The Effects of Nutrient Deficiency and Rust Infection on the Relationship Between Root Dry Weight and Length in Groundsel (Senecio vulgaris L.)

Groundsel (Senecio vulgaris L.) was grown in sand culture ata range of nutrient concentrations. Except when nutrient deficiencywas severe, infection by the rust fungus Puccinia lagenophoraeCooke substantially reduced root dry weight but had little effecton root length. Thus, specific root length (SRL, cm root mg^–1d. wt) was significantly increased in rust-infected plants.The inhibition of root dry weight caused by rust infection wasmost pronounced late in development, especially after floweringwhen, in control plants, root elongation but not dry weightaccumulation ceased. In rusted plants, and in all plants subjectedto severe nutrient deficiency, dry weight accumulation in theroots ceased concurrently with root elongation. Late in developmentat high nutrient concentration adventitious roots with low SRLswere produced. However, infection did not modify the productionof such roots and increases in SRL could not be attributed tochanges in any single type of root. There was an inverse relationship between SRL and root diameter.This relationship was unaffected by rust infection whilst nutrientdeficiency changed only its intercept: at a given SRL rootsof nutrient stressed plants were thinner than those of plantswith adequate nutrient supply. Thus, the smaller diameter ofroots of nutrient-stressed plants occurred independently ofmeasured changes in SRL but, in the absence of nutrient stress,the decrease in root diameter caused by rust was closely relatedto increases in SRL. Changes in the root: length relationships in rusted plants mayhave important implications for root activity in the field.In view of the reported changes in SRL, inhibition of root growthin terms of dry weight may be a poor indicator of potentialchanges in activity. Senecio vulgaris, rust infection, nutrient deficiency, root weight: length ratio, root diameter     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations II. Uptake of N, P and K and Shoot-Root Interactions

Groundsel (Senecio vulgaris), healthy or infected with rust,Puccinia lagenophorae, was grown at a range of nutrient concentrationsin sand culture. Specific absorption rates calculated on thebasis of root dry weight (SAR_W) were greater in rusted thancontrol groundsel for nitrogen, potassium and phosphorus. Whilethe magnitudes of these stimulations varied, they occurred acrossthe whole range of nutrient concentrations. By contrast, specificabsorption rate on the basis of root length (SAR_L) were littlechanged by rust at any external nutrient concentration; SAR_Lfor phosphate and potassium were slightly reduced when nutrientswere freely available. Water flux per unit dry root weight and length was stimulatedby rust because transpiration per unit leaf area was more rapidin infected plants after fungal sporulation. However, water-fluxand the rate of uptake of nutrients were correlated only whenexpressed on the basis of root weight and increased transpirationdid not appear to be the mechanism underlying increased rootactivity. Rather, increased SAR_W for N, P and K could very largelybe attributed to increased shoot demand per unit root, whichresulted from the higher shoot: root (S: R) ratios of infectedindividuals. Changes in S: R accounted for 92, 81 and 57% oftotal variation in SAR_W for K, P and N respectively. Greatervalues for SAR_W were possible because specific root length (SRL)increased, producing more functional root per unit root weight.The lack of stimulation in SAR_L in response to rust could beexplained since the higher SRL of infected plants resulted instable values of shoot weight per unit root length, i.e. shootdemand was not increased by infection on this basis. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient uptake, water uptake, shoot: root interactions     

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     

Changes in Tissue Freezing in Senecio vulgaris infected by Rust (Puccinia lagenophorae)

