Environmental restoration effects of Ranunculus sceleratus L. in a eutrophic sewage system

This study investigated the environmental restoration effects of Ranunculus sceleratus in a sewage system microcosm trial, including the removal of pollutants and algal inhibition. We compared the removal of pollutants by R. sceleratus in a eutrophic sewage system in the presence and the absence of algae. The rate of removal without algae was 16.2–20.5% of that with algae. ${\text{NH}}_4^{+}–\text{N}$ was removed most readily by R. sceleratus. The effects of R. sceleratus on the growth of Microcystis aeruginosa were also investigated in two allelopathic modes. The level of algal inhibition after the addition of an extract of Ranunculus scleratus was 57.1–78.9% greater than that in a co-culture test. To understand the role of allelopathy interference with algal development, we also determined the total flavonoid contents of plants, which ranged from 3.57 g to 20.19 g per plant. The cell density of Microcystis aeruginosa was negatively correlated with the total flavonoids in R. sceleratus, although aquatic macrophytes may contain other allelochemicals involved with algal inhibition in addition to flavonoid compounds. The environmental effects of R. sceleratus were significantly correlated with its growth stage (or water retention time), plant height, and biomass. This study suggests that R. sceleratus has potential for the low-effort and sustainable management of freshwaters, particularly the removal of nutrient pollutants and the reduction of excessive algal growth, which may be attributable to allelochemicals such as flavonoids. The in situ environmental restoration effects of R. sceleratus require further investigation at the ecosystem level.     

不同生境下空心莲子草响应模拟昆虫采食的生长和化学防御策略

外来植物往往可以入侵多种生境并受到多种昆虫的采食,而不同生境条件将可能会影响这些入侵植物对昆虫采食的防御策略。以入侵我国的克隆植物——空心莲子草为研究对象,分别选择生长在水生生境、水陆两栖生境和陆生生境中的无性个体(分株),通过50%去叶处理模拟昆虫采食,分析不同生境下空心莲子草对模拟昆虫采食处理的生长及化学防御响应的差异。模拟昆虫采食处理显著抑制了陆生生境、水陆两栖生境以及水生生境下空心莲子草的根、茎、叶和总生物量,但对3种生境下空心莲子草的生物量分配(根冠比、根生物量分配、茎生物量分配和叶生物量分配)均无显著影响。陆生生境下空心莲子草根、茎和总生物量显著高于水陆两栖生境和水生生境,根冠比显著低于水陆两栖生境和水生生境。模拟昆虫采食处理显著降低了空心莲子草的木质素含量,而对单宁和总酚含量影响不显著。生境对木质素含量无显著影响,但陆生生境下空心莲子草单宁含量显著高于水陆两栖生境和水生生境,且总酚含量显著高于水陆两栖生境,表明陆生生境中空心莲子草具有更强的防御能力。空心莲子草木质素含量与总生物量无显著相关性,但在模拟采食情况下,其总酚含量与总生物量呈显著负相关,而无论模拟昆虫采食处理存在与否,空心莲子草单宁含量与总生物量均呈显著正相关。因此,空心莲子草存在昆虫介导的生长和化学防御之间的权衡,在昆虫采食的情况下可通过减少生长来增加对化学防御物质的投入,但生境对空心莲子草这种生长-防御权衡的影响十分有限。     

Effects of simulated herbivory and resource availability on the invasive plant, Alternanthera philoxeroides in different habitats

