Dynamic Model for the Effects of Soil P and Fertilizer P on Crop Growth, P Uptake and Soil P in Arable Cropping: Experimental Test of the Model for Field Vegetables

In a previous paper (Greenwood et al. Annals of Botany88: 279–291,2001), we described a mechanistic model that calculates theeffects of extractable soil P and fertilizer P on daily incrementsin dry matter yield and P uptake of field crops. This paperdescribes the calibration of that model for six different speciesand subsequent tests of the calibrated model against resultsof independent experiments on the same soil type. Calibrationsfor lettuce, carrot and turnip were obtained by altering onlyone parameter, the effective root radius, while for onion, leekand spinach, both this and one of the parameters linking growthrate to % P in the plant were altered. The validity of the calibratedmodel was tested against results of field experiments that wereharvested at the seedling stage and at commercial maturity.The model predictions of the shapes of the responses of dryweight and of % P to both extractable soil P and fertilizerP were generally not significantly different from those measured.The model also gave satisfactory predictions of the time courseof dry weight and plant % P from emergence to commercial harvestof two crops grown with optimum levels of P fertilizer. In anotherexperiment, reasonably good agreement was obtained between simulatedresponses of plant dry weight yield and % P in the dry matterof carrot at commercial maturity and mid-way through the growingseason. Values of the effective root radius and various rootparameters, and calculations of P fluxes through the soil tothe root surfaces during the course of the simulation were,with few exceptions, consistent with information in the literature.Simulated P responsiveness is very sensitive to changes in thevalues of plant parameters affecting the dependence of P uptakeon plant % P as well as those concerned with the ability ofroots to exploit the soil's reserves of P. Reasons for inter-speciesdifferences in P response are elucidated and weaknesses in themodel identified. The model could form the basis of a short-cutapproach to forecasting optimal fertilizer P practices for differentcrops on different soils. It runs interactively on the Internetat: www.qpais.co.uk/phosmod/phos.htm Copyright 2001 Annals ofBotany Company Vegetable crops, model, simulation, plant phosphate, phosphate fertilizer, soil phosphate, crop response, root radius, species comparison     

Simulating Growth and Root-shoot Partitioning in Prairie Grasses Under Elevated Atmospheric CO2and Water Stress

We constructed a model simulating growth, shoot-root partitioning,plant nitrogen (N) concentration and total non-structural carbohydratesin perennial grasses. Carbon (C) allocation was based on theconcept of a functional balance between root and shoot growth,which responded to variable plant C and N supplies. Interactionsbetween the plant and environment were made explicit by wayof variables for soil water and soil inorganic N. The modelwas fitted to data on the growth of two species of perennialgrass subjected to elevated atmospheric CO₂and water stresstreatments. The model exhibited complex feedbacks between plantand environment, and the indirect effects of CO₂and water treatmentson soil water and soil inorganic N supplies were important ininterpreting observed plant responses. Growth was surprisinglyinsensitive to shoot-root partitioning in the model, apparentlybecause of the limited soil N supply, which weakened the expectedpositive relationship between root growth and total N uptake.Alternative models for the regulation of allocation betweenshoots and roots were objectively compared by using optimizationto find the least squares fit of each model to the data. Regulationby various combinations of C and N uptake rates, C and N substrateconcentrations, and shoot and root biomass gave nearly equivalentfits to the data, apparently because these variables were correlatedwith each other. A partitioning function that maximized growthpredicted too high a root to shoot ratio, suggesting that partitioningdid not serve to maximize growth under the conditions of theexperiment.Copyright 1998 Annals of Botany Company plant growth model, optimization, nitrogen, non-structural carbohydrates, carbon partitioning, elevated CO₂, water stress,Pascopyrum smithii,Bouteloua gracilis, photosynthetic pathway, maximal growth     

