Abstract: Seagrass and algal beds showed a variety of reponses when the water column was treated with low level additions of ammonium, nitrate and phosphate. The nutrients were added separately to 3 uniform seagrass beds of a temperature coastal lagoon during 1979 and 1980. (1) Ammonium caused the production of dense mats of free-floating green algae Enteromorpha plumosa and Ulva lactuca. It also stimulated growth in both the leaf and root-rhizome fractions of Zostera marina. This growth response in Z. marina was greater in the area where current reached 12 cm · s-1 than in the area with little or no current. The concentration of nitrogen in the tissue did not change. In contrast, where current was lacking, Z. marina growth increase with ammonium was small, but the concentration of nitrogen in the tissue doubled over that in control plots. The growth of Ruppia maritima was inversely related to the growth of green algae in the same plots. The red alga Gracilaria tikvahiae did not grow better in ammonium, but its tissue reddened. (2) Nitrate additions enhanced the growth of the green seaweeds Enteromorpha spp. and U. lactuca, but not Z. marina or R. maritima. G. tikvahiae, when fertilized in isolation from other plants, showed a marginal response to this nutrient, and the tissue always reddened. (3) Phosphate enhanced growth in Z. marina and R. maritima exposed to moderate current. G. tikvahiae growing alone showed a small growth response to phosphate. The phosphate made no difference in the growth of the green seaweeds. (4) None of the nutrient supplements noticeably altered the species composition of either epiphytic or planktonic algae associated with the beds, although we did detect small increases in their numbers. The rapid and dense growth of green algae in nitrogen-enriched water probably limited growth of adjacent seagrasses and red algae. Because these seaweeds did not use the phosphate, it became available to other plant components. The overall floral response to nutrient addition in seagrass communities depends, therefore, upon the particular nutrient supplied, the ability of alternate species in the area to compete for that nutrient and the velocity of current in the specific area.

Abstract: Measurements of carbon uptake by lake plankton at different levels of added phosphorus reveal some phytoplankton strategies that contribute to their survival in low-nutrient waters. Nutrient-deficient populations seem to temporarily reduce, rather than enhance, photosynthesis when phosphorus becomes available. This contradicts the basic hypothesis of the 14C bioassay used to determine “limiting” nutrients in natural waters. The reduction of carbon uptake rate continues until either the nutrient addition is taken up or no further storage is possible; at this time carbon upake may be enhanced. Concurrent measurements of phosphorus uptake showed no light response unless the plankton were exposed to significant phosphorus concentrations in the dark for several hours. Phytoplankton seem to be adapted for and dependent upon intermittent events exposing them to nutrient-enriched water. The ability of phosphate-depleted plankton to take up phosphate in excess of their growth requirements was used to develop an index for phosphate deficiency. To normalize for different biomass levels, the optimum photosynthetic rate was divided by the maximum uptake velocity giving a range for the C:P maximum uptake from 1.2 to 206 for plankton samples of varying phosphate deficiency.

Abstract: It has recently been proposed that the frequency of dividing bacterial cells (FDC) can be used to predict growth rates of natural aquatic bacterial assemblages We have examined the relationship between FDC and growth rate in bacteria from southern-temperate, coastal marine waters by using incubation under conditions of manipulated nutrient availability and exclusion of bacterivores The regression of the natural logarithm of bacterial instantaneous growth rate (μ) on FDC resulted in a better fit than regression of untransformed μ on FDC The regression equation was ln μ = 0299FDC − 4961 The coefficient of variation for predicted ln μ at mean FDC was 7% The range of FDC-estimated bacterial instantaneous generation times for coastal Georgia waters was 12 to 68 h, and range of calculated bacterial production rates was 06 to 176 mg of C·m−3· h−1 Unresolved problems of and suggested improvements on the FDC method of predicting growth rate are discussed

