Phosphatverarmung des wurzelnahen Bodens und Phosphataufnahme von Mais und Raps

Phosphate depletion at the soil — root interface and the phosphate uptake of maize and rape Maize and rape plants were grown in flat containers in a ³3P-labelled sandy soil and the distribution of soil phosphate near roots was determined by using densitometric scans of autoradiographs. The concentration of isotopically exchangeable phosphate at the root surface decreased within a few days by 42 per cent with rape and by 50–65 per cent with maize. Initially the width of the depletion zone is very small. Within six days the depletion zone extended to the final distance from the surface of the root cylinders of about 2 mm for maize and 2.6 mm for rape. The soil within the range of the mean length of root hairs (0.7 mm for maize and 1.3 mm for rape) is almost equally depleted. This indicates that root hairs are very important for P-uptake from soil. This is further supported by higher P-uptake rates per cm root length of rape than of maize. The P-concentration of the soil solution was estimated by means of the phosphate desorption curve. Within the root hair cylinder the P-concentration of the soil solution decreased from 0.8 to 0.03 mg P/l. Changes of the P-depletion profile with time were used to calculate P-uptake rates for roots of different age. The results indicate that for the first 3–5 days P-uptake rates remained near maximum, even though the P-concentration of the soil solution at the root surface had strongly decreased within two days. Phosphate uptake rates per cm root length did not decrease unless the whole root hair cylinder had been depleted.     

Differential Growth Performance of 15 Wheat Genotypes for Grain Yield and Phosphorus Uptake on a Low Phosphorus Soil Without and With Applied Phosphorus Fertilizer

ABSTRACT

Two field experiments were conducted to compare 15 wheat genotypes at two phosphorus (P) levels (zero-P control or low P level—without application of P fertilizer on soil with 8 mg extractable P kg^?1, and adequate P level—with P fertilizer applied at 52 kg P ha^?1) for yield, P uptake, and P utilization efficiency (P efficiency ratio—PER, P harvest index—PHI, and P physiological efficiency index—PPEI). On the average of two experiments, substantial and significant differences were observed among wheat genotypes for both grain and straw yields at both P levels. Grain yields ranged from 2636 to 4455 kg ha^?1 in the zero-P control, and from 2915 to 4753 kg ha^?1 at adequate P level. Genotype 5039 produced the maximum grain yield, while 6529-11 had the minimum grain yield at both P levels. Relative reduction in grain yield due to P deficiency stress (PSF) ranged from none to 32%, indicating differential P requirements of genotypes. Genotypes 4943, Pasban 90, Inqlab 91, PB 85, Lu 26s, 4770, Chakwal 86, 4072, 6544-6, and 5039 had little or no response to P application. Phosphorus responsive genotypes included FSD 83, Kohinoor 83, Parvaz-94, Pak 81, and 6529-11. A non-significant correlation (r = ?0.466, P > 0.05) between grain and PSF in zero-P control treatment also indicated the least effect of P deficiency on some wheat genotypes. A wide range of PPEI (270–380 kg grain kg^?1 P absorbed in grain + straw at control P level, and 210–330 kg grain kg^?1 P absorbed in grain + straw at adequate P level) indicated differential utilization of absorbed P by the genotypes for grain production. This indicated that wheat genotypes differed considerably in their P requirement for growth and responsiveness to P application. The findings also suggested that PPEI was a better parameter for measuring P efficiency than other parameters, and can be used for selecting P efficient genotypes, because it relates to the internal concentration of a nutrient and genetic makeup of plant. It is concluded that genotypes having ability to produce relatively high grain yield, good command to tune P within plant and high PPEI are suited to low P soil conditions. Genotypes 4072, Inqlab 91, 4943, Pak 81 and 5039 were P efficient and had above mentioned abilities, while genotypes FSD 83, 6544-6, and 6529-11 were P inefficient. It should be noted that traits related to P efficiency are inheritable and can be used to improve P use efficiency of a genotype through back cross breeding programs.     