Evaluation of a Dynamic Simulation Model for Tomato Crop Growth and Development

A dynamic simulation model for tomato crop growth and development,TOMSIM, is evaluated. Potential crop growth and daily crop grossassimilation rate (P_gc,d) is computed by integration of leafassimilation rates over total crop leaf area throughout theday. Crop growth results fromP_gc,dminus maintenance respirationrate (R_m), multiplied by the conversion efficiency. Dry matterdistribution is simulated, based on the sink strength of theplant organs, which is quantified by their potential growthrate. Within the plant, individual fruit trusses and vegetativeunits (three leaves and stem internodes between two trusses)are distinguished. Sink strength of a truss or a vegetativeunit is described as a function of its developmental stage.In this paper, emphasis is on the interactions between the twosubmodels of, respectively, dry matter production and dry matterdistribution. Sensitivity analysis showed that global radiation,CO₂concentration, specific leaf area (SLA) and the developmentalstage of a vegetative unit at leaf pruning had a large influenceon crop growth rate, whereas temperature, number of fruits pertruss, sink strength of a vegetative unit and plant densitywere less important. Leaf area index (LAI) was very sensitiveto SLA and the developmental stage of a vegetative unit at leafpruning. Temperature did not influence the simulated R_m, asincreased respiration rate per unit of biomass at higher temperatureswas compensated by a decrease in biomass. The model was validatedfor four glasshouse experiments with plant density and fruitpruning treatments, and on data from two commercially growncrops. In general, measured and simulated crop growth ratesfrom 1 month after planting onwards agreed reasonably well,average overestimation being 12%. However, crop growth ratesin the first month after planting were overestimated by 52%on average. Final crop dry mass was overestimated by 0–31%,due to inaccurate simulation of LAI, resulting partly from inaccurateSLA prediction, which is especially important at low plant densityand in a young crop.Copyright 1999 Annals of Botany Company Crop growth, dry matter production, glasshouse, leaf area,Lycopersicon esculentum, partitioning, simulation model, tomato, TOMSIM.     

Soil solution dynamics and plant uptake of cadmium and zinc by durum wheat following phosphate fertilization

A growth chamber study was conducted to evaluate the effect of application of phosphate fertilizer on soil solution dynamics of cadmium (Cd) and Cd accumulation in durum wheat (Triticum turgidum L. var. durum). Treatments consisted of three phosphate fertilizer sources containing 3.4, 75.2, and 232 mg Cd kg^?1 applied at three rates (20, 40 and 80 mg P kg^?1) plus a no fertilization control. An unplanted treatment at 40 mg P kg^?1 was included to separate the effects on soil solution Cd dynamics of the crop from that of the fertilizer. Soil solution samples were obtained using soil moisture samplers every 10 days after germination. The experimental results indicated that plant biomass significantly increased with P application rates and decreased with increased Cd concentration in the phosphate fertilizers. Total cadmium concentration in soil solution was not consistently affected by phosphate fertilization rate and fertilizer sources, and therefore Cd concentration in the fertilizer. Application of phosphate fertilizer, however, increased the concentration and accumulation of Cd and shoot Cd/Zn ratio, and decreased shoot Zn concentration in durum wheat. Phosphate sources had a marginally significant effect (P?=?0.05) on shoot Cd concentration and did not affect Cd accumulation in durum wheat. Concentration of Cd in soil solution was unrelated to Cd concentration in durum wheat. These results suggest that the immediate increase in Cd concentration and Cd accumulation in durum wheat with phosphate application is due more to competition between Zn and Cd for absorption into plants, enhanced root to shoot translocation and enhanced root development, than to a direct addition effect from Cd contained in phosphate fertilizer. In the short term, application of phosphate fertilizers can increase Cd concentration in the crops, regardless of the Cd concentration of the fertilizer. An optimal P fertilization, possibly in combination with Zn application, may offer an important strategy for decreasing Cd concentration and accumulation in crops.     

