施用磷对王桉 (Eucalyptus regnans F. Muell.)幼苗生长及其氨基酸组

王桉 (Eucalyptus regnans F. Muell.) 是澳大利亚桉树中最重要的商业用材和人工造林树种之一.研究王桉的施肥与其体内氨基酸的积累和转化及与食叶虫害之间的相关性具有重要的经济和生态意义.在温室内利用2种不同来源的土壤对王桉幼苗进行了不同磷施用量(100 kg hm~(-2)和 200 kg hm~(-2))处理.结果显示,不同土壤和不同磷施用量对苗木生长影响显著,但均未显著影响苗木各部分的氮和磷含量水平.苗木木质部渗出液中的氨基酸含量以谷氨酰胺为主,并与苗木生长和磷施用量呈反相关.不同土壤和磷施用量对苗木组织中游离氨基酸组分和含量的影响不显著,但游离氨基酸的组分和相对水平随叶龄变化明显,尤其是精氨酸在嫩叶氨基酸总量中只占2%～3%,但在老叶中占到20%多;精氨酸在老叶中的积累极有可能是某些蛋白质降解而精氨酸即时合成所致,因为精氨酸一般不在韧皮部转运.谷氨酰胺在树液中含量最高并与苗木生长呈反相关或许可以作为预测桉树发生食叶昆虫危害的一个有用指标.     

Environmental factors affecting basic nitrogen metabolism and seasonal levels of various nitrogen fractions in tissues of bilberry, Vaccinium myrtillus

Bilberry tissues accumulated nitrogen for the winter in the form of reduced low-molecular weight amino compounds. The storage organ was principally the underground stem and the oldest parts of the aerial shoot. Most of the nitrogen was stored in arginine and ammonium compounds, and less in glutamine and other amino acids. Proteins did not accumulate during the winter. The soluble nitrogenous compounds were discharged from storage in May, when nitrogen was translocated from the lower parts of the stem to the growing leaves and buds. Amino acid compositions and concentrations in winter were almost identical under the snow and in snowless areas, only the concentration of glutamine being lower and that of glutathione higher in the snowless area. The level of total protein, particularly in the leaves and buds was much higher in a nitrogen-polluted industrial area than in unpolluted urban forests. The same difference was observed in total amino compounds, but among individual substances it only appeared in ammonium compounds. Certain species differences in the amino acid pool were recorded between V. myrtillus and V. vitis-idaea.     

Effects of the mineral composition and water content of intact plants on the fitness of the African armyworm

The effects of organic nitrogen, nitrate, phosphorus, potassium and water content of leaves of intact maize plants, grown in a gravel culture system, on the fitness of the African armyworm, Spodoptera exempta (Walker)(Lepidoptera: Noctuidae) were studied. Organic nitrogen concentrations ranged from 1.3% to 3.7% over four treatments differing only in nitrate supply to the plants. Water content and other mineral levels were all positively correlated with the organic nitrogen level. Feeding damage by the caterpillars was most severe on the lowest nitrate treatments, where it could be least well compensated for by new leaf growth. Larval and pupal fitness variables were not affected by treatment, except for larval development on the lowest nitrate treatment which was delayed by just 1 day. The large compensatory capacity of the larvae was underlined by a similar mineral composition of the pupae in all treatments. Adult fitness variables hardly differed between the upper three nitrate treatments, but revealed a trend over all treatments: the higher the organic nitrogen content of the leaves, the shorter the pre-oviposition period and the higher the fecundity. This trend, however, might have been due to differences in available food quantity rather than in food quality. It is concluded that fitness of the African armyworm is only slightly affected over a wide range of nitrogen concentrations in its food. Though effects might be larger under field conditions, the large differences in outbreak development between years seem not to be attributable to observed differences in nitrogen levels in host plants between years in primary outbreak areas. Other environmental factors appear to be of greater importance.     

