氮素形态和韧皮部烫伤对玉米韧皮部铁运输的影响

用营养液培养方法研究了在不同供铁条件下不同形态N和韧皮部烫伤对玉米苗期韧皮部Fe运输的影响。结果表明,韧皮部烫伤提高了玉米根系Fe的再利用,降低了初生叶中Fe的再利用,尤其在缺Fe条件下这种作用更明显,提高和降低的幅度更大。韧皮部烫伤还降低了伤流总量,增加了Fe的浓度。在供应铵态N的条件下,Fe的韧皮部运输比供应硝态N条件下有显著增加,Fe的再利用明显提高。     

Effects of municipal wastewater on soil chemical properties in cultivating turfgrass using subsurface drip irrigation

Knowing the concentrations of the nutrient elements in soils is important due to their toxic effect on humans and the environment. The aims of this study were to assess the effects of water quality, depths, and distances of lateral installation on soil chemical properties during turfgrass cultivation. A field experiment was conducted using a Split-Split-Plot design based on the randomized complete block (RCB) design with two treatments (well water and wastewater) and eight sub-treatments (45 and 60 cm distance of the laterals and 15, 20, 25, and 30 cm depths of laterals) in three replicates on a sandy loam soil, in Shahrekord, Iran. Soil samples were collected from 0 to 30 and 30 to 60 cm depth for measuring nitrate (NO₃^?), electrical conductivity (EC), and pH at the end of the experiment. During the experiment, fecal coliform was also measured at the soil surface. Results indicated that by increasing lateral distance, NO₃^? level increased in both layers. With installing laterals in deeper levels, NO₃^? concentration decreased at the beginning, then increased in the first layer, whereas in the second layer, NO₃^? concentration decreased. In addition, installing laterals in deeper depth caused an increase in soil EC in the top layer, but a decrease in the lower layer. However, the results showed that there was no significant effect of the treatments (well water and wastewater) and the sub-treatments (distance and depths of laterals) on soil pH. The results also show that with increasing laterals depth, fecal coliform level decreased at the soil surface.     

Morphology and Physiology of the Seminal Root System of Young Maize (Zea mays L.) Plants as Influenced by a Locally Restricted Nitrate Supply

In water culture the effect of a locally restricted NO₃ supply to the seminal root system of maize seedlings was studied. For this purpose plants were cultivated in containers with a wide-bore polyethylene tube positioned horizontally. Roots were suited through small holes in this tube and after sealing the holes with a non-toxic silicon putty, root segments in the tube could be exposed to a different nutrient solution from the rest of the root system in the outer compartment. In case of a locally restricted NO₃ supply (NO₃ was just supplied to the root segment within the tube), we observed an increase in root growth beginning at the fifth day after onset of the treatment. NO₃ uptake rate (¹⁵N) within the tube was significantly higher than in control plants (receiving NO₃ to the entire root system) as early as two days after onset of the treatment. One day later respiration (O₂ consumption) of the root segment exposed to NO₃ increased and at the same day we observed an accumulation of ¹⁴C activity (after pulse labelling of the shoots with ¹⁴CO₂) suggesting an increased phloem unloading. It is argued that this leads to the measured increase in IAA activity (Radio Immuno Assay) in the zone of NO₃ supply. Beginning at the fifth day we observed a stimulation of cell division rate (incorporation of ³H-methylthymidine), accompanied by an increase in length of first order lateral roots.     