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.     

Effect of Foliar Application of Phosphorus on Winter Wheat Grain Yield,Phosphorus Uptake,and Use Efficiency

ABSTRACT

One would expect foliar applied phosphorus (P) to have higher use efficiencies than when applied to the soil, but limited information is available concerning this. Experiments were conducted in 2002, 2003, and 2004 to determine the effect of foliar applications of P on winter wheat grain yields, P uptake, and use efficiency. Twelve treatments containing varying foliar P rates (0, 1, 2, and 4 kg ha^{? 1} in 2002 and 2003 and additional 8, 12, 16, and 20 kg ha^{? 1} in 2004) with and without pre-plant rates of 30 kg ha^{? 1} were evaluated. Foliar applications of P at Feekes 7 generally increased grain yields and P uptake versus no foliar P. Use efficiency was higher when P was applied at Feekes 10.54. Results from this study suggested that low rates of foliar applied P might correct mid-season P deficiency in winter wheat, and that might result in higher P use efficiencies.     

Variation in Phosphorus Uptake and Use Efficiencies Between Pigeonpea Genotypes and Cowpea

ABSTRACT

Low bioavailability of soil phosphorus (P) often limits N₂ (nitrogen) fixation and crop production in large parts of the tropics. The efficiency of P acquisition and P use by 21 genotypes of pigeonpea [Cajanus cajan (L.) Millsp.] were studied in a pot experiment using two cowpea [Vigna unguiculata (L.) Waip.] genotypes as controls. The short-duration genotypes produced more dry matter, accumulated more P, and produced more dry matter per unit of absorbed P than the medium-and long-duration genotypes. Dry-matter production correlated positively with the P uptake (r² = 0.72) and P-use efficiency (r² = 0.86). The P uptake correlated positively with the P-use efficiency (r² = 0.36); whereas the P-use efficiency correlated negatively with the P-uptake efficiency (r² = 0.50). Root surface did not determine P acquisition of pigeonpea, which absorbed 1.6 mg P cm^?3 from 33 cm³ soil compared with 0.17 mg P cm^?3 from 387 cm³ soil for cowpea at 66 d.     

Compared Phosphorus Efficiency in Soybean,Sunflower and Maize

ABSTRACT

A more comprehensive understanding of the mechanisms of phosphorus (P) efficiency is agronomically significant to advance in the design of crop management schemes that increase P efficiency and reduce the need of fertilizers. Phosphorus efficiency is defined as the ability of a plant to acquire P from the soil and/or to utilize it in the production of biomass or the harvestable organ. Because most parameters related to P efficiency vary according to the growth conditions and isolation of the individual effect of P efficiency is not straightforward; plants must be grown in uniform experimental conditions to obtain a fair comparison of their nutrient acquisition and utilization. In this work, we compare the ability of soybean, sunflower, and maize to utilize and acquire soil P. Field and greenhouse experiments including different P levels were conducted. The general observation was that the three species ranked differently according to the specific parameter of P efficiency considered. Maize clearly showed higher P utilization efficiency than soybean and sunflower, either expressed as biomass or as grain produced per unit of absorbed P. In turn, soybean and sunflower exhibited higher acquisition efficiency than maize. Soybean showed the shallowest root system: 69% of the total root length was concentrated in the top 20 cm of the soil. Phosphorus uptake per unit root length was rather similar among the three species, but soybean and sunflower had higher P uptake per unit of root weight. This can be explained by the higher specific root length (SRL) and specific root area (SRA) of both dicots. For example, SRL averaged 59, 94, and 34 m g^?1 in field grown soybean, sunflower, and maize, respectively. The more favorable root morphology determined that soybean and sunflower can explore more soil with the same belowground biomass and absorb more P per unit of carbon invested belowground. Since the three species exhibited similar values of P uptake per unit root length, we hypothesize that the capacity of each segment of root to deplete soil P fractions is similar.     