In biological control programs, the insect natural enemy’s ability to suppress the plant invader may be affected by abiotic factors, such as resource availability, that can influence plant growth and reproduction. Understanding plant tolerance to herbivory under different environmental conditions will help to improve biocontrol efficacy. The invasive alligator weed (Alternanthera philoxeroides) has been successfully controlled by natural enemies in many aquatic habitats but not in terrestrial environments worldwide. This study examined the effects of different levels of simulated leaf herbivory on the growth of alligator weed at two levels of fertilization and three levels of soil moisture (aquatic, semi-aquatic, and terrestrial habitats). Increasing levels of simulated (manual) defoliation generally caused decreases in total biomass in all habitats. However, the plant appeared to respond differently to high levels of herbivory in the three habitats. Terrestrial plants showed the highest below–above ground mass ratio (R/S), indicating the plant is more tolerant to herbivory in terrestrial habitats than in aquatic habitats. The unfertilized treatment exhibited greater tolerance than the fertilized treatment in the terrestrial habitat at the first stage of this experiment (day 15), but fertilizer appears not to have influenced tolerance at the middle and last stages of the experiment. No such difference was found in semi-aquatic and aquatic habitats. These findings suggest that plant tolerance is affected by habitats and soil nutrients and this relationship could influence the biological control outcome. Plant compensatory response to herbivory under different environmental conditions should, therefore, be carefully considered when planning to use biological control in management programs against invasive plants.     

Feeding biomechanics in Acanthostega and across the fish–tetrapod transition

Acanthostega is one of the earliest and most primitive limbed vertebrates. Its numerous fish-like features indicate a primarily aquatic lifestyle, yet cranial suture morphology suggests that its skull is more similar to those of terrestrial taxa. Here, we apply geometric morphometrics and two-dimensional finite-element analysis to the lower jaws of Acanthostega and 22 other tetrapodomorph taxa in order to quantify morphological and functional changes across the fish–tetrapod transition. The jaw of Acanthostega is similar to that of certain tetrapodomorph fish and transitional Devonian taxa both morphologically (as indicated by its proximity to those taxa in morphospace) and functionally (as indicated by the distribution of stress values and relative magnitude of bite force). Our results suggest a slow tempo of morphological and biomechanical changes in the transition from Devonian tetrapod jaws to aquatic/semi-aquatic Carboniferous tetrapod jaws. We conclude that Acanthostega retained a primitively aquatic lifestyle and did not possess cranial adaptations for terrestrial feeding.     

Marine invasions by non-sea snakes, with thoughts on terrestrial-aquatic-marine transitions

Few species of snakes show extensive adaptations to aquatic environments and even fewer exploit the oceans. A survey of morphology, lifestyles, and habitats of 2552 alethenophidian snakes revealed 362 (14%) that use aquatic environments, are semi-aquatic, or aquatic; about 70 (2.7%) of these are sea snakes (Hydrophiinae and Laticaudinae). The ancient and aquatic family Acrochordidae contains three extant species, all of which have populations inhabiting brackish or marine environments, as well as freshwater. The Homalopsidae have the most ecologically diverse representatives in coastal habitats. Other families containing species exploiting saline waters with populations in freshwater environments include: the Dipsadidae of the western hemisphere, the cosmopolitan Natricidae, the African Grayinae, and probably a few Colubridae. Species with aquatic and semi-aquatic lifestyles are compared with more terrestrial (fossorial, cryptozoic, and arboreal) species for morphological traits and life histories that are convergent with those found in sea snakes; this may provide clues to the evolution of marine snakes and increase our understanding of snake diversity.     

Comparison of Aerial and Submerged Leaves in Two Amphibious Species,Myosotis scorpioides and Ranunculus trichophyllus

Both amphibious species, Myosotis scorpioides and Ranunculus trichophyllus, thrive in a stressful environment (alternated flooding and drying), which is variable regarding water and radiation regimes. Plants from the field and plants grown under controlled water table maintained at 40 cm were analysed for content of chlorophyll (Chl) and UV-B screening compounds, and the efficiencies of PS2 and electron transport systems. We detected no significant differences in contents of Chl and UV-B screening compounds between submerged and aerial leaves. The measurements of respiratory potential and photochemical efficiency revealed the presence of permanent stress in M. sporpioides in the natural environment. Differences in physiological responses of submerged and aerial leaves indicated that the terrestrial environment was more favourable for M. scorpioides than for R. trichophyllus. Characteristics of both species suggested that R. trichophyllus might be a phylogenetically older aquatic plant than M. scorpioides.     