The maize root system in situ: Evaluation of structure and capability of utilization of phytate and inorganic soil phosphates

• 1 The dependence of the morphology of the maize (Zea mays L.) seminal root system on physical, chemical and biotic parameters was investigated with pot cultures in quartz sand and in a natural loamy sand soil. Low O₂-supply to the soil resulted in a substantially smaller root biomass despite a relative increase in total root length. Reduced N-supply also stimulated root length growth, but also enhanced the formation of laterals. The presence of soil microorganisms, in comparison to sterile cultures, resulted in a reduced length of the main roots, and the production of slender laterals with a decreased root hair density. Generally, the structural variability of laterals in response to different growth conditions was much more pronounced than that of the main roots.
• 2 A major part of the work reported here was dedicated to a detailed study of phosphate (P) acquisition by the maize root system under field conditions. Radioactive labelling of the roots and radioautography of soil cores revealed the in situ distribution pattern of the maize root system. Controlled labelling of the soil with radioactive phosphate allowed the documentation of the development and replenishment of the phosphate depletion zone around roots. Finally, the longevity and phosphate uptake activity of the different parts and tissues of the primary root system of maize was examined by electron microscopy and tracer studies including pulse chase experiments. From these studies the phosphate-acquiring strategy of the maize root system appears as follows: The capability of P uptake decreases in the order: root hairs, 1^st order laterals, 2^nd order laterals, main root. The life-spans of the components of the maize root system increase by the sequence: root hairs, laterals, main root. Inorganic P uptake, therefore, mainly occurs during the first weeks of root development. Dying back of the root occurs in an ordered manner resulting in a relocation of stored P predominantly into the main root cortex. Furthermore, it could be shown that competition for P between roots of the same or of adjacent maize and/or lupin plants virtually does not occur in situ.
• 3 The utilization of phytate-P was studied with ¹⁴C/³²P-labelled Camyo-inositol-hexaphosphate supplied to maize plants grown in sterile quartz sand or in hydroponic cultures. The ratio of P- and C-uptake as well as the incidence of phytate hydrolysis products in the rooting medium indicated the capability of maize roots to acquire P from phytate by enzymatic hydrolysis. This was confirmed by enzyme studies of the root tissues. A specific hydrolyzing enzyme (phytase; molecular weight 51 kD) could be detected in the cell wall of the root, especially in the root tip, which initiates phytate dephosphorylation. Further breakdown is presumably accomplished by monophosphoric phosphohydrolases.

     

Differences between wheat cultivars in acquisition and utilization of phosphorus

In an attempt to evaluate whether breeding and selection for high yielding capacity changed the P requirement of modem wheat cultivars. the response of two wheat cultivars to different levels of P supply was investigated. A traditional cultivar (‘Peragis’) and a modern spring-wheat cultivar (‘Cosir’) were cultivated in a C-loess low in available P and high in CaCO₃ in 120 cm high PVC tubes. In addition and for comparison, nutrient solution experiments were also conducted. Shoot growth, root growth. P uptake. P translocation and P distribution within the shoot at different developmental stages were compared. The grain yield of the modern cultivar ‘Cosir’ was higher at limiting and non-limiting P supply and. therefore, this cultivar can be considered as more P-efficient than the traditional cultivar. Grain yield reduction at low P supply was mainly due to an inhibition of tillering and thus lower number of ears per plant, whereas the number of grains per ear was hardly affected. Reduced tillering at low P supply could not be related to P concentrations in the shoot meristematic tissues which were generally much higher than in other plant tissues and kept at an elevated level even at limiting P supply. Root branching (1^st order laterals) was reduced at limiting P supply in ‘Cosir’ but not in ‘Peragis’ which, generally, had lower numbers of laterals at the beginning of tillering. From the results it can be concluded that the main factors contributing to the higher P efficiency of the modern cultivar ‘Cosir’ are (i) efficient use of assimilates for root-growth characteristics which enhance P acquisition: enhanced root branching and thus smaller mean root diameter and longer root hairs, (ii) an efficient P uptake system, (iii) efficient remobilization of P from vegetative plant organs to the grains, and most importantly (iv) lower P requirement for grain yield formation because of lower ear number per plant but higher grain number per ear.     

