Effect of temperature and food concentration on post-embryonic development, egg production and adult body size of calanoid copepod Eurytemora affinis

Post-embryonic development time, egg production rate and adultbody size of calanoid copepod Eurytemora affinis from Lake Ohnuma,Japan, were determined under six temperature-food conditions(10³,5 x 10³, 10⁴ and 5 x 10⁴ cells ml^–1 at 15°C,5 x 10⁴ cells ml^–1 at 10and20°C) in the laboratory.The measured parameters varied with both temperature and foodconcentration. Development time from hatching to adult femalewas 9.2, 11.4 and 22.8 days at 20, 15 and 10°C respectively,at the highest food concentration. The males developed to adultat one to two days earlier than the females. An effect of foodshortage on development time occurred at the lowest food concentration.This development time was 24.8 days even at 15°C, beingtwice as long as that at the highest food concentration. Prosomelength of these food-limited females was approximately 75% ofwell-fed ones, which reduced by only 10% with increasing temperaturefrom 10 to 20°C. Clutch size (C, eggs clutch^–1) ofwell-fed individuals depended on prosome length of the adultfemale (L, mm), and was expressed as an equation: C = 65.2 L³⁸³. Clutch size of individuals reared at less than 10⁴ cellsml^–1, however, mostly laid below the estimated curve,especially at the lowest food concentration being only 10% ofthat at the highest food concentration. These results suggestthat food availability is a more important factor affectingpopulation growth of E.affinis in Lake Ohnuma than variationof temperature.     

GROWTH OF JUVENILE BITHYNIA TENTACULATA (PROSOBRANCHIA, BITHYNIIDAE) UNDER DIFFERENT FOOD REGIMES: A LONG-TERM LABORATORY STUDY

The growth of juvenile Bithynia tentaculata (Proso-branchia,Bithyniidae) was measured under controlled laboratory conditionsover 18 months. The animals were fed with different concentrationsof suspended food (Chlamydomonas reinhardii at 2, 000 cells.ml^–1and at 10, 000 cells.ml^–1), solid food (lettuce) and combinationsof both (lettuce with 2, 000 cells.ml^–1 and with 10, 000cells.ml^–1 Chlamydomonas). The growth of all animals wasmeasured weekly, and after 1 years final shell sizes, shelldry weights and ash-free dry weights, as well as soft body dryweights and ash-free dry weights were determined. Survival rateof the animals increased from 20% when fed with 2, 000 algalcells.ml^–1 to 75% with lettuce and 10, 000 cells.ml^–1as food. Final shell sizes and shell weights were not influencedby food, but soft body dry weights were significantly reducedwhen animals were fed on suspended food only. Reproduction (i.e.egg laying) was observed at the end of the second summer whenlettuce (with or without algal addition) was given as food.The ecological consequences of these results are discussed. (Received 7 April 1993; accepted 9 August 1994)     

Copepod egg production, moulting and growth rates, and secondary production, in the Skagerrak in August 1988

Measurements of hydrography, chlorophyll, moulting rates ofjuvenile copepods and egg production rates of adult female copepodswere made at eight stations along a transect across the Skagerrak.The goals of the study were to determine (i) if there were correlationsbetween spatial variations in hydrography, phytoplankton andcopepod production rates, (ii) if copepod egg production rateswere correlated with juvenile growth rates, and (iii) if therewas evidence of food-niche separation among co-occumng femalecopepods The 200 km wide Skagerrak had a stratified water columnin the center and a mixed water column along the margins. Suchspatial variations should lead to a dominance of small phytoplanktoncells in the center and large cells along the margins; however,during our study blooms of Gyrodinium aureolum and Ceratium(three species) masked any locally driven differences in cellsize: 50% of chla was >11 µm, 5% in the 11–50µm fraction and 45% <50 µm. averaged for allstations. Chlorophyll ranged from 0.2 to 2.5 µg l^–1at most depths and stations. Specific growth rates of copepodsaveraged 0.10 day^–1 for adult females and 0.27 day^–1for juveniles The latter is similar to maximum rates known fromlaboratory studies, thus were probably not food-limited. Eggproduction rates were food-limited with the degree of limitationvarying among species: 75% of maximum for Centropages typicus, 50% for Calanus finmarchicus, 30% for Paracalanus parvus and 15% for Acartia longiremis and Temora longicornis. Thedegree of limitation was unrelated to female body size suggestingfood-niche separation among adults. Copepod production, summedover all species, ranged from 3 to 8 mg carbon m^–3day^–1and averaged 4.6 mg carbon m^–1 day^–1. Egg productionaccounted for 25% of the total.     

