A Regional Assessment of Changes in Plant–Plant Interactions Along Topography Gradients in Tunisian Sebkhas

Ecosystems - Facilitation among plants in dry ecosystems is crucial for diversity and ecosystem functioning and stability. However, the importance of facilitation in extremely stressful conditions...     

Cyanobacterial–Bacterial Complexes in Plant Syncyanoses

The morphology and ultrastructure of associative microsymbiont complexes (AMC) isolated from the ferns Azolla pinnata and Azolla sp. and the apogeotropic roots of the cycad Cycas revoluta were studied. The composition of the AMC obtained includes the cyanobionts (symbiotic cyanobacteria) and satellite bacteria (SB). It was found that two types of cyanobacteria that substantially differ in their morphological organization are likely present as cyanobionts in the coralloids of C. revoluta. The isolated cyanobiont strains exhibited the morphological traits and regularities of development typical of the genus Nostoc; they were characterized by the ability of their cells to divide in mutually perpendicular planes. When isolating AMC from different morphological zones of C. revoluta apogeotropic roots, SB growth was revealed only around the pieces corresponding to the coralloid apical zone. No AMC components were revealed around the segments of the basal growth zone. Pure cyanobiont cultures were obtained from the AMC of C. revoluta coralloids. The AMC isolated from the ferns A. pinnata and Azolla sp. are characterized by obligate mutual dependence of the partners (the cyanobiont and SB).     

Negative Plant–Soil Feedback and Positive Species Interaction in a Herbaceous Plant Community

Increasing evidence shows that facilitative interaction and negative plant–soil feedback are driving factors of plant population dynamics and community processes. We studied the intensity and the relative impact of negative feedback on clonal growth and seed germination of Scirpus holoschoenus, a ‘ring’ forming sedge dominant in grazed grassland, and the consequences for species coexistence. The structure of aboveground tussocks was described. A Lithium tracer assessed belowground distribution of functional roots. Seed rain and seedling emergence were compared for different positions in relation to Scirpus tussocks. Soil bioassays were used to compare growth on soil taken from inside and outside Scirpus tussocks of four coexisting species (Mentha acquatica, Pulicaria dysenterica, Scirpus holoschoenus and Dittrichia viscosa). We also compared plant performance of dominant plant species inside and outside Scirpus tussocks in the field. The ‘ring’ shaped tussocks of S. holoschoenus were generated by centrifugal rhizome development. Roots were functional and abundant under the tillers and extending outside the tussocks. The large roots mats that were present in the inner tussock zone were almost all dead. Seedling emergence and growth both showed a strong negative feedback of Scirpus in the inner tussock zone. Scirpus clonal development strongly reduced grass biomass. In the degenerated tussock zone, Pulicaria and Mentha mortality was lower, and biomass of individual plants and seed production were higher. This positive indirect interaction could be related to species-specific affinity to soil conditions generated by Scirpus, and interspecific competitive release in the degenerated tussock zone. We conclude that Scirpus negative feedback affects its seedling emergence and growth contributing to the development of the degenerated inner tussock zone. Moreover, this enhances species coexistence through facilitative interaction because the colonization of the inner tussock zone is highly species-specific.     

Plant–plant interactions in tropical alpine environments

Plant–plant interactions are increasingly recognized as a key driver of community organization and ecosystem processes in alpine environments. However, patterns and mechanisms of plant–plant interactions remain largely uncharacterized in tropical alpine ecosystems (TAE) which represent as much as 10% of the total surface area of alpine ecosystems worldwide. In this paper, we review (1) the ecological and environmental features that are specific to TAE in comparison with other alpine ecosystems, (2) the existing literature on plant–plant interactions in TAE, and (3) whether patterns and mechanisms of plant–plant interactions established in extratropical alpine zones can be extended to TAE. TAE are located predominantly in South America, East Africa, and South-East Asia where they show a unique combination of environmental characteristics, such as absence of persisting snow cover, high frequency of diurnal freeze–thaw cycles and needle-ice activity, and a decrease in precipitation with increasing altitude. These environmental characteristics result in the presence of giant growth forms with a great architectural diversity. These biotic and abiotic characteristics influence the outcome of plant–plant interactions by imposing other types of environmental constraints than those found in extratropical alpine environments, and by potentially generating distinctive patterns of niche differentiation/complementarity between species and populations. To generalize the conceptual framework of plant–plant interactions in alpine environments, we advocate that TAE should be investigated more thoroughly by applying designs, methods and hypotheses that are used currently in temperate areas and by conducting studies along large latitudinal gradients that include tropical regions.     

