Competition between isoetids and invading elodeids at different concentrations of aquatic carbon dioxide

1. The growth of submerged macrophytes in softwater lakes is often assumed to be carbon limited. Isoetid species are well adapted to grow at low carbon availability and therefore commonly dominate the submerged macrophyte vegetation in softwater lakes. In many such lakes, however, large‐scale invasions of fast‐growing elodeid species, replacing the isoetid vegetation, have been observed. 2. In a laboratory experiment, we tested how rising aquatic carbon availability, in interaction with different densities of the isoetid Littorella uniflora, affected the growth (and thereby the potential invasion success) of the elodeid Myriophyllum alterniflorum. For this purpose, the growth of M. alterniflorum was determined at a combination of three concentrations of dissolved CO₂ (15, 90, 200 μmol L^?1) and three densities of L. uniflora (0, 553, 1775 plants m^?2). 3. At an ambient CO₂ of 15 μmol L^?1, M. alterniflorum could not sustain itself, whereas at raised CO₂ concentrations, growth became positive and increased with higher CO₂ availability. 4. The presence of L. uniflora, independent of its density, reduced the growth of M. alterniflorum by 50%. Whether this is related to nutrient availability or other factors is not clear. 5. Despite the growth reduction of M. alterniflorum by L. uniflora, at CO₂ ≥90 μmol L^?1, L. uniflora was still overgrown by M. alterniflorum. This may imply that, in field situations, M. alterniflorum can invade softwater systems with relatively high CO₂ availability, even in the presence of dense stands of L. uniflora.     

High resistance of oligotrophic isoetid plants to oxic and anoxic dark exposure

相似文献   

Influence of sediment organic enrichment and water alkalinity on growth of aquatic isoetid and elodeid plants

1. Lake eutrophication has increased phytoplankton blooms and sediment organic matter. Among higher plants, small, oligotrophic rosette species (isoetids) have disappeared, while a few tall, eutrophic species (elodeids) may have persisted. Despite recent reduction of nutrient loading in restored lakes, the vegetation has rarely regained its former composition and coverage. Patterns of recovery may depend on local alkalinity because HCO₃^? stimulates photosynthesis of elodeids and not of isoetids. In laboratory growth experiments with two isoetids (Lobelia dortmanna and Littorella uniflora) and two elodeids (Potamogeton crispus and P. perfoliatus), we test whether organic enrichment of lake sediments has a long‐lasting influence by: (i) reducing plant growth because of oxygen stress on plant roots and (ii) inhibiting growth more for isoetids than elodeids. We also test whether (iii) increasing alkalinity (from 0.17 to 3.20 meq. L^?1) enhances growth and reduces inhibition of organic sediment enrichment for elodeids but not for isoetids. 2. In low organic sediments, higher oxygen release from roots of isoetids than elodeids generated oxic conditions to greater sediment depth for Lobelia (4.3 cm) and Littorella (3.0 cm) than for Potamogeton species (1.6–2.2 cm). Sediment oxygen penetration depth fell rapidly to 0.4–1.0 cm for all four species at even modest organic enrichment and oxygen consumption in the sediments. Roots became shorter and isoetid roots became thicker to better supply oxygen to apical meristems. 3. Growth of elodeids was strongly inhibited across all levels of organic enrichment of sediments being eight‐fold lower at the highest enrichment compared to the unenriched control. Leaf biomass of isoetids increased three‐fold by moderate organic enrichment presumably because of greater CO₂ supply from sediments being their main CO₂ source. At higher organic enrichment, isoetid biomass was reduced, leaf chlorophyll declined up to 10‐fold, root length declined from 7 to <2 cm and mortality rose (up to 50%) signalling high plant stress. 4. Lobelia was not affected by HCO₃^? addition in accordance with its use of sediment CO₂. Biomass of elodeids increased severalfold by rising alkalinity from 0.17 to 3.20 meq. L^?1 in accordance with their use of HCO₃^? for photosynthesis, while the negative impact of organically enriched sediments remained. 5. Overall, root development of all four species was so strongly restricted in sediments enriched with labile organic matter that plants if growing in situ may lose root anchorage. Other experiments demonstrate that this risk is enhanced by greater water content and reduced consolidation in organically rich sediments. Therefore, formation of more muddy and oxygen‐demanding sediments during eutrophication will impede plant recovery in restored lakes while high local alkalinity will help elodeid recovery.     

