The Effects of Light Intensity and External Potassium Level on Root/Shoot Ratio and Rates of Potassium Uptake in Perennial Ryegrass (Lolium perenne L.)

Loliun perenne L. (cv.S. 23) was grown on vermiculite in winterin a heated greenhouse for 8 weeks under factorial combinationsof two potassium regimes (nominally 6 parts/10⁶ and 156 parts/10⁶in Hewitt's solution) and three densities of artificially supplementedvisible radiation flux (36.1, 7.3, and 2.2 W m^–2). Growthand potassium uptake were studied through the calculation ofvarious growth functions from fitted curves. There was little effect of potassium treatment but the experimentalmaterial responded markedly to light. Leaf-area ratio in thethree treatments showed extreme plasticity in increasing from2–3 x 10^–2 through 6 x 10^–2 to 8–9 x10^–2 m² g^–1 as light intensity decreased. Correspondingdecreases in unit leaf rate, however, caused over-all reductionsin relative growth rate. Specific absorption rates for potassium (A_K, dry-weight basis)were strongly reduced at the lower light intensities but alsodisplayed complex ontogenetic drifts. Values of the allometricconstant, k (the ratio of root and shoot relative growth rates),decreased from c. 0.7 at 36.1 W m^–2 through c. 0.3 at7.3 W m^–2 to a value not significantly different fromzero (P < 0.05) at 2.2 W m^–2. In material grown under the two higher light intensities a constantinverse relationship was found between the mass ratio of rootand shoot and the corresponding activity ratio. The resultsconform to this model: Mass ratio = –0.001+45.0 (1/activityratio) where activity ratio is expressed as specific absorptionrate for potassium (in µg g root^–1 h^–1)/unitshoot rate (rate of increase of whole-plant dry weight per unitshoot dry weight, in mg g shoot^–1 h^–1). The implicationsof this relationship are discussed.     

Microclimate, Photosynthesis and Growth of Lucerne (Medicago sativa L.). II. Canopy Structure and Growth

The growth of lucerne var. Europe was examined in the fieldduring 1976. The annual dry matter production of unirrigatedlucerne during 1976, with no nitrogen fertilizer application,was 82.5 per cent greater than unirrigated S.24 perennial ryegrass,with a nitrogen application of 384 kg ha^–1. The mean aboveground growth rate of lucerne was 7.3 g DM m^–2 day^–1between March and early June, of which stem material contributeda maximum of 76.5 per cent. Significant losses of leaves andstems occurred from the end of April, indicating a loss of potentialforage material. Nitrogen analyses of the above ground crop suggested that in56 days lucerne yielded 10.7 per cent more nitrogen than didS.24 annually with a nitrogen fertilizer addition of 280 kgha^–1. Between 13 and 57 per cent of the daily photosynthate is translocatedbelow ground. Medicago sativaL, lucerne, dry matter production, canopy structure, nitrogen analyses     

Effects of Aluminium on Honeylocust (Gleditsia triacanthos L.) Seedlings in Solution Culture

Honeylocust (Gleditsia triacanthos L.) seedlings were grownin solution culture at pH 4.0) with 50, 150, 600 and 1500 mmolm^–3 aluminium. All levels of aiuminium reduced the sizeand weight of roots, shoots and leaves with the exception ofroot elongation at 50 mmol m^–3 Al. Aluminium content ofroots was 50 to 100 times that of shoots. With increasing concentrationof aluminium, aluminium content of leaves and roots increasedexponentially while a linear increase was observed for stems.The nutrient content of seedlings was improved in 50 mmol m^–3where increases in shoot calcium, magnesium, and phosphorusconcentrations were observed. Aluminium concentrations greaterthan 50 mmol m^–3 reduced shoot nutrient content. Presenceof aluminium increased the root phosphorus and calcium levelsbut had no effect on potassium and magnesium concentrations.Results show that honeylocust is an aluminium sensitive treespecies whose growth may be reduced by high soil Al levels. Key words: Aluminium toxicity, Gleditsia triacanthos, nutrient solution     

Effect of Sodium, Potassium, Calcium, Magnesium and Tetraethylammonium on the Transient Voltage Response to a Galvanostatic Step and of the Temperature on the Steady Membrane Conductance of Chara corallina: a Further Evidence for the Involvement of Potassium Channels in the Fast Time Variant Conductance

