Aims Aquatic ecosystems are a priority for conservation as they have become rapidly degraded with land-use changes. Predicting the habitat range of an endangered species provides crucial information for biodiversity conservation in such rapidly changing environments. However, the complex network structure of aquatic ecosystems restricts spatial prediction variables and has hitherto limited the use of habitat models to predict species occurrence in aquatic ecosystems. We used the maximum entropy model to evaluate the potential distribution of an endangered aquatic species, Euryale ferox Salisb. We tested the relative influence of (i) climatic variables, (ii) topographic variables, and (iii) hydrological variables derived from remote sensing data to improve the prediction of occurrence of aquatic plant species.
Methods We considered the southern part of the Korean Peninsula as the modeling extent for the potential distribution of E. ferox. Occurrence records for E. ferox were collected from the literature and field surveys. We applied maximum entropy modeling using remotely sensed environmental variables and evaluated their relative importance as prediction variables with variation partitioning.
Important findings The species distribution model predicted potential habitats of E. ferox that matched the actual distribution well. Floodplain wetlands and shallow reservoirs were the favored habitats of E. ferox. Quantitative loss and fragmentation of wetland habitats appeared to be a major reason for the decrease of E. ferox populations. Our results also imply that hydrological variables (i.e. normalized difference water index) derived from remote sensing data greatly increased model prediction (relative contribution: 10.5–37.0%) in the aquatic ecosystem. However, interspecific competition within a similar niche environment should be considered to increase the accuracy of the distribution model.

Aims Understanding fluctuations in plant reproductive investment can constitute a key challenge in ecology, conservation and management. Masting events of trees (i.e. the intermittent and synchronous production of abundant seeding material) is an extreme example of such fluctuations. Our objective was to establish the degree of spatial and temporal synchrony in common four masting tree species in boreal Finland and account for potential causal drivers of these patterns.
Methods We investigated the spatial intraspecific and temporal interspecific fluctuations in annual seed production of four tree species in Finland, silver birch Betula pendula Roth, downy birch Betula pubescens Ehrh., Norway spruce Picea abies (L.) H.Karst. and rowanberry Sorbus aucuparia L. We also tested to see whether variations in seed production were linked to annual weather conditions. Seeding abundance data were derived from tens of stands per species across large spatial scales within Finland during 1979 to 2014 (for rowanberries only 1986 to 2014).
Important findings All species showed spatial synchrony in seed production at scales up to 1000 km. Annual estimates of seed production were strongly correlated between species. Spring and summer temperatures explained most variation in crop sizes of tree species with 0-to 2-year time lags, whereas rainfall had relatively little influence. Warm weather during flowering (May temperature) in the flowering year (Year t) and 2 years before (t ?2) were correlated with seed production. However, high May temperatures during the previous year (t^-1) adversely affected seed production. Summer temperatures in Year t^-1 was positively correlated with seed production, likely because this parameter enhances the development of flower primordials, but the effect was negative with a time lag of 2 years. The negative feedback in temperature coefficients is also likely due to patterns of resource allocation, as abundant flowering and seed production in these species is thought to reduce the subsequent initiation of potential new flower buds. Since the most important weather variables also showed spatial correlation up to 1000 km, weather parameters likely explain much of the spatial and temporal synchrony in seed production of these four studied tree species.

