The Isolation, Maintenance and Host Range Studies of a Chytrid Rhizophydium planktonicum Canter emend., Parasitic on Asterionella formosa Hassall

The methods of isolation and maintenance in dual clone cultureof the chytrid Rhizophydium planktonicum Canter emend, parasiticon Asterionella formosa Hass. from the plankton are described.The ability of a single fungal isolate to infect other clonesof Asterionella, Fragilaria, Tabellaria, Synedra and Cyclotella,as well as dead material was also tested. All the clones of Asterionella proved to be highly susceptibleto infection whereas only in rare instances could a sporangiumbe found which had grown and dehisced on Fragilaria and Synedra.Very few zoospores encysted on Tabellaria and Cyclotella andthose which did died without further growth. There was no evidenceto suggest that the chytrid could complete its life historyon dead material. freshwater phytoplankton, culture, parasitism, host–parasite relationships, chytridiomycetes, Rhizophydium, Zygorhizidium, diatoms, Asterionella, Fragilaria     

Phosphorus utilization by Asterionella formosa Hass

Observations have been made on the relationship in Lake Windermerebetween the growth of Asterionella formosa and the concentrationof dissolved phosphate. Asterionellaformosa has also been grownin culture and the amount of phosphorus required by this organismhas been determined. These experiments have shown that: (1) Asterionella can take up and store in reserve phosphorusfrom concentrations below those found in phosphorus-poor lakes(i.e. below 1 µg.P/l.). (2) Growth can continue in phosphorus-deficient media by makinguse of such reserves, cell phosphorus being steadily reduced. (3) The limiting requirement per cell of phosphorus is veryminute—about 0—06µg P/10⁶ cells/1, so thatinitial concentrations as low as rog.P/l. can theoreticallyproduce a population of some i6 x io6 cells/l. before limitationby phosphorus deficiency. This has been realized in culture.The behaviour of Asterionella formosa growing in nature hasbeen found to conform with that found in culture. It is concludedfrom such observations that phosphorus deficiency is unlikelyto provide a limit to growth of Asterionella in Windermere,despite the very low initial concentration of dissolved phosphate.Further experiments have shown that Asterionella cells low inphosphorus can rapidly take up added phosphate from lake waterbut not from distilled water. Some factors which affect therate of phosphate uptake of depleted cells are investigated,and attempts have ben made to throw some light on the natureof the apparent difference between lake water on the one handand distilled water and a number of artificial lake waters onthe other. No conclusion is reached on the reason why Asterionellacells behave differently in lake water and in artificial media.     

The Vegetative Growth of Helianthus annuus and Phaseolus vulgaris as Affected by Seasonal Factors in Freetown, Sierra Leone

Sand-culture experiments were carried out in full daylight atsuccessive weekly intervals between March and December 1969,to investigate the effects of seasonal changes in climatic factorson the growth of Helianthus annuus and Phaseolus vulgaris inFreetown. Values for a number of growth parameters were calculatedfrom the dry weights of the leaves, stems, and roots, and fromthe leaf areas. Simultaneously the diurnal changes in climaticfactors were recorded. Multiple regressions linking light, temperature, and relativehumidity with some of the growth parameters were calculated.The total variance accounted for in the regressions of relativegrowth-rate, net assimilation rate, and leaf weight ratio onlight, temperature, and relative humidity ranged from 51 to60 per cent in P. vulgaris. In H. annuus relative humidity wasless important; the percentage proportion of total varianceaccounted for in the regression of leaf weight ratio (and leafarea ratio in both species) on light and temperature was notsignificant. The results showed that H. annuus grew faster than P. vulgaris,but the latter's growth was depressed less by the dull weatherof the rainy season. The relative growth-rates of both specieswere positively dependent on light and temperature while theirnet assimilation rates were negatively dependent on relativehumidity, and their leaf area ratios negatively dependent onlight. All parameters used except leaf area ratio and leaf areato leaf weight ratio showed seasonal variations correspondingto dry and rainy seasons. The initial and final values of leafarea ratio and weight ratios were always different but did notvary in the same direction in both species. The results are discussed in relation to similar work done elsewhere.     