Food type induces different reproductive responses in the copepod Centropages typicus

Egg production and hatching success were determined for individualCentropages typicus fed two diatoms (Thalassiosira rotula andPhaeodactylum tricomutum) and two dinoflagellates (Prorocen-trumminimum and Gonyaulaxpolyedrd). Both reproductive responseswere strongly affected by food type. Females incubated withoutmales produced eggs with all diets, but fecundity was twiceas high with the larger T. rotula and G.polyedra cells. In contrast,hatching success was 2–3 times higher with the dinoflagellatediets. The presence of males did not enhance egg productionrates. Males also did not improve hatching success when thediet consisted of the diatom T.rotula. However, egg viabilitywas higher for couples fed the dinoflagellate G.polyedra, indicatingthat egg viability was possibly being controlled by both rematingand food type. Egg viability was artificially lowered by exposingnewly spawned eggs to high concentrations (10⁴–10⁹ pgC) of extracts from T.rotula, whereas the development of eggsproceeded normally at all concentrations of extracts from P.minimum.Blockage of egg development was not due to anoxia, but to thepresence of intracellular, deleterious chemical compounds indiatoms, suggesting that bottom-up prey control mechanisms underlieseasonal fluctuations in C.typicus populations at sea.     

Discontinuite hydrobiologique dans le detroit du Pas-de-Calais

Hydrobiological studies in the Straits of Dover show a differencebetween the characteristics of the French coastal water andthe open sea water. A cruise between Boulogne-sur-mer and Dover(October 15, 1985) confirms the existence of a frontal area(4 miles off the French coast). This area is characterized byan increase of the salinity (1%) and decrease of the suspendedmatter content (from 27 to 20 mg l^–1), of primary production(from 15 to 3 mg C m^–3h^–1) and of chlorophyll aconcentration (from 4.5 to 1.5 mg m^–3). The presence ofdifferent zooplanktonic species in the two water masses alsocharacterizes this discontinuity. Oncaea sp., Corycaeus anglicus,Centropages typicus and Calanus helgolandicus are indicatorspecies of open sea water, while Cyciopina littoralis and ‘Saphirella’are only present in coastal water.     

The seasonal abundance of the phototrophic ciliate Mesodinium rubrum in Southampton Water, England

The abundance of the marine phototrophic planktonic ciliateMesodinium rubrum was monitored throughout an annual cycle attwo stations in the Southampton Water estuary. Seasonal changesin the concentration of nitrate, ammonia and phosphate weremonitored both at the inner estuary station (NW Netley) andouter estuary station (Calshot). Nutrient levels in the winterwere similar at both stations, and were diminished during sequentialdiatom blooms dominated initially by Sketetonema costatum andthen by Rhizosolenia dclicatula. Nitrate was reduced to a seasonalminimum in the outer estuary following these spring diatom blooms,but in the inner estuary was sustained >500 µg I^–1until the onset of the M.rubrum bloom. During the developmentof a visible red tide of M.rubrum in June/July at NW Netley,nutrient concentrations were considerably reduced. Cell numbersof M.rubrum varied between 2 and 3 cells ml^– during winterto >400 cells ml^–1 during the bloom at NW Netley, whereasat Calshot cell abundance did not increase above 25 cells ml^–1at any time of the year. At NW Netley, dense accumulations ofthe ciliate occurred over restricted depth intervals duringthe bloom and possible factors influencing the observed verticaldistribution of cells are considered. ¹Present address: Biology Department, Faculty of Science, AddisAbaba University, PO Box 1176, Addis Ababa, Ethiopia     

Infection of Coscinodiscus granii by the parasitoid nanoflagellate Pirsonia diadema: III. Effects of turbulence on the incidence of infection

The influence of turbulence on the incidence of infection ofthe diatom Coscinodiscus granii by the parasitoid nanoflagellatePirsonia diadema was investigated experimentally with two initialhost densities. Independently of the initial diatom densitiesof 7 and 44 cells ml^–1, under calm conditions both diatomsand parasitoids became extinct within 6–9 days. Turbulence,however, led to the survival of diatoms at a reduced densityof 0.1–2 cells ml^–1 for >30 days. A population-dynamicmodel is formulated that takes into account the non-homogeneousdistribution of infecting flagellates among host diatoms. Applicationof the results to parasitoid–diatom interactions in naturalwaters suggests that, under turbulent conditions, endemic infectionsmay effectively prevent the mass development of host diatoms.     

