Uptake Efficiency Of Roots Research Articles

Effects of Exogenous Zinc on Growth and Root Architecture Classification of Maize Seedlings Under Cadmium Stress

To explore the effects of different concentrations of zinc （Zn） on the growth and root architecture classification of maize seedlings under cadmium （Cd） stress， a hydroponic experiment was conducted to study the effects of different concentrations of Zn （0， 10， 25， 50， 100， 200， and 400 μmol·L-1） on the growth， root architecture and classification characteristics， Cd content， root Cd uptake capacity， and photosynthetic system of maize seedlings under Cd stress （50 μmol·L-1） by using Zhengdan 958 as the experimental material. Principal component analysis and the membership function method were used for comprehensive evaluation. The results showed that the 50 μmol·L-1 Cd stress had a significant toxic effect on maize seedlings， which significantly reduced chlorophyll content and photosynthetic parameters. The main root length， plant height， biomass， root forks， and root tips， including the root length and root surface area of the grade Ⅰ-Ⅲ diameter range and the root volume of the grade Ⅰ-Ⅱ diameter range， decreased significantly， which hindered the normal growth and development of maize seedlings. Compared with that under no Zn application， 100 μmol·L-1 and 200 μmol·L-1 Zn application reduced the uptake of Cd by maize seedlings， significantly reduced the Cd content in shoots and roots and the Cd uptake efficiency. The toxic effect on maize seedlings was alleviated， and the fresh weight， dry weight， tolerance index， and root forks of shoots and roots were significantly increased. The photosynthesis of maize seedlings was significantly enhanced， and the photosynthetic rate and the total chlorophyll content was significantly increased. The RL， SA， and RV in the Ⅰ-Ⅱ diameter range reached the maximum at 100 μmol·L-1 Zn， and the RL， SA， and RV in the Ⅲ diameter range reached the maximum at 200 μmol·L-1 Zn， which were significantly higher than those without Zn treatment. The comprehensive evaluation of the growth tolerance of maize seedlings showed that 100 μmol·L-1 and 200 μmol·L-1 Zn had better effects on alleviating Cd toxicity. Comprehensive analysis showed that the application of appropriate concentration of Zn could reduce the Cd content in maize seedlings， the Cd uptake capacity， and Cd uptake efficiency of roots； increase the biomass accumulation of maize seedlings； reduce the effect of Cd toxicity on root architecture； reduce the effect on the light and system； and improve the tolerance of maize seedlings to Cd.

Impact of rhizosphere microorganisms on arsenic (As) transformation and accumulation in a traditional Chinese medical plant.

Panax notoginseng is an important traditional medicinal plant, but the commercial value is threatened by root-rot disease caused by rhizosphere microbes and a potential health risk caused by plant arsenic (As) accumulation. Whether rhizospheric microbes isolated from P. notoginseng rhizosphere soil could impact As uptake and transport into P. notoginseng is not yet known. Among the three root-rot disease-causing pathogens Fusarium flocciferum (PG 1), Fusarium oxysporum (PG 2), and Fusarium solani (PG 3) and one root-rot disease biocontrol fungus Trichoderma koningiopsis (FC 1) and five biocontrol-exerting bacterial species Bacillus siamensis (BC 1), Delftia acidovorans (BC 2), Brevibacillus formosus (BC 3), Mortierella alpine (BC 4), and Bacillus subtilis (BC 5), one As-resistant pathogen and four biocontrol microorganisms with As-resistant ability were identified. The As-transforming ability of the identified fungi and bacteria was ranked in the order of FC 1 > PG 1 and BC 2 > BC 3 > BC 1, respectively. Then, the As-resistant biocontrol and pathogenic microbes were initiated to colonize the rhizosphere of 1-year-old P. notoginseng seedlings growing in artificially As(V)-contaminated soil to evaluate the impact of microbe inoculation on P. notoginseng As uptake and transport capacity. Concentration of As in P. notoginseng tissues decreased in the order of the sequence stem > root > leaf. Compared to treatment without colonization by microorganism, inoculation with microorganisms increased As root uptake efficiency and root As concentration, especially under treatment of inoculation by BC 2 and PG 1 + BC 2. As transport efficiency from root to stem decreased by inoculation with microorganism, especially under treatment with inoculation of BC 2 and PG 1 + BC 2. However, the impact of microorganism colonization on As stem to leaf transport efficiency was not obvious. In summary, inoculation with rhizosphere microbes may increase As accumulation in P. notoginseng root, especially when using bacteria with high As transformation ability. Therefore, it is necessary to evaluate the As transformation capacity before applying biological control microorganism to the rhizosphere of P. notoginseng.

