Root morphological traits related to phosphorus‐uptake efficiency of soybean,sunflower, and maize

Many of the plant acquisition strategies for immobile nutrients, such as phosphorus (P), are related to the maximization of soil exploration at minimum metabolic cost. Previous studies have suggested that soybean (Glycine max L.), sunflower (Helianthus annuus L.), and maize (Zea mays L.) differ in their P uptake efficiency. In this investigation we employed these three species to evaluate: (1) the effect of suboptimal P conditions on root morphological traits related to root porosity and fineness and (2) how these traits are related to P‐uptake efficiency. Opaque 25‐L plastic containers were used to grow plants hydroponically. The three species were compared under two P availability levels (low P and high P). Most of the observed responses were in the direction to favor P uptake under low‐P conditions. Compared to P‐sufficient plants, P‐stressed plants of the three species showed higher root‐to‐shoot ratio, specific root length, root porosity and root aerenchyma, and a lower root density. For example, P‐stress increased root porosity by a factor of 2.0, 1.4, and 1.4 in soybean, sunflower, and maize, respectively. Soybean and sunflower were the species with the highest P‐uptake efficiency, expressed as P uptake either per unit root biomass or length. The results demonstrate the central role of aerenchyma development in modifying root length per unit root biomass and, thus, reducing the root's foraging costs. Consequently, aerenchyma is suggested to be a possible mechanism for better P‐uptake efficiency.     

Phosphatversorgung von Sommerweizen (Triticum aestivum L.) in Mischkultur mit Weißer Lupine (Lupinus albus L.)

Phosphorus nutrition of spring wheat (Triticum aestivum L.) in mixed culture with white lupin (Lupinus albus L.). Spring wheat (Triticum aestivum L. ?Schirokko”?) and white lupin (Lupinus albus L.) were grown in mixed culture in Mitscherlich pots with 20 kg of soil in a green house. The soil used was a B_t of a Parabraunerde-Pseudogley from loess low in available P and limed from pH 4.6 to pH 6.5. Phosphorus was added as phosphate rock. In half of the pots cylinders of stainless steel screen prevented intertwining of the roots of the plant species. Independent of P addition, white lupin had higher dry matter production and P uptake than wheat, even although wheat had thinner roots and higher root densities than lupin, factors which favour the utilization of soil and fertilizer P. The higher P efficiency of white lupin was due to higher P uptake rates per unit root length mainly through mobilization of P especially in the rhizosphere of the proteoid roots. When the roots of the two species were allowed to intertwine, shoot dry matter production of wheat was nearly double because of improved tillering. Higher P concentrations and a more than 2-fold higher P uptake indicated that the increase in dry matter production of wheat was due to improved P nutrition. Nitrogen concentrations, however, remained unaffected at sufficient levels. An increased P uptake rate per unit root length was responsible for the better utilization of P by wheat, rather than the increase in total root length, due to the extended root volume. White lupin was able to mobilize P in the rhizosphere in excess of its own requirements. Thus mobilized P may be available to less P-efficient plants grown in mixed culture.     

PHOSPHORUS UPTAKE AND USE EFFICIENCY IN FIELD CROPS

Phosphorus (P) is required by crop plants for many physiological and biochemical functions. Knowledge of phosphorus uptake and its use by crop plants is essential for adequate management of this essential nutrient. A field experiment was conducted during four consecutive years to determine P uptake and use efficiency by upland rice, dry bean, corn and soybean grown in rotation on a Brazilian Oxisol. Plant samples were taken at different growth stages during the growth cycle of each crop for phosphorus analysis. Phosphorus concentration (content per unit dry matter) significantly decreased in a quadratic fashion with the advancement of plant age in four crop species. Phosphorus concentration was higher in legumes compared to cereals. Phosphorus uptake in shoot, however, significantly increased in an exponential quadratic fashion with the advancement of plant age of crop species. At harvest, P uptake was higher in grain compared to shoot, indicating importance of this element in improving crop yields. Phosphorus use efficiency (grain or straw yield per unit P uptake) was higher in cereals compared to legumes. The P use efficiency for grain production was 465 kg kg^?1 for upland rice, 492 kg kg^?1 for corn, 229 kg kg^?1 for dry bean and 280 kg kg^?1 for soybean. The higher P use efficiency in cereals was associated with higher yield of cereals compared to legume species.     

