Long-Term Contaminant Exposure Alters Functional Potential and Species Composition of Soil Bacterial Communities in Gulf Coast Prairies.

Environmental pollution is a persistent threat to coastal ecosystems worldwide, adversely affecting soil microbiota. Soil microbial communities perform critical functions in many coastal processes, yet they are increasingly subject to oil and heavy metal pollution. Here, we assessed how small-scale contamination by oil and heavy metal impacts the diversity and functional potential of native soil bacterial communities in the gulf coast prairie dunes of a barrier island in South Texas along the northern Gulf of Mexico. We analyzed the bacterial community structure and their predicted functional profiles according to contaminant history and examined linkages between species diversity and functional potential. Overall, contaminants altered bacterial community compositions without affecting richness, leading to strongly distinct bacterial communities that were accompanied by shifts in functional potential, i.e., changes in predicted metabolic pathways across oiled, metal, and uncontaminated environments. We also observed that exposure to different contaminants can either lead to strengthened or decoupled linkages between species diversity and functional potential. Taken together, these findings indicate that bacterial communities might recover their diversity levels after contaminant exposure, but with consequent shifts in community composition and function. Furthermore, the trajectory of bacterial communities can depend on the nature or type of disturbance.

Habitat modification by marram grass negatively affects recruitment of conspecifics.

Ecosystem engineers alter their environment often benefiting their own survival and growth yielding self-reinforcing feedbacks. Moreover, these habitat modifications have been found to facilitate recruitment of conspecifics for some species, while for others engineering inhibits recruitment. Whether dune grasses facilitate or inhibit recruitment of conspecifics is yet unknown. Here, we investigated how habitat modification by European marram grass (Ammophila arenaria) through embryonic dune development affects recruitment from seeds and marine dispersed rhizome fragments. Specifically, we tested at three locations with different dune morphologies how habitat modification affected natural seed and rhizome presence and shoot emergence from plots in which seeds or rhizome fragments were added. In addition, we investigated how sediment burial (i.e., the main effect of habitat modification by dune grasses) affected germination and emergence in a controlled experiment. Results show that regardless of habitat modification or beach width, seeds and rhizomes were absent in natural conditions. Habitat modification negatively affected shoot emergence from seeds (8 × less) and rhizomes (4 × less) and was negatively related to sediment dynamics. Furthermore, fewer seedlings were found with higher elevations. In controlled laboratory conditions, the highest seedling emergence was found with slight burial (0.5-3 cm); both germination and seedling emergence decreased as seeds were buried deeper or shallower. Overall, habitat modification by marram grass negatively affects recruitment of conspecifics through increased sediment dynamics and elevation. Consequently, storm events or eradication programs that include removal of adult vegetation-which leads to an unmodified system-might benefit new recruitment from seeds or clonal fragments.

The Amelioration of Grazing through Physiological Integration by a Clonal Dune Plant.

Rhizomatous growth and associated physiological integration can allow a clonal dune species to potentially compensate for the selective removal of leaves associated with herbivory. Hydrocotyle bonariensis is a rhizomatous clonal plant species that is abundant in the coastal dune environments of the southeastern United States that are inhabited by large feral horse populations. H. bonariensis has been shown to integrate resources among ramets within extensive clones as an adaptation to resource heterogeneity in sandy soils. In this study, we hypothesized that clonal integration is a mechanism that promotes H. bonariensis persistence in these communities, despite high levels of herbivory by feral horses. In a field experiment, we used exclosures to test for herbivory in H. bonariensis over a four-month period. We found that feral horses utilized H. bonariensis as a food species, and that while grazing will suppress clonal biomass, H. bonariensis is able to maintain populations in a high grazing regime with and without competition present. We then conducted an experiment in which portions of H. bonariensis clones were clipped to simulate different levels of grazing. Half of the clones were severed to eliminate the possibility of integration. We found that after 12 weeks, the mean number of leaves and ramets increased as the grazing level increased, for integrated clones. Integrated clones had significantly increased biomass production compared to the severed equivalents. Our research suggests that rhizomatous growth and physiological integration are traits that allow clonal plant species to maintain populations and to tolerate grazing in coastal dune environments.