Aims As an exotic species colonises a new continent, it must overcome enormous environmental variation in its introduced range. Local adaptation of introduced species has frequently been observed at the continent scale, particularly in response to latitudinal climatic variation. However, significant environmental heterogeneity can also exist at the landscape scale. A small number of studies have provided evidence that introduced species may also be capable of phenotypic and genetic differentiation at much smaller spatial scales. For example, previously we found US agricultural and non-agricultural populations of Sorghum halepense (Johnsongrass) to be phenotypically and genetically distinct. In this study, we investigated whether this phenotypic differentiation of agricultural and non-agricultural populations of S. halepense is the result of fine-scale local specialisation.
Methods We surveyed a nationally collected S. halepense germplasm panel and also collected neighbouring agricultural and non-agricultural sub-populations of S. halepense at four sites throughout Western Virginia, USA, raising seedlings in common conditions mimicking both agricultural and non-agricultural habitats.
Important findings At the national scale, we found evidence of habitat differentiation but not specialisation. However, at the local scale, we found evidence of specialisation in two of the four local populations to non-agricultural habitat, but no evidence of specialisation to agricultural habitat. These results show that local specialisation is a possible, but not guaranteed consequence of kilometre-scale habitat heterogeneity in invasive species. This finding contributes to a growing awareness of the importance of fine-scale local adaptation in the ecology and management of introduced and weedy species.

Aims How species respond to climate change at local scales will depend on how edaphic and biological characteristics interact with species physiological limits and traits such as dispersal. Obligate seeders, those species that depend on fire for recruitment, have few and episodic opportunities to track a changing climate envelope. In such cases, long-distance seed dispersal will be necessary to take advantage of rare recruitment opportunities. We examine recruitment patterns and seedling growth below, at and above the timberline of an obligate-seeding Australian montane forest tree (Eucalyptus delegatensis) after stand-replacing fire, and place these changes in the context of regional warming.
Methods We use two methods to detect whether E. delegatensis can establish and persist above the timberline after stand-replacing wildfire in montane forests in south-east Australia. First, we examine establishment patterns by using belt transects at six sites to quantify how changes in post-fire recruit density with increasing distance above the timberline seven years post-fire. Second, to determine whether dispersal or physiological constraints determine post-fire establishment patterns, we transplanted seedlings and saplings into bare ground above (100 m elevation), at, and below (50 m elevation) timberline 18-months after fire. We monitored seedling growth and survival for one growing season.
Important findings There was minimal upslope migration of the species after fire with most saplings observed near seed-bearing timberline trees, with only occasional outpost saplings. Transplanted seedlings and saplings survived equally well across one growing season when planted above existing timberlines, relative to saplings at or below the timberline. Seedling and sapling growth rates also did not differ across these location, although seedlings grew at much faster rates than saplings. These findings suggest that upslope growing season conditions are unlikely to limit initial range expansion of trees after fire. Instead, it is more likely that seed traits governing dispersal modulate responses to environmental gradients, and global change more generally.

Aims Space-for-time substitution (SFT) is often used for vegetation status estimation during the recovery process of deserts. However, the evaluated accuracy of SFT remains uncertain. An eight-year located observation was used to assess the validity of SFT for vegetation state prediction.
Methods This study analyzed a chronosequence of Caragana microphylla Lam. plantings using the located observation method to test the accuracy of SFT for vegetation state prediction in the mobile sand dunes of the Horqin Sandy Land in northeastern China from July 2005 to June 2013.
Important findings According to SFT, simple vegetation parameters (density, coverage and biomass) were found to be unstable, while sophisticated vegetation parameters (species diversity and evenness) were relatively stable across the experimental treatments during the study period. Conversely, both the simple and sophisticated parameters were found to be relatively stable when tested using the located observation method. Furthermore, most simple vegetation parameters slightly increased, while sophisticated parameters slightly decreased after eight years of field observations. Thus, long-term restoration management facilitated improvements in the simple parameters, but may have adversely impacted the sophisticated parameters in the post-restoration community. Our results suggest that sophisticated vegetation parameter states can be predicted by SFT, while simple vegetation parameter states are not well predicted by SFT. In conclusion, located observations or other effective evaluation methods must be employed to offset the deficiency of the SFT method for the prediction of vegetation parameters.

