Coexistence Of Plant Species Research Articles

Nonstandard finite differences numerical methods for a vegetation reaction–diffusion model

In this work we derive NonStandard Finite Differences (NSFDs) (Anguelov and Lubuma, 2001; Mickens, 2020) numerical schemes to solve a model consisting of reaction–diffusion Partial Differential Equations (PDEs) that describes the coexistence of plant species in arid environments (Eigentler and Sherratt, 2019). The new methods are constructed by exploiting a-priori known properties of the exact solution, such as positivity and oscillating behavior in space. Furthermore, we extend the definition of NSFDs inspired by the Time-Accurate and High-Stable Explicit (TASE) (Bassenne et al., 2021) methodology, also exploring the existing connections between nonstandard methods and the Exponential-Fitting (EF) (Ixaru, 1997; Ixaru and Berghe, 2010) technique.Several numerical tests are performed to highlight the best properties of the new NSFDs methods compared to the related standard ones. In fact, at the same cost, the former are much more stable than the latter, and unlike them preserve all the most important features of the model.

Vegetation analysis and environmental indicators of an arid tropical forest ecosystem of Pakistan

Vegetation composition and/or plant species co-existence is influenced by the environmental variations in any region. The ecological knowledge and order of importance of selected environmental variations is important in conservation and management of plant resources. Based on relevant knowledge gap, the study area of district Jhelum, Pakistan lying in an arid-tropical zone was selected to explore the vegetation types and their driving environmental factors by using latest multivariate statistical approaches. For this, the entire district was ecologically explored to collect the natural wild vegetation and environmental data from January 2018 to December 2020. The study area was partitioned into 171 grids (5 × 5 km2). In each grid, three sites were randomly selected (i.e. 513 samples), and subsequently-nine plots were laid at each sampling site (i.e. 1539 plots). Different statistical tests including Monte Carlo permutation test, Indicator Species Analysis (ISA), hierarchical classification, ordination, and variation partitioning were applied to seek the potential number of vegetation types, plant species composition, classification of the studied samples, order of importance of the considered predictors and groups of environmental variables respectively. The findings of this study indicated that all the documented 291 plant species belong to five statistically significant (p < 0.05) plant communities. Out of thirty (30) considered environmental variables, canonical correspondence analysis suggested the significant role of distance from the river, altitude, latitude, slope, temperature, rainfall, distance from the cropland, grazing and deforestation pressure, and soil pollutants including chromium, arsenic and nickel concentrations. Similarly, plant diversity patterns were found strongly associated with the selected local environmental conditions. This study concluded that distance from the river (a potential leading proxy of ground water table depth) is relatively more important than the rainfall variability in this tropical arid area. Hence, the relative proportion of xerophytic plant species was found higher in the western parts compared to eastern parts adjoining the river Jhelum. Anthropogenic disturbances and potentially toxic metals were found disrupting the normal ecosystem functioning at the local scale in this arid tropical region, and need immediate attention to save the valuable local biodiversity.

Tree mycorrhizal type mediates conspecific negative density dependence effects on seedling herbivory, growth, and survival.

Tree mycorrhizal type plays an important role in promoting plant species diversity and coexistence, via its mediating role in conspecific negative density dependence (CNDD), i.e., the process by which an individual's performance is impaired by the density of conspecific plants. Previous findings suggest that ectomycorrhizal (EM) tree species are generally less susceptible to CNDD than arbuscular mycorrhizal (AM) tree species, due to the chemical and physical protection that EM fungi provide their host with. We examined how CNDD effects on leaf herbivory, seedling growth, and survival differ between AM and EM seedlings of ten tree species collected over 3years in an old-growth temperate forest in northeastern China. We found that AM and EM seedlings differed in how conspecific density affected their leaf herbivory, seedling growth, and survival. Specifically, AM seedlings leaf herbivory rates significantly increased with increasing conspecific seedling and adult density, and their growth and survival rates decreased with increasing conspecific adult density, these patterns were, however, absent in EM seedlings. Our work suggests that AM seedlings have a performance disadvantage relative to EM seedlings related to the negative effects from conspecific neighbors. We highlight the importance of integrating information on seedling leaf herbivory, seedling growth, to provide further understanding on potential mechanisms driving differences in CNDD between AM and EM tree seedlings.