Fertilizer‐use efficiency of different inorganic polyphosphate sources: effects on soil P availability and plant P acquisition during early growth of corn

Polyphosphate‐based fertilizers are worldwide in use, and their effect on crop yield is often reported to be similar to orthophosphate products, although some studies showed higher yields with polyphosphate applications. However, information on how these fertilizers may influence plant P acquisition is very limited. A pot experiment was carried out under controlled conditions with corn (Zea mays L.) growing on a sandy soil (pH 4.9) and a silty‐loam soil (pH 6.9) differing in P‐sorption properties. The objective was to evaluate phosphorus fertilizer–use efficiency (PFUE) of several polyphosphate (poly‐P) compounds (pyrophosphate [PP], tripolyphosphate [TP], and trimetaphosphate [TMP]) using orthophosphate (OP) as a reference. Focus was put on evaluating plant parameters involved in plant P acquisition, i.e., root length and P uptake per unit of root length. Furthermore, soil P availability was characterized by measuring ortho‐P and poly‐P concentrations in soil solution as well as in CAL (calcium‐acetate‐lactate) extracts. The P availability was differentially influenced by the different P sources and the different soils. In the silty‐loam soil, the application of poly‐P resulted in higher ortho‐P concentrations in soil solution. In the same soil, CAL‐extractable ortho‐P was similar for all P sources, whereas in the sandy soil, this parameter was higher after OP application. In the silty‐loam soil, poly‐P concentrations were very low in soil solution or in CAL extracts, whereas in the sandy soil, poly‐P concentrations were significantly higher. Phosphorus fertilizer–use efficiency was significantly higher for poly‐P treatments in the silty‐loam soil and were related to a higher root length since no differences in the P uptake per unit of root length among poly‐P and OP treatments were found. However, in the sandy soil, no differences in PFUE between OP and poly‐P treatments were observed. Therefore, PFUE of poly‐P compounds could be explained by better root growth, thereby improving plant P acquisition.     

菌根对紫色土上间作玉米生长及磷素累积的影响

丛枝菌根真菌(arbuscular mycorrhizal fungi,AMF)在土壤与植物系统的磷素循环中发挥着关键的作用。本文通过盆栽模拟试验研究了不同AMF接种状况[不接种(NM)、接种Glomus mosseae(GM)、接种G.etunicatum(GE)]和玉米/大豆间作体系不同根系分隔方式(不分隔、尼龙网分隔、塑料膜分隔)对间作玉米植株生长及磷素吸收累积的影响。研究结果表明:GM处理下的间作玉米根系侵染率在不同根系分隔方式之间的差异不显著,而GE处理则在塑料膜分隔处理下对玉米的侵染率最高。接种不同AMF对间作玉米促生效果不同,GM和GE处理在不同根系分隔情况下表现出各自的优势,与未接种处理相比,GM处理能使玉米生物量、株高有一定程度增加并在根系不分隔处理下玉米磷吸收较多、生长较好;GE处理能使植株生物量有一定程度增加并在尼龙网分隔处理下的玉米磷吸收较多、生长较好。间作体系不同根系分隔方式对玉米的影响也不同,其中玉米地上部生物量在根系分隔处理下普遍小于不分隔处理,但根系生物量的大小情况则刚好相反。另外,无论何种接种状况,玉米根系磷含量及吸收量均以尼龙网分隔处理显著较高。而根系磷吸收效率则以接种G.mosseae且不分隔根系处理显著高于分隔处理。所有复合处理中,以接种G.etunicatum与尼龙网分隔根系组合处理对间作玉米的生长及磷素累积的促进作用最好,若应用于滇池流域,可望有效控制坡耕地土壤磷素的迁移。     