Freezing of healthy and rust (Puccinia lagenophorae) infectedleaves of Senecio vulgaris was compared calorimetrically bythermal analysis. In fully expanded leaves the threshold freezingtemperature was in the range –6.8 to –8.4 °Cin controls but –3.0 to –5.1 °C in leaves withsporulating rust sori. Comparable values in expanding leaveswere –5.0 to –8.9 °C and –3.9 to –6.7°C for healthy and rusted tissues, respectively. The bulktissue freezing point was between –1.0 and –4.0°C in both fully expanded and expanding healthy leaves,and was increased by infection by between +0.2 and 2.5 °C.Whereas healthy leaves supercooled by 3.1–5.8 °C,rusted leaves supercooled by only 1.8–4.9 °C Supercoolingof control leaves was reduced by dusting with aeciospores, particularlywhen leaves were wounded to simulate the rupture of the surfacecaused by sporulation, but wounding alone had no significanteffect. Supercooling of distilled water was also significantlyreduced by aeciospores, suspended at a concentration of 10⁵spores ml^–1. It is concluded that rust-induced changes in leaf freezing inS. vulgaris grown in controlled environments were due to anincrease in the number of sites for ice nucleation, caused bythe presence of the aeciospores, and increased penetration ofice into internal tissues, resulting from damage to the cuticleand epidermis. Although data for frost resistance obtained inthe growth-room are similar to previous field observations,the role of the above mechanisms under field conditions remainsunproven. Senecio vulgaris (groundsel), Puccinia lagenophorae (rust), low temperature, freezing resistance     

Relative Nitrogen Limitation at Steady-state Nutrition as a Determinant of Plasticity in Five Grassland Plant Species

Partitioning of biomass between roots and different shoot partshas often been used to explain the response of plants to variationsin resource availability. There are still many uncertaintiesin the importance of this trait for plant performance, and clearguidelines on how partitioning should be quantified in relationto growth rate and resource supply are of fundamental importancefor such an understanding. This paper reports an attempt toshow how plant nitrogen status relates to root:shoot partitioningand other plastic responses, in a manner that can be used forquantitative predictions. The reactions to nitrogen limitationof five grassland plant species, with different ecological demands,were compared. The species used were the forbs Polygala vulgarisand Crepis praemorsa, and the grasses Danthonia decumbens, Agrostiscapillaris and Dactylis glomerata. The experiment was conductedin a climate chamber where the plants were grown hydroponically(1) under non-limiting nutrient conditions and (2) at a steady-statenitrogen limitation, which enabled the plants to express halfof their growth potential. The relative growth rate (RGR) ofthe species was strongly related to plant nitrogen concentration(PNC) and leaf area ratio (LAR), whereas the effects on netassimilation rate (NAR) were very small. Despite large differencesin maximum relative growth rate, the species showed remarkablesimilarities in dry matter partitioning between root and shoot.It is concluded that root:shoot partitioning can be treatedas a direct function of the relative resource limitation ofthe plant. The difficulty of attaining well-defined levels ofresource limitation in soil, other solid substrates and manyhydroponic systems may be the most important reason for thedivergent results in earlier studies. Better knowledge of soil-rootinteractions, and plant responses to the whole span of resource-supplylevels, is required for a thorough understanding of how nutrientslimit growth. Copyright 1999 Annals of Botany Company Growth rate, plant strategies, plasticity, partitioning, biomass, nitrogen, nutrient limitation, grassland.     

Nitrogen Uptake and Plant Growth I. Effect of Nitrogen Removal on Growth of Polygonum cuspidatum

Polygonun cuspidatum was grown hydroponically to examine theeffect of nitrogen removal from the nutrient solution upon plantgrowth and the partitioning of dry matter and nitrogen amongorgans. Nitrogen removal reduced the growth rate mainly dueto the reduced growth of leaf area. Accelerated root growthwas observed only in plants which earlier had received highlevels of nitrogen. Nitrogen removal caused almost exclusiveallocation of available nitrogen to root growth. Nitrogen fluxfrom the shoot to the root occurred in plants which had receivedlow nitrogen. Not only was net assimilation rate (NAR) littleaffected by nitrogen removal, but it also was not correlatedwith the concentration of leaf nitrogen on an area basis. Light-saturatedCO₂ exchange rate (CER) was highly correlated with the concentrationof leaf nitrogen. Nitrogen use efficiency (NUE) in CER (CERdivided by leaf nitrogen) remained constant against leaf nitrogen,indicating efficient use of nitrogen under light saturation,while NUE in terms of NAR decreased with higher concentrationof leaf nitrogen. Polygonum cuspidatum Sieb. et Zuce., CO₂ exchange rate, growth analysis, leaf nitrogen, net assimilation rate, nitrogen use efficiency, partitioning of dry matter and nitrogen     