Characterization and selection for phosphorus deficiency tolerance in 99 spring wheat genotypes in Montana

Phosphorus (P) deficiency in soil is a common spring wheat production-limiting factor in Montana. In a pot experiment, three groups of spring wheat genotypes based on source (association mapping, 2016 off-station, and nested association mapping) were grown in 5 (P5) and 30 (P30) mg P kg^?1 potting mix conditions and screened for P deficiency tolerance. Plant height, tiller and head number, grain yields per pot measured were significantly different between P5 and P30 conditions (p?<?.05). Spring wheat genotypes: Unity, Peace, Vida, Reeder, CLTR 15134, ONeal and Fortuna yielded more grains, and equally took up more P in P5 conditions, revealing some degree of P deficiency tolerance. The genetic variability identified in this study for grain yields and P uptake could be used in wheat improvement programs for selecting genotypes with low P tolerance in P deficient soils as well as in organic spring wheat production.     

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.     

不同水稻品种磷利用效率与耐铝性的关系研究

铝毒和磷缺乏是酸性土壤上作物生产的主要限制因子。本研究中我们探究了5个粳稻和5个籼稻品种的磷利用效率和耐铝性之间的相互关系。结果表明,粳稻品种的耐铝性显著高于籼稻品种。对于耐铝性强的水稻品种,施加磷肥后地上部生物量显著增加,而铝敏感的品种对磷肥响应较小,这可能是由于其耐铝性差而酸性土壤中的铝毒导致根系结构和功能受损,从而影响养分的吸收和利用。不同水稻品种的耐铝性和磷吸收效率呈正比而与磷利用效率呈反比,且粳稻的地上部磷浓度及磷吸收效率高于籼稻,但磷利用效率则低于籼稻。这些结果对于酸性土壤中筛选耐铝和磷高效利用的水稻品种具有重要意义。     

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.     

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.     

Root growth and phosphorus efficiency among sweet potato genotypes under low phosphorus

Abstract

A column experiment was conducted to investigate the responses of root growth and phosphorus (P) efficiency among sweet potatoes—JiHei1 (JH1), NingZi2 (NZ2), SuShu11 (S11) and SuShu17 (S17)—under low P and normal P conditions. Root growth was inhibited by low P in root length and surface area across diameter classes, except for in S17. The P absorption was influenced and led to variations in P content among organs. A high correlation was observed in root dry matter (DM) and P uptake. The tuber DM declined among genotypes under low P, and different P efficiencies were determined. A higher phosphorus utilization efficiency was observed in S11 and S17, suggesting that more P was needed to maintain their normal growth. Physiological efficiency and phosphorus utilization efficiency were significantly positively correlated with the tuber DM, indicating that low P limited the growth of sweet potatoes. These results benefit the production and breeding of sweet potatoes in response to P deficiency.     

Yield and Yield Components of Dry Bean Genotypes as Influenced by Phosphorus Fertilization

Dry bean is an important legume for South American population, and phosphorus (P) deficiency is the most yield-limiting nutrient for crop production in South American soils. A greenhouse experiment was conducted with the objective of evaluating influence of P fertilization on grain yield and yield components of 30 dry bean genotypes. The P levels used were 0 mg P kg^?1 (natural level of the soil) and 200 mg P kg^?1 applied with triple superphosphate fertilizer. Yield and yield components were significantly influenced with P as well as genotype treatments. The P?×?genotype interactions were significant for yield as well as yield components, indicating different responses of genotypes at two P levels. Root dry weight and maximum root length were also significantly increased with the addition of P fertilization. There were also significant differences among the genotypes in the growth of root system. Based on grain yield efficiency index (GYEI), genotypes were classified as P efficient, moderately efficient, and inefficient. Among 30 genotypes, 17 were classified as efficient, 12 were classified as moderately efficient, and 1 was classified as inefficient. Yield components such as pods per plant and seeds per pod were having significant positive association with grain yield. In addition, grain harvest index (GHI) was also having significant linear association with grain yield. Hence, it is possible to improve grain yield of dry bean in Brazilian Oxisol with the addition of adequate rate of P fertilization as well as use of P-efficient genotypes.     

