Nutrient Supply, Dry-matter Production and Nutrient Uptake of Forest Tree Seedlings

The dry-matter production and nutrient uptake of forest-treeseedlings grown under controlled levels of nutrition in sub-irrigatedsand culture were investigated. Hardwood seedlings attainedgreater dry weight than conifer seedlings, and Pinus radiataa greater dry weight than P. contorta and P. nigra, but thesegreater dry weights were not related to greater leaf/weightratios, although seed size may have been an important influenceon final seedling dry weight. P. radiata was found to have alower requirement for P than P. contorta and P. nigra in oneexperiment. The demand (total nutrient uptake per unit of time) made bythree species for nutrients upon a site was shown to dependmore upon growth-rate per annum than on efficiency (quantityof nutrients required to produce a unit of dry matter). It isconcluded that the ability of tree species to grow satisfactorilyon soils of low nutrient status depends largely on their abilityfor relatively slow growth. On the other hand, species showinggood response to favourable sites may also make satisfactorygrowth on poor sites.     

Seasonal Changes of Bioelements in the Litter and their Potential Return to Green Leaves in four Species of the Argentine Subtropical Forest

The aim of this work was to analyse the nutrient concentrationsof N, P, Ca, Mg, K and Na in mature leaves, branches and fruitsand to investigate relationships between the contents of thesebioelements in senescent and fresh leaves in four forest species:Gleditsia amorphoides ( Espina Corona), Patagonula americana(Guayaibí),Chlorophora tinctoria ( Mora) and Astroniumbalansae (Urunday). The study site was located in the ColoniaBenítez Estricta Nature Research (Chaco, Argentina).In this subtropical forest, total litter was collected monthlyand was sorted into three groups: (1) leaves; (2) branches andfruit; (3) unidentified. Total dry matter was recorded and analysedfor N, P, Ca, Mg, K and Na. Espina Corona had the highest leafconcentrations of N, while Mora had the highest concentrationsof Ca and Mg. The highest leaf concentrations of P were foundin Espina Corona, Mora and Urunday. No significant differencesin K were found among the different species. Na concentrationswere higher in Espina Corona and Guayaibí than Mora andUrunday. A marked seasonal variability was observed in the concentrationsof N, P and K, with no important differences for Ca and Mg,except in Espina Corona. These variations in nutrient concentrationswere greater in leaves than in branches and fruits. N and Pwere translocated to other tree organs and Ca, Mg and Na wereaccumulated in mature leaves. The bioelement K is the only onethat undergoes leaching and mobilization in all species. ResorbedN and P can be used for the production of new leaf organs inthe following annual cycle. This resorption supports a portionof the production of new foliage, diminishing the demand fromsoil.Copyright 2000 Annals of Botany Company Above-ground production, potential return, nutrient resorption, leaf analysis, tropical forest, Gleditsia amorphoides, Patagonula americana, Chlorophora tinctoria, Astronium balansae, Espina Corona, Guayaibí, Mora, Urunday.     

An empirical model of primary productivity (14C) using mesocosm data along a nutrient gradient

The two parameters of the hyperbolic tangent equation, P_m and, were estimated from in situ vertical profiles of primary productionusing mesocosm data along a nutrient gradient. The parameters,derived from 4-h (around noon) ¹⁴C incubations, were used togetherwith the photosynthesis-light curve and hourly solar radiationdata to calculate daily primary production rates (P_d). Approximately40% of the daily production occurred in the 4 h around noon.Considering parameter uncertainty, there was no indication ofan increase in variation in production with increased nutrientloading, nor did biomass-specific P-I parameters increase. Annualproduction ranged from 82 to 901 g C m^–2 year^–1and was highest in the highest nutrient treatment tank. Dailyproductivity ranged from 0.02 to 9.1 g C m^–2 day^–1and was significantly correlated, in all treatments, with acomposite parameter BI₀/k (where B is phytoplankton biomass;I₀ is daily radiation and k is the extinction coefficient).Linear regressions of P_d against BI₀/k indicated that much ofthe variability (86%) in productivity was explained by lightavailability and phytoplankton biomass. Two approaches for predictingproductivity were compared: (i) predicting production directlyfrom environmental variables (i.e. BI₀/k) and (ii) predictingthe parameters of the P-I curve from environmental variablesand using these to calculate daily production.     

