Roots Of Aquatic Plants Research Articles

Iron plaques improve the oxygen supply to root meristems of the freshwater plant, Lobelia dortmanna

* High radial oxygen loss (ROL) from roots of aquatic plants to reduced sediments is thought to deplete the roots of oxygen and restrict the distribution of those species unable to form a barrier to oxygen loss. Metal precipitates with high iron content (Fe-plaques) frequently form on roots of aquatic plants and could create such a diffusion barrier, thereby diverting a larger proportion of downward oxygen transport to the root meristems. * To investigate whether Fe-plaques form a barrier to oxygen loss, ROL and internal oxygen concentrations were measured along the length of roots of the freshwater plant Lobelia dortmanna using platinum sleeve electrodes and Clark-type microelectrodes. * Measurements showed that ROL was indeed lower from roots with Fe-plaques than roots without plaques and that ROL declined gradually with thicker iron coating on roots. The low ROL was caused by low diffusion coefficients through root walls with Fe-plaques resulting in higher internal oxygen concentrations in the root lacunae. * By diverting a larger proportion of downward oxygen transport to root meristems in L. dortmanna, the presence of Fe-plaques should diminish root anoxia and improve survival in reduced sediments.

Trace metals in mangrove seedlings: role of iron plaque formation

Metal-rich mineral deposits on the roots of aquatic plants, denominated iron plaques, may moderate the uptake of essential, but potentially toxic metals by roots. We investigated the iron plaque formation on the fine, nutritive roots of mangrove seedlings growing in contrasting environments (oxidizing sand flat sediments and reducing mangrove forest sediments) in southeast Brazil. The results indicate that Avicennia schaueriana, Laguncularia racemosa, and Rhizophora mangle seedlings developed an efficient exclusion of Fe, Mn, and Zn through iron plaque formation. This process seems to be influenced substantially by species-specific responses to environmental conditions. While Fe and Zn translocation to leaves appear to be suppressed by accumulation within root tissues, this did not appear to occur for Mn, suggesting that Mn trapping in rhizosphere sediments and iron plaque formation are the main mechanisms responsible for the Mn exclusion from the organism level. In addition to factors well recognized as affecting mangrove seedling development (e.g., salinity stress and nutrient availability), the mediation of trace metal uptake by iron plaque formation possibly contribute to determine the seedling adaptability to waterlogged conditions.

Identification of rice root associated nitrate, sulfate and ferric iron reducing bacteria during root decomposition

Leakage of O 2 from roots of aquatic plants supports the oxidation of ammonia to nitrate and of sulfide to sulfate in the rhizosphere, so that these electron acceptors may become available to the root microbial communities and affect their activity. We studied the composition of the bacterial community active in anoxically incubated rice roots by analysis of terminal restriction fragment length polymorphism (T-RFLP) and by cloning and sequencing targeting bacterial 16S rRNA. The bacterial ribosomal abundance in unamended rice roots, which were naturally encrusted with ferric iron, were initially dominated (about 65% of total 16S rRNA) by Clostridium, Bacillus and Geobacter/Pelobacter, but after 5 d clostridia decreased and members of the Cytophaga– Flavobacterium– Bacteroides (CFB) phylum increased (up to 30% of total 16S rRNA). Addition of nitrate or sulfate to the root incubations resulted in bacterial growth detected by fluorescent in situ hybridization (FISH). It also affected the steady state concentrations of H 2, acetate, propionate and butyrate that were measured in the root incubations. Nitrate reducers were apparently involved in consumption of all of these compounds. Sulfate reducers, on the other hand, showed net production of acetate during utilization of propionate. Nitrate stimulated populations of Bacillus and Dechloromonas to become active, the latter temporarily increasing to 25% of total 16S rRNA, but suppressed the increase of CFB bacteria. Sulfate, on the other hand, stimulated Desulfosporosinus and Geobacter/Pelobacter, increasing to about 15% of total 16S rRNA, and suppressed CFB bacteria to become active. In conclusion, our study showed the potential effect of exogenous electron acceptors on the composition and activity of the bacterial community in rice root incubations, and identified the phylogenetic groups of the root microbial communities that respond to an increased availability of nitrate or sulfate.

