Ecological Aspects of Some Coral-Boring Gastropods and Bivalves of the Northwestern Red Sea

More than 17 molluscan species were obtained from burrows incoral substrata at Al-Ghardaga (Hurghada on maps) on the RedSea coast, six of which in particular bore into livingcolonies.The species reported in this paper belong to the families Mytilidae,Coralliophilidae, and Gastrochaenidae. The direction of boringin living corals is to the outside, the borers keeping pacewith the growing coral layer to maintain their burrows open.Coral growth is generally of a higher rate than that of borers,and burrows are accordingly mostly much larger than their inhabitants.There is evidence in such cases that burrows form initiallyby growth of coral around the settling young. Boring of Lithophagaspecies is mostly due to the abrasive action of the shell whichmoves straight and posteroventrally without any rotation. Incoralliophilids,boring is also executed mechanically by the turning movementsof the shell. Boring in dead coral is directed inwards, andburrows are nearly as large as the borers. The latter avoidthe blocking of their burrows (e.g., by a living coral incrustation)either by great siphonal extension (Rocellaria) or the freeends of the shell may be strengthened to maintain the capabilityof boring in the opposite direction (Lithophaga laevigata).Both L. luevigata and Modiola chmamomeus bore mainly mechanicallyby the rocking movements of the shell. Chemical boring is stilla possibility,particularly in the posterior narrow region ofburrows of Modiola lodging the extended pallial siphons whichare deprived of any effective mechanical devices for boring.Therole of boring algae in rarefying bored coral material hasalso to be included as an indirect chemical factor.     

DISTRIBUTION, HABITAT AND MORPHOLOGY OF THE CARIBBEAN CORAL- AND ROCK-BORING BIVALVE,LITHOPHAGA BISULCATA (d'ORBIGNY) (MYTILIDAE: LITHOPHAGINAE)

Lithophaga bisulcata is the most common Caribbean and Atlanticlithophagine and is the only species of the genus known to occurfrequently in both living and dead coral. The abundance in livingcorals is non-random and variable. Most common hosts are Siderastereasiderea and Stephanocoenia michelini. The bivalves are moreabundant in their preferred hosts than in dead coral. Individualsfrom the two habitats are indistinguishable in shell shape,musculature and size of boring and posterior pallia! glands,indicating a single population. Boreholes differ in the twohabitats with respect to size and lining. Linings are formedat the "inactive" end of the burrow; therefore living coralinhabitants line the anterior end of the burrow and dead coralborers line the posterior end. Recruitment rates are unknownin dead coral but were very low in living coral (Received 9 June 1987;     

Shell-Boring Mechanism of the Gastropod, Purpura (Thais) lapillus: a Physiological Demonstration of the Role of Carbonic Anhydrase in the Dissolution of CaCO3

Measurement of carbonic anhydrase (CA) activity in homogenatesof accessory boring organs of the muricid gastropod,Purpuralapillus, by Meldrum and Roughton's manometric method showedthat CA is always present in boring as well as in inactive ABOs,but in variable amounts. Tests by the same method on whole ABOsin an isotonic solution were negative, proving that CA remainsintracellularly. Experiments in vivo on inhibition and activation demonstratedclearly that CA is responsible for demineralization of the valvesof lamellibranchs by Purpura:(a) at low concentrations of Diamox,partial inhibition of the enzymeoccurred, that is, the numberof complete holes decreased or disappeared and etchings increased;and at higher concentrations full inhibition took place. Inhibitionis reversed when snails are replaced in normal sea water; (b)action of pure CO₂ or mixtures of CO₂ and O₂ accelerated boring:in the optimal mixture, three times more boreholes were producedby snails than in the controls, and in about half the time.Under these conditions the reaction catalyzed by CA goes tothe right with hydration of CO₂ and is accompanied by releaseof H⁺ ions; in the presence of an increased concentration ofCO₂, the reaction is intensified and results in an additionalrelease of H⁺ ions. Consequently, destruction of CaCO₃ by theABO of Purpura in sea water enriched with CO₂ is accelerated. To identify the nature of the exchanged ion, we tested the effectof NaCl and KC1 on the boring mechanism in vivo by increasingthe amount of these salts in the seawater of snails with prey.In this case augmentation of the boring activity was noticed.These results suggest that the boring activity is accompaniedby complex ionic exchanges.     