Response of phytoplankton and bacteria to nutrients and zooplankton: a mesocosm experiment

Although both nutrient inputs and zooplankton grazing are importantto phytoplankton and bacteria in lakes, controversy surroundsthe relative importance of grazing pressure for these two groupsof organisms. For phytoplankton, the controversy revolves aroundwhether zooplankton grazers, especially large cladocerans likeDaphnia, can effectively reduce phytoplankton populations regardlessof nutrient conditions. For bacteria, little is known aboutthe balance between possible direct and indirect effects ofboth nutrients and zooplankton grazing. However, there is evidencethat bacteria may affect phytoplankton responses to nutrientsor zooplankton grazing through direct or apparent competition.We performed a mesocosm experiment to evaluate the relativeimportance of the effects of nutrients and zooplankton grazingfor phytoplankton and bacteria, and to determine whether bacteriamediate phytoplankton responses to these factors. The factorialdesign crossed two zooplankton treatments (unsieved and sieved)with four nutrient treatments (0, 0.5, 1.0 and 2.0 µgphosphorus (P) l^–1 day^–1 together with nitrogen(N) at a N:P ratio of 20:1 by weight). Weekly sieving with 300µm mesh reduced the average size of crustacean zooplanktonin the mesocosms, decreased the numbers and biomass of Daphnia,and increased the biomass of adult copepods. Nutrient enrichmentcaused significant increases in phytoplankton chlorophyll a(4–5x), bacterial abundance and production (1.3x and 1.6x,respectively), Daphnia (3x) and total zooplankton biomass (2x).Although both total phytoplankton chlorophyll a and chlorophylla in the <35 µm size fraction were significantly lowerin unsieved mesocosms than in sieved mesocosms, sieving hadno significant effect on bacterial abundance or production.There was no statistical interaction between nutrient and zooplanktontreatments for total phytoplankton biomass or bacterial abundance,although there were marginally significant interactions forphytoplankton biomass <35 µm and bacterial production.Our results do not support the hypothesis that large cladoceransbecome less effective grazers with enrichment; rather, the differencebetween phytoplankton biomass in sieved versus unsieved zooplanktontreatments increased across the gradient of nutrient additions.Furthermore, there was no evidence that bacteria buffered phytoplanktonresponses to enrichment by either sequestering P or affectingthe growth of zooplankton.     

Dynamics of Competition in Populations of Carrot (Daucus carota)

Populations of carrot (Daucus carota) were raised over a widerange of densities (79–5763 plants m^-2) to examine thedynamics of competition in terms of yield–density relationshipsand size variability, and to investigate the effects of nutrientsupply on competition. While the relationship between shootyield and density was asymptotic, the relationship between rootand total yield and density tended to be parabolic. For a giventime and density series the relationship between yield per unitarea and density could best be described by the model: y=w_mD_(1+aD)^b wherey is the yield per unit area,D is density,w_m, a andb arefitted parameters. The parametersw_m anda increased over timebut nutrient availability affected onlyw_m. An extension of thebasic yield-density model is proposed to describe the dynamicsof the yield–density relationship over time: y=kD_{[1+cexp(-rt)]{1+}     

Potential contributions of vertically migrating Rhizosolenia to nutrient cycling and new production in the open ocean