Which adaptations of some invasive Ludwigia spp. (Rosidae,Onagraceae) populations occur in contrasting hydrological conditions in Western France?

Biological invasions in wetlands by Water Primroses (Ludwigia grandiflora ssp. hexapetala and L. peploides ssp. montevidensis) are an increasing problem especially in wet meadows. The aim of this paper is to quantify differences between species and the adaptation of these amphibious plants in order to establish the consequences for site managers. The hypotheses were: (i) that these species differ in biomass and morphology, and (ii) that terrestrial habitats determine particular adaptations such as reduced biomass, more roots and a bushy form. Biomasses from five sites were collected, following seasonal changes and biological traits were measured on selected plants. Comparing species in aquatic habitats, L. peploides produced less biomass than L. grandiflora. Comparing habitats for L. grandiflora, the biomass in meadows was almost twice that in dykes, particularly due to old stems, the converse of the hypothesis. Terrestrial forms were characterized by a bushy morphology, with shorter internodes and stems, as well as more secondary ramifications, while in aquatic habitats the plant architecture was simpler. Models were built linking morphology to species, sites and water conditions. Adaptations to terrestrial habitats of a particularly resistant form with a significant potential biomass are practical constraints for farmers and managers.     

Nutrient availability and nutrient use efficiency in plants growing in the transition zone between land and water

The transition zone between terrestrial and freshwater habitats is highly dynamic, with large variability in environmental characteristics. Here, we investigate how these characteristics influence the nutritional status and performance of plant life forms inhabiting this zone. Specifically, we hypothesised that: (i) tissue nutrient content differs among submerged, amphibious and terrestrial species, with higher content in submerged species; and (ii) PNUE gradually increases from submerged over amphibious to terrestrial species, reflecting differences in the availability of N and P relative to inorganic C across the land–water ecotone. We found that tissue nutrient content was generally higher in submerged species and C:N and C:P ratios indicated that content was limiting for growth for ca. 20% of plant individuals, particularly those belonging to amphibious and terrestrial species groups. As predicted, the PNUE increased from submerged over amphibious to terrestrial species. We suggest that this pattern reflects that amphibious and terrestrial species allocate proportionally more nutrients into processes of importance for photosynthesis at saturating CO₂ availability, i.e. enzymes involved in substrate regeneration, compared to submerged species that are acclimated to lower availability of CO₂ in the aquatic environment. Our results indicate that enhanced nutrient loading may affect relative abundance of the three species groups in the land–water ecotone of stream ecosystems. Thus, species of amphibious and terrestrial species groups are likely to benefit more from enhanced nutrient availability in terms of faster growth compared to aquatic species, and that this can be detrimental to aquatic species growing in the land–water ecotone, e.g. Ranunculus and Callitriche.     

Assessing the role of large herbivores in the structuring and functioning of freshwater and marine angiosperm ecosystems

While large herbivores can have strong impacts on terrestrial ecosystems, much less is known of their role in aquatic systems. We reviewed the literature to determine: 1) which large herbivores (> 10 kg) have a (semi‐)aquatic lifestyle and are important consumers of submerged vascular plants, 2) their impact on submerged plant abundance and species composition, and 3) their ecosystem functions. We grouped herbivores according to diet, habitat selection and movement ecology: 1) Fully aquatic species, either resident or migratory (manatees, dugongs, turtles), 2) Semi‐aquatic species that live both in water and on land, either resident or migratory (swans), 3) Resident semi‐aquatic species that live in water and forage mainly on land (hippopotamuses, beavers, capybara), 4) Resident terrestrial species with relatively large home ranges that frequent aquatic habitats (cervids, water buffalo, lowland tapir). Fully aquatic species and swans have the strongest impact on submerged plant abundance and species composition. They may maintain grazing lawns. Because they sometimes target belowground parts, their activity can result in local collapse of plant beds. Semi‐aquatic species and turtles serve as important aquatic–terrestrial linkages, by transporting nutrients across ecosystem boundaries. Hippopotamuses and beavers are important geomorphological engineers, capable of altering the land and hydrology at landscape scales. Migratory species and terrestrial species with large home ranges are potentially important dispersal vectors of plant propagules and nutrients. Clearly, large aquatic herbivores have strong impacts on associated species and can be critical ecosystem engineers of aquatic systems, with the ability to modify direct and indirect functional pathways in ecosystems. While global populations of large aquatic herbivores are declining, some show remarkable local recoveries with dramatic consequences for the systems they inhabit. A better understanding of these functional roles will help set priorities for the effective management of large aquatic herbivores along with the plant habitats they rely on.     