Variation in tissue element concentrations in Quercus ilex L. over a range of different soils

In order to study the variability in nutrient concentrations in four tissues of Q. ilex in relation to soil properties, we selected fifteen stands in both Quercus ilex forests and Q. ilex-Pinus halepensis mixed forests. These stands had developed on soils derived from eight different parent materials. Three soil groups were differentiated according to their chemical properties: calcareous soils, siliceous soils, and volcanic soils. Across sites, nutrient concentrations were generally less variable in current-year tissues than in older tissues. Nitrogen and potassium showed the lowest variability among sites, their concentrations in current-year leaves ranging from 1.17% to 1.39% for N and from 0.53% to 0.68% for K. There were few statistically significant correlations between tissue element concentrations, the most frequent being the antagonistic relationship between calcium and magnesium. Nitrogen concentration in current-year leaves was negatively correlated with soil chemical fertility (nitrogen, phosphorus and potassium). This may reflect a nutritional imbalance between nitrogen and other nutrients, some of which may be more limiting than nitrogen to Q. ilex growth in Catalonia forests. Negative correlations were also found between plant magnesium and soil calcium, and positive correlations between plant calcium and soil calcium.     

Development of improved defined media for Clostridium botulinum serotypes A, B, and E.

The minimal nutritional growth requirements were determined for strains Okra B and Iwanai E, which are representatives of groups I and II, respectively, of Clostridium botulinum. These type B and E strains differed considerably in their nutrient requirements. The organic growth factors required in high concentrations by the Okra B strain (group I) were arginine and phenylalanine. Low concentrations (less than or equal to 0.1 g/liter) of eight amino acids (methionine, leucine, valine, isoleucine, glycine, histidine, tryptophan, and tyrosine) and of five vitamins (pyridoxamine, p-aminobenzoic acid, biotin, nicotinic acid, and thiamine) were also essential for biosynthesis. The 10 required amino acids could be replaced by intact protein of known composition by virtue of the bacterium's ability to synthesize proteases. Glucose or other carbohydrates were not essential for Okra B, although they did stimulate growth. Quantitatively, the most essential nutrients for Okra B were arginine and phenylalanine. In contrast, the nonproteolytic strain, Iwanai E (group II), did not require either arginine or phenylalanine. It required glucose or another carbohydrate energy source for growth and did not utilize arginine or intact protein as a substitute source of energy. Iwanai E utilized ammonia as a nitrogen source, although growth was stimulated significantly by organic nitrogenous nutrients, especially glutamate and asparagine. Iwanai E also required biosynthesis levels of seven amino acids (histidine, isoleucine, leucine, tryptophan, tyrosine, valine, and serine), adenine, and six vitamins (biotin, thiamine, pyridoxamine, folic acid, choline, and nicotinamide). Calcium pantothenate also stimulated growth. On the basis of the nutritional requirements, chemically defined minimal media have been constructed for C. botulinum serotypes A, B, E, and F (proteolytic).(ABSTRACT TRUNCATED AT 250 WORDS)     

Dependence of amino acid composition upon nitrogen availability in birch (Betula pendula)

Small birch plants ( Betula pendula Roth .) were grown at different rates of exponentially increasing nitrogen supply. This resulted in plants with different relative growth rates and different internal nitrogen concentrations. Within a nitrogen treatment, both of these variables remained constant with time.
Free amino acids were measured in leaves and roots of the seedlings at two different harvests. At greater nitrogen supply, higher concentrations of total amino acid nitrogen were found in roots and leaves. The ratio of amino acid nitrogen to total nitrogen was low albeit greater at higher nitrogen supply. Higher concentrations of amino acid nitrogen were mainly due to high concentrations of citrulline, glutamine, γ-aminobuitric acid and arginine.
Greater leaf concentrations of amino acid nitrogen at higher nitrogen supply may be related lo increased concentrations in the xylem sap and/or may be indicative of small excesses of nitrogen with respect to current nitrogen usage in protein synthesis.     

