Plant Niche Research Articles

The Populus holobiont: dissecting the effects of plant niches and genotype on the microbiome

BackgroundMicroorganisms serve important functions within numerous eukaryotic host organisms. An understanding of the variation in the plant niche-level microbiome, from rhizosphere soils to plant canopies, is imperative to gain a better understanding of how both the structural and functional processes of microbiomes impact the health of the overall plant holobiome. Using Populus trees as a model ecosystem, we characterized the archaeal/bacterial and fungal microbiome across 30 different tissue-level niches within replicated Populus deltoides and hybrid Populus trichocarpa × deltoides individuals using 16S and ITS2 rRNA gene analyses.ResultsOur analyses indicate that archaeal/bacterial and fungal microbiomes varied primarily across broader plant habitat classes (leaves, stems, roots, soils) regardless of plant genotype, except for fungal communities within leaf niches, which were greatly impacted by the host genotype. Differences between tree genotypes are evident in the elevated presence of two potential fungal pathogens, Marssonina brunnea and Septoria sp., on hybrid P. trichocarpa × deltoides trees which may in turn be contributing to divergence in overall microbiome composition. Archaeal/bacterial diversity increased from leaves, to stem, to root, and to soil habitats, whereas fungal diversity was the greatest in stems and soils.ConclusionsThis study provides a holistic understanding of microbiome structure within a bioenergy relevant plant host, one of the most complete niche-level analyses of any plant. As such, it constitutes a detailed atlas or map for further hypothesis testing on the significance of individual microbial taxa within specific niches and habitats of Populus and a baseline for comparisons to other plant species.

Bacillus subtilis, the model Gram-positive bacterium: 20years of annotation refinement.

SummaryGenome annotation is, nowadays, performed via automatic pipelines that cannot discriminate between right and wrong annotations. Given their importance in increasing the accuracy of the genome annotations of other organisms, it is critical that the annotations of model organisms reflect the current annotation gold standard. The genome of Bacillus subtilis strain 168 was sequenced twenty years ago. Using a combination of inductive, deductive and abductive reasoning, we present a unique, manually curated annotation, essentially based on experimental data. This reveals how this bacterium lives in a plant niche, while carrying a paleome operating system common to Firmicutes and Tenericutes. Dozens of new genomic objects and an extensive literature survey have been included for the sequence available at the INSDC (AccNum AL009126.3). We also propose an extension to Demerec's nomenclature rules that will help investigators connect to this type of curated annotation via the use of common gene names.

Effects of Climate Change on the Climatic Niches of Warm-Adapted Evergreen Plants: Expansion or Contraction?

Climate change has modified the structure and functions of ecosystems, affecting human well-being. Evergreen plants in the warm-temperate ecosystems will lose climatically suitable habitats under climate change but have not drawn much scholarly interest. Therefore, the present research aimed to predict the future climatic niches of eight coastal warm-adapted evergreen trees under climate change to provide information for an effective management practice. For this purpose, we used the ensemble species distribution models (SDMs) weighted by the TSS value in modelling the climatic niches of those evergreen trees and then ensembled their future distributions predicted under 20 future climate scenarios. Except for Neolitsea sericea (True Skill Statistic (TSS) = 0.79), all projections for the current climatic niches of evergreens showed excellent predictive powers (TSS > 0.85). The results showed that the climatic niches of the four evergreens—Castanopsis cuspidata, Pittosporum tobira, Raphiolepis indica var. umbellate, and Eurya emarginata—would expand to the northern part of the Korean Peninsula (KP) under climate change, but the ones of the remaining four—Kadsura japonica, Neolitsea sericea, Ilex integra, and Dendropanax morbiferus—would shrink. While the climatic niches of Pittosporum tobira showed the rapidest and greatest expansion under climate change, Dendropanax morbiferus was predicted to experience the greatest loss of habitat. On the other hand, regardless of whether the future distributions of climatically suitable habitats would expand or contract, the highly suitable habitats of all species were predicted to decline under climate change. This may indicate that further climate change will degrade habitat suitability for all species within the distribution boundary and restrict continuous habitat expansions of expanding species or accelerate habitat loss of shrinking species. In addition, the future distributions of most coastal evergreens were found to be confined to coastal areas; therefore, sea-level rise would accelerate their habitat loss under climate change. The present study provides primary and practical knowledge for understanding climate-related coastal vegetation changes for future conservation planning, particularly on the Korean Peninsula.