Resolving the Activation Site of PositiveRegulators in Plant PhosphoenolpyruvateCarboxylase

Dear Editor, Phosphoenolpyruvate carboxylase （PEPC; EC 4.1.1.31） islocated at an important branch point in the carbohydratemetabolism of plants. The enzyme is a homotetramer andcatalyzes the addition of bicarbonate to phosphoenolpyru-vate （PEP） to form oxaloacetate and phosphate. PEPC isregulated by metabolites and phosphorylation. AIIostericfeedback inhibition is mainly regulated by L-malate andL-aspartate which bind to a site separated from the activecenter （Kai et al., 1999; Paulus et al., 2013）. Structure analy-sis of PEPC from Escherichia coli （Kai et al., 1999; Matsumuraet al., 2002）, Zea rnays （Matsumura et al., 2002）, Flaveria trin-ervia, and F. pringlei （Paulus et al., 2013） revealed that thesubstrate PEP and the feedback inhibitors bind to separatesites within each monomer.     

Invasibility of Nectarless Flowers in Plant–Pollinator Systems

This paper considers plant–pollinator systems in which plants are divided into two categories: The plants that secret a substantial volume of nectar in their flowers are called secretors, while those without secreting nectar are called nonsecretors (cheaters). The interaction between pollinators and secretors is mutualistic, while the interaction between pollinators and nonsecretors is parasitic. Both interactions can be described by Beddington–DeAngelis functional responses. Using dynamical systems theory, we show global dynamics of a pollinator–secretor–cheater model and demonstrate mechanisms by which nectarless flowers/nonsecretors can invade the pollinator–secretor system and by which the three species could coexist. We define a threshold in the nonsecretors’ efficiency in translating pollinator–cheater interaction into fitness, which is determined by parameters (factors) in the systems. When their efficiency is above the threshold, non-secretors can invade the pollinator–secretor system. While the nonsecretors’ invasion often leads to their persistence in pollinator–secretor systems, the model demonstrates situations in which the non-secretors’ invasion can drive secretors into extinction, which consequently leads to extinction of the nonsecretors themselves.     

Plant–bacteria interactions in the removal of pollutants

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Highlights► Rhizobacteria degrade a wide range of pollutants and efficiently colonize plant roots. ► Plants have an effect on the selection of their own rhizospheric microorganisms. ► Catabolic pathways can be induced by natural secondary plant products. ► Horizontal gene transfer has an important role in bioremediation. ► Manipulation of plant/microbe interactions could improve rhizoremediation outcomes.     

Calcium Signaling in Plant Endosymbiotic Organelles： Mechanism and Role in Physiology

Recent studies have demonstrated that chloroplasts and mitochondria evoke specific Ca2＋ signals in response to biotic and abiotic stresses in a stress-dependent manner. The identification of Ca2＋ transporters and Ca2＋signaling mol- ecules in chloroplasts and mitochondria implies that they play roles in controlling not only intra-organellar functions, but also extra-organellar processes such as plant immunity and stress responses. It appears that organellar Ca2＋ signaling might be more important to plant cell functions than previously thought. This review briefly summarizes what is known about the molecular basis of Ca2＋ signaling in plant mitochondria and chloroplasts.     

