Role of the clasping-leaved pondweed (Potamogeton perfoliatus) polysaccharides in formation of its bacterial environment

The effect of the polysaccharides of clasping-leaved pondweed (Potamogeton perfoliatus) on the formation of a bacteriocenosis of this plant was demonstrated by research on chemoreception, relative surface hydrophobicity, and the growth characteristics of the members of five bacterial genera abundant in this micro biocenosis. The plant heteropolysaccharides of anionic and cationic nature were found to participate in selective stimulation or inhibition of growth of some microbial groups in surrounding water. These findings improve our understanding of the spectrum of physiological activity of glycopolymers of diverse origin.     

Antibacterial compounds in estuarine submersed aquatic plants

Estuarine seagrasses often exist in nutrient-rich waters and thus might benefit from mechanisms to control exterior growth of epiphytic microorganisms. In this study, we tested extracts from three estuarine seagrass species, Potamogeton pectinatus L. (sago pondweed), Potamogeton perfoliatus L. (redhead grass) and Ruppia maritima L. (wigeon grass), for antibacterial activity. Methanolic extracts of axenic cultured plants were effective against all gram-positive bacteria tested, inhibiting growth of 12 species in the genera Micrococcus, Staphylococcus, Streptococcus, Bacillus, Aerococcus, Mycobacterium and Corynebacterium. Some gram-negative species in the genera Vibrio, Listonella and Pasteurella were also sensitive. Other gram-negative bacteria were resistant. Antibacterial activity was detected in field-collected plants in spring, but appeared absent in plants collected in fall. These seagrass species thus appear to possess an antibacterial agent. It has not been identified and may consist of one or multiple compounds. The antibacterial agent in P. pectinatus was released into the water column in vitro at concentrations sufficient to inhibit or kill sensitive bacterial species. The agent was stable, with an in vitro half-life of 12 days at 25 °C and 6.6 days at 37 °C. It is possible that antibacterial production has ecological effects upon the bacterial and faunal communities associated with seagrass ecosystems.     

Plant species richness,identity and productivity differentially influence key groups of microbes in grassland soils of contrasting fertility

The abundance of microbes in soil is thought to be strongly influenced by plant productivity rather than by plant species richness per se. However, whether this holds true for different microbial groups and under different soil conditions is unresolved. We tested how plant species richness, identity and biomass influence the abundances of arbuscular mycorrhizal fungi (AMF), saprophytic bacteria and fungi, and actinomycetes, in model plant communities in soil of low and high fertility using phospholipid fatty acid analysis. Abundances of saprophytic fungi and bacteria were driven by larger plant biomass in high diversity treatments. In contrast, increased AMF abundance with larger plant species richness was not explained by plant biomass, but responded to plant species identity and was stimulated by Anthoxantum odoratum. Our results indicate that the abundance of saprophytic soil microbes is influenced more by resource quantity, as driven by plant production, while AMF respond more strongly to resource composition, driven by variation in plant species richness and identity. This suggests that AMF abundance in soil is more sensitive to changes in plant species diversity per se and plant species composition than are abundances of saprophytic microbes.     

Effects of plant species richness and evenness on soil microbial community diversity and function

Understanding the links between plant diversity and soil communities is critical to disentangling the mechanisms by which plant communities modulate ecosystem function. Experimental plant communities varying in species richness, evenness, and density were established using a response surface design and soil community properties including bacterial and archaeal abundance, richness, and evenness were measured. The potential to perform a representative soil ecosystem function, oxidation of ammonium to nitrite, was measured via archaeal and bacterial amoA genes. Structural equation modeling was used to explore the direct and indirect effects of the plant community on soil diversity and potential function. Plant communities influenced archaea and bacteria via different pathways. Species richness and evenness had significant direct effects on soil microbial community structure, but the mechanisms driving these effects did not include either root biomass or the pools of carbon and nitrogen available to the soil microbial community. Species richness had direct positive effects on archaeal amoA prevalence, but only indirect impacts on bacterial communities through modulation of plant evenness. Increased plant evenness increased bacterial abundance which in turn increased bacterial amoA abundance. These results suggest that plant community evenness may have a strong impact on some aspects of soil ecosystem function. We show that a more even plant community increased bacterial abundance, which then increased the potential for bacterial nitrification. A more even plant community also increased total dissolved nitrogen in the soil, which decreased the potential for archaeal nitrification. The role of plant evenness in structuring the soil community suggests mechanisms including complementarity in root exudate profiles or root foraging patterns.     