分室磷添加下菌根对滇池流域红壤间作玉米生长及磷素利用的影响

随着全球范围内磷矿资源短缺问题的日益严重,间作或菌根技术强化作物对土壤磷(P)的利用及增产增收的效应受到越来越多的关注。通过三室隔网盆栽模拟试验研究了分室磷处理[不添加磷(P0)、添加有机磷(OP50)、添加无机磷(IOP50)]和根室不接种(NM)、根室接种丛枝菌根真菌Glomus mosseae(GM)对与大豆间作的玉米的生长及磷素利用的影响。研究结果表明:所有复合处理中,以间作?GM?IOP50组合处理下的玉米根系最短和地上部生物量最高;OP50处理下,间作玉米的菌根侵染率显著高于单作处理。间作条件下,无论分室磷添加与否,接种GM处理的玉米地上部生物量明显高于NM处理;接种GM处理的玉米根系生物量和株高均显著高于NM处理,且根系生物量以间作?GM?OP50组合处理下最高。接种GM条件下,P0、IOP50、OP50处理下的间作植株生物量较单作处理分别提高45.98%、111.33%、33.56%。单作条件下,无论分室磷添加与否,接种GM处理的玉米地上部磷含量均显著高于NM处理;无论何种种植模式及分室磷添加与否,接种GM处理的植物根系磷含量均显著高于NM处理。无论磷添加与否,间作?GM组合条件下的玉米地上部磷吸收量均显著较高,其中IOP50处理下的地上部磷吸收量显著高于OP50处理。间作?GM组合条件下,IOP50处理玉米根系的磷吸收效率均显著高于OP50处理。可见,接种GM、分室磷添加和间作各自在一定程度上促进了玉米的生长。综合菌根侵染、生物量及磷含量与吸收量、磷吸收效率等指标,所有复合处理中以间作?GM?IOP50组合对玉米地上部的促生作用最好,玉米磷素吸收最多,可望有效强化滇池流域红壤坡耕地磷素的利用。     

Nitrogen Fertilization of Soybean Affects Root Growth and Nodulation on Two Soil Types in Mississippi

Greenhouse studies were conducted to evaluate the influence of nitrogen (N) sources [urea + ?N-(n-butyl) thiophosphoric triamide, NBPT (urease inhibitor) and polymer-coated urea (PCU)] and rates on soybean root characteristics, nodule formation, and biomass production on two soil types (silt loam and clay) commonly cropped to soybean in Mississippi. About 15% less belowground biomass was produced in clay soil than in silt loam soil directly corresponding to all other root parameters including root length, root area, root diameter, and nodule number. Pooled across N rates, N additions resulted in 19% and 52% decrease in belowground biomass and number of nodules, respectively, across soils compared to soybean receiving no N. The N rate was the most critical factor as it influenced all root growth parameters. Number of nodules were 24% greater with PCU than urea + NBPT. Nitrogen additions and clay soil negatively impacted soybean root growth, nodulation, and belowground biomass production.

Abbreviations: Polymer-coated urea, PCU; N-(n-butyl) thiophosphoric triamide, NBPT     

Improved phosphorus efficiency of three new wheat genotypes from CIMMYT in comparison with an older Mexican variety