Radial Hydraulic Conductivity of Individual Root Tissues of Opuntia ficus-indica (L.) Miller as Soil Moisture Varies

The constraints on water uptake imposed by individual root tissueswere examined forOpuntia ficus-indicaunder wet, drying, andrewetted soil conditions. Root hydraulic conductivity (L_P) andaxial conductance (K_h) were measured for intact root segmentsfrom the distal region with an endodermis and from midroot witha periderm;L_Pwas then measured for each segment with successivetissues removed by dissection. Radial conductivity (L_R) wascalculated fromL_PandK_hfor the intact segment and for the individualtissues by considering the tissue conductivities in series.Under wet conditions,L_Rfor intact distal root segments was lowestfor the cortex; at midroot, where cortical cells are dead,L_Rforthe cortex was higher and no single tissue was the predominantlimiter ofL_R.L_Rfor the endodermis and the periderm were similarunder wet conditions. During 30d of soil drying,L_Rfor the distalcortex increased almost three-fold due to the death of corticalcells, whereasL_Rfor the midroot cortex was unaffected;L_Rforthe endodermis and the periderm decreased by 40 and 90%, respectively,during drying. For both root regions under wet conditions, thevascular cylinder had the highestL_R, which decreased by 50–70%during 30d of soil drying. After 3d of rewetting, new lateralroots emerged, increasingL_Rfor the tissues outside the vascularcylinder as well as increasing uptake of an apoplastic tracerinto the xylem of both the roots and the shoot. The averageL_Rforintact root segments was similar under wet and rewetted conditions,but the conductivity of the tissues outside the vascular cylinderincreased after rewetting, as did the contribution of the apoplasticpathway to water uptake. Opuntia ficus-indica; prickly pear; root hydraulic conductivity; endodermis; periderm; apoplast; lateral root emergence     

Evaluation of sewage sludge, septic waste and sludge compost applications to corn and forage: yields and N, P and K content of crops and soils

This paper presents the data from two years of experiments concerned with the application of aerobically-digested sewage sludge, anaerobic lagoon septic sludge, sewage sludge compost or fertilizer to soils for grass forage and feed corn (Zea mays L.) production at two different sites 45 km from Truro, Nova Scotia. Crop yields, plant tissue and Mehlich-1 extractable soil nutrients were evaluated; 15 elements were analyzed in the plant tissue and nine elements in the soil extracts. This paper describes the results of crop yields, plant N, P and K content and Mehlich-1 extractable P and K. The research demonstrated the fertilizer produced higher yields of grass forage than the sludge and the compost but equivalent to the sludge in corn yields. Forage and corn N, P and K contents, however, varied with treatment, crop and year, while the compost-amended soils were highest in extractable nutrients. Both sludges and the compost, therefore, could be effective sources of N, P and K for crop production. Compared to the conventional fertilizer, the nutrient availability from the organic amendments (especially N and P) was considerably lower than the 50% assumed at the start of the experiment; the sludges however, provided higher nutrient availability than the compost.     

Wheat Cultivars Respond Differently to a Drying Top Soil and a Possible Non-Hydraulic Root Signal

Research has shown that when plant roots are exposed to a dryingsoil a non-hydraulic (chemical) signal is produced in the rootand transported to the shoot, causing stomatal closure and growthretardation. This study was designed to reveal genetic diversityin wheat response to soil conditions which elicit a root signal,as the first step in the investigation of the genetic controlof the production of and the response to the root signal. Five spring wheat (Triticum aestivum L.) cultivars were establishedin the growth chamber in soil-filled polyvinyl chloride tubes,120 cm long and of an internal diameter of 10·2 cm. Soilwas well fertilized and wet to field capacity at emergence whentwo treatments were imposed: (1) tubes were watered from thetop as needed to eliminate stress (control); and (2) tubes hada constant water table at a soil depth of 100 to 120 cm, withno applied water. Measurements were performed on five dateson leaf water status and stomatal diffusive resistance. Above-groundbiomass and grain yield per plant were determined at maturity. The water table treatment resulted in dry and hard top soilconditions which were previously indicated to elicit a possibleroot signal. Under these experimental conditions, cultivarsdiffered in their leaf water status, stomatal diffusive resistance(R_s) and plant production. In the control treatment, R_s of cultivarsincreased with reductions in their relative water content (RWC)and leaf water potential (LWP), indicating the expected controlof R_s by leaf water status. Under conditions of a drying topsoil, relative water content (RWC) and leaf water potential(LWP) increased in cultivars that had a higher R_s, indicatingthat stomatal activity was controlling leaf water status. Itwas therefore suggested that the drying top soil elicited aroot signal which caused stomatal closure and reduced plantproduction. Under such conditions, two cultivars (Bethlehemand V748) consistently maintained relatively low R_s and highplant production, despite their relatively lower RWC and LWP,as compared with cvs C97, V747 and V652. Limited observationssuggest that in these two cultivars relatively fewer roots mayhave been exposed to the drying top soil, as compared with theother three cultivars. Key words: Triticum aestivum, cultivars, soil moistrue, drought stress, root, root signal, stomata, relative water content, leaf water potential, biomass, yield     