Effect of Root and Shoot Meristem Temperature on Shoot to Root Dry Matter Partitioning and the Internal Concentrations of Nitrogen and Carbohydrates in Maize and Wheat

Maize (Zea mays L.) and spring wheat (Triticum aestivum L.)were grown in nutrient solution at uniformly high air temperature(20 °C), but different root zone temperatures (RZT 20, 16,12 °C). To manipulate the ratio of shoot activity to rootactivity, the plants were grown with their shoot base includingthe apical meristem either above (i.e. at 20 °C) or withinthe nutrient solution (i.e. at 20, 16 or 12 °C). In wheat, the ratio of shoot:root dry matter partitioning decreasedat low RZT, whereas the opposite was true for maize. In bothspecies, dry matter partitioning to the shoot was one-sidedlyincreased when the shoot base temperature, and thus shoot activity,were increased at low RZT. The concentrations of non-structuralcarbohydrates (NSC) in the shoots and roots were higher at lowin comparison to high RZT in both species, irrespective of theshoot base temperature. The concentrations of nitrogen (N) inthe shoot and root fresh matter also increased at low RZT withthe exception of maize grown at 12 °C RZT and 20 °Cshoot base temperature. The ratio of NSC:N was increased inboth species at low RZT. However this ratio was negatively correlatedwith the ratio of shoot:root dry matter partitioning in wheat,but positively correlated in maize. It is suggested that dry matter partitioning between shoot androots at low RZT is not causally related to the internal nitrogenor carbohydrate status of the plants. Furthermore, balancedactivity between shoot and roots is maintained by adaptationsin specific shoot and root activity, rather than by an alteredratio of biomass allocation between shoot and roots.Copyright1994, 1999 Academic Press Wheat, Triticum aestivum, maize, Zea mays, root temperature, shoot meristem temperature, biomass allocation, shoot:root ratio, carbohydrate status, nitrogen status, functional equilibrium     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Some Effects of Potassium and Magnesium on the Growth of Subterranean Clover (Trifolium subterraneum)

Subterranean clover plants (Trifolium subterraneum L., cv. Mt.Barker) were grown in culture solutions at optimum nutrientlevels and on the 23rd day after sowing transferred to solutionswithout magnesium or potassium. A third group remained at thesame nutrient levels as before (controls). Magnesium deficiency caused a particularly rapid decline inroot growth, followed later by a net loss of root dry matter.This, and the fact that leaf expansion declined relatively morethan the increase in laminae dry matter, resulted in an accumulationof assimilates per unit leaf area. Transfer of magnesium-deficientplants to complete solutions on day 35 caused a preferentialdistribution of dry matter to the roots, then to petioles andrelatively less to the laminae. These changes caused a pronouncedfall in the root: shoot ratio as the deficiency became moresevere and a rise in the ratio during recovery. Plants in solutions without potassium showed no marked shiftsin dry matter distribution between plant parts. The root: shootratio remained close to that for control plants, except duringthe recovery, when there was a decrease in the ratio. Net rates of CO₂ uptake by laminae from potassium-deficientplants showed little change during the first 10 days of thedeficiency although values were somewhat lower than those forcorresponding control laminae. After transfer to complete solutionsthere was a marked response in photosynthesis, rising to a finalvalue close to that for control laminae. Laminae of plants placedin solutions without magnesium showed a rapid decline in photosynthesisonly 4 days later; there was little response when plants weretransferred to complete solutions a week later. Trifolium subterraneum L., subterranean clover, growth, root: shoot ratio, potassium deficiency, magnesium deficiencies     

Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency

The influence of varied supply of phosphorus (10 and 250 mmolP m^–3) potassium (50 and 2010 mmol K m^–3) and magnesium(20 and 1000 mmol Mg m^–3) on the partitioning of dry matterand carbohydrates (reducing sugars, sucrose and starch) betweenshoots and roots was studied in bean (Phaseolus vulgaris) plantsgrown in nutrient solution over a 12 d period. Shoot and rootgrowth were quite differently affected by low supply of P, K,and Mg. The shoot/root dry weight ratios were 4.9 in the control(sufficient plants), 1.8 in P-deficient, 6.9 in K-deficientand 10.2 in Mg-deficient plants. In primary (source) leaves,but not in trifoliate leaves, concentrations of reducing sugars,sucrose and starch were also differently affected by low nutrientsupply. In primary leaves under K deficiency and, particularlyMg deficiency, the concentrations of sucrose and reducing sugarswere much higher than in control and P-deficient plants. Magnesiumdeficiency also distinctly increased the starch concentrationin the primary leaves. In contrast, in roots, the lowest concenfrationsof sucrose, reducing sugars and starch were found in Mg-deficientplants, whereas the concentrations of sucrose and starch wereparticularly high in P-deficient plants. There was a close relationshipbetween shoot/root dry weight ratios and relative distributionof total carbohydrates (sugars and starch) in shoot and roots.Of the total amounts of carbohyd rates per plant, the followingproportions were parti tioned to the roots: 22.7% in P-deficient,15.7% in control, 3.4% in K-deficient and 0.8% in Mg-deficientplants. The results indicate a distinct role of Mg and K in the exportof photosynthates from leaves to roots and suggest that alterationin photosynthate partitioning plays a major role in the differencesin dry matter distribution between shoots and roots of plantssuffering from mineral nutrient deficiency. Key words: Bean, carbohydrates, magnesium nutrition, phosphorus nutrition, potassium nutrition, shoot/root growth     

Studies in the Nutrition of Apple Rootstocks: 1. Effects of Deficiencies of Iron and Magnesium on Growth

Plants of the apple rootstock M.VII were grown for a singleseason by spraying their roots continuously with nutrient solutions:(a) complete, (b) low iron, (c) low magnesium, and (d) low ironand low magnesium. Detailed records were taken throughout theseason of fresh weight, shoot length, diameter, and leaf area,while the fresh and dry weights of component parts were determinedon harvested samples. The leaves of the iron-deficient plants were chlorotic and hada lower dry weight and higher water content per unit area thanthose of the control plants. Growth and net assimilation ratewere both reduced but the distribution of assimilates was similarto that in the controls. Total growth was also markedly reduced by the low-magnesiumtreatment, but the leaf symptoms were different and the plantswere morphologically distinct from the control plants. Verylittle chlorosis occurred, but necrosis and severe defoliation,progressing up the shoot, reduced the leaf area ratio and probablylargely accounted for the low net assimilation rate and relativegrowth rate. The diameter of the shoot was affected much morethan its length and the shoot/root ratio was greatly increased. Plants deficient in both iron and magnesium showed less defoliationthan when magnesium alone was low. More dry matter accumulatedin the old stem and less in the new shoot than would have occurredwith a simple combination of the single deficiencies.     

Nutrient-limited growth rates: quantitative benefits of stress responses and some aspects of regulation

Young sunflower plants (Helianthus annuus L.) under stress oflow nitrate or phosphate availability exhibited increases inroot: shoot ratio and in kinetic parameters for uptake. Theyshowed no significant changes in photosynthetic utilizationof either nutrient. Increases in root: shoot ratio were achievedby early and persistent suppression of shoot growth, but notroot growth. Affinity for phosphate uptake, 1/K_m(P), increasedwith phosphate stress, as did affinity for nitrate uptake, 1/K_m(N),with nitrate stress. Maximal uptake rate, V_max, for phosphateuptake increased with phosphorus stress; V_max for nitrate didnot increase with nitrogen stress. Phosphate V_max was relatedstrongly to root nutrient status. Decreases in V_max with plantage were not well explained by changes in age structure of roots.Estimated benefits of acclimatory changes in root: shoot ratioand uptake kinetics ranged up to 2-fold increases in relativegrowth rate, RGR. The relation of RGR to uptake physiology followedpredictions of functional balance moderately well, with somesystematic deviations. Analyses of RGR using growth models implyno significant growth benefit from regulating Vmax, specifically,not from down-regulating it at high nutrient availability. Quantitativebenefits of increases in root: shoot ratio and uptake parametersare predicted to be quite small under common conditions whereinnutrient concentrations are significantly depleted by uptake.The root: shoot response is estimated to confer the smallestbenefit under non-depleting conditions and the largest benefitunder depleting conditions. Even then, the absolute benefitis predicted to be small, possibly excepting the case of heterogeneoussoils. Depleting and non-depleting conditions are addressedwith very different experimental techniques. We note that atheoretical framework is lacking that spans both these cases,other than purely numerical formulations that are not readilyinterpreted. Key words: Nutrient stress, nutrient uptake, nutrient use efficiency, relative growth rate, Helianthus annuus     