Niche differentiation and expansion of plant species are associated with mycorrhizal symbiosis

Abstract Mycorrhizal symbiosis is a widespread association between plant roots and mycorrhizal fungi, which is thought to contribute to plant niche differentiation and expansion. However, this has so far not been explicitly tested. To address the effect of mycorrhizal symbiosis on plants’ realized niches, we addressed how mycorrhizal status (i.e. the frequency of occurrence of mycorrhizal symbiosis), flexibility (i.e. the ability to grow both with and without mycorrhizal symbiosis) and type of a plant species affect the realized niche optima, widths and volumes. For this, we used co‐occurrence data from the flora of the Netherlands along soil fertility, moisture, pH, salinity, light and temperature gradients. Phylogenetic dependency of the species was taken into account using phylogenetic generalized least squares models. We show that facultatively and flexibly mycorrhizal plants have the widest niches compared to non‐mycorrhizal and obligately mycorrhizal, and inflexible plants respectively. Among obligate plant symbionts, ecto‐ and ericoid mycorrhizal plants exhibited the widest niches compared to plants with other mycorrhizal types. Also, plants with different mycorrhizal statuses and types differed in their realized niche optima. Synthesis. Our results indicate that mycorrhizal symbiosis mediates plant niche differentiation and expansion, facilitating the understanding of current distribution patterns of plant species, as well as predicting shifts in plant distribution and dominance due to environmental changes.

The Multidimensional Stoichiometric Niche

The niche concept is essential to understanding how biotic and abiotic factors regulate the abundance and distribution of living entities, and how these organisms utilize, affect and compete for resources in the environment. However, it has been challenging to determine the number and types of important niche dimensions. By contrast, there is strong mechanistic theory and empirical evidence showing that the elemental composition of living organisms shapes ecological systems, from organismal physiology to food web structure. We propose an approach based on a multidimensional elemental view of the ecological niche. Visualizing the stoichiometric composition of individuals in multivariate space permits quantification of niche dimensions within and across species. This approach expands on previous elemental characterizations of plant niches, and adapts metrics of niche volume, overlap and nestedness previously used to quantify isotopic niches. We demonstrate the applicability of the multidimensional stoichiometric niche using data on carbon, nitrogen, and phosphorus of terrestrial and freshwater communities composed by multiple trophic groups. First, we calculated the stoichiometric niche volumes occupied by terrestrial and freshwater food webs, by trophic groups, by individual species, and by individuals within species, which together give a measure of the extent of stoichiometric diversity within and across levels of organization. Then we evaluated complementarity between these stoichiometric niches, through metrics of overlap and nestedness. Our case study showed that vertebrates, invertebrates, and primary producers do not overlap in their stoichiometric niches, and that large areas of stoichiometric space are unoccupied by organisms. Within invertebrates, niche differences emerged between freshwater and terrestrial food webs, and between herbivores and non-herbivores (detritivores and predators). These niche differences were accompanied by changes in the covariance structure of the three elements, suggesting fundamental shifts in organismal physiology and/or structure. We also demonstrate the sensitivity of results to sample size, and suggest that representative sampling is better than rarefaction in characterizing the stoichiometric niche occupied by food webs. Overall, our approach demonstrates that stoichiometric traits provide a common currency to estimate the dimensionality of stoichiometric niches, and help reduce and rationalize the number of axis required to characterize populations or communities.

Vertical root distribution of individual species in a mountain grassland community: Does it respond to neighbours?

Abstract Vertical differentiation in root placement is one of the potential mechanisms of plant niche differentiation. It can be due to the remarkable plasticity of roots in response to nutrients and neighbours, but most data on it come from pot or garden experiments. The roles of vertical differentiation and of plasticity in it in the field are thus not well known. We examined species‐specific root vertical distribution in a montane grassland using quantitative real‐time PCR. We asked whether individual species differ in their rooting depths, whether such differences are associated with above‐ground functional traits (such as height or specific leaf area), and whether they respond to the presence of a competitor. This response was assessed by comparison of species‐specific vertical profiles between control plots and plots where the dominant species, Festuca rubra, had been removed. Vertical profiles of individual species varied considerably, from species with most root biomass concentrated in the uppermost (<2 cm) soil layer, through species with uniform vertical distribution, to a species with roots predominantly below 8 cm (Nardus stricta). Species at the fast end of the plant economy spectrum were more likely to place their roots in the uppermost layers. Grassland species, thus, exploit different parts of the below‐ground resources in spite of their short stature, minor differences in height above‐ground and shallow soil. While below‐ground and above‐ground biomasses of most species were higher in the removal plots, species rooting patterns did not change in response to the removal. The interspecific differences in vertical profiles were thus due to species' innate differences, not to plastic responses to the presence of the dominant species. Synthesis. The findings imply that vertical root differentiation in the field is strong and can contribute to niche differentiation. However, the role of root plasticity in natural systems may be considerably weaker than in artificial systems with few species and strong nutrient gradients. This absence of the plastic response in the field is likely to be due to a fairly homogeneous distribution of nutrients in the soil and to the predominantly symmetric nature of below‐ground competition.