ANATOMICAL NOTES ON THE AUSTRALIAN CAMAENID LAND SNAIL SPHAEROSPIRA FRASERI (GRIFFITH & PIDGEON)

The anatomy of Sphaerospira fraseri is described as a preliminaryto the revision of the larger eastern Australian Camaenidae.Sphaerospira agrees in many character states with the generaof American Camaenidae. The camaenid pallial configuration maybe unique to the family and the advanced helicoids cannot beconsidered simply as camaenids which have acquired a dart apparatus. ^*Present address, University Museum of Zoology, Downing Street,Cambridge CB2 3EJ (Received 19 July 1977;     

Morphological and functional specializations of the shell, musculature and pallial glands in the Lithophaginae (Mollusca: Bivalvia)

The structure of the pallial glands in limestone and coral boring species of Lithophaga (Bivalvia: Lithophaginae) is examined and related to evolutionary trends in habitat specialization. Boring glands of all species occur in the middle mantle fold but display a progressive degree of complexity from simple epithelial to ducted sub-epithelial structures coinciding with increasing specialization of habitat from natural limestone to species specific live coral dwellers. The size of this gland is relatively reduced anteriorly and along the entire length of the mantle in live coral borers.     

HOMOLOGY OF THE PALLIAL AND PULMONARY CAVITY OF GASTROPODS

The development and morphology of the pallial and pulmonarycavities of various gastropods has been investigated using epoxy-resinserial sections. In the veliger larvae of Cellana sandwicensis(Patellogastro-poda), Gibbula adansonii (Vetigastropoda), Modulustectum (Caenogastropoda) and Ovatella myosotis (Pulmonata) theformation of the pallial cavity is nearly identical. After shellformation a shallow dorsal pallial groove develops beneath themantle edge. During the late veliger stage, the ectoderm formsa deep invagination along the bottom of the pallial groove onthe right side of the larva, giving rise to the pallial cavity.In the ellobiid O. myosotis the pallial cavity becomes the lung(=pulmonary cavity), without any major post-metamorphic modification.Thus, the lung of this species is clearly homologous with thepallial cavity of prosobranchs. The lung of pulmonates withveliger development, as well as of fresh water basommatophoransand stylommatophorans, can be shown to be homologous by comparisonof adult morphology. In contrast to previous views, the pulmonatelung should be regarded as truly homologous with the pallialcavity of prosobranchs and opisthobranchs. In the onchidiidpulmonate Onchidium cf. branchiferum, the larval pallial cavityshifts posteriorly after metamorphosis, where it gives riseto a lung and a cloaca. Contrary to previous interpretations,it can be shown that the onchidiid lung is homologous with atleast part of the pallial cavity. Smeagol climoi has only asmall pallial cavity and no separate lung. The previously described‘lung’ is shown to be a gland. The re-evaluationof the development and morphology of the pulmonate lung hasimportant systematic implications: (1) The pulmonary cavitydoes not represent a synapomorphic character of pulmonates.(2) The gymnomorphs cannot be separated from the remaining pulmonatesbased on lung development. (3) The lack of a lung in the smeagolidsmight give reason to reconsider this group's systematic placementwithin the pulmonates.     

The influence of food resources on the development, survival and reproduction of the two cyclopoid copepods: Cyclops vicinus and Mesocyclops leuckarti

Laboratory experiments were conducted to determine whether thetwo cyclopoid copepods. Cyclops vicious and Mesocyclops leuckaru.exploit the same food resources. The food requirements of juvenilesof the two cyclopoid copepods were investigated. Moreover, theimportance of algae for the predaceous adults was studied. Naupliiof both M leuckaru and C.vicinus successfully developed intocopepodites when fed the motile algae Chlamydomonas reinhardtii.Chlamydomonas sphaeroides and Cryptomonas sp. Threshold foodconcentrations for naupliar development varied between offeredalgae and between the two cyclopoid species. The food thresholdfor successful naupliar development, when reared on C.reinhardui,was lower for M.leuckarti (0.3 mg C 1^–1) than for C.vicinus(0.5 mg C l^–1) whereas a similar food threshold was foundusing Cryptornonas sp (0.3 mg C ^–1) and C.sphaeroides(<0.2 mg C 1^–1), Naupliar development time was inverselyrelated to food concentration. Food required for copepoditedevelopment differed for the two cyclopoid species. Cyclopsvicinus was able to develop to the adult stage on a pure dietof any one of the three algal species. whereas M.leuckarti requireda prey supply of the rotifer Brachionus rubens. Food composition.i.e. algal species, algal concentration and rotifer abundance,influenced copepodite survivorship of both cyclopoids and wasalways higher in the presence of B.rubens. Under similar foodconditions, mortality was higher for M.leuckarti than for Cvicinus. Mesocyclops leuckaru females were very dependent onanimal food. The predation rate of M.leuckaru was not lowerin the presence of algae. Egg production of M.leuckarti waslow on a pure algal diet and significantly higher when B rubenswas present. The results were used to discuss the life cyclestrategy and the possibility of exploitative competition ofthe two cyclopoid copepods.     