Could rising aquatic carbon dioxide concentrations favour the invasion of elodeids in isoetid‐dominated softwater lakes?

1. During the past century, isoetid vegetation types in softwater lakes have often been invaded by faster‐growing elodeids. In these C‐limited systems, this may be related to rising aquatic CO₂ levels. 2. In a laboratory experiment we tested the growth response of two elodeid species, Myriophyllum alterniflorum and Callitriche hamulata, at four different CO₂ levels, ranging from 20 to 230 μmol L⁻¹. In addition, we tested the effect of the nutrient status of the sediment on the growth of C. hamulata at the different CO₂ levels. 3. Shoot and root growth increased with rising CO₂ availability. Irrespective of sediment type, growth was minimal to negative at the lowest CO₂ treatment level, while becoming positive at CO₂ levels around 40–50 μmol L⁻¹. Substantial growth was only obtained when the macrophytes were growing on mesotrophic sediments. The plants reached close to maximal growth at CO₂ levels of c. 100 μmol L⁻¹. 4. Within this experiment, the growth of C. hamulata at CO₂ levels above 90 μmol L⁻¹ may have been limited by N and P availability in both sediment types. The growth rate of M. alterniflorum did not seem to be limited by N and P availability, most likely due to its much higher relative root production. 5. The experimental results show that neither M. alterniflorum nor C. hamulata is able to invade isoetid‐dominated softwater lakes at very low aquatic CO₂ concentrations. However, if the sediments contain enough nutrients, a rise in aquatic CO₂ could allow the invasion of elodeid species leading to the subsequent disappearance of slow‐growing isoetids.     

Massive uprooting of Littorella uniflora (L.) Asch. during a storm event and its relation to sediment and plant characteristics

During spring storms massive uprooting of Littorella uniflora occurred in a shallow Dutch softwater lake. The aim of this study was to test whether changes in plant morphology and sediment characteristics could explain the observed phenomenon. Uprooting was expected to occur in plants having a high shoot biomass and low root to shoot ratio (R:S), growing on sediments with a high organic matter content. Normally, uprooting of the relative buoyant L. uniflora is prevented by an extensive root system, expressed as a high R:S. This was studied by sampling floating and still rooted L. uniflora plants, as well as sediment and sediment pore water, along a gradient of increasing sediment organic matter content. Increasing organic matter content was related to increasing L. uniflora shoot biomass and consequently decreasing R:S. Furthermore, the results indicated that uprooting indeed occurred in plants growing on very organic sediments and was related to a low R:S. The increased shoot biomass on more organic sediments could be related to increased sediment pore water total inorganic carbon (TIC; mainly CO₂) availability. Additionally, increased phosphorus availability could also have played a role. The disappearance of L. uniflora might lead to higher nutrient availability in the sediments. It is suggested that this could eventually promote the expansion of faster‐growing macrophytes.     

Rapid oxygen exchange across the leaves of Littorella uniflora provides tolerance to sediment anoxia

1. Littorella uniflora and Lobelia dortmanna are prominent small rosette species in nutrient‐poor, soft‐water lakes because of efficient root exchange of CO₂ and O₂. We hypothesise that higher gas exchange across the leaves of L. uniflora than of L. dortmanna ensures O₂ uptake from water and underlies its greater tolerance to sediment anoxia following organic enrichment. 2. We studied plant response to varying sediment O₂ demand and biogeochemistry by measuring photosynthesis, gas exchange across leaves and O₂ dynamics in plants during long‐term laboratory and field studies. Frequent non‐destructive sampling of sediment pore water was used to track changes in sediment biogeochemistry. 3. Addition of organic matter triggered O₂ depletion and accumulation of , Fe²⁺ and CO₂ in sediments. Gas exchange across leaf surfaces was 13–16 times higher for L. uniflora than for L. dortmanna. Oxygen in the leaf lacunae of L. uniflora remained above 10 kPa late at night on anoxic sediments despite organic enrichment. Leaf content of N and P of L. uniflora remained sufficient to keep up photosynthesis despite prolonged sediment anoxia, whereas nutrient content was too low for long‐term survival of L. dortmanna. 4. High gas exchange across L. uniflora leaves improves its performance and survival on anoxic sediments compared with L. dortmanna. Lobelia dortmanna uses the same gas‐tight leaves in air and water, which makes it highly susceptible to sediment anoxia but more cost‐effective in ultra‐oligotrophic environments because of slow leaf turnover.     