Growth, Physiology and Nutrient Use Efficiency in Eugenia dysenterica DC under Varying Rates of Nitrogen and Phosphorus.

The production of high-quality seedlings and their use in commercial planting reduce pressure on natural areas. Eugenia dysenterica DC is a native fruit tree from the Brazilian Cerrado, whose nutritional requirements are still unclear. This study aimed to evaluate the effects of nitrogen (N) and phosphorus (P) supplementation on the physiology, growth and nutrient uptake, and use efficiencies of E. dysenterica seedlings grown in glasshouse conditions. The following rates were used in separate experiments: 0, 50, 100, 200, and 400 mg dm−3 N and 0, 100, 200, 400, and 600 mg dm−3 P. The experiment was conducted in a randomized block with four replications. The lowest N rate (50 mg dm−3) increased the stomatal conductance (gS) and, consequently, resulted in the highest transpiration (E), electron transport (ETR), and photosynthetic (A) rates. Also, rates of 50 mg dm−3 and 100 mg dm−3 N increased the Root Uptake Efficiency (RUE) and plant Nutrient Use Efficiency (NUE) for macronutrients and the RUE for micronutrients, stimulating plant growth. Phosphorous fertilization resulted in the maximum values for photosynthesis, electron transport rate, total dry mass, and NUE at the 200 mg dm−3 rate. The results of this study suggest that fertilization with 50 mg dm−3 N and 200 mg dm−3 P is suitable for the development of E. dysenterica seedlings.

Foliar-applied lanthanum chloride increases growth and phosphorus acquisition in phosphorus-limited adzuki bean seedlings

Lanthanum, a rare earth element, is used in agriculture and forestry to promote plant growth and productivity. We aimed to investigate its role in altering the roots and alleviating P deficiency in the adzuki bean Vigna angularis. The adzuki bean variety “Jin No. 5” was pre-cultivated in sand. Fourteen-day-old seedlings were sprayed twice with 0.4 mM LaCl3 solution. Next, we treated the seedlings with half-strength Hoagland solution containing P reduced to 1% of its original concentration (P-deficient); P reduced to 5% of the original (P-marginal); and unadjusted solution (P-sufficient). We measured plant growth, root structure, root hydraulic conductivity, P content, gas exchange, and photosynthetic pigment levels in all groups. LaCl3 application significantly increased leaf P concentration, effectively improving the P uptake efficiency of roots, shoots, and leaves under severe P stress. Root morphology and acid phosphatase (APase) activity varied significantly in response to LaCl3 under low-P stress. A greater leaf area, gas exchange ability, chlorophyll content, and carotenoid content were observed in the presence of LaCl3 under P-marginal stress. The application of LaCl3 can promote growth and P acquisition in adzuki beans under P limitation by inducing changes in root morphology, APase activity, and hydraulic conductivity.