Seed P-enrichment as an effective P supply to wheat

Most fertilizer phosphorus (P) is sorbed by soil rather than being taken up by crops. We hypothesize enriching wheat seed with P before sowing the crop will reduce requirement of fertilizer P for subsequent wheat production. We produced P-enriched wheat (Triticum aestivum L.) seed by soaking the seed in different concentrations of potassium phosphate solution. We found that ~0.35 M potassium phosphate was the most effective concentration for P-enrichment of the seed. In pot and field experiments we found that the P-enriched seed required ~60% less fertilizer P than seed not soaked with potassium phosphate before sowing. Increases in shoot P content could not be explained only by the increase of seed P-enrichment, suggesting that P acquisition from soil was also enhanced. Under hydroponic conditions we found that root length was greater in seedlings grown from P-enriched seed with higher specific root length than in seedlings grown from non-P-enriched seed. We conclude P-enrichment of wheat seed before sowing reduces fertilizer P requirements of plants.     

Effects of CO2 enrichment and intraspecific competition on biomass partitioning, nitrogen content and microbial biomass carbon in soil of perennial ryegrass and white clover

Seedlings of perennial ryegrass (Lolium perenne L. cv. Parcour)and white clover (Trifolium repens L. cv. Karina) grown at fivedifferent plant densities were exposed to ambient (390 ppm)and elevated (690 ppm) CO₂ concentrations. After 43 d the effectsof CO₂ enrichment and plant density on growth of shoot and root,nitrogen concentration of tissue, and microbial biomass carbon(C_mic) in soil were determined. CO₂ enrichment of Lolium perenneincreased shoot growth on average by 17% independent of plantdensity, while effects on root biomass ranged between -4% and+ 107% due to an interaction with plant density. Since tilernumber per plant was unaffected by elevated CO₂, the small responseof shoot growth to CO₂ enrichment was atributed to low sinkstrength. A significant correlation between nitrogen concentrationof total plant biomass and root fraction of total plant drymatter, which was not changed by CO₂ enrichment, indicates thatnitrogen status of the plant controls biomass partitioning andthe effect of CO₂ enrichment on root growth. Effects of elevatedCO₂ and plant density on shoot and root growth of Trifoliumrepens were not significantly interacting and mean CO₂-relatedincrease amounted to 29% and 66%, respectively. However, growthenhancement due to elevated CO₂ was strongest when leaf areaindex was lowest. Total amounts of nitrogen in shoots and rootswere bigger at 690 ppm than at 390 ppm CO₂. There was a significantincrease in C_mic in experiments with both species whereas plantdensity had no substantial effect. Key words: CO₂ enrichment, intraspecific competition, biomass partitioning, Lolium perenne, Trifolium repens, grassland     

Compensatory Roles of Nitrogen Uptake and Photosynthetic N-use Efficiency in Determining Plant Growth Response to Elevated CO2: Evaluation Using a Functional Balance Model