We present a numerical model of nutrient uptake and photosynthesisduring migrations of the marine diatom Rhizosolenia that wasdeveloped to estimate fluxes of carbon and nitrogen due to thesemigrations in the open ocean. The predicted specific rate ofincrease of Rhizosolenia was 0.11–0.15 day¹, whereas thetotal time for one migration cycle ranged between 3 and 5 days.Using published estimates of Rhizosolenia abundance, we estimatethat new primary production due to Rhizosolenia migrations rangesbetween 0.018 and 0.033 mmol N m^–2 day^–1. Thesevalues represent up to 17% of new production due to turbulentdiffusive fluxes of nitrate into the euphotic zone and are ofthe same order of magnitude as new production due to nitrogenfixation in tropical oceans. Large-scale contributions of Rhizosoleniato oceanic new production are limited by their relatively lowstanding crop. Variations in the formulation of losses withdepth greatly affected gross and net fluxes of carbon and nitrogen.Better characterization of losses of Rhizosolenia and improvedestimates of its abundance will help determine more accuratelythe contributions of Rhizosolenia to global biogeochemical cycles. ¹Present address: Department of Agricultural and EnvironmentalScience, The Queen's University of Belfast New forge Lane, BelfastBT95PX, UK     

Ecological investigations of blooms of colonial Phaeocystis pouchetti--I. Abundance, biochemical composition, and metabolic rates

A winter bloom of the colonial stage of the prymnesiophyte Phaeocystispouchetit was studied in the 13-m³ mesocosms of the Marine EcosystemResearch Laboratory on Narragansett Bay, Rhode Island The tankswere temperature regulated at 4±2°C but differedin their nutrient concentrations and in situ irradiances. Oneof the tanks was a control without added nutrients, one receiveda temporary nutrient spike and two others received daily N/P/Siinputs. Photosynthesis and growth rates of colonies exposedto a range of natural light levels were measured at weekly intervals.Particulate carbon production and release of dissolved organiccarbon (DOC) by the entire plankton community was determinedconcurrently. Photosynthesis and growth rates of Phaeocystisin tanks receiving daily nutrient additions were asymptoticfunctions of irradiance. Light-saturated rates exhibited asymptoticrelationships with dissolved inorganic nitrogen (N) levels.N-Limited populations showed more variable responses. Althoughirradiance and N availability regulated the population dynamicsof Phaeocystis, the presence or absence of silicate (S₁) influencedits relative importance in each tank. Phaeocystis dominatedcommunity metabolism in the absence of Si, but co-occurred withextensive stands of diatoms when Si was available. A significantpositive correlation was found between the contribution by Phaeocystisto community production and the proportion of photosynthatereleased as DOC In all tanks, Phaeocystis populations exhibitedcycles of abundance in which division of cells within coloniespreceded the multiplication of colonies. The production of newcolonies apparently occurred via two mechanisms: the formationof colonies from solitary cells, and the cleavage of largercolonies into smaller daughter colonies. Phaeocystis in tankswith near undetectable nutrient levels contained C:N, C:Chla, and C:ATP ratios several times higher than colonies in nutnent-repletetanks. Phaeocystis C:Chl a and C:ATP ratios were substantiallygreater than those of non-gelatinous phytoplankton due to carbohydratestorage in colony gelatin In contrast, C:N ratios in Phaeocystisand non-gelatinous phytoplankton were similar, suggesting astorage depot of organic N outside of the cells. The resultssupport the notion that Phaeocystis colonies function as biologicalentities rather than as passive aggregations of cells.     

Structure and Function of an Age Series of Eucalypt Plantations in Central Himalaya, II. Nutrient Dynamics

This paper deals with nutrient dynamics in 2- to 8-year-oldplantations of Eucalyptus tereticornis Sm. previously investigatedfor dry matter dynamics. The nutrient concentrations changedin the order: herb > shrub > tree. The nutrient concentrationsin the different components of these vegetation types also decreasedwith plantation age. The nutrient content in trees and shrubsincreased and in herbs it decreased with increase in plantationage. The uptake of nutrients by vegetation and also by componentswith or without adjustment for retranslocation, has been calculatedseparately. Turnover time for different nutrients ranged between1.05 and 1.35 years. Compartmental models for nutrient dynamicshave been developed to represent the distribution of nutrientcontents and net annual fluxes within the system. Eucalyptus tereticornis plantation, nutrient concentration, standing state, uptake, turnover, nutrient cycling     

Spatial characterization of nutrient dynamics in the Bay of Tunis (south-western Mediterranean) using multivariate analyses: consequences for phyto- and zooplankton distribution

