Elevated Phosphorus Impedes Manganese Acquisition by Barley Plants

The occurrence of manganese (Mn) deficiency in cereal crops has increased in recent years. This coincides with increasing phosphorus (P) status of many soils due to application of high levels of animal manure and P-fertilizers. In order to test the hypothesis that elevated P my lead to Mn deficiency we have here conducted a series of hydroponics and soil experiments examining how the P supply affects the Mn nutrition of barley. Evidence for a direct negative interaction between P and Mn during root uptake was obtained by on-line inductively coupled plasma mass spectrometry (ICP-MS). Addition of a pulse of KH2PO4 rapidly and significantly reduced root Mn uptake, while a similar concentration of KCl had no effect. Addition of a P pulse to the same nutrient solution without plants did not affect the concentration of Mn, revealing that no precipitation of Mn–P species was occurring. Barley plants growing at a high P supply in hydroponics with continuous replenishment of Mn2+ had up to 50% lower Mn concentration in the youngest leaves than P limited plants. This P-induced depression of foliar Mn accelerated the development of Mn deficiency as evidenced by a marked change in the fluorescence induction kinetics of chlorophyll a. Also plants growing in soil exhibited lower leaf Mn concentrations in response to elevated P. In contrast, leaf concentrations of Fe, Cu, and N increased with the P supply, supporting that the negative effect of P on Mn acquisition was specific rather than due to a general dilution effect. It is concluded that elevated P supply directly interferes with Mn uptake in barley roots and that this negative interaction can induce Mn deficiency in the shoot. This finding has major implications in commercial plant production where many soils have high P levels

Interactions between leaf nitrogen status and longevity in relation to N cycling in three contrasting European forest canopies

Seasonal and spatial variations in foliar nitrogen (N) parameters were investigated in three European forests with different tree species, viz. beech (Fagus sylvatica L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and Scots pine (Pinus sylvestris L.) growing in Denmark, the Netherlands and Finland, respectively. The objectives were to investigate the distribution of N pools within the canopies of the different forests and to relate this distribution to factors and plant strategies controlling leaf development throughout the seasonal course of a vegetation period. Leaf N pools generally showed much higher seasonal and vertical variability in beech than in the coniferous canopies. However, also the two coniferous tree species behaved very differently with respect to peak summer canopy N content and N re-translocation efficiency, showing that generalisations on tree internal vs. ecosystem internal N cycling cannot be made on the basis of the leaf duration alone. During phases of intensive N turnover in spring and autumn, the NH4+ concentration in beech leaves rose considerably, while fully developed green beech leaves had relatively low tissue NH4+, similar to the steadily low levels in Douglas fir and, particularly, in Scots pine. The ratio between bulk foliar concentrations of NH4+ and H+, which is an indicator of the NH3 emission potential, reflected differences in foliage N concentration, with beech having the highest values followed by Douglas fir and Scots pine. Irrespectively of the leaf habit, i.e. deciduous versus evergreen, the majority of the canopy foliage N was retained within the trees. This was accomplished through an effective N re-translocation (beech), higher foliage longevity (fir) or both (boreal pine forest). In combination with data from a literature review, a general relationship of decreasing N re-translocation efficiency with the time needed for canopy renewal was deduced, showing that leaves which live longer re-translocate relatively less N during senescence. The Douglas fir stand, exposed to relatively high atmospheric N deposition, had by far the largest peak summer canopy N content and also returned the largest amount of N in foliage litter, suggesting that higher N fertility leads to increased turnover in the ecosystem N cycle with higher risks of losses such as leaching and gas emissions.Peer reviewe