Aims Biological and environmental factors determine geographic patterns of plant nutrient stoichiometry jointly. Unraveling the distribution pattern and the potential drivers of nutrient stoichiometry is therefore critical for understanding the adaptive strategies and biogeochemistry cycling. Aimed to determine how leaf nitrogen (N):phosphorus (P) stoichiometry is linked to biological and environmental factors, we investigated the patterns of psammophyte leaf N:P stoichiometry in sandy region, northern China, and the potential factors affecting leaf N:P stoichiometry were explored.
Methods Based on 10 m × 10 m quadrates survey, the leaves of 352 dominant psammophyte samples belonging to 167 species were collected cross a 3000 km east-west transect in sandy environments, northern China. The samples were further classified into the following groups on the basis of plant life forms and functional groups (photosynthesis pathways and nitrogen fixation). The structural equation modeling was employed to clarify the importance of biological and environmental factors on leaf N:P stoichiometry.
Important findings Generally, the higher leaf N and P concentrations, but lower N:P ratio were found in psammophyte compared with other ecosystems. Mean annual temperature (MAT) influenced the leaf N, P concentrations negatively, while mean annual precipitation (MAP) did positively. MAP played greater influence on leaf N, P concentrations than MAT did. MAP affected leaf N, P concentrations directly or indirectly through phylogeny, while MAT only shown direct effect on leaf N concentration. The psammophyte was more limited by N, rather P, in sandy region of northern China. These results suggest that phylogeny of psammophyte and climate jointly influence leaf N:P stoichiometry, and the results could be helpful in modeling biogeochemical nutrients cycling in vulnerable ecosystems like sandy environment.

Aims Soil plays an important role in the formation and heterogeneity of habitats and thus can cause changes in vegetation structure and plant diversity. The differentiation between Cerrado/savanna and forest is well known, but the relationship between soil and habitats from savannic or forest formations still needs to be better understood, particularly in tropical ecotonal areas. We studied the association between attributes of plant communities, namely structure and diversity, and physicochemical characteristics of soils in the Caatinga domain at the transition to Cerrado in Brazil.
Methods Chemical and physical analyses of soils were performed in samples of 38 plots from savannic formations and 30 plots from forest formations. Vegetation was characterized floristically and structurally in all plots, five habitats being assessed in each plant formation. Soil features and vegetation parameters were highly distinct among the different habitats.
Important findings In general, forest habitats were more nutrient rich than savannic formation. Furthermore, soil variables showed effects both on vegetation structure and on its species diversity, more pronouncedly in the savannic formations. Habitats were structurally distinct, and diversity differed between savannic and forest communities; however, a higher differentiation occurred when the savannic formation habitats were compared among them. Although plant diversity did not differ among forest formation habitats, soil attributes showed a close relationship with edaphic factors and can contribute for similar vegetation. The soil–vegetation relationship in highly diverse ecotonal landscapes is important from the conservation biology point of view and aid in the execution of proactive plans for the maintenance of biodiversity. Thus, we noticed that diversity and soil behaves distinctly between savannic and forest communities.

Aims Changes in the structure and composition of forests, whether caused by natural or anthropic events, alter the microenvironment, sometimes irreversibly. Since the local environment has a direct impact on basic ecological processes, this has become a key component of research. Mexican beech forests (Fagus grandifolia subsp. mexicana) in the Sierra Madre Oriental are restricted to sites with specific climate, soils and topography, making them an ideal natural system for ecological research. The objectives of this study were to identify the relationship between the microenvironment and the tree and shrub structure and composition of Mexican beech forests in the state of Hidalgo, and to compare the floristic similarity of these forests on the country scale using data from seven localities.
Methods Specimens were collected for a period of one year at all localities in the state of Hidalgo where beech forests are located. At each locality, five 400 m 2 plots were established, and structural attributes (basal area, coverage, density and species richness) and six environmental variables were measured in the plots. The relationship between structure and microenvironment was estimated by simple correlation and canonic correspondence analysis (CCA). In addition, floristic similarity between different beech forest localities in the Sierra Madre Oriental was estimated by correspondence analysis (CA).
Important findings Twenty tree species and eight shrub species were identified; at all localities studied F. grandifolia subsp. mexicana dominated the canopy. The multivariate analysis indicated that (i) in the four localities in the state of Hidalgo, all microenvironmental variables except pH are related to the variation observed in species composition and structure; (ii) the El Gosco locality had both tree and shrub species and microenvironmental factors different from those observed in the Fagus forests at the other localities in the study and (iii) the localities studied in order to draw country-scale comparisons could be divided into three groups by floristic similarity. The first group consisted of the Hidalgo localities, the second of the Veracruz localities, and the third, more different from the others, of the Tamaulipas locality. The results of this study provide the first reference for the relationship between the range of microenvironments and species structure in Mexican beech forests. Microenvironmental conditions in the larger beech forests could be used as a model for designing management and conservation programs for this plant association. Because of its particular ecological and historical characteristics, this association could serve as an example of biodiversity conservation in Mexico.