Petiole Growth in Ranunculus sceleratus L.: Ethylene Synthesis and Submergence

Petioles of the celery-leaved buttercup (Ranunculus sceleratusL.) elongate in response to treatment with ethylene in air whenthe leaf blades are attached. An enhanced rate of elongationgrowth also occurs when the leaves are submerged. Submergencecauses an increase in extractable ethylene gas within the tissues,and these levels appear to approach those required to saturatethe ethylene-promoted elongation growth response. Coincidentwith a rise in ethylene in the tissues is a dramatic increasein the level of I-aminocyclopropane-1-carboxylic acid (ACC),the precursor of ethylene. Both the petiole and leaf blade tissueshave a similar capacity to evolve ethylene in the presence ofadded ACC. However, in air the leaf blade evolves more ethylenefrom endogenous resources than the petiole. The simultaneousincreases in ethylene and ACC levels in submerged tissues areconsidered in terms of the low diffusivity of ethylene in water,the ‘autocatalytic’ effect of ethylene on ethylenebiosynthesis and the rôle of both carbon dioxide and oxygenfluxes in ethylene metabolism of submerged tissues. Ranunculus sceleratus, celery-leaved buttercup, petiole growth, submergence, ethylene metabolism     

Associations Between Mycobacterium ulcerans and Aquatic Plant Communities of West Africa: Implications for Buruli Ulcer Disease

Numerous studies have associated Buruli ulcer (BU) disease with disturbed aquatic habitats; however, the natural reservoir, distribution, and transmission of the pathogen, Mycobacterium ulcerans, remain unknown. To better understand the role of aquatic plants in the ecology of this disease, a large-scale survey was conducted in waterbodies of variable flow throughout three regions of Ghana, Africa. Our objectives were to characterize plant communities and identify potential relationships with M. ulcerans and other mycolactone-producing mycobacteria (MPM). Waterbodies with M. ulcerans had significantly different aquatic plant communities, with submerged terrestrial plants identified as indicators of M. ulcerans presence. Mycobacterium ulcerans and MPM were detected on 14 plant taxa in emergent zones from both lotic and lentic waterbodies in endemic regions; however, M. ulcerans was not detected in the non-endemic Volta region. These findings support the hypothesis that plants provide substrate for M. ulcerans colonization and could act as potential indicators for disease risk. These findings also suggest that M. ulcerans is a widespread environmental bacteria species, but that it is absent or reduced in regions of low disease incidence. A better understanding is needed regarding the mechanistic associations among aquatic plants and M. ulcerans for identifying the mode of transmission of BU disease.     

Was the Early Eocene proboscidean Numidotherium koholense semi-aquatic or terrestrial? Evidence from stable isotopes and bone histology

The Early Eocene deposits of El Kohol, Algeria, have yielded numerous remains of Numidotherium koholense, one of the most primitive and oldest known proboscideans in Africa. The Upper Eocene proboscideans of the Fayum locality (Egypt), Barytherium sp. and Moeritherium sp., were recently interpreted as aquatic or semi-aquatic, according to the stable isotopic compositions (δ¹³C and δ¹⁸O) of their tooth enamel. These data led us to reinvestigate the adaptations of N. koholense. Stable isotopic analysis and observations of histological sections of its long bones reveal that it was essentially terrestrial. According to its position within the phylogenetic tree of Eocene proboscideans, the adaptation to semi-aquatic life appears to have evolved independently in different lineages of Middle and Upper Eocene proboscideans during their adaptive radiation in Africa. Moreover, these new results reopen the debate about the hypothesis that Eocene to Recent proboscideans are derived from semi-aquatic ancestors.     

