Feeding, growth and food conversion of the marine cladoceran Penilia avirostris

Ingestion and clearance rates, feeding behaviors and life historyvariables of the marine cladoceran Penilia avirostris were evaluatedover a range of food concentrations encountered in nature (0.01–3.0mm³ 1^–1 of Isochrysis galbana). Ingestion rates increasedand clearance rates decreased with increasing food concentration.No maximum feeding thresholds were observed over the range ofalgal concentrations offered. Weight-specific ingestion ratesdecreased with increasing body weight. Feeding behaviors suchas mandibular activity, abdominal claw rejections of cloggedfeeding structures and feeding appendage activity decreasedat a food level of 0.3 mm³ l^–1 of l. galbana. Peniliaavirostris had very poor survivorship at extremely low (0.01mm³ l^–1 and high (3.00 mm³ l^–1) food levels. Mortalitywas hardly affected at food levels of 0.03–1.0 mm³ l^–1Reproduction did not occur at food levels of     

Effects of different natural regimes of temperature and food on survival, growth and development of Artemia monica Verrill

Each year, two generations of Artemia monica Verrill developunder different environmental conditions in hypersaline MonoLake, California, USA. The first generation develops duringspring when food levels are high and temperatures are low andwarming slowly. The second generation develops during summerat low food levels and higher initial temperatures which continueto warm. In three experimental treatments, the development,growth and survival of first-and second-generation Artmia weredetermined under laboratory conditions which tracked the naturaltemperature and food regimes in the lake. Two food treatmentswere administered concurrently at low temperatures to first-generationshrimp, representing the high levels usually found during thespring (spring-high-food) and reduced food levels observed duringa recent 6 year period of meromixis (spring-low-food). The thirdtreatment of low food and higher temperatures was administeredto second-generation shrimp in summer (summer-low-food). Thedevelopment to adulthood and onset of reproduction occurred5 days sooner in the high-food treatment than in the low-foodtreatment of the spring experiment, while development was 2–3times faster in the warmer, summer-low-food treatment. Underspring-high-food conditions, shrimp had a higher survival toadulthood (46%) and lower daily mortality rate (0.012 day^–1)than in the spring-low-food treatment (30% survival and a 0.015day^–1 mortality rate). Survival to adult hood of summer-low-foodanimals (49%) was similar to that in spring-high-food; however,the daily mortality rate was twice as high (0.029 day^–1).While instar-specific length did not vary among treatments,instar-specific weights of juveniles and adults were lower inthe summer-low-food treatment than in the other two treatments.Since food in the summer-low-food treatment was lower and temperatures higher than in the spring-low-food treatment, thelower weights in summer may be explained by food rather thantemperature, or by both. The cumulative secondary productionof single cohorts was lowest in the summer (0.32 mg dry weightindividual^–1) due to low individual weights and highestunder spring-high-food conditions (1.1 mg dry weight individual^–1).     

The fate of the carotenoid pigment fucoxanthin during passage through the copepod gut: pigment recovery as a function of copepod species, season and food concentration

The amount of fucoxanthin, a taxonomically diagnostic carotenoid,recovered after passage through the guts of the copepods Acartiacalifomiensis and Calanus pacificus, was determined after thecopepods had fed on low (50 µg Cl^–1) and high (350µg C1^–1 for Acartia; 500 ug C H for Calanus) concentrationsof the diatom Thalassiosira weissftogii, during spring (May)and winter (December). Changes in pigment concentrations andcell abundances were assessed in experimental (with copepods)and control (without copepods) samples by standard incubationexperiments. Pigment recovery was assessed by (i) comparingthe amount of ingested pigment recovered in the experimentalgroups with that predicted to have been ingested from cell countdata and (ii) comparing fuco-xanthin/cell ratios in controland experimental samples. Both techniques suggested that pigmentloss is substantial (usually 60–100%), regardless of species,food availability or season. Patterns of pigment conservationdiffered between species, although pigment recovery was alwayshigher at high, than at low, food concentrations. Pigment recoveryin Acartia was higher (9.4–28.0%) in the spring than duringthe winter (0 recovery), regardless of food concentration. InCalanus, however, pigment recovery was always higher at high(34.9–67.8%) than at low (0 recovery) food concentrations,regardless of season.     