Effects of soil resistance to root penetration on leaf expansion in wheat (Triticum aestivum L.): kinematic analysis of leaf elongation

Wheat leaves (Triticum aestivum L.) elongated 50% more slowlywhen plants were grown in soils with high mechanical resistanceto penetration (R_s. The profiles of epidermal cell lengths alongthe growth zone of expanding leaves and the locations of newlyformed walls were recorded in order to compare the kineticsof elongation and partitioning of both meristematic and non-meristematiccells. In leaf 5, which completely developed under stress, highR_s, did not affect the flux of mature cells through the elongationzone; leaf elongation was reduced only because these cells wereshorter. This reduced size reflected a reduction in cell lengthat partitioning, associated with shorter cycling time. The relativerates of cell elongation before and after partitioning wereunchanged. Cell fluxes were similar because the population ofmeristematic cells was reduced, offsetting their increased partitioningrate. In contrast, in leaf 1, high R_s, had no effect on thenumber of dividing cells; elongation rate was reduced becauseof slower relative cell expansion rate and slower cell partitioningrate. These differences could reflect differences in the stageat which successive leaves perceived root stress and also time-dependentchanges in the responsiveness of leaf development to stress-inducedroot signals or in the nature of these signals. The data reveal that cell cycling time may in fact be decreasedby unfavourable growth conditions and is not directly relatedto cell expansion rates; they also show that the elongationrate of meristematic cells is partly independently controlledfrom that of non-meristematic cells. Key words: Wheat, kinematics of leaf expansion, cell partitioning, cell elongation, root impedance     

The Effect of Light and Darkness Upon Infection of Asterionella formosa Hassall by the Chytrid Rhizophydium planktonicum Canter emend

Observations, both experimental and microscopic, indicate thatzoospores of Rhizophydium planktonicum Canter emend., can remainalive, but rarely become adherent upon cells of Asterionellaformosa Hassall under conditions of very low light or in completedarkness. The behaviour patterns of zoospores towards host cells underdarkened conditions were compared with those which took placeunder well illuminated conditions leading to the settlementof zoospores on host cells. The differences noted may help toexplain the lack of zoospores found upon inadequately illuminateddiatom cells. Some evidence suggests that young zoospores lack the abilityto adhere to host cells. After the encystment of zoospores uponAsterionella cells in the light, their further growth and developmentcan continue in darkness. Rhizophydium planktonicum Canter emend., Asterionella formosa Hassall, chytrid, diatom, infra-red illumination, zoospore     

Mature Tissue and Crop Canopy Respiratory Characteristics of Rye, Triticale and Wheat

Crop dry matter and its chemical composition, together withcanopy and mature tissue respiration rates were measure at equivalentgrowth stages and temperatures for spring and winter rye, triticaleand wheat crops grown under irrigated field conditions. Canopyrespiration was partitioned into growth and maintenance respirationusing information from the chemical composition analysis ofthe crop biomass. Rates of dry matter accumulation early inthe growing season were significantly greater for rye cropsin comparison to triticale and wheat. However, when dry matterwas measured at similar ontogenetic stages, the productivityadvantage of the rye crop was no longer evident. Nevertheless,canopy respiration rates per unit ground area were significantlylower for rye than wheat over all temperatures and growth stages.Intergeneric differences in the respiration rates of matureleaf and stem tissues were consistent with those measured atcanopy scales. Differences in the chemical composition of thebiomass among genera were minimal, and insufficient to accountfor differences in canopy respiration due to synthesis respirationrequirement. Estimates of biomass maintenance requirements appearto be significantly lower for rye than wheat when calculatedat similar temperatures and ontogenetic stages. The maintenancecoefficient (m) depended on stage of development, suggestingthat m will decline earlier chronologically for rye than wheat,which implies that greater carbon retention is another aspectcontributing to the higher early-season crop growth rates ofspring and winter rye. Considering the lower respiration ratesof mature stems relative to leaves, the dependence of m on stem:leafratio was suggested as a useful approach to modelling ontogeneticeffects on maintenance respiration.Copyright 1993, 1999 AcademicPress Rye, triticale, wheat, dry matter, growth and maintenance respiration     

