Accumulation and Retranslocation of Mineral Nutrients in Developing Needles in Relation to Seasonal Growth of Young Radiata Pine Trees

The growth, accumulation and movement of mineral nutrients (nitrogen,phosphorus, potassium (calcium) and chlorophyll in needles ofyoung radiata pine trees (Pinus radiata D. Don) were examined,from bud break in spring through the following year. Retranslocationof nutrients from needles was measured and is discussed in relationto nutrient requirements for seasonal growth. During the first 4–5 months after bud break when mostneedle growth occurred, all nutrients and chlorophyll accumulatedprogressively, although the concentrations of nitrogen, phosphorusand potassium decreased. During summer, substantial amounts of phosphorus were withdrawnfrom needles less than 6 months old, regardless of positionon the tree and silvicultural practice. In young needles andunder certain environmental conditions, this led to a markedtemporary decline in concentrations, even in fertilized treeson a fertile site. However, the phosphorus content of needleswas quickly restored following autumn rains. Similar fluctuations,including nutrient withdrawal in summer, occurred for nitrogenand potassium, but these were smaller than those observed forphosphorus. Phosphorus was also withdrawn from relatively olderneedles during summer. It was estimated that on a tree basis 86, 48 and 39 per centof the phosphorus, nitrogen and potassium, respectively, insummer shoots could have come from the retranslocation of nutrientsfrom young needles formed during the preceding spring. These results highlight the importance of nutrients stored inneedles to meet the nutrient requirements for growth when environmentalfactors may not be conducive to nutrient uptake from the soil. Pinus radiata D. Don, mineral nutrition, retranslocation, phosphorus, nitrogen, seasonal effects, pine needle growth     

Growth and Nutrient Retranslocation in Needles of Radiata Pine in Relation to Nitrogen Supply

The effects of N application on tree growth and the retranslocationof N, P, and K from young needles to new growth were examinedin young radiata pine (Pinus radiata D. Don) trees. Nitrogen fertilization increased the number and size of needles,rates of shoot production, stem volume growth and tree biomass.Foliar N and P contents (µg per needle) fluctuated ina cyclic fashion with prominent phases of accumulation, retranslocationand replenishment. The patterns of these fluctuations in controland N-fertilized trees were similar, although the fluxes ofN, P and K in and out of needles were increased by N fertilization.Greater translocation (g per tree) of N and K from needles ofN fertilized trees occurred because fertilization increasedthe needle weight and the proportion of N and K retranslocatedfrom individual needles. Nitrogen fertilization increased theretranslocation of P largely as a result of higher needle mass.Trees supplied with more than adequate amounts of P in the soilretranslocated up to 58 per cent of the initial pool of P fromyoung needles. The periods of high retranslocation coincidedwith periods of high concentrations of soil mineral N and withshoot production. Conversely, the periods of rapid replenishmentof N and P into the needles coincided with the time of slowshoot growth and low concentration of soil mineral N. The growthrate of trees, rather than the availability of nutrients inthe soil was the main factor controlling retranslocation. For radiata pine, retranslocation from needles is not a mechanismspecific for coping with low soil fertility. It seems to bea mechanism which enhances the nutrient supply to apical growingpoints, especially during periods of flushing. Pinus radiata, nitrogen supply, shoot growth, nutrient fluctuations and retranslocation, nutrient use and adaptation     

Ageing in Woody Plants

The shoot systems of trees undergo characteristic changes withtime, as they increase in size and complexity. Certain of thesechanges, such as reduced annual growth increment, loss of apicaldominance, and changes in the geotropic responses, are easilyreversible, by pruning or by grafting shoots from older treeson to young stocks. These changes are referred to as ‘ageing’. This paper describes the changes occurring in Pinus sylvestrisand Larix leptolepis during ageing and reports an investigationinto the possible mechanisms controlling these changes. Pruningexperiments suggest that ageing is due to increased competitionfor nutrients between the various constituent shoots as thebranch systems increase in complexity, but the distributionof available nutrients is modified by apical dominance. Theseconclusions were supported by the results of experiments involvingthe injection of radioactive phosphorus (²²P), in associationwith the pruning treatments.     