Interacting influence of mycorrhizal symbiosis and competition on plant diversity in tallgrass prairie

In tallgrass prairie, plant species interactions regulated by their associated mycorrhizal fungi may be important forces that influence species coexistence and community structure; however, the mechanisms and magnitude of these interactions remain unknown. The objective of this study was to determine how interspecific competition, mycorrhizal symbiosis, and their interactions influence plant community structure. We conducted a factorial experiment, which incorporated manipulations of abundance of dominant competitors, Andropogon gerardii and Sorghastrum nutans, and suppression of mycorrhizal symbiosis using the fungicide benomyl under two fire regimes (annual and 4-year burn intervals). Removal of the two dominant C₄ grass species altered the community structure, increased plant species richness, diversity, and evenness, and increased abundance of subdominant graminoid and forb species. Suppression of mycorrhizal fungi resulted in smaller shifts in community structure, although plant species richness and diversity increased. Responses of individual plant species were associated with their degree of mycorrhizal responsiveness: highly mycorrhizal responsive species decreased in abundance and less mycorrhizal responsive species increased in abundance. The combination of dominant-grass removal and mycorrhizal suppression treatments interacted to increase synergistically the abundance of several species, indicating that both processes influence species interactions and community organization in tallgrass prairie. These results provide evidence that mycorrhizal fungi affect plant communities indirectly by influencing the pattern and strength of plant competitive interactions. Burning strongly influenced the outcome of these interactions, which suggests that plant species diversity in tallgrass prairie is influenced by a complex array of interacting processes, including both competition and mycorrhizal symbiosis. Received: 7 April 1999 / Accepted: 30 July 1999     

Effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on associated soil bacterial communities: A field‐based experiment

Loss of plant biodiversity can result in reduced abundance and diversity of associated species with implications for ecosystem functioning. In ecosystems low in plant species diversity, such as Neotropical mangrove forests, it is thought that genetic diversity within the dominant plant species could play an important role in shaping associated communities. Here, we used a manipulative field experiment to study the effects of maternal genotypic identity and genetic diversity of the red mangrove Rhizophora mangle on the composition and richness of associated soil bacterial communities. Using terminal restriction fragment length polymorphism (T‐RFLP) community fingerprinting, we found that bacterial community composition differed among R. mangle maternal genotypes but not with genetic diversity. Bacterial taxa richness, total soil nitrogen, and total soil carbon were not significantly affected by maternal genotypic identity or genetic diversity of R. mangle. Our findings show that genotype selection in reforestation projects could influence soil bacterial community composition. Further research is needed to determine what impact these bacterial community differences might have on ecosystem processes, such as carbon and nitrogen cycling.     

Species richness and soil properties in Pinus ponderosa forests: A structural equation modeling analysis

Question: How are the effects of mineral soil properties on understory plant species richness propagated through a network of processes involving the forest overstory, soil organic matter, soil nitrogen, and understory plant abundance? Location: North‐central Arizona, USA. Methods: We sampled 75 0.05‐ha plots across a broad soil gradient in a Pinus ponderosa (ponderosa pine) forest ecosystem. We evaluated multivariate models of plant species richness using structural equation modeling. Results: Richness was highest at intermediate levels of understory plant cover, suggesting that both colonization success and competitive exclusion can limit richness in this system. We did not detect a reciprocal positive effect of richness on plant cover. Richness was strongly related to soil nitrogen in the model, with evidence for both a direct negative effect and an indirect non‐linear relationship mediated through understory plant cover. Soil organic matter appeared to have a positive influence on understory richness that was independent of soil nitrogen. Richness was lowest where the forest overstory was densest, which can be explained through indirect effects on soil organic matter, soil nitrogen and understory cover. Finally, model results suggest a variety of direct and indirect processes whereby mineral soil properties can influence richness. Conclusions: Understory plant species richness and plant cover in P. ponderosa forests appear to be significantly influenced by soil organic matter and nitrogen, which are, in turn, related to overstory density and composition and mineral soil properties. Thus, soil properties can impose direct and indirect constraints on local species diversity in ponderosa pine forests.     