Homble F. 1985. Effect of sodium, potassium, calcium, magnesiumand tetraethylammonium on the transient voltage response toa galvanostatic step and of the temperature on the steady membraneconductance of Chara corallina: A further evidence for the involvementof potassium in the fast time variant conductance.—J.exp. Bot. 36: 1603–1611. Potassium channels of Chara corallina have an activation energyof 36±1 kJ mol^–1 and 50±2 kJ mol^–1at temperatures higher and lower than 15°C respectively.The fast time variant conductance property of potassium channelsis insensitive to sodium and magnesium ions and is depressedby the presence of calcium, potassium and tetraethylammoniumions. It is suggested that in Chara two different kinds of potassiumchannels exist, each kind being distinguished by their kineticsand their response to calcium and magnesium ions. Key words: —Chara corallina, membrane conductance, potassium channels, temperature     

Maintenance and Growth Components of Carbon Dioxide Efflux from Growing Pea Fruits

Carbon dioxide efflux from 5- to 20-day-old pea fruits was measuredfor plants grown in controlled environment at 15 °C and600 µmol s^–1 m^–2 photon flux density in a16 h photoperiod. The rate of CO₂ output per fruit increasedquickly from 0.005 to 0.018 mg CO₂ min^–1 during fruitelongation and subsequently more slowly to 0.030 mg CO₂ min^–1as the fruits inflated. On a d. wt basis the rate was highest,0.175 mg CO₂ g^–1 min^–1, in the youngest fruits anddeclined curvilinearly with increasing fruit weight to 0.02mg CO₂ g^–1 min^–1. Separation of maintenance andgrowth components was achieved by starvation methods and bymultiple regression analysis. From the latter method estimatesof the maintenance coefficient declined hyperbolically from150±8.7 mg carbohydrate g^–1 d. wt day^–1 inthe very young fruits (0.05 g) to 10.4±0.36 mg carbohydrateg^–1 d. wt day^–1 in older fruits (2.0 g). On a nitrogenbasis maintenance costs decreased from 2240 to 310 mg carbohydrateg^–1 nitrogen day^–1 while nitrogen concentrationfell from 6.7 to 3 per cent d. wt. A simple linear relationshipbetween maintenance cost per unit d. wt and nitrogen concentrationwas not observed. A growth coefficient of 50±6.7 mg carbohydrate g^–1growth (equivalent to a conversion efficiency, Y_G, of 0.95)was estimated for all fruits examined. The overall efficiency, Y, increased from a mean of 0.70 to0.85 during fruit elongation and subsequently declined to 0.80.For a given fruit weight, efficiency increased asymptoticallywith relative growth rate; both asymptote and slope of the relationshipincreased as the fruits grew. Pisum sativum L., garden pea, legume fruit, carbon dioxide efflux, maintenance respiration, growth respiration     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

Feeding and metabolism of the siphonophore Sphaeronectes gracilis

The in situ predation rate of the siphonophore Sphaeronectesgracilis was estimated from gut content analysis of hand-collectedsiphonophores and from laboratory data on digestion rates ofprey organisms. At daytime prey densities of 0.25 copepods 1^–1,S. gracilis was estimated to consume 8.1 – 15.4 prey day^–1siphonophore^–1. From data on abundances of siphonophoresand copepods, S. gracilis was estimated to consume 2–4%of the copepods daily. In laboratory experiments, ingestionrates averaged 13.8 prey day^–1 siphonophore^–1 atprey densities of 5 copepods 1^–1 and 36.9 at 20 copeods1^–1. This was equivalent to a specific ingestion rate(for both carbon and nitrogen) of –17% day^–1 and45% day^–1, respectively, while specific ingestion in situwas only 2% day^–1. Ammonium excretion averaged 0.095 µg-atsiphonophore^–1 day^–1 at 5 prey 1^–1, and 0.162at 20 prey 1^–1. The specific respiration (carbon) andspecific excretion (nitrogen as ammonium) were calculated tobe 3% day^–1 at the lower experimental food level, and5% day^–1 at the higher food level. ¹Contribution from the Catalina Marine Science Center No. 66. ²Present address: Dept. of Biology, University of Victoria,Victoria, B.C., Canada V8W 2Y2.     