Isolation of Bacteria from the Corallum of Porites lobata (Vaughn) and Its Possible Significance

Bacteria were recovered from loci within skeletal regions ofthe glomerate coral,Porites lobata. The origin of these bacteriais unknown, although areas of discoloration suggest invasionfrom the substratum in the region of basal attachment. Weakenedareas of internal corallum contained from 10⁴ to 10⁵ bacteriaper gram dry weight as determined by plate counts on a peptone-agarmedium. Some of the isolated bacteria were capable of digestingchitin in vitro. This rinding suggested that the mechanism forskeletal weakening might be bacterial breakdown of the organicmatrix. Absence of change from aragonitic to calcitic crystalsfrom a discolored region supported the contention that skeletalweakening was due to the breakdown of organic matrix ratherthan dissolution of carbonate. Results were obtained as part of a survey to determine the numberand distribution of bacteria in some coral reef environments.     

A Comparison of the Growth, Photosynthesis, Stomatal Conductance and Water Use Efficiency of Moricandia and Brassica Species

When grown in pots and well-watered, the relative growth ratesof the above ground parts of two species of Moricandia (M. arvensis,an intermediate C₃–C₄ species, and M. moricandioides,a C₃ species) were inferior to those of two cultivated Brassicaspecies (B. campestris and B. napus). The Moricandia specieshad thicker leaves (greater d.wt per unit leaf area) with morechlorophyll than the Brassica species and had slightly greaterrates of photosynthesis per unit leaf area at an irradiance(400–700 nm) of 2000 µmol quanta m^–2 s ^–1.Leaves of M. arvensis, known to have a CO₂ compensation pointbetween that of C₃ and C₄ species, had a lower ratio of theintercellular to atmospheric partial pressure of CO₂ (C₁/C_a)and a greater instantaneous water use efficiency (WUE) thanthose of M. moricandioides and the Brassica species. Carbon isotope discrimination (     

DESCRIPTION OF A NEW SPECIES OF PHYLLIDIOPSIS BERGH (NUDIBRANCHIA: DORIDOIDEA: PHYLLIDIIDAE) FROM THE TROPICAL WESTERN PACIFIC, WITH COMMENTS ON THE ATLANTIC SPECIES

A new species of phyllidiid nudibranch, Phyllidiopsis shireenae,is described. The new species has a middorsal crest insteadof being flattened dorso-ventrally like most phyllidiids. Itsbody is a very pale shade of pink with black bands, and itsrhinophores are salmon pink. The anatomy of the alimentary systemand reproductive system are described. Characters originallyused by Bergh (1875) to differentiate the genus are supportedby this new species. Phyllidiopsis shi-reenae is presently knownfrom coral reef habitats in the extreme western Pacific Ocean.A review of the taxonomic status of the Atlantic specis of Phyllidiopsisis required. ^*Present address: Australian Biological and Environmental Survey.Australian National Parks and Wildlife Service, GPO Box 1383,Canberra. ACT 2601. Australia. (Received 15 August 1989; accepted 8 January 1990)     

MAINWARINGIA NEVILL, 1885, A LITTORINID GENUS FROM ASIATIC MANGROVE FORESTS, AND A CASE OF PROTANDROUS HERMAPHRODITISM

On the basis of reproductive anatomy and radula, the poorlyknown genus Mainwaringia Nevill, 1885, is shown to belong tothe Littorinidae. The genus is represented by two species, M.leithii (E.A. Smith, 1876) from India to Vietnam, and a newspecies, M. rhizophila, from Malaysia to Hong Kong. Both occurin mangrove forests. The reproductive anatomy of M, rhizophilais described in detail, and it is interpreted as a protandroushermaphrodite, a condition unique in the Littorinacea. In theintersexual and female stages both closed pallial oviduct andopen prostate are present in the mantle wall, suggesting thatthese structures are not strictly homologous. The affinitiesof Mainwaringiaare discussed, and it is concluded that it maybe most closely related to Littorina s.s. (Received 30 May 1986;     