Heterophylly in Ranunculus flabellaris Raf.: The Effect of Abscisic Acid

Ranunculus flabellaris Raf., the Yellow Water-Crowfoot, is aheterophyllous semi-aquatic dicotyledonous plant, showing strikingmorphological and anatomical differences between terrestrialleaves and those formed underwater. After plants are submergedin a 25 µM solution of abscisic acid, leaves are producedat a normal rate but they exhibit many of the characteristicsof terrestrial leaves. Ranunculus flabellaris Raf., Yellow Water-Crowfoot, heterophylly, abscisic acid     

Comparative genomics reveals insights into cyanobacterial evolution and habitat adaptation

Cyanobacteria are photosynthetic prokaryotes that inhabit diverse aquatic and terrestrial environments. However, the evolutionary mechanisms involved in the cyanobacterial habitat adaptation remain poorly understood. Here, based on phylogenetic and comparative genomic analyses of 650 cyanobacterial genomes, we investigated the genetic basis of cyanobacterial habitat adaptation (marine, freshwater, and terrestrial). We show: (1) the expansion of gene families is a common strategy whereby terrestrial cyanobacteria cope with fluctuating environments, whereas the genomes of many marine strains have undergone contraction to adapt to nutrient-poor conditions. (2) Hundreds of genes are strongly associated with specific habitats. Genes that are differentially abundant in genomes of marine, freshwater, and terrestrial cyanobacteria were found to be involved in light sensing and absorption, chemotaxis, nutrient transporters, responses to osmotic stress, etc., indicating the importance of these genes in the survival and adaptation of organisms in specific habitats. (3) A substantial fraction of genes that facilitate the adaptation of Cyanobacteria to specific habitats are contributed by horizontal gene transfer, and such genetic exchanges are more frequent in terrestrial cyanobacteria. Collectively, our results further our understandings of the adaptations of Cyanobacteria to different environments, highlighting the importance of ecological constraints imposed by the environment in shaping the evolution of Cyanobacteria.Subject terms: Phylogenetics, Microbial ecology     

Root morphological and structural comparisons of introduced and native aquatic plant species in multiple substrates

Invasions of introduced plants are considered among the greatest threats to biodiversity worldwide. Aquatic habitats suffer invasion more frequently and extensively than do terrestrial habitats. Although the role of roots in plant anchoring and support is important, previous studies have focused much attention on the morphological traits of above-ground parts, with relatively less attention given to the root structures of aquatic plants. In this study, we aimed to compare differences in root morphological and structural traits between introduced and native plants in response to different substrates. We hypothesized that introduced aquatic plants have an advantage over native plants with regard to root trait values and plasticity. A total of six aquatic plants were used: Two invasive and one exotic noninvasive species were paired with their native counterparts according to life form (amphibious emergent, submerged and floating-leaved) and cultivated in substrates of clay, a clay/sand mixture (v:v = 1:1) or sand. Root morphological traits, topological indices and root relative distance plasticity indices were quantified. The results indicated that different substrates have various effects on the root traits of these six aquatic plants; the introduced plants generally exhibited higher plasticity than did their native counterparts of the same life form.     

Aquatic adventitious root development in partially and completely submerged wetland plants Cotula coronopifolia and Meionectes brownii

Background and Aims

A common response of wetland plants to flooding is the formation of aquatic adventitious roots. Observations of aquatic root growth are widespread; however, controlled studies of aquatic roots of terrestrial herbaceous species are scarce. Submergence tolerance and aquatic root growth and physiology were evaluated in two herbaceous, perennial wetland species Cotula coronopifolia and Meionectes brownii.

Methods

Plants were raised in large pots with ‘sediment’ roots in nutrient solution and then placed into individual tanks and shoots were left in air or submerged (completely or partially). The effects on growth of aquatic root removal, and of light availability to submerged plant organs, were evaluated. Responses of aquatic root porosity, chlorophyll and underwater photosynthesis, were studied.