Wurzelstudien und Phosphat-Aufnahme von Weidelgras und Rotklee unter Feldbedingungen

Root studies and phosphorus uptake of rye-grass and red clover under field conditions Root parameters (fresh weight, density, surface, length, cation exchange capacity) and phosphate uptake were studied with rye grass and red clover, grown in the field on a brown podsolic soil. In all root parameters, ry grass was superior to red clover. Also, phosphate uptake of rye grass was higher than that of red clover. The greatest difference between both species was found in root length, that of rye grass being about five times longer than that of red clover. Rye grass had longer root hairs than red clover; whereas root diameter of clover was about twice as thick the average rye grass. Significant correlations were observed between root parameters and phosphate uptake in the plants studied. The highest correlation coefficients were obtained for the relationship P-uptake versus root length (clover 0.91***, grass 0.87***) and P-uptake versus root fresh weight (clover 0.92***, grass 0.88***). The phosphate uptake per unit root parameters was significantly higher in red clover, compared with rye grass, for the parameters root fresh weight, cation exchange capacity and root length. Because of this high P-uptake rate for clover it is assumed that clover also requires a higher P-concentration in soil solution as compared with grass. Thus grass may still grow with low P concentrations in the soil solution without P deficiency at which clover cannot grow. It is for this reason that in mixed swards clover is depressed by grass, if the available P in the soil is low.     

Root architectural responses of wheat cultivars to localised phosphorus application are phenotypically similar

Differences in nutrient recovery from fertiliser bands may improve cereal variety selection. The objective of this study was to identify the variation in root plasticity across commonly grown Australian wheat (Triticum aestivum L.) cultivars in response to a phosphorus (P)‐enriched band. Ten wheat cultivars were screened for root proliferation within a 150 mg P kg⁻¹ band in P‐responsive soil. Plants were destructively harvested at the four‐leaf phenological stage and various growth parameters, including root length density (RLD), were measured on banded and uniformly adequate P treatments. All wheat cultivars increased RLD between three and nine times in the P band. However, there was no significant difference in root plasticity among the cultivars tested. Although all cultivars produced longer, though ≈ 9% thinner roots when responding to the P band, the phenotypic response was unable to compensate fully for the lower P status encountered in the soil. Despite 23% longer root lengths in the P‐band treatments, P uptake per unit root length was 78% lower than in uniformly adequate P treatments. Our results indicate that root plasticity of wheat cultivars in a P‐enriched band was phenotypically similar. Further research is necessary before selecting for wheat cultivars that respond to localised nutrient patches with increased RLD.     

Growth, P uptake and rhizosphere properties of intercropped wheat and chickpea in soil amended with iron phosphate or phytate

Intercropping has been shown to increase total yield and nutrient uptake compared to monocropping. However, depending on crop combinations, one crop may dominate and decrease the growth of the other. Interactions in the soil, especially in the rhizosphere, may be important in the interactions between intercropped plant genotypes. To assess the role of the rhizosphere interactions, we intercropped a P-inefficient wheat genotype (Janz) with either the P-efficient wheat genotype (Goldmark) or chickpea in a soil with low P availability amended with 100 mg P kg⁻¹ as FePO₄ (FeP) or phytate. The plants were grown for 10 weeks in pots where the roots of the genotypes could intermingle (no barrier, NB), were separated by a 30 μm mesh (mesh barrier, MB), preventing direct root contact but allowing exchange of diffusible compounds and microorganisms, or were completely separated by a solid barrier (SB). When supplied with FeP, Janz intercropped with chickpea had higher shoot and grain dry weight (dw) and greater plant P uptake in NB and MB than in SB. Contact with roots of Janz increased shoot, grain and root dw, root length, shoot P concentration and shoot P uptake of chickpea compared to SB. Root contact between the two wheat genotypes, Janz and Goldmark, had no effect on growth and P uptake of Janz. Shoot and total P uptake by Goldmark were significantly increased in NB compared to MB or SB. In both crop combinations, root contact significantly increased total plant dw and P uptake per pot. Plant growth and P uptake were lower with phytate and not significantly affected by barrier treatment. Differences in microbial P, available P and phosphatase activity in the rhizosphere among genotypes and barrier treatments were generally small. Root contact changed microbial community structure (assessed by fatty acid methyl ester (FAME) analysis) and all crops had similar rhizosphere microbial community structure when their roots intermingled.     