Temporal variability in the night-time distribution of epipelagic siphonophores in the North Atlantic Ocean at Bermuda

The temporal variability of siphonophores was compared on night-to-night,month-to-month and year-to-year scales in open-net collectionsmade at or near the Bermuda Atlantic Time Series (BATS) site.These collections were made as oblique tows to 100 m on (i)one summer night in each of 1986, 1989 and 1991, (ii) one nightper month on 13 cruises between April 1991 and August 1992,and (iii) three consecutive summer nights of 1992. The meanwet displacement volume (WDV) of sipho nophores in the thesecollections was 1.4 ± 0.6 ml per 100 m³ or 20 ±10% of the total catch biovolume. The most common species belongedto the Calycophorae families Diphyidae and Abylidae: the combinednumerical abundance of Chelophyes appendiculala, Eudoxoidesmitra, Lensia subtilis. Eudox-oides spiralis, Bassia bassensisand Abytopsis eschscholtzi averaged 300–400 per 100 m³.Combined numbers of these common species varied little whensampled hour by hour at the same location during consecutivesummer nights or at different night-time sampling locations10¹–10² km apart when these were sampled within 3–5h. In contrast, most of these six species exhibited 2- to 3-folddifferences in night-time abundance between summers of differentyears and between seasons. Three seasonal groups were detected,with a winter group being the most distinct from the others.Changes in the abundance of several species were correlatedwith seasonal changes in the depth of the mixed layer.     

Impact of Daphnia pulex on a metalimnetic microbial community

A well-structured metalimnetic community, composed mainly ofphototrophic purple bacteria, Cryptomonas, and a few speciesof ciliates and rotifers, was regularly found between 1984 and1991 in Lake Cis. These populations appeared during spring,reached high concentrations and remained in the metalimnionuntil winter mixing. We had previously postulated that thesemetalimnetic populations could persist in such high numbersbecause they were free of efficient predation, since the oxygen-sulfideinterface provided a refuge from predation. In September 1992,an abundant Daphnia pulex population developed in the lake whichresulted in drastic changes in the formerly stable community.The presence of D.pulex induced an extreme clear-water phasein the epilimnion and the metalimnetic populations were severelyreduced. Feeding experiments with Cryptomonas and heterotrophicand phototrophic bacteria as food for D.pulex resulted in clearancerates around 0.7 ml individual^–1 h^–1. The impactwas very high on the microaerophilic populations, whereas theanaerobic populations were least affected, since sulfide limitedthe vertical distribution of ^D.pulex. We conclude from thisevidence that the metalimnetic populations in previous yeanwere mostly food limited (bottom-up control) and that theirhigh abundances were in great part due to a lack of efficientpredation.     

Life history, biomass and production of two planktonic cyclopoid copepods in a shallow subtropical reservoir

Two planktonic cyclopoid copepods (Tropocyclops prasinus andMesocyclops longisetus) were raised in the laboratory to obtainlife history information (duration of embryonic and post-embryonicdevelopment, reproductive performance, longevity, and stage-specificlength and weight values). Animals were maintained at 20 and25°C, and fed ad libitum. Development times were temperaturedependent when food was not limiting, with shorter periods ofembryonic and post-embryonic development and decreased longevityat 25°C. Laboratory data on the duration of developmentand biomass, together with population dynamics data obtainedin the field, were used to estimate summer and winter biomassand production of these species in a shallow reservoir, LagoaDourada, Brazil. The maximum production rate of T. prasinus,attained during summer, was 2.8 mg dry weight (DW) m^–3day^–1 and the highest daily production:biomass (P:B) ratiowas 0.29, whereas for M. longisetus the maximum production ratewas 1.4 mg DW m^–3 day^–1 and the highest daily P:Bratio was 0.39, in the winter. Over short time intervals (everyother day), there was great variability of the species productionrates. Species production rates were low compared to valuesreported in the literature for the same or other species ofequivalent sized copepods from both tropical and subtropicalregions.     