Soil Environmental Conditions and Microbial Build-Up Mediate the Effect of Plant Diversity on Soil Nitrifying and Denitrifying Enzyme Activities in Temperate Grasslands

Random reductions in plant diversity can affect ecosystem functioning, but it is still unclear which components of plant diversity (species number – namely richness, presence of particular plant functional groups, or particular combinations of these) and associated biotic and abiotic drivers explain the observed relationships, particularly for soil processes. We assembled grassland communities including 1 to 16 plant species with a factorial separation of the effects of richness and functional group composition to analyze how plant diversity components influence soil nitrifying and denitrifying enzyme activities (NEA and DEA, respectively), the abundance of nitrifiers (bacterial and archaeal amoA gene number) and denitrifiers (nirK, nirS and nosZ gene number), and key soil environmental conditions. Plant diversity effects were largely due to differences in functional group composition between communities of identical richness (number of sown species), though richness also had an effect per se. NEA was positively related to the percentage of legumes in terms of sown species number, the additional effect of richness at any given legume percentage being negative. DEA was higher in plots with legumes, decreased with increasing percentage of grasses, and increased with richness. No correlation was observed between DEA and denitrifier abundance. NEA increased with the abundance of ammonia oxidizing bacteria. The effect of richness on NEA was entirely due to the build-up of nitrifying organisms, while legume effect was partly linked to modified ammonium availability and nitrifier abundance. Richness effect on DEA was entirely due to changes in soil moisture, while the effects of legumes and grasses were partly due to modified nitrate availability, which influenced the specific activity of denitrifiers. These results suggest that plant diversity-induced changes in microbial specific activity are important for facultative activities such as denitrification, whereas changes in microbial abundance play a major role for non-facultative activities such as nitrification.     

Ecosystem responses to woody plant encroachment in a semiarid savanna rangeland

Woody plant encroachment alters the structure and function of rangeland ecosystems. The objective of this study was to explore the association between woody plant encroachment and various ecosystem properties (i.e. vascular plant species diversity, richness, evenness, soil organic matter, herbaceous biomass, leaf litter and bare ground cover) in a semiarid savanna rangeland, and also to test whether the relationships were influenced by woody species composition, elevation and site. We carried out a vegetation survey in four rangeland sites in the lower Omo region of southwestern Ethiopia, and regressed each one of the ecosystem properties, separately, against woody plant density, elevation and site using multiple linear regressions. We found that vascular plant species diversity, richness and evenness increased with woody plant density, most likely due to increased spatial heterogeneity and soil microclimate improvement. Bare ground cover increased significantly, whereas herbaceous biomass and soil organic matter did not respond to woody encroachment. In a subsequent investigation, we used a redundancy analysis to assess whether ecosystem properties were influenced by the identity of encroaching woody plant species. Species diversity and richness responded positively to Lannea triphylla, whereas leaf litter responded positively to Grewia tenax and G. villosa. Our findings suggest that woody plant encroachment in a semiarid rangeland does alter ecosystem properties. However, its impact is highly variable, influenced by a set of factors including the level of encroachment and identity of encroaching woody species.     