Relationships between fecal pellet production and feeding in the calanoid copepod Boeckella

The number, size (mm³ pellet ^–1) and total volume of fecalpellets produced (mm³ h^–1) by Boeckella titicacae increasedwith concentration of Chlorella and natural seston in threedifferent lakewaters from Bahia de Puno and Lago Grande of LakeTiticaca and nearby Laguna Arapa. The three lakewaters differedin the size and number of fecal pellets produced at seston concentrations>0.5 mg dry wt l^–1. However, the total volume of fecalpellets egested varied little. Large-sized food (>10 µg)resulted in larger pellets but smaller total fecal production.Food concentration had parallel effects on the production offeces and on feeding rates. Both fecal production and feedingincreased linearly with food concentration with saturation between5 and 7.5 x 10⁵ Chlorella ml^–1 (3.7–5.6 mg dry wtl^–1). Varied responses in fecal production when fed differentsize fractions of lake seston suggest Boeckella has a complexand flexible feeding behavior. Feeding preferences of B.titicacaeand B.occidentalis (Ivlev index) for two seston size fractionsare generally reflected by fecal production.     

Development, growth and egg production of Centropages abdominalis in the eastern subarctic Pacific

Centropages abdominalis is a neritic, omnivorous, temporallyabundant copepod present throughout the subarctic Pacific andits marginal seas. The two main objectives of this study wereto determine how temperature influences the development of C.abdominalis and whether growth rates of in situ populationsmay be limited by available food. At 6.9°C, median developmenttime from eggs laid to 50% adults was 42 days and the averageweight-specific somatic growth rate was 0.17 day^–1. At4.6°C, median development time to adult was 59 days (projected)and growth rate averaged 0.08 day^–1, suggesting that 4.6°Cmay be approaching the lower temperature for development andgrowth in this species. The functional relationship betweendevelopment time and temperature was established over the temperaturerange in which this species occurs. The in situ adult growthrates between 10 and 13°C averaged 0.14 day^–1 andwere generally lower than the laboratory-reared juvenile growthrates, which may indicate that adult C. abdominalis are foodlimited in the field during summer and autumn.     

Food selection and growth of the planktonic ciliate Coleps hirtus isolated from a monomictic subtropical lake

A strain of Coleps hirtus (Ciliophora, Prorodontida) was isolatedfrom the epilimnion of monomictic Lake Kinneret. Growth of thisciliate was tested in response to 12 species of planktonic algaeand seven species of cultured bacteria from lake isolates whichwere offered as food. Eight species of algae (one Cryptophyceaeand seven Chlorophyceae) and four bacteria supported good toexcellent growth of C.hirtus. Growth rates (µ) and doublingtimes (DT) ranged from 0.008 to 0.029 h^–1 and from 23.9to 90.8 h respectively. C.hirtus was able to grow on bacteriaat concentration levels as low as 2–8 x 10⁵ cells ml^–1.No correlation was observed between growth rate of C.hirtusand cell volume of the prey. ^aPresent address: Istituto di Ecologia, Universita di Parma,43100 Parma, Italy     

The relative importance of food and temperature to copepod egg production and somatic growth in the southern Benguela upwelling system

The fecundity and somatic growth rates of Calanus agulhensisand Calanoides carinatus, the dominant large calanoid copepodsin the southern Benguela upwelling system, as well as the fecundityof several other common copepods, were measured between Septemberand March of 1993/94 and 1994/95. Mean egg production of mostcopepods was low at >30 eggs female^-1 day^-1 {Calanoides carinatus23.7, Calanus agulhensis 19.0, Neocalanus tonsus 16.1 and Rhincalanusnasutus 26.1), whereas the mean fecundity of Centropages brachiatuswas significantly greater (83.6 eggs female^–1 day^-1).This study also presents the first comprehensive field estimatesof the fecundity of Nanno-calanus minor (mean: 26.1 eggs female^–1day^–1, range: 0.0–96.2 eggs female^–1 day^–1)and of somatic growth of N6 and all copepodite stages of Calanoidescarinatus (decreasing from 0.58 day^–1 for N6 to 0.04 day^–1for C5). Somatic growth rates of Calanus agulhensis also declinedwith age: from 0.57 day1 for N6 to 0.09 day1 for C5. Data ongrowth rates were used to assess the relative importance offood [as measured by total chlorophyll (Chi) a concentration],phytoplankton cell size (proportion of cells >10 µm)and temperature to the growth of copepods. Multiple regressionresults suggested that fecundity and somatic growth rates werepositively related to both Chi a concentration and phytoplanktoncell size, but not to temperature. Although it was not possibleto separate the effects of Chi a concentration and phytoplanktoncell size, data from previous laboratory experiments suggestthat copepod growth is not limited by small cells per se, butby the low Chi a concentrations that are associated with theseparticles in the field. Despite growth not being directly relatedto temperature, a dome-shaped relationship was evident in somespecies, with slower growth rates at cool (<13°C) andwarm (>18°C) temperatures. The shape of this relationshipmirrors that of Chi a versus temperature, where poor Chi a concentrationsare associated with cool and warm temperatures. It is concludedthat the effect of food limitation on growth of copepods outweighsthat of temperature in the southern Benguela region. Sourcesof variability in relationships between growth and Chi a concentrationare discussed.     