Ethanol synthesis, nitrogen, carbohydrates, and growth in tissues from nitrogen fertilized Pseudotsuga menziesii (Mirb.) Franco and Pinus ponderosa Dougl. ex Laws. seedlings

 Seedlings of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco, and ponderosa pine, Pinus ponderosa Dougl. ex Laws., were grown in a controlled environment and fertilized with nutrient solutions containing 150 ppm (+N), or 0 ppm nitrogen (−N). These treatments greatly altered seedling growth, and the concentrations of N and carbohydrates in their tissues. Metabolically active tissues, such as roots, incubated with a limited supply of O₂ became hypoxic faster and synthesized more ethanol than less active tissues, such as needles. All tissues that were incubated for 4 h in N₂ synthesized ethanol. Needles incubated in N₂ and light had much lower quantities of ethanol than needles in N₂ and dark, suggesting that O₂ from photosynthetsis limited internal anoxia. Most tissues from +N seedlings synthesized greater quantities of ethanol in N₂ anoxia than tissues from −N seedlings, probably because they were able to produce more enzymes with a greater availability of N. However, this increase in ethanol synthesis between N treatments was most pronounced in the phloem. Ethanol and soluble sugar concentrations were negatively related in needles and positively related in roots of N+ seedlings, but not −N seedlings. Starch concentrations had no effect on the amount of ethanol produced by any tissue. Regardless of N treatments, all tissues from ponderosa pine produced more N₂-induced ethanol than Douglas-fir, in part because its tissues contained different concentrations of soluble sugars and N as a consequence of phenological differences between the species. However, ponderosa pine tissues may also maintain greater quantities of anaerobic enzymes, or their isozymes than Douglas-fir. Received: 22 February 1998 / Accepted 23 June 1998     

Co-inoculation with Glomus intraradices and Rhizobium tropici CIAT899 increases P use efficiency for N2 fixation in the common bean (Phaseolus vulgaris L.) under P deficiency in hydroaeroponic culture

Common bean (Phaseolus vulgaris L.) genotypes CocoT and Flamingo were inoculated with Rhizobium tropici CIAT899 and Glomus intraradices (Schenck & Smith) and grown under sufficient versus deficient phosphorus supply for comparing the effects of double inoculation on growth, nodulation, mycorrhization of the roots, phosphorus use efficiency and total nitrogen. Although the double inoculation induced a significant increase in all parameters whatever the phosphorus supply in comparison to control, significant differences were found among genotypes and treatments. Nevertheless, the highest phosphorus use efficiency and plant total nitrogen were found under P deficiency in combination with arbuscular mycorrhizal fungi. It is concluded that inoculation with rhizobia and arbuscular mycorrhizal fungi could improve symbiotic nitrogen fixation even under phosphorus deficiency.     

Decomposition of litter in sub-alpine forests of Eucalyptus delegatensis,E. pauciflora and E. dives

The rate of decomposition of summer leaf-fall (abscised leaves), winter leaf-fall (containing some green leaves) and mature green (picked) leaves was assessed in sub-alpine forests of E. delegatensis (R. T. Baker), E. pauciflora (Sieb. ex Spreng) and E. dives (Schau.) in the Brindabella Range, Australian Capital Territory, using litter bag and tethered leaf techniques. The relative contribution of leaching, microbial respiration and grazing by invertebrate macrofauna to loss of leaf weight was determined. The effect of leaching and microbial respiration was assessed in terms of weight loss per unit area of leaf (specific leaf weight), while losses due to macro-faunal grazing were assessed by measuring reductions in leaf area. Litter decomposition constants for litter components (leaf, bark, wood) and total litter were determined from long-term records of litterfall and accumulated litter. Weight losses of abscised leaves during the initial 12 months ranged from 25% for E. pauciflora to 39% for E. delegatensis and were almost entirely due to reduction in specific leaf weight. Losses in the weight of leaves falling in winter ranged from 38 to 49%, while green leaves lost 45 - 59%. Approximately 50% of the total weight loss of green leaves was due to a loss in leaf area caused by skeletonization by litter macrofauna. Thus abscised leaves rather than green leaves must be used for measuring litter decomposition rates since abscised leaves constitute most of the litterfall in eucalypt forests. Leaves placed in the field in autumn decomposed slowly during the first summer, while the rate increased during the second winter and summer. Low litter moisture content appears to limit decomposition in the initial summer period in all communities, after which litterfall provides a mulch which reduces the rate of desiccation of lower litter layers. A simple linear regression model relating decomposition rate to the number of days (D) when litter moisture content exceeded 60% ODW accounted for 63-83% of the variation in decomposition of leaves in the field. Inclusion of mean monthly air temperature (T) and the product of D and T (day degrees when litter was wet) in a multiple linear regression increased the variation in decomposition accounted for to 80 – 90%. The rate of weight loss showed a positive linear relationship with the initial concentration of nitrogen (N) or phosphorus (P) in the leaf. These concentrations are an index of the decomposability of leaf substrates (e.g. degree of sclerophylly or lignification). The rate of loss of specific weight was similar for tethered leaves and for leaves enclosed in mesh bags. Measured loss in specific leaf weight after 70 – 90 weeks was less than that predicted using decomposition constants (k).     