筑坝扩容下高原湿地拉市海植物群落分布格局及其变化

基于遥感与地理信息系统技术、结合实地调查与验证,对高原湿地拉市海筑坝扩容13a来湿地植物群落类型、物种组成、空间分布格局进行研究,对比分析筑坝扩容前后植物群落变化特征。结果表明,拉市海当前分布有水葱 (Scirpus tabernaemontani)、两栖蓼 (Polygonum amphibium) 等2个挺水植物群落,鸭子草 (Potamogeton tepperi)、菱 (Trapa bispinosa)等2个浮叶植物群落,穗状狐尾藻 (Myriophyllum spicatum)、篦齿眼子菜 (Potamogeton pectinatus)、菹草 (Potamogeton crispus)、穿叶眼子草 (Potamogeton perfoliatus)、小叶眼子菜 (Potamogeton pusillns)等5个沉水植物群落,草甸植被分布于湖周。湿地植物物种共计61种,隶属于25科、48属,物种丰富度随沉水→浮叶→挺水→草甸逐渐增加。沉水植物群落分布面积最大(615.08 hm²),其次是草甸(214.60 hm²)、浮叶植物群落(140.01 hm²),挺水植物群落分布面积最小 (9.34 hm²),群落垂直层次随沉水→浮叶→挺水呈复杂化的趋势。筑坝13a来,拉市海植物群落类型从单一的沉水型植物群落发展成为由沉水、浮叶、挺水型组成的、水平空间多样化配置的湿地植被系统,其中穗状狐尾藻、篦齿眼子菜、小眼子菜等植物群落在筑坝蓄水13a后没有发生演替得以保留,而扇叶水毛茛(Butrachium bungei)、马来眼子菜(Potamogeton malaianus)和轮藻(Chara spp.)群落发生演替而消失。研究掌握了筑坝扩容下拉市海湿地植物群落分布格局及其变化特征,为科学评估筑坝蓄水对湿地生态系统的影响提供了基础性数据,同时也为水文改变下高原湿地生态系统的保护、管理以及资源可持续利用提供了一定的理论依据。     

Genotypic diversity of an invasive plant species promotes litter decomposition and associated processes

Following studies that showed negative effects of species loss on ecosystem functioning, newer studies have started to investigate if similar consequences could result from reductions of genetic diversity within species. We tested the influence of genotypic richness and dissimilarity (plots containing one, three, six or 12 genotypes) in stands of the invasive plant Solidago canadensis in China on the decomposition of its leaf litter and associated soil animals over five monthly time intervals. We found that the logarithm of genotypic richness was positively linearly related to mass loss of C, N and P from the litter and to richness and abundance of soil animals on the litter samples. The mixing proportion of litter from two sites, but not genotypic dissimilarity of mixtures, had additional effects on measured variables. The litter diversity effects on soil animals were particularly strong under the most stressful conditions of hot weather in July: at this time richness and abundance of soil animals were higher in 12-genotype litter mixtures than even in the highest corresponding one-genotype litter. The litter diversity effects on decomposition were in part mediated by soil animals: the abundance of Acarina, when used as covariate in the analysis, fully explained the litter diversity effects on mass loss of N and P. Overall, our study shows that high genotypic richness of S. canadensis leaf litter positively affects richness and abundance of soil animals, which in turn accelerate litter decomposition and P release from litter.     

Effects of Habitat-Forming Species Richness,Evenness, Identity,and Abundance on Benthic Intertidal Community Establishment and Productivity

In a context of reduced global biodiversity, the potential impacts from the loss of habitat-forming species (HFS) on ecosystem structure and functioning must be established. These species are often the main community primary producers and have a major role in the establishment of organisms through facilitation processes. This study focuses on macroalgae and mussels as HFS within an intertidal zone along the St. Lawrence estuary (Quebec, Canada). Over a 16-week period, we manipulated the in situ diversity profile (richness, evenness, identity, and abundance) of the dominant HFS (Fucus distichus edentatus, F. vesiculosus, and Mytilus spp.) in order to define their role in both the establishment of associated species and community primary production. Contrary to expectation, no general change in HFS richness, evenness, abundance, or identity on associated species community establishment was observed. However, over the study period, the HFS diversity profile modified the structure within the trophic guilds, which may potentially affect further community functions. Also, our results showed that the low abundance of HFS had a negative impact on the primary productivity of the community. Our results suggest that HFS diversity profiles have a limited short-term role in our study habitat and may indicate that biological forcing in these intertidal communities is less important than environmental conditions. As such, there was an opportunistic establishment of species that ensured rapid colonization regardless of the absence, or the diversity profile, of facilitators such as HFS.     

