Effects of nitrogen supply on growth and nitrogen uptake by Miscanthus sinensis during establishment

The effect of nitrogen (N) supply on growth and N uptake of Miscanthus sinensis during the establishment was determined. Seven different N addition regimes were compared in a nutrient solution experiment. In the treatments N111 (severe deficient), N222 (moderate deficient), N333 and N444 (optimal for maximum growth) different N concentration ranges were held constant during the entire growing season. In the treatments N144, N414 and N441 plants were subjected to low (1) N concentration in one of three experimental periods, whereas the N concentration was high (4) in the other two periods. Depending on the N demand of the plants, N concentrations were adjusted to 250–500 μM (N1), 500–1000 μM (N2), 1250–2500 μM (N3) and 2500–5000 μM (N4) when the N concentration in the N222 treatment had dropped below 100 μM. The other elements in the solution were replenished according to the estimated element ratios in the plants. As a reference the potassium concentration in the solution was measured regularly. During the first year plants with a non-limited N supply (N444) produced new tillers and increased the length of individual tillers until the end of the growing season. This resulted in a 48% shoot dry matter increase late in the growing season between August and October and a linear increase of cumulative N uptake between July and October. Limited N supply during the entire growing season (N111, N222) caused lower shoot yields but rhizome and particularly root dry weights were less affected. Significant final yield losses were also observed when the N supply was limited only during the first 7 weeks of growth (N144). By contrast, final shoot yield was hardly affected when the plants were exposed to limited N supply over a period of 9 weeks at the end of the growing season (N441). In the second year regrowth of shoots in spring was affected by the previous year's N supply, since five weeks after the beginning of regrowth, shoot dry matter was significantly positively correlated with N contents in rhizomes and shoots in the previous October. Our results show, that N supply at the beginning of the growing season has a major effect on final yield in the first establishment year of M. sinensis. However, from the second year on, the capacity of N reserves in rhizomes and roots affects spring growth much more than current N supply.     

Aluminum inhibits apoplastic flow of high–molecular weight solutes in root apices of Zea mays L.

Using an aluminum (Al)‐sensitive maize cultivar, we investigated the influence of Al on the apoplastic solute bypass flow and its relationship with Al‐induced (1 h, 50 μM) callose formation and root growth. We selected the fluorescent probes 8‐hydroxypyrene‐1,3,6‐trisulfonic acid, trisodium salt (MW 524) (HPTS) and dextran‐Texas Red (TR) conjugates (MW 3,000, 10,000, and 40,000) to monitor their apoplastic transport. Confocal laser–scanning microscopy (CLSM) analysis and spectrofluorometric quantification showed Al‐induced callose formation in peripheral root cells within 1 h. Pretreatment of plants with the callose synthesis inhibitor 2‐deoxy‐D‐glucose (DDG) reduced the callose formation by half. Uptake experiments with both HPTS and dextrans showed uniform dye distribution in control root apices. After Al treatment for 1 or 2 h, which inhibited root growth by 32% or 50%, respectively, the dyes accumulated in the epidermal and outer cortical cell layers, especially in the 1–2 mm apical root zone. Al treatment reduced the export of the dyes out of the apical 1 cm treatment zone. This was due to strong sorption of HPTS but not of dextrans by Al‐loaded cell walls. Aluminum treatment reduced loading into the xylem sap particularly of higher–molecular weight dextrans. Pretreatment of roots with DDG and presence of 50 mM mannitol during the Al treatment partially forestalled the inhibitory effect of Al on the dye transport, but only slightly reduced the Al‐induced growth inhibition. Exudation experiments revealed that xylem water flow remained unaffected by the Al treatment of the root tips. The results with dextran suggest that Al binding in cell walls of the root apex inhibits apoplastic bypass flow of higher–molecular weight solutes, which might contribute to Al‐induced inhibition of root growth.     

Abschätzung von N2O-Emissionen mit Hilfe eines Windtunnels - ein Methodenvergleich

Estimation of N₂O-losses with a windtunnel - a comparison of methods No systematical investigations into the interactions between NH₃-emissions and N₂O-losses with different kinds of sludge applications have published so far. The use of a windtunnel, which is used for NH₃-measurements, as a possible alternative method to measure N₂O-emissions should be tested. Simultaneous measurements with open chambers and a windtunnel on a Catena in the country of Kraichgau (Baden-Württemberg) were done. Changing the construction of the windtunnel, it was possible to optimize the N₂O-measurements and to eliminate constructional mistakes. But still the dilution factor is too big to take representative amounts of N₂O.     