Abstract: Birch (Betula verrucosa Ehrh.) and grey alder (Alnus incana Moench) seedlings were grown with varied relative addition rates of all nutrients, up to optimum for vegetative growth. The root medium was basically distilled water to which the nutrients, contained in stock solutions in fixed proportions, were added every second hour and in exponentially increased amounts for consumption during the subsequent period. The nutrient weight proportions previously found to be required in birch (100 N:65 K:13 P) were used in all treatments. However, the nutrient proportions required in grey alder were found to be somewhat different (100 N:50 K:18 P). The use of the required proportions in the additions was important for maintenance of maximum growth, efficient nutrient utilization, and low concentrations in the root medium. Luxury consumption and inefficiency occurred at high concentrations. The results show that the nutrient requirements are sufficiently defined, for different relative growth rates, by the nutrient proportions and the relative addition rate. No clear relationships were found between conductivity or concentration in the root medium and the addition rate, net uptake rate, nutrient status, or relative growth rate. The results are in good agreement with data from low concentration and depletion experiments reported in the literature, showing that non-limited uptake rates occur down to very low concentrations. Thus, there is strong evidence that concentration has been incorrectly used when applied as the treatment variable for plant nutrition in plant science and cultivation practice. The dominant factors in sub-optimum and optimum nutrition are the amounts of nutrients available per unit of time, the growth rate, and the nutrient proportions. At low concentration levels, physical factors such as stirring and flow rate of nutrient solution and boundary layer effects are decisive for the rates with which the nutrients become available to the roots. Therefore, at low levels, concentration alone cannot be used as the factor determining nutrient uptake rate. At high levels, concentration is effective as a supra-optimum factor and increased internal percentage contents cause decreased uptake efficiency, thus counter-acting the concentration effect. Nitrogen effects dominated the stress indications when the internal nitrogen percentage content decreased from optimum to the level of the treatments in the beginning of the experiments. Leaf deficiency symptoms disappeared and the root/shoot ratio change ceased when nitrogen status stabilized. Strong linear regressions were found between any two of the variables: relative addition rate of nutrients, relative growth rate, and nutrient status.

Abstract: (1) Soil characteristics and vegetation were studied in vehicle tracks and adjacent undisturbed tundra along local moisture gradients at four tundra sites in northern Alaska. Vehicle tracks generally had 2 OC higher soil temperatures, deeper thaw, and higher concentrations of available soil phosphate than adjacent undisturbed tundra, but did not differ consistently from controls in soil bulk density, volumetric moisture content, pH, or soil organic content. (2) Vegetation in vehicle tracks had fewer species than controls, reflecting decreased abundance of shrubs, particularly evergreens, and increased dominance by a few species of graminoids. (3) Wet and mesic tracks exhibited a 2to 15-fold increase in above-ground standing crop of nitrogen and phosphorus as a result of increased leaf nutrient concentrations and increased leaf biomass of graminoids, a consequence of increases in both shoot density and shoot weight. (4) We reject our original hypothesis that the known temperature effects upon root growth, nutrient absorption, and organic matter mineralization account for the increased standing crop of biomass and nutrients in vehicle trails. We conclude that other factors, perhaps related to soil water and nutrient movement, are in large part responsible for the increased nutrient status and production of vehicle tracks and exert an important control over growth in undisturbed tundra.

Abstract: Selected indices of structure and function were used to evaluate the effect of differing soil thermal regimes on soil-permafrost-dominated (muskeg) and permafrost-free (north-slope) black spruce ecosystems in interior Alaska. The poorly drained, permafrost site displayed cooler soil temperatures and higher soil moisture content than were encountered on the well-drained north slope. Mineral soil nutrient pools generally were largest on the permafrost site. However, low soil temperature acted as a negative feedback control, suppressing soil biological activity, nutrient mineralization, and tree primary production to lower levels on the soil-permafrost-dominated site as compared with the permafrost-free site. Forty percent larger accumulation of tree biomass and 80% greater annual tree productivity occurred on the warmer site.