Spatial and temporal association of As and Fe species on aquatic plant roots.

The formation of an Fe(III) precipitate (plaque) on the surface of aquatic plant roots may provide a means of attenuation and external exclusion of metals. Presently, the mechanisms of metal(loid) sequestration at the root surface are unresolved. Accordingly, we investigated the mechanisms of Fe and As attenuation and association on the roots of two common aquatic plant species, Phalaris arundinacea (reed canarygrass) and Typha latifolia (cattail) using X-ray absorption spectroscopy and X-ray fluorescence microtomography. Iron plaque of both P. arundinacea and T. latifolia consist predominantly of hydrated iron oxides (ferrihydrite) with lesser amounts of goethite and minor levels of siderite. Typha latifolia, however, differs from P. arundinacea by having a significant contribution from lepidocrocite as well as a greater proportion of crystalline minerals. Coexistence of goethite and lepidocrocite suggests the presence of chemically diverse microenvironments at the root surface. Arsenic exists as a combination of two sorbed As species, being comprised predominantly of arsenate- (approximately 82%) with lesser amounts (approximately 18%) of As(III)-iron (hydr)oxide complexes. Furthermore, both spatial and temporal correlations between As and Fe on the root surfaces were observed. While the iron (hydr)oxide deposits form a continuous surficial rind around the root, As exists in isolated regions on the exterior and interior of the root. Root surface-associated As generally corresponds to regions of enhanced Fe levels and may therefore occur as a direct consequence of Fe phase heterogeneity and preferential As sorption reactions.

Characterization of Fe plaque and associated metals on the roots of mine-waste impacted aquatic plants.

Iron plaque on aquatic plant roots are ubiquitous and sequester metals in wetland soils; however, the mechanisms of metal sequestration are unresolved. Thus, characterizing the Fe plaque and associated metals will aid in understanding and predicting metal cycling in wetland ecosystems. Accordingly, microscopic and spectroscopic techniques were utilized to identify the spatial distributions, associations, and chemical environments of Fe, Mn, Pb, and Zn on the roots of a common, indigenous wetland plant (Phalaris arundinacea). Iron forms a continuous precipitate on the root surface, which is composed dominantly of ferrihydrite (ca. 63%) with lesser amounts of goethite (32%) and minor levels of siderite (5%). Although Pb is juxtaposed with Fe on the root surface, it is complexed to organic functional groups, consistent with those of bacterial biofilms. In contrast, Mn and Zn exist as discrete, isolated mixed-metal carbonate (rhodochrosite/hydrozincite) nodules on the root surface. Accordingly, the soil-root interface appears to be a complex biochemical environment, containing both reduced and oxidized mineral species, as well as bacterial-induced organic-metal complexes. As such, hydrated iron oxides, bacterial biofilms, and metal carbonates will influence the availability and mobility of metals within the rhizosphere of aquatic plants.

In Situ Collection of Diagenetic and Induced Oxyhydroxide Precipitates from Riverine and Estuarine Sediments

The use of plastic sheets as collectors of diagenetically-formed oxyhydroxides from riverine and estuarine sediments was evaluated. In a range of materials tested in the laboratory, Teflon and polycarbonate were found to be the most efficient collector materials. Laboratory optimisation experiments indicated that the deposition of oxyhydroxides on both materials occurred quickly (<2 weeks). In the field, oxyhydroxides were collected on Teflon sheets as depositional bands just below the sediment-water interface. These bands were much wider and more variable (1–5 cm) than those observed in laboratory experiments (typically 0.5 cm). This was attributed to the frequently changing redox conditions at the field sites caused by a combination of sediment movement and tidal processes. The deposits collected were predominantly iron with lesser amounts of manganese. At several sites strong correlations were observed between the concentrations of manganese and zinc deposited on the Teflon collector surfaces. In both the laboratory and field experiments, biologically-mediated iron oxyhydroxide deposition in anoxic sediments was frequently observed (mainly caused by the activities of burrowing organisms). The mechanism of iron deposition on polycarbonate was investigated in detail. This plastic contains high concentrations of oxygen which is released over sustained periods, thereby inducing the deposition of iron oxyhydroxide even in anoxic sediments. It is proposed that polycarbonate may be used for investigating the impacts of oxygen introduction to anoxic sediments by processes such as bioturbation and oxygen release from aquatic plant roots.