Modelling facilitation or competition within a root system: importance of the overlap of root depletion and accumulation zones

Aims: The concept of intra-plant, inter-root competition considers the overlap of nutrient depletion zones around roots, but neglects the spatial pattern of root exudates that can increase nutrient availability. We tested the hypothesis that interactions between nutrient accumulation zones due to exudation by different roots can lead to intra-plant inter-root facilitation. Methods: We used the PARIS model (Raynaud et al. 2008) to simulate phosphorus uptake by a population of roots that are able to increase phosphorus availability by exuding citrate. We carried out several simulations with the same parameters but with increasing root density in order to study out if changes in root densities would alter nutrient uptake per unit root. Results: Emerging relationships between root uptake efficiency and root length density indicated cases of inter-root competition or facilitation. The sizes of the accumulation and depletion zones were calculated to explain these results. Our simulations showed a continuum between cases of inter-root competition and facilitation. Facilitation occurred at low exudation rates, when phosphorus supply was not saturated within the phosphorus depletion zone surrounding roots. Low exudation systems led to a lower phosphorus uptake per unit root length, but minimized phosphorus losses in the process. Conclusions: Based on our model, we derived conditions that allowed predicting whether competition, facilitation or no interaction, is the dominant interaction between roots within a root system, based on the different distances to which an isolated root alters P concentration and supply.

Phosphorus Uptake by Young Citrus Trees in Low-P Soil Depends on Rootstock Varieties and Nutrient Management

Because low-phosphorus (P) availability limits citrus growth, rootstocks with a relatively high capacity for P uptake are desirable. An experiment was conducted with trees on Cleopatra mandarin (CM) and Rangpur lime (RL). Treatments consisted of P rates (20, 40, and 80 mg kg−1 of soil) applied in soil layers of 0–0.30 m and/or 0.31–0.60 m, besides an unfertilized control. The P fertilization increased root and shoot growth, and P nutrition was improved as indicated by greater leaf P concentration, P uptake, and P root uptake efficiency (PUE). The P applied in both soil layers improved shoot growth, P uptake, and PUE. Trees on RL took up 23–126% more P and had root systems with greater growth and PUE compared to those on CM. Thus, P uptake by citrus trees in low-P soils can be improved by augmenting the depth of fertilizer application and the use of more adapted rootstocks.

Evaluation of the effectiveness of soil-applied plant derivatives of Meliaceae species on nitrogen availability to peach trees

We assessed the effect of soil-applied derivatives of melia ( Melia azedarach L.) and neem ( Azadirachta indica A. Juss) on nitrogen (N) soil availability, root uptake and peach ( Prunus persica L.) growth. First we evaluated the effectiveness of experimentally prepared amendments made with fresh ground melia leaves or commercial neem cake incorporated into the soil as nitrification inhibitors, then we evaluated the effect of fresh ground melia fruits and neem cake on growth and N root uptake of potted peach trees, and on soil microbial respiration. Soil-applied fresh ground melia leaves at 10 and 20 g kg −1 of soil as well as commercial neem cake (10 g kg −1) were ineffective in decreasing the level of mineral N after soil application of urea-N as a source of mineral N, rather they increased soil concentration of nitric N and ammonium N. The incorporation into the soil of fresh ground melia fruits (at 20 and 40 g kg −1) and neem cake (at 10 and 20 g kg −1) increased N concentration in leaves of GF677 peach × almond ( Prunus amygdalus) hybrid rootstock alone or grafted with one-year-old variety Rome Star peach trees. An increase in microbial respiration, leaf green color and plant biomass compared to the control trees were also observed. The Meliaceae derivatives did not affect, in the short term (7 days), N root uptake efficiency, as demonstrated by the use of stable isotope 15N, rather they promoted in the long term an increase of soil N availability, N leaf concentration and plant growth.

Water uptake, active root volume, and solute leaching under drip irrigation: A numerical study