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.     

Quantification of the phosphorus released by zooplankton in an oligotrophic lake (La Caldera, Spain): regulating factors and adjustment to theoretical models

Using an in situ approach, we have evaluated the phosphorusinputs from zooplankton in a high-mountain oligotrophic lake.Values of the specific gross release rate (SGRR) fluctuatedbetween 0.2 and 2.9 µg P mg^–1 dry weight h^–1,and were higher when the nauplii of Mixodiaptomus laciniatusdominated the zooplankton community. The rate of P recyclingby the zooplankton was high, reaching 1.6 µg P l^–1day^–1, and showed a highly consistent seasonal patternfrom one year to the next, with maxima in midsummer. Zooplanktonsize accounted for as much as 85% of the variance obtained inthe measurements of the specific rate of P release, while otherfactors, such as the quality or quantity of food, did not significantlyinfluence the SGRR changes. Among the models tested, only theone proposed by Peters (Int, Ver. Theor. Angew. Limnol. Verh.,19, 273–279, 1975) was useful for predictions in thissystem. The stoichiometric model of Hessen and Andersen (Arch.Hydrobiol., 35, 111–120, 1992), applied in this oligotrophicsystem, adequately predicted the phyto- and zooplankton dynamics,whereas the values of P release estimated using this model werefar higher than the excretion rates obtained experimentally.These differences were related to the type of egestion (formationof faecal pellets) of metazooplankton and to the relative importanceof the food resistance to digestion. We believe that in communitieswhere copepods constitute a substantial percentage of the zooplankton,an evaluation of the P release which is readily available [solublereactive phosphate (SRP), total dissolved phosphate (TDP)] toalgae and bacteria would not fit the predictions of generalmodels of mass balance; under these circumstances, assimilationefficiency proves to be the key parameter for predicting thereadily available P (excreted P).     

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)     

Size structures of microplankton biomass and production in Jiaozhou Bay, China

Seasonal investigations of size-fractionated biomass and productionwere carried out from February 1992 to May 1993 in JiaozhouBay, China. Microplankton assemblages were separated into threefractions: pico- (0.7–2 µm), nano- (2–20 µm)and netplankton (20–200 µm). The biomass was measuredas chlorophyll a (Chi a), paniculate organic carbon (POC) andparticipate organic nitrogen (PON). The production was determinedby ¹⁴C and ¹⁵N tracer techniques. The seasonal patterns in biomass,though variable, were characterized by higher values in springand lower values in autumn and summer (for Chi a only). Theseasonal patterns in production, on the other hand, were moreclear with higher values occurring in summer and spring, andlower values occurring in autumn and winter. Averaged over thewhole study period, the respective proportions of total biomassaccounted for by net-, nano- and picoplankton were 26, 45 and29% for Chi a, 32, 33 and 35% for POC, and 26, 32 and 42% forPON. The contributions to total primary production by net-,nano- and picoplankton were 31, 35 and 34%, respectively. Therespective proportions of total NH₄⁺–N uptake accountedfor by net-, nano- and picoplankton were 28, 33 and 39% in thedaytime, and 10, 29 and 61% at night. The respective contributionsto total NO₃^–-N uptake by net-, nano- and picoplanktonwere 37, 40 and 23% in the daytime, and 13, 23 and 64% at night.Some comprehensive ratios, including C/N biomass ratio, Chla/C ratio, C uptake/Chl a ratio, C:N uptake ratio and the f-ratio,were also calculated size separately, and their biological andecological meanings are discussed.     