Big-sized trees and species-functional diversity pathways mediate divergent impacts of environmental factors on individual biomass variability in Sri Lankan tropical forests

In tropical forests, several studies have explored the effects of environmental factors and tree species diversity as well as functional trait diversity and trait composition on aboveground biomass (AGB) stock. However, these abiotic and biotic effects on individual biomass variability (BioVar) are still largely unexplored, which limits our understanding of the plant-plant interactions for species coexistence. Here, we used the Partial Least Squares Structural Equation Models (PLS-SEMs), and other complementary analyses, on data from 189 tropical forest plots in Sri Lanka, to test the linkages amongst climate (a latent variable of solar radiation and potential evapotranspiration), soil (pH and cation exchange capacity), plot (plot size and stand density) conditions, big-sized trees, species-functional diversity, and BioVar. The PLS-SEMs showed that climate conditions decreased BioVar directly but increased indirectly via integrative promoting direct effects on soil conditions, species-functional diversity and big-sized trees. In contrast, soil conditions increased BioVar directly but decreased indirectly via integrative suppressing direct effects on species-functional diversity and big-sized trees. Interestingly, we found that the divergent indirect effects of climate and soil conditions on BioVar via big-sized trees mattered when the direct effect of big-sized trees on species-functional diversity was considered as compared to the reverse effect in PLS-SEMs. Also, the indirect positive effect of plot properties on BioVar was nearly equal to the direct effect because plot properties affected big-sized trees as similar as or lower than species-functional diversity. The positive effect of species-functional diversity on BioVar was mediated by the structural attributes of big-sized trees, indicating increased plant species co-existence. This study suggests that individual tree biomass variability (i.e., BioVar) should be considered for managing natural tropical forests in the context of the plant-plant interactions for species coexistence.

Light heterogeneity affects understory plant species richness in temperate forests supporting the heterogeneity-diversity hypothesis.

One of the most important drivers for the coexistence of plant species is the resource heterogeneity of a certain environment, and several studies in different ecosystems have supported this resource heterogeneity–diversity hypothesis. However, to date, only a few studies have measured heterogeneity of light and soil resources below forest canopies to investigate their influence on understory plant species richness. Here, we aim to determine (1) the influence of forest stand structural complexity on the heterogeneity of light and soil resources below the forest canopy and (2) whether heterogeneity of resources increases understory plant species richness. Measures of stand structural complexity were obtained through inventories and remote sensing techniques in 135 1‐ha study plots of temperate forests, established along a gradient of forest structural complexity. We measured light intensity and soil chemical properties on six 25 m² subplots on each of these 135 plots and surveyed understory vegetation. We calculated the coefficient of variation of light and soil parameters to obtain measures of resource heterogeneity and determined understory plant species richness at plot level. Spatial heterogeneity of light and of soil pH increased with higher stand structural complexity, although heterogeneity of soil pH did not increase in conditions of generally high levels of light availability. Increasing light heterogeneity was also associated with increasing understory plant species richness. However, light heterogeneity had no such effects in conditions where soil resource heterogeneity (variation in soil C:N ratios) was low. Our results support the resource heterogeneity–diversity hypothesis for temperate forest understory at the stand scale. Our results also highlight the importance of interaction effects between the heterogeneity of both light and soil resources in determining plant species richness.

Root phosphatase activity aligns with the collaboration gradient of the root economics space.