A Comparison between the Uptake of Potassium by Plants from Solutions of Constant Potassium Concentration and during Depletion

A comparison was made between two methods of measuring the relationshipbetween the external [K⁺] and the flux of K⁺ into whole plantsof Lolium perenne and Raphanus sativus. The values of flux obtainedfrom solutions of 1.2 µM K⁺ held constant around the rootswere three and six times greater for Lolium and Raphanus respectivelythan the values obtained at the same concentration in a depletionexperiment in which the solutions, initially 100 µM K⁺,were depleted to below 1.2 µM K⁺ by plant uptake. In thedepletion experiment with Lolium, the flux was higher into plantsgrown at low [K⁺] than into plants grown at 100 µM eventhough [K⁺] within the plant was about the same for all groupsof plants. It is suggested that Lolium grown at low [K⁺] hasan efficient mechanism for K⁺ uptake which continues to operatefor some time after the plants have been transferred to a higherconcentration. With both species, K_m was 15–20 µMin the depletion experiment and below 1 µM when concentrationswere held constant.     

Growth of Actinorhizal Plants as Influenced by the Form of N with Special Reference to Myrica gale and Alnus incana

Growth of two actinorhizal species was studied in relation tothe form of N supply in water culture. Non-nodulated bog myrtle(Myrica gale) and grey alder (Alnus incana) were grown withNH₄⁺, NH₄NO₃^– or NO₃^– (4 mol m^–3 N). A nodulatedseries of bog myrtle was also cultivated in N-free medium. Relative growth rate (RGR), utilization rate of N, and shoot/rootratio were highest for the two species with the N completelysupplied as NH₄⁺. In both species, nitrate was largely reducedin the roots and the presence of NO₃^– in combined-N supplyalways affected the RGR and N utilization rate negatively. BothN₂ fixation and complete NO₃^– nutrition represented conditionsof relative N-deficiency resulting in relatively low tissue-Nconcentrations and a greater allocation of dry mass to the roots.The physiological N status of nodulated M. gale plants was comparativelygood, as indicated by a normal nodule weight ratio and a relativelyhigh N₂-fixing rate per unit nodule mass. However, whole-plantN₂-fixing capacity remained relatively low in comparison withacquisition rates of N in combined-N plants. The anion charge from the nitrate reduction was largely directlyexcreted as an OH^– efflux. H ⁺ /N ratios generally agreedwith the theory. In comparison with NH₄⁺ nutrition, carboxylateconcentrations were higher in N₂-fixing M. gale plants and theH ⁺ /N ratio in nodulated plants was less than unity below thevalue for ammonium plants as previously found for other actinorhizalspecies. Therefore, NH₄⁺ should be an energetically more attractiveN source for actinorhizal plants than N₂. The results agree with commonly accepted views on energeticsof N uptake and assimilation in higher plants and support theconcept of a basically similar physiological behaviour betweennon-legumes and legumes. Key words: Actinorhizal symbioses, ammonium, H⁺/OH^– efflux, nitrate, N₂ fixation, NRA     

Soil Solution Chemistry Controlling the Field Distribution of Melica ciliata L.

Germination, establishment and growth of Melica ciliata L.,an 'acidifuge' species of rocky habitats in Europe, were studiedexperimentally and related to chemical properties of the soilsolution, including pH, base cation composition, Al concentrationand speciation, and Mn concentration. M. ciliata failed to establishin acid leptite soil. However, it was able to grow in solutionat pH 3·6 and exhibited vigorous growth at pH 3·9,a typical soil solution pH of leptite sites, which Melica isunable to colonize. Higher concentrations of Mn than those measuredin any leptite soil solutions did not influence growth. Exposureto 0·037 mmol l^-1 (1 mg l^-1) of Al³⁺, a concentrationusually exceeded in the soil solution of leptite sites, severelyretarded root growth. Speciation technique applied to Al insoil solutions obtained by centrifugation demonstrated a closerelationship between H⁺ and Al concentrations and, in particular,between H⁺ and free ionic (quickly reacting) Al species. Soilsolution concentrations of free ionic Al proved to be < 0·002mmol l^-1 in sites lacking Melica , but often > 0·10mmol l^-1 in site lacking Metalica . It is concluded that theinability of M. ciliata to establish in acid soils is not primarilydue to the high H⁺ concentration but to the high soil solutionconcentrations of Al, especially free Al ionic species at lowsoil pH.Copyright 1993, 1999 Academic Press Melica ciliata, distribution, soil solution, pH, aluminium speciation, manganese, base cations, iron     

