Root exudation of sugars,amino acids,and organic acids by maize as affected by nitrogen,phosphorus, potassium,and iron deficiency

Root exudates play a major role in the mobilization of sparingly soluble nutrients in the rhizosphere. Since the amount and composition of major metabolites in root exudates from one plant species have not yet been systematically compared under different nutrient deficiencies, relations between exudation patterns and the type of nutrient being deficient remain poorly understood. Comparing root exudates from axenically grown maize plants exposed to N, K, P, or Fe deficiency showed a higher release of glutamate, glucose, ribitol, and citrate from Fe‐deficient plants, while P deficiency stimulated the release of γ‐aminobutyric acid and carbohydrates. Potassium‐starved plants released less sugars, in particular glycerol, ribitol, fructose, and maltose, while under N deficiency lower amounts of amino acids were found in root exudates. Principal‐component analysis revealed a clear separation in the variation of the root‐exudate composition between Fe or P deficiency versus N or K deficiency in the first principal component, which explained 46% of the variation in the data. In addition, a negative correlation was found between the amounts of sugars, organic and amino acids released under deficiency of a certain nutrient and the diffusion coefficient of the respective nutrient in soils. We thus hypothesize that the release of dominant root exudates such as sugars, amino acids, and organic acids by roots may reflect an ancient strategy to cope with limiting nutrient supply.     

Effect of External Nitrogen and Potassium Supply on Xylem Sap Composition of Sugarcane

ABSTRACT

This study was conducted to evaluate the effect of nitrogen (N) and potassium (K) availability on root exudate composition of two sugarcane cultivars known to differ with regard to their resistance to drought and salinity stress. The plants were hydroponically grown in a greenhouse and subjected to three levels of N (0.1, 1.0, and 10 mM N) and three levels of K (0.02, 0.2, and 2 mM K). Nitrogen and K stress altered the xylem sap composition. Nitrogen stress significantly reduced nitrate (NO₃ ^?), ammonium (NH₄ ⁺), calcium (Ca), magnesium (Mg), and amino acid content and increased the pH, phosphorus (P), and K content. Whereas, K stress significantly decreased pH, K, NH₄ ⁺, and amino acid content but increased Ca, Mg, and P content. Nitrogen and K stress had opposing effects on xylem sap pH and osmolality. Results indicated that sugarcane plants recycle compounds between the phloem and xylem. The results also suggested that the NO₃ ^? and K concentration of xylem sap could be effectively used to estimate the N and K status of the soil solution.     

Growth attributes,xylem sap composition,and photosynthesis in common bean as affected by nitrogen and phosphorus deficiency

The effects of nitrogen (N‐) and phosphorus (P‐) deficiency, isolatedly or in combination, on growth, nitrogenous fraction, and inorganic phosphate in xylem exudade, and photosynthesis of common bean (Phaseolus vulgaris L. cv. Negrito) were investigated. Plants were grown in nutrient solution adjusted daily to pH 5.5 and aerated continuously. Ten days after emergence mineral deficiency was imposed. Plants were then supplied with high N (7.5 mol m^‐3) or low N (0.5 mol m^‐3), and also with high P (0.5 mol m^‐3) or low P (0.005 mol m^‐3). All sampling and measurements were made 28 days after emergence. N‐ or P‐deprivation brought about large decreases in total leaf area by inhibiting the emergence of new leaves and primarily the expansion of the leaves. The specific leaf area did not change under N‐ but decreased under P‐limitation. The decreased shoot to root ratio in all deficiency treatments was a consequence of a lowering mass of above‐ground organs, especially of leaves.

The content of chlorophylls declined significantly only under N‐deficiency alone; carotenoids declined under both N‐ and combined N‐ and P‐limitation. No alteration in amino acid concentration in xylem exudate occurred in plants experiencing N‐starvation, while ureides increased by 79%, and nitrate and inorganic phosphate decreased greatly. Under P‐deprivation, amino acids and nitrate in xylem sap dropped by about half; ureides were held relatively constant, and phosphate was severely depressed. Total upward translocation of N through xylem was estimated to be about 16% higher in N‐deficient plants than in plants without mineral limitation, but leaf N levels in the former were lower as compared to control plants. The net carbon (C) assimilation decreased similarly regardless of the imposed deficiency treatment. Such a decrease was mainly determined by non‐stomatal factors. In general, no additive effect between N‐ and P‐limitation on any of measured parameters was observed.     