Nitrogen partitioning in greenhouse‐grown broccoli in response to varying NH+ 4:NO− 3 ratios

Abstract

Broccoli (Brassica oleracea var. italica) plants were grown in the greenhouse and supplied continuously with 18 mM N in the following NH⁺ ₄:NO^? ₃ ratios: 100:0, 75:25, 50:50, 25:75, 0:100. At commercial maturity, the plant characteristics and partitioning of nitrogen in xylem and phloem saps and in plant tissue were determined. Plants fed solely with NH⁺ ₄ were stunted, exhibited signs of marginal necrosis on the lower leaves, and accumulated NH⁺ ₄ in the foliage. The maximum yield and shortest harvest time, together with minimal NO^? ₃ and NH⁺ ₄ accumulation were found at a ratio of 75:25. Ammonium concentrations in xylem sap decreased linearly with decreasing NH⁺ ₄ portion in the nutrient solution, whereas the NO^? ₃ concentrations reached a maximum when NO^? ₃ constituted 50% of the N supply. The glutamate family dominated the amino acid composition of both xylem and phloem saps, but did not vary much with NH⁺ ₄:NO^? ₃ ratio. It is suggested that the NH⁺ ₄ concentration in xylem sap may be used to assess NH⁺ ₄ vs NO^? ₃ utilization by broccoli grown under field conditions.     

The influence of phosphorus nutrition on growth,chlorophyll formation and 14CO2 fixation of chlorophyllous carrot callus cultures

Freshly isolated carrot root sec. phloem explants were cultured in nutrient solution plus inositol, IAA and kinetin and a varied supply of inorganic phosphorus. ¹⁴CO₂ fixation experiments with the greened cultures were carried out under steady state conditions at the age of 21 days in light and darkness for four minutes. The results show that photosynthetic CO₂ fixation by the Calvin cycle is greatly reduced in phosphorus deficient cultures whereas CO₂ fixation via PEPC is enhanced. Under phosphorus deficiency the export of primary photosynthetates from the chloroplasts seems to be suppressed while the radioactivity of the labelled insoluble fraction, which represents mainly chloroplastic starch after this short time of ¹⁴CO₂ fixation, was increased. The results are discussed with respect to the influence of phosphorus nutrition on photosynthetic CO₂ fixation and PEP carboxylation in carrot tissue cultures.     

Root morphology of maize under homogeneous or spatially separated supply of ammonium and nitrate at three concentration ratios

Maize (Zea mays L. cv. Anjou 256) seedlings were grown hydroponically for 10 d in a split‐root system (3mM N; pH 5.5) under either a homogeneous supply (HS) or a simultaneous, but spatially separated supply (SS) of NH₄ ⁺ andNO₃ ^‐. Treatments comprised three NH₄ ⁺:NO₃ ^‐ ratios (1:4, 1:1, 4:1). Shoot dry matter and various root traits (dry matter, number of laterals, length of main axes, total root length and total root surface area) were determined. For all NH₄ ⁺:NO₃ ^‐ ratios, shoot dry matter, root dry matter, total root length, and root surface area, were greater under HS than under SS. Under both SS and HS, increasing NH₄ ⁺:NO₃ ^‐ ratios resulted in decreased shoot and root dry matter production, but did not alter the shoot:root dry matter ratio. Under SS, root dry matter, root length, and root surface area was greater on the NO₃ ^‐‐fertilized side than on the NH₄ ⁺ ‐fertilized side. The allocation of root dry matter, root length, and root surface area to the NH₄ ⁺ or NO₃ ^‐ compartments was unaffected by changes in the NH₄ ⁺:NO₃ ^‐ ratio. Enhanced NH₄ ⁺ nutrition has detrimental effects on top growth, but roots are apparently unable to avoid excessive NH₄ ⁺ uptake by proliferating in zones where NO₃ ^‐ is the only form of N.     

Response of shoot and root growth to supply of different nitrogen forms is not related to carbohydrate and nitrogen status of tobacco plants

In the present study, we investigated effects of homogeneous or localized supply of different nitrogen (N) forms on shoot and root growth of tobacco. While homogeneous supply of NH₄⁺ and N deprivation inhibited shoot growth compared with application of NO₃^—, the N form had no significant effect on root growth. In contrast, in a split-root experiment, application of NH₄⁺ or N deprivation in one half of the root system repressed root growth compared with the other part of the root, which was supplied with NO₃^—. However, shoot growth was not affected by localized NH₄⁺ application or local N deprivation. Inhibitory effects on shoot and root growth by variations of N supply could not be related to limitations in N or C status of the plants or to NH₄⁺ toxicity. A possible involvement of NO₃^— as a signal compound including of phytohormones is discussed.     