The Distribution of Nitrate Assimilation Between Root and Shoot in Vicia faba L.

Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO₃^–: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO₃^–: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis     

Seedling vigour and the early growth of transplanted rice (Oryza sativa)

Previous studies suggest that the positive response of transplanted rice (Oryza sativa L.) to nursery fertiliser application was due to increased seedling vigour or possibly to increased nutrient content. This paper presents results of two glasshouse experiments designed to test the hypothesis that seedling vigour was responsible for the response of transplanted seedlings to nursery treatments. The aim of the present study was to explore the concept of seedling vigour of transplanted rice and to determine what plant attributes conferred vigour on the seedlings. Seedling vigour treatments were established by subjecting seedlings to short-term submergence (0, 1 and 2 days/week) in one experiment and to leaf clipping or root pruning and water stress in another to determine their effect on plant growth after transplanting. Submerging seedlings increased plant height but depressed shoot and root dry matter and root:shoot ratio of the seedling at 28 days after sowing. After transplanting these seedlings, prior submergence depressed shoot dry matter at 40 days. Nursery nutrient application increased plant height, increased root and shoot dry matter, but generally decreased root:shoot ratio. Pruning up to 60% of the roots at transplanting decreased shoot and root dry matter, P concentration in leaves at panicle initiation (PI) and straw dry matter and grain yield at maturity. By contrast, pruning 30% of leaves depressed shoot and root dry matter by 30% at PI, and root dry matter and straw and grain yield by 20% at maturity. The combined effects of leaf clipping and root pruning on shoot, root and straw dry matter were largely additive. It is concluded that the response of rice yield to nursery treatments is largely due to increased seedling vigour and can be effected by a range of nutritional as well as non-nutritional treatments of seedlings that increase seedling dry matter, nutrient content, and nutrient concentration. Impairment of leaf growth and to a lesser extent root growth in the nursery depressed seedling vigour after transplanting. However, rather than increasing stress tolerance, seedling vigour was more beneficial when post transplant growth was not limited by nutrient or water stresses.     

Effects of Selected Herbicides on the Germination and Infection Process of Puccinia lagenophora,a Biocontrol Pathogen of Senecio vulgaris

The herbicides 2,4-D, glyphosate, linuron, and MCPP at rates of 1X (recommended field rate), 0.25X, 0.025X, and 0.0125X were evaluated in vitro for their effects on the rust fungus Puccinia lagenophorae, a biocontrol agent for the annual weed Senecio vulgaris. Herbicides applied at 1X and 0.25X completely prevented aeciospore germination. Glyphosate was toxic even at 0.0125X and 0.025X. Aeciospores germinated in linuron, 2,4-D, and MCPP at 0.025X and 0.0125X at rates similar to the water control. Abnormal germ-tube growth was observed with 2,4-D at 0.25X and 0.025X, with linuron at 0.025X, and with glyphosate at 0.0125X. Further in planta studies were perfomed with two inbred lines of S. vulgaris inoculated with aeciospores of P. lagenophorae and treated with water, linuron, and 2,4-D at 0.025X at different times of application. Quantitative analysis of the infection process revealed that both herbicides reduced spore deposition on the leaves and altered leaf morphology. The herbicides had no effect on disease severity at this low rate although linuron significantly reduced the formation of infection peg. Timing of herbicide application had no influence on the infection process, and the effect of the herbicides on fungal development did not differ between the two plant lines. Thus, the herbicides applied at 0.025X did not increase plant susceptibility to the rust fungus, and the rates of 1X, 0.25X, and 0.025X would prevent, inhibit, or delay fungal development. Therefore, joint application of P. lagenophorae with these herbicides to control S. vulgaris cannot be recommended.     