Tree Suppression and the Self-thinning Rule in a Monoculture of Pinus radiata D. Don

An experiment comparing different initial planting densitiesof Pinus radiata D. Don was established in 1940 at Mt. Burrin south-east South Australia. It had been measured periodicallyto age 40 years. It is shown that after some years the treesof each individual plot of the experiment segregated into agroup of ‘suppressed’ trees which grew little indiameter and a group of actively growing ‘dominant’trees. This is consistent with other work that has suggestedthat monocultures tend to produce a two-tiered canopy. The slopeof the relationship between the logarithm of the mean weightper tree and the logarithm of the density of the various plotsof the experiment (the ‘competition-density effect’)was computed at each age at which the experiment was measured,both for all live trees of the plots and for the dominants only.For this analysis tree weights were estimated using the allometricrelationship between weight and diameter at breast height. Forthe dominants, the slope rapidly declined with age until itapproached – 1.5, which is the limiting slope of the competition-densityeffect or the so-called ‘self-thinning rule’. Whenall live trees of the plots were used, the slope declined slowlywith age but remained far from – 1.5. Previously, theself-thinning rule has been seen as determining the way in whichmortality, i.e. self-thinning, occurs in stands. In the presentwork, the rule is found to apply to the larger, actively growingtrees of the stands soon after they start to suppress the smallertrees and long before substantial mortality has occurred inmany stands. Thus tree suppression, rather than mortality, isseen to determine the rule. The pattern of diameter growth oftrees of the various stands of the experiment is found to beconsistent with previous findings that skewness of the frequencydistribution of diameters of trees of stands increases withtime. Pinus radiata D. Don, radiata pine, self-thinning, competition     

Shoot Elongation in Scots Pine: Diurnal Variations and Response to Temperature

Kanninen, M. 1985. Shoot elongation in Scots pine: Diurnal variationsand response to temperature.—J. exp. Bot. 36: 1760–1770. Time series analysis is used to study the diurnal variationsin the rate of shoot elongation of Scots pine (Pinus sylvestrisL.) seedlings, and its response to temperature. The shoot elongation of three 5-year-old Scots pine seedlingswas measured at 2 h intervals over a 12 d period in June 1979.Ambient temperature, measured with a thermocouple, was continuouslyrecorded during the same period. The measurements were carriedout in the field. Time series analysis of the data was carried out by estimatedauto-correlation and partial auto-correlation functions. A multiplicative‘seasonal’ model was applied to both the input andoutput series to ‘prewhiten’ the data set. Serialcross-correlation analysis of the prewhitened series was usedto identify the structure of the transfer function model betweentemperature and growth rate. There was a phase shift between the air temperature and shootextension. The cross-correlation function peaked at 2 h lagvalue. The influence of temperature on the growth rate was adequatelydescribed by a first-order transfer function model. The characteristicfeature of the model was a time constant of 3.3 h and a basetemperature of 6.3 °C for the response of shoot elongationto temperature. Key words: Scots pine, Pinus sylvestris L., shoot elongation, temperature response, time-series analysis     

A Study of the Growth of Four Provenances of Pinus contorta Dougl

A study was carried out on the growth of third- and fourth-yearseedlings of four provenances of Pinus contorta, two of whichwere from high elevations and two from coastal sites. Markeddifferences in height growth were observed, the two coastalprovenances showing significantly greater growth than the twomontane ones. These growth differences were due to differencesin the numbers of needle and stem ‘internode’ primordialaid down in the resting buds in the preceding year, and notto differences in ‘internode’ length in the annualextension shoots. The differences in height growth were paralleledby differences in dry weight. A greater relative height growthrate was shown by one coastal provenance and probably also bythe second, than by the montane provenances. The levels of reservematerials were similar in all provenances. These results arediscussed and it is concluded that the growth of montane provenancesmay be ‘sink limited’ rather than ‘sourcelimited’ when they are grown at lower altitudes.     