The use of saline water for irrigation is based on the concept that increasing irrigation water quantity may offset in part the negative effects associated with higher salinity. The main goals of this paper were (1) to investigate the impact of the controllable variables, the relative quantity (Qr), and the quality (C0) of the irrigation water on water uptake, active root volume, and solute leaching under daily drip irrigation in fine (clay) and coarse (sandy) textured soils; (2) to test the hypothesis that the reduced active root zone associated with salt accumulation may further reduce water uptake by plant roots; and (3) to assess consequences of using (C0‐Qr) substitutions based on the FAO recommendations on salinity control with respect to agricultural and environmental aspects. Novel findings of this study suggest that in the clay soil mean water extraction rate, Sw is quite robust to C0‐Qr substitutions, and the decrease in transpiration, T, induced by increasing C0 is mainly due to the decrease in the soil volume providing most (90%) of the root water uptake, Vs. In contrast, in the sandy soil, Vs may increase with C0‐Qr substitutions, and the decrease in T is mainly due to the decrease in Sw, induced by osmotic pressure head reduction. Consequently, in the clay soil, a simultaneous increase of Qr and C0 based on the FAO substitution curve may lead to an increase in root uptake efficiency, T/Vs, while it may cause the opposite effect in the sandy soil. Furthermore, compensation for the adverse effects of increasing C0 on relative transpiration, Tr, by C0‐Qr substitutions is more efficient in the clay soil than in the sandy soil. The C0‐Qr substitution approach may lead to an increase in the salt load leached below the root zone, thus increasing the potential for polluting groundwater resources. Results of the present study suggest that for both soils, from both agricultural and, particularly, environmental points of view, irrigation with high‐quality water which may comply with economical criteria is desirable.

Biomass production and phosphorus use of forage grasses fertilized with two phosphorus sources

A major constraint to agricultural production in acid soils of tropical regions is the low soil P availability, due to the high adsorption capacity, low P level in the source material and low efficiency of P uptake and use by most of the modern varieties grown commercially. This study was carried out to evaluate the biomass production and P use by forage grasses on two soils fertilized with two P sources of different solubility. Two experiments were carried out, one for each soil (Cambisol and Latosol), using pots filled with 4 dm³ soil in a completely randomized design and a 4 x 2 factorial scheme. The treatments consisted of a combination of four forage plants (Brachiaria decumbens, Brachiaria brizantha, Pennisetum glaucum and Sorghum bicolor) with two P sources (Triple Superphosphate - TSP and Arad Reactive Phosphate - ARP), with four replications. The forage grasses were harvested at pre-flowering, when dry matter weight and P concentrations were measured. Based on the P concentration and dry matter production, the total P accumulation was calculated. With these data, the following indices were calculated: the P uptake efficiency of roots, P use efficiency, use efficiency of available P, use efficiency of applied P and agronomic efficiency. The use of the source with higher solubility (TSP) resulted, generally, in higher total dry matter and total P accumulation in the forage grasses, in both soils. For the less reactive source (ARP), the means found in the forage grasses, for use efficiency and efficient use of available P, were always higher when grown in Latosol, indicating favorable conditions for the solubility of ARP. The total dry matter of Brachiaria brizantha was generally higher, with low P uptake, accumulation and translocation, which indicated good P use efficiency for both P sources and soils. The forage plants differed in the P use potential, due to the sources of the applied P and of the soils used. Less than 10 % of the applied P was immobilized in the forage dry matter. Highest values were observed for TSP, but this was not reflected in a higher use efficiency of P from this source.

Comparison of Root‐System Efficiency and Arsenic Uptake of Two Fern Species

This greenhouse study examined the root characteristics (biomass, length, area, and diameter) and root uptake efficiency of Pteris vittata, an arsenic (As) hyperaccumulator and Nephrolepis exaltata, not an As hyperaccumulator, in relation to plant uptake of As and nutrients in an As‐contaminated and a control soil. After 8 weeks of growth, on a per plant basis, P. vittata accumulated 7.3–8.8 g of biomass and removed 2.51 mg of As from the As‐contaminated soil compared to 2.4–2.7 g of biomass and 0.09 mg of As for N. exaltata. This was partially because P. vittata developed a more extensive root system, 2.4–3.8 times greater (biomass, length, and area), and possessed a greater proportion of fine roots than N. exaltata. In addition, the As root‐uptake efficiency (defined as As concentrations in plant tissue per unit root) for fronds of P. vittata was 15–23 times greater than that of N. exaltata in both soils. Whereas N. exaltata removed phosphorus (P) more efficiently from the soils, P. vittata removed As more efficiently. The larger root biomass coupled with more efficient root‐uptake systems for As may have contributed to As hyperaccumulation by P. vittata.