Reproductive Allocation in Three Macrophyte Species from Different Lakes with Variable Eutrophic Conditions

Reproductive allocation is a key process in the plant life cycle and aquatic plants exhibit great diversity in their reproductive systems. In the present study, we conduct a field investigation of three aquatic macrophytes: Stuckenia pectinata, Myriophyllum spicatum, and Potamogeton perfoliatus. Our results showed that widespread species, including S. pectinata and M. spicatum had greater plasticity in their allocation patterns in the form of increased sexual and asexual reproduction, and greater potential to set seeds and increase fitness in more eutrophic environments. P. perfoliatus also exhibited a capacity to adopt varied sexual reproductive strategies such as setting more offspring for the future, although only in clear conditions with low nutrient levels. Our results establish strategies and mechanisms of some species for tolerating and surviving in varied eutrophic lake conditions.     

Evidence for indirect effects of plant diversity and composition on net nitrification

Abiotic controls on net nitrification rates are well documented, but the potential effects of plants on this important ecosystem process are poorly understood. We evaluated four structural equation models to determine the relative importance of plant community composition, aboveground herbaceous production, and plant species richness on nitrifier abundance and net nitrification following restoration treatments in a ponderosa pine forest. Model selection criteria indicated that species richness was the best predictor of nitrifier abundance, but a model that included community composition effects also had some support in the data. Model results suggest that net nitrification was indirectly related to plant species richness via a positive relationship between species richness and nitrifier abundance. Community composition was indirectly related to nitrifier abundance through its relationship with species richness. Our model indicates that species-rich plant communities dominated by C₃ graminoids and legumes are associated with soils that have high abundances of nitrifiers. This study highlights the complexity of deciphering effects of ecological treatments on a system response when multiple interacting factors are simultaneously affected. Our results suggest that plant diversity and composition can both respond to forest thinning, prescribed fire and fuel manipulations, and can be factors that might indirectly influence an ecosystem process such as nitrification. Ecological restoration treatments designed to increase plant diversity and alter community composition may have cascading effects on below-ground processes.     

Dynamics of Nutrient Contents (Phosphorus,Nitrogen) in Water,Sediment and Plants After Restoration of Connectivity in Side‐Channels of the River Rhine

During the last century, canalization of the Rhine river led to disconnection of side‐arms, over‐sedimentation of these channels, loss of the fluvial dynamics, and aquatic vegetation change or disappearance. Recent restoration projects aim to reconnect disconnected arms to the main channel. The objective of this study was to assess the nutrient dynamics in restored channels during the vegetation colonization process. In spring, summer, and autumn 2009, the phosphorus and nitrogen contents were measured in water, sediment, and plants, sampled in six channels, two reference sites and four restored ones at different dates. Aquatic vegetation was monitored during the same period. Sites were mesotrophic related to the water nutrient concentrations. However, vegetation communities indicated a eutrophic level, as they were dominated by species like Elodea nuttallii, Myriophyllum spicatum, and Potamogeton perfoliatus. Sites were discriminated by P content and mineral nitrogen in the sediment. We showed an effect of species and season on the plant nutrient content, but there was no relationship between plant nutrient content and nutrients in water and sediment. A negative correlation between mean N plant content and the cover of each species was found. Vegetation characteristics (species richness and cover) and bioavailable phosphorus in the sediment were also correlated. In the restored side‐arms of the river Rhine, phosphorus‐rich sediment seems to be important in the recolonization dynamics, as it was linked to higher species richness, whereas nitrogen played a role in the colonization patterns as a growth limiting factor.     