In a field trial in Northwest Mexico, the phosphorus efficiency of three advanced bread wheat lines (Triticum aestivum L.) from CIMMYT were compared with an older Mexican variety Curinda, under irrigation, on an alkaline clay soil (3.7 mg Olsen-P kg^—1 soil) without (P-0) and with P-fertilisation (P-35; 35 kg P ha^—1). Dry matter, P-content, P-uptake of above ground biomass and root growth (root length densities in different soil depths) were measured at different growth stages, and the net P-uptake rates per unit root length calculated. All four genotypes responded positively to P-fertilisation. The three new genotypes showed significantly higher grain yields compared with the old variety Curinda, on the average, 54% and 42% higher at P-0 and P-35, respectively. The higher grain yield was mainly due to a larger number of kernels per ear, higher thousand kernel weight as well as a higher harvest index. The old variety Curinda had the same (P-0) or greater (P-35) number of spikes m^—2 than the new genotypes. In conclusion of this experiment, the three new genotypes could be classified as more P-efficient. The P-uptake at harvest averaged 35% and 24% more than the old variety Curinda at the P-0 and P-35 level, respectively. The improved P-efficiency was mainly due to a more efficient P-uptake. However, there were only small differences in P-utilisation efficiency (kg grain per kg P in shoots) between old and new varieties (8—11%). The differences in the root systems were more decisive in the P-0 treatment than with P-fertilisation. At low P, the improved P-uptake per ha of the advanced lines was due to a higher root length density especially after flowering, while at high P, a higher P-influx rate per unit root length played a more important role than the root length density. The superiority of the new genotypes at both P levels is obviously due to the good adaptation of their root system (root length density, uptake rate per unit root) to variable P availability in soil.     

Rhizosphere phosphorus depletion by three crops differing in their phosphorus critical levels

It has been reported for many soils that maize (Zea mays L.) has a higher soil‐P critical level than soybean (Glycine max L.) and sunflower (Helianthus annuus L). The objective of this work was to compare the rhizosphere P depletion in these three species in order to investigate if they differ in their capacity to acquire soil P. Sequential P fractionation and pH were determined in rhizosphere and nonrhizosphere soil samples from field and greenhouse experiments. Neither sunflower (the species with highest rhizosphere acidification) nor soybean or maize showed a significant relationship between P depletion and rhizosphere pH. The labile P fraction and the NaOH‐P_i fraction had lower values in the rhizosphere than in the bulk soil in 38% and 77% of the studied cases, respectively. Sunflower and especially maize presented a more intense P_i depletion than soybean. The comparison between sunflower and maize revealed that neither of them took a clear advantage over the other in terms of P depletion. Rhizosphere P_i depletion was associated with the amount of P acquired by the plants. We conclude that the accessibility to different P pools does not explain the differences in soil‐P critical levels among the three species.     

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

Abstract

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.     

施磷水平对玉米大豆间作系统氮素吸收与分配的影响

[目的]研究施磷对玉米大豆间作系统氮素吸收、分配和间作优势的影响,为优化玉米与大豆间作系统氮、磷养分管理提供参考.[方法]两年盆栽试验设置3种种植方式:玉米单作、大豆单作、玉米与大豆间作;4个P2O5施用水平:0、50、100、150 mg/kg,分别以P0、P50、P100和P150表示.在玉米小喇叭口期、大喇叭口期...     

栽培模式及施肥对玉米和大豆根际土壤磷素有效性的影响

栽培模式及施肥管理对作物吸收利用土壤磷素的影响较大,本研究为探明玉米/大豆套作系统作物根系交互作用下根际土壤无机磷组分动态变化特征,利用盆栽试验测定了玉米/大豆套作(M/S)、玉米单作(MM)和大豆单作(SS)3种栽培模式以及不施肥(CK)、施氮钾肥(NK)和施氮磷钾肥(NPK)3种施肥处理下玉米和大豆地上部生物量及吸磷量和根际与非根际土壤速效磷、无机磷组分含量,以期为优化玉米/大豆套作系统磷素管理提供理论依据。研究结果表明同一施肥水平下,套作玉米的籽粒产量显著高于单作玉米;施磷显著提高了单作玉米籽粒产量,而对套作玉米籽粒产量影响不大。无论施肥与否,套作大豆秸秆及籽粒产量均高于单作大豆。所有施肥处理均表现为套作模式下单株作物地上部磷积累量显著高于单作模式。玉米成熟期,CK、NK处理下套作玉米根际土壤速效磷含量分别比单作玉米高54.2%和71.8%;大豆始花期,NPK处理下套作大豆根际土壤速效磷含量比单作大豆高19.8%。大豆成熟期,NK、NPK处理下套作大豆根际土壤速效磷含量分别比单作大豆高23.8%和108.0%。无论是单作还是套作模式,玉米根际土壤Al-P含量在3个施肥处理下均低于非根际土壤。CK和NK处理下单作玉米根际土壤Al-P含量分别是套作玉米的1.19倍和1.22倍;NPK处理下单作玉米根际土壤Fe-P含量是套作玉米的1.21倍。在CK、NK和NPK施肥处理下,单作大豆根际土Al-P含量分别是套作大豆1.12倍、1.30倍和1.25倍,单作大豆非根际土Al-P含量分别是套作大豆的1.22倍、1.30倍和1.06倍。CK、NK处理下单作大豆根际土壤Fe-P含量分别是套作大豆的1.47倍和1.12倍。研究得出结论,低磷条件下,与单作相比,玉米/大豆套作更有利于作物对土壤Al-P、Fe-P的活化吸收。     