Absorção e utilização do fósforo pelas culturas da soja e do feijão e por plantas daninhas

A aplicação de fertilizantes pode, em determinadas situações, beneficiar mais as plantas daninhas do que as próprias culturas. O manejo de fertilizantes em sistemas agrícolas pode ser um importante componente em programas de manejo integrado das culturas. O objetivo deste trabalho foi avaliar a eficiência na absorção e utilização do P pelas culturas da soja e do feijão e por espécies de plantas daninhas. O experimento foi realizado em casa de vegetação, no período de agosto a novembro de 2002. O delineamento experimental utilizado foi o de blocos casualizados com três repetições; os tratamentos originaram-se de esquema fatorial 6 x 4, sendo seis espécies vegetais: soja (Glycine max), feijão (Phaseolus vulgaris), dois biótipos de Euphorbia heterophylla (suscetível e resistente aos herbicidas inibidores de ALS), Bidens pilosa e Desmodium tortuosum; e quatro doses de P (0,00 12,00; 24,00 e 48,00 mg dm-3), aplicadas na semeadura sob a forma de superfosfato simples. A soja foi a espécie que revelou maior aumento na sua massa seca de raízes com o incremento do fornecimento de P. D. tortuosum, soja e B. pilosa apresentaram maior resposta à adição de doses crescentes de P em relação ao acúmulo de massa seca. O maior teor de P foi constatado para o feijão, independente da dose de P aplicada, contudo D. tortuosum foi a única espécie a ter seu teor de P aumentado em quase três vezes, quando cultivado com o dobro da dose aplicada (48,00 mg dm-3), com base nas necessidades da cultura do feijão. Até a avaliação realizada no início do florescimento, as plantas de soja e D. tortuosum foram as espécies que acumularam a maior quantidade de P em seus tecidos, porém, durante a fase reprodutiva foi D. tortuosum a qual, juntamente com feijão, apresentaram variações quanto à eficiência de suas raízes em absorver P, de acordo com a dose desse nutriente, enquanto as demais espécies mantiveram a mesma eficiência radicular, independente do teor de P do solo. A eficiência na utilização do P absorvido, observado para D. tortuosum, soja e feijão, diminuiu com o aumento da dose. Nos biótipos de E. heterophylla e no feijão, foi verificado baixo desempenho quanto ao uso eficiente do P disponível no solo. A maior porcentagem de recuperação do P aplicado até à fase de formação de propágulos foi constatada nas plantas de D. tortuosum.

Nitrate Uptake and Nitrogen Use Efficiency by Kentucky Bluegrass Cultivars

Efficient utilization of fertilizer-nitrogen (N) by turfgrasses is probably related to N uptake efficiency of roots and metabolic efficiency of absorbed N in roots and shoots. This study evaluated Kentucky bluegrass (Poa pratensis L.) cultivars for potential differences in nitrate uptake rate (NUR), temporal variation in NUR, and the relationship between NUR and N use efficiency (NUE), defined as grams dry matter per gram N. Six cultivars were propagated from tillers of seeded plants, grown in silica sand, mowed weekly, and watered daily with a complete nutrient solution containing 1.0 mm nitrate. A nutrient depletion method from an initial nitrate concentration of 0.5 mm was used to determine NUR of 5-month-old plants. NUR (μmol·h-1 per plant) of the six cultivars ranked as follows: `Blacksburg' > `Conni' > `Dawn' > `Eclipse' = `Barzan' > `Gnome'. When NUR was based on root weight, `Conni' ranked highest; when NUR was based on root length, surface, or volume, `Eclipse' ranked highest. Averaged across cultivars, NUR on the second day was greater than NUR for the first day of nitrate exposure. Temporal variation was greatest in `Blacksburg', while none was noted in `Conni' or `Eclipse'. Cultivar differences in NUE were significant in fibrous roots, rhizomes, and leaf sheaths, but not in leaf blades and thatch. Total nitrate uptake was positively related to total N recovered and total plant dry matter, but NUR based on root weight was negatively correlated with NUE of the whole plant.