We used a modified functional balance (FB) model to predictgrowth response of Helianthus annuus L. to elevated CO₂. Modelpredictions were evaluated against measurements obtained twiceduring the experiment. There was a good agreement between modelpredictions of relative growth rate (RGR) responses to elevatedCO₂and observations, particularly at the second harvest. Themodel was then used to compare the relative effects of biomassallocation to roots, nitrogen (N) uptake and photosyntheticN-use efficiency (PNUE) in determining plant growth responseto elevated CO₂. The model predicted that a rather substantialincrease in biomass allocation to root growth had little effecton whole plant growth response to elevated CO₂, suggesting thatplasticity in root allocation is relatively unimportant in determininggrowth response. Average N uptake rate at elevated comparedto ambient CO₂was decreased by 21–29%. In contrast, elevatedCO₂increased PNUE by approx. 50% due to a corresponding risein the CO₂-saturation factor for carboxylation at elevated CO₂.The model predicted that the decreased N uptake rate at elevatedCO₂lowered RGR modestly, but this effect was counterbalancedby an increase in PNUE resulting in a positive CO₂effect ongrowth. Increased PNUE may also explain why in many experimentselevated CO₂enhances biomass accumulation despite a significantdrop in tissue nitrogen concentration. The formulation of theFB model as presented here successfully predicted plant growthresponses to elevated CO₂. It also proved effective in resolvingwhich plant properties had the greatest leverage on such responses.Copyright 2000 Annals of Botany Company Elevated CO₂, functional balance model, Helianthus annuus L., N uptake, photosynthetic nitrogen use efficiency, root:shoot ratio     

Root Zone Temperature Effects on Growth and Phosphate Absorption in Rape Brassica napus cv. Emerald

Solution culture experiments with fodder rape (Brassica napuscv. Emerald) show that reduced root temperatures appear to havelittle effect on phosphate inflow over a wide range of P concentration.At a cool root temperature (10 ?C) plant growth rate was reducedbut this was compensated for by a low root: shoot ratio, sothat inflow remained relatively steady. An increased inflowper unit length of root was only achieved at an elevated roottemperature of 35 ?C. The minimum phosphate concentration towhich plants could lower the culture solution (C_mln) rangedfrom 0.15 to 2.5 mmol m^–3 according to whether roots wereat a low (5 ?C) or high (35 ?C) temperature respectively. Thetotal phosphorus concentration in tissues was affected by rootzone temperature and at low root temperatures this could bea growth limiting factor. The organic (assimilated) fractionof P in shoot tissues was smaller in low temperature plants.These showed visual symptoms of apparent P deficiency. Levelsof inorganic P in roots may also be a factor in feedback ofcontrol of inflow. Key words: Temperature, Roots, Phosphate, Rape (Brassica napus)     

Use of the Expolinear Growth Model to Analyse the Growth of Faba bean, Peas and Lentils at Three Densities: Fitting the Model

The expolinear equation for crop growth (Goudriaan and MonteithAnnalsof Botany66: 695–701, 1990) was fitted to measurementsof above ground dry weight made on two cultivars of each ofthree species, faba bean (Vicia fabaL.), peas (Pisum sativumL.)and lentils (Lens culinarsMedic.), each grown at three densitiesat the University of Reading, UK in 1992 and 1993. The expolinearequation fitted the data well but required frequent samplingto obtain good estimates of the parameters. The equation hasthree parameters,R_mthe maximum relative growth rate,C_ma maximumcrop growth rate, andt_bthe time at which the crop effectivelyreaches a linear phase of growth.R_mdid not differ between densities,cultivars or species but differed between years.C_mincreasedwith increased density and was lower for lentils than for fababeans or peas.t_bdecreased with increased density for faba beanbut not for the other species. Incorporating an extinction coefficientfor solar radiation and the maximum fraction of radiation interceptedenabled reasonably accurate time courses of leaf area indexto be derived, as suggested by Goudriaan (1994. In: MontiethJL, Scott RK, Unsworth MH, eds.Resource capture by crops. Nottingham:Nottingham University Press, 99–110).Copyright 1998 Annalsof Botany Company Expolinear equation, grain legumes, crop growth rate, crop density, relative growth rate, growth modelling, faba bean,Vicia fabaL., peas,Pisum sativumL., lentils,Lens culinarsMedic.     