The adoption of diverse resource acquisition strategies is critical for plant growth and species coexistence. Root phosphatase is of particular importance in the acquisition of soil phosphorus (P), yet it is often overlooked in studies of root trait syndromes. Here, we evaluated the role of root phosphatase activity (RPA) within the root economics space and the order-based variation of RPA, as well as the correlations between RPA and a suite of leaf traits and soil properties over a range of evergreen tree species in a subtropical forest. Root phosphatase activity exhibited a high degree of inter-specific variation. We found that there were two leading dimensions of the multidimensional root economics space, the root diameter-specific root length axis (collaboration trait gradient) and the root tissue density-root nitrogen concentration axis (classical trait gradient), and RPA aligned with the former. Root phosphatase activity is used as a 'do it yourself' strategy of soil P acquisition, and was found to be inversely correlated with mycorrhizal colonization, which suggests a trade-off in plant P acquisition strategies. Compared with soil and foliar nutrient status, root traits mattered most for the large inter-specific changes in RPA. Furthermore, RPA generally decreased from first- to third-order roots. Taken together, such diverse P-acquisition strategies are conducive to plant coexistence within local forest communities. The use of easily measurable root traits and their tight correlations with RPA could be a feasible and promising approach to estimating species-specific RPA values, which would be helpful for better understanding plant P acquisition and soil P cycling.

Conspecific leaf litter induces negative feedbacks in Asteraceae seedlings.

The plant soil feedback (PSF) framework has been instrumental in understanding the impacts of soil microbes on plant fitness and species coexistence. PSFs develop when soil microbial communities are altered due to the identity and density of a particular plant species, which can then enhance or inhibit the local survival and growth of that plant species as well as different plant species. The recent extension of the PSF framework to aboveground microbiota, termed here as plant phyllosphere feedbacks (PPFs), can also help to determine the impact of aboveground microbes on plant fitness and species interactions. However, experimental tests of PPFs during early plant growth are nascent and the prevalence of PPFs across diverse plant species remains unknown. Additionally, it is unclear whether plant host characteristics, such as functional traits or phylogenetic distance, may help to predict the strength and direction of PPFs. To test for the prevalence of litter-mediated PPFs, recently senesced plant litter from 10 native Asteraceae species spanning a range of life history strategies was used to inoculate seedlings of both conspecific and heterospecific species. We found that exposure to conspecific litter significantly reduced the growth of four species relative to exposure to heterospecific litter (i.e., significant negative PPFs), three species experienced marginally significant negative PPFs, and the PPF estimates for all 10 species were negative. However, neither plant functional traits, nor phylogenetic distance were predictive of litter feedbacks across plant species pairs, suggesting that other mechanisms or traits not measured may be driving conspecific negative PPFs. Our results indicate that negative, litter-mediated PPFs are common among native Asteraceae species and that they may have substantial impacts on plant growth and plant species interactions, particularly during early plant growth.

Germination of small tropical seeds has distinct light quality and temperature requirements, depending on microhabitat.

The coexistence of plant species in tropical rainforests is related to specific abiotic resources, varying according to the occurrence microhabitat of each species. Light quality is the main abiotic factor influencing germination of small seeds; however, studies often do not discriminate its effect from that of light irradiance. This study compared specific requirements for seed germination of ten small-seeded species, with restricted occurrence in only one of three contrasting microhabitats: forest understorey, edge of clearings and open areas. Laboratory experiments were carried out to test temperature regime (constant or fluctuating), light quality (R:FR) and light irradiance (PAR), which reproduce high and low conditions commonly found in the microhabitats. Seed germination of all species occurred between 20 and 30°C, only seeds of open area species were able to germinate at 35°C and no species required alternating temperatures to germinate. Irrespective of species and microhabitat, a decrease in the R:FR reduced the germination percentage; however, there were differences in the capacity to germinate at low R:FR. The values of R:FR50% were higher for open area and edge species (0.441-0.345) than for understorey species (0.181-0.109), with few exceptions. For all species and most of the tests, germination was not influenced by PAR. Light quality is the most important light signal for germination of small seeds; irradiance has little effect. Our results suggest two distinct patterns of germination for small-seeded species: open area and edge species are light-demanding and require high R:FR to germinate, while understorey species are shade-tolerant and germinate at low R:FR. These differences are responsible for distinct microhabitat occurrence and help to explain the coexistence of species in tropical forests.