Effect of indigenous mycorrhizal colonization on phosphorus‐acquisition efficiency in soybean and sunflower

Despite a general consent about the beneficial contribution of arbuscular mycorrhizal fungi (AMF) on natural ecosystems, there is an intense debate about their role in agricultural systems. In this work, soybean (Glycine max L.) and sunflower (Helianthus annuus L.) field plots with different P availabilities were sampled across the Pampean Region of Argentina (> 150 samples from Mollisols) to characterize the relationship between available soil P and indigenous mycorrhizal colonization. A subsequent pot experiment with soybean and sunflower was carried out to evaluate the effect of P supply (0, 12, and 52 mg P kg^–1) and AMF inoculation on AMF colonization and crop responsiveness to P in a Mollisol. Both crops showed high AMF colonization in the field (average: 55% for soybean and 44% for sunflower). While mycorrhizal colonization in soybean was significantly and negatively related to available soil P, no such trends were apparent in sunflower. Also, total biomass was 3.5 and 2.0 times higher in mycorrhizal than in nonmycorrhizal pot‐grown soybean under low‐ and medium‐P conditions, respectively. Sunflower, on the other hand, did not benefit from AMF symbiosis under medium and high P supply. While mycorrhization stimulated P‐uptake efficiency in soybean, the generally high P efficiency in sunflower was not associated with AMF symbiosis.     

Biomass Production and Phosphorus Use Efficiency in Two Tithonia diversifolia (Hemsl.) Gray Genotypes

Little information exists on the phosphorus (P) use efficiency of Tithonia diversifolia under varying levels of soil P availability. This study evaluated biomass production, changes in tissue P concentration, P uptake, and P uptake and utilization efficiencies in a Costa Rican and Colombian T. diversifolia genotype when 0, 0.3, 5, and 30 mg P g^?1 were available. Biomass, root length and tissue P concentration increased significantly (P < 0.05) with increasing levels of P availability and with time. Phosphorus uptake (mg plant^?1) was significantly higher (P < 0.05) at 30 mg P g^?1. Phosphorus uptake (mg P mg^?1 P_f) and utilization (mg mg^?1 P) efficiencies were greatest at 0.3 and 5 mg P g^?1. Differences between genotypes showed that T. diversofilia from Colombia had a significantly higher (P < 0.05) biomass, tissue P concentration, root length, and a more effective uptake and utilization of P when availability of this nutrient was low.     