Warmer Temperature and Spatiotemporal Dynamics during Primary Succession on Tropical Coastal Dunes.

Coastal dunes are sensitive indicators of climate change: it is expected that higher precipitation and warmer temperature will promote vegetation growth and sand stabilization. Alternatively, dunes may become active during severe droughts, which would reduce plant cover and increase sand mobility. Consequently, it is relevant to explore community shifts and self-organization processes to better understand how coastal dunes vegetation will respond to these projected changes. Primary succession allows the exploration of community assembly and reorganization processes. We focused on three environmental variables (bare sand, temperature, and precipitation) and five successional groups (facilitators, colonizers, sand binders, nucleators, and competitors). For 25 years (from 1991 to 2016), species turnover was monitored in 150 permanent plots (4 × 4 m) placed on an initially mobile dune system located on the coast of the Gulf of Mexico. The spatiotemporal dynamics observed during primary succession were consistent with the facilitation nucleation model. As late colonizers grew and expanded, psammophytes became locally extinct. The spatial patterns revealed that ecological succession did not occur evenly on the dunes. In addition, the increased mean yearly temperature during the last decades seemed to be associated with the accelerated increment in plant cover and species richness, which had not been registered before in Mexico.

Relationship between the distribution of vegetation and the environment in the coastal embryo dunes of Jalisco, México.

Background: The poorly developed soils of the embryo dunes imply little capacity for plant support, however, the adaptation mechanisms of plants respond sensitively to environmental variations, even when these variations are small, which results in a set of specialized habitats and flora that are rarely shared with other terrestrial ecosystems. The coastal dunes of the Mexican Pacific remain vaguely studied, this is why this research explored the relationship between environmental properties and the presence of plant species in the embryo dunes of the coast of Jalisco, Mexico. Methods: Twenty-nine sites were sampled, one or two sites per embryo dune, with a random stratified design. Geomorphological and vegetation data were collected at site. Laboratory determinations included soil color, particle size, organic matter, pH, electrical conductivity, magnetite content, and moisture retention. Statistical analysis included correlation analysis to identify relationships between environmental variables; principal component analysis (PCA) and cluster analysis to group dune sites by environmental properties; canonical correspondence analysis (CCA) to determine a possible significant relationship between the presence of plant species and environmental variables; cluster analysis to group dune sites by presence/absence of plant species and correlate both clusters to validate the relationship between them, the salient aspects of this relationship were described and the spatial distribution of the groups was mapped. Results: Eleven plant species were identified, six of them exclusive to the embryo dunes and the rest ubiquitous. The incipient development of these soils is reflected in a low content of organic matter, silt, clay, and moisture retention, with scattered data on granulometry, electrical conductivity, organic matter, and magnetite. Some significant correlations were found between some environmental properties, and the CCA showed a significant relationship between the presence of plant species and environmental variables (p-value of the Monte Carlo test = 0.026). The cluster analysis of dune sites according to environmental variables and the cluster analysis by presence/absence of plant species produces the formation of five groups of sites with significant environmental differences and five groups of sites with significant floristic differences. A significant connection (r = 0.471, p = 0.01) between the two clustering schemes also evidences the meaningful relationship between the presence of plant species and the environmental characteristics of the embryo dunes of Jalisco, Mexico. Differences in habitat preferences were observed among plant species exclusive to the embryo dunes; thus, Abronia maritima, Uniola pittieri, and Pectis arenaria showed a preference for embryo dunes with poor edaphic conditions, in contrast to Okenia hypogaea, Canavalia rosea, and Scaevola plumieri, which were mostly found in embryo dunes with higher fertility.