PREDATION ON THE BIVALVE CHOROMYTILUS MERIDIONALIS (KR.) BY THE GASTROPOD NATICA (TECTONATICA) TECTA ANTON

The effects of a population of the boring gastropod Natica tectaon the bivalve Choromytilus meridionalis were investigated atBailey's Cottage, False Bay, South Africa. In July 1979 theN. tecta density on the mussel bed averaged 69 m^–2 andthe population consisted mainly of reproductively mature individualsbetween 20–33 mm shell width. Laboratory experiments on N. tecta showed that prey size selectionis an increasing function of predator size. The prey size rangetaken by large N. tecta is also greater than that taken by smallindividuals. The position of the borehole on the mussel shellis a function of the way in which the shell is held by the footduring the boring process. Consumption rates measured in thelaboratory showed an increase from approximately 1 kJ per weekin 18 mm N. tecta to 4.5 kJ per week in 28 mm individuals. Populationconsumption in the field was calculated as 663 kJ m^–2month^–1. It was estimated that at this rate the standingcrop of mussels in the pool would be eliminated within 10 months.Field measurements showed significant depletion after 6 months. New spat settlement of mussels occur every 4–6 years.The growth curve shows that after one year the population meansize exceeds 30 mm shell length, which is beyond the prey selectionsize range of small N. tecta. It was concluded that at the timeof a new mussel settlement a niche is provided for the simultaneoussettlement and growth of juvenile N. tecta in high densities.However, within one year the increase in prey size, togetherwith depletion due to over-exploitation, limits population growthand density in N. tecta. (Received 14 March 1980;     

Interannual changes in the biomass of the Black Sea gelatinous zooplankton

The 15 year changes in the total gelatinous biomass consistof a general trend to increase, from 250 gm^–2 in 1980to 2500 g m^–2 in 1995, and fluctuations with a periodof –4 years performed against the background of this trendin the upper 150 m layer. Different species occupying distincttrophic niches form these peaks. When represented as the percentageof the total zooplankton biomass, Aurelia aurita and Mnemiopsisleidyi exhibit the contra-phase fluctuations where a sharp increasein M.leidyi is accompanied by a decrease in the A.aurita biornass.     

Nitrogen utilization by plant species from acid heathland soils: II. Growth and shoot/root partitioning of NO3- assimilation at constant low pH and varying NO3-/NH4+ ratio

The growth of four heathland species, two grasses (D. flexuosa,M. caerulea) and two dwarf shrubs (C. vulgaris, E. tetralix),was tested in solution culture at pH 4.0 with 2 mol m^–3N, varying the N0₃^–/NH₄⁺ ratio up to 40% nitrate. In addition,measurements of NRA, plant chemical composition, and biomassallocation were carried out on a complete N0₃^–/NH₄⁺ replacementseries up to 100% nitrate. With the exception of M. caerulea, the partial replacement ofNH₄⁺ by NO₃^– tended to enhance the plant's growth ratewhen compared to NH₄⁺ only. In contrast to the other species,D. flexuosa showed a very flexible response in biomass allocation:a gradual increase in the root weight ratio (RWR) with NO₃^–increasing from 0 to 100%. In the presence of NH₄⁺, grassesreduced nitrate in the shoot only; roots did not become involvedin the reduction of nitrate until zero ambient NH₄⁺. The dwarfshrubs, being species that assimilate N exclusively in theirroots, displayed an enhanced root NRA in the presence of nitrate;in contrast to the steady increase with increasing NO₃^–in Calluna roots, enzyme activity in Erica roots followed arather irregular pattern. Free nitrate accumulated in the tissuesof grasses only, and particularly in D. flexuosa. The relative uptake ratio for NO₃^– [(proportion of nitratein N uptake)/(proportion of nitrate in N supply)] was lowestin M. caerulea and highest in D. flexuosa. Whereas M. caeruleaand the dwarf shrubs always absorbed ammonium highly preferentially(relative uptake ratio for NO₃^– <0.20), D. flexuosashowed a strong preference for NO₃^– at low external nitrate(the relative uptake ratio for N0₃^– reaching a value of2.0 at 10% NO₃^–). The ecological significance of thisprominent high preference for NO₃^– at low NO₃^–/NH₄⁺ratio by D. flexuosa and its consequences for soil acidificationare briefly discussed. Key words: Ammonium, heathland lants, N0₃^–/NH₄⁺ ratio, nitrate, nitrate reductase activity, soil acidification, specific absorption rate     