Rooting pattern and nitrogen uptake of three cauliflower (Brassica oleracea var. botrytis) F1‐hybrids

In a two‐year field trial at the sites Ruthe (Germany, loess soil, Orthic Luvisol) and Schermer (The Netherlands, marine clay soil, Eutric Fluvisol) the cauliflower F₁‐hybrids Marine, Lindurian and Linford were compared in their efficiency of N use from limiting and optimum supplies of N. Limiting N was N_min at planting. Optimum N was 250 kg ha^—1 as the sum of inorganic N content of the soil (N_min) at planting and fertilizer‐N. Marine was the most efficient variety, producing the highest shoot dry‐matter and quality (% class 1 curds) at both limiting and optimum N supplies. The N supply did not affect the horizontal and vertical distribution of root length density per soil volume (RLD, cm cm^—3) irrespective of variety. The RLD decreased exponentially with increasing soil depth. Varietal differences in RLD were not found at Ruthe, whereas at Schermer Marine had the highest RLD in all soil layers investigated (0 to 60 cm). No correlations were found between RLD and residual N_min at harvest, except at limiting N supply in Schermer where a strong negative correlation was found between RLD in the 45 to 60 cm layer and N_min at harvest. Thus, varietal differences in N efficiency are speculated to be rather due to different internal N‐use efficiency than to differences in N‐uptake efficiency.     

Yield,Potassium Uptake,and Use Efficiency in Upland Rice Genotypes

Potassium (K) is an essential nutrient for higher plants. Information on K uptake and use efficiency of upland rice under Brazilian conditions is limited. A greenhouse experiment was conducted with the objective to evaluate influence of K on yield, K uptake, and use efficiency of six upland rice genotypes grown on Brazilian Oxisol. The K rate used was zero (natural soil level) and 200 mg K kg^–1 of soil. Shoot dry weight and grain yield were significantly influenced by K level and genotype treatments. However, K × genotype interactions were not significant, indicating similar responses of genotypes at two K levels for shoot dry weight and grain yield. Genotypes produced grain yield in the order of BRS Primavera > BRA 01596 > BRSMG Curinga > BRS 032033 > BRS Bonança > BRA 02582. Potassium concentration in shoot was about sixfold greater compared to grain, across two K levels and six genotypes. However, K utilization efficiency ratio (KUER) (mg shoot or grain yield / mg K uptake in shoot or root) was about 6.5 times greater in grain compared to shoot, across two K level and six genotypes. Potassium uptake in shoot and grain and KUER were significantly and positively associated with grain yield. Soil calcium (Ca), K, base saturation, acidity saturation, Ca saturation, K saturation, Ca/K ratio, and magnesium (Mg)/K ratio were significantly influenced by K application rate.     

Root growth and N‐uptake activity of oilseed rape (Brassica napus L.) cultivars differing in nitrogen efficiency