The hydrological structure and nutrient dynamics of the Bayof Tunis (south-western Mediterranean), and the abundance ofits principal plankton groups (diatoms, dinoflagellates, tintinids,rotifers, appendicularians, copepods, medusae, siphonophores,chaetognaths and cladocerans), were studied over 2 years. Despitethe small size of the Bay (361 km²), the nutrient concentrationsvaried greatly between the sampling stations. We distinguishedspatial from temporal variations using a newly-developed methodfor regionalization based on multivariate cluster analysis,and the changes over time of any similarities between stations.The method allowed us to obtain an optimal geographical divisionof any degree of grouping of the sampling stations (i.e. fora chosen number of zones). We also calculated the optimum partitionof stations using a multivariate matrix obtained from multi-parametersampling over time. The application of the method to a time-seriesof nutrient concentrations in the Bay of Tunis produced fourzones of similar nutrient dynamics. Each zone was then characterizedby the median and the variability of its nutrient, physicaland biological parameters. A statistical test was used to assessthe significance of the differences between zones for the variousparameters. Comparison of the medians of the various parametersallowed us to synthesize the underlying differences in nutrientdynamics and also in plankton ecosystem components. This analysisrevealed a relative nutrient enrichment in the west and south-westernareas of the Bay. Silicates did not contribute to the high variabilityof nutrients in the Bay. The pattern of phytoplankton biomass(chlorophyll a) and the abundance of diatoms and dinoflagellateswere similar to those of the sampled nutrients. The highestvalues were measured in the first zone, where the highest nutrientconcentrations were also recorded. The coastal zones were characterizedby zooplankton groups of small size (tintinids, rotifers andsmall copepods) with a limited diversity. These zones were alsovery turbid and shallow. Central zones, on the other hand, wererich in zooplankton species. Meso-zooplankton groups (e.g. siphonophres,chaetognaths) were also more abundant in this zone.     

Effects of elevated carbon dioxide on three grass species from montane pasture II. Nutrient uptake, allocation and efficiency of use

Agrostis capillaris L.⁴ Festuca vivipara L. and Poa alpinaL.were grown in outdoor open-top chambers at either ambient (340µmol mol^–1) or elevated (680 µmol^–1)CO² for periods from 79 to 189 d. Under these conditions thereis increased growth of A. caplllarls and P. alpina, but reducedgrowth of F. vivipara. Nutrient use efficiency, nutrient productivity(total plant dry weight gain per unit of nutrient) and nutrientallocation of all three grass species were measured in an attemptto understand their individual growth responses further andto determine whether altered nutrient-use efficiencies and productivitiesenable plants exposed to an elevated atmospheric CO₂ environmentto overcome potential limitations to growth imposed by soilfertility. Total uptake of nutrients was, in general, greater in plantsof A. capillaris and P. alpina (with the exception of N andK in the latter) when grown at 680 µmol mol^–1 CO₂.In F. vivipara, however, uptake was considerably reduced inplants grown at the higher CO₂ concentration. Overall, a doubling of atmospheric CO₂ concentration had littleeffect on the nutrient use efficiency or productivity of A.capillaris. Reductions in tissue nutrient content resulted fromincreased plant growth and not altered nutrient use efficiency.In P. alpina, potassium, magnesium and calcium productivitieswere significantly reduced and photosynthetic nitrogen and phosphorususe efficiencies were doubled at elevated CO₂ with respect toplants grown at ambient CO₂ F. vivipara grown for 189 d showedthe most marked changes in nutrient use efficiency and nutrientproductivity (on an extracted dry weight basis) when grown atelevated CO₂, F. vivipara grown at elevated CO₂ however, showedlarge increases in the ratio of non-structural carbohydrateto nitrogen content of leaves and reproductive tissues, indicatinga substantial imbalance between the production and utilizationof assimilate. Key words: Nutrient, allocation, nutrient use efficiency, grasses, nutrient productivity, elevated CO₂, cliniate change     