Abstract: A synoptic study of photosynthetic and respiratory activity of plankton communities in different Amazon surface waters indicates that large—scale events such as flooding can have a major impact upon the cycling of carbon and nutrients in these aquatic ecosystems. During high water, the major factors influencing primary production appeared to be nutrient concentrations in the mouthbays and varzea (floodplain) lakes and high levels of suspended matter in the Amazon mainstem. In riverine systems, plankton primary production (PPP) averaged 4.04 mg C°m—3°h—1, and measures of respiration (Re) averaged 0.67 mg C°m—3°h—1. In the more productive varzea lakes and mouthbays, PPP averaged 26.37 mg C°m—3°h—1 and Re averaged 2.30 mg C°n—3°h—1. Bacterial densities, 14 C—acetate rate constants for uptake, and plankton carbon: ATP ratios implied that heterotrophic microbiota were important components of the plankton communities in riverine waters. The importance of terrestrial organics to metabolic activity in all waters was implied by high particulate carbon: nitrogen ratios (20:1). These features were especially evident in riverine surface waters where integrated respiration rates exceeded those of plankton primary production. Riverine respiratory levels may be attributed to several factors: adequate supplies of terrestrial organic carbon, sufficient dissolved nutrient concentrations, increased surface area of suspended matter for microbial attachment and growth, and shading of phytoplankton by suspended matter which reduces photosynthetic activity. Observed supersaturation of Amazon waters by carbon dioxide was similar to observations for other rivers of the world. Shifts of CO2 solute components to CO2 in surface waters of varzea lakes and mouthbays and of some tributaries implied high partial pressures of carbon dioxide (°500—1500 Pa). The primary source of CO2 is most likely decomposing organic matter in planktonic and benthic environments of the rivers, lakes, and flooded terrestrial lowlands. The hypothesis that respiratory input of CO2 balanced by evasion (gas lost to atmosphere) is sufficient to explain high CO2 vapor pressures in the Amazon River appeared true from our calculations but needs further examination. Particular attention should be given to periods of rising water, when planktonic respiration appears to be two orders of magnitude greater than at periods of high water. Subsequent seasonal studies of the Amazon and other large rivers are needed to determine how the plankton community, the chemistry of terrestrially derived organics and their biological oxidation in water, and inorganic factors control CO2 supersaturation and exchange with the atmosphere.

Abstract: The ability of Salix aquatica Smith, S. fragilis L. and S. viminalis L. to absorb nitrogen at varied growth rates was investigated in nutrient solutions. The effects of five nitrogen addition rates on growth rates, nitrogen contents of the plants, nitrogen concentration of the media, and dry matter distribution between roots, stems and leaves, were studied. These clones are highly efficient in absorbing nitrogen at low concentrations in the root medium, independent of growth rate. Strong linear regressions were found between any two of the three factors: relative rate of nitrogen supply (RN), nitrogen content (plant), and relative growth rate (R). Dry matter production per unit nitrogen taken up and unit time (N-productivity) and per unit nitrogen taken up independent of time (N-efficiency) was closely correlated to the nitrogen status of the plant. Root development was favoured in the sub-optimum treatments, and leaf development in the optimum treatments. With regard to their ability to absorb nitrogen, these Salix clones appear satisfactory for efficient short rotation energy forestry.

Abstract: Although plants or plant parts can be cultured on various organic nitrogen forms, particularly amino acids, under natural conditions the majority of plants depend upon inorganic nitrogen sources. Exceptions to this may be various parasitic and semi-parasitic plants which may be provided with organic nitrogenous nutrients of host origin, and insectivorous plants which partially satisfy their nitrogen demands by utilizing organic nitrogen constituents released by lysis of trapped insects.