Influence of potassium:rubidium ratios on the xylematic transport of solutes in cucumber plants grown with nitrate plus ammonium

The influence of three potassium:rubidium (K:Rb) ratios (6:0, 5:1, and 4:2) on the xylematic transport of solutes in cucumber plants cv. Medusa supplied with both nitrate (NO₃ ^‐) (60%) and ammonium (NH₄ ⁺) (40%) was studied in greenhouse conditions. In the xylem sap of plants grown with a K:Rb ratio of 4:2, there was an increase in the transport of NO₃ ^‐, phosphate (H₂PO₄ ^‐), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), manganese (Mn) and boron (B) while that of organic‐N, organic‐P, K⁺, zinc (Zn), organic acids, and carbohydrates decreased, if compared with the sap of the plants supplied with K alone. The translocation of NO₃ ^‐, H₂PO₄ ^‐, Ca²⁺, Mg²⁺, and Mn was enhanced and that of K⁺ and organic acids decreased when the plants were supplied with a K:Rb ratio of 5:1. The K:Rb ratio detected in the xylem sap was the same K:Rb ratio as in the solutions. However, in the cucumber plant substituting 33% of total K by Rb resulted in an alteration in the transport of solutes, probably due to a competition between Rb and K rather than between the latter two and NH₄ ⁺.     

Chemical composition of xylem sap of tomato grown on bicarbonate containing medium

Incorporation of bicarbonate (HCO₃ ^‐) by the roots of tomato seedlings resulted in an increase in biomass production and changed the chemical composition of xylem sap. In the xylem sap of seedlings grown on a medium enriched with HCO₃ ^‐ (5.68 mM dm^‐3, series II) compared with the control (series I) the element content increased by about 27% and 33% for cations and anions, respectively. Potassium was the major cation in the xylem sap and constituted 69% of the total concentration of all the inorganic cations determined. Calcium attained 19% of this amount. The anionic load in the xylem sap was chiefly nitrate, constituting about 90% of the content of all the inorganic anions. The exudate was analysed for seven organic acids. In general, malic (MA), maleic, and citric (CA) occurred in xylem exudate at greater concentrations, constituting about 95% of the total content of organic acids. Cultivation of seedlings on the medium enriched with HCOJ brought about an increased content of organic acids, exceeding the control by about 60%. The concentration of MA increased by about 104% and that of CA and maleic acid exceeded the control by about 40% and 14%, respectively. Twenty amino acids were identified in tomato xylem sap. Glutamic, aspartic and y‐arninobutyric acid, and particularly the amides aspargine and glutamine occurred in greater amounts. Their total concentration was about 60% and 70% of the total amino acid content in series I and II, respectively. The remaining amino acids occurred at concentrations ≥ 90 μM. The cultivation of plants on the medium containing HCO₃ ^‐ resulted in an increase in amino acid content in xylem sap by about 28% as compared with the control. The ratio of amino acid to organic acid content was 2: 2.5 and 2: 3 for series I and II, respectively. The similar value of the ratio in the two series suggests that the synthesis of both groups of compounds be equally favoured by the carbon source (endogenous in the control and from the medium enriched with HCO₃ ^‐ in series II). The increased level of elements and organic compounds in xylem sap in the case of plants supplied with HCO₃ ^‐ is discussed in the work in respect of metabolic processes of roots.     