Temperature but not moisture response of germination shows phylogenetic constraints while both interact with seed mass and lifespan

AbstractUnderstanding how plant traits interact with climate to determine plant niches is decisive for predicting climate change impacts. While lifespan and seed size modify the importance of germination timing, germination traits such as base temperature and base water potential directly translate climatic conditions into germination timing, impacting performance in later life stages. Yet we do not know how base temperature, base water potential, seed mass, lifespan and climate are related. We tested the relationships between base temperature and base water potential for germination, seed size and lifespan while controlling for bioclimatic regions. We also quantified the phylogenetic signal in germination traits and seed size using Pagel's λ. We used a worldwide data set of germination responses to temperature and moisture, seed size and lifespan of 240 seed plants from 49 families. Both germination temperature and moisture are negatively related to seed size. Annual plants show a negative relation between seed size and base water potential, whereas perennials display a negative relation between base temperature and seed mass. Pagel's λ highlighted the slow evolution of base temperature for germination, comparable to seed mass while base water potential was revealed to be labile. In the future, base water potential and seed mass can be used when moisture niches of plants are to be predicted. Lifespan, seed size and base temperature should be taken into account when analysing thermal limits of species distributions.

Do David and Goliath Play the Same Game? Explanation of the Abundance of Rare and Frequent Invasive Alien Plants in Urban Woodlands in Warsaw, Poland.

Invasive Alien Plants occur in numbers differing by orders of magnitude at subsequent invasion stages. Effective sampling and quantifying niches of rare invasive plants are quite problematic. The aim of this paper is an estimation of the influence of invasive plants frequency on the explanation of their local abundance. We attempted to achieve it through: (1) assessment of occurrence of self-regenerating invasive plants in urban woodlands, (2) comparison of Random Forest modelling results for frequent and rare species. We hypothesized that the abundance of frequent species would be explained better than that of rare ones and that both rare and frequent species share a common hierarchy of the most important determinants. We found 15 taxa in almost two thirds of 1040 plots with a total number of 1068 occurrences. There were recorded 6 taxa of high frequency–Prunus serotina, Quercus rubra, Acer negundo, Robinia pseudoacacia, Impatiens parviflora and Solidago spp.–and 9 taxa of low frequency: Acer saccharinum, Amelanchier spicata, Cornus spp., Fraxinus spp., Parthenocissus spp., Syringa vulgaris, Echinocystis lobata, Helianthus tuberosus, Reynoutria spp. Random Forest’s models’ quality grows with the number of occurrences of frequent taxa but not of the rare ones. Both frequent and rare taxa share a similar hierarchy of predictors’ importance: Land use > Tree stand > Seed source and, for frequent taxa, Forest properties as well. We conclude that there is an ‘explanation jump’ at higher species frequencies, but rare species are surprisingly similar to frequent ones in their determinant’s hierarchy, with differences conforming with their respective stages of invasion.

Is phylogenetic diversity a good proxy for functional diversity of plant communities? A case study from urban habitats

AbstractQuestionIt is often assumed, but poorly tested, that patterns of phylogenetic diversity reflect functional diversity in plant communities. Here we test whether phylogeny can be used as a proxy for functional diversity in general and specifically for diversity in plant niche preferences, dispersal strategies and competitiveness‐related traits.LocationCentral Europe, Belgium and the Netherlands.MethodsWe used a species composition data set from seven urban habitats, each sampled in 32 large cities of ten countries, and combined this with information about species phylogeny and functional traits, the latter divided into categories representing niche preferences, dispersal strategies and competitiveness.ResultsWe found positive significant, yet very weak, relationships between phylogenetic diversity and overall functional diversity, and between phylogenetic diversity and diversity in both species dispersal strategies and competitiveness. The relationship between phylogenetic diversity and diversity in species niche preferences was not significant.ConclusionsWe suggest that the combination of multiple trait states that co‐exist in urban plant communities and even within the same lineages weakens the phylogeny–function relationship. Phylogenetic diversity is a weak proxy for functional diversity of urban plant communities. For some facets of functional diversity, the phylogeny–function relationship may not apply at all.