Environmental variables affecting an arid coastal nebkha.

Foredunes in arid coastal dune systems comprise nebkhas, which originate by interactions between vegetation and aeolian sedimentation. While continuous foredunes in temperate climates have been widely studied, knowledge of interactions between biotic and abiotic drivers in foredunes formed by nebkha is still scarce. With the aim of exploring variables affecting arid foredunes, a range of morphological, sedimentological, and vegetation characteristics were measured on a single nebkha formed by a Traganum moquinii plant located in the foredune of Caleta de Famara beach (Lanzarote, Canary Islands). Variables were sampled at 120 plots in a 0.5 × 0.5 m square grid. A two-step process using multiple linear regression (MLR) analyses was developed to characterize 1) the influence that morphological variables and distance from the sea have on plant and sediment patterns on nebkha, and 2) the influence of plants on depositional sediment characteristics. Results indicate close relationships between distance from the sea, plant coverage, and sediment patterns. Empirical results were used to develop a conceptual model that explains the spatial distribution of bio- and geo-morphological characteristics of an arid nebkha foredune.

Successional Development of the Phototrophic Community in Biological Soil Crusts on Coastal and Inland Dunes.

(1) Biological soil crusts (biocrusts) are microecosystems consisting of prokaryotic and eukaryotic microorganisms growing on the topsoil. This study aims to characterize changes in the community structure of biocrust phototrophic organisms along a dune chronosequence in the Baltic Sea compared to an inland dune in northern Germany. (2) A vegetation survey followed by species determination and sediment analyses were conducted. (3) The results highlight a varying phototrophic community composition within the biocrusts regarding the different successional stages of the dunes. At both study sites, a shift from algae-dominated to lichen- and moss-dominated biocrusts in later successional dune types was observed. The algae community of both study sites shared 50% of the identified species while the moss and lichen community shared less than 15%. This indicates a more generalized occurrence of the algal taxa along both chronosequences. The mosses and lichens showed a habitat-specific species community. Moreover, an increase in the organic matter and moisture content with advanced biocrust development was detected. The enrichment of carbon, nitrogen, and phosphorus in the different biocrust types showed a similar relationship. (4) This relation can be explained by biomass growth and potential nutrient mobilization by the microorganisms. Hence, the observed biocrust development potentially enhanced soil formation and contributed to nutrient accumulation.

Coastal dunes as a sink and secondary source of marine plastics: A study at Perran Beach, southwest England.

Plastic food packaging and containers (n = 263) have been retrieved from the scarped foredunes at Perran Beach, SW England, following a storm surge. Samples displayed evidence of cracking, scratching, discolouration, staining and hydroxyl and carbonyl stretching, but legible text indicating their origin, dates of manufacture/expiration, packaging codes and logos, coupled with online product searches, allowed 25 food packets and 87 containers to be aged. Estimates of food packaging age spanned a 43-year period (1975-2018), with a median age of 25 years, while estimates for containers spanned 57 years (1962-2019), with a median age of 19 years. Plastic derived from local littering and offshore sources appears to be trapped within the foredunes for years to decades and subsequently released as "fresh" beach litter following surges sufficient to effect scarping. Dunal systems may act as significant reservoirs of historical plastics and play a critical role in their recycling and retention in the coastal zone.

Carpobrotus spp. patches as trap for litter: Evidence from a Mediterranean beach.

Dunal plants may affect the patterns of deposition of beach litter. In this study, we aimed at evaluating if Carpobrotus spp. patches may act as a litter trap in coastal dune systems. To do so, we counted the number of macrolitter occurring in both Carpobrotus and control (embryo dune vegetation) patches classifying each item into categories according to the Marine Strategy. Totally, we observed a significant difference between litter trapped in Carpobrotus (331 items, representing 62.4% of the total beach litter) and control (199, 37.6%). Plastic fragments were the most trapped items by both Carpobrotus (46.2%) and control patches (47.2%). We also calculated the item co-occurrence, obtaining a random aggregated 'litter community'. The main emerging output is that Carpobrotus patches act as filter in respect to different anthropogenic materials (overall plastics), suggesting that alien plant management actions may contribute to solve beach litter issues as well.

