greatest where both specialization on pollinators and mutual dependence was high. Abiotic conditions were of little or no importance to seed set. Intra- and interspecific plant–pollinator interactions respond to spatio-temporal heterogeneity arising from agroecological management affecting wild plant species reproduction. The interplay of pollinator interactions within and between ecological scales affecting seed set implies a co-occurrence of pollinator-mediated facilitative and competitive interactions among plant species and individuals.     

Mechanisms of plant and microbial adaptation to heavy metals in plant–microbial systems

The data on heavy metal (HM) accumulation and detoxification by plants and bacteria in plant–microbial systems (PMS) are reviewed. Bacteria are shown to be the labile component of the system, responsible for a considerable amelioration of HM stress impact on plants and for improved PMS adaptation to heavy metals. Simulation of plant–microbial interactions under conditions of soil contamination by HM revealed the protective role of bacterial migration from the rhizoplane to the rhizosphere.     

Ontogenetic shifts in plant–plant interactions in a rare cycad within angiosperm communities

Gymnosperms and angiosperms can co-occur within the same habitats but key plant traits are thought to give angiosperms an evolutionary competitive advantage in many ecological settings. We studied ontogenetic changes in competitive and facilitative interactions between a rare gymnosperm (Dioon sonorense, our target species) and different plant and abiotic neighbours (conspecific-cycads, heterospecific-angiosperms, or abiotic-rocks) from 2007 to 2010 in an arid environment of northwestern Mexico. We monitored survival and growth of seedlings, juveniles, and adults of the cycad Dioon sonorense to evaluate how cycad survival and relative height growth rate (RHGR) responded to intra- and interspecific competition, canopy openness, and nearest neighbour. We tested spatial associations among D. sonorense life stages and angiosperm species and measured ontogenetic shifts in cycad shade tolerance. Canopy openness decreased cycad survival while intraspecific competition decreased survival and RHGR during early ontogeny. Seedling survival was higher in association with rocks and heterospecific neighbours where intraspecific competition was lower. Shade tolerance decreased with cycad ontogeny reflecting the spatial association of advanced stages with more open canopies. Interspecific facilitation during early ontogeny of our target species may promote its persistence in spite of increasing interspecific competition in later stages. We provide empirical support to the long-standing assumption that marginal rocky habitats serve as refugia from angiosperm competition for slow-growing gymnosperms such as cycads. The lack of knowledge of plant–plant interactions in rare or endangered species may hinder developing efficient conservation strategies (e.g. managing for sustained canopy cover), especially under the ongoing land use and climatic changes.     

Drought alters plant‐soil feedback effects on biomass allocation but not on plant performance

Plant and Soil - Drought events can alter the composition of plant and soil communities, and are becoming increasingly common and severe due to climate change. However, how droughts affect...     

Coevolution between interspecific plant competitors?

The most important aspect of an individual's environment may be its individual neighbours; if so, microevolutionary selection pressure could be dominated by the competitors. Since biotic differentiation and coevolution of plant populations is a developing field in which there is strong interest, it has provoked keen discussion. Trifolium repens represents a particularly suitable example for an overview of the advances and criticism voiced in this research field.     

Biogenic volatile organic compounds from an invasive species: impacts on plant–plant interactions

Invasive plant species impact both ecosystems and economies worldwide, often by displacing native biota. Many plant species exude/emit compounds into the surrounding environment with minor consequences in their native habitat due to a long coevolutionary history. However, upon introduction to ecosystems naïve to these compounds, unpredictable interactions can manifest. The majority of the putative allelochemicals studied have been root exudates, despite the large number of plant species that emit volatile organic compounds. We quantified the concentrations and ecological consequences of volatile monoterpenes from the North American invasive perennial Artemisia vulgaris. Ambient monoterpene-mixing ratios inside an A. vulgaris canopy were 0.02–4.15 ppbv in May and 0.01–0.05 ppbv in August, but were negligible (below instrument detection limit of 0.01 ppbv) 10 m away. Foliar disturbance increased total monoterpene concentration to a maximum of 27 ppbv. However, this level remains 1,000-fold lower than that shown to be phytotoxic to sensitive species in laboratory assays. In contrast, soil monoterpene concentrations were >74-fold higher inside [≤35 ± 11 ng g^?1 (SDW)] and 19-fold higher at the edge [9 ± 3 ng g^?1 (SDW)], compared to outside the A. vulgaris stand [0.48 ± 0.05 ng g^?1 (SDW)]. A common native competitor species, Solidago canadensis, grown in pots and resident soil in situ yielded up to 50% less aboveground biomass inside as compared to outside the A. vulgaris stand. Activated carbon had no effect on greenhouse-grown S. canadensis performance when grown with A. vulgaris, suggesting root-derived exudates are not responsible for field observations. Results from this study suggest that A. vulgaris-derived monoterpenes have little direct activity in their volatile gaseous state, but are concentrated in the soil matrix within and bordering the A. vulgaris stand, thereby reducing interspecific performance and potentially fostering the subsequent local invasion of this species.