Plant–pollinator interactions in a Mexican Acacia community

Competition for pollination is thought to be an important factor structuring flowering in many plant communities, particularly among plant taxa with morphologically similar and easily accessible flowers. We examined the potential for heterospecific pollen transfer (HPT) in a community of four Acacia species in a highly seasonal tropical habitat in Mexico. Partitioning of pollen flow among sympatric species appears to be achieved, in part, through segregation of flowering in seasonal time, and interspecific differences in pollinator guilds. However, two coflowering species (Acacia macracantha and Acacia angustissima) shared multiple flower visitors, raising the possibility of HPT. Each of these coflowering species showed high intraspecific daily synchrony in pollen release, but dehisce at different times of day. Pollinators rapidly harvested available pollen from one species before abandoning it to visit the flowers of the second later in the day. The activity of shared pollinators, predominantly bees, is thus structured throughout the day, and potential for HPT reduced. Suggestive evidence in favour of a resource partitioning explanation for this pattern is provided by the fact that A. macracantha showed significantly greater intraspecific synchrony when coflowering with a potential competitor (A. angustissima) than when flowering alone. We discuss our results in light of previous work on coflowering acacia assemblages in Tanzania and Australia. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.

Positive Interactions： Crucial Organizers in a Plant Community

For more than a century, ecologists have concentrated on competition as a crucial process for community organization. However, more recent experimental investigations have uncovered the striking Influence of positive Interactions on the organization of plant communities. Complex combinations of competition and positive interactions operating simultaneously among plant species seem to be widespread In nature. In the present paper, we reviewed the mechanism and ecological importance of positive Interactions In plant communities, emphasizing the certainties and uncertainties that have made It an attractive area of research. Positive Interactions, or facilitation, occur when one species enhances the survival, growth, or richness of another. The Importance of facilitation in plant organization increases with ablotlc stress and the relative Importance of competition decreases. Only by combining plant interactions and the many fields of biology can we fully understand how and when the positive Interactions occur.     

Plant survival in Iceland during periods of glaciation?

Aim The paper addresses the classical question of possible plant survival in Iceland during the last glacial period in the light of a palaeobotanical record from northern Iceland, spanning the period 11,300–9000 BP , including the Younger Dryas stadial. We review the Late Cenozoic fossil plant record, the past debate on glacial plant refugia in Iceland, and the evidence for ice-free areas during the Weichselian. Location The investigated lake sediment record comes from Lake Torfadalsvatn, which is situated in the northwestern part of the Skagi peninsula in northern Iceland. Methods The sediment chronology was constructed from the cccurrence of the Vedde Ash and the Saksunarvatn ash, two well-dated Icelandic tephras, together with the results from five AMS and conventional radiocarbon dates performed on bulk sediment samples. The vegetational reconstruction was based on detailed pollen analysis of the sediment sequence. Results The pollen analysis revealed that many of the taxa present in the area prior to the Younger Dryas stadial continued to produce pollen during that cold event. The more or less immediate reappearance of a few other pollen taxa at the Younger Dryas-Preboreal boundary suggests that these plants also survived, even if they did not produce sufficient pollen to be recorded during the Younger Dryas stadial. Main conclusions We conclude that the relatively high plant diversity found in high Arctic areas and present-day nunataks in Iceland and Greenland, together with the fact that many plant species were able to survive the Younger Dryas stadial on the Skagi peninsula, suggest that species with high tolerance for climate fluctuations also survived the whole Weichselian in Iceland. This conclusion is supported by recent palaeoclimatic data from ice-cores and deep-sea sediments, indicating that Icelandic climate during the last glacial was only occasionally slightly colder than during the Younger Dryas stadial.     

Plant—Phytoseiid Interactions Mediated by Herbivore-Induced Plant Volatiles: Variation in Production of Cues and in Responses of Predatory Mites

Phytoseiid mites use herbivore-induced plant volatiles in long-range prey-habitat location and are arrested by these volatiles in a prey patch. The responses of predatory mites to these volatiles are considered to be an important factor in the local extermination of prey populations by phytoseiids such as Phytoseiulus persimilis. Prey-induced plant volatiles are highly detectable and can be reliable indicators of prey presence and prey identity. The composition of herbivore-induced plant volatiles depends on plant species and plant cultivar. Moreover, the composition may also vary with the herbivore species that infests a plant. The responses of phytoseiids to prey-induced plant volatiles from a specific plant-herbivore combination are highly variable. Causal factors include starvation, specific hunger, experience, pathogen infestation and the presence of competitors. Investigating variation in the phytoseiid's behavioural response in relation to these factors is important for understanding how and why behavioural strategies maximize phytoseiid fitness.     