根系分隔方式对玉米/大豆根际土壤碳含量及磷有效性的影响

【目的】豆科与禾本科间作体系中对磷有效性的影响主要集中在根系分泌物的活化作用,由根际沉淀引起的土壤碳含量与磷酸酶活性变化及其对红壤磷有效性的影响机制尚不清楚。【方法】本研究以间作玉米大豆为研究对象,设置根系完全分隔、尼龙网分隔、不分隔3种方式,在0、21.83、43.67、65.50和87.34 P mg kg-1（分别记为P0、P1、P2、P3和P4）磷肥施用水平下进行盆栽试验,研究根系分隔方式对间作玉米大豆根际土壤微生物量碳（MBC）、溶解性有机碳（DOC）、根际土壤有机碳（ROC）、酸性磷酸酶活性（ACP）、碱性磷酸酶活性（ALP）、速效磷和Hedley磷组分的影响。【结果】相比完全分隔,根系不分隔可提高玉米和大豆根际土壤MBC含量,显著降低玉米根际土壤DOC含量,低磷水平（P0、P1）时显著提高大豆DOC含量,显著提高玉米（仅在低磷时）和大豆根际土壤ACP活性,低磷时显著提高大豆根际土壤ALP活性。除玉米活性磷组分外,根系分隔方式对间作玉米大豆根际土壤速效磷、磷组分有显著或极显著影响。根系不分隔较完全分隔可通过降低大豆根际活性无机磷（Pi）(P0除外)和中活性Pi从而提高玉米根...     

Response of Mycorrhizal Infection to Glyphosate Applications and P Fertilization in Glyphosate-Tolerant Soybean,Maize, and Cotton

Glyphosate and phosphorus (P) fertilizer may alter arbuscular mycorrhizal (AM) fungal infection rates of glyphosate-tolerant cotton, maize, and soybean in low-P soil. Microbial biomass, water soluble P, Mehlich-3 P, and acid and alkaline phosphatase activities were not significantly impacted by glyphosate or P in the greenhouse. Phosphorus fertilization decreased mycorrhizal infection rates in cotton and maize and increased shoot biomass and shoot P in soybean in 2005, and decreased mycorrhizal infection in soybean and increased shoot biomass in cotton and maize and shoot P in all three crops in 2006. In pasteurized soil, glyphosate decreased percent mycorrhizal infection in maize, increased infection in cotton, and did not significantly affect infection in soybean. When soil was not pasteurized, glyphosate did not significantly alter mycorrhizal infection in any crop. The potential for glyphosate to alter AM fungal infection in glyphosate-tolerant plants may depend on whether soil microbial communities are compromised by other factors.     

Nutrient Composition and Distance from Point Placement to the Plant Affect Rice Growth

Point placement of urea is an efficient technology to improve urea use efficiency in transplanted rice (Oryza sativa L.), but it is largely unknown how nutrient composition in the point placement and the distance from placement site to the plant influence rice root distribution and growth, nutrient uptake, and rice grain yield. A controlled greenhouse experiment was conducted using both N-and P-deficient soil with point placement of N only or N and P together (N + P) at a distance close to or far from the plant, in comparison to an N-spilt application and a no-N control. Both nutrient composition and distance significantly affected rice root growth. Compared with the N point placement, the N + P point placement led to smaller root length and mass densities, higher specific root length (SRL) around the placement site, smaller root system, higher straw mass and grain yield, and higher N and P uptake. The difference between the N + P and N point placements was greater when close to the plant than when far from the plant. It is suggested that higher SRL around the placement site is essential for improving nutrient uptake and rice grain yield, and simultaneous point placement of N and P has a synergistic effect on rice growth.     

Modern wheat cultivars have greater root nitrogen uptake efficiency than old cultivars