In situ filtration responses of Daphnia galeata to changes in food quality

In the stoichiometric study of phyto–zooplankton interactions,a controversy exists about how Daphnia species regulate theirfeeding rate when submitted to low-quality food (i.e. high dietarycarbon:phosphorus [C:P] ratio). In this study, we gathered dataover 3 years on in situ clearance rates of a Daphnia galeatapopulation, by conducting grazing experiments from April 1998to October 2000 in the Esch-sur-Sûre reservoir (Grand-Duchyof Luxembourg). Observed clearance rates (2.5–13.5 mLindividual^–1 day^–1, mean 7.0 mL individual^–1day^–1) were correlated with population and environmentalvariables. Mean body size of Daphnia individuals was the bestpredictor of clearance rate (r² = 0.639), followed by watertemperature (r² = 0.262) and P concentration in the seston (r²     

Ion Transport in Suaeda maritima: Its Relation to Growth and Implications for the Pathway of Radial Transport of Ions across the Root

The ion relations of the halophytc Suaeda maritima are described.When plants grew in 340 mol m^–3 sodium chloride (—1•76MPa) leaf solute potentials decreased, and were sustained around—2•5 MPa Inorganic ion concentration (mostly of sodiumchloride) accounted for this. Comparable shoot ion concentrationsof potassium, nitrate and sulphate occurred when plants grewon different salinity types characterized by these ions. Netsodium transport and shoot sodium concentration increased dramaticallywith increases in external sodium chloride concentration upto 85 mol m^–3; thereafter, further increases in externalsodium chloride concentration had relatively little effect uponeither shoot sodium concentration or upon net transport of sodiumto the shoot. The net transport of sodium plus potassium onlydoubled when the external concentration of sodium plus potassiumincreased from 24 to 687 mol m^–3 Shoot ion concentrationswere remarkably constant with time, external concentration andsalinity type. The membrane flux rates and symplasmic ion concentrations neededto sustain the observed net transport of sodium (of some 10mmol g^–1 dry wt. of roots d^–1) are calculated fromanatomical and stereological data for the root system of thisspecies. The minimum net sodium chloride flux to load the symplasmwould be 260 nmol m^–2s^–1 if the whole cortical andepidermal plasmalemmal surface area were used uniformly, butthe flux rate required would be 3000 nmol m^–2s^–1if uptake took place only at the root surface. A flux rate ofat least 1000 nmol m^–2s^–1 is needed between symplasmand xylem. The symplasmic concentration of NaCl would be atleast 80 mol m^–3. It is argued (1), that both symplasmicand xylem loading are likely to be passive processes mediatedby ion channels rather than active carriers, (2), that net iontransport at 340 mol m^–3 sodium chloride is close to themaximum which is physiologically sustainable and (3), that growthof this halophyte is limited by NaCl supply from the root. Key words: Suaeda maritima, halophyte, salinity, roots, radial ion transport     

Minerals, Carbohydrates and Amino Acids of Pollens from some Woody and Herbaceous Plants

The mineral, carbohydrate, protein, amino acid, lipid and energycontents of the seven main pollens gathered by honey-bees insouth-east Scotland were determined. Neither dry matter (mean73 per cent) nor ash (mean 3 per cent) were very variable. Thecalcium content of all pollens was relatively similar as werethe magnesium, potassium and sodium contents but manganese whichwas relatively high in ericaceae and phosphorus which was lowin Trifolium were more variable. Acer pollen contained mostprotein and Fagus least, and of the amino acids only serine,cystine and histidine were significantly different in the differentpollens. Over 30 per cent of all pollens was a mixture of fructoseand glucose, ericaceae containing most and Acer least. Hemicellulose(mean 7 per cent) was high in Ranunculus and low in Acer, cruciferaeand Fagus. ‘Cellulose’ (mean 0•5 per cent)was high in cruciferae and low in ericacea. Ether extract (mean5 per cent) was high in cruciferae and Fagus. The mean grossenergy of pollen was 23 kJ g^–1. Fresh pollen is comparable with lean meat as a source of energyand protein, and is more like dormant plant seeds than herbagein its water, ash and protein content but stores energy as sugarrather than starch or lipid.     