Nitrate‐N uptake from soil depends on root growth and uptake activity. However, under field conditions N‐uptake activity is difficult to estimate from soil‐N depletion due to different loss pathways. We modified the current mesh‐bag method to estimate nitrate‐N‐uptake activity and root growth of two oilseed‐rape cultivars differing in N‐uptake efficiency. N‐efficient cultivar (cv.) ‘Apex' and N‐inefficient cv. ‘Capitol' were grown in a field experiment on a silty clayey gleyic fluvisol near Göttingen, northern Germany, and fertilized with 0 (N₀) and 227 (N₂₂₇) kg N ha^–1. In February 2002, PVC tubes with a diameter of 50 mm were installed between plant rows at 0–0.3 and 0–0.6 m soil depth with an angle of 45°. At the beginning of shooting, beginning of flowering, and at seed filling, the PVC tubes were substituted by PVC tubes (compartments) of the same diameter, but with an open window at the upper side either at a soil depth of 0–0.3 or 0.3–0.6 m allowing roots to grow into the tubes. Anion‐exchange resin at the bottom of the compartment allowed estimation of nitrate leaching. The compartments were then filled with root‐free soil which was amended with or without 90 mg N (kg soil)^–1. The newly developed roots and nitrate‐N depletion were estimated in the compartments after the installing period (21 d at shooting stage and 16 d both at flowering and grain‐filling stages). Nitrate‐N depletion was estimated from the difference between NO ‐N contents of compartments containing roots and control compartments (windows closed with a membrane) containing no roots. The amount of nitrate leached from the compartments was quantified from the resin and has been taken into consideration in the calculation of the N depletion. The amount of N depleted from the compartments significantly correlated with root‐length density. Suboptimal N application to the crop reduced total biomass and seed‐yield formation substantially (24% and 38% for ‘Apex’ and ‘Capitol’, respectively). At the shooting stage, there were no differences in root production and N depletion from the compartments by the two cultivars between N₀ and N₂₂₇. But at flowering and seed‐filling stages, higher root production and accordingly higher N depletion was observed at N₀ compared to N₂₂₇. Towards later growth stages, the newly developed roots were characterized by a reduction of root diameter and a shift towards the deeper soil layer (0.3–0.6m). At low but not at high N supply, the N‐efficient cv. ‘Apex’ exhibited higher root growth and accordingly depleted nitrate‐N more effectively than the N‐inefficient cv. ‘Capitol’, especially during the reproductive growth phase. The calculated nitrate‐N‐uptake rate per unit root length was maximal at flowering (for the low N supply) but showed no difference between the two cultivars. This indicated that the higher N‐uptake efficiency of cv. ‘Apex’ was due to higher root growth rather than higher uptake per unit of root length.     

低磷胁迫对不同磷效率基因型烟草苗期生长及生理特征的影响

为揭示不同磷效率烟草对低磷胁迫的响应机理,以磷高效且耐低磷基因型K326和云烟105及磷低效且低磷敏感基因型G28和中烟101为试验材料,设置低磷(0.01 mmol·L^-1,LP)和正常磷(1.00 mmol·L^-1,NP)2个处理,研究不同磷效率基因型烟草苗期主要农艺性状及生理指标对低磷处理的反应。结果表明,磷高效基因型的农艺指标(株高、地上部干重、根系干重等)在2种处理中均显著高于磷低效基因型,表明磷高效基因型在LP和NP水平下均能较好生长,对磷素具有较高的吸收或利用效率;在LP下,磷高效基因型的主根长增幅较大,干重、株高等降幅较小,即磷高效品种的生长受低磷影响较小,耐低磷性较强。在生理指标方面,LP条件下磷高效基因型的3种保护酶[过氧化氢酶(CAT)、超氧化物歧化酶(SOD)、过氧化物酶(POD)]和酸性磷酸酶(ACP)活性及可溶性糖和游离脯氨酸含量的增幅较磷低效基因型大,丙二醛(MDA)含量的增幅较小,可溶性蛋白含量、根系活力的降幅较小,水培营养液的pH值降幅较大;磷高效基因型的农艺性状及生理指标的耐低磷指数均高于磷低效基因型。综上,在低磷胁迫中,磷高效基因型烟草具有较强的活性氧清除能力,可累积较多渗透调节物质以维持细胞渗透势,较好地保护细胞,增强体内ACP活性,提高对磷素的吸收利用效率,维持自身的正常生长与代谢。本研究结果为烟草磷素高效吸收利用提供了一定的理论依据。