Plant Trait Diversity Buffers Variability in Denitrification Potential over Changes in Season and Soil Conditions

Background

Denitrification is an important ecosystem service that removes nitrogen (N) from N-polluted watersheds, buffering soil, stream, and river water quality from excess N by returning N to the atmosphere before it reaches lakes or oceans and leads to eutrophication. The denitrification enzyme activity (DEA) assay is widely used for measuring denitrification potential. Because DEA is a function of enzyme levels in soils, most ecologists studying denitrification have assumed that DEA is less sensitive to ambient levels of nitrate (NO₃ ⁻) and soil carbon and thus, less variable over time than field measurements. In addition, plant diversity has been shown to have strong effects on microbial communities and belowground processes and could potentially alter the functional capacity of denitrifiers. Here, we examined three questions: (1) Does DEA vary through the growing season? (2) If so, can we predict DEA variability with environmental variables? (3) Does plant functional diversity affect DEA variability?

Methodology/Principal Findings

The study site is a restored wetland in North Carolina, US with native wetland herbs planted in monocultures or mixes of four or eight species. We found that denitrification potentials for soils collected in July 2006 were significantly greater than for soils collected in May and late August 2006 (p<0.0001). Similarly, microbial biomass standardized DEA rates were significantly greater in July than May and August (p<0.0001). Of the soil variables measured—soil moisture, organic matter, total inorganic nitrogen, and microbial biomass—none consistently explained the pattern observed in DEA through time. There was no significant relationship between DEA and plant species richness or functional diversity. However, the seasonal variance in microbial biomass standardized DEA rates was significantly inversely related to plant species functional diversity (p<0.01).

Conclusions/Significance

These findings suggest that higher plant functional diversity may support a more constant level of DEA through time, buffering the ecosystem from changes in season and soil conditions.     

Severe plant invasions can increase mycorrhizal fungal abundance and diversity

Invasions by non-native plants can alter ecosystem functions and reduce native plant diversity, but relatively little is known about their effect on belowground microbial communities. We show that invasions by knapweed (Centaurea stoebe) and leafy spurge (Euphorbia esula, hereafter spurge)—but not cheatgrass (Bromus tectorum)—support a higher abundance and diversity of symbiotic arbuscular mycorrhizal fungi (AMF) than multi-species native plant communities. The higher AMF richness associated with knapweed and spurge is unlikely due to a co-invasion by AMF, because a separate sampling showed that individual native forbs hosted a similar AMF abundance and richness as exotic forbs. Native grasses associated with fewer AMF taxa, which could explain the reduced AMF richness in native, grass-dominated communities. The three invasive plant species harbored distinct AMF communities, and analyses of co-occurring native and invasive plants indicate that differences were partly driven by the invasive plants and were not the result of pre-invasion conditions. Our results suggest that invasions by mycotrophic plants that replace poorer hosts can increase AMF abundance and richness. The high AMF richness in monodominant plant invasions also indicates that the proposed positive relationship between above and belowground diversity is not always strong. Finally, the disparate responses among exotic plants and consistent results between grasses and forbs suggest that AMF respond more to plant functional group than plant provenance.     

Inter-annual variability of Potamogeton perfoliatus stands

Yearly differences in the composition and nutrient content of submerged macrophyte stands, mainly of the long-term dominant Potamogeton perfoliatus L. were observed at 10 stations along 83 km route of the Estonian shore of L. Peipsi (total area 3555 km²) in the period of 1999–2002. Changes consisted in the differences in the presence of plants (three stations), replacement of dominant (one station), removal of mud sediment (one station), mass propagation of Lemna trisulca (all stations) in 1999 and of Cladophora glomerata on P. perfoliatus (six stations) in 2000. The amount of C. glomerata on pondweed, similar to the biomass of host plant, decreased in 2001–2002, whereas markedly thick layer of epiphytic microalgae covered P. perfoliatus in 2002. In the samples of P. perfoliatus collected at the stations of the mass propagation of C. glomerata in the next year, 2001, inflorescences were absent. The appearance of an increase in P. perfoliatus stands was probably associated with improving sediment conditions in the period of low water level in the last observation years. A trend of constant increase in the mean molar N/P ratio in the tissues of P. perfoliatus in the study period (from 17.8 to 25.2) was statistically significant (p = 0.003). Classical canonical analysis, used to study two complexes correlated between themselves characteristics of P. perfoliatus and environmental conditions, revealed that plant growth factor (including biomass, tissue N%, P% and N/P) was in strong correlation (p < 0.0001) with water condition factor (including mean temperature in May, sum of temperatures between ice break and sampling, mean water level, N_tot and P_tot of water in June). More important for water condition factor were mean temperature in May and P_tot of water in June. Also the independent significance of water N_tot and P_tot for pondweeds was tested and confirmed by ANOVA analysis.     