Increases in Phosphorus Requirements for CO(2)-Enriched Pine Species

Pinus radiata D. Don (half-sib families 20010 and 20062) and Pinus caribaea var hondurensis (an open-pollinated family) were grown for 49 weeks at seven levels of phosphorus and at CO₂ concentrations of either 340 or 660 microliters per liter, to establish if the phosphorus requirements differed between the CO₂ concentrations and if mycorrhizal associations were affected. When soil phosphorus availability was low, phosphorus uptake was increased by elevated CO₂. This may have been related to changes in mycorrhizal competition. When the phosphorus concentration in the youngest fully expanded needles was above 600 milligrams per kilogram the shoot weight of all pine families was greater at high CO₂ due to increases in rates of photosynthesis. More dry weight was partitioned to the stems of P. radiata family 20010 and P. caribaea. At foliar phosphorus concentrations above 1000 milligrams per kilogram (P. radiata) and 700 milligrams per kilogram (P. caribaea), growth did not increase at 340 microliters of CO₂ per liter. Soluble sugar levels in the same needles mirrored the growth response, but the starch concentration declined with increasing phosphorus. At 660 microliters of CO₂ per liter, shoot weight and soluble sugar concentrations were still increasing up to a foliar P concentration of 1800 milligrams per kilogram for P. radiata and 1600 milligrams per kilogram for P. caribaea. The starch concentrations did not decline. These results indicate that higher foliar phosphorus concentrations are required to realize the maximum growth potential of pines at elevated CO₂.     

The effect of crown position and date of sampling on biomass,nutrient concentrations and contents of needles and shoots in European larch

 The nutrient concentrations and contents of needles and shoots of 22-year-old European larch (Larix decidua Mill.) were evaluated with respect to crown position, age of tissues and sampling date during a complete growing season. Concentrations of N, P, K, Ca, Mg and Zn in the needles and of N, P and K in the shoots differed significantly among the dates of sampling. The concentrations of N and Mn in the needles and all nutrients in the shoots (except Mg) also differed significantly with crown position. Maximum needle biomass was observed in the middle crown position (55% of the total) and maximum shoot biomass, in the lower crown position (52% of the total). Maximum needle and shoot nutrient contents were observed in the middle position of the living crown for long shoot, short shoot-1, short shoot-2, short shoot-3 and, short shoot-4 age classes while highest contents for short shoot-5 and short shoot-6 age classes were observed in the lower crown position. Biases up to 42% for Mg in the needles and 200% for K in the shoots were obtained when only long shoot tissues are used for content evaluation. For needles and shoots, Mg and K are more difficult nutrients to evaluate. A sampling methodology is proposed for evaluating nutrient contents of the living crown. Accepted: 10 August 1995     

Regeneration from Rhizome Fragments of Agropyron repens (L.) Beauv. III. Effects of Nitrogen and Temperature on the Development of Dominance Amongst Shoots on Multi-node Fragments

Not all buds developed equally when 7-node rhizome fragmentsof Agropyron repens (L.) Beauv. were incubated in the dark at23 °C. Instead, after an initial flush of several shoots,buds were inhibited in a highly ordered sequence to leave onlyone dominant shoot growing. Applying an exogenous supply ofnitrogen KNO₃) early during this sequence increased the meanshoot lengths and delayed the onset of dominance. Additionally,the application of nitrogen after eight days incubation alteredthe sequence of shoot growth such that, in some instances, smallrapidly-growing basal shoots ‘dominated’ largerand more slowly-growing apical ones. Dominance (correlativeinhibition) was maintained in untreated fragments for up to383 days Numbers of active budsand shoot extensionrate weremaximal intherange 13°to 23 °C where dominance was establishedwithin 30 days. Incontrast only 6 per cent of rhizome fragmentskept at 33 °C had dominant shoots after 65 days. At 3 °Cshoot growth was so slow that dominance was not permanentlyestablished within 150 days. Numbers ofactive budsand shoot extensionrate weremaximal intherange 13° to 23°C where dominance was establishedwithin 30 days. Incontrast only 6 per cent of rhizome fragmentskept at 33 °C had dominant shoots after 65 days. At 3 °Cshoot growth was so slow that dominance was not permanentlyestablished within 150 days It is suggested that the effects of nitrogenand temperatureon dominance in multi-noderhizome fragments can be interpretedin terms of competition for nutrients between shoots, and theantagonistic effects of nitrogen on an auxin-mediated inhibitionby the dominant shoot.     