Winter Growth of Autumn-sown White Lupin (Lupinus albus L.) Main Apex Growth Model

The winter growth of winter white lupin (cv. Lunoble) was investigated.Over three consecutive years, 1987–1989, it was sown atdifferent times at Lusignan (France) and in 1989, at nine differentlocations with various sowing times. The production of primordia,the vernalization requirements and the final number of leaveson the main stem were related to field measurements of dailymaximum and minimum temperatures. A statistical model for the main apex growth with a system oftwo equations was developed, with a threshold level for leafprimordia production at 3 °C. The number of leaf primordiaproduced by a vegetative apex (y) in terms of the cumulativesums of temperature over 3 °C (x) followed the curvilinearregression y = 4.76 + 00268x + 00000156x². The upper and lowertemperature limits for vernalization were estimated as 14 andI °C respectively. The vernalization requirements of a vegetative apex (y) decreasedwhen the number of initials produced (x) increased accordingto the negative exponential regression y = exp (7.2 + 002626.x). The two equations were used for the prediction of the finalnumber of leaves of a lupin crop. The predictive accuracy ofthe model was checked against independent data. The agreementbetween observed and predicted final leaf number was often close,but some deviations did occur with low leaf number. The modeldescribed most of the growth phenomena which occur during thephase sowing to floral initiation of the main stem of a winterlupin crop, and its possible uses are discussed. Lupinus albus L., white lupin, growth, model, vernalization, primordia, apex, thermal time     

A Nitrate-Inducible Plasma Membrane Protein of a Marine Alga, Heterosigma akashiwo

The rate of nitrate uptake by Heterosigma akashiwo cells thathad been cultured in medium with nitrate or ammonium ions asthe source of nitrogen was measured using¹⁵NO_3– The ratioof ¹⁵N/¹⁴N increased dramatically in nitrate-grown cells. Inammonium-grown cells, the ratio of ¹⁵N/¹⁴N did not increasefor 3 h but then it began to increase. Even when nitrate reductaseactivity was inhibited by tungstate, nitrate-grown cells couldtake up nitrate. Plasma membranes from nitrate-grown and ammonium-grown cellswere purified by the silica-microbead method, and polypeptidesassociated with the membranes were analyzed by SDS-PAGE andimmunostaining. A major polypeptide with a molecular mass of26 kDa appeared 3 h after the transfer of ammonium-grown cellsto nitrate-containing medium, and it disappeared 2 d after thetransfer of nitrate-grown cells to ammonium-containing medium.The 26 kDa polypeptide also appeared when cell growth shiftedfrom the logarithmic phase to the stationary phase and the ammoniumcontent of the medium decreased, even when the cells were culturedin ammonium-containing medium. (Received April 10, 1992; Accepted July 30, 1992)     

H+ tolerance of Chara Internodal Cells and Apparent Net Influx of H+ in Weakly Acidic Solutions: Implication of the Net Flux of H+ as a Minor Component among the Total Net Flux of Ions across the Intact Cell Membrane of Chara

Precise measurements of the net flux of protons in Chara internodalcells were made with a recently designed high-resolution pH-meter.Survival of intact Chara internodal cells in artificial pondwater (APW) that contained HC1 at various concentrations wasalso examined. The apparent net flux of H⁺ was inward and muchsmaller than that reported so far. In APW at pH 4.005, a valuehigher than the extracellular pH expected from the values ofH⁺ efflux reported to date, all of the intact Chara internodalcells died within a day. With reference to the data on the circadianflow of ions in the pulvinus of Phaseolus [Kiyosawa (1979) PlantCell Physiol. 20: 1621–1634, Hosokawa and Kiyosawa (1983)Plant Cell Physiol. 24: 1065–1072] and ionic regulationin Chara L-cells [Kiyosawa and Okihara (1988) Plant Cell Physiol.29: 9–19], a discussion is presented of the prossiblyminor contribution of the net flux of H⁺ in the generation ofthe electrical membrane potential. Regulation of the net fluxof H⁺ in weakly acidic APW is also discussed. (Received September 4, 1989; Accepted January 25, 1990)     

Laboratory study of the spawning rate of the calanoid copepod Centropages typicus: effect of fluctuating food concentration

The spawning rate of laboratory-reared Centropages typicus fedHymenomonas elongala increases with food concentration, up toa value of {small tilde}2800 µg C (16 500 cells) ml^–1.An alternation of a low food (1000 cells ml^–1) and highfood concentration (16 500 cells ml^–1) is not favourableto egg release when its periodicity is 1 or 2 days, whereasit may be of advantage if it is longer (3–6 days). Inthe latter case, Centropages typicus will benefit best fromthe rich food diet if this coincides with (or just follows)the last moult.     