Development of improved defined media for Clostridium botulinum serotypes A, B, and E

The minimal nutritional growth requirements were determined for strains Okra B and Iwanai E, which are representatives of groups I and II, respectively, of Clostridium botulinum. These type B and E strains differed considerably in their nutrient requirements. The organic growth factors required in high concentrations by the Okra B strain (group I) were arginine and phenylalanine. Low concentrations (less than or equal to 0.1 g/liter) of eight amino acids (methionine, leucine, valine, isoleucine, glycine, histidine, tryptophan, and tyrosine) and of five vitamins (pyridoxamine, p-aminobenzoic acid, biotin, nicotinic acid, and thiamine) were also essential for biosynthesis. The 10 required amino acids could be replaced by intact protein of known composition by virtue of the bacterium's ability to synthesize proteases. Glucose or other carbohydrates were not essential for Okra B, although they did stimulate growth. Quantitatively, the most essential nutrients for Okra B were arginine and phenylalanine. In contrast, the nonproteolytic strain, Iwanai E (group II), did not require either arginine or phenylalanine. It required glucose or another carbohydrate energy source for growth and did not utilize arginine or intact protein as a substitute source of energy. Iwanai E utilized ammonia as a nitrogen source, although growth was stimulated significantly by organic nitrogenous nutrients, especially glutamate and asparagine. Iwanai E also required biosynthesis levels of seven amino acids (histidine, isoleucine, leucine, tryptophan, tyrosine, valine, and serine), adenine, and six vitamins (biotin, thiamine, pyridoxamine, folic acid, choline, and nicotinamide). Calcium pantothenate also stimulated growth. On the basis of the nutritional requirements, chemically defined minimal media have been constructed for C. botulinum serotypes A, B, E, and F (proteolytic).(ABSTRACT TRUNCATED AT 250 WORDS)     

The Role of Plant Size and Nutrient Concentrations in Associations between Medicago, and Rhizobium and/or Glomus

The aim of this research was to carry out a critical study of the method of obtaining size equivalence between non-symbiotic alfalfa and alfalfa associated with Glomus and/or Rhizobium by applying fixed addition rates of nutrients to the non-symbiotic controls. The experimental design included three nutrient response curves in which the levels of added phosphorus and/or nitrogen were constant during the whole plant growth process: 1) a phosphorus response curve, in order to compare the growth of double symbiotic plants with that of only-Rhizobium inoculated ones; 2) a nitrogen response curve, that consisted of a comparison between the growth of double symbiotic alfalfa and four treatments associated only with Glomus; 3) a phosphorus and nitrogen response curve, to compare the growth of non-inoculated alfalfa with that of double symbiotic plants. Although similar size was achieved among some treatments at harvest, shoot growth over time and nutrient concentrations in tissues differed, indicating that growth equivalence did not mean functional equivalence. A second experimental design was performed taking into account the establishment of microsymbionts for determining the adequate moment to add supplemental phosphorus and/or nitrogen. It included four treatments: a) double symbiotic plants (MR); b) plants inoculated with Rhizobium only (R); c) plants inoculated with Glomus only (M), and d) non-inoculated plants (N). Great similarity in terms of plant growth and nutrient contents in tissues were obtained. Moreover, symbiotic plants were able to produce similar dry matter than non-symbiotic ones under P and N limitations.     