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     

Sinking rates of heterogeneous, temperate phytoplankton populations

Throughout the summer of 1978, the sinking rates of phytoplanktonwithin the Controlled Experimental Ecosystems (CEE's) were monitoredusing a technique based upon measurement of the transit timeof radioactively (¹⁴C) labeled cells. The experimental frameworkof FOODWEB 1 offered an unprecedented opportunity to documentthe sinking rates of heterogeneous phytoplankton of diversetaxonomic composition, growing under a variety of nutrient regimes;the absence of advective exchange in the CEE's provided knowledgeof the preconditioning history of the phytoplankton sampledat any given time. Sinking rates of whole phytoplankton assemblages (not size-fractioned)ranged from 0.32 – 1.69 m·day^–1; the averagerate (± s.d.) observed was 0.64 ± 0.31 m·day^–1.The most notable deviations from the mean value occurred whenthe population size distribution and taxonomic composition shifteddue to blooms. The relationship between phytoplankton sinkingand ambient nutrient levels was studied by following the ratesof a given size fraction (8–53 µm) for ten daysfollowing nutrient enrichment of a CEE. Over this time sinkingrates ranged from 1.08– 1.53 m·day^–1; decreasedrates occurred after nutrification, yet over the course of theentire trial sinking rates were not significantly (p >0.05)correlated to the ambient levels of any single nutrient species. The sinking rate implications of spore formation were also studied,and showed that sinking rates of Chaetoceros constrictus andC. socialis spores (2.75 ± 0.61 m·day^–1)were ca 5-fold greater than rates measured when the vegetativestages of these species dominated the population, reflectingthe influence of physiological mechanisms in controlling phytoplanktonbuoyancy. An example of the potential influence of colony formation uponbuoyancy was noted in observations of C. socialis which occasionallywas found to exist in large spherical configurations made ofcoiled cell chains and having low (0.40 m·day^–1)sinking rates. A hydrodynamic rationale is presented to showhow such a colony together with enveloped water may behave asa unit particle having lower excess density, and therefore lowobserved sinking rate, despite its conspicuously large size. Overall, sinking rates were not significantly correlated withany of the measured nutrient or photic parameters. There were,however, trials and comparisons which showed evidence for: (1)higher sinking rates in populations dominated by large cells,(2) decreased sinking rates after nutrient enrichment, and (3)buoyancy response to light levels. It is suggested that correlationof sinking rates with synoptic environmental measurements atany given time is not explicit because the associations mayinvoke lag times of physiological response. The interpretationmade from these findings is that the preconditioning historyof the population, rather than the prevailing conditions atthe time of a given measurement, is most closely associatedwith population buoyancy modifications.     

Adaptation and Functional Balance Between Shoot and Root Activity of Sunflower Plants Grown at Different Root Temperatures

Helianthus annuus L. plants were grown with the shoots at normalair temperature and with the roots in nutrient solution at 10,20 or 30 °C. The higher the root temperature the greaterthe growth of the leaves, resulting in higher production ofphotosynthates. Irrespective of growth conditions an equilibriumwas established between the maintenance respiratory activityof shoot and roots. A constant proportion of the photosynthateproduced was used in respiration. The results are discussedin relation to a thermodynamic theory of stability of biologicalsystems. It is suggested that changes in energy partition betweenmaintenance and growth, and then in relative growth rates ofshoots and roots during an adaptation period, represent a majorhomeostatic mechanism. shoots, roots, maintenance respiration, growth, relative growth rate, respiration, adaptation, sunflower, Helianthus annuus L.     

Measuring production and viability of eggs in Calanus helgolandicus

The effect of several biotic and abiotic factors on the fecundityand hatching success of Calanus helgolandicus was tested duringshort- and long-term incubations. The results show that thevariations of the reproductive responses of C.helgolandicusare time dependent and rely on the type of factor tested. Whenstandardized over a 24 h incubation period, estimates ofin situproduction and egg viability can be obtained with good accuracy.     