Cellular Growth in Roots of a Gibberellin-Deficient Mutant of Tomato (Lycopersicon esculentum Mill.) and its Wild-type

The role of gibberellins in regulating the growth of tomatoroots was investigated by comparing various cellular parametersin cultured roots of the gibberellin-deficient mutant gib-l/gib-lwith those in roots of the near-isogenic wild-type. In addition,wild-type roots treated with 0?1 µM 2S,3S paclobutrazol,an inhibitor of gibberellin biosynthesis, and mutant roots treatedwith 0?1 µM GA₃ were also compared: the former roots constitutea phenocopy of the mutant, whereas the latter roots appear tobe ‘normalized’ and similar to wild-type. The elongationof mutant and phenocopied roots were similar, their maximumelongation rates being about half or two-thirds that of wild-typeor GA₃-treated mutant roots, respectively. These rates wereinterpreted in terms of the numbers and lengths of cells withinthe meristematic and non-meristematic portions of the elongationzone. Mean meristem length tended to be shorter in both themutant and the 2S,3S paclobutrazol-treated wild-type roots thanin the other two types of root. A major difference between thetwo pairs of mutant and normal roots was their mean final celllengths: mean lengths of cortical cells of the mutant and 2S,3Spaclobutrazol-treated roots were, respectively, 39% and 25%shorter than the mean length of wild-type roots. Final celllength in the GA³-treated mutant roots were similar to wild-type.By contrast, the diameters of mature cortical cells of the mutantand phenocopy were about 20% greater than the diameters of equivalentwild-type or ‘normalized’ mutant cells. The meanvolumes of cortical cells in all four types of roots showedno significant differences. Knowledge of the distribution ofcortical cell lengths, widths and volumes along the root axis,together with information about the rate of root elongation,permitted comparisons of the relative elemental growth ratesof each of these three cellular parameters. The available evidence suggests that the level of endogenousgibberellins in mutant roots is lower than in wild-type roots.The present results, therefore, suggest that endogenous gibberellinsare necessary for normal growth of cultured tomato roots andthat they regulate the relative amounts of growth at the longitudinaland transverse walls of the cells which, in turn, affects theshape of the elongating cells. Key words: Cell growth, cultured roots, gibberellin, gib-l mutant, Lycopersicon esculentum, 2S,3S paclobutrazol, relative elemental growth rate, root meristem     

Development, growth and egg production of the two copepod species Centropages hamatus and Centropages typicus in the laboratory

Laboratory experiments were set up in order to determine andcompare developmental rates, growth rates, generation timesand egg production rates for the two calanoid copepod speciesCentropages typicus and Centropages hamatus. The nauplii showeda higher developmental rate than the copepodites for both specieswith quite different individual stage durations, which gaveno indication of isochronal development. For C typicus equiproportionaldevelopment was found. The growth rates were exponential andhighest for the largest species C typicus, and for both speciesthe juvenile growth rates were very similar to the egg productionrates of the adults.     