Short-lived legacies of Prunus serotina plant-soil feedbacks.

Plant-soil feedbacks (PSFs) are often involved in fundamental ecological processes such as plant succession and species coexistence. After a plant initiating PSFs dies, legacies of PSFs occurring as soil signatures that influence subsequent plants could persist for an unknown duration. Altered resource environments following plant death (especially light availability) could affect whether legacy effects manifest and persist. To evaluate PSFs and their legacies, we obtained soils from a chronosequence of Prunus serotina harvests. In a greenhouse experiment, we planted conspecific seedlings under two light levels in these soils of varying time since the influence of live Prunus serotina, and compared seed/seedling survival in soils from live trees, stumps, and surrounding forest matrix within each site and across the chronosequence. PSF legacies were measured as the difference between seedling performance in live tree and stump soils within a site. Negative PSF legacies of P. serotina were short-lived, lasting up to 0.5years after tree removal. These effects occurred under 5% but not 30% full sun. PSFs and their legacies manifested in seed/seedling survival, but not biomass. Though restricted to low light, short-lived legacies of P. serotina PSFs could have lasting impacts on plant community dynamics during post-disturbance regeneration by disfavoring P. serotina regeneration in small tree-fall gaps.

Soil biota and soil substrates influence responses of the rhizomatous clonal grass Leymus chinensis to nutrient heterogeneity

The positive effects of spatial heterogeneity in soil nutrients on plant performance have been well documented, but whether such effects depend on the presence of soil biota or the substrate type in which the heterogeneity is manipulated remains largely unknown. In a greenhouse experiment, we grew the rhizomatous clonal grass Leymus chinensis in three different substrates (i.e., field soil, potting soil, and mixtures of ceramsite and quartz) that were subjected to two different soil nutrient treatments (i.e., a homogeneous treatment and a heterogeneous treatment consisting of low- and high-nutrient soil patches) and inoculated with either live or sterilized soil biota. In the presence of the live soil biota, L. chinensis produced more biomass in the homogeneous than in the heterogeneous treatment, independent of the substrate type. With the sterilized soil biota, however, L. chinensis produced more biomass in the heterogeneous than in the homogeneous treatment. In the heterogeneous treatment consisting of the field soil and the potting soil, L. chinensis produced more biomass in the high-nutrient patches than in the low-nutrient patches. In contrast, it produced more biomass in the low-nutrient patches than in the high-nutrient patches in the heterogeneous treatment consisting of the field soil and the mixture of quartz and ceramsite. Both soil biota and soil substrates can influence the responses of clonal plants to soil nutrient heterogeneity. Our results highlight the vital importance of including soil biota and soil physical properties in studies designed to examine the effects of soil nutrient heterogeneity on plant performance, population dynamics, species coexistence and ecosystem functioning.

Rare plant species are at a disadvantage when both herbivory and pollination interactions are considered in an alpine meadow.

Rare plant species often suffer less damage than common species because of positive density-dependent herbivory, and it has been suggested that this 'rare species advantage' fosters plant species coexistence. However, it is unknown whether rare species have an advantage when pollination interactions are also considered. We hypothesized that a 'positive density-dependent pollination success' across plant species would result in common plants experiencing higher seed set rates compared to rare species, and that positive density-dependent effects would negate or even override the positive density-dependent damage due to herbivory resulting in higher seed loss rates in common plant species. We tested this hypothesis by concurrently examining a plant-predispersal seed predator system and a plant-pollinator system for 24 Asteraceae species growing in an alpine meadow community (Sichuan Province, China). Having previously reported a positive density-dependent effect on seed loss rates due to seed predators, we here focus on the density-dependent effects on pollination success by investigating pollinator species richness, visitation frequencies and seed set rates for each plant species. We also estimated the seed output rate of each plant species as the product of seed set rate and the rate of surviving seeds (i.e. 1-the seed loss rate). Consistent with our hypothesis, a positive density-dependent effect was observed for pollinator species richness, visitation frequencies and seed set rates across plant species. Moreover, the positive effect overrode the negative density-dependent effect of herbivores on seed production, such that common species tended to have a higher seed output rate than rare species (i.e. we observed a 'rare species disadvantage'). These results indicate that the low seed output rate of rare species might result from a pollination limitation, and that both mutualistic and antagonistic interactions should be examined simultaneously to fully understand plant species coexistence in local communities.