Aims Grazing is associated with several plant traits that may confer resistance to herbivores. However, cross-species analyses do not allow for the differentiation between adaptive evolution and common ancestry. In this study, we evaluated the effect of grazing on 5 morphological traits in 41 native grasses growing in natural grasslands of Uruguay and investigated whether such effects are independent of phylogeny.
Methods We used data of grass species from 17 paired, grazed and ungrazed plots located in different regions of natural grasslands of Uruguay. For each species, we calculated the Grazing Response Index (GRI) and estimated the culm length, blade length, blade width, blade length/width ratio and caryopsis length. Trait values were calculated as the mean of the maximum and minimum values reported in a public database. We assessed the relationship between the GRI and the morphological traits using cross-species correlations, and we re-examined the correlations using phylogenetically controlled comparative analysis.
Important findings Culm length and blade length were significantly correlated with the GRI. Species with higher culms and longer blades diminished their cover under grazing. This association remained significant after statistical control of phylogenetic relatedness among species. By contrast, blade width, blade length/width ratio and caryopsis length did not show any significant relationship with the GRI. Many studies in temperate grasslands recognized that several plant traits respond to grazing but were rarely evaluated in a phylogenetic context. Our results are consistent with the idea that grazing is a selective force with a clear effect on the evolution of grass stature, selecting smaller plants with shorter blades.

Aims Key herbivory interaction traits such as plant defensive compounds may differ among populations of a single species due to the spatial variation in herbivore feeding guilds and the strength of the interaction. Moreover, the genealogy of population lineages could represent an additional source of variation interacting with the predominant eco-clinal trends. We tested for the existence of genetically based intraspecific variation in chemical defence profiles across the range of the relict tree Prunus lusitanica L. Additionally, we investigated geographical variation in defence inducibility and tested for the existence of a trade-off between qualitative and quantitative defences.
Methods We conducted a greenhouse experiment where 210 plants were grown under a common environment, comprising 10 different populations throughout the distribution range of the species and spanning three separate regions: Iberia, Morocco and Macaronesia. To test for the inducibility of defences, we artificially defoliated plants. Three treatments were established within each population: undamaged, defoliated and sampled after 2 h, and defoliated and sampled after 72 h. The concentration of cyanogenic glycosides (prunasin) and phenolics was determined in leaf samples for all treatments.
Important findings Basal levels of cyanogenics and phenolics significantly differed among populations and regions across the range of P. lusitanica, with this variation having a heritable basis. Cyanogenics (prunasin) were significantly higher in ancient Macaronesian populations, while phenolic concentrations were larger in Iberia. The higher cyanogenic levels found in Macaronesia could be a consequence of the known stronger herbivory pressure in the islands than in Iberia or the likely longer coevolutionary history with herbivores in this region. These findings indicate that the geographical variation of key ecological traits such plant chemical defences can be imprinted by phylogeographical signals, particularly in relict species. Regarding defence inducibility, prunasin increased after simulated herbivory whereas phenolics mostly decreased after defoliation. Variation in defence inducibility across populations and regions was evident, although no consistent patterns related to the variation in herbivore feeding guilds were observed, particularly among regions with and without ungulate browsing pressure. Finally, a trade-off among induced levels of qualitative (prunasin) and quantitative (phenolics) defences was detected in one of the defoliated treatments, likely as a result of a stronger resource limitation in damaged plants.