Effects of Intercropping on Growth and Reproductive Capacity of Late-emerging Senecio vulgaris L., with Special Reference to Competition for Light

Due to increased emphasis on long-term management of weed populationsin cropping systems with a reduced reliance on herbicides, theproduction of seeds by weeds that emerge after the criticalperiod for weed control is increasingly important. It was hypothesizedthat increased soil cover and light interception by a crop canopywould shorten the critical period for weed control and reducegrowth and fecundity of late-emerging weeds. This hypothesiswas tested in a series of field and glasshouse experiments inwhich competition for light was manipulated. Senecio vulgaris,an important weed in vegetable production systems, was chosenas the target plant, and canopies of pure and mixed stands ofleek and celery were used to provide shade. The time courseof light interception differed among the crop canopies. Increasingcompetition for light caused morphological changes to S. vulgaris,including a vertical shift in leaf area distribution. Increasedshading reduced biomass, capitula:shoot ratio and seed productionof S. vulgaris. However, the viability of seeds produced bythe shaded weed plants was not affected. Results indicate thatintercropping can increase light interception in a weakly competitivecrop such as leek and can contribute to weed suppression ina long-term strategy for weed management. Copyright 2001 Annalsof Botany Company Competition for light, late-emerging weeds, critical period, Apium graveolens L., celery, Allium porrum L., leek, Senecio vulgaris L., common groundsel, seed production, weed management, intercropping     

Root Confinement and its Effects on the Water Relations, Growth and Assimilate Partitioning of Tomato (Lycopersicon esculentum Mill)

Although it is well established that the root growth in manyspecies is very sensitive to mechanical impedance or to confinementin small volumes, little is known about the consequent effectson growth of the whole plant and the mechanisms involved. Thiswork investigated the effects of root confinement on the waterrelations, growth and assimilate partitioning of tomato (Lycopersiconesculentum Mill) grown in solution culture. Six-week old plants were transferred to either 4500 ml or 75ml containers filled with nutrient solution, and allowed togrow for 14 d. Transpiration, leaf-air temperature differences,and leaf diffusive resistances were measured frequently. Leaf,stem and shoot dry masses, leaf area and root length, were estimatedwhen the treatments were imposed and at the end of the experiment.After 14 d growth the root and shoot hydraulic resistances wereestimated from measurements of leaf water potential and transpirationrate, using a steady-state technique. Confining root growth to the small containers substantiallyreduced shoot and root growth and increased the proportion oftotal dry matter present in the stems. These effects were dueto drought stress. The hydraulic resistance of the root systemwas greatest in the confined plants. This led to more negativeleaf water potentials, increased leaf diffusive resistance,and reduced the net assimilation rate by a factor of 2.5. Transpirationper unit leaf area was less affected. However, cumulative transpirationwas also reduced by a factor of 2.5. mostly because of the smallerleaf area on the confined plants. Root hydraulic resistivitywas measured at 3.1 x 10¹²s m^–1 in the control treatment,but increased to 3.9 x 10¹² s m^–1 for roots in the smallcontainer. The mechanisms by which root confinement caused drought stressand disrupted the pattern of assimilate partitioning are discussedin detail. Assimilate partitioning, Lycopersicon esculentum, root confinement, plant growth, root growth, root resistance, shoot resistance, tomato, transpiration, water-use efficiency     