Disentangling the interactive effects of climate change and Phytophthora cinnamomi on coexisting Mediterranean tree species

The structure and function of Mediterranean mixed oak forests are seriously threatened by climate change and the exotic pathogen Phytophthora cinnamomi. Both factors have been individually studied in some detail, but we have a poor understanding of their interactive effects on plant performance and species coexistence. We conducted a greenhouse experiment where seedlings of three coexisting species with contrasting susceptibility to the pathogen (Quercus suber, Quercus canariensis and Olea europaea var. sylvestris) were planted in pairs under different scenarios of drought (control vs. 30% rainfall reduction), warming (control vs. 3°C increase) and pathogen presence (control vs. soil infested with P. cinnamomi). At the end of the experiment, we assessed the severity of root symptoms and plant morphological traits (shoot and root biomass, root tissue density and specific root length). Results showed that seedlings of the three species, including O. europaea and Q. canariensis (species considered as resistant and tolerant to the pathogen, respectively), showed in general significantly higher root symptoms and lower shoot and root biomass than non-inoculated seedlings, independently of the drought, warming and plant treatments. We found, however, some interactive effects of the climatic treatments and P. cinnamomi on root traits of the two Quercus species. Variations in the specific root length (SRL) and root tissue mass density (RTD) of Quercus spp. suggest a compensation of the negative effects of both stressors on seedling performance. Overall, our results suggest that the warming and drought predicted for Mediterranean forests during spring might not have a relevant impact on the infectivity ability of P. cinnamomi, supporting its great adaptability to these changing climatic conditions. Therefore, in Mediterranean forests infected by P. cinnamomi, it becomes crucial to avoid the spread and multiplication of the pathogen during spring, since its destructive ability at high inoculum levels is largely independent of environmental conditions.

Mountain ecology under climate change

Trophic Ecology Climate warming causes shifts in the distributions of organisms and different organisms may move at different rates, resulting in changes in the composition and functioning of ecological communities. These effects are rarely considered in forecasts about the effects of climate change on biodiversity. Using experimental translocations, Descombes et al. investigated how differential upslope migration in alpine plants and their insect herbivores affects community interactions. Lowland herbivores modify the three-dimensional vegetation structure at higher altitudes, and this modified vegetation structure favors the coexistence of plant species, especially by favoring small-stature species. Reorganized trophic interactions will play an important role in driving plant community changes under future climate change. Science , this issue p. [1469][1] [1]: /lookup/doi/10.1126/science.abd7015

Novel trophic interactions under climate change promote alpine plant coexistence.

Herbivory and plant defenses exhibit a coupled decline along elevation gradients. However, the current ecological equilibrium could be disrupted under climate change, with a faster upward range shift of animals than plants. Here, we experimentally simulated this upward herbivore range shift by translocating low-elevation herbivore insects to alpine grasslands. We report that the introduction of novel herbivores and increased herbivory disrupted the vertical functional organization of the plant canopy. By feeding preferentially on alpine plants with functional traits matching their low-elevation host plants, herbivores reduced the biomass of dominant alpine plant species and favored encroachment of herbivore-resistant small-stature plant species, inflating species richness. Supplementing a direct effect of temperature, novel biotic interactions represent a neglected but major driver of ecosystem modifications under climate change.