The influence of plants on concentration and fractionation of Zn, Pb, and Cu in salt marsh sediments (Tagus Estuary, Portugal)

Sediment cores were collected from two sites of the Tagus estuary salt marshes which differed in degree of metal contamination. At each site, six 60-cm-long cores were taken, three from a non-vegetated intertidal zone, and one from each of areas colonized by salt marsh plants, Spartina maritima, Halimione portulacoides and Arthrocnemum fruticosum, respectively. Total concentrations and concentrations in sequential extractions of Zn, Pb, and Cu were determined in several sediment layers. Sediment slices containing most of the roots (5–15-cm depth) were enriched in metals in comparison with other depths in the core and with non-vegetated cores. Additionally, metals in sediment slices with roots were preferentially linked to the residual fraction. These results are evidence that aquatic plant roots can have a strong influence on metal concentration and speciation in sediments. Since metals become immobilized in vegetated sediments, the preservation of salt marshes or the creation of artificial wetlands could be considered as an efficient natural means for maintaining ecosystem health or restoring ecosystem quality.

The measurement of gas spaces in the roots of aquatic plants — Archimedes revisited

The volume of gas space within the root systems of pot-grown mangrove plants was determined by three methods based on Archimedes' principle: pycnometry, measurement of the upthrust on the root system when immersed in water, and measurement of the volume of water displaced. The results obtained using the upthrust and displacement methods were highly consistent. Although individual estimates obtained by pycnometry varied considerably from those by upthrust or displacement, there was no statistically significant difference overall between the three methods. This indicates that there is probably no systematic under- or overestimation of the actual value by any of the methods. The upthrust and displacement methods were much quicker than pycnometry, and have the further advantages of usually not requiring subsampling of the root system and of being non-destructive. We eventually settled on the displacement method because of the greater simplicity of the equipment required.

Predation of Mansonia (Diptera: Culicidae) by native mosquitofish in southern Florida.

In experimental tanks and wading pools, the mosquitofish Gambusia holbrooki reduced densities of Mansonia larvae which, because of their attachment to the roots of aquatic plants, have been regarded previously as relatively impervious to predation. Exoskeletal remains of larval Mansonia were recovered from 43.5% of stomachs dissected from G. holbrooki, but not from Heterandria formosa (least killifish) collected from two undisturbed ponds covered with water lettuce (Pistia stratiotes L.). After 24 h in aquaria exposed to ambient light, predation by G. holbrooki reduced densities of Mansonia on water lettuce to one-third that of controls but in the dark, no significant differences were observed. In reduced light, densities of second- and fourth-instar Mansonia were reduced significantly after 1 wk of exposure to G. holbrooki. Video recordings of predation in aquaria revealed that G. holbrooki glean water lettuce roots to locate attached Mansonia and also capture free-swimming, dislodged larvae.

Estimating thermal properties of simulated aquatic soils from their composition

Heat penetration and thermal lag in the submersed soil surrounding the roots of aquatic plants depends on two fundamental thermal properties of the substrate, volumetric heat capacity (CV) and thermal conductivity (k). The relationship of these parameters to the fractions of organic and mineral matter, gas and water in natural and simulated aquatic soils was investigated. The gas fraction was found to be insignificant and it was possible to make good estimates of CV and k from a knowledge of substrate water content alone.

Effects of diet, body size, age and temperature on growth rates in the amphipod Gammarus pulex