Host-rhizobia interaction for effective inoculation: evaluation of the potential use of the ureide assay to monitor the symbiotic performance of tepary bean (Phaseolus acutifolius A. Gray)

Domesticated and wild-type tepary beans (Phaseolus acutifolius A. Gray) were grown with or without inoculation with rhizobia in pots under bacteriologically controlled conditions in a temperature-controlled glasshouse. Seeds were inoculated with a mixture of seven strains isolated from nodules collected from domesticated field-grown tepary bean in Arizona, USA, or with a commercial inoculant strain for Phaseolus vulgaris (CC511). Different degrees of plant reliance upon N₂ fixation for growth were generated by supplying the inoculated plants throughout growth with nutrients containing a range of concentrations of ¹⁵N-labeled NO₃ (0, 1, 2, 5 or 10 mM). An uninoculated treatment that received 10 mM ¹⁵N-labeled NO₃ was included to provide data for plants solely dependent upon NO₃ for growth. Six weeks after sowing, shoots were harvested for dry matter determination and subsequent ¹⁵N analysis, root-bleeding xylem sap was collected, and nodulation assessed. With regard to shoot biomass production, domesticated lines were more responsive to inoculation, but less responsive to applied N than wild types. All inoculated plants were nodulated, but the field isolates from tepary bean were more effective in N₂ fixation than strain CC511. It was concluded that tepary bean requires a specific inoculant to benefit from fixation of atmospheric N₂. Xylem sap samples were analysed for ureides (allantoin and allantoic acid), amino acid content (α-amino-N), and NO₃ concentration. The amount of ureide-N present in xylem sap was expressed as a percentage of total solute N, described as the relative abundance of ureide-N (RUN), for each N treatment and was compared to the proportion of plant N derived from N₂ fixation (%Ndfa) calculated using a ¹⁵N dilution technique. The RUN values ranged from 8% for saps collected from uninoculated plants provided with 10 mM NO₃ in the nutrient solution (%Ndfa=0) to 86-91% for nodulated plants grown in the absence of externally supplied NO₃ (%Ndfa=100). These data indicated that ureides were the principal product of N₂ fixation exported from the nodules to the shoot in xylem sap. Since RUN values were closely related to %Ndfa, it was proposed that N-solute analysis of xylem sap could provide a valuable analytical tool to monitor the symbiotic performance of tepary bean.     

Mineral Nitrogen Associated Changes in Growth and Xylem-N Compounds in Amazonian Legume Tree

In nodulated young Inga edulis plants, nodule and plant growth, nitrogen (N) in xylem sap and tissues total contents of amino acid, ureide, and nitrate were determined in response to nutrition with nitrate, ammonium, or no mineral N. Additionally, the amount of soluble sugars in the different plant tissues was quantified. It was found that mineral N improved plant growth in height and diameter especially with ammonium. However, nitrate dramatically reduced nodule dry weight on a root dry weight basis and impaired N organic transport by xylem sap. Additionally, a higher amount of amino acids was observed in the roots and nodules of plants fed with mineral N but sugar levels remained constant. Although nitrate inhibited symbiosis, data support the idea that I. edulis is able to use both molecular and mineral nitrogen during the life cycle.     

Study on ammonium tolerance of cucumber plants

The influence of N form on xylem exudate and the guttation fluid concentration in cucumber plants was studied under greenhouse conditions. Plants were hydroponically grown with three NO₃:NH₄ ratios (100:0, 80:20, and 60:40) at a constant pH of 6.0 in the nutrient solutions. Plants supplied with 60:40 NO₃:NH₄ ratio displayed a significant decrease of NO₃‐N, total‐N, organic‐P, and Mn concentrations in the xylem sap and an increase of H₂PO₄‐P, SO₄‐S, Cl, B, and Zn concentrations. Potassium and Ca uptake in these plants was slightly reduced, indicating that pH control was an important factor for cationic nutrition in cucumber plants fed with NH₄. The major ions present in the nutrient solutions are concentrated in the xylem sap, particularly for NO₃, K, Ca, and Na. The NO₃:NH₄ ratio had a small effect on the ionic levels of the guttation fluid. The concentrations of all nutrients in the guttation fluid were substantially reduced, except for Cl, showing that the leaf tissues of cucumber plants remove the excess of Cl ion. Finally, in this study, secondary effects of N source on ion uptake and release were minimized by controlling nutrient solution pH.     

Jahreszeitliche Veränderung der NO3−-Konzentrationen im Xylemsaft des unteren Stammteiles von Buchen (Fagus sylvatica L.)