Effects of microtopography and nutrients on biomass production and plant species diversity in experimental wetland communities

We performed a mesocosm study to examine the effects of microtopography and nutrients on biomass production, plant species diversity, and the relationships between these indices in wetland ecosystems. Although we found significant contributions (p < .05) of microtopography toward shoot coverage, above-ground dry weight, and total dry weight, the effects of nutrients on most indices of biomass production and diversity were more prominent (p < .001) than those of microtopography. Relatively low biomass production and high diversity were found under low nutrient conditions, whereas directly opposite results were obtained under fertilized conditions, indicating negative linear correlations between biomass production and diversity. Relatively short species such as Eleocharis congesta and E. yokoscensis were more frequent under low nutrient conditions, whereas relatively tall species such as Echinochloa crus-galli, Panicum dichotomiflorum, and Persicaria hydropiper were more common under fertilized conditions. In particular, an invasive species (Paspalum distichum) also showed relatively high importance value under fertilized conditions. In the context of wetland construction, restoration and management, we suggest that nutrient status should be considered before microtopography, particularly in wetland ecosystems under the early phase of secondary succession. Oligotrophic status should be maintained particularly for the co-existence of diverse plant species including rare species.

Effect of Seasonal Rains and Floods on Seedling Recruitment and Compositional Similarity in Two Lowland Tropical Forests

Research Highlights: Seasonally flooded and terra firme forests are characteristic ecosystems of the Colombian Orinoco Basin and of great importance in the maintenance of regional biodiversity and ecosystem function. These forests have a unimodal precipitation regime that can cause a temporal effect on the seedling regeneration niche. This could partly explain the high diversity and coexistence of plant species in these forests, as well as the similarity in composition of seedlings and trees. Background and Objectives: Seedlings are a key factor in the assembly of plant communities. We evaluated the effect of flooding and rains on the dissimilarity and compositional affinity between trees and seedlings of seasonally flooded and terra firme forests. Materials and Methods: the tree community of these forests in San Martín (Meta, Colombia) was characterized and compared with their respective seedling communities before (June) and after (December) rain and flooding (during the rainy season). We evaluated plant species diversity and abundance (Shannon diversity and Pielou eveness index), as well as the compositional dissimilarities of each tree community with their corresponding seedling community sampled at the beginning and end of rains and flooding (Bray–Curtis dissimilarity). We also compared sampling site composition using a NMDS analysis. Results: We found that the terra firme forest had higher diversity compared to the flooded forest. Seedling density in the seasonally flooded forest decreased significantly after the flood but not in the terra firme forest at the end of the rainy season. The compositional dissimilarity between trees and seedlings in the seasonally inundated forest also decreased after the flood. However, this pattern was not evident in the terra firme forest. Conclusions: These results indicate that seasonal flooding generates a strong ecological filter that affects the realized niche of plants in these forests. Our results can contribute valuable information for the effective development of assisted restoration and conservation programs.

Conspecific negative density dependence in rainy season enhanced seedling diversity across habitats in a tropical forest.

Conspecific negative density dependence (CNDD) could be one of the most important local-scale mechanisms shaping plant species coexistence. However, the spatial and temporal changes in the strength CNDD and the implications for the plant diversity remain unknown. We used 10years of seedling data, in a seasonal tropical rainforest, to discover how CNDD influences tree seedling survival across habitats and seasons. We also evaluated the relation between CNDD and species diversity. We found the strength of CNDD in the valley habitat was significantly stronger than in ridge habitat in rainy season, but not significantly different in dry season. Corresponding to expectations of CNDD as mechanism of diversity maintenance, seedling species diversity was significantly higher in valley habitat than in ridge habitat and significantly correlated with CNDD. Additionally, conspecific and heterospecific seedling neighbour densities positively affected the survival of tree seedlings, but heterospecific adult neighbour density had a weak effect. Our study finds that CNDD varied significantly across habitats and was correlated with local seedling diversity. Our results highlight the importance of CNDD in driving species diversity at the local scale. Recognizing the spatial and temporal variation in the strength of CNDD will aid efforts to model and understand species coexistence.