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     

Cluster Roots in Casuarinaceae: Role and Relationship to Soil Nutrient Factors

N₂-fixing actinorhizal trees in the family Casuarinaceae areeconomically of great interest in tropical and sub-tropicalzones because they are used for many purposes including protectionagainst wind, stabilization of sand dunes and the productionof firewood and charcoal. They are usually able to grow in sandysoils with low fertility by virtue of their ability to fix N₂.The objective of this review is to discuss briefly the roleof mycorrhizas and, more extensively, that of cluster (proteoid)roots, developed by a number of species of Casuarinaceae toimprove the absorption of nutrients other than N from soil,especially those needed for N₂fixation and growth. After evaluatingthe actual relationships between mycorrhizas and the Casuarinaceae,we highlight the possible role of cluster roots as an effectivealternative to mycorrhizas, and as a means of improvement ofgrowth of the trees in nutrient-deficient soils. This raisesthe question of what triggers the formation of cluster rootsin the Casuarinaceae. In addition to phosphorus deficiency,iron deficiency seems to be a major factor inducing the formationof cluster roots in Casuarina glauca and C. cunninghamiana.The number of cluster roots and the precocity of their formationare directly related to plant chlorosis due to Fe deficiency,as expressed by the critical concentration of chlorophyll inthe shoot (0.60 mg g ^{- 1}shoot f.wt). The effect of the nitrogensource on cluster root formation is discussed in relation topH values in the plant culture solution. The number of clusterroots formed in nitrate-fed plants increases with pH in therange of 5 to 9. Experiments carried out with alkaline and acidicsoils show that cluster roots are only produced when they areneeded to overcome soil nutrient deficiency due to the immobilizationof nutrient elements (P and Fe) by soil alkalinity. The possibleinvolvement of ethylene in the initiation and/or the morphogenesisof cluster roots is discussed. Copyright 2000 Annals of BotanyCompany Casuarinaceae, Casuarina cunninghamiana, Casuarina glauca, cluster roots, ethylene, iron deficiency, phosphorus deficiency, proteoid roots     

Effects of P deficiency on the uptake, flows and utilization of C, N and H2O within intact plants of Ricinus communis L.

The influence of P deficiency on the uptake, flow and utilizationof C, N and H₂0 by intact NO₃-fed castor bean plants {Ricinuscommunis L.) was studied over a 9 d period in the middle oftheir vegetative growth. The modelling techniques incorporateddata on net increments or losses of C, N and H₂O in plant parts,photosynthetic gains in and respiratory losses of C, molar C:Nratios of solutes in phloem and xylem sap and transpirationallosses of H₂0. Plant growth was inhibited within 3 d of withholdingP supply and dry matter production was less than one-third ofthe controls. Leaf growth was particularly depressed, whileroot growth was much less affected than that of the shoot. Shoot:rootratio of low-P plants was 1.5 compared with 2.6 under P supply.Over the 9 d study period total plant C and N increased by 560and 47 mmol, respectively, in the controls, but by only 113and 6.9 mmol in the low-P treatment. The particularly low incrementof N in P-deficient plants was due principally to decreasedN0₃^- uptake. Flows of C and N during the study period were markedlydifferent between control and P-deficient plants. The partitioningprofile for C in P-deficient plants showed a dramatic inhibitionof net photosynthesis and attendant photoassimilate flow. Proportionaldownward to upward allocation of carbon increased with increasein sink size of the root relative to shoot. This was reflectedin greater relative allocation of C to root dry matter and rootrespiration than in P-sufficient plants, and suppressed cyclingof C from root to shoot via xylem. Nitrogen intake and xylemtransport to the shoot of P-deficient plants were only 15% ofthe control and, as in the case of C, downward allocation ofN predominated over upward phloem translocation. Apart fromthese severe changes, however, the basic patterns of N flowsincluding xylem-to-phloem and xylem-to-xylem transfer of N werenot changed, a feature highlighting the vital nature of thesetransfer processes even under deficiency conditions. The alterationsin flows and partitioning of C, N and H₂O in response to low-Pconditions are discussed in relation to the corresponding effectsof moderate salt stress in Ricinus and the conclusion is reachedthat changes in nutrient flows under P deficiency were morehighly co-ordinated than when plants experience salt stress.Flow profiles under P deficiency which favour root growth andactivity are viewed as a means for increasing the potentialcapability of the plant to acquire P from the nutrient medium. Key words: Ricinus communis L., P deficiency, carbon, nitrogen, water, partitioning, xylem transport, phloem transport     