Transcriptional reprogramming and phenotypic switching associated with the adaptation of Lactobacillus plantarum C2 to plant niches.

Lactobacillus plantarum has been isolated from a large variety of ecological niches, thus highlighting its remarkable environmental adaptability as a generalist. Plant fermentation conditions markedly affect the functional features of L. plantarum strains. We investigated the plant niche-specific traits of L. plantarum through whole-transcriptome and phenotypic microarray profiles. Carrot (CJ) and pineapple (PJ) juices were chosen as model systems, and MRS broth was used as a control. A set of 3,122 genes was expressed, and 21 to 31% of genes were differentially expressed depending on the plant niche and cell physiological state. L. plantarum C2 seemed to specifically respond to plant media conditions. When L. plantarum was cultured in CJ, useful pathways were activated, which were aimed to sense the environment, save energy and adopt alternative routes for NAD+ regeneration. In PJ the acidic environment caused a transcriptional switching, which was network-linked to an acid tolerance response involving carbohydrate flow, amino acid and protein metabolism, pH homeostasis and membrane fluidity. The most prominent phenotypic dissimilarities observed in cells grown in CJ and PJ were related to carbon and nitrogen metabolism, respectively. Summarising, a snapshot of a carrot and pineapple sensing and adaptive regulation model for L. plantarum C2 was proposed.

Colour pattern variation can inform about extinction risk in moths

Theory posits that species with inter-individual variation in colour patterns should be less vulnerable to extinction, compared with species that do not vary in colour. To evaluate this prediction, we explored whether differences in colour pattern diversity was associated with extinction risk, using red-list status for more than 350 species of noctuid moths in Sweden. We also evaluated six other species characteristics that have been proposed to influence extinction risk namely: host plant niche breadth, habitat type, area of occupancy, body size, overwintering life-history stage and length of flight activity period. We found that species with variable colour patterns had reduced extinction risk overall compared with species having non-variable colour patterns, and that this difference was pronounced more strongly among species having smaller areas of occupancy. There were also significant associations with host plant niche breadth and habitat type, extinction risk being lower on average in polyphagous species and in generalist species that occupied different habitat types. These findings represent the first evidence for insects that variable colouration is associated with reduced extinction risks. Information on colour pattern variation is readily available for many taxa and may be used as a cost-effective proxy for endangerment in the work of halting national and global biodiversity loss.

Improved Predictions of the Geographic Distribution of Invasive Plants Using Climatic Niche Models.

Climatic niche models for invasive plants are usually constructed with occurrence records taken from literature and collections. Because these data neither discriminate among life-cycle stages of plants (adult or juvenile) nor the origin of individuals (naturally established or man-planted), the resulting models may mispredict the distribution ranges of these species. We propose that more accurate predictions could be obtained by modelling climatic niches with data of naturally established individuals, particularly with occurrence records of juvenile plants because this would restrict the predictions of models to those sites where climatic conditions allow the recruitment of the species. To test this proposal, we focused on the Peruvian peppertree (Schinus molle), a South American species that has largely invaded Mexico. Three climatic niche models were constructed for this species using high-resolution dataset gathered in the field. The first model included all occurrence records, irrespective of the life-cycle stage or origin of peppertrees (generalized niche model). The second model only included occurrence records of naturally established mature individuals (adult niche model), while the third model was constructed with occurrence records of naturally established juvenile plants (regeneration niche model). When models were compared, the generalized climatic niche model predicted the presence of peppertrees in sites located farther beyond the climatic thresholds that naturally established individuals can tolerate, suggesting that human activities influence the distribution of this invasive species. The adult and regeneration climatic niche models concurred in their predictions about the distribution of peppertrees, suggesting that naturally established adult trees only occur in sites where climatic conditions allow the recruitment of juvenile stages. These results support the proposal that climatic niches of invasive plants should be modelled with data of naturally established individuals because this improves the accuracy of predictions about their distribution ranges.