Seasonal variation of NO₃^? concentration in xylem sap of the lower trunk part of beeches (Fagus sylvatica L.) From October 1988 to October 1989 five beech trees from a 35-year-old and a 42-year-old stand were felled in 14 day intervals. Xylem sap was extracted from the lower 100 cm of the trunk by means of liquid displacement. In general there was an increase of NO₃^? xylem sap concentrations in summer. Higher xylem sap nitrate concentrations were accompanied by an almost equal but opposite pH decrease. It is assumed that the rapid surge in NO₃^? concentration of the xylem sap was due to summer acidification pushes in the forest soil.     

Stickstoff-Assimilation in der Wurzel und Transport von N-Verbindungen mit dem Blutungssaft der Wurzeln in Abhängigkeit von der Mn-Versorgung

Nitrogen Assimilation in Roots and the Transport of Nitrogen Compounds in the Bleeding Sap of Roots in relation to Manganese Nutrition. The assimilation of nitrogen in the roots of 27 days old pumpkin plants was examined in relation to manganese nutrition. The transport of nitrogen compounds in the xylem was determined in roots and in the bleeding sap of roots using nitrate as the N-source. The maximum NO₃ content in the roots was observed in the Mn treatment which resulted in the highest shoot yields (0.05 ppm Mn). The bleeding sap of this treatment was lowest in nitrate concentration, but showed the highest rate of transport of organic nitrogen compounds. In experiments with ¹⁵N in the nutrient solution the isotope was found in the roots in organic and in inorganic compounds. The composition of the fraction of free amino acids differed between roots and xylem sap. In the bleeding sap glutamine was especially dominant. In the roots the amino acid composition depended on the extent of Mn-supply. Lowest glutamine concentrations were found in the xylem sap from the treatment with maximum shoot yields. A numerical difference was found in the xylem sap between organic N (N_(org)) and the amino acid nitrogen. This difference which account for more than 50 % of the organically bound nitrogen is suggested to be made up in part by low molecular weight peptides, amino sugars and other compounds. In Mn deficiency a general reduction in the intensity of nitrogen metabolism was found. With Mn toxicity the N assimilation activity was more intensive than for the low Mn supply. Simultaneously, however, the transport of organic N compounds from the root was lower.     

Changes in mineral nutrient concentrations and C‐N metabolism in cabbage shoots and roots following macronutrient deficiency

The responses of metabolic networks to mineral deficiency are poorly understood. Here, we conducted a detailed, broad‐scale analysis of macronutrient concentrations and metabolic changes in the shoots and roots of cabbage (Brassica rapa L. ssp. pekinensis) plants in response to N, P, K, Ca, and Mg deficiency in nutrient solution. To standardize individual macronutrient‐deficient treatments, the concentrations of the other nutrients were maintained via substitution with other ions. Individual nutrient deficiencies had various effects on the uptake and accumulation of other mineral nutrients. Phosphorus deficiency had relatively little effect on other mineral nutrient levels compared to the other treatments. Cation deficiency had little effect on N and P concentrations but had a somewhat negative effect on the uptake or concentrations of the other nutrients. Primary metabolic pathways, such as energy production and amino acid metabolism, were greatly affected by mineral nutrient deficiency. Compared to the control treatment, soluble sugar levels increased under –N conditions and decreased under –Ca and –Mg conditions. The levels of several organic acids involved in glycolysis and the TCA cycle decreased in response to –N, –P, or –K treatment. The levels of most amino acids decreased under ‐ N treatment but increased under –P, –K, –Ca, or –Mg treatment. Mineral depletion also led to the activation of alternative biochemical pathways resulting in the production of secondary metabolites such as quinate. Notable changes in metabolic pathways under macronutrient deficiency included (1) a quantitative increase in amino acid levels in response to Mg deficiency, likely because the restriction of various pathways led to an increase in protein production and (2) a marked increase in the levels of quinate, a precursor of the shikimate pathway, following cation (K, Ca, and Mg) deficiency. These findings provide new insights into metabolic changes in cabbage in response to mineral deficiency and pave the way for studying the effects of the simultaneous deficiency of more than one macronutrient on this crop.     