Growth Analysis of Contrasting Cultivars of Zea mays L. at Different Rates of Nitrogen Supply

The effects of nitrogen supply on the growth and nitrogen contentsof four cultivars of Zea mays L. of different origins were examinedunder water-culture conditions at the seedling stage. Seedlingsof cultivars CNIA12, LG11, Tusa Finn, and UNPHU XC301 were grownunder three different relative addition rates of nitrogen. Growthparameters were determined by means of functional growth analysisconducted on 10 to 19 d-old seedlings. No differences in relativegrowth rates were found among cultivars when nitrogen supplywas high. However, at the lowest rate of nitrogen supply, TusaFina and LG11 showed lower relative growth rates than CNIA12and UNPHU XC301, where relative growth rates were sustainedeven at the lowest rate of nitrogen supply, due to a higherunit leaf rate. The higher unit leaf rate of these two cultivarscorresponds directly to higher leaf and plant nitrogen contents.High positive correlations were found between plant nitrogencontents and both relative growth rate and unit leaf rate. Theresults suggest a potential for selection of genotypes withimproved performance under conditions where high rates of nitrogen-fertilizerapplication are too costly or not desirable.Copyright 1994,1999 Academic Press Maize, Zea mays, growth analysis, maize, nitrogen nutrition, nitrogen content, relative addition rates, relative growth rates, unit leaf rate     

Studies on Foliar Penetration: IX. PATTERNS OF PENETRATION OF 2,4-DICHLOROPHENOXYACETIC ACID INTO THE LEAVES OF DIFFERENT SPECIES

The comparative patterns of penetration of 2,4-dichlorophenoxyaceticacid (2,4-D) into the leaves of Phaseolus vulgaris, Zea mays,Pisum sativum, Beta wlgaris, Helianthus annuus and Gossypiumhirsuium have been examined. Save for Zea and Gossypium where there is little change withthe stage of leaf development the rates of penetration intoboth surfaces decrease as the leaf matures. The relative ratesare dependent on the species and the age of the leaf but thereare differences between the surfaces. In Phaseolus the characteristicsof primary leaves differ from those of trifoliate leaves sinceonly in immature trifoliate leaves is penetration into the adaxialsurface greater. In darkness the rates of penetration over 24 h remain constantor fall but slightly for all species. Light consistently promotespenetration but with Beta there is a lag before entry is acceleratedinto the abaxial surface as has previously been reported foryoung primary leaves of Phaseolus. For the remaining speciesthe courses of penetration in both light and darkness into bothsurfaces follow similar patterns. As the light intensity isincreased entry is enhanced but the limit of response variesbetween species, between surfaces within species, and in trifoliateleaves of Phaseolus with age. For the six species the order of the relative rates of entryis closely similar whether comparisons are made in light ordarkness or between abaxial and adaxial surfaces: viz. Zea >Helianthus > Phaseolus (primary) > Phaseolus (trifoliate)> Pisum = Beta = Gossypium. The observed specific differencesare discussed in relation to variations in leaf structure, theproperties and thickness of the cuticle and the physiologicaland metabolic processes which influence transport within theepidermal tissues after it has passed through the cuticle bydiffusion.     

Effect of the Rht3 dwarfing gene on dynamics of cell extension in wheat leaves, and its modification by gibberellic acid and paclobutrazol

The second leaf of wheat was used as a model system to examinethe effects of the Rht3 dwarfing gene on leaf growth. Comparedto the rht3 wild type, the Rht3allele decreased final leaf length,surface area and dry mass by reducing the maximum growth rates,but without affecting growth duration. Gibberellic acid (GA₃)increased final leaf length and maximum growth rate in the rht3wild type, but was without effect on the Rht3 mutant, whichis generally regarded as being non-responsive to gibberellin(GA). Paclobutrazol, an inhibitor of GA biosynthesis, decreasedfinal leaf length and maximum growth rate in the rht3 wild typeto values similar to those in the untreated Rht3 mutant. NeitherGA₃ nor paclobutrazol affected the duration of leaf growth.The decrease in leaf length was produced by reduction of celllength rather than cell number. The maximum relative elementalgrowth rate (REGR) for cell extension was essentially the samein all treatments, as was the time between the cells leavingthe meristem and achieving maximum extension rate. The differencesbetween the genotypes and treatments were all almost entirelydue to differences in the time taken from the attainment ofmaximum REGR of cell extension to the cessation of extension.This was reflected in the length of the extension zone, whichwas approximately 6–8 per cent of final leaf length. Theeffects of the Rht3 allele, GA₃ and paclobutrazol all appearto be on the processes which promote the cessation of cell elongation. Key words: Cell extension, gibberellin, leaf growth, Rht3 gene, Triticum, wheat     