Effects of Gibberellin, Clone and Environment on Cone Initiation, Shoot Growth and Branching in Pinus contorta

Effects of photoperiod, temperature and gibberellin applicationwere clearly separated from clonal differences when small rootedcuttings, originating from two ‘floriferous’ treesof the same provenance of Pinus contorta Dougl., were treatedwith a simple micro-injection technique and grown in growthcabinets. Short days (10 h) for 11 weeks induced six times asmany female cones as long days (19.5 h), completely inhibitedfurther needle elongation after 5 weeks, and also led to enhancedbranching by year 3. Cool temperatures appeared to favour malecone initiation in year 1, and (in conjunction with long days)significantly promoted height in year 2. Injection with 1 mgGA_4/7 led to substantial and highly significant increases inbud growth in year 1, and in height, needle number and totalneedle length in year 2. Gibberellin treatment also increasedbranching but did not significantly affect internode elongationin year 2, nor cone initiation or needle elongation in year1. Highly significant clonal differences occurred, with onegenotype having longer leaves and buds in year 1, and up to80 per cent greater numbers and total lengths of needles inyear 2. Marked clonal differences in height growth, branchingand sex ratio were also found. The implications of both resultsand approach are discussed in relation to developmental physiology,genetic selection and advances in forestry research. leaf growth, height growth, branching, cone initiation, sex, photoperiod, temperature, controlled environments, gibberellin, vegetative propagation, clonal differences, Pinus contorta,, pine     

The Movement of Zinc through Excised Stems of Seedlings of Pinus radiata D. Don.

Radioactive Zn solns were drawn through 10 cm stem sectionsexcised from seedlings of P. radiata to determine the locationand quantity of ⁶⁵Zn remaining in the stems and the concn of⁶⁵Zn in the exudate. Zinc was removed from solns passing through the excised stemsby processes which appeared to be non-metabolic because coolingthe inflow solns did not decrease the proportion of Zn removedand non-specific because Ca competed with Zn for ‘exchangesites’. The formation of anionic or uncharged complexes between Zn andEDTA, or citrate resulted in more Zn passing through the excisedstems. Consistent with the greater stability of Zn-EDTA complexesmore Zn passed through stems treated with EDTA than with citrate.Decreasing the pH of solns containing Zn, Ca and potassium citrateincreased the amount of Zn deposited in the basal (inflow) endof the stems, probably by decreasing the amount of Zn boundto citrate. Increasing the conen of Zn in test solns containingZn, Ca and potassium citrate did not change the distributionof ⁶⁵Zn in the stems as the capacity of the stems to removeZn from soln was large enough to remove all the free Zn in allthe solns Pinus radiata D. Don, pine, zinc, movement, stems     

Nutritional and root development factors affecting growth of tissue culture plantlets of loblolly pine

Tissue culture plantlets of loblolly pine ( Pinus taeda L.) were compared to seedlings to quantify growth and developmental differences. The two plant types were grown in containers in a greenhouse and sampled periodically for twenty weeks. Dry weights and nitrogen and phosphorus concentrations of the shoots and roots were determined every two weeks.
During the twenty weeks in the greenhouse, seedlings grew to a greater size than the plantlets, but the relative rates of growth were approximately equal. Plantlets had significantly lower concentrations of nitrogen and phosphorus per g of shoot dry weight. Seedlings were much more efficient at nutrient uptake per g of dry weight of root. Plantlets had thick, unbranched roots, which were inefficient at nitrogen and phosphorus uptake. Nutrient uptake based on an index of root surface area was equal in the plantlets and seedlings.
The main differences between plantlets and seedlings apparently were related to root system morphology rather than physiological processes. The uptake of nutrients showed the greatest difference between the plant types.     