The Effect of Cycloheximide on Absorption of Ions by Bean (Phaseolus vulgaris L) Roots

10^–7 M cycloheximide inhibited bean (Phaseolus vulgaris)root elongation by about 20 per cent but it inhibited absorptionof rubidium, sodium, and phosphate ions to a much greater extent(34–71 per cent). Tips of intact plant roots grown inthe inhibitor showed more inhibition in ion uptake than adjacentproximal portions of the same roots and this is taken to indicatethat 10^–7 M cycloheximide does not exert its effect onion uptake by any uncoupling action. Sodium uptake from 0.5 or 10 mM NaCl solutions by root tipswas inhibited by 10^–7 M cycloheximide to twice the extentthat it was in the elongating region of the root. Assuming thatthe inhibitor affects the plasmalemma more than the tonoplast,Epstein's model of parallel operation of system 1 and system2 at the plasmalemma is supported.     

Analysis of Shoot Apical Growth of Picea sitchensis Seedlings

During the first 100 days after sowing (March-June) the followingchanges took place at the terminal shoot apices of Picea sitchensisseedlings: plastochrones (T) decreased from over 24 h to 4 h;apical domes enlarged from less than 0·20 mm to 0·45mm diameter (D); the ‘projected’ area of tissuesproduced by the apical domes (i.e. viewed from above) increasedin amount from less than 0·012 to 0·024 mm² day^-1;about 15 per cent of this tissue was re-invested in the apicaldomes, the rest was used to produce primordia; and the volume-doublingtimes of the apical dome tissues decreased from over 150 h to50 h. After 100 days there was no further re-investment in theapical domes, but the domes did not decrease abruptly in size.Less tissue was produced per day, but the primordia were smallerso that the rate of primordia formation did not fall precipitously.Plastochrone ratios were inversely related to D, but the relationshipbetween T and D depended on whether T was decreasing or increasing.Progenies which were known to be fast growing tended to build-uptheir apical domes rapidly (i.e. have large ‘re-investmentratios’) and to be capable of producing small primordia.These attributes can evidently be evaluated on seedlings andcould help to lessen the cost of tree breeding progeny-testprogrammes. meristem, Picea sitchensis, Sitka spruce, growth, shoot apex     

N2 Fixation and Nitrate Uptake by White Clover Swards in Response to Root Temperature in Flowing Solution Culture

Nodulated white clover plants (Trifolium repens L. cv. Huia)were grown as simulated swards for 71 d in flowing nutrientsolutions with roots at 11 C and shoots at 20/15 C, day/night,under natural illumination. Root temperatures were then changedto 3, 5, 7, 11, 13, 17 or 25 C and the total N₂, fixation over21 d was measured in the absence of a supply mineral N. Alltreatments were subsequently supplied with 10 mmol m^–2NO₂ ^– in the flowing solutions for 14 d, and the relativeuptake of N by N₂, fixation and NO₃ ^– uptake was compared.Net uptake of K⁺ was measured on a daily basis. Root temperature had little effect on root d. wt over the 35-dexperimental period, but shoot d. wt increased by a factor of3.5 between 3 and 25 C, with the sharpest increase occurringat 7–11 C. Shoot: root d. wt ratios increased from 25to 68 with increasing temperature at 7–25 C. N₂-fixationper plant (in the absence of NO₂ ^–) increased with roottemperature at 3–13C, but showed little change above13 C. The ratios of N₂ fixation: NO₂ ^– uptake over 14d (mol N: mol N) were 0.47–0.77 at 3–7 C, 092–154at 11–17 C, and 046 at 25 C, reflecting the dominanceof NO₃ ^– uptake over N₂ fixation at extremes of high andlow root temperature. The total uptake of N varied only slightlyat 11–25 –C (095–110 mmol N plant^–1),the decline in N₂ fixation as root temperature increased above11 C was compensated for by the increase in NO^– ₃ uptake.The % N in shoot dry matter declined with decreasing root temperature,from 32% at 13 C to 15% at 3 C. In contrast, concentrationsof N expressed on a shoot water content basis showed a modestdecrease with increasing temperature, from 345 mol m^–3at 3 C to 290 mol m^–3 at 25 C. Trifolium repens L, white clover, root temperature, N₂ fixation, potassium uptake, nitrate uptake, flowing solution culture     