Root Distribution, Growth, Respiration, and Hydraulic Conductivity for Two Highly Productive Agaves

Cultivated Agave mapisaga and A. salmiana can have an extremelyhigh above-ground dry-weight productivity of 40 Mg ha^–1yr^–1. To help understand the below-ground capabilitiesthat support the high above-ground productivity of these Crassulaceanacid metabolism plants, roots were studied in the laboratoryand in plantations near Mexico City. For approximately 15-year-oldplants, the lateral spread of roots from the plant base averaged1.3 m and the maximal root depth was 0.8 m, both considerablygreater than for desert succulents of the same age. Root andshoot growth occurred all year, although the increase in shootgrowth at the beginning of the wet season preceded the increasein growth of main roots. New lateral roots branching from themain roots were more common at the beginning of the wet season,which favoured water uptake with a minimal biomass investment,whereas growth of new main roots occurred later in the growingseason. The root: shoot dry weight ratio was extremely low,less than 0.07 for 6-year-old plants of both species, and decreasedwith plant age. The elongation rates of main roots and lateralroots were 10 to 17 mm d^–1, higher than for various desertsucculents but similar to elongation rates for roots of highlyproductive C₃ and C₄ agronomic species. The respiration rateof attached main roots was 32 µmol CO₂ evolved kg^–1dry weight s^–1 at 4 weeks of age, that of lateral rootswas about 70% higher, and both rates decreased with root age.Such respiration rates are 4- to 5-fold higher than for Agavedeserti, but similar to rates for C₃ and C₄ agronomic species.The root hydraulic conductivity had a maximal value of 3 x 10^–7ms^–1 MPa^–1 at 4 weeks of age, similar to A. deserti.The radial hydraulic conductivity from the root surface to thexylem decreased and the axial conductivity along the xylem increasedwith root age, again similar to A. deserti. Thus, although rootsof A. mapisaga and A. salmiana had hydraulic properties perunit length similar to those of a desert agave, their highergrowth rates, their higher respiration rates, and the greatersoil volume explored by their roots than for various desertsucculents apparently helped support their high above-groundbiomass productivity Key words: Crassulacean acid metabolism, productivity, root elongation rate, root system, water uptake     

Effects of temperature and light on the population dynamics of the Asterionella-Rhizophydium association

Growth parameters of the diatom Astenonella formosa Hass, andits fungal parasite Rhizophydium planktoniacum Canter emend,were measured at five temperatures and six light intensitieswith a 15?9 h light:dark cycle, using laboratory cultures ofboth organisms. With the parameter values obtained, thresholdhost densities were calculated in order to estimate the effectsof light and temperature on survival and epidemic developmentof the parasite The uninfected host reached light-saturatedgrowth rates between 0.917 day^–1 at 21?C and 0 285 day¹at 2?C. Under light limitation the optimum growth temperaturefor Asterionella decreased because of a reduced growth efficiencyGrowth inhibition at high irradiances was only observed at 2?CThe parasite reached the highest zoospore production at 2?Cand saturating irradiances: 30 2 zoospores per sporangium. Thisvalue was consistently reduced by lower irradiances and highertemperatures to only 2.2 zoospores at the opposite light andtemperature extremes Low light conditions depressed also theinfectivity of the zoospores At very low irradiances, they becamecompletely uninfective The light dependence of zoospore productionand infectivity was restricted to light intensities that limitedthe growth rate of the host. The development time of the sporangiaand the mfecti ve lifetime of the zoospores were not affectedby light but only by temperature, and ranged from 19.0 and 121 days respectively at 2?C to 1.9 and 2 1 days at 21?C- Theseeffects result in optimal conditions for the development ofa Rhizophydium epidemic at 11?C and a moderate light limitationof Astenonella At temperature above 7?C, the possibilities forepidemic development are only slightly affected by light andtemperature, except for very low irradiance levels, when thezoospores of the parasite become uninfective. However, below5?C the development of an epidemic is only possible at limitinglight levels. Conditions for survival of the parasite at lowhost densities are optimal at low temperatures and high irradiancelevels     