Facilitation contributes to Mediterranean woody plant diversity but does not shape the diversity-productivity relationship along aridity gradients.

The diversity-productivity relationship (humped-back model (HBM)) and the stress-gradient (SGH) hypotheses may be connected when productivity is limited primarily by aridity. We analytically connect both hypotheses and assess the contribution of facilitation to woody plant richness along the aridity gradient of the Western Mediterranean floristic region. We monitored regeneration niches of woody plants, obtaining rarefied species richness and plant relative interaction indices in 54 forests and scrublands in a 1750-km geographical range across Spain, Morocco and the Canary Islands. We verified the monotonic increase in facilitation with aridity postulated by SGH and the humped-shape pattern of species richness expected from HBM, which became manifest after expanding the aridity gradient or crossing vegetation types. Along the gradient, interaction balance turned into facilitation earlier in forest than in scrublands. The effects of aridity and interaction balance on species diversity were additive rather than interdependent. Facilitation is an important driver of woody species richness at macroecological scales because it added up to diversity in most sites, with enhanced contribution with increased stress. The HBM was not shaped by species interactions. Results suggest that facilitation may act in Mediterranean vegetation buffering against critical transitions between states allowing woody plant communities to cope with the rise in aridity expected with global warming.

Small Changes in Flooding Have Large Consequences: Experimental Data from Ten Wetland Plants

Flooding regime is a major determinant of vegetation composition in wetlands. Flooding regimes are also commonly altered by human activity. We used an experimentally-created elevation gradient on mineral soil to measure the responses of ten common marsh species to flood regimes ranging from 0 to 100 % of the growing season. We asked three questions. (1) What are the minimum and maximum tolerances of these ten species to a flood duration gradient? (2) Is there one duration of flooding that is physiologically optimal for a majority of the species? (3) How sensitive are these species to minor changes in flood duration? We found that the number of species, the cover and the aboveground biomass were highest when flood duration was less than a third of the growing season. All species showed a pattern of inclusive fundamental niches for flooding duration, with a preference for shorter periods of flooding, for less than a third of the growing season. Narrow-leaved graminoids became relatively more common with longer flooding duration. This study challenges our notions of the fundamental niches of these wetland emergent plants. Other factors beyond flooding tolerance must be acting to structure wetland communities along wetland depth gradients.

Acido‐ and neutrophilic temperate forest plants display distinct shifts in ecological pH niche across north‐western Europe

Ecological niches of organisms vary across geographical space, but niche shift patterns between regions and the underlying mechanisms remain largely unexplored. We studied shifts in the pH niche of 42 temperate forest plant species across a latitudinal gradient from northern France to boreo‐nemoral Sweden. We asked 1) whether species restrict their niches with increasing latitude as they reach their northern range margin (environmental constraints); 2) whether species expand their niches with increasing latitude as regional plant species richness decreases (competitive release); and 3) whether species shift their niche position toward more acidic sites with increasing latitude as the relative proportion of acidic soils increases (local adaptation). Based on 1458 vegetation plots and corresponding soil pH values, we modelled species response curves using Huisman–Olff–Fresco models. Four niche measures (width, position, left and right border) were compared among regions by randomization tests. We found that with increasing latitude, neutrophilic species tended to retreat from acidic sites, indicating that these species retreat to more favorable sites when approaching their range margin. Alternatively, these species might benefit from enhanced nitrogen deposition on formerly nutrient‐poor, acidic sites in southern regions or lag behind in post‐glacial recolonization of potential habitats in northern regions. Most acidophilic species extended their niche toward more base‐rich sites with increasing latitude, indicating competitive release from neutrophilic species. Alternatively, acidophilic species might benefit from optimal climatic conditions in the north where some have their core distribution area. Shifts in the niche position suggested that local adaptation is of minor importance. We conclude that shifts in the pH niche of temperate forest plants are the rule, but the directions of the niche shifts and possible explanations vary. Our study demonstrates that differentiating between acidophilic and neutrophilic species is crucial to identify general patterns and underlying mechanisms.