Nebkha development and sediment supply.

This study examines the role of sediment supply in controlling the formation and the spatial patterns of nebkha, numbers and sizes, present in foredunes fronting coastal dunefields of the arid northwest African and the Canary Islands coasts. Sediment supply is estimated qualitatively and quantitatively by various measures, and the number and size of nebkhas are obtained on a range of beach-dune systems. In the case of the Canary Islands, LiDAR data and orthophotos with high spatial resolution (0.25 m) are used to measure sediment supply/activity, nebkha numbers and sizes, and vegetation variables, whereas data availability is less on the African coast. Results show that sediment supply exerts a major control on nebkha development such that as sediment supply increases, the number of coastal nebkha decreases, and the size of individual plants/nebkha increases. Once sediment supply is large, nebkha can only form on the immediate backshore if space is available, and a point is reached when the sediment supply is so large that nebkha do not, or cannot form. The data presented here provide two indicators which could be applicable to other dune systems. Firstly, by estimating the number of nebkha and the vegetation cover, the degree of aeolian sedimentary activity or sediment supply might be estimated. Secondly, the type of aeolian landform present provides a qualitative indication of sediment supply and aeolian activity.

Integrated methods and scenarios for assessment of sand dunes ecosystem services.

Anthropogenic and natural ecosystems in coastal dunes provide considerable benefits to human well-being. However, to date, we still lack a good understanding of how ecosystem services (ES) supply varies from young dunes (e.g., embryo and fore dunes) to mature dunes (e.g., brown and red dunes). This study proposed a novel modelling methodology by integrating an expert-based matrix, a Bayesian Belief Network (BBN), a structural equation model, and a scenario development method. It aims at evaluating dune ecosystem services for the sustainable development of coastal areas. The model was tested using data collected from dunes in Vietnam. An expert-based matrix to assess the supply capacity of 18 ES in different types of dunes was generated with the participation of 21 interdisciplinary scientists. It was found that red dune ecosystems could supply the most regulation and cultural ecosystem services, while gray dunes provided the least amount. Results from a scenario analysis recommended that decision-making is able to optimize multiple ES by: (i) keeping embryo/fore dunes in their natural state instead of using them for mineral mining and urbanization; (ii) enlarging certified and protected forests areas in gray and yellow dunes; and (iii) optimizing cultural ES supply in red dunes.

Different tolerance to salinity of two populations of Oenothera drummondii with contrasted biogeographical origin.

Oenothera drummondii is a native species from the coastal dunes of the Gulf of Mexico that has nowadays extended to coastal areas in temperate zones all over the world, its invasion becoming a significant problem locally. The species grows on back beach and incipient dunes, where it can suffer flooding by seawater, and sea spray. We were interested in knowing how salinity affects this species and if invasive populations present morphological or functional traits that would provide greater tolerance to salinity than native ones. To this end, we conducted a greenhouse experiment where plants from one native and from one invading population were irrigated with five salinity treatments. We measured functional traits on photosynthetic, photochemical efficiency, water content, flowering, Na+ content, pigment content, and biomass. Although O. drummondii showed high resistance to salinity, the highest levels recorded high mortality, especially in the invasive population. Plants exhibited differences not only in response to time under salinity conditions, but also according to their biogeographic origin, the native population being more resistant to long exposure and high salt concentration than the invasive one. Native and invasive populations showed different response to salt stress in photosynthesis and transpiration rates, stomatal conductance, water use efficiency, carboxylation efficiency, electron transport rate, electron transport efficiency, energy used in photochemistry, among others. The increasing salinity levels resulted in a progressive reduction of photosynthesis rate due to both stomatal and biochemical limitations, and also in a reduction of biomass and number and size of flowers, compromising the reproductive capacity.