The colonial cyanobacterium Trichodesmium as a physical and nutritional substrate for the harpacticoid copepod Macrosetella gracilis

The pelagic harpacticoid copepod Macrosetella gracilis usesthe colonial cyanobacterium Trichodesmium not only as a physicalsubstrate for juvenile development, but also as a food source.By associating itself with a buoyant colonial cyanobacterium,M.gracilis has developed a successful mode of life for existencein the plankton. Further evidence of M.gracills' dependenceon Trichodesmium as a physical substrate is demonstrated bypreviously undescribed microscopic observations of a gravidM.gracilis female attaching eggs to a Trichodesmium colony.Shipboard experiments investigating the ingestion and assimilationof Trichodesmium carbon (C) were conducted in September 1991and January/February 1992 in waters of the Bahamas and the Caribbean,respectively. Macrosetella gracilis not only ingested, but rapidlyincorporated, cyanobacterial organic matter into its own cellularmaterial. Utilization of ingested Trichodesmium by M.graciliswas investigated by assessing the metabolic partitioning andincorporation of ¹⁴C-labelled Trichodesmium into copepod lipids,proteins, polysaccharides and low-molecular-weight (LMW) compoundsusing sequential biochemical fractionation techniques. Despitevariations in grazing rates between the two sites and times(September 1991,0.017 µg C^* µg^–1 C h^–1;January 1992, 0.134 µg C ^* µg^–1 C h^–1,the partitioning of incorporated C into the different biochemicalfractions was relatively consistent. There was rapid assimilationof ingested C into the LMW ({small tilde}60%) and polysaccharidefractions ({small tilde}30%) in the first few hours, with asubsequent increase in the percent C incorporated into protein.On average, {small tilde}21% of the Trichodesmium C ingestedby M.gracilis was assimilated. Therefore, M.gracilis is an importantsecondary link in the food web of oligotrophic waters whereTrichodesmium is abundant.     

THE PALLIAL EYES OF CTENOIDES FLORIDANUS (BIVALVIA: LIMOIDEA)

The structure of the pallial eye in the Limidae has neverbeen elucidated properly, largely because they are difficultto see among the mass of surrounding mantle tentacles and becausethey are few, small, and lose their pigmentation when preserved.Possibly two eye types are present, simple cup-shaped receptorsin species of Lima, like those seen in the Arcoida, and morecomplex invaginated ones in Ctenoides. The pallial eyes (;18on both lobes) of Ctenoides floridanus are formed by invaginationof the middle mantle fold at the periostracal groove, so thatall its contained structures are derived from the outer andlight is perceived through the inner epithelia of this fold.The eye comprises a simple multicellular lens and a photoreceptiveepithelium beneath it of lightly pigmented cells and alternatingvacuolated, support cells. In some species of the Arcoidea, Limopsoidea and Pterioidea, pallialeyes occur on the outer mantle fold and thus beneath the periostracum(and shell). The pallial eyes of Ctenoides floridanus and otherpterioideans, e.g. species of the Pectinidae, occur on the middlefold and may thus have improved vision. In the Cardiodea, Tridacniidaeand Laternulidae (Anomalodesmata) pallial eyes occur on theinner folds. There is thus a loose phylogenetic trend, in which Ctenoidesis a critical link, of increasing eye sophistication correlatedwith the historical age of the clades possessing them. (Received 16 November 1999; accepted 20 January 2000)     

Sodium Accumulation in Pappophorum I. Uptake, Transport and Recirculation

The uptake, transport and accumulation of sodium were comparedin two grasses: Pappophorum pappifervm (Lam.) O. Kuntze, a glycophyteand P. philippianum L. R. Parodi, a facultative halophyte. Atlow salinity levels, (50 mM NaCl) shoots of salt-treated P.pappiferum accumulated lower Na⁺ concentrations than the otherspecies. This difference does not seem to be related to Na⁺uptake, as in short-time experiments (< I h), whole plantsof both species showed similar rates of Na⁺ uptake and transport Sodium recirculation was assessed in split-root experiments.It was similar in control (previously non-salinized) plantsof both species, but in salt-treated plants it was more significantin P. pappiferum. This mechanism, along with increased lossof recently acquired Na⁺, could contribute to keep Na⁺ levelslower in shoots of P. pappiferum than in P. philippianum. Pappophorum, Gramineae, sodium recirculation, salinity