Mineral Depletion and Leaf Senescence in Soya Bean as Influenced by Foliar Nutrient Application During Seed Filling

Senescence, as judged by the time courses of leaf lamina photosynthesis,soluble protein and chlorophyll contents, was studied in relationto mineral redistribution in field-grown soya beans [Glycinemax (L.) Merr] to investigate the hypothesis that the depletionof nutrients m the leaves by the developing seeds is the causeof soya bean senescence. A mineral nutrient solution was appliedto the canopy during the seed-filling period, and the effectson senescence and mineral depletion of the leaves were determinedin three cultivars, at two leaf positions, weekly from beginningof seed filling through physiological maturity. The onset of senescence occurred shortly after the beginningof rapid seed filling Photosynthetic rate declined about 60per cent within 3 weeks. Protein dropped by 52 per cent andchlorophyll by 48 per cent over the same period. Foliar nutrient application, at a rate previously shown to givesignificant yield increases in soya beans, increased the concentrationsof N, P and K in the leaf laminae, but tended only to delaytheir decline and failed to either delay the onset or alterthe course of senescence. The results of this experiment seem to indicate that, undernormal growth conditions, the events of senescence in the soyabean are not causally related to the N, P or K concentrationsof the leaf laminae Glycme max (L.) Merr., soya bean, nitrogen, phosphorus, potassium, leaf protein, chlorophyll, photosynthesis, foliar nutrient application, mineral depletion, leaf senescence     

Growth Consequences of Soil Nutrient Heterogeneity for two Old-field Herbs,Ambrosia artemisiifoliaandPhytolacca americana, Grown Individually and in Combination

Plant species can respond to small scale soil nutrient heterogeneityby proliferating roots or increasing nutrient uptake kineticsin nutrient-rich patches. Because root response to heterogeneitydiffers among species, it has been suggested that the distributionof soil resources could influence the outcome of interspecificcompetition. However, studies testing how plants respond toheterogeneity in the presence of neighbours are lacking. Inthis study, individuals of two species,Phytolacca americanaL.andAmbrosia artemisiifoliaL. were grown individually and incombination in soils with either a homogeneous or heterogeneousnutrient distribution. Above-ground biomass of individuallygrown plants of both species was greater when fertilizer waslocated in a single patch than when the same amount of fertilizerwas distributed evenly throughout the soil. Additionally, bothspecies proliferated roots in high-nutrient patches.A. artemisiifoliaexhibitedlarger root:shoot ratios, increased nitrogen depletion fromnutrient patches, and a higher growth rate thanP. americana,suggestingA. artemisiifoliais better suited to find and rapidlyexploit nutrient patches. In contrast to individually grownplants, soil nutrient distribution had no effect on final above-groundplant biomass for either species when grown with neighbours,even though roots were still concentrated in high nutrient patches.This study demonstrates that increased growth of isolated plantsas a consequence of localized soil nutrients is not necessarilyan indication that heterogeneity will affect interspecific encounters.In fact, despite a significant below-ground response, soil nutrientheterogeneity was inconsequential to above-ground performancewhen plants were grown with neighbours.Copyright 1999 Annalsof Botany Company Phytolacca americana, pokeweed,Ambrosia artemisiifolia, ragweed, nutrient heterogeneity, root proliferation, plasticity, foraging, nutrient patches.     

Structure and Function of an Age Series of Poplar Plantations in Central Himalaya. II Nutrient Dynamics