Aquatic macrophytes and water current velocity in the Danube River

Water currents are among the strongest environmental variables determining the occurrence and/or abundance of aquatic plants and the European Water Framework Directive (WFD) considers river morphology and current conditions important aspects of reference conditions. We used the database of the Joint Danube Survey JDS-2, organised by the International Commission for the Protection of the Danube River (ICPDR, Vienna), to assess the relationship between water flow velocity and the occurrence and abundance of aquatic macrophyte to be species along the navigable reach of the Danube River. Species abundance was assessed in accordance with European Standard EN 14184-2003. Flow velocities were assessed close to the plant stands and estimated in 4 classes, worked out in earlier studies in combination with flow meter measurements, which is appropriate for the conditions in this large river. Statistical analysis revealed that only survey units with either no visible flow or those with fast flow were characterised by indicator species with high significance. Still water conditions or barely visible flow (flow class 1) were indicated by Potamogeton friesii, Nitellopsis obtusa and Trapa natans, and by Potamogeton perfoliatus, Potamogeton nodosus and Stuckenia pectinata. Lemna minor, indicative for flow class 1 as well, was detected in all the other flow classes, too: in all these cases it established its stands closely intermingled with other aquatic species. For survey units with slow (flow class 2) or intermediate flow (flow class 3). No statistically significant indicator species could be determined. The highest flow velocities (flow class 4) were significantly indicated by Fissidens rufulus, Cinclidotus fontinaloides and Cinclidotus riparius. Occurrence of aquatic mosses was also highly related to the Berger–Parker dominance index in NMDS analysis. In the same analysis, but towards the smallest flow velocities, the majority of vascular species and the Simpson diversity index were closely related. The spectrum of life forms was considerably reduced under medium and high flow velocity conditions. With regard to Simpson species diversity, our analysis indicates an agglomeration of diversity in the Middle Danube reach that includes the Iron Gates impoundment. Our results offer a first look at the macrophyte/water flow relationship of a very large river in Europe, the Danube.     

Spatial distribution of nematode genera in relation to host plants of Western Ghats,Tamil Nadu,India

A survey of plant parasitic nematodes (PPN) abundance and diversity was conducted in foothills of Western Ghats at Coimbatore and Nilgiris districts in Tamil Nadu, India. Our study pointed to evaluate the PPN association with weeds, shrubs, and herbs including some agricultural crop cover both agro and forest ecosystems. Soil samples were collected around the rhizosphere of the plants and nematodes were isolated, counted under a microscope and identified by morphological characters. We collected 415 soil samples around the rhizosphere of 84 major plant families. Among 84 plant families, we found 13 PPN genera those generally responsible for cash crop yield loss. The genus Helicotylenchus spp., and Meloidogyne spp., were found frequent (226,136 samples) and rarely Hemicycliophora spp.,. The PPN diversity was measured by Shannon diversity index which showed that the diversity of PPN found higher in plant species those from the families Rosaceae (2.20) and Rubiaceae (2.13). We also recorded the PPN richness was dominated in four plant families. This result reveals that the PPN diversity and richness are positively correlated with host plant species diversity and altitude. Further, our study concludes that a wild plant in the forest ecosystem behaves like a reservoir of PPN.