Plant functional diversity in tropical Andean páramos

ABSTRACT

Background: Tropical high mountains present extreme daily temperature variations, frequent high air evaporative demands and seasonal differences in soil water availability. Plants have adapted to these conditions through different avoidance-tolerance mechanisms. This review focuses on plant-growth forms and their adaptive strategies.

Aims: This integrated review of páramo plant traits aims at contributing to understanding the functioning of plant-growth forms and their significance on ecosystem properties under environmental climate and land-use changes.

Methods: Plant responses are presented along avoidance-tolerance gradients considering three main aspects: freezing resistance, water relations and gas exchange characteristics. Results from 45 herbaceous and 42 woody species along elevational gradients in the Venezuelan high Andes were analysed.

Results: Leaf supercooling is the common avoidance response of woody plants to night-time freezing temperatures, while herbaceous plants tolerate frost. Trees and caulescent rosettes maintain more positive leaf water potentials under water deficit conditions compared to more tolerant herbaceous species. All plant growth-forms showed strong stomatal control under dry-season conditions.

Conclusions: Páramo plant growth-forms may be separated according to an avoidance-tolerance gradient in response to water deficit and low temperature resistance. Woody growth-forms tend to avoid both freezing and water stress, while herbaceous forms tolerate frost and resist an unfavourable water status. Grasses and cushion plants are at the tolerant extreme of the gradient and coincide in that both reach the highest elevations in the páramo. Andean giant rosettes are freezing avoidant, particularly susceptible to water deficit and the most vulnerable, of all growth-forms, to changing environmental conditions.     

Mathematical Modeling of the Dynamics of Plant Mineral Nutrition in the Fertilizer–Soil–Plant System

A numerical simulation of the spatial–temporal dynamics of a multi-parameter system has been developed. The components of this system are plant biomass, the mobile and stationary forms of mineral nutrition elements, rhizosphere microorganisms, and environmental parameters (temperature, humidity, and acidity). Parametric identification and verification of the adequacy of the model were carried out based on the experimental data on the growth of Krasnoufimskaya-100 spring wheat on peat lowland soil. The results are represented by temporal distributions of biomass from agricultural crops and the findings on the contents of the main nutrition elements within the plant (nitrogen, phosphorus, and potassium). An agronomic assessment and interpretation of the results are given.

     

Knights in Action： Lectin Receptor-Like Kinases in Plant Development and Stress Responses

The Receptor-Like Kinase （RLK） is a vast protein family with over 600 genes in Arabidopsis and 1100 in rice. The Lectin RLK （LecRLK） family is believed to play crucial roles in saccharide signaling as well as stress perception. All the LecRLKs possess three domains： an N-terminal lectin domain, an intermediate transmembrane domain, and a C-terminal kinase domain. On the basis of lectin domain variability, LecRLKs have been subgrouped into three subclasses： L-, G-, and C-type LecRLKs. While the previous studies on LecRLKs were dedicated to classification, comparative structural analysis and expression analysis by promoter-based studies, most of the recent studies on LecRLKs have laid special emphasis on the potential of this gene family in regulating biotic/abiotic stress and developmental pathways in plants, thus mak- ing the prospects of studying the LecRLK-mediated regulatory mechanism exceptionally promising. In this review, we have described in detail the LecRLK gene family with respect to a historical, evolutionary, and structural point of view. Furthermore, we have laid emphasis on the LecRLKs roles in development, stress conditions, and hormonal response. We have also discussed the exciting research prospects offered by the current knowledge on the LecRLK gene family. The multitude of the LecRLK gene family members and their functional diversity mark these genes as both interesting and worthy candidates for further analysis, especially in the field of crop improvement.