CO2浓度增加和不同氮肥水平对冬小麦根系呼吸及生物量的影响

 依托FACE(Free-air CO₂ enrichment)研究平台, 利用特制分根集气生长箱, 采用静态箱-GC(Gas chromatography)法, 连续两年研究 了大气CO₂浓度升高和不同氮肥水平对冬小麦拔节期、孕穗抽穗期和灌浆末期的根系呼吸及生物量的影响。两季结果表明, CO₂浓度升高和高氮 肥量均不同程度地增加了3个阶段的地上部和地下部的生物量, 这有利于增加根茬的还田量; CO₂浓度升高对冬小麦不同生长阶段的根系呼吸影 响不同, 在拔节期影响较小;孕穗抽穗期显著增加了根系呼吸, 2004~2005季分别增加33.8%(148.1 mg N&;#8226;kg^-1 干土, HN)和43.9%(88.9 mg N&;#8226;kg^-1 干土, LN), 2005~2006季分别为23.8%(HN)和28.9%(LN); 而灌浆末期显著降低了根系呼吸, 2004~2005季分别降低31.4%(HN)和23.3% (LN), 2005~2006季分别为25.1%(HN)和18.5%(LN); 高施氮量比低施氮量促进了根系呼吸; 随着作物生长根系呼吸与地下生物量呈显著线性负相 关, 高CO₂环境中的R²变小,表明随着作物生长发育高CO₂浓度降低了作物根系呼吸与地下部生物量积累间的相关性.     

Acid Phosphatase Activity in Karri (Eucalyptus diversicolor F. Muell.) in Relation to Soil Phosphate and Nitrogen Supply

O'Connell, A. M. and Grove, T. S. 1985. Acid phosphatase activityin karri (Eucalyptus diversicolor F. Muell.) in relation tosoil phosphate and nitrogen supply.—J. exp. Bot. 36: 1359–1372 Soluble acid phosphatase activity was measured in tissues ofkarri (Eucalyptus diversicolor F. Muell.) seedlings and fiveyear old karri trees to which P and N fertilizer had been applied.Addition of P from 0 to 1250 mg P kg^–1 soil with a basaltreatment of other nutrients produced significant increasesin growth, P content and P concentration of karri seedlings.In each of five plant components (shoot tips, partly expandedleaves, mature leaves, young stems and old stems) soluble acidphosphatase activity was greatest at low levels of added P anddecreased with increasing soil P supply. The range of acid phosphataseactivity (0·5-6·5 µmol NPP g^–1 f.wt.min^–1) was similar to that reported for a number of agriculturaland horticultural plants. Enzyme activity was highest for shoottips and lowest for old stems. However, the relative changein activity with decreasing soil P supply was greatest for stems(4·3 fold) and least for shoot tips (2·7 fold) Mature leaves of seedlings grown in ‘high P’ and‘low P’ soil at four levels of added N showed, inaddition to the effect of P, a significant N-P interaction onsoluble acid phosphatase activity. In leaf samples from fiveyear old karri trees there was a significant decrease in solubleacid phosphatase with increasing P fertilization. Addition ofN fertilizer had no significant effect on enzyme activity, probablybecause added N had little effect on foliar N concentrations Exponential models relating (1) plant growth to enzyme activityand (2) plant growth to P concentration in stems and matureleaves of plants grown in soil with a range of added P accountedfor 78–92% and 63–87%, respectively, of the variationin top dry weight. The results suggest that for the diagnosisof plant P status, (1) stem components may be the most appropriatetissue to sample, and (2) nutrient and enzyme assays may complementeach other, P concentration being most useful where P supplyis adequate and phosphatase activity where P supply limits growth Key words: Phosphatase activity, Eucalyptus diversicolor, nutrients, phosphorus, nitrogen, forests     