Aims Elevated ozone and CO₂ can differentially affect the performance of plant species. Variation among native, exotic and invader species in their growth and defense responses to CO₂ and ozone may shape CO₂ and ozone effects on invasions, perhaps in part also due to variation between native and invasive populations of invaders.
Methods We manipulated ozone (control or 100 ppb) and CO₂ (ambient or 800 ppm) in a factorial greenhouse experiment in replicated chambers. We investigated growth and defense (tannins) of seedlings of Triadica sebifera from invasive (USA) and native (China) populations and pairs of US and China tree species within three genera (Celtis, Liquidambar and Platanus).
Important findings Overall, ozone reduced growth in ambient CO₂ but elevated CO₂ limited this effect. T. sebifera plants from invasive populations had higher growth than those from native populations in control conditions or the combination of elevated CO₂ and ozone in which invasive populations had greater increases in growth. Their performances were similar in elevated CO₂ because native populations were more responsive and their performances were similar with elevated ozone because invasive populations were more susceptible. Compared to other species, T. sebifera had high growth rates but low levels of tannin production that were insensitive to variation in CO₂ or ozone. Both China and US Platanus plants reduced tannins with increased CO₂ and/or ozone and US Liquidambar plants increased tannins with the combination of elevated CO₂ and ozone. The growth results suggest that intraspecific variation in T. sebifera will reduce the effects of CO₂ or ozone alone on invasions but increase their combined effects. The tannin results suggest that defense responses to CO₂ and ozone will be variable across native and exotic species. The effects of CO₂ and ozone on growth and defense of native and exotic species indicate that the benefit or harm to species from these global change drivers is an idiosyncratic combination of species origin and genus.

Aims A plant has a limited amount of resources at any time and it allocates them to different structures. In spite of the large number of previous studies on allocation patterns within single species, knowledge of general patterns in species allocation is still very limited. This is because each study was done in different conditions using different methodology, making generalization difficult. We investigate intraspecific above- versus below-ground biomass allocation among individuals across a spectrum of dry-grassland plant species at two different developmental stages and ask whether allocation is age- and species specific, and whether differences among species can be explained by their life-history traits and phylogeny.
Methods We collected data on above- and below-ground biomass of seedlings and adult plants of 20 species from a common garden experiment. We analysed data on shoot–root biomass allocation allometrically and studied the relationship between the allometric exponents (slopes on log–log scale), species life-history traits and phylogenetic distances.
Important findings We found isometric as well as allometric patterns of biomass allocation in the studied species. Seedlings and adult individuals of more than half of the species differed in their above- versus below-ground biomass allometric exponents. Seedlings and adult individuals of the remaining species differed in their allometric coefficients (intercepts). Annual species generally allocated proportionally more to above- than below-ground biomass as seedlings than as adults, whereas perennial species showed the opposite pattern. Plant life-history traits, such as plant life span, age of first flowering, month in which the species begin flowering and specific leaf area were much more important in explaining differences in shoot–root allometry among species than were phylogenetic relationships. This suggests that allocation patterns vary greatly among closely related species but can be predicted based on species life-history traits.