Lime-induced growth depression in Lupinus species: Are soil pH and bicarbonate involved?

In a series of experiments, the effect of elevated pH on root growth of different lupin genotypes and lime-tolerant Pisum sativum was assessed. Seedlings were cultivated in pH-controlled but unbuffered nutrient or test solutions with pH 5—8 under constant light or constant darkness. Moderately increased solution pH did not affect root elongation. At high pH, root elongation rates were reduced by less than 35%, L. luteus being most sensitive. In a further experiment, effects of 10 mM bicarbonate (HCO₃^-) and organic buffers (MES, TES) were examined. Bicarbonate severely affected root elongation of lupins, sensitivity increasing in the order Lupinus albus < L. angustifolius < L. luteus. Since the reduced root elongation was not accompanied by a decreased root weight, specific root weight was increased. Shoot growth was not affected by HCO₃^-. Addition of organic buffers to alkaline nutrient solution, similarly to HCO₃^-, reduced elongation of main roots, but not that of laterals. Both treatments increased citrate concentrations in roots of sensitive L. luteus, but not of tolerant L. albus. Other carboxylates were not related to growth inhibition. Xylem exudate pH was always below 5.8, indicating that HCO₃^- was probably not translocated to the shoot. It is concluded that HCO₃^- is a key factor for lime-induced growth inhibition of calcifuge lupins, with the roots, not the shoots, being primarily affected.     

2-Phenylethylisothiocyanate concentration and microbial community composition in the rhizosphere of canola

Canola crops have been shown to inhibit soil-borne pathogens in following crops. This effect is mainly attributed to the release of low molecular S-containing compounds, such as isothiocyanates, during microbial degradation of the crop residues. We have assessed the effect of low concentrations of phenylethylisothiocyanate (PEITC) on soil microbial communities as well as its rate of degradation in soil and determined the concentration of PEITC and the microbial community structure in the rhizosphere of canola. PEITC was degraded within 96 h by soil microorganisms. PEITC added to the soil daily for 5 d affected both bacterial and eukaryotic community structure, determined by PCR-DGGE. Community structures of bacteria and eukaryotes changed at PEITC concentrations between 1300 and 3790 pmol g⁻¹ soil fresh weight but was unaffected at lower concentrations. The PEITC concentration in the rhizosphere of living canola roots was greater in first order laterals than in second order laterals. The maximal PEITC concentration detected in the rhizosphere was 1827 pmol g⁻¹. Redundancy analysis of the DGGE banding patterns indicated a significant correlation between the PEITC concentration in the rhizosphere and the community structure of the active fraction of eukaryotes and bacteria in the rhizosphere. Other important factors influencing the microbial community structure were soil moisture and plant dry matter. It is concluded that canola may affect the soil microbial community structure not only after incorporation of canola residues but also during active growth of the plants.     