The dynamic role of root-water uptake in coupling potential to actual transpiration

The relationship between actual ( E act) and potential ( E p) transpiration above a grass-covered forest clearing was investigated numerically and experimentally from simultaneous measurements of soil moisture content profiles, mean meteorological conditions, turbulent heat and water vapor fluxes in the atmospheric surface layer, and soil hydraulic properties for two drying periods. The relationship between E act/ E p was found to be approximately constant and insensitive to variability in near-surface soil moisture content. To explore this near-constant E act/ E p, a model that relates potential and actual transpiration and accounts for root-uptake efficiency, potential transpiration rate, and root-density distribution was proposed and field-tested. The total amount of water consumed by the root system was integrated and compared with eddy-correlation latent heat flux measurements (field scale) and total water storage changes (local scale). Model calculations suggested that the deeper and more efficient roots are primarily responsible for the total water loss within the root zone when the near-surface soil layer approaches their wilting point.

Nitrogen and Phosphorus Uptake in Pearl Millet and Its Relation to Nutrient and Transpiration Efficiency

AbstractDepending on soil and rainfall characteristics, pearl millet [Pennisetum glaucum (L.) R. Br.] production in the Sahel can be limited by inefficient use of nutrients, especially N and P, or by inefficient use of water. This study measured pearl millet N and P uptake and compared the efficiency with which N, P, and water are used for growth under varied soil P and water availability. Millet was grown outdoors in semiarid West Texas using rain‐sheltered pots of low pH, P‐deficient sandy soil. Treatments consisted of four P levels (0–56 g−2) and two water treatments (stressed and not). Plant P concentration decreased strongly with plant age; added P and water stress increased stem and leaf P concentration. Plant N concentration also decreased with age and increased with water stress, but decreased with added P. Because of the effects of age, water availability, and P level on organ nutrient concentration, P‐use efficiency (PUE) increased with age, decreased with water stress, and decreased with added P. Nitrogen‐use efficiency (NUE) also increased with age and decreased with water stress, but tended to increase with added P. Shoot transpiration efficiency (WUET) increased with water stress and added P, and so varied inversely with PUE throughout the growth cycle. Phosphate root uptake efficiency (PRE) was less sensitive than PUE to age, P availability, and water stress, because of the compensating effect of root growth; PRE was also positively correlated with WUET and yield. For crop improvement programs interested in increasing both P‐ and water‐use efficiency, PRE is probably a better selection index than PUE.

Phosphorus uptake of maize as affected by ammonium and nitrate nitrogen ‐ Measurements and model calculations ‐

AbstractPhosphorus uptake is often enhanced by ammonium compared to nitrate nitrogen nutrition of plants. A decrease of pH at the soil‐root interface is generally assumed as the cause. However, an alteration of root growth and the mobilization of P by processes other than net release of protons induced by the source of nitrogen may also be considered. To study these alternatives a pot experiment was conducted with maize using a fossil Oxisol high in Fe/Al‐P with low soil solution P concentration. Three levels of phosphate (0, 50, 200 mg P kg−1) in combination with either ammonium or nitrate nitrogen (100 mg N kg−1) were applied. Plants were harvested 7 and 21 d after sowing, P uptake measured and root and shoot growth determined. To assess the importance of factors involved in the P transfer from soil into plants, calculations were made using a model ofBarberandClaassen.In the treatments with no and low P supply NH4‐N compared to NO3‐N nutrition increased the growth of the plants by 25 % and their shoot P content by 38 % while their root growth increased by 6 % only. The rhizosphere pH decreased in the NH4‐N treatments by 0.1 to 0.6 units as compared to the bulk soil while in the NO3‐N treatments it increased by 0.1 to 0.5 units. These pH changes had a minor influence on P uptake only, as was demonstrated by artificially altering the soil pH to 4.7 and 6.3 respectively. At the same rhizosphere pH, however, P influx was doubled by the application of NH4‐compared to NO3‐N. It is concluded that in this soil the enhancement of P uptake of maize plants after ammonium application cannot be attributed to the acidification of the rhizosphere but to effects mobilizing soil phosphate or increasing P uptake efficiency of roots. Model calculation showed that these effects accounted for 53 % of the P influx per unit root length in the NO3‐N and 72 % in the NH4‐N supplied plants if no P was applied. With high P application the respective figures were only 18 and 19%.