Aims UV-B radiation is known to affect plant physiology and growth rate in ways that can influence community species composition and structure. Nevertheless, comparatively little is known about how UV-B radiation induced changes in the performance of individual species cascades to affect overall community properties. Because foliage leaves are primarily responsible for photosynthesis and carbon gain and are the major organ that senses and responds to UV-B radiation, we hypothesized that, under reduced UV-B radiation, species with larger leaf areas per plant would manifest higher growth rates and hence tend to improve their community status compared to species with smaller leaf areas per plant in herbaceous plant communities.
Methods We tested this hypothesis by examining plant traits (leaf area per plant and plant height), plant growth rate (aboveground biomass per plant and plant biomass per area) and community status (species within-community relative biomass) for 19 common species in a two-year field experiment in an alpine meadow on Tibetan Plateau.
Important findings Aboveground biomass per plant, as well as per area, progressively increased in a 39% reduced (relative to ambient) UV-B treatment during the experimental period. At the second year, 11 out of 19 species significantly or marginally significantly increased their plant height, leaf area per plant and aboveground biomass per plant. No species was negatively affected by reducing UV-B. As hypothesized, the increase in aboveground biomass per plant increased with increasing leaf area per plant, as indicated by cross-species regression analysis. Moreover, the change in species within-community status increased with increasing leaf area per plant. Our study demonstrates that UV-B radiation has differential effects on plant growth rate across species and hence significantly affects species composition and plant community structure. We suggest that UV-B radiation is an ecological factor structuring plant communities particularly in alpine and polar areas.

Aims The abandonment of agronomic practices in subalpine systems has led to shrub encroachment, which has transformed grasslands into woodlands. The competitive and facilitative interactions among incoming shrub species might influence vegetation succession and might be affected by climate change. This study aimed to identify the nature of shrub species interactions between an early colonizer and a secondary succession shrub in the successional encroachment process and whether it differs between two contrasting climatic conditions.
Methods The interactions between the two main encroaching shrub species in the Central Pyrenees (Spain), Buxus sempervirens and Echinospartum horridum, were studied at the current upper limit of the altitudinal range of B. sempervirens, where it coexists with E. horridum (high site), and in a milder location at lower elevation (low site). In the studied areas, E. horridum is the first shrub species that encroaches upon the abandoned grasslands and B. sempervirens enters the system after E. horridum has become established. A neighbor-removal experiment was used to assess the bidirectional interactions between both species, and whether those interactions differed among the life stages of B. sempervirens (seedlings, juveniles and adults), at the two study sites. Survival, annual crown growth and developmental instability (error in development caused by stress) were the performance indices used to quantify plant responses. Differences in air temperatures and soil nutrient amelioration were evaluated as possible mechanisms of facilitation of E. horridum on B. sempervirens .
Important findings E. horridum enhanced the survival of B. sempervirens seedlings under its crown, whereas, B. sempervirens adults outcompeted E. horridum. Therefore, the invasion of the grasslands by E. horridum facilitated the settlement and expansion of B. sempervirens, promoting vegetation succession at the Pyrenees. In addition, climatic differences associated with elevation affected shrub interactions. Under low temperatures at the upper limit of B. sempervirens altitudinal range, the presence of E. horridum enhanced the growth of B. sempervirens juveniles. At low elevation, under a milder climate, B. sempervirens exerted a high degree of competition toward E. horridum. An increase in temperatures associated with climate change would benefit B. sempervirens juveniles growth which might affect the successional process because it would increase their competitive ability when B. sempervirens juveniles become adults.