盐胁迫下氮素形态对油菜和水稻幼苗离子运输和分布的影响

【目的】土壤盐碱化是制约农作物产量的主要因素之一,盐胁迫影响养分运输和分布,造成植物营养失衡,导致作物发育迟缓,植株矮小,严重威胁着我国的粮食生产。在必需营养元素中,氮素是需求量最大的元素,NO-3和NH+4是植物吸收氮素的两种离子形态。植物对盐胁迫的响应受到不同形态氮素的调控,研究不同形态氮素营养下植物的耐盐机制对提高植物耐盐性及产量具有重要的意义。【方法】本文以喜硝植物油菜(Brassica napus L.)和喜铵植物水稻(Oryza sativa L.)为试验材料,采用室内营养液培养方法,研究了NO-3和NH+4对Na Cl胁迫下油菜及水稻苗期生长状况、对Na+运输和积累的影响,以对照与盐胁迫植株生物量之差与Na+积累量之差的比值,评估Na+对植株的伤害程度。【结果】1)在非盐胁迫条件下,硝态氮营养显著促进油菜和水稻根系的生长;盐胁迫条件下,油菜和水稻生物量均显著受到抑制,Na Cl对供应铵态氮营养植株的抑制更为显著。2)盐胁迫条件下,两种供氮形态下,油菜和水稻植株Na+含量均显著增加,硝态氮营养油菜叶柄Na+显著高于铵态氮营养,叶柄Na+含量/叶片Na+含量大于铵营养油菜,硝态氮营养水稻根系Na+含量显著低于铵营养,地上部则相反。3)铵营养油菜和水稻Na+伤害度显著高于硝营养植株。4)盐胁迫条件下,硝态氮营养油菜地上部和水稻根系K+含量均显著高于铵态氮营养。5)盐胁迫条件下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株。【结论】与铵营养相比,硝营养油菜和水稻具有更好的耐盐性。硝态氮处理油菜叶柄Na+显著高于铵态氮处理,能够截留Na+向叶片运输。同时,供应硝态氮营养更有利于油菜和水稻吸收K+,有助于维持植物体内离子平衡。盐胁迫下,硝营养油菜和水稻木质部Na+浓度,韧皮部Na+和K+浓度及水稻木质部K+浓度均高于铵营养植株,表明硝态氮营养油菜和水稻木质部-韧皮部对离子有较好的调控能力,是其耐盐性高于铵营养的原因之一。     

The relationship between grain yield and plant potassium concentration in Lupinus angustifolius cv. Unicrop

Abstract

The relationship between potassium concentration in the plant at various growth stages and the grain yield of L. angustifolius cv. Unicrop was derived from a rates and times of application of KCl field trial.

Critical levels were defined as those associated with 90% of maximum yield. Critical % K levels in the whole tops were 3.1 at the 4–6 leaves stage, 2.9 at 8–10 leaves, 1.5 at first flowering, 1.2 with flowers on higher order laterals and 0.9 post flowering.

The effect of plant part sampled was examined at early flowering. Critical levels at that stage were 1.2% K for petioles 1–5, 0.6% K for petioles 6–10, 1.3% K for leaves 1–5, 0.5% K for leaves 6–10 and 2.1% K in the growing point of the plant.

Grain K concentrations were very insensitive to changes in supply, and are of little use as a diagnostic tool. The ratio of K concentration in pods to that in seeds increased from 0.5 under extreme deficiency to 1.3 under conditions of adequate supply, and should be a useful diagnostic tool at maturity.     

Diurnal Macronutrients Uptake Patterns by Lettuce Roots under Various Light and Temperature Levels

In order to reduce nutrient wastes to the environment the supply should be in accordance to the demand for these. Two experiments were conducted to study and quantify the effect of temperature, irradiance, and plant age on the uptake of nitrate (NO₃^?), ammonium (NH₄⁺), dihydrogen phosphate ion (H₂PO₄^?), potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), and sulfate (SO₄²). In the first experiment, various levels of temperature and irradiance were applied to plants in a growth chamber, while in the second experiment the uptake was studied along the crop season under greenhouse conditions. The uptake rates were calculated at 2-hour intervals through sampling the nutrient solution and analyzing it by inductively coupled plasma atomic emission spectrometry (ICP-AES). Increasing light and temperature enhance the uptake rates, while the rates decrease with plant age. Nitrogen absorption was similar during the day as during the night. No differences were found in the absorption of H₂PO₄^?, K⁺, Ca²⁺, Mg²⁺, and SO₄^2? between day and night. Nitrate absorption was found to have a positive correlation with the absorption of all the ions except for NH₄⁺.     