Effects of rotifers and ciliates on the growth and survival of Daphnia

Daphnia can suppress ciliates and rotifers through predationand interference competition, but it is not known whether thisproduces any direct benefit to Daphnia. We conducted survivorshipand cohort lifetable experiments to determine whether Daphniacan utilize ciliates and rotifers as food. Three species ofoligotrich ciliates (Halteria grandinella, Strobilidium gyransand Strobilidiumvelox) and one rotifer (Keratella cochlearis)were used. Lifetable experiments were conducted with a basallevel of algae (Cryptomonas sp.), plus either ciliates or rotifers,while survivorship experiments had only the rotifers or ciliates.Densities of 30 H.grandinella ml^–1, 50 S.gyrans ml^–1and 15 S.velox ml^–1 enhanced Daphnia pulex's populationgrowth rate 35–50% over controls with only algae. TenS.gyrans ml^–1 did not produce a significant change inDaphnia's growth rate. Densities of 100 and 300 K.cochlearis^–1 increased Daphnia population growth rates by II and10%, respectively. Both 10 and 50 S.gyrans ml^–1 enhancedDaphnia's survivorship compared to starved controls, but neither100 nor 300 K.cochlearis l^–1 enhanced its survivorship.The amount of enhancement of Daphnia growth rates by rotifersand ciliates is roughly proportional to the death rates imposedby Daphnia. The death rate imposed by Daphnia on rotifers isa function of both algal density and Daphnia size. Per unitbiomass, neither ciliates nor Keratella appear to be as nutritiousfor Daphnia as is Cryptomonas.     

Copepod grazing on a phytoplankton community containing the toxic dinoflagellate Dinophysis acuminata

Copepod grazing on the toxic dinofiagellate Dinophysis acuminatafrom the west coast of France (La Rochelle) was studied witha concentrated (40–70 µm) phytoplankton assemblagedominated by Leptocylindrus danicus, D.acuminata, Ceratium fususand Ceratium furca. Copepod nauplii were also present. Threeto five copepods/copepodites (Acartia clausi, Isias clavipesand Centropages typicus) were incubated together with the phytoplankton.Dinophysis acuminata was grazed upon by all copepod species.However, to some extent, I.clavipes and C.typicus avoided itas food. Dinophysis acuminata cells represented for them only5–10% of total ingested carbon during the first 24 h,and almost all individuals survived and thrived well. In contrast,A.clausi did not avoid D.acuminata. which represented 30% ofingested carbon in 1 day. Acartia clausi then had a lower survivalthan the two other copepod species. However, the survival ofA.clausi was high in control incubations, where a plankton communitywithout D.acuminata was used as food. It is concluded that theokadaic acid of D acuminata is potentially toxic to some grazers,and/or might function as an allelopathic grazer repellent.     

Effects of Olisthodiscus luteus on the feeding and reproduction of the marine rotifer Synchaeta cecilia

The chrysophyte Olisthodiscus luteus is not ingested by Synchaetacecilia. It inhibits the feeding on other, acceptable food atO. luteus densities as low as 50 cells ml^–1 and reducessurvival and reproduction at O. luteus densities > 10³ cellsml^–1. The possible mechanisms and implications of thisphenomenon for the distribution and abundance of S. ceciliaare discussed.     