EFFECTS OF CHLORAMPHENICOL AND KINETIN ON UPTAKE AND INCORPORATION OF AMINO ACIDS BY TOBACCO LEAF DISKS

The effects of chloramphenicol and kinetin on uptake and incorporationof ³⁵S-methionine and some ₁₄C-amino acids have been investigatedin leaf-disks of Nicotiana rustica in light and dark. Chloramphenicolin a concentration of 1 mg per ml inhibits the uptake of aminoacids from 30 to 60 per cent compared with the water control.The incorporation of amino acids into bulk protein is stronglyinhibited in light (40 to 70 per cent), but only to a smalldegree in dark (10 to 20 per cent), as revealed also by ¹⁴CO₂-photosynthesisof the disks and following treatment with chloramphenicol indark. The stimulating effect of kinetin on uptake and incorporationof amino acids is dependent upon its concentration (10^–5to 10^–6 M ; but 10^–4 M solution inhibits stronglyboth uptake and incorporation). The stimulation seems to influencemore incorporation than uptake processes. Possible interactionsof chloramphenicol and kinetin in the protein metabolism oftobacco leaves have been discussed. (Received April 27, 1964; )     

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.     

The Effect of Root Temperature on Growth and Uptake of Ammonium and Nitrate by Brassica napus L. in Flowing Solution Culture: I. GROWTH

Macduff, J. H., Hopper, M. J. and Wild, A. 1987. The effectof root temperature on growth and uptake of ammonium and nitrateby Brassica napus L. in flowing solution culture. I. Growth.—J.exp. Bot. 38: 42–52 Oilseed rape (Brassica napus L. cv. Bien venu) was grown for49 d in flowing nutrient solution at pH 6?0 with root temperaturedecrementally reduced from 20?C to 5?C; and then exposed todifferent root temperatures (3, 5, 7, 9, 11, 13,17 or 25?C)held constant for 14 d. The air temperature was 20/15?C day/nightand nitrogen was supplied automatically to maintain 10 mmolm^–3 NH₄NO₃ in solution. Total dry matter production wasexponential with time and similar at all root temperatures givinga specific growth rate of 0?0784 g g^–1 d^–1. Partitioningof dry matter was influenced by root temperature; shoot: rootratios increased during treatment at 17?C and 25?C but decreasedafter 5 d at 3?C and 5?C. The ratio of shoot specific growthrate: root specific growth rate increased with the ratio ofwater soluble carbohydrates (shoot: root). Concentrations ofwater soluble carbohydrates in shoot and root were inverselyrelated to root temperature; at 3, 5 and 7?C they increasedin stem + petioles throughout treatment, coinciding with a decreasein the weight of tissue water per unit dry matter. These resultssuggest that the accumulation of soluble carbohydrates at lowtemperature is the result of metabolic imbalance and of osmoticadjustment to water stress. Key words: Brassica napus, oilseed rape, root temperature, specific growth rate     

Growth and ingestion rates of larval fish populations in the coastal waters of Israel

Clupeoid larvae were collected on eight cruises between February1984 and February 1985 in the coastal waters of Israel. Fromanalysis of daily growth increments of otoliths, growth ratesof the abundant clupeoids, Engraulis encrasicolus, Sardina pilchardusand Sardinella aurita were found to be 0.55 mm day^–1,0.67 mm day^–1 and 0.60 mm day^–1, respectively, duringthe first month after hatching. Ingestion rates were estimatedusing an equation from the literature relating ingestion andgrowth of larval fish. Ingestion calculated for populationsof fish larvae in pelagic waters ranged from 0 to >23 mgC m^–2 day^–1 with maximum rates observed in April.Annual ingestion by larval fish at a pelagic station near Haifawas calculated to be 2.2 g C m^–2 year^–1, 10–20%of annual primary production estimated from ¹⁴C uptake.     