Regulation of Apoplastic NH(4)(+) Concentration in Leaves of Oilseed Rape

Regulation of apoplastic NH(4)(+) concentration in leaves of oilseed rape (Brassica napus L.) was studied using a vacuum-infiltration technique that allowed controlled manipulations of the apoplastic solution. In leaves infiltrated with NH(4)(+)-free solution, the apoplastic NH(4)(+) concentration returned in less than 1.5 min to the preinfiltration level of 0.8 mm. Infiltrated (15)NH(4)(+) was rapidly diluted by (14)NH(4)(+)/(14)NH(3) effluxed from the cell. The exchange rate of (15)N/(14)N over the apoplast due to combined (14)N efflux from the symplast and (15)N influx from the apoplastic solution was 29.4 μmol g(−1) fresh weight h(−1) between 0 and 5 min after infiltration. The net uptake of NH(4)(+) into the leaf cells increased linearly with apoplastic NH(4)(+) concentrations between 2 and 10 mm and could be partially inhibited by the channel inhibitors La(3+) and tetraethylammonium and by Na(+) and K(+). When apoplastic pH increased from 5.0 to 8.0, the steady-state apoplastic NH(4)(+) concentration decreased from 1.0 to 0.3 mm. Increasing temperature increased the rate of NH(4)(+) net uptake and reduced the apoplastic steady-state NH(4)(+) concentration. We conclude that the apoplastic solution in leaves of oilseed rape constitutes a highly dynamic NH(4)(+) pool

Leaf Scorching following Foliar Fertilization of Wheat with Urea or Urea–Ammonium Nitrate Is Caused by Ammonium Toxicity

Foliar fertilization is a potential tool to increase the use-efficiency of nitrogen (N) fertilizers. However, whilst leaf scorching has frequently been reported, the underlying physiological processes are not clear. In the present work, we investigate the intensity of leaf scorching as affected by the balance between ammonium assimilation and accumulation. Leaves were sprayed with urea–ammonium nitrate (UAN) solution without surfactant or applied liquid droplets of urea in different N concentrations with surfactant. UAN solutions without surfactant containing >10% N caused leaf scorching already after 24 h and the severity increased with the N concentration. The same pattern was observed 3 days after the application of urea solutions containing >4% N together with surfactant. The scorching was accompanied by a massive increase in foliar and apoplastic ammonium (NH4+) concentration. Moreover, the activity of glutamine synthetase (GS), most pronouncedly that of the chloroplastic isoform (GS2), decreased a few hours after the application of high N-concentrations. Along with this, the concentration of glutamate—the substrate for GS—decreased. We conclude that leaf scorching is promoted by NH4+ accumulation due to a limitation in N assimilation capacity

Optimising the foliar uptake of zinc oxide nanoparticles: do leaf surface properties and particle coating affect absorption?

Foliar absorption of zinc (Zn) is limited by several barriers, the first of which is the leaf cuticle. In this study, we investigated the absorption of Zn from Zn oxide nanoparticles (ZnO-NPs) in wheat (Triticum aestivum cv Gladius) and sunflower (Helianthus annuus cv Hyoleic 41) to determine the importance of NP surface coating for Zn absorption. Fourier transform infrared (FTIR) spectroscopy showed a higher polysaccharide content in the wheat cuticle than sunflower, indicated by a more pronounced glycosidic bond at 1020 cm , but wax and cutin content was similar. Scanning electron microscopy (SEM) revealed that trichome density was twice as high in wheat (3600 ± 900 cm ) as in sunflower (1600 cm ) and stomatal density four times higher in sunflower (6400 ± 800 cm in wheat and 22900 cm in sunflower). Suspensions of ZnO-NPs with coatings of different hydrophobicity were applied to leaves to compare Zn absorption using X-ray fluorescence microscopy (XFM) and inductively coupled plasma mass spectroscopy (ICP-MS). Absorption of Zn was similar between wheat and sunflower when Zn was applied at 1000 mg Zn L , but much less Zn was absorbed from all ZnO products than from soluble Zn fertiliser. Particle coating did not affect Zn absorption, but it may facilitate particle adhesion to leaves, providing a longer-term source of resupply of Zn ions to the leaves. Differences in leaf surface characteristics did not affect Zn absorption, indicating that the cuticle is the main pathway of absorption under these conditions. This article is protected by copyright. All rights reserved