A framework for partitioning plant rooting profiles from neighbours using multiple data types

Aim Vertical root distributions (‘profiles’) influence plant water use and productivity, and the differentiation of root profiles between neighbouring species can indicate the degree of plant interactions and niche partitioning. However, quantifying multiple species' root distributions in the field can be labour intensive and highly destructive to the soil and plants. We describe a method for partitioning multiple species roots using minimally destructive methods to determine if neighbour interactions alter the root profile of a common desert shrub, Larrea tridentata (creosote bush). Location Sonoran Desert, central Arizona, USA. Methods We obtained root and soil samples from soil cores collected around Larrea growing alone and next to three different neighbouring species. Bulk root mass was measured for each soil sample, and Larrea and neighbouring species root presence was determined with molecular identification methods. Water extracted from the soil and paired stem samples was analysed for its stable isotope composition (D and 18O). Species-specific (i.e. Larrea and neighbouring species) root biomass and fractional active root area were estimated through a hierarchical statistical modelling approach that combined all three data sets and accounted for detection errors. Results The combined data model successfully partitioned Larrea root biomass from neighbouring plants and provided biologically relevant estimates of rooting profiles with greater certainty than individual analyses of each data source. The data model results indicate that plant neighbours alter Larrea's root profile; Larrea growing under tree species had significantly higher root biomass in shallow soil layers than Larrea growing alone. Conclusions Our framework requires minimally destructive sampling methods, and accounts for sampling errors associated with different methods. We demonstrate the utility of our approach with a common desert shrub species, which illustrated that plant neighbours can alter the Larrea vertical root profile. Our approach is useful in problematic study systems fraught with sample collection issues or supporting species with inhibitory compounds that prohibit the use of more sophisticated molecular methods to identify the presence of other species' roots.

Tracing sources of Listeria contamination in traditional Italian cheese associated with a US outbreak: investigations in Italy.

In 2012 a US multistate outbreak of listeriosis was linked to ricotta salata imported from Italy, made from pasteurized sheep's milk. Sampling activities were conducted in Italy to trace the source of Listeria monocytogenes contamination. The cheese that caused the outbreak was produced in a plant in Apulia that processed semi-finished cheeses supplied by five plants in Sardinia. During an 'emergency sampling', 179 (23·6%) out of 758 end-products tested positive for L. monocytogenes, with concentrations from <10 c.f.u./g to 1·1 × 106 c.f.u./g. Positive processing environment samples were found in two out of four processing plants. A 'follow-up sampling' was conducted 8 months later, when environmental samples from three out of six plants tested positive for L. monocytogenes and for Listeria spp. PFGE subtyping showed 100% similarity between US clinical strains and isolates from ricotta salata, confirming the origin of the outbreak. The persistence of strains in environmental niches of processing plants was demonstrated, and is probably the cause of product contamination. Two PFGE profiles from clinical cases of listeriosis in Italy in 2011, stored in the MSS-TESSy database, were found to have 100% similarity to one PFGE profile from a US clinical case associated with the consumption of ricotta salata, according to the US epidemiological investigation (sample C, pulsotype 17). However, they had 87% similarity to the only PFGE profile found both in the US clinical case and in 14 ricotta cheese samples collected during the emergency sampling (sample B, pulsotype 1). Sharing of molecular data and availability of common characterization protocols were key elements that connected the detection of the US outbreak to the investigation of the food source in Italy. Simultaneous surveillance systems at both food and human levels are a necessity for the efficient rapid discovery of the source of an outbreak of L. monocytogenes.

Global patterns of mainland and insular pollination networks

AbstractAimInteraction networks are being increasingly used to evaluate macroecological patterns. We explored a global dataset to identify differences in the structure of pollination networks from islands (of oceanic and continental origin) and mainlands. For oceanic islands, we further evaluated the effects of key island traits on network structural parameters.LocationFifty‐two quantitative plant–pollinator networks from continental islands (n = 23), oceanic islands (n = 18) and mainlands (n = 11) located world‐wide.MethodsThe effect of geographical origin upon network structure was explored by means of generalized mixed models, accounting for biogeographical region, sampling intensity, latitude and network size. For oceanic island networks, the influence of area, age, elevation and isolation was also evaluated.ResultsThe structure of pollination networks was fairly consistent between mainland and continental islands and only a few differences were noted. Oceanic island networks, however, were smaller and topologically simplified, showing a lower interaction diversity, and higher plant niche overlap than mainland and continental island networks. Isolation and elevational range of oceanic islands influenced the total number of species and interactions. Networks from higher‐elevation oceanic islands were less nested and those located towards the equator exhibited higher interaction richness. Island area showed no significant effect on any of the network metrics studied here.Main conclusionsPollination networks appear structurally similar regardless of their geographical origin. However, networks from continental islands are more similar to their mainland counterparts than to those from oceanic islands, probably due to the geological nature of continental islands, which are fragments of the mainland to which they were once connected. Oceanic island networks are the least species‐ and link‐rich, and exhibit the lowest interaction diversity and the highest plant niche overlap, possibly due to lower pollinator richness. The most isolated and low‐elevation islands show the simplest networks, and are thus probably the most vulnerable to pollination disruptions.