Nutrition and growth of coniferous seedlings at varied relative nitrogen addition rate

The growth of two provenances of Pinus sylvestris L. were compared with two provenances of Picea abies (L.) Karst. and with Pinus contorta Dougl. when grown in solution cultures with low nutrient concentrations. Nitrogen was added at different exponentially increasing rates, and the other nutrients were added at a rate high enough to ensure free access of them to the seedlings. During an initial period of the culture (a lag phase), when the internal nutrient status was changing from optimum to the level of the treatment, deficiency symptoms appeared. The needles yellowed and the root/shoot ratio increased. The initial phase was followed by a period of exponential growth and steady-state nutrition. The needles turned green again, and the root/shoot ratio stabilized at a level characteristic of the treatment. These patterns were the same as previously reported for other tree species. The relative growth rate during exponential growth was numerically closely equal to the relative nitrogen addition rate. The maximum relative growth rates were about 6 to 7.5% dry weight increase day^-1. This is a much lower maximum than for broad-leaved species (about 20 to 30% day^-1) under similar growth conditions. The internal nitrogen concentrations of the seedlings and the relative growth rates were stable during the exponential period. Close linear relationships were found between these parameters and the relative addition rate up to maximum growth. During steady state the relative growth rates of the different plant parts were equal. However, there were large differences between genotypes in absolute root growth rate at the same seedling size because of differences in root/shoot ratio. Lodgepole pine had the highest root growth rate, whereas that of Norway spruce, especially the southern provenance, was remarkably low. Yet, Norway spruce had a high ability to utilize available nutrients. In treatments with free nutrient access, growth allocation to the shoot had a high priority in all genotypes, but there was still a marked tendency for luxury uptake of nutrients. Nitrogen productivity (growth rate per unit of nitrogen) was lower than in broadleaved species and highest in lodgepole pine. The relevance of the dynamic factors, i.e. maximum relative growth rate, nutrient uptake rate, nitrogen productivity, growth allocation and root growth rate, are discussed with regard to conifer characteristics and selection value.     

Developmental Genetics and Morphological Evolution of Flowering Plants, Especially Bladderworts (Utricularia): Fuzzy Arberian Morphology Complements Classical Morphology

This review compares new developmental models on flowering andother vascular plants with evolutionary hypotheses formulatedby Agnes Arber (1879–1960) and like-minded botanists.Special emphasis is laid on philosophical basics such as perspectivism,pluralism about evolutionary modelling, continuum way of thinking,and fuzzy logic. Arber's perspective is best labelled as F uzzyA rberian M orphology (FAM Approach). Its proponents (‘FAMmers’)treat structural categories (e.g. ‘roots’, ‘shoots’,‘stems’, ‘leaves’, ‘stipules’)in vascular plants as concepts with fuzzy borderlines allowingintermediates (including transitional forms, developmental mosaics).The FAM Approach complements Cla ssical Plant M orphology (ClaMApproach), which is the traditional approach in botany. ClaMproponents (‘ClaMmers’) postulate that the structuralcategories of vascular plants are regarded as concepts withclear-cut borderlines and without intermediates. However, duringthe evolution of vascular plants, the root-shoot distinctionand the stem-leaf distinction have become blurred several timesdue to developmental changes, resulting in organs with uniquecombinations of features. This happened, for example, in thebladderworts (Utricularia, Lentibulariaceae). When focusingon the ‘leaf’, the FAM Approach is identical toArber's ‘partial-shoot theory of the leaf’ and Sinha's‘leaf shoot continuum model’. A compound leaf canrepeat the developmental pathway of the whole shoot, at leastto some degree. For example, compound leaves of Chisocheton(Meliaceae)with indeterminate apical growth and three-dimensional branchingmay be seen as developmental mosaics sharing some growth processeswith whole shoots! We focus here on the FAM Approach becausethis perspective is especially promising for developmental geneticistsstudying flowering and other vascular plants. Copyright 2001Annals of Botany Company Review, body plan, developmental mosaics, leaf development, history of botany, homeosis, homeotic genes, Lentibulariaceae, morphological evolution, process morphology, stipules, Utricularia, flowering plants     

The Effect of Bud Position on Branch Growth and Bud Abscission in Quercus petraea (Matt.) Liebl.