Cassava varietal response to phosphorus fertilization. II. Phosphorus uptake and use efficiency

In Latin America, where cassava is commonly grown, yield is partly limited by low-P soil. Previous trials conducted at Centro Internacional de Agricultura Tropical (CIAT) indicated a wide range of response for adaptation to low-P soils in cassava germplasm. The objectives of this study were to identify plant characteristics and possible mechanisms involved in varietal response to P and to assess the relative importance of P uptake and internal use. Two-year trials with four varieties were conducted in a field low in P with three levels (0, 50 and 100 kg ha −1) of P application. Five sequential harvests (with determination of P uptake) were carried out during each of two growth cycles, and VAM infection rates of fine roots and root length density in the surface soil layer were measured. In all varieties P uptake increased with P fertilization, and cultivar variation in P uptake was related to differences in fine root length density more than to VAM infection rates. Uptake efficiency of roots (as uptake rate per unit root length) did not differ among varieties. Phosphorus-use efficiency (as root yield per accumulated P in the whole plant) and patterns of dry matter allocation to roots and shoots were significantly different among varieties. It was concluded that cultivar differences in response to applied P were mainly due to contrasting patterns of dry matter partitioning and P-use efficiency. Adaptation to low-P soils could be enhanced by selection of varieties with high fine-root length density, moderate top growth and stable harvest index.

Variability and Inheritance of Sulfate Uptake Efficiency and ATP‐Sulfurylase Activity in Maize1

Sulfate uptake efficiency of roots and ATP‐sulfurylase activity in leaves and in roots were evaluated in maize (Zea mays L.) inbreds W75, 65B, 103B, and in the diallel set of F1 hybrids, in order to assay the variability and the inheritance of the two characters. The correlation at the level of genetic regulation between the uptake and the first step of sulfate metabolism was also determined. Wide genetic differences were seen in the uptake efficiency and in enzyme activity. These traits demonstrated a close correlation and a high level of heterosis. The kinetics of sulfate uptake was also affected by crossing; Vmax followed the same pattern as uptake efficiency, while Km, with the exception of the 103B ✕ 65B cross, showed a low level of heterosis.

Uptake efficiency of roots in plants at different ploidy levels

SummaryThe uptake efficiency of roots for sulphate and potassium was evaluated in wheat, sugar beet, and tomato, at different ploidy levels. At increasing ploidy, wheat and sugar beet showed higher, tomato lower efficiency, the polyploid absorption system being characterized in sugar beet by higher Vmax and Km, in wheat by higher Vmax and unchanged Km, in tomato by lower Vmax and Km. Uptake efficiency of roots appears tightly bound to the evolutionary progress, that is to the level of environment adaptation of plants, and should be susceptible of further improvement by breeding practices.

The effect of phosphate deficiency on the kinetics of phosphate absorption by sterile excised barley roots, and some factors affecting the ion uptake efficiency of roots

Abstract The influence of phosphate nutrition on the kinetics of phosphate absorption by sterile excised barley roots was examined. The roots of seedlings grown in dilute CaSO4 showed uptake kinetics similar to roots grown in phosphate deficient nutrient culture. The absence of microorganisms did not abolish the dual form of the absorption isotherm at pH 4.0 The most important effect of phosphate deficiency for uptake at low phosphate concentration was a marked decrease in the apparent dissociation constant of the ion‐carrier complex postulated to be involved in the uptake process. The results are discussed in relation to kinetic factors which may influence the efficiency of ion uptake by roots of different species of plants, including the apparent dissociation constant, the rate constant for uptake and the concentration of the ion‐carrier system.