Water use and chemical composition of ryegrass (Lolium) cultivars

Summary Significant differences in total dry matter yields of shoots and roots were found between 11 ryegrass (Lolium) cultivars grown in a glasshouse. Although shoot yield varied significantly between individual cultivars there was no overall difference between the annual and perennial cultivars; whereas for roots, the yields of the perennial plants were much smaller than those of the annual types. Water use (g H₂O g total DM^–1) also varied significantly between cultivars. However, there was no relationship between efficient water use and dry matter production.No significant differences were found in shoot composition between the cultviars for nitrogen, phosphorus, and potassium; however, concentrations of sulphur, magnesium, calcium, and sodium varied significantly. Sodium concentrations were generally higher in the annual compared to the perennial cultivars. For roots only nitrogen, phosphorus, and sulphur differed significantly between cultivars. Of the elements only calcium in the shoots was shown to be related to water use. Thus cultivars which were low users of water also had significantly lower calcium concentrations in their shoots. Water use appeared to affect the absorption of calcium by the root to a far greater extent than the transport from roots to shoot. An apparent relationship between magnesium concentration in the shoots and water use was shown to be due to the close association of magnesium with calcium in the plant.     

Growth of the conchocelis phase of Porphyra columbina (Bangiales, Rhodophyta) at different temperatures and levels of light, nitrogen and phosphorus

Temperature, light, nitrogen and phosphorus all had significant effects on the growth of conchocelis colonies of Porphyra columbina Montagne when grown in vitro using a shell substrate. High rates of growth were recorded at 15°C and at 8°C under low light levels. These fight and temperature conditions are similar to those found in the subtidal environment of southern New Zealand coastlines. Little growth occured at 22°C. Nitrogen stimulated growth at concentrations far greater than are likely to be found in situ, while at concentrations of 120 μmol/L and above phosphorus had an inhibitory effect on growth, The culture parameters were strongly interactive in their effect on growth, in particular temperature and light. Conchosporangia formed in all treatments 14 days after alteration of the photoperiod to 10 h light: 14 h dark. Optimal conditions for culture of the conchocelis of P. columbina from southern New Zealand are a water temperature of approximately 15°C, light levels between 10 and 50 μmol m^?2s^?1 and seawater nitrogen levels maintained above 100 μmol/L.     

Effect of nitrogenous resource on growth,biochemical composition and ultrastructure of Isochrysis galbana (Isochrysidales,Haptophyta)

The nitrogenous resource used to promote algal growth has cost implications for mass culture processes. The present study therefore aimed to determine the effect of different nitrogenous resources (nitrate, ammonium and urea) on various performance parameters (growth, final cell yield, pigmentation, lipid yield and cellular and sub‐cellular characteristics) in Isochrysis galbana. Growth rate was unaffected by nitrogenous resource, but the final cellular yield in the nitrate and urea treatments far exceeded that evident in the ammonium treatments. The reduced cell yield in ammonium treatments and the earlier onset of the stationary phase was brought about by nitrogen‐starvation due to an increase in pH and resultant ammonia volatilization. This starvation initiated an early onset of lipid accumulation, chlorophyll depletion and an increase in the carotenoid to chlorophyll ratio relative to the other nitrogen (N) source treatments. Hence, in spite of being potentially the preferred source of N by algae (due to its reduced state), ammonium‐nitrogen is undesirable for mass culture. The performance parameters of Isochrysis grown in urea (an organic N source) and nitrate (an inorganic N source) were similar, but lipid accrued earlier in cells grown in medium supplemented with urea. This is advantageous for lipid acquisition for the production of biodiesel since it would reduce the duration of photobioreactor runs. Urea is easily available and considerably cheaper than all the other N sources tested and is thus recommended as the nitrogenous resource for large‐scale culture of I. galbana for biodiesel production.     

The effect of altered sink-source relations on photosynthetic traits and matter transport during the phase of reproductive growth in the annual herb <Emphasis Type="Italic">Chenopodium album</Emphasis>