Abstract: A synoptic study of photosynthetic and respiratory activity of plankton communities in different Amazon surface waters indicates that large-scale events such as flooding can have a major impact upon the cycling of carbon and nutrients in these aquatic ecosystems. During high water, the major factors influencing primary production appeared to be nutrient concentrations in the mouthbays and varzea (floodplain) lakes and high levels of suspended matter in the Amazon mainstem. In riverine systems, plankton primary production (PPP) averaged 4.04 mg C m-3. h- , and measures of respiration (R,,) averaged 0.67 mg C m-3 h-1. In the more productive varzea lakes and mouthbays, PPP averaged 26.37 mg C.m 3 h and R, averaged 2.30 mg C m-3 h-1. Bacterial densities, '4C-acetate rate constants for uptake, and plankton carbon : ATP ratios implied that heterotrophic microbiota were important components of the plankton communities in riverine waters. The importance of terrestrial organics to metabolic activity in all waters was implied by high particulate carbon:nitrogen ratios (20:1). These features were especially evident in riverine surface waters where integrated respiration rates exceeded those of plankton primary production. Riverine respiratory levels may be attributed to several factors: adequate supplies of terrestrial organic carbon, sufficient dissolved nutrient concentrations, increased surface area of suspended matter for microbial attachment and growth, and shading of phytoplankton by suspended matter which reduces photo- synthetic activity. Observed supersaturation of Amazon waters by carbon dioxide was similar to observations for other rivers of the world. Shifts of CO, solute components to CO2 in surface waters of varzea lakes and mouthbays and of some tributaries implied high partial pressures of carbon dioxide ( 500-1500 Pa). The primary source of CO2 is most likely decomposing organic matter in planktonic and benthic environments of the rivers, lakes, and flooded terrestrial lowlands. The hypothesis that respiratory input of CO2 balanced by evasion (gas lost to atmosphere) is sufficient to explain high CO2 vapor pressures in the Amazon River appeared true from our calcula- tions but needs further examination. Particular attention should be given to periods of rising water, when planktonic respiration appears to be two orders of magnitude greater than at periods of high water. Subsequent seasonal studies of the Amazon and other large rivers are needed to determine how the plankton community, the chemistry of terrestrially derived organics and their biological oxidation in water, and inorganic factors control CO2 supersaturation and exchange with the atmo- sphere.

Abstract: Two years with contrasting weather, 1976 and 1977, were used to investigate the effects of nitrogen fertilizer on the uptake of nitrogen by crops of winter wheat and on the rate of photosynthesis of flag leaves. The studies involved a number of crops which received various amounts of nitrogen fertilizer at various stages of growth. Weekly measurements were made of the amount of nitrogen in the crops and its distribution within the plant, while a mobile gas exchange system measured the photosynthesis of individual flag leaves.While the treatments imposed in 1976 resulted in different concentrations of nitrogen in the flag leaves, the maximum rate of photosynthesis and its efficiency in dull light were both unaffected when leaves of the same age were compared. The 2 years gave contrasting results in terms of the amounts of nitrogen taken up during grain growth: in the very dry summer of 1976 it could account for only 25% of the nitrogen in the ear at harvest while in 1977 it could account for almost 50%. These different amounts of translocation to the grain were accompanied by different photosynthetic behaviours of the flag leaves and our analysis shows that, in all treatments, the maximum rate of photosynthesis after anthesis was related to the fractional loss of nitrogen from the leaves.The implications of these results for farming practice and for techniques used to investigate the effects of nitrogen on photosynthesis are discussed.

Abstract: Cladophora aff. albida, a nuisance benthic alga, appears to store nutrients during winter and spring, periods of high nutrient input, for use in summer and autumn. Tissue nutrient values were usually above the critical concentrations of 21 mg per g dry weight for N and always below the critical concentration of 33 mg per g dry weight for P. Nutrient sources are surface sediments and decomposing Cladophora and phytoplankton. The few weeks of high river flow in winter do not allow the Cladophora to reach full storage potential of nutrients. Phosphorus regulation may be an important factor in control of this alga in the estuary.