A study of feeding in predacious ciliates using prey ciliates labeled with fluorescent microspheres

Feeding in predacious estuarine ciliates was investigated ina series of laboratory experiments using a new method of preylabeling which facilitates microscopic indentification of ingestedprey items. Ingestion rates of Mesodinium pulex, Euplotes vannusand E.woodruffi were estimated using the appearance, insidethe predator, of bacteriovorous ciliates (Metanophrys sp., Cyclidiumsp.and Pleuronema sp ) labeled with fluorescent microspheres. Preyremain motile and have presumably unaltered surface characteristics.Ingestion rates of log-growth phase predators increased withprey density. Mesodinium pulex ingested 0 15–0.32 cellsh^–1 over a prey concentration of 60–2300 ml^–1.Maximum ingestion rates of E. woodruffi and E. vannus were 4.5and 3.4 cells h^–1 respectively, estimated at prey abundancesof 75 and 172 cells ml^–1 respectively. Comparisons offeeding rates on prey of different sizes, and the effects ofstarvation, indicated that ingestion is likely limited by differentfactors in ‘raptorial’ (M pulex) and ‘filterfeeding’ (Euplotes spp.) predators.     

Is fecundity modified by crowding in the copepod Centropages typicus?

Experiments were conducted to test the effect of overcrowdingon egg production rates in the copepod Centropages typicus.Fertility was not significantly reduced by the presence of otherconspecifics when the volume of water was the same for femalesincubated alone or in the presence of other females and males.There was no evidence of chemical cues affecting egg productionwhen females were kept in large (1 female in 100 ml sea water[SW] or small (1 female in 25 ml SW) volumes of water, withor without partitions, and in the presence or absence of foodor males. Also, spawning rate was not reduced when females wereincubated in flow-through experimental chambers which alloweddiffusion of pheromones between females incubated alone or inhigh densities (100 ind. in 50 ml SW). Only when females wereplaced at unnaturally high densities (1 female ml^–1) wasegg production significantly reduced, probably due to physicaldisturbance and increased number of collisions rather than chemicalcommunication among individuals. The results show that chemicalcues do not affect spawning behaviour when population densitiesare close to field conditions. By contrast, overcrowding inducedby swarming or aggregation may potentially limit reproductivesuccess due to reduced feeding, and production and cannibalismof eggs.     

Density and distribution of bacterioplankton and planktonic ciliates in the Bering Sea and North Pacific

The total number of planktonic bacteria in the upper mixed layerof the Bering Sea during the late spring-early summer periodranged between 1 and {small tilde}4 x 10⁶ ml^–1 (biomass10–40mg C m^–3). In the northern Pacific, along 47–52⁶N,the corresponding characteristics of the bacterioplankton densityin the upper mixed water layer were: total number 1–2x 10⁶ cells ml^–1 and biomass 15–46mg C m^–3Below the thermocline at 50–100 m, the density of bacterioplanktonrapidly decreased. At 300 m depth, it stabilized at 0.1–0.2x 106 cells ml^–1. The integrated biomass of bacterioplanktonin the open Bering Sea ranged between 1.2 and 3.6 g C m^–2(wet biomass 6–18 g m^–2) Its production per dayvaried from 2 to 23 mg C m^–3 days^–1 in the upper0–100 m. The numerical abundance of planktonic ciliatesin this layer was estimated to be from 3 to l0 x 10³ cells l^–1,and in the northern Pacific from 0.4 to 4.5 x 10³ l^–2.Their populations were dominated by naked forms of Strombidium,Strombilidium and Tontonia. In some shelf areas, up to 40% ofthe total ciliate population was represented by the symbioticciliate Mesodinium rubrum. The data on the integrated biomassof basic groups of planktonic microheterotrophs are also presented,and their importance in the trophic relationships in pelagiccommunities of subarctic seas is discussed.     

Growth and development of Neocalanus flemingeri/plumchrus in the northern Gulf of Alaska: validation of the artificial-cohort method in cold waters

In situ growth and development of Neocalanus flemingeri/plumchrusstage C1–C4 copepodites were estimated by both the artificial-cohortand the single-stage incubation methods in March, April andMay of 2001–2005 at 5–6°C. Results from thesetwo methods were comparable and consistent. In the field, C1–C4stage durations ranged from 7 to >100 days, dependent ontemperature and chlorophyll a (Chl a) concentration. Averagestage durations were 12.4–14.1 days, yielding an averageof 56 days to reach C5, but under optimal conditions stage durationswere closer to 10 days, shortening the time to reach C5 (fromC1) to 46 days. Generally, growth rates decreased with increasingstage, ranging from 0.28 day^–1 to close to zero but weretypically between 0.20 and 0.05 day^–1, averaging 0.110± 0.006 day^–1 (mean ± SE) for single-stageand 0.107 ± 0.005 day^–1 (mean ± SE) forartificial-cohort methods. Growth was well described by equationsof Michaelis–Menten form, with maximum growth rates (G_max)of 0.17–0.18 day^–1 and half saturation Chl a concentrations(K_chl) of 0.45–0.46 mg m^–3 for combined C1–3,while G_max dropped to 0.08–0.09 day^–1 but K_chl remainedat 0.38–0.93 mg m^–3 for C4. In this study, in situgrowth of N. flemingeri/plumchrus was frequently food limitedto some degree, particularly during March. A comparison withglobal models of copepod growth rates suggests that these modelsstill require considerable refinement. We suggest that the artificial-cohortmethod is the most practical approach to generating the multispeciesdata required to address these deficiencies.     