Editorial: The Next Step: Disentangling the Role of Plant-Soil Feedbacks in Plant Performance and Species Coexistence Under Natural Conditions

Effects of plant-induced changes in soil properties, which impact subsequent plant growth, have received increasing attention in plant ecology (e.g., Smith-Ramesh & Reynolds 2017). These plant-soil feedbacks (PSFs) are considered to be important for plant performance and plant-community composition in many terrestrial ecosystems (e.g., van der Putten et al. 2013). However, so far most conclusions on the importance of PSFs in natural systems have been drawn from experiments performed under highly controlled and artificial conditions. Under natural conditions, the growth and development of plants as well as that of soil organisms is influenced by many more abiotic and biotic interactions than in the greenhouse. Hence, there is an urgent need to investigate PSFs under more natural conditions and to better understand the interactions between PSFs and environmental drivers (De Long et al. 2019). This Research Topic comprises 14 articles - ranging from Original research articles, meta-analytical Reviews and Perspectives - that aim to advance our understanding of the contribution of PSFs to plant growth and plant community composition in different environmental contexts.

Coexistence of plant species under harsh environmental conditions: an evaluation of niche differentiation and stochasticity along salt marsh creeks

BackgroundEcologists have achieved much progress in the study of mechanisms that maintain species coexistence and diversity. In this paper, we reviewed a wide range of past research related to these topics, focusing on five theoretical bodies: (1) coexistence by niche differentiation, (2) coexistence without niche differentiation, (3) coexistence along environmental stress gradients, (4) coexistence under non-equilibrium versus equilibrium conditions, and (5) modern perspectives.ResultsFrom the review, we identified that there are few models that can be generally and confidently applicable to different ecological systems. This problem arises mainly because most theories have not been substantiated by enough empirical research based on field data to test various coexistence hypotheses at different spatial scales. We also found that little is still known about the mechanisms of species coexistence under harsh environmental conditions. This is because most previous models treat disturbance as a key factor shaping community structure, but they do not explicitly deal with stressful systems with non-lethal conditions. We evaluated the mainstream ideas of niche differentiation and stochasticity for the coexistence of plant species across salt marsh creeks in southwestern Denmark. The results showed that diversity indices, such as Shannon–Wiener diversity, richness, and evenness, decreased with increasing surface elevation and increased with increasing niche overlap and niche breadth. The two niche parameters linearly decreased with increasing elevation. These findings imply a substantial influence of an equalizing mechanism that reduces differences in relative fitness among species in the highly stressful environments of the marsh. We propose that species evenness increases under very harsh conditions if the associated stress is not lethal. Finally, we present a conceptual model of patterns related to the level of environmental stress and niche characteristics along a microhabitat gradient (i.e., surface elevation).ConclusionsThe ecology of stressful systems with non-lethal conditions will be increasingly important as ongoing global-scale climate change extends the period of chronic stresses that are not necessarily fatal to inhabiting plants. We recommend that more ecologists continue this line of research.

Seed dormancy release of Halenia elliptica in response to stratification temperature, duration and soil moisture content

BackgroundAlthough the effect of cold stratification on seed dormancy release has been extensively studied for many species, knowledge of the role of stratifying temperature, soil moisture content and duration of stratification on seed dormancy release at the population level is limited. Here, we aimed to determine the response of seed dormancy release to these factors in six populations of Halenia elliptica.ResultsSeed dormancy release was more responsive to low than high temperatures, and no dormancy break occurred at 8 °C. Seed germination percentage increased first and then remained unchanged as stratifying soil moisture content increased from 0 to 24%. Seed dormancy release of populations from low altitude was more sensitive to increased stratifying temperature and decreased soil moisture content than those from high altitudes.ConclusionsTemperature and soil moisture changes resulting from global warming could affect seed dormancy release and consequently seedling establishment. Thus, incorporating data on seed dormancy release involving temperature, soil moisture content and stratification duration is beneficial for predicting plant species regeneration, migration and coexistence in a scenario of climate change.