Annual plants transport a large portion of carbohydrates and nitrogenous compounds from leaves to seeds during the phase of reproductive growth. This study aimed to clarify how reproductive growth affects photosynthetic traits in leaves and matter transport within the plant in the annual herb Chenopodium album L. Plants were grown in pots and either reproductive tissues or axillary leaves were removed at anthesis. Matter transport was evaluated as temporal changes in dry mass (as a substitute of carbohydrates) and nitrogen content of aboveground organs: leaves, axillary leaves, stems and reproductive tissues. Photosynthetic capacity (light-saturated photosynthetic rate under ambient CO₂ concentration), nitrogen, chlorophyll and soluble protein content were followed in the 20^th leaf that was mature at the start of the experiment. Removal of reproductive tissues resulted in accumulation of dry mass in leaves and axillary leaves, and accumulation of nitrogen in stem as nitrogen resorption from leaves and axillary leaves proceeded with time. Removal of axillary leaves proportionally reduced dry mass and nitrogen allocation to reproductive tissues, thus affecting the quantity but not quality of seeds. Removal treatments did not alter the time course of photosynthetic capacity, nitrogen, chlorophyll or soluble protein content during senescence in the 20^th leaf, but changed the photosynthetic capacity per unit of leaf nitrogen according to demand from reproductive tissues. Together, the results indicate that reproductive tissues affected carbon and nitrogen economy separately. The amount of carbon was adjusted in leaves through photosynthetic capacity and carbohydrate export from them, and the amount of nitrogen was adjusted by transport from stem to reproductive tissues. The plant’s ability to independently regulate carbon and nitrogen economy should be important in natural habitats where the plant carbon-nitrogen balance can easily be disturbed by external factors.     

Variation in foliar nutrients in Eucalyptus trees in eastern and Western Australia

Abstract Levels of nitrogen, phosphorus and potassium were measured for the foliage of two co-dominant eucalypts at each of two sites, one in eastern Australia and the other in Western Australia. In eastern Australia, foliage was sampled in the canopy and subcanopy for narrow-leaved ironbark Eucalyptus crebra and grey box E. mollucana and in Western Australia, for jarrah E. marginata and marri E. calophylla. The Western Australian trees were also sampled for ‘young’ and ‘old’ leaves. Both eucalypts in eastern Australia had greater nitrogen and phosphorus levels, but lower potassium, than E. marginata or E. calophylla. Eucalyptus calophylla foliage had greater levels of all three nutrients than E. marginata foliage as did E. crebra relative to E. mollucana. At both sites, foliar nutrient levels were greater in the canopy than subcanopy foliage, and, at least in Western Australia, the younger leaves had greater nutrient levels than the older leaves. The observed differences in foliar nutrient levels are consistent with observed trends in the abundance and diversity of foliage arthropods and the use of the trees as foraging substrates by birds.     

Influences of water column nutrient loading on growth characteristics of the invasive aquatic macrophyte <Emphasis Type="Italic">Myriophyllum aquaticum</Emphasis> (Vell.) Verdc.

Nuisance growth of Myriophyllum aquaticum has often been attributed to high amounts of nutrients. The uptake of nitrogen and phosphorus from sediments and their allocation have been documented in both natural and laboratory populations. However, nutrient loading to surface water is increasingly becoming an important issue for water quality standards. Aquatic macrophytes that develop adventitious roots may be able to survive through the uptake of water column nutrients. Our objectives for this study were to assess M. aquaticum growth when combinations of nitrogen and phosphorus were added to the water column. Mesocosm experiments were conducted where nitrogen (1.8, 0.8, and 0.4 mg l⁻¹; high, medium, and low) and phosphorus (0.09, 0.03, 0.01 mg l⁻¹; high, medium, and low) concentrations were paired and added to the water column. After 12 weeks, the combination of 1.80:0.01 N:P resulted in greater (P < 0.01) total biomass and greater biomass for all plant tissues. Total biomass at the 1.80:0.01 N:P combination was 53% greater than biomass at all other combinations. The yield response of M. aquaticum was a quadratic function of tissue nutrient content. Yield was positively (r ² = 0.82) related to increasing nitrogen content, whereas a negative (r ² = 0.89) relationship was determined for increasing phosphorus content. We propose the negative relationship is due to increased nutrient competition and shading by algae resulting in reduced M. aquaticum growth. Tissue nutrient content indicated that critical concentrations (1.8% nitrogen and 0.2% phosphorus) for growth were not attained except for nitrogen in plants grown in the 1.80:0.01 N:P combination. These data provide further evidence that M. aquaticum requires high levels of nitrogen to achieve nuisance growth. Survival through uptake of water column nutrients may be a mechanism for survival during adverse conditions, a means of long distance dispersal of fragments, or may offer a competitive advantage over species that rely on sediment nutrients.     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations I. Concentrations, Contents and Distribution of N, P and K