Key Results

Both species tolerated 4 weeks of complete or partial submergence. Extensive, photosynthetically active, aquatic adventitious roots grew from submerged stems and contributed up to 90 % of the total root dry mass. When aquatic roots were pruned, completely submerged plants grew less and had lower stem and leaf chlorophyll a, as compared with controls with intact roots. Roots exposed to the lowest PAR (daily mean 4·7 ± 2·4 µmol m⁻² s⁻¹) under water contained less chlorophyll, but there was no difference in aquatic root biomass after 4 weeks, regardless of light availability in the water column (high PAR was available to all emergent shoots).

Conclusions

Both M. brownii and C. coronopifolia responded to submergence with growth of aquatic adventitious roots, which essentially replaced the existing sediment root system. These aquatic roots contained chlorophyll and were photosynthetically active. Removal of aquatic roots had negative effects on plant growth during partial and complete submergence.     

Herbivory and growth in terrestrial and aquatic populations of amphibious stream plants

1. Many amphibious plant species grow in the transition between terrestrial and submerged vegetation in small lowland streams. We determined biomass development, leaf turnover rate and invertebrate herbivory during summer in terrestrial and aquatic populations of three amphibious species to evaluate advantages and disadvantages of aerial and submerged life.
2. Terrestrial populations had higher area shoot density, biomass and leaf production than aquatic populations, while leaf turnover rate and longevity were the same. Terrestrial populations experienced lower percentage grazing loss of leaf production (average 1.2–5.1%) than aquatic populations (2.9–17.3%), while the same plant dry mass was consumed per unit ground area.
3. Grazing loss increased linearly with leaf age apart from the youngest leaf stages. Grazing loss during the lifetime of leaves was therefore 2.4–3.1 times higher than mean apparent loss to standing leaves of all ages. The results imply that variation in density of grazers relative to plant production can account for differences in grazing impact between terrestrial and aquatic populations, and that fast leaf turnover keeps apparent grazing damage down.
4. We conclude that the ability of amphibious plants to grow submerged permits them to expand their niche and escape intense competition on land, but the stream does not provide a refugium against grazing and constrains plant production compared with the terrestrial habitat.     

Mitochondrial OXPHOS genes provides insights into genetics basis of hypoxia adaptation in anchialine cave shrimps

Cave shrimps from the genera Typhlatya, Stygiocaris and Typhlopatsa (TST complex) comprises twenty cave-adapted taxa, which mainly occur in the anchialine environment. Anchialine habitats may undergo drastic environmental fluctuations, including spatial and temporal changes in salinity, temperature, and dissolved oxygen content. Previous studies of crustaceans from anchialine caves suggest that they have possessed morphological, behavioral, and physiological adaptations to cope with the extreme conditions, similar to other cave-dwelling crustaceans. However, the genetic basis has not been thoroughly explored in crustaceans from anchialine habitats, which can experience hypoxic regimes. To test whether the TST shrimp-complex hypoxia adaptations matched adaptive evolution of mitochondrial OXPHOS genes. The 13 OXPHOS genes from mitochondrial genomes of 98 shrimps and 1 outgroup were examined. For each of these genes was investigated and compared to orthologous sequences using both gene (i.e. branch-site and Datamonkey) and protein (i.e. TreeSAAP) level approaches. Positive selection was detected in 11 of the 13 candidate genes, and the radical amino acid changes sites scattered throughout the entire TST complex phylogeny. Additionally, a series of parallel/convergent amino acid substitutions were identified in mitochondrial OXPHOS genes of TST complex shrimps, which reflect functional convergence or similar genetic mechanisms of cave adaptation. The extensive occurrence of positive selection is suggestive of their essential role in adaptation to hypoxic anchialine environment, and further implying that TST complex shrimps might have acquired a finely capacity for energy metabolism. These results provided some new insights into the genetic basis of anchialine hypoxia adaptation.