SUMMARY. Increase in body wet weight of Gammarus pulex fed on decaying elm leaves was followed to senescence and death. Growth in juveniles was approximately exponential; from birth to death it conformed to a logistic growth curve, with maximum absolute increments in weight about half‐way through a life span of 350–450 days at 15°C. Some individuals lived longer, for up to 640–700 days. The instantaneous or specific growth rate was maximal near birth, at c. 5–6% wet wt day−1, and declined exponentially with increasing size and age. Over the range 4.7–14.8°C there was a log‐log relationship between temperature and specific growth rate. Growth was maximal at 20°C in newborn animals and at 15°C in 6–9‐mg animals.The specific growth rate of young individuals was fastest on decaying leaves of elm with a well developed flora of fungi and other microorganisms. Leached elm leaves without this flora supported growth at a lower rate. The latter diet was sufficient for survival and growth of newborn individuals; detritus, faeces or other food items were not needed. Isolated specimens grew as fast as those kept in groups. Growth was generally slower on leached leaves of oak and sycamore. In newborn animals fed on the fine roots of aquatic plants (Veronica, Rorippa and Glyceria), growth was as fast as on decaying elm leaves; growth on the green living leaves of the plants was slower, as on detritus from two streams and on a pure culture of an aquatic fungus.Consumption of leached elm leaves was related to leaf thickness. In a full gut the wet weight (1.34–1.37 mg) and volume (3.8–4.1 mm3) (for 20‐mg animals) was independent of leaf thickness but dependent on animal size, increasing 4‐fold over the range 2–50 mg body wt. Daily consumption (dry wt) was approximately equivalent to 50% body dry wt at 5 mg and 20% at 50 mg body wet wt. Individuals fed on thick leaves ingested 50% more dry weight per day and absorbed more in the gut than when fed on thin leaves, but the relative efficiency of absorption was the same at 36–59% for 10–20‐mg animals. Weight‐specific absorption in the gut was highest in juveniles and decreased with increasing body weight; relative efficiency of absorption was generally lower in the larger individuals. Assuming an energy value of 5 cal mg−1 dry wt for elm leaves, daily mean energy intake by absorption in thegutof G. pu/ex was2.2 cal mg−1 animaldry wt (9.2 J mg−1) in individuals of 0.4 mgdry wt (2 mg wet wt), decreasing to 0.3 cal mg−1 (1.3 J mg−1) at 10 mg dry wt (50 mg wet wt).Growth in Gammarus is briefly reviewed in the hght of work on other animals and it is emphasized that all aspects of feeding, growth and metabol‐ism should be specifically related to size and age of the individuals, using well defined diets.

Uptake of phosphorus from sediment by aquatic plants, Myriophyllum spicatum and Hydrilla verticillata

Eurasian water milfoil( Myriophyllum spicatum L.) and hydrilla ( Hydrilla verticillata Royle) took up most or all of their P from the hydrosoil (sediment) when the water contained 0.015 μg P ml −1 Myriophyllum continued to utilize largely hydrosoil-P with 0.5 μg P ml −1 in the water; however, when 2.0 μg P ml -1 was present in the water, the uptake of hydrosoil-P decreased and the of uptake of water-P increased. Stems of Myriophyllum cut off 2 cm above the crown transferred only 4–20 μg P/plant of hydrosoil-P into the water in the first 18 h after decapitation; thereafter, no further P release occurred. A harvesting operation would thus result in the direct transfer of only a small amount of hydrosoil-P into the water; however, the organically bound-P removed in the harvested Eurasian water milfoil plants would be derived largely from the hydrosoil, not the water body. The procedure would not be effective in reducing the P content of the lake unless its P content was higher than 0.5 μg ml −1. The specific activity of the P taken up by hydrilla was similar to that of the water extracted from the hydrosoil. It differed greatly from the specific activity of the P adsorbed on the sediment that was extracted from the hydrosoil by a weak NH 4FHCI extract. This adsorbed-P fraction, believed to be important in non-aquatic soils, was not supplying the P to the solution feeding the aquatic plant roots or was not in equilibrium with the hydrosoil solution-P.