The time at which a bud began to expand was related to its positionnot only on an individual shoot but also within the crown. Thedistribution of buds and branches on the shoot was uneven; theshoot tip, where they were densely clustered, was termed the‘whorl; and the remainder of the shoot, where they werewidely spaced, the ‘interwhorl’ stem. In spring,the terminal bud started expanding before the ‘whorl’buds which preceded the ‘interwhorl’ stem buds;completion of the flush of growth, determined by the end ofleaf expansion, occurred in the reverse order, ‘interwhorl’> ‘whorl’ > terminal. Similarly bud expansionstarted at the top of the crown and progressed downwards, andthe first shoots to complete their flush were at the bottomof the crown. Approximately 60% of the buds on each shoot beganexpanding in spring but only about half of these formed branches.Bud abscission began in May and by Sep. 45% of buds originallypresent had abscised. Most of-the buds that did not abscisewere the small buds at the base of the shoot that were not originallyassociated with a leaf. Approximately 42% of ‘whorl’buds and 28% of MnterwhorP stem buds formed branches. ‘Whorl’branches were approx. 60% longer that ‘interwhorl’stem branches; buds on the lower surface of the shoot producedlonger branches than those on the upper surface. The implicationsof the results for the development of crown form and selectionof superior oak are discussed. Quercus petraea, oak, buds, branches, crown form     

Nitrogen Utilization in N-limited Barley During Vegetative and Generative Growth: IV. TRANSLOCATION AND REMOBILIZATION OF NITROGEN

Barley (Hordeum vulgare L., cvs Golf and Laevigatum) was grownunder nitrogen limitation in solution culture until near maturity.Three different nitrogen addition regimes were used: in the‘HN’ culture, the relative rate of nitrate-N additionwas 0·08 d^–1 until day 48 and then stepwise decreasedto, finally, 0·005 d^–1 during late grain-filling;the ‘LN’ culture received 45% of the nitrogen addedin HN; the ‘CN’ culture was maintained at RA 0·0375d^–1 throughout growth. At four different growth stages(vegetative,anthesis, and twice during grain-filling), ¹⁵N-nitrate was fedto the plants. In some cases (‘split root cultures’),label was fed only to one-half of the root system. These wereharvested directly after labelling, whereas ‘standardcultured’ plants were harvested at termination of theexperiment (day 148). Absorption of added nitrate was nearlycomplete in the HN and LN cultures, and translocation of nitrogenwithin the plants could thus be studied independently of differencesin nitrate absorption. Cycling of nitrogen absorbed by vegetativeplants accounted for up to 50% of the nitrogen recovered inthe roots. The sink strength of the roots for cycling nitrogen,however, declined during post-anthesis growth, and net lossof nitrogen from both roots and vegetative shoot tissue occurredconcomitantly with incorporation of labelled ¹⁵N-nitrogen. Thenitrogen of the vegetative shoot tissue was substantially lesslabelled than the nitrogen entering the ears, indicating thattranslocation of recently absorbed nitrogen to ears occurs withminor prior exchange with the bulk nitrogen of shoots. In caseswhere the sink strength of the ears was weak, as in LN-culturedLaevigatum (due to high frequency of sterile flowers) and inCN-cultured Golf, nitrogen translocated from roots appearedto be incorporated into the vegetative shoot tissue. There werealso indications that a fraction of the remobilized nitrogenwas actually lost from the plants in these cases. It is concludedthat the root remains efficient in translocation of nitrogento the aerial parts throughout ontogeny and that nitrogen takenup during grain–filling is preferentially directly translocatedto the developing grains. The further translocation of nitrogenreceived by vegetative shoot parts to ears appears mainly relatedto the potential of the ear to accumulate nitrogen. Nitrogenabsorbed/remobilized in excess of the sink strength of the earsis either invested in continued shoot growth, or is irreversiblylost from the plants. Key words: Barley, ¹⁵N-labelling, post-anthesis, remobilization, translocation     

The Effect of Applications of a Synthetic Cytokinin on Shoot Dominance and Grain Yield in Spring Barley