Vergleich von Nitrat- und Amino-N-Schnelltest zur Charakterisierung des Stickstoff-Versorgungsgrades von Winterweizen

Comparison of the rapid tests for nitrate and amino-N for evaluating the N-status of winter wheat Nitrogen fertilizer trials with winter wheat were conducted in 1985 and 1986 to compare the efficacy of the rapid test for nitrate (in the stem base) and a newly developed rapid test for amino-N (in fully expanded green leaves) for evaluating the N-status of plants. In addition, the influence of weather conditions on the results given by both tests when using ammonium nitrate (NH₄NO₃ + CaCO₃) (AN) and urea-ammonium nitrate solution (UAN), was evaluated to determine wether the rapid test for amino-N gives more accurate information on the N-status of winter wheat than the rapid test for nitrate. The results show that the rapid test for nitrate is suitable to characterize the N-status of winter wheat when nitrogen is predominantly taken up by roots as nitrate. This is normaly the case when plants are fertilized with the salt form of nitrogen, als well as with liquid fertilizer, such as UAN applied through tubes in the soil, as for fertilization of winter wheat at later growing stages. However, during dry weather (1986 field trial) UAN application on leaves at shooting and ear emergence can result in high nitrogen uptake by leaves, causing an underestimation of plant N-status by the rapid test for nitrate, and thus, subsequent excess N-fertilizer application may be recommended (order of magnitude: 20 kg N/ha). Under these conditions the rapid test for amino-N in leaves (pressed sap) is a more accurate test for estimation of plant N-status because it determines glutamine and amino acids, the most important storage forms of reduced nitrogen in plants. When UAN fertilizer on leaves is washed off by rain (1985 field trial), crop N-fertilizer requirements predicted by both tests are comparable. If storage of nitrate in the stem base occurs, due, for example to low radiation intensity during spring (lower nitrate reduction), with the rapid test for amino-N an underestimation of plant N-status can be obtained.     

Aluminium-Toleranz von Ackerbohne (Vicia faba), Lupine (Lupinus luteus), Gerste (Hordeum vulgare) und Roggen (Secale cereale). I. Sproß- und Wurzelwachstum in Abhängigkeit vom Aluminium-Angebot

AI tolerance of horse bean, yellow lupin, barley and rye. I. Shoot and root growth as affected by Al supply In solution culture considerable differences existed in Al tolerance between the plant species horse bean (Vicia faba ?Herz Freya”?), yellow lupin (Lupinus luteus ?Schwako”?), barley (Hordeum vulgare ?Roland”?) and rye (Secale cereale ?Kustro”?): compared to barley (0.05 μg Al l^?1 = 1.85 μM Al) an 80 fold higher concentration of Al was necessary for lupin and rye for comparable growth depression and for horse bean a 5 times higher Al concentration. Injury by Al after 7 days of Al treatment was most effectively and sensitively characterized by an inhibition of elongation of seminal and especially of lateral roots. Numbers of laterals were also reduced. Dry matter production of roots and shoots was less affected by Al. In lupin, low Al supply even slightly increased the dry weight. The high Al tolerance of rye and yellow lupin in solution culture during the seedling stage is in good agreement with their adaptation to acid mineral soils.     

Does apoplastic ascorbic acid enhance manganese tolerance of Vigna unguiculata and Phaseolus vulgaris?

In cowpea (Vigna unguiculata), the development of manganese (Mn) toxicity is considered to be accompanied by the formation of reactive oxygen species, oxidized Mn, and phenoxy radicals in the leaf apoplast. Ascorbic acid (AA) is a common antioxidant in plants, and the oxidation of AA, particularly in the leaf apoplast, contributes to the first line of defence against several biotic and abiotic stress factors. The objective of the present study was to contribute to a better understanding of the role of AA in Mn leaf‐tissue tolerance of cowpea and common bean (Phaseolus vulgaris). Five cowpea cultivars (cvs.) differed greatly in Mn tolerance, which was expressed in differences in numbers of brown spots on leaves and in peroxidase (POD) activity in the apoplastic washing fluid (AWF). In a Mn‐sensitive cv., after 3 d of Mn treatment, brown spots were formed, and POD activities were increased, accompanied by a release of proteins into the apoplast. In the AWF, the concentration of AA and the ratio of AA : (AA+DHA) decreased already after 1 d, and to only 2% after 3 d. In the leaf tissue, the ratio was nearly unaffected, and the total AA+DHA content in the leaf tissue was even increased with advanced expression of Mn toxicity. The application of AA solutions in the range of 5–10 μM via the petiole slightly enhanced Mn tolerance as indicated by the reduction of brown spots (however inconsistently) and POD activity (consistently) in the AWF. Common bean cultivars differing in ozone tolerance, which has been reported to be due to a high AA availability in the leaf apoplast, were studied for their Mn tolerance. Clear differences in Mn tolerance between the cultivars existed, however, these differences were not related to their ozone tolerance. From these results, we conclude that the maintenance of sufficient AA levels in the leaf apoplast contribute to Mn tolerance, but does not fully explain genotypic differences in Mn tolerance in cowpea and common bean.     