Respiration in low oxygen partial pressures: The adults of Donacia simplex that respire from the roots of aquatic plants

The adults of Donacia simplex are found on the roots of aquatic plants during the winter. Oxygen diffuses from the gas spaces in the roots into the gas-filled cocoons through the root scar. The root scar slows down the diffusion of oxygen into the cocoons. During the winter the adults have a lower oxygen uptake between 4 and 14°C than do the emerged adults found in June. In January the respiratory rate does not vary much at different temperatures, but later in the year the QO 2 increases progressively above 8°C. The adults emerge from their cocoons when kept at 11 and 14°C in the laboratory. Adults with a high respiratory rate have a higher critical oxygen pressure than adults with a lower oxygen uptake. At low oxygen pressures (0·1 per cent) the oxygen uptake was found to be the same whatever the initial oxygen uptake in air. Adults responded to 3 days' exposure to lowered oxygen pressures (1 and 0·1 per cent) in two ways. The oxygen uptake may be depressed after the exposure to the lowered oxygen conditions compared with the initial rate in air or an oxygen debt may be accumulated. The response depended on the initial QO 2 in airand the pO 2 experienced. The adults appear to be adapted to respiration in low oxygen pressures (commonly met with on the roots of the plants during the winter) but not to the complete absence of oxygen. The respiration rate in response to temperature can be related to the temperatures likely to be encountered and the oxygen supply from the roots.

The Production of Root Hairs by Aquatic Plants

The roots of aquatic plants have received relatively little attention. They are the least known, least understood, and least appreciated parts of aquatic plants. A vivid mental picture of an aquatic plant seldom includes the roots or root hairs. The frequently grossly inaccurate statements regarding the nature and extent of root hairs in aquatic plants have suggested the need of the present study-an intensive survey of the occurrence of root hairs on the roots of aquatic plants. A record of such factual data is a necessary preliminary step before it is possible to evaluate some of the opinions regarding the occurrence and functions of roots of aquatic plants.

Biology of Mosquitoes and the Disappearance of Malaria in Denmark

AN interesting memoir on the biology of Danish Culicidas has recently been completed by Dr. C. Wesenberg-Lund (Mem. Acad. Roy. Sc. et Lettres de Danemark, Section des Sciences, Series 8, vol. 7, No. 1, 1921). Forty forest-ponds were subjected to regular fortnightly exploration for some years, and from them twenty-five species have been obtained, twenty of which have been reared from larvæ. Among these are four species of Ochlerotatus known from America, but not hitherto found in Europe. Observations on the habits of the larvae lead the author. to support the general conclusion reached by other recent workers that the anal gills are best developed in those larvas which feed at the bottom of the water. The pupæ are, as every one knows, capable of movement, but they are much more stationary than is usually believed; indeed, the author goes so far as to say that usually there is no locomotion during the whole of the pupal stage. An attempt has been made to work out the life-history of each species of Culicine from the laying of the egg onwards, and the author records many interesting observations. For instance, Ochlerotatus communis was found to lay its eggs singly on withered leaves or on the ground under neath these; the eggs are hatched in midwinter or early spring—many of them in April—and the imagines emerge in the first half of May. Mating takes place shortly afterwards, but the craving for blood does not arise until the latter part of June. Eggs are deposited upon dry bottoms from August to December, but do not hatch until they have passed through a period of frost. The biology of Taeniorhynchus Richardii also presents features of special interest; the siphon of the larva pierces the submerged roots of aquatic plants and gains access to the air in the intercellular spaces; the siphons of the pupas are brought into close apposition at their tips and are inserted into submerged roots.

Societies and Academies

PARIS. Academy of Sciences, October 5.—M. Albert Gaudry in the chair.—The influence of water on the structure of the aerial.roots of orchids, by M. Gaston Bonnier. Contact with water produces an effect on the aerial roots of many orchids, either by preventing the sclerification or lignification of the tissues' of the central' cylinder, a result which seems natural when compared with the modifications of the roots of aquatic plants, or by provoking a reaction tissue in the pericycle, capable of protecting the rest of the cylinder against the action of water.—On a class of: linear differential equations, by M, Alexander Cheasin.—The conditions which determine the sign and the magnitude of electrification by contact, by M. Jean Perrin. The contact charge between a solid and a liquid can be readily studied by means of electrical osmosis, the charge being always greater when the body, is a good ioniser, such as water.—The heats of combustion of organic compounds considered as additive properties; alcohols and phenols, ether-oxides, aldehydes and ketones, by M. P. Lemoult By assigning definite values to certain atomic groupings it is possible to calculate the heats of combustion of organic compounds of the above-mentioned classes with considerable accuracy.—The action of phosphorous acid upon mannite; remarks on mannide, by M. P. Carré. The ether