Azetidine-2-carboxylic Acid and Lily Pollen Tube Elongation

Azetidine-2-carboxylic acid (AZC), which occurs naturally inLiliaceous plants, is reported to be a proline (pro) analoguePlant cell walls contain ‘extensin’, which is richin hydroxyproline (hyp). Peptidyl hyp arises through hydroxylationof peptidyl pro followed by glycosylation (arabinose attachment)of hyp Because AZC replaces peptidyl prolyl residues, it maybe a useful tool for evaluating the significance of hyp-o-arabinoselinkages in cell elongation. Therefore, we determined the effectof AZC on [¹⁴C]pro uptake, incorporation and conversion to wall-bound[¹⁴C]hyp in relation to elongation of lily pollen tubes whosewalls consist, in part, of hyp-containing glycopeptides TheAZC suppressed pollen germination 9–42 per cent (1–10mM) and subsequent tube elongation 40–54 per cent (0·1–1mM without affecting respiration In contrast, similar hyp concentrationswere without effect on tube elongation Whereas uptake of [¹⁴C]prowas 16·5–6·2 per cent of the control at0·1–1 mM AZC, [¹⁴C]leucine uptake was 85–25per cent of the control. Light microscope radioautography revealedfewer silver grains over tubes elongated in 0·1–1mM AZC than in its absence. Incorporation of [¹⁴C]pro into tnchloroaceticacid (TCA)-precipitable cytoplasm was reduced by only 10 percent at 0·01–1 mM but 43 per cent at 10 mM AZCGel filtration of cytoplasm from pollen germinated without AZCbut with [¹⁴C]pro resulted in labelled void volume (V) and threeretarded peaks (RI–III) Incorporation into V and RI wasinhibited at both 0·01 and 1 mM AZC These AZC concentrationsreduced conversion of [¹⁴C]pro to wall-bound hyp by 20 percent However, total incorporation of [¹⁴C]pro into salt-water-purifiedwall fractions was suppressed 47–53 per cent (0·1–1mM AZC). Lilium longiflorum, lily, hydroxyproline, proline, azetidine-2-carboxylic acid, pollen, pollen tube elongation     

Nutrient Cycling in an Age Sequence of Western Washington Douglas-fir Stands

The cycling of nitrogen, phosphorus, calcium, magnesium andpotassium in a series of western Washington Douglas-fir [Pseudotsugamenziesii (Mirb.) Franco] stands ranging in age from 9 to 95years has been described. The stands were of relatively lowproductivity being limited by low nitrogen. The content of nitrogen,phosphorus, magnesium and potassium in tree foliage all tendedto stabilize at about 40 years whereas calcium continued toincrease. The content of all nutrients in the wood continuedto increase with stand age. Nitrogen in the forest floor accumulatedconstantly at about 5.7 kg ha^–1 year^–1 and thistogether with the above-ground tree accumulation meant about10.5 kg ha^–1 year^–1 nitrogen was immobilized. Calciumalso increased with time in the forest floor with age whereasthe other nutrients were fairly constant after about 30 years.Understorey nutrient content reached a peak at about 20 years,while understorey litter-fall was significant throughout theage sequence. Internal redistribution, especially of nitrogen,represented an increasingly greater proportion of stand requirementwith increasing stand maturity. Pseudotsuga menziesti (Mirb.) Franco, Douglas-fir, biomass, litter-fall, nutrient content, nutrient cycling     

Haploid Plantlet Formation from Female Gametophytes of Ephedra foliata Boiss. in vitro

Female gametophytes (at the archegonial stage) excised fromyoung ovules of Ephedra foliata Boiss, were cultured on a basalmedium (Murnshige and Skoog's combinations of major and minorsalts, Iron source, vitamins, myo-inositol along with 2 percent sucrose and 10 per cent coconut milk) under aseptic conditions.Growth and morphogenetic responses of the explants to auxinswere compared at different concentrations and a study of theirinteractions with cytokinins has also been made. At 2 mg 1^–1,2, 4-D induced profuse callusing which subsequently producedroots. NAA at 4 mg 1^–1 was optimal for callus growth androoting. Combinations of 2,4-D and kinetin were more effectivein inducing roots and shoot buds than those of 2,4-D and benzylamino-purine (BAP). Addition of BAP (0.05 mg ^1–1) to themedium containing optimal concentrations of NAA resulted information of a large number of roots. Kinetin induced only rootingin the presence of 4 mg 1^–1 NAA. A high concentrationof BAP (8 mg 1^–1), stimulated shoot bud formation. Forthe further development of shoot buds, neither auxin nor cytokininwas needed. Cytological observations revealed the presence ofhaploid number of chromosomes, i.e. seven. Ephedra foliata, tissue culture, callus, regeneration, 2,4-dichlorophenoxyacetic acid, naphthalene acetic acid, kinetin, benzyl amino-purine