The role of the apoplast in aluminium toxicity and resistance of higher plants: A review

In acid mineral soils excess of aluminium ions (AI) is one of the most important factors determining plant species and ecotype distribution, and limiting growth and yield of crops. Aluminium preferentially accumulates in the root tips as sites of cell division and cell elongation. Whether inhibition of cell-division rate is due to direct interaction of Al with the chromatin in the nuclei is rather questionable because of the low radial mobility of Al in the root and the rapidity of cessation of root elongation after Al addition to the growth medium. Externally applied Al instantaneously binds to binding sites in the apoplast. Cross binding of pectates by Al may affect extensibility and water permeability of the cell wall. Interaction of Al with other cell-wall constituents is most likely but needs clarification. Aluminium also affects plasma-membrane characteristics. Ca²⁺ influx and K⁺ efflux are inhibited, and synthesis of callose is induced. Induction of callose suggests an increase rather than a decrease in cytosolic Ca²⁺ as initial response to Al. There is little evidence suggesting major disruption of plasma membrane and cytoplasmic functions by AI. K⁺ uptake, H⁺ extrusion, Fe(III) reducing capacity and lipid peroxidation are hardly affected even in roots severely inhibited in elongation by Al. Al uptake and physiological/biochemical effects of Al on intact plant roots can be mimicked even more sensitively using cell suspension cultures which, therefore, represent a powerful tool for the study of Al toxicity. Large differences in Al resistance exist between plant species and cultivars of a species. Root elongation-rate and callose formation can be used as indicators for Al injury. Since short term Al injury is mainly expressed in the apoplast. Al resistance requires exclusion of Al from or/and inactivation of Al in the apoplast. Generally, Al-resistant genotypes are characterized by lower Al accumulation of the root apical meristems. This is achieved by a lower cation-exchange capacity/surface negativity or complexation of Al through root exudates (mucilage, organic acids). Long term exposure of plants to Al also inhibits shoot growth via induction of nutrient (Mg, Ca, P) deficiencies, drought stress and phytohormone imbalances. Such longer term effects have to be taken into consideration when selecting genotypes for high yielding capacity on acid soils high in available Al.     

Measurement of ammonia emissions after liquid manure application: I. Construction of a windtunnel system for measurements under field conditions

A windtunnel system is presented applicable for measuring ammonia emissions under field conditions. With this system two objectives are achieved:

• 1. No alteration of the microclimatic conditions in the testing area
• 2. Reliable determination of the volumetric air flow and the ammonia concentration

The use of a transparent foil, the precise adjustment of the flow velocity to the windspeed outside, and the constant cross-sectional area over the whole length of the tunnel are the most important constructional details of the system.     

Effects of ammonia,ammonium sulphate and sulphur dioxide on the frost sensitivity of scots pine (Pinus sylvestris L.).

The deterioration of forest vitality has been at least partly attributed to air pollution. Especially NH₃, originating from intensive livestock farming and locally deposited in high concentrations, may contribute to forest decline in The Netherlands. Therefore, the effect of NH₃ and SO₂ fumigations on cold stress and water stress of Pinus svlvestris were examined. P. sylvestris trees (3 yr old) were exposed to ambient air supplemented with several NH₃ concentrations, with SO₂ or a combination of NH₃ and SO₂.Tops of branches were then exposed to various subzero temperatures and the effect of air pollution on frost damage was examined. Neither ambient air, NH₃ or SO₂ significantly influenced from sensitivity at –4 or –7°C. Following freezing treatments of –10°C, the influence of NH₃ and SO₂ became apparent. The effect of the combination of these pollutants is synergistic. Exposure to NH₃ alone followed by freezing temperatures lower than –10°C resulted in more severe frost damage in early autumn and spring than in the winter. It also increased the susceptibility of P. sylvestris to water stress. A greater loss of water was observed in NH₃-fumigated needles following drought stress, suggesting increased cuticular transpiration. Bud burst and subsequent shoot growth was also strongly reduced by NH₃ fumigations.     

Körnung von Saproliten als methodenabhängige Größe

Particle size distribution of saprolites – a method dependent parameter Saprolites and saprolite-derived young soils contain a heavily weathered, kaolinized and more or less soft material, which is further fractured by roots, frost, tillage etc. The particle size distribution of the derived soils depends mainly on the distribution of saprolite fragments. Mechanical crushing, chemical dispersion and especially the application of ultrasonic with variable energy cause shifts in particle size distribution. In some soft saprolites the application of high energy sonication led to two- to threefold increase in clay content reaching 60%. A conventional method for preliminary mechanical treatment and for the determination of particle size distribution of saprolites and saprolitic soils is recommended.