The effects of species immigrations and changing conditions on isoetid communities

Historical data from the 1930s were compared with new data gathered during the 2000s to evaluate the effects of increased numbers of larger stature submersed species (both elodeids and characeans) on resident isoetid communities. The cover and species richness of submersed species were assessed in 23 seepage lakes in northwestern Wisconsin, USA, using randomly located 1 m × 1 m plots. Water clarity, conductivity and residential land use were determined on a whole-lake basis and the sediment type and water depth were recorded at each plot. The probability of elodeids or characeans occurring in isoetid plots increased with the number of elodeids and characeans gained by a lake since the 1930s, with additions ranging from two to 15 species per lake. However, not all species were equally likely to co-occur with isoetids. Six elodeid species (Najas flexilis, Najas gracillima, Potamogeton gramineus, Potamogeton pusillus, Potamogeton spirillus and Vallisneria americana) along with Chara spp. were the most frequent isoetid associates, while other species that were common in the lakes, such as Elodea canadensis and Potamogeton robbinsii, were less frequent in isoetid plots. The lake-wide proportion of isoetid plots colonized by elodeids or characeans ranged from 5% to 100%, with increasing conductivity and total elodeids (plus Chara spp. and Nitella spp.) the strongest predictors of this colonization. Approximately half (49.6%) of all isoetid plots sampled had elodeids or characeans present (39.2% elodeids, 7.4% elodeids and characeans, 3.0% characeans), and isoetid cover and species richness were lower when these larger stature species were present. The risks this colonization poses for the long-term viability of isoetid species appeared to depend on multiple factors, including whole-lake characteristics, opportunities for refuge, and connections among regional isoetid populations. There was evidence of a time lag between the introduction of elodeid or characean species to a lake and invasion of isoetid plots within the lake, a process that deserves further study.     

Chemical Profiling of the Essential Oils of Syzygium aqueum,Syzygium samarangense and Eugenia uniflora and Their Discrimination Using Chemometric Analysis

The essential oil compositions of the leaves of three related Myrtaceae species, namely Syzygium aqueum, Syzygium samarangense and Eugenia uniflora, were investigated using GLC/MS and GLC/FID. Altogether, 125 compounds were identified: α‐Selinene (13.85%), β‐caryophyllene (12.72%) and β‐selinene constitute the most abundant constituents in S. aqueum. Germacrene D (21.62%) represents the major compound in S. samarangense whereas in E. uniflora, spathulenol (15.80%) represents the predominant component. Multivariate chemometric analyses were used to discriminate the essential oils using hierarchical cluster analysis (HCA) and principal component analysis (PCA) based on the chromatographic results. The antimicrobial activity of the popularly used E. uniflora essential oil was assessed using broth microdilution method against six Gram‐positive, three Gram‐negative bacteria and two fungi. The oil showed moderate antimicrobial activity against Bacillus licheniformis exhibiting MIC and MMC of 0.63 mg/ml. The cytotoxic activity of E. uniflora essential oil was investigated against Trypanosoma brucei brucei (T. b. brucei) and MCF‐7 cancer cell line using MTT assay. It showed moderate activity against MCF‐7 cells with an IC₅₀ value of 76.40 μg/ml. On the other hand, T. brucei was highly susceptible to E. uniflora essential oil with IC₅₀ of 11.20 μg/ml, and a selectivity index of 6.82.     

Impact of acidification and eutrophication on macrophyte communities in soft waters. II. Experimental studies