Spring barley cv Ark Royal was grown in pots in the open, andsoil drenches containing 6-benzyl-aminopurine were repeatedlyapplied during the pre-heading phase starting either ‘early’when the main shoot apex had reached the glume primordium stage,during tillering, or ‘later’ at the anther primordiumstage, at the start of stem elongation Although grain yield was unaffected by the ‘late’cytokinin treatments, it was increased by up to 57 per centby the ‘early’ treatments. The increase was dueto greater grain yields of the smaller shoots of each plantthere was no effect on the yields of the two largest shootsor on the total number of fertile shoots The increased grain yield of these smaller shoots was attributableto increased weights of their individual kernels, especiallyin the basal and distal parts of the ears such that a greateruniformity of kernel size within the ear was achieved Thus the cytokinin treatment increased uniformity both betweenshoots and between spikelets within the ears Hordeum vulgare L, spring barley, cytokinin, 6-benzylaminopunne, shoot dominance, harvest index, grain yield     

Effects of Soil Temperature on the Growth and Hormone Content of Dactylis glomerata L. (Cocksfoot) in Controlled Environments

A comparison was made of effects of ‘low’ and ‘high’soil temperature (LST and HST, about 9 and 21·5 °Crespectively) on shoot growth of Norwegian and Portuguese populationsof Dactylis glomerata. In experiments lasting 8 short days (SD,8 h photoperiods) LST decreased leaf extension more markedlyin the Portuguese population. No differential effect of LSTon leaf growth was recorded in experiments lasting 20 or 21SD or in experiments of 8 d duration in long days (LD, 16 hphotoperiods). Since the meristem and region of cell extensionis close to the soil surface LST could directly influence bothroot and shoot growth. The application of gibberellic acid enhanced leaf extension,particularly in plants grown at HST. 6-Benzylaminopurine tendedto decrease leaf length. Extractable gibberellin levels wererelatively low after 8 SD in shoots of both races grown at LST.Cytokinin levels increased at LST, more so in shoots of Portugueseplants which sustained the greater reduction in leaf extension. The data suggest that LST may reduce the production of endogenousgibberellins important for leaf growth in Dactylis glomerata.Cytokinins are probably necessary for growth processes but theirlevel may reflect, rather than direct, the rate of leaf growth.     

Seasonal ionic fluctuations and annual growth rates in stands of Pinus silvestris L. and Picea abies Karst. (L.)

Seasonal variations in potassium, calcium, nitrogen, phosphorus, and magnesium contents of needles from two different stands of Pinus silvestris L. and Picea abies (L.) Karst. were determined monthly during a period of two years, and the growth rates once a year during five years. The stands were growing on sand or on clay. The supposed transport of potassium to the shoot during autumn could not be demonstrated. The nutrient status of pine and spruce growing on sand and clay was very similar, except for calcium and magnesium. There were only small differences in ion contents between pine and spruce, except for calcium. On soils with low water-holding capacity, the available water in dry years is the limiting factor affecting the growth rate of spruce but not of pine. It is concluded that the nutrient status of the leaves, the growth rates and the available water in the soil are factors that should have an important part in any discussion of fertilization of coniferous forests.     

A Comparative Study of some Methods for Measuring Cell Growth Potentials in Vigna radiata Hypocotyl, in situ and after Excision

Prat, R. 1985. A comparative study of some methods for measuringcell growth potentials in Vigna radiata hypocotyl, in situ andafter excision.—J. exp. Bot. 36: 1150–1158. Accurate estimations of growth rates are required to understandthe development of physiological and biochemical parametersinvolved in growth processes. Growth measurements can be madeeither ‘in situ’ on whole seedlings by marking successivelevels or ‘in vitro’, after excision of successivehypocotyl segments. These different methods have been comparedin order to determine which measurements allow one to assessaccurately the normal growth characteristics. In vitro measurementsperformed with excised segments required a prolonged incubationperiod before stable growth rates were achieved. The growthpotentials of the successive hypocotyl levels remain unchangedafter excision. These in vitro measurements can therefore beused to assess the growth characteristics of cells in hypocotyls. Key words: Vigna radiata, hypocotyl, growth measurements