Diurnal variations in uptake,transport and assimilation of NO3 ‐and efflux of OH‐ in maize plants

Maize plants, grown for 7 and 21 days on a nutrient solution with NO₃ ^‐ as the sole nitrogen source showed a clear diurnal pattern with respect to the in vivo NRA. Especially in roots dark/light fluctuations of the enzyme activity were high. Also in NO₃ ^‐ uptake, OH^‐ efflux and endogenous content of water soluble carbohydrates a diurnal variation was found. The plant age did not significantly affect the daily rhythm.

Because day/night changes of the in vivo root NRA and nitrate uptake were proportional, the relative content of reduced N in the xylem sap of the plants was constant during a day/night interval. At both day 7 and day 21 about 40–50% of the N was transported via the xylem as amino N. As a result of non‐synchronous variation of the specific root and shoot NRA, root reduction capacity showed a great within‐day variation. It varied between 20 and 40% of the whole plant reduction capacity. Since the ratio N‐organic to N‐total in the xylem sap was about 0.5, cycling of organic nitrogen was very likely in these maize plants.     

Influence of ammonium uptake on bean nutrition

A glasshouse experiment was carried out in order to study the effect of ammonium supply [0 and 1.5 mmol L^‐1 in the nutrient solution, whereas total nitrogen (N) concentration was 9.5 mmol L^‐1] on nutrient uptake, leaves, and xylem sap composition and growth of bean plants in sand culture. Ammonium supply caused higher nitrogen, phosphorus (P), potassium (K), and calcium (Ca) uptake. However, K, Ca, and magnesium (Mg) concentrations in the plants (in xylem sap and leaves) were lower when ammonium was supplied. Plants vegetative growth was higher with ammonium supply than without it, specially after four weeks of cultivation.     

Differential responses of soybean and dry bean to zinc deficiency 1

Whether a legume obtains its nitrogen (N) from the air, through dinitrogen fixation, or from the soil, as nitrate (NO₃), may influence its susceptibility to zinc (Zn) deficiency. The influence of N source [potassium nitrate (KNO₃)+ native soil N versus rhizobium‐inoculated seed + native soil N] and phosphorus (P) (0 and 200 mg P/kg), and Zn fertilizers (0, 1, and 8 mg Zn/kg) on growth and nutrient composition of soybean (Glycine max L. cv. McCall) and navy bean (Phaseolus vulgaris L. cv. Seafarer) grown on a calcareous soil were studied under greenhouse conditions. Inoculated plants, but not their KNO₃‐treated counterparts, had root nodules. However, due to N deficiency resulting from suboptimal N fixation, growth of these inoculated plants, especially of navy bean, was poorer than that of similarly treated KNO₃‐fed plants. As a consequence of this restricted growth, responses to P and Zn fertilizers were generally greater in KNO₃‐treated plants. Added P decreased the yield of KNO₃‐treated navy bean in the absence of added Zn, but P‐induced Zn deficiency had little effect on the growth of similarly treated inoculated plants. Plant excess bases (EB)/total plant N ratios [EB = 1/2 Ca + l/2Mg + Na + K ‐ Cl ‐ total S (S = divalent) ‐ total P (P = monovalent)] were less in KNO₃‐treated soybean than in correspondingly treated navy bean. Therefore, rhizosphere pH values around navy bean roots were probably less than those around soybean roots. Despite the hypothesized lower rhizosphere pH values, KNO₃‐treated navy bean was more susceptible to Zn deficiency than soybean. This greater susceptibility of navy bean to Zn deficiency was apparently at least partly due to poor translocation of Zn from the roots to the tops.     