In The Netherlands, there has been a dramatic decline during the last 30 years in the number of stands belonging to the phytosociological alliance Littorellion. Generally, the communities classified within this alliance occur in poorly buffered, oligotrophic waters, with very low phosphate, nitrogen and carbon dioxide levels in the water layer and considerably higher nutrient levels in the sediment. The plant species dominating these communities are isoetids such as Litoorella uniflora (L.) Aschers., Lobelia dortmanna L. and Isoetes lacustris L., which show various adaptations to make successful growth possible under these conditions.Field observations showed that the water where Littorella uniflora had disappeared or strongly decreased could be divided into two groups. A major group (77%) was characterized by the presence of submerged Juncus bulbosus L. and/or Sphagnum species. These water appeared to be strongly acidified (pH < 4.5) and had increased nitrogen levels with ammonium as the dominant N-source. Within this group, the waters with luxuriant growth of Juncus bulbosus and/or Sphagnum spp. had strongly increased carbon dioxide levels in both sediment and water.Different types of experiments proved causal relationships between the observed changes in macrophytes and the changed physico-chemical parameters. Ecophysiological experiments showed that Juncus bulbosus lacks the typical adaptations of the isoetid plant species, i.e. it uses very low amounts of sediment-CO₂ and releases only a little oxygen from the roots. However, Juncus bulbosus is more able than Littorella uniflora to use CO₂ from the water layer. From the nutrient-uptake experiments, the decreased nitrate and increased ammonium levels seem to be favourable to Juncus bulbosus. The culture experiments clearly demonstrated that the biomass of Juncus bulbosus only increased strongly when the sediment was poorly buffered and the pH of water was low. When combining factors like CO₂ enrichment of the sediment, with and without phosphate, and/or ammonium enrichment of the water in the culture experiments, it is clearly shown that phosphate and/or ammonium enrichment without CO₂ enrichment do not lead to an increase in biomass of Juncus bulbosus. Therefore, it is obvious that the changes in the macrophyte community can be ascribed primarily to changes in the carbon budget as a result of acidification.A minor group of waters (23%) was characterized by the absence of submerged Juncus bulbosus and/or Sphagnum spp. In most of these waters, submerged plant species occurred, such as Myriophyllum alterniflorum DC or non-rooted species such as Riccia fluitans L. These waters were not acidified, and generally had an increased alkalinity and higher nitrogen and phosphate levels of sediment and/or water. Culture experiments showed that phosphate enrichment of the sediment alone leads to luxuriant growth of submerged macrophyte species such as Myriophyllum alterniflorum, whereas phosphate enrichment of both sediment and water leads to mass development of non-rooted plant species such as Riccia fluitans.     

Effects of arbuscular mycorrhizae on biomass and nutrients in the aquatic plant Littorella uniflora

1. It has been hypothesised that the symbiosis with arbuscular mycorrhizal fungi (AMF) leads to a higher uptake of phosphorus (P) and nitrogen (N) in aquatic plants, but it has never been shown experimentally without the use of fungicides. In particular, the symbiosis may be important for nutrient uptake by isoetids in oligotrophic lakes, where low concentrations of inorganic N and P both in the water and in the sediment limit the growth of plants and where symbiosis facilitates the uptake of nutrients from the sediment. 2. Plants of the isoetid Littorella uniflora were propagated under the sterile conditions without an AMF infection. The plants were then grown for 60 days with and without re‐infection by AMF, and with either high (150 μm ) or low (ambient concentration approximately 15 μm ) CO₂ concentration. 3. The study proved that the symbiosis between AMF and L. uniflora had a positive impact on the retention of N and P in the plants at very low nutrient concentrations in the water and on biomass development. Shoot biomass and standing stocks of both P and N were significantly higher in re‐infected plants. 4. Raised CO₂ concentration resulted in a fivefold increase in hyphal infection, but had no impact on the number of arbuscules and vesicles in the cross sections. There were significantly higher biomass and lower tissue P and N concentrations in the plants from high CO₂ treatments. This resulted in similar standing stocks of P and N in plants from low and high CO₂ treatments. 5. The results from this study showed that the symbiosis between AMF and L. uniflora is an important adaptation enabling isoetids to grow on nutrient‐poor sediments in oligotrophic lakes.     

A model on the competition between two macrophyte species in acidifying shallow soft-water lakes in the Netherlands

To predict changes in vegetation as a result of acidification in shallow Dutch lakes a mathematical model was formulated which describes the growth ofLittorella uniflora andJuncus bulbosus, species characteristic for non-acidified and acidified situations, respectively. The two species compete for light, CO₂ and nutrients. The model integrates current knowledge about the ecophysiology of the species. The results generated by the model are similair to field data concerning dominance of the species in different habitats.L. uniflora is able to grow well under environmental conditions associated with acidification, as long as it is not outcompeted byJ. bulbosus. The competitive advantage of morphological adaptions of the macrophyte species are discussed in relation to the model results.     