有机肥和化肥长期配合施用对土壤及不同粒级供氮特性的影响

通过间隙淋洗培养试验 ,研究水旱轮作下有机肥与化肥长期配合施用后土壤及不同粒级中氮的矿化特性。结果表明 ,经 14年 2 9茬连续施肥后土壤氮素矿化势明显增加 ,不同处理间的顺序为 :猪粪 化肥 (3 10mgkg- 1) >秸秆 化肥 (2 98mgkg- 1) >化肥 (2 76mgkg- 1) >对照 (2 0 4mgkg- 1)。长期施肥对土壤氮素矿化速率常数影响较小 ,反映了在相同土壤条件下有机氮矿化的共性。经 16周连续培养各处理土壤氮素的矿化率均在 17%左右。土壤不同粒级中氮的矿化量和矿化势均为 0～ 2 μm >2～ 10 μm >50～ 10 0 μm >10～ 50 μm ,有机肥与化肥长期配合施用显著增加了 0～ 2和 2～ 10 μm粒级氮的矿化势和矿化量。与盆栽试验结果相比 ,培养过程矿化释放的氮明显高于同期土壤的供氮量 ,表明在使用矿化氮评价土壤供氮能力时必须加以矫正。     

不同氮源与钾水平对杂交组合及常规稻生长和养分吸收的影响

采用营养液培养法研究了不同氮源和钾水平对杂交稻及其亲本和常规稻生长、叶绿素含量、养分吸收的影响。结果表明 ,水稻生长、叶绿素的含量及养分吸收与氮源供应密切相关。在供钾充足的条件下 ,杂交稻上位叶的干物质产量以硝态氮营养的最高 ,其次为硝态氮与铵态氮混合营养 ;保持系与杂交稻的趋势一致。杂交稻下位叶和根系干物质积累量受 3种氮源的影响与恢复系相一致 ,即 :硝 +铵混合 硝态氮 铵态氮。硝态氮营养比硝 +铵混合及铵态氮更有效地提高杂交稻功能叶片中的叶绿素含量。杂交稻与其亲本植株地上部全氮含量受 3种氮源的影响为 :硝 +铵混合 硝态氮 铵态氮 ;然而杂交稻地上部的吸氮量受氮源的影响为硝态氮硝 +铵混合 铵态氮 ,与保持系的规律一致。杂交稻地上部钾含量及吸收量在 3种氮源处理间有差异 ,表现为硝态氮 硝 +铵混合 铵态氮 ,保持系的趋势一致 ,但与恢复系不同。研究结果还表明 ,杂交稻对硝态氮的营养特性具有明显杂种优势。 3种氮源对水稻生长、营养吸收的影响程度与钾营养状况及水稻品种有关 ;杂交水稻及其亲本较常规稻受影响更大。在高钾供应时 ,各项指标受到氮源影响的程度都明显高于低钾处理 ,其中以硝态氮为氮源更有利于杂交水稻生理及营养优势特性的发挥。     

Langstreckentransport von Natrium in Bohnenpflanzen

Long distance transport of sodium in bean plants In 8–10 days old bean plants Na⁺ (²²Na) has been applied to either a certain root zone, the stem, or the base and tip respectively of a primary leaf and the long distance transport of Na⁺ was studied in the following 12–48 h. The long distance transport of Na⁺ applied to the root zone 9–12 cm behind the tip was strongly restricted towards the shoot and hardly detectable towards the root tip (phloem transport). Presence of K⁺ in the surrounding solution strongly increased the Na⁺ efflux from the roots. After leaf application within 48 h 30–40% of the absorbed Na⁺ had been translocated out of the leaf in direction of the root where, from the basal root zones, intensive Na⁺ efflux took place. This Na⁺ efflux was hardly affected by presence of K⁺ in the external medium and was usually more than 10% of the Na⁺ taken up by the leaves. From the Na⁺ taken up by the hypocotyl within 12 h more than 25% had been released from the basal root zones into the nutrient solution. Less than 1% of the Na⁺ applied either to the leaf or the stem was translocated towards the shoot apex. Separation of the hypocotyl into cortex and stele at the end of the experiment demonstrated the high capacity of the stele for Na⁺ accumulation. Within the hypocotyl the transfer of Na⁺ from the stele to the cortex and the phloem seems to be a rapid process whereas the release of Na⁺ from the phloem into the stele is obviously very restricted. The long distance transport of Na⁺ within the phloem of the shoot is strictly basipetal and very efficient. Low Na⁺ contents of bean leaves are therefore the result of several regulating mechanisms: K⁺ stimulated Na⁺ efflux in the roots, restricted long distance transport in the xylem due to high Na⁺ accumulation in the stele, Na⁺ pumps at the phloem in stem and leaves for phloem loading of Na⁺, and finally strictly basipetal retranslocation of Na⁺ in the phloem into the roots and efflux into the solution from basal root zones.     