Stochastic dynamics of barrier island elevation.

Barrier islands are ubiquitous coastal features that create low-energy environments where salt marshes, oyster reefs, and mangroves can develop and survive external stresses. Barrier systems also protect interior coastal communities from storm surges and wave-driven erosion. These functions depend on the existence of a slowly migrating, vertically stable barrier, a condition tied to the frequency of storm-driven overwashes and thus barrier elevation during the storm impact. The balance between erosional and accretional processes behind barrier dynamics is stochastic in nature and cannot be properly understood with traditional continuous models. Here we develop a master equation describing the stochastic dynamics of the probability density function (PDF) of barrier elevation at a point. The dynamics are controlled by two dimensionless numbers relating the average intensity and frequency of high-water events (HWEs) to the maximum dune height and dune formation time, which are in turn a function of the rate of sea level rise, sand availability, and stress of the plant ecosystem anchoring dune formation. Depending on the control parameters, the transient solution converges toward a high-elevation barrier, a low-elevation barrier, or a mixed, bimodal, state. We find the average after-storm recovery time-a relaxation time characterizing barrier's resiliency to storm impacts-changes rapidly with the control parameters, suggesting a tipping point in barrier response to external drivers. We finally derive explicit expressions for the overwash probability and average overwash frequency and transport rate characterizing the landward migration of barriers.

Functional seed traits and germination patterns predict species coexistence in Northeast Mediterranean foredune communities.

BACKGROUND AND AIMS: The structure of plant communities, which is based on species abundance ratios, is closely linked to ecosystem functionality. Seed germination niche plays a major role in shaping plant communities, although it has often been neglected when explaining species coexistence. The aim of this work is to link the seed germination niche to community ecology, investigating how functional seed traits contribute to species coexistence. METHODS: Species selection was based on a database of 504 vegetation surveys from the Veneto coast (Italy). Through cluster analysis we identified the foredune community and selected all of its 19 plant species. By using the 'Phi coefficient' and frequency values, species were pooled in different categories (foundation species, accidental species of the semi-fixed dune and aliens), then the 19 species were grouped according to their germination responses to temperature and photoperiod through cluster analyses. For each germination cluster, we investigated germination trends against temperature and photoperiod by using generalized linear mixed models. KEY RESULTS: We identified four germination strategies: (1) high germination under all tested conditions ('high-germinating'); (2) high germination at warm temperatures in the dark ('dark warm-cued'); (3) high germination at warm temperatures in the light ('light warm-cued'); and (4) low germination, regardless of conditions ('low-germinating'). Foredune foundation species showed a narrow germination niche, being 'low-germinating' or 'dark warm-cued'. Annual species of semi-fixed dunes were 'high-germinating', while alien species were the only members of the 'light warm-cued' cluster. CONCLUSIONS: Our research suggests that different categories of species have dissimilar seed germination niches, which contributes to explaining their coexistence. Climatic events, such as rising temperature, could alter germination patterns, favouring seed regeneration of certain categories (i.e. alien and semi-fixed dune species) at the expense of others (i.e. foundation species, pivotal to ecosystem functioning), and hence potentially altering the plant community structure.

Sediment availability provokes a shift from Brownian to Lévy-like clonal expansion in a dune building grass.

In biogeomorphic landscapes, plant traits can steer landscape development through plant-mediated feedback interactions. Interspecific differences in clonal expansion strategy can therefore lead to the emergence of different landscape organisations. Yet, whether landscape-forming plants adopt different clonal expansion strategies depending on their physical environment remains to be tested. Here, we use a field survey and a complementary mesocosm approach to investigate whether sediment deposition affects the clonal expansion strategy employed by dune-building marram grass individuals. Our results reveal a consistent shift in expansion pattern from more clumped, Brownian-like, movement in sediment-poor conditions, to patchier, Lévy-like, movement under high sediment supply rates. Additional model simulations illustrate that the sediment-dependent shift in movement strategies induces a shift in optimisation of the cost-benefit relation between landscape engineering (i.e. dune formation) and expansion. Plasticity in expansion strategy may therefore allow landscape-forming plants to optimise their engineering ability depending on their physical landscape.