Concentration of sugars, phenolic acids, and amino acids in forest soils exposed to elevated atmospheric CO2 and O3

Concentrations of soluble soil sugars, soluble phenolic acids, and free amino acids were measured in three forest communities at the FACTS-II Aspen FACE Site near Rhinelander, WI, in order to better understand how elevated atmospheric CO₂ and O₃ are influencing soil nutrient availability and cycling. Sugars, phenolic acids, and amino acids are mostly derived from plant and microbial processes, and have the potential to be influenced by changes in carbon inputs. We hypothesized that concentrations in the soil would parallel increases seen in biological activity, due to greater net primary productivity under elevated CO₂ and seasonal patterns of root growth. Chemical analysis of soils revealed marginally significant increases of total soluble sugars and total soluble phenolic acids in the elevated CO₂ treatment (+27 mg kg⁻¹, +0.02 μmol g⁻¹), but there were no significant differences in concentrations due to elevated O₃ or CO₂+O₃. Total free amino acid concentrations were not affected by any of the treatments, but significant shifts in individual amino acids were observed. Elevated CO₂ and the interaction treatment (elevated CO₂+O₃) increased aspartic acid concentrations, while elevated O₃ treatment decreased the concentration of valine. Concentrations of sugars increased throughout the growing season, while phenolic acids were constant and amino acids decreased. The birch-aspen community had the highest concentration of phenolic acids and sugars overall, while maple-aspen had the lowest. These findings suggest that concentrations of soluble sugars, soluble phenolic acids, and free amino acids in the soil are strongly influenced by soil properties, plant and microbial activity, plant community composition, and to a lesser degree, changes in atmospheric CO₂ and O₃.     

Effects of calcium deficiency on nutrient concentration of xylem sap of excised tomato plants

The effects of calcium (Ca) deficiency on cation uptake and concentration of xylem sap from tomato roots after excision of the aerial parts, were studied. The measurements were made on tomato plants grown on nutrient solutions with +Ca or without‐Ca, over a period of 48 hours. Calcium deficiency entailed a significant increase of the flux of xylem sap between the 6th and 14th hour on the first day after excision. In spite of the lack of Ca in the nutrient solution, the Ca concentration in xylem sap was unaffected in regard to that of excised roots with +Ca. The maintenance of the Ca concentration in xylem sap of plants grown on a Ca deficient solution was related to a reuse of the Ca from the apoplastic root stores. So, this regulation indicates a possible translocation of the Ca available in the root supply and a mobility of this element out of the roots only during the early stages of exposure to a Ca deficiency. The presence of NH₄ ⁺ in xylem sap with both +Ca and‐Ca treatments confirms the nitrogenous reduction activity of tomato roots. The accumulation of free ammonium 24 h after excision in both xylem saps (+Ca and‐Ca) is likely to be evidence of an alteration process of protein synthesis which is related to the depletion of the root water soluble carbohydrate supply.     

Comparison of hydroponic solutions for poinsettia nutritional studies 1

Poinsettia cultivars Supjibi and Freedom were grown in eight hydroponic solutions to develop a baseline solution for further nutritional studies. Four solutions contained nitrogen (N) from Ca(NO₃)₂‐4H₂O and KNO₃ (denoted as ‐NH₄) and four contained Ca(NO₃)₂‐4H₂O, KNO₃, nitric acid, and NH₄NO₃ as the N sources (denoted as +NH₄). The four ‐NH₄ and +NH₄ solutions were further divided by an IX or 2X rate of micronutrients [boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), and zinc (Zn)] (denoted as IX or 2X). A factorial of these four solutions at 2 concentrations (100 mg L¹ of N and potassium (K) and 15 mg L¹ phosphorus (P), or 300 mg L¹ of N and K and 46 mg L^‐1 P) was studied. Greater leaf and stem dry weight for both ‘Supjibi’ and ‘Freedom’ was observed in plants grown with the +NH₄ solutions, with a larger increase occurring with’ Supjibi’. Leaf NH₄‐N content for both cultivars was higher for both the 100 and 300 mg L^‐1 N and K fertilization rates when NH₄‐N was included. The leaf K content was highest for the plants grown with the +NH/2X solution for ‘Supjibi’, for both fertilization rates, and leaf K content increased as the K application rate increased. Results indicate that for nutritional studies with poinsettias, hydroponic solutions should include between 12.5% to 33% of the N in the NH₄ form, a calcium magnesium (Ca:Mg) ratio of 2:1, and a micronutrient concentration of (mg I/¹) 0.5, 0.02, 6.6, 0.5, 0.1, and 0.05, respectively, for B, Cu, Fe, Mn, Mo, and Zn, for adequate plant growth.     