Direct and Maternal Effects of Elevated CO2on Early Root Growth of GerminatingArabidopsis thalianaSeedlings

Individuals ofArabidopsis thaliana, collected in different naturalpopulations, were grown in controlled and elevated CO₂in a glasshouse.Following germination, root growth of progeny of different linesof these populations was studied in control and elevated atmosphericCO₂. No significant direct effect of atmospheric CO₂concentrationcould be demonstrated on root growth. An important parentaleffect was apparent, namely that root length and branching weredecreased in seeds collected from a mother plant which had beengrown in elevated CO₂. This was correlated with smaller seeds,containing less nitrogen. These parental effects were geneticallyvariable. We conclude that CO₂may affect plant fitness via parentaleffects on seed size and early root growth and that the geneticvariability shown in our study demonstrates thatArabidopsispopulationswill evolve in the face of this new selective pressure.Copyright1998 Annals of Botany Company Root growth, root branching, seed, elevated CO₂, natural population,Arabidopsis thaliana, parental effect.     

Soil Amendments Affecting Nickel and Cobalt Uptake by Berkheya coddii: Potential Use for Phytomining and Phytoremediation

Plants with inordinately high concentrations of heavy metals(‘hyperaccumulators’) can be used for phytoremediation(removal of contaminants from soils) or phytomining (growinga crop of plants to harvest the metals). Pot trials were usedto investigate the effects of MgCO₃, CaCO₃, sulphur, chelatingagents (NTA, DTPA, EDTA) and acid mine tailings on nickel andcobalt uptake by the South African nickel hyperaccumulator Berkheyacoddii. Plants were grown in a nickel-rich ultramafic (‘serpentine’)soil diluted with pumice. Both MgCO₃and CaCO₃caused significantdecreases in the uptake of both metals, as well as decreasingtheir solubility in the soil. After the addition of MgCO_3,therewas a significant increase in soil pH, so the reduction in plant-metaluptake could not be solely attributed to the action of magnesiumalone. Since CaCO₃had no significant effect on soil pH, thisindicated that calcium inhibits the uptake of both cobalt andnickel. All three chelating agents caused a significant reductionin plant uptake of nickel, despite increasing the solubility(plant availability) of these elements in the soil. Cobalt uptakewas unaffected. Sulphur, and the addition of acid mine tailings,caused a highly significant increase in nickel and cobalt uptake,relative to the controls. Sulphur could be used as a low-costsoil amendment to enhance the metal uptake of crops grown onultramafic soils. Thus, land management procedures would enhancephytoremediation and phytomining operations for nickel and cobalt.Copyright1999 Annals of Botany Company Nickel, cobalt, phytoremediation, phytomining.     

长期施肥对麦田土壤微生物垂直分布的影响

应用微量热法研究了长期轮作下麦田不同土层中的微生物活性, 以及施肥对微生物垂直分布的影响。结果表明, 微生物活性基本随深度的增加而下降; 随着土层加深, 可培养细菌菌落数减少, 且可培养细菌菌落数目与最大时间(Peak time)P_t值(表示从微生物生长开始到达到峰值的时间)呈负相关; 热功率(P)-时间(t)曲线由陡变缓, 由规则变得起伏不定, 侧翼变得更短, 峰高也降低; 不同土层的微生物生长速率常数(Microbial growth rate constant) µ、峰高(Peak height)P_h值变化明显, 基本随深度增加而减小。施肥土样和不施肥土样的曲线形状不同, 特别是上层土样施肥后的曲线明显比不施肥的曲线陡, 侧翼也明显变短; 施肥土样的µ和P_h值都大于不施肥土样, 且施肥土样的P_t都小于对照。这说明, 在不同的土壤深度有不同的微生物群落结构, 长期的施肥处理改变了土壤微生物的垂直分布特征。