The availability of nitrogen (N) contained in crop residues for a following crop may vary with cultivar, depending on root traits and the interaction between roots and soil. We used a pot experiment to investigate the effects of six spring wheat (Triticum aestivum L.) cultivars (three old varieties introduced before mid last century and three modern varieties) and N fertilization on the ability of wheat to acquire N from maize (Zea mays L.) straw added to soil. Wheat was grown in a soil where ¹⁵N‐labeled maize straw had been incorporated with or without N fertilization. Higher grain yield in three modern and one old cultivar was ascribed to preferred allocation of photosynthate to aboveground plant parts and from vegetative organs to grains. Root biomass, root length density and root surface area were all smaller in modern than in old cultivars at both anthesis and maturity. Root mean diameter was generally similar between modern and old cultivars at anthesis but was greater in modern than in old cultivars at maturity. There were cultivar differences in N uptake from incorporated maize straw and the other N sources (soil and fertilizer). However, these differences were not related to variation in the measured root parameters among the six cultivars. At anthesis, total N uptake efficiencies by roots (total N uptake per root weight or root length) were greater in modern than in old cultivars within each fertilization level. At maturity, averaged over fertilization levels, the total N uptake efficiencies by roots were 292?336 mg N g^?1 roots or 3.2?4.0 mg N m^?1 roots for three modern cultivars, in contrast to 132?213 mg N g^?1 roots or 0.93?1.6 mg N m^?1 roots for three old cultivars. Fertilization enhanced the utilization of N from maize straw by all cultivars, but root N uptake efficiencies were less affected. We concluded that modern spring wheat cultivars had higher root N uptake efficiency than old cultivars.     

Comparison of Phosphorus Use Efficiency Among Various Winter Wheat Accessions Grown in Acid and Calcareous Soils

The objective was to differentiate and estimate phosphorus (P)-uptake and P-utilization efficiency among several winter wheat accessions. Twenty-two accessions were characterized for their ability to uptake and utilize P in two low P soils (acid and calcareous). Plants were grown for 28 days in two different sized pots and analyzed for biomass and total P concentration. Total P uptake and biomass was greater in the large pot and calcareous soil. However, there were no significant correlations between the small and large pot for biomass, P uptake, and P concentration, indicating that rooting conditions were different for the two pots, which allowed differentiation between P-utilization and P-uptake efficiency. Possession of ALTM1 gene for malate excretion did not appear to be related to P-uptake efficiency. Several accessions were found to be either P-uptake or P-utilization efficient in both soils. Phosphorus use efficiency mechanisms may contribute to acid soil tolerance.     

Availability in Soil and Acquisition by Plants as the Basis for Phosphorus and Potassium supply to Plants

This report summarizes research aimed at describing the processes and quantifying the factors affecting transfer of P and K from soil into plants. Soil properties related to availability and plant properties reflecting nutrient acquisition were determined. Their interactions in the rhizosphere and their importance for nutrient supply of plants were studied by a combination of measurements and calculations using a simulation model. Phosphorus and potassium uptake by roots decreased P and K concentration at the root surface and caused characteristic depletion profiles in the adjacent soil. The shape of the profiles depended on the effective diffusion coefficient, the concentration of the nutrient in soil, morphological properties of the roots and on influx into roots. The degree of depletion at the root surface indicated the proportion of the nutrient potentially available in the soil. The shape of the depletion profiles reflected the amount of the nutrient taken up by a root section. The parameters found to describe nutrient acquisition are (i) influx per unit root length, (ii) root length per unit shoot weight (root/shoot ratio), and (iii) the period of time a root section absorbs nutrients. Plant species differed considerably in these properties. In order to integrate the processes involved and to evaluate the importance of individual factors, the Claassen-Barber model was used. Depletion profiles and nutrient uptake calculated with this model were in good agreement with measured values in a number of cases. However, at low P supply, plants absorbed substantially more P than the model predicted. This indicates that influx in this case is supported by mechanisms not properly taken into account yet. Influx per unit root length depends on morphological properties of and nutrient mobilization by roots. Root hairs increase root surface area per unit root length. In addition, because of their small diameter and geometric arrangement in soil, root hairs are specially apt to gain from diffusion when concentration gradients are small. This applies even more to VA-mycorrhizae. Their hyphae are longer and thinner than root hairs and can thus deplete larger volumes of soil per unit root length. Root-induced changes of soil pH increased the size of P depletion profiles, indicating that roots can mobilize soil P by this mechanism. Both acid and alkaline phosphatase enzyme activities were found to be markedly increased at the soil-root interface suggesting that soil organic P may contribute to the P supply of plants.