Ontogeny of growth, respiration and feeding rate of the freshwater calanoid copepod Eudiaptomus graciloides

The calanoid copepod, Eudiaplomus graciloides, was reared fromegg to adult on uni-algal diets (0.1. 0.5 and 2.5 mg dry wt1^–1) using the green alga, Chlamydomonas reinhardtii,as food, or on a mixed diet consisting of Lake Esrom water filteredthrough a plankton net with pore size 45 µm and supplementedwith C. reinhardtii (2.5 mg dry wt 1^–1). On the mixeddiet at 21.0°C growth in body dry wt (W, µg dry wt)was exponential, and the growth constants were 0.21 day^–1in the early to mid juvenile stage (N1 - C4) and 0.11 day^–1in the late juvenile to early adult stage (C4-A). At 14.5°Cthe corresponding growth rate constants were 0.10 and 0.08 day^–1.Similar growth rates were found at uni-algal concentrationsof 0.5 and 2.5 mg dry wt I^–1, and it was argued that thethreshold concentration for growth in Eudiaptomus was closeto 0.1 mg dry wt I^–1. The clearance (C, ml h^–1)of copepodites was measured on the uni-algal diets. The constantsof the regression (C = aW^b) were: a = 0.125, b = 0.858 (2000C. reinhardtii ml^–1), a = 0.068, b = 0.849 (10 000), a= 0.028, b = 0.875 (50 000). Ingestion rates were calculatedfrom the clearances and the average algal concentrations. Atthe three food levels the average daily rations were 30, 67and 125% of body dry wt. The respiration rate (R, nl O₂ h^–1)was measured in individuals reared on the mixed diet. The constantsof the regression (R = aW^b) were: a = 4.82, b = 1.07 (nauplii,14.5°C), a = 4.17, b = 0.904 (copepodites and adults, 14.5°C),a = 6.87, b = 0.757 (copepodites and adults, 21.0°C). Nosignificant difference in the respiration rate of copepoditesreared on uni-algal diets and the mixed diet could be demonstrated.Energy budgets were calculated. The assimilation efficiencyand the gross growth efficiency of copepodites decreased markedlywith increasing food concentration, the net growth efficiencyvaried from an average of 0.44 at the lowest algal concentrationto 0.60 on the mixed diet. The results are discussed in relationto previous findings with both freshwater and marine copepods.     

The Composition of Phloem Exudate and Xylem Sap from Tree Tobacco (Nicotiana glauca Grah.)

The composition of xylem sap and exudate from stem incisionsof Nicotiana glauca Grah. was compared in detail. Exudationfrom stem incisions occurred over a 5 min period in certainplants, enabling collection of 5–30 µl of sap. Therate of exudation showed an exponential decline. Exudate hada high dry matter content (170–196 mg ml^–1) andhigh sugar (sucrose) levels. Xylem sap had a low pH (5.8) andexudate a pH of 7.9. Glutamine dominated the amino compoundsin xylem sap and exudate, and K⁺ was the major cation. Totalamino compounds in stem exudate reached 10.8 mg ml^–1 whereasxylem sap contained much lower levels (0.28 mg ml^–1).All mineral elements and amino compounds with the exceptionof calcium were more concentrated in stem exudate than in xylemsap. Sucrose was labelled heavily in stem exudate following pulsingof an adjacent leaf with ¹⁴CO₂. A concentration gradient ofsugar (2.1 bar m^–1) was recorded for stems. Levels ofsucrose, amino compounds and K⁺ ions in stem exudate showeda diurnal periodicity. Each commodity reached maximum concentrationat or near noon and minimum concentration about dawn. The evidencesuggests that exudate from stem incisions of N. glauca is arepresentative sample of solutes translocated in the phloem. Nicotiana glauca Grah., phloem sap, xylem sap, sucrose, amino compounds, mineral ions