Fire severity effects on resprouting of subtropical dune thicket of the Cape Floristic Region.

It has been hypothesised that high-intensity fires prevent fire-dependent fynbos from being replaced by fire-avoiding subtropical thicket on dune landscapes of the Cape Floristic Region (CFR). Recent extensive fires provided an opportunity to test this hypothesis. We posit that (1) fire-related thicket shrub mortality would be size dependent, with smaller individuals suffering higher mortality than larger ones; and (2) that survival and resprouting vigour of thicket shrubs would be negatively correlated with fire severity. We assessed survival and resprouting vigour post-fire in relation to fire severity and pre-fire shrub size at two dune landscapes in the CFR. Fire severity was scored at the base of the shrub and categorised into four levels. Pre-fire size was quantified as an index of lignotuber diameter and stem count of each shrub. Resprouting vigour consisted of two variables; resprouting shoot count and resprouting canopy volume. A total of 29 species were surveyed. Post-fire survival of thicket was high (83-85%). We found that smaller shrubs did have a lower probability of post-fire survival than larger individuals but could detect no consistent relationship between shrub mortality and fire severity. Fire severity had a positive effect on resprouting shoot count but a variable effect on resprouting volume. Pre-fire size was positively related to survival and both measures of resprouting vigour. We conclude that thicket is resilient to high-severity fires but may be vulnerable to frequent fires. Prescribed high-intensity fires in dune landscapes are unlikely to reduce the extent of thicket and promote fynbos expansion.

Plant response to water stress of native and non-native Oenothera drummondii populations.

Invasive plants can spread over climatically diverse areas. We explore the effects of drought on gas exchange and water relations on the invasive dune species Oenothera drummondii, using plants from four populations with different rainfall and temperatures regimes. Plant material was obtained germinating plants from one native and three non-native populations in a greenhouse. Drought stress was induced by withholding water. Responses to drought stressed plants were then compared to well-watered controls. Measurements of gas exchange, chlorophyll fluorescence and leaf traits were taken initially and every 10 days after water was withheld, until day 36 when plants were re-watered and recover capacity was measured. The effect of water stress was more evident in Fv/Fm and gas exchange variables. The results suggest that this species possess a mechanism of thermal dissipation of energy. Leaf relative water content was significant lower in drought stressed than control plants. At the end of withholding water period, stressed plants are separated from control plants along the axis I of the ordination analysis evidencing differences in functional traits. All plants recovered well after re-watering. Our results provide evidence for permanent differences in morphological traits and functional responses to drought stress among native and invasive populations of O. drummondii. Although we have only studied four populations, these results may provide evidence for the role of plasticity in contributing to the invasion success of this species.

Resilience of beach grasses along a biogeomorphic successive gradient: resource availability vs. clonal integration.