This paper elucidates nutrient dynamics in 5- to 8-year-oldpoplar (Populus deltoides) clone D₁₂₁ plantations previouslyinvestigated for dry matter dynamics. The nutrient concentrationin different layers of the vegetation were in the order: tree> shrub > herb, whereas the standing state of nutrientswere in the order: tree > herb > shrub. Soil, litter andvegetation, respectively, accounted for 80-89, 2-3 and 9-16%of the total nutrients in the system. Considerable reductions(trees 42-54, shrubs 31-37 and herbs 15-23%) in concentrationof nutrients in leaves occurred during senescence. The uptakeof nutrients by the vegetation and also by the different components,with and without adjustment for internal recycling, has beencalculated separately. Annual transfer of litter nutrient tothe soil by vegetation was 113·7-137·6 N, 11·6-14·6P and 80·1-83·2 K kg ha^-1 year^-1. Turnover rateand time for different nutrients ranged between 0·72-0·89year^-1 and 1·12-1·39 years, respectively. Thehigh turnover rate of litter on the forest floor indicates thegreater productivity of the stands, which was due to the higherdry matter dynamics and nutrient release for the growing vegetation.The nutrient use efficiency in poplar plantations ranged from159-175 for N, 1405-1569 for P and 295-332 for K. Compared withEucalyptus, there was a higher proportion of nutrient retranslocationin poplars largely because of higher tissue nutrient concentrations;this indicates lower nutrient use efficiency as compared tothe eucalypt plantation. Compartment models for nutrient dynamicshave been developed to represent the distribution of nutrientpools and net annual fluxes within the system.Copyright 1995,1999 Academic Press Populus deltoides plantations (Clone D₁₂₁), nutrient retranslocation, net nutrient uptake, nutrient use efficiency, nutrient cycling, nutrient pool, nutrient fluxes     

A Dynamic Growth Model of Vegetative Soya Bean Plants: Model Structure and Behaviour under Varying Root Temperature and Nitrogen Concentration

A differential equation model of vegetative growth of the soyabean plant (Glycine max (L.) Merrill cv. ‘Ransom’)was developed to account for plant growth in a phytotron systemunder variation of root temperature and nitrogen concentrationin nutrient solution. The model was tested by comparing modeloutputs with data from four different experiments. Model predictionsagreed fairly well with measured plant performance over a widerange of root temperatures and over a range of nitrogen concentrationsin nutrient solution between 0.5 and 10.0 mmol in the phytotron environment. Sensitivity analyses revealedthat the model was most sensitive to changes in parameters relatingto carbohydrate concentration in the plant and nitrogen uptakerate. Key words: Glycine max (L.) Merrill, dry matter, nitrogen uptake, partitioning, photosynthesis, respiration, sensitivity analysis     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations I. Concentrations, Contents and Distribution of N, P and K

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae was grown in sand and fedwith a complete nutrient medium diluted to give a range of concentrations.Analysis of bulked, dried tissues of the plant showed that undernutrient-rich conditions rust infection resulted in increasedconcentrations of total (Kjeldahl) nitrogen and potassium buthad little effect on phosphorus concentration. Thus, despitereduced dry weight growth, total plant nitrogen contents wereno less in rusted than control plants. Although total contentsof phosphorus and potassium were reduced by rust, effects wereprobably related to loss of these nutrients in fungal spores. Interactions between rust infection and nutrient supply weresignificant but differed between nutrients: rust caused increasednitrogen concentrations only under nutrient-rich conditionsbut increased phosphorus concentrations only when nutrient supplywas limited. Increased concentrations were not confined to infectedtissues. Mechanisms underlying rust-nutrient interactions appearto be complex and to depend inter alia on the partitioning andrecycling of the particular nutrient within the plant. Rust-inducedincreases in potassium concentration occurred under both highand low nutrient conditions but were confined to infected tissues.Potassium accumulation in nutrient deficient conditions wasprobably due to increased transpirational flux into infectedtissues, but under nutrient-rich conditions reduced potassiumexport appeared to assume greater significance. The possible implications of the changed nutrient relationsfor the wider interactions of rust-infected plants in naturalvegetation are discussed. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient deficiency, nutrient content, nutrient concentration, nutrient distribution     

A System for Measuring the Uptake of Ions by Plants from Flowing Solutions of Controlled Composition

A system is described for growing plants in flowing solutionin which the concentration (activity) of some nutrient ionsis continuously monitored and held almost constant by meansof ion-selective electrodes which control the operation of nutrientpumps. By recording the concentration of a given ion in theflowing nutrient solution and the amount of that ion which isdelivered by the nutrient pumps, it is possible to follow nutrientuptake over long and short periods. A brief account is givenof the operation of the system using a nitrate ion-selectiveelectrode to examine aspects of uptake by perennial ryegrass (Lolium perenne L.).