Assessment of the potential impact of the mysid shrimp, Neomysis mercedis, on Daphnia

Neomysis mercedis, an important invertebrate predator in somelakes and estuaries in North America, occurred at high densities(>2 mysids m^-3) in Lake Washington in the early 1960s, aperiod when Daphnia were scarce in the lake. Because Neomysisfeed selectively on Daphnia, it was hypothesized that mysidpredation contributed significantly to the scarcity of Daphnia.To evaluate this hypothesis, mysid abundance was monitored inthe lake (July 1989–February 1992), and whole lake predationimpacts on Daphnia were estimated. Mysid abundance varied from319 million, 0.1 mysids m^-3 (February 1992) to 4276 million,1.7 mysids m^-3 ( June 1991), and mysid biomass ranged from 1153(October 1991) to 4700 kg dry weight (November 1990). A peakin Daphnia consumption was noted during autumn, when total mysidbiomass was high. In late autumn/winter mysid consumption month^-1accounted for 28–95% of Daphnia biomass and 13–38%of production. Mysid densities in this study were 18x and 5xlower than in 1962 and 1975, respectively. By extrapolation,at a density of 3.5 mysids m^-3 observed in the early 1960s,total Neomysis consumption demand month^-1 exceeded 100% of Daphniabiomass (late autumn–early spring), and 100% of Daphniaproduction (late autumn–winter). Estimates of the totalmysid consumption demand in this study are thus in accord withthe hypothesis that Neomysis could control Daphnia abundancein Lake Washington.     

Winter Growth of Autumn-sown White Lupin (Lupinus albus L.) Main Apex Growth Model

The winter growth of winter white lupin (cv. Lunoble) was investigated.Over three consecutive years, 1987–1989, it was sown atdifferent times at Lusignan (France) and in 1989, at nine differentlocations with various sowing times. The production of primordia,the vernalization requirements and the final number of leaveson the main stem were related to field measurements of dailymaximum and minimum temperatures. A statistical model for the main apex growth with a system oftwo equations was developed, with a threshold level for leafprimordia production at 3°C. The number of leaf primordiaproduced by a vegetative apex (y) in terms of the cumulativesums of temperature over 3°C (x) followed the curvilinearregression y = 4.76+ 0.0268x + 0000015 6x². The upper and lowertemperature limits for vernalization were estimated as 14 and1°C respectively. The vernalization requirements of a vegetative apex (y) decreasedwhen the number of initials produced (x) increased accordingto the negative exponential regression y = exp (7.2— 0.02626.x). The two equations were used for the prediction of the finalnumber of leaves of a lupin crop. The predictive accuracy ofthe model was checked against independent data. The agreementbetween observed and predicted final leaf number was often close,but some deviations did occur with low leaf number. The modeldescribed most of the growth phenomena which occur during thephase sowing to floral initiation of the main stem of a winterlupin crop, and its possible uses are discussed Lupinus albus L, white lupin, growth, model, vernalization, primordia, apex, thermal time     

Egg production, growth and development of the cyclopoid copepod Oithona similis

Egg production, growth and development rates of Oithona similiswere measured in the laboratory as a function of food concentrationand composition. On an optimum diet, development is isochronaland growth is near exponential. The maximum juvenile growthrate at 15C (0.2 day^–1) is similar to juvenile growthin calanoid copepods. The maximum weight-specific egg productionrate (0.1 day^–1), on the other hand, is substantiallyless than in free-spawning calanoids, but similar to that inegg-carrying calanoids. In the Kattegat, Oithona spp. egg productionis strongly limited by food during summer and controlled bytemperature during winter. The seasonal signal in fecundityand population biomass is much weaker than in the co-occurringfree-spawning calanoid genera, where fecundity and populationbiomass undergo dramatic seasonal viaration. ¹Present address: Instituto Nacional de Investigacin y DesarrolloPesquero, INIDEP, CC 175, Playa Grande, Mar del Plata, Argentina     