Interacting Effects of Light and Day and Night Temperatures on the Growth of Four Species in the Vegetative Phase

A comparative examination has been made under controlled conditionsof the interacting effects on growth in the vegetative phasewhich takes place when the diurnal temperature is either maintainedconstant at 20 and 25 ?C or reduced at night by 5 and 10 ?Cand the plants subjected daily to either 2.16 or 4.32 ? 10⁴lx for 14 h. For each species (Gossypium hirsutum, Hclianthusannuus, Phaseolus vulgaris and Zea mays) the changes in netassimilation rate, the leaf area ratio and the relative growthrates in plant weight and leaf area were recorded. Contrary to some previous findings, none of these componentsof growth are favoured by cool nights. Rather such reductionsin temperature retard the growth processes to a varying degreeaccording to the species and the component. In general, significantreductions are more evident for the two relative growth rateswhen a drop from 20 to 10 ?C is combined with the lower levelof illumination. The implications of these results are considered in relationto a prior study where for similar light conditions the samespecies plants were subjected to constant temperatures rangingfrom 10 to 25 ?C.     

Comparison of carbon-specific growth rates and rates of cellular increase of phytoplankton in large limnetic enclosures

Potential carbon-specific growth rates of phytoplankton wereestimated from a series of measurements of photosynthetic radio-carbonuptake over 4- and 24-h exposure periods in the light fieldsof three large limnetic enclosures (‘Lund Tubes’),each providing different limnological and trophic conditions.Photosynthetic behaviour and short-term, chlorophyll-specificcarbon-fixation rates conformed to well-established criteriabut, over 24 h, the net retention represented 23–82% ofthe carbon fixed during the daylight hours. Potential mean growthrates (k'_p, of the photo-autotrophic community were calculatedas the net exponential rates of daily carbon-accumulation relativeto derived, instantaneous estimates of the cell carbon-content.Apparent actual community growth rates (k'_D were calculatedas the sum of the exponential rates of change of each of themajor species present, corrected for probable rates of in situgrazing and sinking, and expressed relative to the fractionof total biomass for which they accounted. The correspondingvalues were only occasionally similar, k'_p generally exceedingK'_D by a factor of between 1 and 30 or 1 and 14, depending uponthe carbon:chlorophyll ratio used. The ratio, K'_p/K'_D was foundto vary inversely both to k'_D and to k_n, the net rate of changein phytoplankton biomass, suggesting that measured carbon fixationrates merely represent a capacity for cellular increase which,owing to other likely limitations upon growth, is seldom realized.Apparent rates of loss of whole cells do not account for theloss of carbon; that the ‘unaccounted’ loss rates(K'_p–K'_D varied in direct proportion to K'_p (i.e., losseswere least when chlorophyll-specific photosynthetic productivitywas itself limited) is best explained by physiological voidingof excess carbon (for instance, by respiration, photorespiration,excretion) prior to the formation of new cells.     