Submarine Groundwater Discharge as a nitrogen source to the Ria Formosa studied with seepage meters

Submarine Groundwater Discharge (SGD) has been frequently ignored as a nutrient source to marine ecosystems because it is difficult to identify and quantify. However, recent studies show its ubiquity and ecological importance to the coastal zone, particularly when associated with contaminated continental aquifers. The Ria Formosa is a coastal lagoon located in the south of Portugal and surrounded by an intensely farmed area. Following a 12-month field study using seepage meters, we identified groundwater discharge in the intertidal zone of the lagoon. The seeping fluid was a mixture of two water types: one with low salinity and high nitrate concentration and another similar to local seawater. Based on the integration of monthly seepage rate measurements throughout the year, we estimate the mean discharge of submarine groundwater into the lagoon to be 3.6 m³ day⁻¹ per linear meter of coastline with freshwater contributions (per volume) ranging from 10% to 50%. The results of this study suggest a continental origin for the freshwater component, thus linking the biogeochemical cycles in the lagoon to anthropogenic activities taking place in the neighboring coastal plain. We further identify SGD as an important nutrient source to the Ria Formosa, estimating annual loads of 36.2 mol (0.507 kg) of Nitrogen, 1.1 mol (0.034 kg) of Phosphorus and 18.6 mol (0.522 kg) of Silicon per meter of coastline. Based on these results, we suggest that SGD is a potential contributor to the observed nutrification status of the Ria Formosa lagoon. All the authors were previously in Biogeochemistry Research Group, CIMA/IMAR (Centro de Investigacao Marinha e Ambiental/Instituto do Mar), Campus de Gambelas, 8000, Faro.     

Putative local adaptations modulate the interactions of the carnivorous plant Drosera uniflora Willd (1809) (Droseraceae) with cushion and shrub nurse plants

Cushion and shrub plants are typical high mountain nurse plants. In Magellanic tundras of the Cordillera del Sarao on the coast of Chile, the carnivorous plant Drosera uniflora grows in association with cushions of Donatia fascicularis and the shrubs Chusquea montana var. nigricans and Lepidothamnus fonkii. The different microhabitats for recruitment, in addition to the limited gene flow of D. uniflora, enable us to hypothesise that this plant manifests putative local adaptations, expressed in seed germination and population abundance. Our aim was to evaluate the local adaptation of D. uniflora to cushion and shrub microhabitats by estimating germination and abundance. Local adaptation of seed germination was determined by means of reciprocal transplant experiments. Abundance was determined in small plots located inside, on the edge and outside the nurse plants. Seed origin and growth substrate play a decisive role in D. uniflora germination. Seeds that originate from cushions plant habitat and germinate in the same substrate do so in greater numbers than when those which originate from shrubby habitats. Conversely, seeds that originate from shrubby habitat and germinate in the same substrate do not exhibit significant differences. Abundance was always greater inside than outside of the nurse plants. We concluded that availability and quality of different microhabitats for seed germination and recruitment, together with a limited gene flow, would trigger putative local adaptations in D. uniflora, modulating a long history of interactions with the plants that act as nurse plants.     

Influence of quantity and lability of sediment organic matter on the biomass of two isoetids,Littorella uniflora and Echinodorus repens