Abstract: SUMMARY Oxygen concentrations in the soil atmosphere greatly influenced the growth and mineral uptake of Eupatorium odoratum inoculated with Glomus macrocarpus. Shoot and root dry weights and length of mycorrhizal plants increased with O2 concentration up to 16%. Mycorrhizal plants at 21% O2 or non-aerated controls were smaller than those at 12 and 16% O2. Non-mycorrhizal plants had lower shoot and root dry wts than mycorrhizal plants at all O2 levels except at 0%. Phosphorus concentration in mycorrhizal and non-mycorrhizal plants differed significantly but did not increase with increasing O2. Mycorrhizal plants contained higher quantities of N, K, Ca and Mg than non-mycorrhizal and showed positive response in nutrient uptake to increase in soil O2. Inoculation and increased soil O2 resulted in higher concentrations of K and Mg but not of N and Ca. The development of Glomus macrocarpus exhibited quantitative and qualitative response to different soil O2 levels.

Abstract: Nitrogen to phosphorus ratios and concentrations of nitrate and soluble reactive phosphate are presented for an array of Southwestern streams as evidence that nitrogen is the limiting nutrient where such limitation occurs. Nitrate uptake in sections of intermittent streams was attributable to autotrophic activity. Uptake of soluble reactive phosphate was unrelated to any indicator of autotrophic activity, thus concentrations of this nutrient in desert and semi-desert stream waters may be controlled by other factors.

Abstract: Previous studies have shown increases in the concentration of ethylene in the soil and roots of plants when the soil is water saturated (flooded). In Zea mays L. this occurs in association with an overall reduction in growth but without extensive foliar senescence and in conjunction with the development of an adventitious root system. We have assessed the possibility that ethylene may be involved in these responses to flooding. Mixtures of the gas in air were therefore supplied to the roots and stem-base of Z. mays growing in nutrient solution. Seven or 14 d exposure to ethylene (1 or 5 νl 1−1) inhibited seminal root elongation and growth in dry weight and accelerated the emergence of adventitious roots, although their final length and dry weight were depressed. Leaf extension was inhibited by 0.1,1.0 or 5.0 μl 1−1 ethylene around the roots; leaves extending rapidiy at the start of treatment were the most sensitive. Final shoot fresh and dry weights were depressed by the gas but tie shootrroot dry weighl ratio and percentage dry matter were not affected greatly. Leaf chlorosis was not observed but the concentration of phosphorus in the shoots was 26 to 31% below normal. When aeration of the nutrient solution was stopped, the concentration of dissolved oxygen declined and the concentration of ethylene in the roots increased. Similar changes occur in response to soil flooding. Root and shoot growth was slowed by non-aeration although the shootroot dry weight ratio remained unchanged. The phosphorus concentration of the shoots was depressed but there was little chlorosis or leaf death. The similarity in these respects between the effects of ethylene and non-aeration suggests that in flooded Z. mays, ethylene contributes to their development by accelerating the emergence of adventitioos roots, inhibiting phosphorus accumulation in the shoots and by a non-toxic inhibition of plant growth.

Abstract: Plantago major L. ssp. major, a grassland species from a relatively nutrient-rich habitat, was grown in nutrient-rich and nutrient-poor culture solutions. Half of the plants were transferred from high to low or from low to high nutrient conditions. The rate of dry matter accumulation in both shoots and roots decreased slowly upon transfer of plants to low nutrient conditions and the shoot to root ratio was unaffected. The rate of structural growth of both roots and shoots increased upon transfer from low to high nutrient conditions and the shoot to root ratio, if calculated from non-structural-carbohydrate-free dry weights, increased. Photosynthesis was largely independent of the nutrient supply. Root respiration, particularly the activity of the alternative oxidative pathway, decreased with increasing age. This decrease was ascribed to a decreased shoot to root ratio, which reduced the relative amount of carbohydrates translocated to the roots and thus the amount available for the alternative pathway. It is calculated that in young as well as in old plants grown in full nutrient solution 48% of the daily produced photosynthates was translocated to the roots. This is at variance with data on P. lanceolata, where a decreasing proportion of the daily produced photosynthates was translocated to the roots when the plants grew older. It is concluded that shoot growth plus shoot respiration consumed a constant amount of the daily produced photosynthates in P. major and that the rest was left for translocation. It is further calculated that in P. major plants grown in full nutrient solution c. 25% and c. 2% of the daily produced photosynthates in young and old plants, respectively, was respired in a way that is not involved in production of energy that is utilized in growth and maintenance (‘inefficient root respiration’). The results are discussed in comparison with those of P. lanceolata, a species from a relatively nutrient-poor habitat.