The importance of pH and sand substrate in the revegetation of saline non-waterlogged peat fields

A partially peat-extracted coastal bog contaminated by seawater was barren and required revegetation as a wetland. Peat fields were rectangular in shape, cambered in cross-section profile, and separated by drainage ditches. Common to all peat fields were symmetrical patterns in micro-topography with slopes between differences in elevation. Saline non-waterlogged slopes of ∼5% occurred as a symmetrical pair on each side of the crest of the cambered profile, at one end of each peat field. Three rows were laid across this slope (Top, Middle, and Bottom rows) and transplanted with naturally-growing plant species with their sand substrate, in three experiments, and grown for a year. In the Spartina pectinata experiment, bare root stem sections were also planted. Another experiment was conducted to determine changes in the characteristics of a volume of sand when incubated in saline peat fields. We found the salinity of peat increased with moisture downslope, and pH decreased with increase in salinity. S. pectinata grew best when planted with its sand substrate compared with bare root stem section, and when planted in Bottom rows. Juncus balticus had excellent growth in all rows. Unexpectedly, Festuca rubra that was inconspicuous beneath the J. balticus canopy in the natural donor site grew densely within the J. balticus sods. Agrostis stolonifera grew well but seemed to show intolerance to the surrounding acidic peat by curling up its stolons. The pH of the incubated sand volume was much higher than the surrounding peat. These studies suggest that recognition of plant niches and pH manipulation are important in the revegetation of disturbed Sphagnum peatlands that are found abundantly in the northern hemisphere. Results are also relevant to the reclamation of other disturbed lands.

Calcium intolerance of fen mosses: Physiological evidence, effects of nutrient availability and successional drivers

Species composition of peatlands is determined by the dominance of either Sphagnum or non-sphagnaceous (brown) mosses. Sphagnum species are more or less intolerant to alkaline waters rich in calcium bicarbonate, but the physiological background of this intolerance is poorly understood. Recently, sphagna have been widening their realized niches, expanding to alkaline brown-moss fens and altering their functioning. One possible reason is increased nutrient availability, but existing evidence is equivocal. We approached this problem by a series of laboratory experiments with 15 fen moss species cultivated submerged in solutions corresponding to natural poor- to rich-fen waters. We tested basic ecophysiological mechanisms of calcium tolerance (ion compartmentalization, cell-wall cation-binding properties, phosphorus and iron uptake), the breadth of fundamental pH/calcium niches for protonemata and adult plants, interspecific competition, and relationships between nutrient availability and pH/calcium tolerance. Our results suggest that calcium toxicity in calcifugous bryophytes is caused by insufficient control over the balance of intracellular Ca2+ uptake/efflux. Cell-wall cation-exchange sites of living mosses remain unsaturated with Ca2+ even in calcareous solutions, contradicting the proposed inhibitory effect of Ca2+-oversaturation on cell-wall expansion and monovalent cation uptake. Growth and biomass accumulation of brown mosses was highest in alkaline fen waters, but they could also survive and germinate in poor-fen waters. Calcium-tolerant sphagna survived along the entire poor–rich gradient, but their growth was inhibited by calcium bicarbonate. The three most obviously expanding sphagna produced protonemata even under calcareous conditions. Flowing but not stagnant alkaline fen waters were toxic for calcifugous sphagna, the strongest competitors in poor-fen waters. Increased potassium availability facilitated the survival of calcifugous sphagna in alkaline fens, corroborating field observations that potassium facilitates sphagnum expansion. Surprisingly, the rare and declining moss Hamatocaulis vernicosus was supported by nitrogen and phosphorus more than its competitors. Our comparison of fundamental and realized niches suggests that the dominance of particular moss functional groups in fens is governed by a competitive hierarchy altered by different calcium levels. The expansion of calcium-tolerant sphagna into brown-moss fens therefore requires perturbation that weakens competition. Additionally, expansion of calcifugous sphagna to alkaline environments may be stimulated by potassium availability.