SHELL GROWTH OF THE COCKLE CERASTODERMA EDULE IN THE MUNDACA ESTUARY (NORTH SPAIN)

In order to establish a growth curve for the life-span, agedetermination based on shell-ring analysis was undertaken ina population of the cockle Cerastoderma edule located in theMundaca Estuary (Basque Country, North Spain). Mean values ofheight at shell rings showed non-significant differences betweengenerations, meaning absence of interannual variations in growthrate. Frequent sampling and shell measurements over a 20 monthperiod allowed determination of the seasonal pattern of shellgrowth, which was subsequently incorporated into a growth curve. An attempt has been made to relate growth rates to latitudefor different populations of C. edule, using both data fromthe literature and the results of this study. The highly significantcorrelation found (P<0.01) confims the existence of a latitudinaltrend, with growth rates increasing southwards. Low rates ofgrowth recorded for cockles from Mundaca, by camparison withpupulations of similar latitude, are interpreted in terms ofnutritional restrictions associated with both the high tidalposition of the population and poor productivity conditionswithin this particular estuary. (Received 24 March 1989; accepted 20 June 1989)     

Translocation and Temperature

The apparent diffusion constant, K, derived from profiles ofradioactivity during labelled sucrose translocation, is temperature-dependentwith a Q₁₀ of 2.9 in Pteridium. This value is similar to thoseobtained by other authors for mass transfer rates. The behaviourof K with temperature supports a translocation mechanism ofthe ‘activated-diffusion’ type and is consistentwith the Canny and Phillips translocation model which also suggestsa basis for the 25-30° C temperature optimum in translocation.     

Seedling Growth in Elymus farctus after Episodes of Burial with Sand

Episodes of burial by wind-blown sand are a frequent hazardfor Elymus farctus in the strandline and foredunes. We haveinvestigated the ability of seedlings to withstand and recoverfrom experimental burial. The burial treatments were appliedat the two-leaf stage, either for one or two weeks, and thegrowth in them was compared with that in unburied controls.The method of B-splines, with knots defined at the beginningand end of the burial period, proved to be appropriate for fittingrelationships between In dry mass and time for growth analysis.The relative growth rates derived from these relationships werepartitioned into component relative growth rates for individualplant organs, to reveal the responses to burial in terms ofdry matter allocation. No plants survived two weeks of burial but all those buriedfor one week recovered. There was respiratory loss of dry massduring burial, although fitted relative growth rates were notsignificantly different from zero. On re-exposure, relativegrowth rates increased to equal the maximum values in unburiedplants. Dry mass losses were from the root and stem fractions.Leaf 1 was unaffected, whereas the development of leaf 2 wascurtailed. Apart from their delayed appearance, leaves 3–5behaved similarly to their non-buried counterparts. The maintenanceof leaves at the expense of other organs during burial may becrucial to the survival of E. farctus seedlings. Sand burial, survival, recovery, growth analysis, splined cubic regression, Elymus farctus, sand couch grass     

Diel and vertical variability of seston food quality and quantity in a small subalpine oligomesotrophic lake

Vertical profiles of seston food quality and quantity were measuredin subalpine Castle Lake for particulate carbon, chlorophylla, fatty acids and phosphorus in addition to abiotic parametersincluding water temperature and dissolved oxygen levels. Fieldand laboratory incubation experiments were employed to manipulateDaphnia rosea growth environments. Sestonic eicosapentaenoicacid (EPA) content was much lower, whereas carbon to phosphorus(C:P) ratios were much higher in the epilimnion compared tothe deep-water chlorophyll maximum (16–20 m). In a temperature-controlledincubation, Daphnia grew faster when fed seston from the deep-waterchlorophyll maximum. In in situ cage incubations, D. rosea grewfastest in the epilimnion. Daphnia rosea in a migrating treatmentexhibited intermediate growth rates between the ones for epilimnionand hypolimnion. A projection of D. rosea growth rates by growthmodels without regard to water temperature showed much highergrowth potentials in the hypolimnion. However, with inclusionof water temperature, epilimnetic water always gave higher potentialgrowth rates. In this lake, warmer temperatures of epilimneticwater override the higher food quality and quantity providedby the deep-water chlorophyll maximum.     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.