Abstract: Plantago lanceolata L., a grassland species from a relatively nutrient-poor habitat, was grown in nutrient-rich and in nutrient-poor culture solutions. Half of the plants were trensferred from high to low or from low to high nutrient conditions. Shoot growth was immediately reduced upon transfer to low nutrient conditions, whilst it reacted more slowly upon transfer of plants to high nutrient conditions. Root growth was less dependent on the supply of nutrients, but it was slightly reduced upon transfer of plants to high nutrient conditions. Photosynthesis was largely independent of the nutrient supply, apart from an initial increase upon transfer of plants to low nutrient conditions. Photosynthesis decreased with age in all treatments, and this decrease was not due to mutual shading. The decrease of photosynthetic rate was not accompanied by a decreased relative growth rate: it was compensated by a more efficient root respiration, since the activity of the alternative nonphosphorylating pathway continuously decreased in plants grown in a high nutrient environment. It is concluded that the alternative pathway was of significance in removal of carbohydrates, which could not be utilized for growth, energy production, etc., due to a temporary or structural imbalance between assimilate production and requirement. The alternative pathway also appeared to allow P. lanceolata plants to adapt to a changed environment as regards mineral nutrition. The experimental value for root growth respiration of P. lanceolata grown under high nutrient conditions was compared with a theoretical value, calculated from the biochemical composition of plant dry matter and the known energy costings for biosynthetic and transport processes. A good correlation between the experimental and theoretical value of root growth respiration was found if it was assumed that ion uptake required c. 1.0 molecule of ATP per ion per membrane passage.

Abstract: A flowing nutrient culture system permitted relatively rapid determination of the steady-state net nitrogen influx by an intact barley ( Hardeum vulgare L. cv Kombar and Olli) plant. Ion-selective electrodes monitored the depletion of ammonium and nitrate from a nutrient solution after a single pass through a root cuvette. Influx at concentrations as low as 4 micromolar was measured. Standard errors for a sample size of three plants were typically less than 10% of the mean. When grown under identical conditions, a variety of barley bred for cold soils had higher nitrogen influx rates at low concentrations and low temperatures than one bred for warm soils, whereas the one bred for warm soils had higher influx rates at high concentrations and high temperatures. Ammonium was more readily absorbed than nitrate by both varieties at all concentrations and temperatures tested. Ammonium and nitrate influx in both varieties were equally inhibited by low temperatures.