Aims There are a number of mechanisms that regulate germination; among these, seed dormancy, one of the most important, is an adaptative mechanism in plants to promote survival by dispersing germination in space and time until environmental conditions are favourable for germination. The main goals of this study were to determine the temperature requirements for seed dormancy release and germination of Gentiana lutea subsp. lutea, to identify the class and level of seed dormancy and to suggest an optimal germination protocol.
Methods Seeds belonging to two different localities were subjected to various pre-treatments, including cold stratification (0 and 5°C), warm stratification (25/10°C) and different combinations of these, and then incubated at a range of constant temperatures (5–25°C) and 25/10°C. Embryo growth during pre-treatments and incubation conditions were assessed at different times by measuring the embryo to seed length ratio (E:S ratio). The final germination percentage (FGP) and the germination rate (t 50) were calculated.
Important findings Fleshy mature seeds of G. lutea subsp. lutea have linear underdeveloped embryos. Cold stratification at 0°C was effective in overcoming the physiological dormancy (PD) and promoted embryo growth and subsequent germination. After cold stratification at 0°C, both the root and the shoot emerged readily under a wide range of temperatures. G. lutea subsp. lutea seeds showed an intermediate complex morphophysiological dormancy (MPD). As regards the optimal germination protocol for this taxon, we suggest a period of cold stratification at ca. 0°C followed by seed incubation at 10–20°C. The optimal germination temperatures found for seeds of this taxon, as well as its pre-chilling requirement at 0°C, suggest that it is well adapted to a temperate climate; this behavior highlights an increasing threat from global warming for G. lutea, which could reduce the level of natural emergence in the field, prejudicing also the long-term persistence of the natural populations in Sardinia.

Aims Understanding the role of genetics in biological invasions has become an important aspect for modern plant ecology. Many studies suggest that increased ploidy level benefits the success of an invasive species, but the basis for this phenomenon is not fully understood. In its native, North American range, Solidago gigantea has three geo-cytotypes comprising di-, tetra- and hexaploid populations, while in Europe, where it is highly invasive, S. gigantea stands are composed primarily of tetraploid individuals. Our study investigates whether North American hexaploids can induce a greater risk of invasion, due to their higher performance in a non-native range, as compared to the existing tetraploids of that range.
Methods We performed greenhouse and common garden experiments along with microsatellite analyses to test whether differences in chromosome number and origin of the species mean superior fitness in the introduced range.
Important findings Genetic diversity was significantly higher in the native hexaploid populations (A R = 6.04; H e = 0.7794), rather than the non-native tetraploid populations (A R = 4.83; H e = 0.6869). Furthermore, differentiation between geo-cytotypes was moderate (ρ ST = 0.1838), which was also confirmed by their clear segregation in principal component analysis and structure analyses, proving their different genetic structure. In contrast to genetic diversity, the non-native tetraploid geo-cytotype performed better in the common garden experiment, implying that higher genetic diversity does not always mean better success. Our results suggest that native hexaploids do not present a greater risk, as assessed by their performance in the introduced range, when compared to the non-native tetraploids, as was suggested by previous studies. Nevertheless, their introduction is still undesirable due to their different genetic structure, which, through hybridization, could give a new drive to the invasion of S. gigantea .

Aim Mirabilis himalaica (Nyctaginaceae) is an endangered medicinal plant mainly distributed in the plateau region of northern Tibet, China. The outer surface of M. himalaica achenes is covered by a pectinaceous mucilaginous layer upon hydration. However, the role of the achene mucilage is poorly understood. In this study, we investigated the effects of mucilage on achene germination and sprout growth under abiotic stress to explain how M. himalaica survive the alpine environment.
Methods We investigated the effect of mucilage on achenes germination by contrast the capacity of water absorption, dehydration and respiration of intact achene and the achene with mucilage removal. We performed abiotic stresses experiments including drought stress, salt stress, cold stress and high temperature stress, and quantified the effects of mucilage removal on achene germination rate, root and shoot lengths of seedlings.
Important findings Mucilage is extremely hydrophilic, and the mass of intact achenes can be 9-fold greater than that of demucilaged achenes. The removal of the mucilaginous layer did not significantly change final germination percentages under ideal conditions, but intact achenes (i.e. with mucilage) took longer to germinate. The mucilage significantly decreased seed respiration rates by acting as a physical barrier that prevented oxygen diffusion. Germination rates, shoot and root growth of intact achenes were higher than those of demucilaged ones during exposures to cold, heat, osmotic and salt stresses. Achene mucilage presumably plays an ecologically important role in the life cycle of M. himalaica by aiding the critical achene germination and early seedling growth in the stressful habitats of the plateau region of northern Tibet.