1. Despite real improvement in the water quality of many previously eutrophic lakes, the recovery of submerged vegetation has been poor. This lack of recovery is possibly caused by the accumulation of organic matter on the top layer of the sediment, which is produced under eutrophic conditions. Hence, our objective was to study the combined effects of quantity and lability of sediment organic matter on the biomass of Echinodorus repens and Littorella uniflora and on the force required to uproot plants of L. uniflora. 2. Lake sediments, rich in organic matter, were collected from four lakes, two with healthy populations of isoetids and two from which isoetids had disappeared. The four lake sediments were mixed with sand to prepare a range of experimental sediments that differed in quantity and lability of sediment organic matter. Two isoetid species, E. repens and L. uniflora, were grown in these sediments for 8 weeks. Sediment quality parameters, including elemental composition, nutrient availability and mineralisation rates, were determined on the raw sources of sediment from the lakes. Porewater and surface water were analysed for the chemical composition in all mixtures. At the end of the experiment, plants were harvested and their biomass, tissue nutrient concentration and (for L. uniflora) uprooting force were measured. 3. For both species, all plants survived and showed no signs of stress on all types of sediment. The biomass of E. repens increased as the fraction of organic matter was increased (from 6 to 39% of organic content, depending upon sediment type). However, in some of the sediment types, a higher fraction of organic matter led to a decline in biomass. The biomass of L. uniflora was less responsive to organic content and was decreased significantly only when the least labile sediment source was used to create the gradient of organic matter. The increase in shoot biomass for both species was closely related to higher CO₂ concentrations in the porewater of the sediment. The force required to uproot L. uniflora plants over a range of sediment organic matter fitted a Gaussian model; it reached a maximum at around 15% organic matter and declined significantly above that. 4. Increasing organic matter content of the sediment increased the biomass of isoetid plants, as the positive effects of higher CO₂ production outweighed the negative effects of low oxygen concentration in more (labile) organic sediments. However, sediment organic matter can adversely affect isoetid survival by promoting the uprooting of plants.     

Nutrient concentrations in a Littorella uniflora community at higher CO2 concentrations and reduced light intensities

1. Oligotrophic softwater lakes represent a special type of aquatic ecosystem with unique plant communities where generalisations from other aquatic plant communities to rising CO₂ in the water column may not apply. 2. In the present study, we set up large in situ mesocosms and supporting laboratory experiments with isoetid vegetation (Littorella uniflora) where water column CO₂ and light could be manipulated in order to test whether (i) light and CO₂ availability affect nutrient concentrations in isoetid vegetation, and (ii) if changes in light and CO₂ climate affect fluxes of inorganic nitrogen (N) and phosphorus (P) from sediment to water column, which potentially could result in increased growth of epiphytic algae. 3. The results showed that the standing stocks of phosphorus and nitrogen in the L. uniflora vegetation were significantly influenced by CO₂ concentration and light intensity. Both standing stocks of P and N were significantly higher in the mesocosm treatments with high CO₂ concentration than in those at low CO₂ concentration. Similarly, standing stocks of P and N enhanced with increasing light intensity. 4. Measurements of nutrient fluxes both in the field and the laboratory did not show any significant release of nutrients to the water column from plants or sediments at any of the light or CO₂ treatments. However, mats of epiphytic algae developed from the beginning of June to late September and caused a light reduction for the isoetid vegetation. 5. Increasing CO₂ concentrations in the water column may over time potentially result in a change in soft water plant communities.     

Water‐level fluctuations affect sediment properties,carbon flux and growth of the isoetid Littorella uniflora in oligotrophic lakes

相似文献   

Differential responses of <Emphasis Type="Italic">Myriophyllum alterniflorum</Emphasis> DC (Haloragaceae) organs to copper: physiological and developmental approaches

Copper is an essential element for the function of metabolic pathways in many living organisms like photosynthesis in plants. But, for the last decades, anthropogenic sources and release of Cu lead to environmental pollution particularly in aquatic ecosystems. The aquatic plant, Myriophyllum alterniflorum, known as a bioindicator of metal pollution, could be used as biomonitor. The aim of this study is to evaluate biomarkers responses of watermilfoil during Cu pollution at high environmental levels (100 μg l⁻¹ CuSO₄) in controlled conditions. Morphological and anatomical features like a new double endodermis (DE) layer were evidenced in response to Cu treatment. Moreover, physiological parameters like pigments contents, osmotic potential and proline content present a differential response to Cu stress in young and old leaves of watermilfoil. Finally, despite a rapid and strong phytoaccumulation of Cu, only young leaves are slightly affected in their cell membrane integrity as indicated by MDA content. In comparison with the Cu effect on other aquatic macrophytes, M. alterniflorum develops particular protection mechanisms like the ROS scavenging using proline rather than carotenoids, the reduction of water loss with the DE and the heavy metal elimination through senescence to protect preferentially the photosynthetic components of the young leaves and the main-stem elongation. Due to its Cu sensitivity, M. alterniflorum appears as important in the field of environmental studies using plant biomarkers.     