Abstract: Four consecutive trifoliate leaves of 56-day-old symbiotic or nonsymbiotic soybean plants were evaluated individually for CO2 exchange rates (CER), leaf area and dry weight, and leaf N, P, and starch concentrations. Plants had been inoculated with the vesicular-arbuscular mycorrhizal (VAM) fungus Glomus mosseae and Rhizobium japonicum, with either of the endophytes alone, or with neither at time of planting. Plants lacking one or both endophytes received N and/or P fertilizers to produce plants of equal total leaf dry weight in all four treatments. Photosynthetic P-use efficiency (CER per unit leaf P) was higher in the leaves of VAM plants than in P-fertilized plants regardless of the N source (N2 fixation or combined N). Photosynthetic N-use efficiency was also higher in VAM than in non-VAM plants, but it was affected by the N source, with higher CER in the nodulated plants. The greatest differences in CER, starch accumulation and leaf area were found between the nonsymbiotic plants and those with both endophytes. Statistical evaluations of leaf parameters for treatment or nutrient concentration (N and P) effects between the tripartite and the nonsymbiotic treatments showed significant changes in concentration of P, but not N, with decreasing leaf age. Both endophytes apparently enhance CO2 fixation at N and/or P concentrations lower than those of the nonsymbiotic plants. The effects of the endophytes on CO2 fixation were additive. The microsymbionts of the legume root, the VAM2 fungus and the diazotrophic bacterium Rhizobium, may be regarded as the primary sources of P and N to legumes growing in soils deficient in plant-available forms of those nutrients (4). The sink demand resulting from the growth and metabolic activity of these root endophytes has been associated with a compensatory increase in activity by the C source of the association, the chloroplast (21). Given these premises, endophyte effects on source activity for C and sink demand for N and P by leaves should be measurable in terms of CER and N and P concentrations, and these parameters should be different from those found in nonsymbiotic plants of equivalent development. In particular, since the effects of sinks and sources on one another (especially in young annual plants) are inversely proportional to the distances separating them (28), there should be a shift in endophyte effects on CER in individual leaves with position along the stem. This change, as influenced by the complex three-way source-sink relationships of the tripartite legume association (6), should be different in magnitude from that found in nonsymbiotic plants if the symbiotic N or P sources differ in C-sink activity from the nonsymbiotic ones. Changes in the activity of a plant in providing a product relative to the utilization or availability of a necessary requirement affect the efficiency of its resource utilization. Efficiency has many facets. Generally, nutrient-use efficiency has been defined in terms of dry matter produced per unit of nutrient applied or absorbed (10, 11, 24). A more specialized aspect of nutrient-use efficiency relates to the activity of a specific plant process as a function of that nutrient in the tissue involved. Our use of the term photosynthetic nutrient-use efficiency sensu Sage and Pearcy (23) is defined as CER per unit of leaf N or P, and is particularly useful in comparing the nutrient-use potentials of symbiotic legumes relative to nonsymbiotic controls. The purpose of this study was to investigate the effects of symbiotic and nonsymbiotic N and P supplies on CER in order to determine the response of CER to the presence or absence of the endophytes and to differences in leaf N and P concentrations resulting from the nature of the supply. MATERIALS AND METHODS Biological Materials. Soybean (Glycine max [L.] Merr. cv Hobbit) plants were inoculated with the diazotrophic bacterium Rhizobium japonicum strain USDA 136 (abbreviated 'R') and/or with the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe ('G'). Plants without R. japonicum received N fertilizer ('N'), and those without G. mosseae received P fertilizer ('P'). A control set of nonsymbiotic plants received only the combined fertilizer ('PN'). Fertilizer regimes were adjusted to produce plants of the same weight when harvested after 56 to 59 d of growth. Details of soil, inocula, and growing conditions

Abstract: Effects of increasing rates of lime and phosphorus addition on concentrations of available nutrients in soil and on P, Al and Mn uptake by two pasture legumes, lotus (Lotus pedunculatus Cav.) and white clover (Trifolium repens L.), were studied in a pot experiment using a highly leached acid (pH 4.2) soil.

Abstract: In experiments with pea cv. Rondo grown hydroponically for 6 wk with nitrate as the only N source, an acidic nutrient uptake pattern was observed. When effectively nodulated plants were fixing nitrogen, however, cation absorption exceeded anion absorption resulting in an alkaline ion uptake pattern. Maintaining ambient temp. at 13 deg C allowed for comparison of the effects of N acquisition on nutrient absorption and proton or hydroxyl/bicarbonate excretion by the roots in plants with similar DM yield and N content.The amount of excreted alkalinity or acidity for both nitrate-supplied and nitrogen-fixing plants corresponded well with the respective excess absorption of nutritive anions or cations. Physiological and agronomic consequences of the alkaline nutrient uptake pattern and acidity generation by nitrogen-fixing legumes are discussed. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Abstract: Insectivorous plants and ant-fed plants represent the two ways in which plants have evolved to utilize directly nutrients derived from animals. This paper addresses the limitations under which selection acts to favour the evolution of one or the other of these nutrient-gathering tactics. Both tactics have evolved independently at least six times under similar ecological conditions, indicating that the evolutionary solutions to ecological problems are limited by the historical make-up of communities and are, to some extent, predictable. Both insectivorous and ant-fed plants evolve in environments with very low levels of availability of nutrients in the substrate; the primary use of the animal-food is probably nitrogen; the vast majority of species are perennial, and most species are tropical or subtropical, although some insectivorous genera are primarily temperate. Although these two nutrient-gathering tactics evolve in response to similar ecological problems, whether plants evolve an insectivorous habit or the ant-fed habit depends on the growth forms of the plants and the habitats in which they grow. Most insectivorous plants evolve as herbs in wet, sterile soils or in sterile aquatic habitats; ant-fed plants evolve as epiphytes on trees in open-canopied habitats. These kinds of animal-plant interactions are relatively rare because the environments in which they are favoured by selection are uncommon.