Coastal ecosystems are often formed through two-way interactions between plants and their physical landscape. By expanding clonally, landscape-forming plants can colonize bare unmodified environments and stimulate vegetation-landform feedback interactions. Yet, to what degree these plants rely on clonal integration for overcoming physical stress during biogeomorphological succession remains unknown. Here, we investigated the importance of clonal integration and resource availability on the resilience of two European beach grasses (i.e. Elytrigia juncea and Ammophila arenaria) over a natural biogeomorphic dune gradient from beach (unmodified system) to foredune (biologically modified system). We found plant resilience, as measured by its ability to recover and expand following disturbance (i.e. plant clipping), to be independent on the presence of rhizomal connections between plant parts. Instead, resource availability over the gradient largely determined plant resilience. The pioneer species, Elytrigia, demonstrated a high resilience to physical stress, independent of its position on the biogeomorphic gradient (beach or embryonic dune). In contrast, the later successional species (Ammophila) proved to be highly resilient on the lower end of its distribution (embryonic dune), but it did not fully recover on the foredunes, most likely as a result of nutrient deprivation. We argue that in homogenously resource-poor environments as our beach system, overall resource availability, instead of translocation through a clonal network, determines the resilience of plant species. Hence, the formation of high coastal dunes may increase the resistance of beach grasses to the physical stresses of coastal flooding, but the reduced marine nutrient input may negatively affect the resilience of plants.

Ontogenetic variation in salinity tolerance and ecophysiology of coastal dune plants.

BACKGROUND AND AIMS: Global climate change includes shifts in temperature and precipitation, increases in the frequency and intensity of extreme weather events and sea level rise, which will drastically impact coastal ecosystems. The aim of this study is to quantify salinity tolerance and to identify physiological mechanisms underlying tolerance across wholeplant ontogeny in two widespread native coastal plant species in Hawai'i, Jacquemontia sandwicensis (Convolvulaceae) and Sida fallax (Malvaceae). METHODS: At the seed, seedling, juvenile and mature ontogenetic stages, plants were exposed to high salinity watering treatments. Tolerance was assayed as the performance of stressed compared with control plants using multiple fitness metrics, including germination, survival, growth and reproduction. Potential physiological mechanisms underlying salinity tolerance were measured at each ontogenetic stage, including: photosynthesis and stomatal conductance rates, leaf thickness, leaf mass per area and biomass allocation. KEY RESULTS: Salinity tolerance varied between species and across ontogeny but, overall, salinity tolerance increased across ontogeny. For both species, salinity exposure delayed flowering. Physiological and morphological leaf traits shifted across plant ontogeny and were highly plastic in response to salinity. Traits enhancing performance under high salinity varied across ontogeny and between species. For J. sandwicensis, water use efficiency enhanced growth for juvenile plants exposed to high salinity, while chlorophyll content positively influenced plant growth under salinity in the mature stage. For S. fallax, transpiration enhanced plant growth only under low salinity early in ontogeny; high transpiration constrained growth under high salinity across all ontogenetic stages. CONCLUSIONS: That salinity effects vary across ontogenetic stages indicates that demographic consequences of sea level rise and coastal flooding will influence population dynamics in complex ways. Furthermore, even coastal dune plants presumably adapted to tolerate salinity demonstrate reduced ecophysiological performance, growth and reproduction under increased salinity, highlighting the conservation importance of experimental work to better project climate change effects on plants.

Patterns and effects of heterospecific pollen transfer between an invasive and two native plant species: the importance of pollen arrival time to the stigma.

PREMISE: Invasive plant species can integrate into native plant-pollinator communities, but the underlying mechanisms are poorly understood. Competitive interactions between invasive and native plants via heterospecific pollen (HP) and differential invasive HP effects depending on HP arrival time to the stigma may mediate invasion success, but these have been little studied. METHODS: We evaluated patterns and effects of HP receipt on pollen tube growth in two native and one invasive species in the field. We also used hand-pollination experiments to evaluate the effect of invasive HP pollen and its arrival time on native reproductive success. RESULTS: Native species receive smaller and less-diverse HP loads (5-7 species) compared to invasive species (10 species). The load size of HP had a negative effect on the proportion of pollen tubes in both native species but not in the invasive, suggesting higher HP tolerance in the latter. Invasive HP arrival time differentially affected pollen tube success in native species. CONCLUSIONS: Our results highlight the need to study reciprocal HP effects between invasive and native species and the factors that determine differential responses to HP receipt to fully understand the mechanisms facilitating invasive species integration into native plant-pollinator communities.