Effects of Salinity and Nitrogen on Growth,Contents of Pigments,and Ion Accumulation of a Euhalophyte Suaeda Salsa in an Intertidal Zone and on Saline Inland

The different responses of two populations of Suaeda salsa (Linn.) Pall. (saline seepweed) from an intertidal zone and a saline inland zone to salinity [1 or 500 mM sodium chloride (NaCl)] and nitrogen [N; 0.05, 1, or 10 mM nitrate (NO₃ ^?)‐N] were investigated. Greater NO₃ ^?‐N supply (10 mM) increased shoot dry weight for the two populations of S. salsa, especially for S. salsa from the saline inland zone. Greater NO₃ ^?‐N supply (10 mM) increased the concentrations of chlorophyll and carotenoid in leaves and the NO₃ ^? and potassium (K⁺) concentrations in shoots for both populations. Greater NO₃ ^?‐N supply (10 mM) increased shoot Na⁺ in S. salsa from the intertidal zone. In conclusion, S. salsa from the saline inland zone is more responsive to NO₃ ^?‐N supply than the intertidal population. Greater NO₃ ^?‐N supply can help the species, especially the intertidal population, to grow and to mediate ion homeostasis under high salinity.     

Shoot and root growth of rice seedlings as affected by soil and foliar zinc applications

Abstract

The present study investigated how foliar zinc (Zn) application affects seedling growth and Zn concentration of rice grown in a Zn-deficient calcareous soil with different soil Zn treatments. Seeds were sown in soil with five rates of Zn (0, 0.02, 0.1, 0.5 and 5.0?mg kg^?1 soil) with and without foliar application of 0.5% ZnSO₄. Seedlings were harvested at 35?days and separated into (i) the youngest leaves, (ii) the remaining shoot parts and (iii) roots. In soil with no Zn supply, shoot and root dry weight of the rice seedlings were significantly increased by foliar and soil Zn treatments. Plant growth was not clearly increased in low soil Zn treatments, while at each soil Zn treatment, foliar Zn application promoted growth of plants. Plants with adequate Zn supply had the highest Zn concentrations in the youngest leaf. Foliar Zn spray improved Zn concentration of the new growth formed after foliar spraying which shows that Zn is phloem mobile and moved from treated leaves into youngest new leaves. The results indicate clearly in rice seedlings that shoot growth shows more responsive to low Zn than the root growth. The results obtained in the present study are of great interest for proper rice growth in Zn-deficient calcareous soils but needs to be confirmed in other rice genotypes.     

N2 fixation and growth of legumes as affected by sulphur fertilization

The influence of three sulphur application rates in combination with two nitrogen application rates on N₂ fixation and growth of different legumes was investigated. N was applied as N-labelled ¹⁵NH₄ ¹⁵NO₃. The ¹⁵N isotope dilution technique was used to estimate N₂ fixation. At both N increments dry matter yield was highest with high S supply. Independently of the N supply, the high S application rate resulted in a significantly higher N accumulation, which was mainly caused by a higher N₂ fixation rate. With the grain legumes the weight of nodules was increased by the high S application rate. The higher number of nodules per pot with optimum S supply was the result of a better root growth. Rates of acetylene reduction correlated significantly with S supply.