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae was grown in sand and fedwith a complete nutrient medium diluted to give a range of concentrations.Analysis of bulked, dried tissues of the plant showed that undernutrient-rich conditions rust infection resulted in increasedconcentrations of total (Kjeldahl) nitrogen and potassium buthad little effect on phosphorus concentration. Thus, despitereduced dry weight growth, total plant nitrogen contents wereno less in rusted than control plants. Although total contentsof phosphorus and potassium were reduced by rust, effects wereprobably related to loss of these nutrients in fungal spores. Interactions between rust infection and nutrient supply weresignificant but differed between nutrients: rust caused increasednitrogen concentrations only under nutrient-rich conditionsbut increased phosphorus concentrations only when nutrient supplywas limited. Increased concentrations were not confined to infectedtissues. Mechanisms underlying rust-nutrient interactions appearto be complex and to depend inter alia on the partitioning andrecycling of the particular nutrient within the plant. Rust-inducedincreases in potassium concentration occurred under both highand low nutrient conditions but were confined to infected tissues.Potassium accumulation in nutrient deficient conditions wasprobably due to increased transpirational flux into infectedtissues, but under nutrient-rich conditions reduced potassiumexport appeared to assume greater significance. The possible implications of the changed nutrient relationsfor the wider interactions of rust-infected plants in naturalvegetation are discussed. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient deficiency, nutrient content, nutrient concentration, nutrient distribution     

Mepiquat chloride seed treatment and germination temperature effects on cotton growth, nutrient partitioning, and water use efficiency

Cotton seed (Gossypium hirsutum L. cv. Stoneville 825), treated with 0, 0.2, 1.0, and 2.0 g active ingredient (a.i.) mepiquat chloride (MC) kg^–1, was evaluated for the effect of MC on early plant growth. Emergence rate and total emergence of MC-treated seed and control were similar regardless of germination temperature. However, the number of leaves and squares and the dry weight of leaves, stems, and roots for hydroponically grown cotton plants were significantly lower at lower germination temperatures (15°C for 3 day/30°C for 1 day and 15°C for 4 days) than at higher germination temperatures (30°C for 4 days and 30°C for 3 days/15°C for 1 day). All MC treatments significantly decreased the number of nodes, leaves, and squares, as well as dry weight of leaves, stems, and roots, as compared to control plants at 28 days after emergence. MC seed treatments also significantly reduced plant height and total leaf area compared to controls. Water-use efficiency (WUE) was significantly lower for the 1.0 g a.i. MC treatment than for control plants. In general, the highest rate of MC seed treatment resulted in greater concentrations of calcium, phosphorus, and nitrogen in plant leaves and stems and also in greater concentrations of magnesium, phosphorus, and nitrogen in roots than in controls.     

Symbiotic dinitrogen fixation and host-plant growth during development of and recovery from phosphorus deficiency

Characterization of nodule growth and function, phosphorus and nitrogen status of plant tissues and host-plant growth of nodulated soybean ( Glycine max L. Merr.) plants developing and recovering from phosphorus deficiency was used to evaluate the role of phosphorus in symbiotic dinitrogen fixation. The sequence of physiological responses during recovery from phosphorus deficiency was; (1) rapid uptake of phosphorus, (2) rapid increases in the phosphorus concentration of leaves and nodules, (3) enhanced growth and function of nodules, (4) increased nitrogen concentrations in all plant organs and (5) enhanced plant growth. The sequence of physiological responses to onset of phosphorus deficiency was; (1) decreased phosphorus uptake, (2) decreased phosphorus concentrations in leaves and nodules, (3) decreased nodule function, (4) decreased nitrogen concentration in plant organs and (5) decreased plant growth. These results, in conjunction with previously published data (Sa and Israel, Plant Physiol. 97: 928–935, 1991), support an interpretation that the total response of symbiotic dinitrogen fixation in soybean plants to altered phosphorus supply is a function of both indirect effects on host-plant growth and more direct effects on the metabolic function of nodules.