Nitrogen Use Efficiency in Growth of Polygonum cuspidatum Sieb. et Zucc

The growth of Polygonum cuspidatum in sand culture was analysedunder varying nutrient conditions. Nitrogen availability influencednitrogen uptake of plants through the uptake rate per unit rootweight rather than the amount of root. In turn, the differentamounts of nitrogen taken up affected plant growth through theireffects on the rate of leaf expansion. Net assimilation rate (NAR) increased with nitrogen contentper unit leaf area (C), but further increase in leaf nitrogencaused diminishing returns of NAR Optimal nitrogen content perunit leaf area (C_opt) to maximize dry-matter production of aleaf could be determined by drawing a tangent from the onginto a curvilinear relation between NAR and C. This optimal contentdivides a nitrogen-limiting range (C < C_opt) from a carbon-limitingone (C> C_opt) along the axis of nitrogen content. Under nitrogenlimitation, efficiency of nitrogen use in dry-matter productioncould increase if the plant had a larger carbon sink. This givesa qualitative explanation to reduced shoot-to-root ratio underlimited availability of nitrogen. Polygonum cuspidatum Sieb. et Zucc, Japanese knotweed, carbon sink, growth analysis, leaf nitrogen, net assimilation rate, nitrogen use efficiency     

Enhancement of cadmium effects on growth and nutrient composition of birch (Betula pendula) by buthionine sulphoximine (BSO)

Binding of Cd to non-specific metal-binding peptides (phytochelatins)in birch roots has been suggested as an explanation for toleranceto Cd toxicity in birch (Betula pendula). In the present study,the tolerance of birch roots to Cd was further investigatedby using buthionine sulphoximine (BSO) as an inhibitor of phytochelatinsynthesis. Birch seedlings, grown in nutrient solution at pH4.2, were exposed to 0 or 2 µM CdCl₂ combined with 0 or0.1 mM BSO for 6 d. Plant growth (fresh weight increase andshoot to root dry weight ratio) and the nutrient compositionin fine roots, whole roots and shoots were determined. The effectsof Cd on growth confirms the results of earlier studies on birch,suggesting a reduced shoot growth, but preserved or stimulatedroot growth. When Cd and BSO were combined, overall plant growthwas severely reduced. BSO was also shown to aggravate Cd-inducedreductions of root and shoot concentrations of K, Ca and Mgbut to impede the accumulation of Cd. The results suggest that phytochelatins participate in protectingthe root against Cd interferences with growth, possibly by restrictingCd-induced changes in the nutrient composition of the plant. Key words: Betula pendula, buthionine sulphoximine, cadmium, phytochelatins, roots, tolerance     

Santalum album: Kernel Composition, Morphological and Nutrient Characteristics of Pre-parasitic Seedlings under Various Nutrient Regimes

Omission of all nutrients or individual minerals (N, K, P, S,Ca) from the growth medium of pre-parasiticSantalum album seedlingsproduced significant morphological effects. Compared with fullyfertilized seedlings, shoot and root length, leaf area, leaflength and width, leaf number, internode length, shoot length/rootlength ratio, chlorophyll levels, fresh mass and dry mass wereall reduced; leaf thickness increased and stomatal numbers,petiole lengths, root lengths and haustorial numbers showedvariable but significant responses. Mineral-specific deficiencysymptoms were evident in all omission treatments after 3 months.Treatments in which N, K or all minerals were omitted had thegreatest dwarfing effect and increase in height and leaf numberceased after 3 months: only seedlings with no added nutrients(dependent on kernel nutrition) were healthy. The mineral contentof no-nutrient seedlings approximated that in kernels. The distributionof minerals between plant parts for each treatment is given.K concentrations and K/Ca ratios were relatively high in leavesof seedlings which received treatments containing K, especiallywhen Ca was absent. A high K/Ca ratio may be inherent inS. albumseedlings rather than acquired after subsequent host connection.All fully fertilized seedlings developed haustoria within 3months suggesting readiness for early host attachment. Seedlingsin no-nutrient, no-N, no-K or no-P treatments had fewer haustoria. Santalum album ; Indian sandalwood; sandalwood kernels; sandalwood seedlings; nutrient omission; healthy characteristics; deficiency characteristics