Evidence for the Involvement of Calcium Ions in the Photoperiodic Induction of Flowering in Pharbitis nil

The effects of ethyleneglycol-bis-(ß-aminoethyl ether)N,N,N',N'-tetraacetic acid, a specific chelator of Ca²⁺ ions;lanthanum chloride, a calcium channel blocker; and chlorpromazine,a calmodulin antagonist, on the photoperiodic induction of floweringin Pharbitis nil were studied by perfusing the plants with aqueoussolutions of the various compounds. All these compounds inhibitedflowering when applied before an inductive 16-h dark periodbut they did not inhibit flowering when applied after the inductivedark period. The results imply that Ca²⁺ ions are involved inthe photoperiodic induction of flowering in P. nil. (Received August 14, 1992; Accepted November 24, 1992)     

Vertical distribution, life cycle and production of the chaetognath Sagitta crassa in Tokyo Bay, Japan

The daytime vertical distribution of Sagiita crassa in TokyoBay was examined from February 13, 1988 to February 20, 1989.High densities of larger-size chaetognaths were found near thesea bottom, whereas the smaller animals tended to inhabit theupper layers. This feature of distribution is discussed in relationto the distribution of their main food organisms, e g. Pseudodiaptomusmarinus, Acartia omoru, Centropages abdomialis and Oithona davisae.The two periods of replacement of two morphs were confirmedby the variation only in mean body length of this chaetognath,unlike the previous authors who made additional morphologicalobservations. It was hypothesized that S.crassa has at leastfive generations Two generations, including mostly the largerforms, had higher growth rates than the generation consistingmainly of the small form. Yearly respiration of S.crassa was8.2 g C m^–Abstract. Yearly production of this animal wasestimated to be 3.8 g C m^–. A feeding estimate revealedthat chaetognaths require a prey production of 13.1 g C m^–year^–1. The impact of this chaetognath on the prey populationin Tokyo Bay and the propriety of an estimated value of annualproduction of S crassa is discussed.     

Temperature Response of Early Foliar Expansion of Potato and Wheat

We studied the course of early leaf area expansion and specificleaf area (S_LA) in potato (Solanum tuberosum L.) and wheat (Triticumaestivum L.) genotypes and tested whether air temperature explainsdifferences in these courses within different environments.Such knowledge can be used to improve crop growth modelling.The relative rate of leaf area expansion (R_L) of potato andwheat decreased with thermal time, but was nearly linear upto a leaf area index (L) of 1.0. TheR_L (L < 1; mean: 17.9x 10^-3°C^-1 d^-1) of potato showed an interaction betweengenotype and environment, and varied with year. TheR_L (L <1; mean: 7.1 x 10^-3°C^-1 d^-1) of winter wheat was lower thanthat of spring wheat (mean: 10.9 x 10^-3°C^-1 d^-1), and bothvaried with year. S_LAof potato increased nearly linearly withthermal time from 5 to 15 m² kg^-1at 50% emergence, to 20 to25 m² kg^-1at 155°Cd, and then decreased slightly. The S_LAofboth winter and spring wheat began at 16 to 23 m² kg^-1and inmost cases increased slightly with thermal time. In potato,regression parameters of S_LAwith thermal time were affectedby environment (management conditions and year) and genotype;in wheat they were affected by environment (year and site).Treatment effects on R_Lof potato were not correlated with thoseon S_LA , and were only partly correlated for wheat. Thereforewe conclude that the early foliar expansion of potato is associatedwith a strong increase in S_LA , and not so for wheat. For bothcrops the course of early leaf area expansion and ofS_LA withair temperature is not robust over environments and genotypes.The consequences of these results for modelling are discussed.Copyright 2000 Annals of Botany Company Triticum aestivum, spring wheat, winter wheat, Solanum tuberosum, leaf area expansion, specific leaf area, early growth, genotype, environment, modelling