Responses of physiological parameters,grain yield,and grain quality to foliar application of potassium nitrate in two contrasting winter wheat cultivars under salinity stress

An experiment was conducted to test whether foliar application of KNO₃ on wheat in the heading stage could reduce salinity‐induced injuries, produce high grain yield, and improve grain quality. Salt‐resistant DK961 and salt‐sensitive JN17 wheat cultivars under 0 or 100 mM–NaCl conditions were foliarly watered with distilled water or a 10 mM–KNO₃ solution. The four treatments included: T₁ (CK₁), 0 mM NaCl + distilled water; T₂, 0 mM NaCl + 10 mM KNO₃; T₃ (CK₂), 100 mM NaCl + distilled water; T₄, 100 mM NaCl + 10 mM KNO₃. The results indicate that there were no differences (p > 0.05) in plant growth, grain yield, and grain quality between T₂ and T₁ in both cultivars, but these response variables were significantly lower in T₃ than in T₁. K⁺ : Na⁺ ratio, chlorophyll content, photosynthetic capacity, grain yield, flour yield, water absorbance, ash content, dough‐development time and dough‐stability time were significantly higher in T₄ than in T₃, while protein concentration, wet‐gluten concentration, and antioxidant enzyme activities were lower. Although foliar application of KNO₃ on JN17 enhanced plant growth, grain yield, and grain quality, these parameters were still lower in T₄ than in T₁. Our findings suggest that cultivating the salt‐resistant wheat cultivar combined with foliar application of KNO₃ at heading stage may alleviate salinity injuries and produce higher grain yield and better grain quality under saline conditions.     

YIELD,FRUIT QUALITY AND NITROGEN UPTAKE OF ORGANICALLY AND CONVENTIONALLY GROWN MUSKMELON WITH DIFFERENT INPUTS OF NITROGEN,PHOSPHORUS, AND POTASSIUM

The effects of varied amounts of fertilization on yield, fruit quality, and nitrogen (N) uptake of muskmelons (Cucumis melo L. var reticulatus Naud) grown under both organic and conventional farming conditions were evaluated. Organic fertilizer (0.0, 0.55, 1.1, and 2.2 kg m^?2) and mineral fertilizers containing the same amounts of estimated plant available nutrients [N, phosphorus (P), and potassium (K)] were applied to organic and conventional farming plots, respectively, in both the spring and autumn seasons of 2005. In comparison to conventional farming conditions, muskmelons grown under organic farming conditions had the same yield, total soluble solids (TSS) and soluble sugar contents in both growing seasons, and fruit pulp nitrate content was significantly reduced by 12% on average in spring and 16% on average in autumn. At harvest maturity the aboveground plant N concentration was significantly higher in the conventional treatments than in the organic treatments. At the vine growth stage, the plant N concentrations were similar in all treatments in both seasons. The ratios of nitrate N to total N amount in aboveground biomass were higher in conventional and high fertilized organic treatments than in low or not fertilized organic treatments under limited N supply from the soil. Muskmelon plants absorbed mainly inorganic N, and the protein N fraction in the xylem sap was larger than the amino acid N fraction. Plants grown in the organic system had a higher proportion of organic N in their xylem sap, especially when manure input was low.     

Influence of phosphorus supply on tomato plant nutrition

Four nutrient solutions with different P‐levels (0.2; 0.5; 2.0 and 4.0 mmol P/l) were studied in order to optimize P nutrition of the tomato plant. A N/P ratio decrease in sap and the leaf was observed when P supply increased. Moreover, excessive and deficient P levels in the nutrient solution resulted in a flavonol glycosides decrease in leaves, specially at flowering. Chlorophyll a/chlorophyll b ratios and chlorophyll a percentages, as compared with the total, were lower in the P‐0.2 and P‐0.5 treatments than in the P‐2.0 treatment.