Fluctuated water depth with high nutrient concentrations promote the invasiveness of Wedelia trilobata in Wetland

The distribution of invasive and native species in wetlands is determined by hydrological conditions; whereas conditions such as water depth fluctuations, variations in the nutrient concentrations are expected to affect the growth and physiological traits of plants. For the assessment of such effects, we conduct greenhouse experiment with three factors; 1) water depth of 5 cm and 15 cm (static and fluctuated); 2) three levels of nutrient concentrations (i) full‐strength Hoagland solution (N1), (ii) ¼‐strength Hoagland solution (N2), and (iii) ¹/₈‐strength Hoagland solution (N3); and 3) species, invasive Wedelia trilobata (L.) and its congener, native Wedelia chinensis (Osbeck.) under mono and mixed culture. Water depth of 5 cm combined with any of the nutrient treatments significantly restrained the photosynthesis, intracellular CO₂ concentration and leaf chlorophyll of both W. trilobata and W. chinensis. Increase in the water depth to 15 cm with low‐nutrient treatment N3 did not sustain the physiological traits of W. chinensis under mono and mixed planting. A great loss was noted in the growth of W. chinensis at 15 cm static and fluctuated water depth with low‐nutrient treatment (N3) and under mixed culture. In addition, water depth fluctuations with both low‐ and high‐nutrient treatments significantly affected the root‐shoot ratio, relative growth rate, and interspecific interaction among these two species. W. trilobata benefited more from competitive interaction index (CII) under fluctuated water depth at 15 cm with high nutrients, and the value of CII was clearly positive. Therefore, higher competitive ability may contribute to the invasiveness of W. trilobata in wetlands.     

Phylogeography and ecological niche modelling in Eugenia uniflora (Myrtaceae) suggest distinct vegetational responses to climate change between the southern and the northern Atlantic Forest

In this study, we evaluate phylogeographic patterns and predictions of ecological niche modelling (ENM) for Eugenia uniflora (Myrtaceae), a widely distributed taxon in the Atlantic forest domain, to understand the effect of past climatic oscillations on the demographic history of this species. An analysis of phylogeographic population structure and demography was conducted on E. uniflora from 46 localities in natural environments across the distribution range of the species based on three plastid markers. ENM was also performed to predict suitable environments and areas of dramatic decrease in future suitability for the species under distinct representative concentration pathways (RCPs). Eugenia uniflora exhibited higher haplotype and nucleotide diversity in the southern part of its distribution than in the northern part. Two divergent lineages were revealed in the phylogenetic analysis of haplotypes, with an estimated divergence at c. 4.9 Mya. The populations in the northern and central regions of the range probably experienced population growth, whereas populations in the southern region are marked by historical demographic stability. ENM results indicate that the distribution of E. uniflora was fragmented in cool periods and was broader and more connected during warm periods during Pleistocene. The results suggest distinct evolutionary histories in southern to northern populations, indicating region‐specific responses to changes.     

Groundwater input affecting plant distribution by controlling ammonium and iron availability

Question: How does groundwater input affect plant distribution in Alnus glutinosa (black alder) carrs? Location: Alder carrs along the river Meuse, SE Netherlands. Methods: Three types of site, characterized by groundwater flow, were sampled in 17 A. glutinosa carrs. Vegetation and abiotic data (soil and water chemistry) were collected and analysed using a Canonical Correspondence Analysis. Based on the results, a laboratory experiment tested the effect of groundwater input (Ca²⁺) on pore water chemistry (NH₄⁺ availability). Results: Environmental factors indicating groundwater input (Ca²⁺ and Fe²⁺), correlating with the NH⁺₄ concentration in the pore water, best explained the variation in plant distribution. NH₄⁺ availability was determined by Ca²⁺ input via the groundwater and subsequent competition for exchange sites in the sediment. As a result, nutrient‐poor seepage locations fully fed by groundwater were dominated by small iron resistant plants such as Caltha palustris and Equisetum fluviatile. More nutrient‐rich locations, fed by a combination of groundwater and surface water, allowed the growth of taller iron resistant plant species such as Carex paniculata. Nutrient‐rich locations with stagnating surface water were hardly fed by groundwater, allowing the occurrence of fast growing and less iron tolerant wetland grasses such as Glyceria fluitans and G. maxima. Conclusion: Groundwater input affects plant composition in A. glutinosa carrs along the river Meuse by determining nutrient availability (ammonium) and concentrations of toxic iron.