Abstract: The translocation of nutrients into and out of outer canopy leaves of ten eastern deciduous forest species was calculated from the temporal patterns of foliar nutrient pools sampled through a growing season. The calculations accounted for average chemical leaching effects due to rainfall. There were no significant differences in translocation rate between species within the evergreen, understory, or overstory-deciduous tree groups. Evergreen species had lower translocation rates than deciduous trees. Translocation rates into leaves of deciduous species showed a very rapid increase during spring; however, by late May, foliar phosphorus was being translocated at a slow rate back to stems. A similar trend was established for nitrogen by mid-June. An internal storage pool is suggested as the major source of foliar nitrogen during the spring flush since a simulation of nitrogen uptake from soil could only account for one-fourth of the quantity of nitrogen transported to leaves by the end of May. Simulation further showed that trace levels of soluble nitrogen (0.01 ppm) in soil were sufficient to supply a deciduous forest with an estimated nitrogen uptake of 100 kg N ha/sup -1/ year/sup -1/.

Abstract: In the littoral zone of a shallow, tropical lake (Lake Naivasha, Kenya), average nutrient composition of emergent macrophytes along a permanent transect (0–2m depth) on a dry weight basis was: P 0.23%; N 0.96%; and S 0.11%. In the hydrosoil the average composition was much lower, sediments were: P 0.03%; N 0.24%; and S 0.05%. The water depth varied, with lake edge being exposed during the annual drawdown for a part of the year and subsequently being inundated. Water quality varied considerably during the year (temperature 19–28°C; pH 7.0–8.0; conductivity 282–975 μ Scm-1). Of the three nutrients in the water of the littoral zone, N had the highest mean concentration (4.25 mg·1-1) while P was intermediate (1.90) and sulphur had the least (0.99). The distribution of nutrients followed a decreasing gradient from shore to open water. High levels of nutrients were recorded in September following the inundation of drawdown soil and plant material. The large stock of nutrients generated in the littoral zone helps to replenish nutrients in the open lake where low concentrations are typical.

Abstract: Changes in total and mineral nitrogen and organic carbon were measured over a nine year period in two contrasting soils of northern New South Wales after various durations of grazed lucerne, extended fallowing and continuous wheat growing. At least 2 1/2 years of lucerne ley were required to raise the total soil nitrogen above the original level on both soil types. For each year of lucerne growth the average increase (above the control treatments) in total soil nitrogen (0-15 cm) was equivalent to about 140 kg nitrogen ha-1 in the black earth and about 110 kg nitrogen ha-1 in the red-brown earth. Significantly higher levels of soil nitrogen were maintained after the lucerne treatments throughout the 9 years of measurement on the black earth and for 5 years on the red-brown earth. Lucerne had a much larger effect on nitrogen than on organic carbon, which was significantly increased only in the black earth. There were very large increases in mineral nitrogen (0-15 cm) in the first year of measurement after lucerne. Levels remained greater than they were originally for the first 4 years, and they were greater for 7 years in the black earth and 4 years in the red-brown earth following lucerne than following continuous wheat or extended fallow. The decline in mineral nitrogen during wheat cropping after lucerne was greatly increased by excessive rainfall (574 mm or more) during the fallow. Leaching was greater in the red-brown earth than in the black earth, and this explained occasional differences in nitrogen uptake by wheat between the two soil types. Some evidence suggested that under moderately moist conditions nitrogen mineralization from lucerne-fixed nitrogen was greater in the red-brown earth than in the black earth but under drier conditions it was less.