Interaction of straw amendment and soil NO3- content controls fungal denitrification and denitrification product stoichiometry in a sandy soil

The return of agricultural crop residues are vital to maintain or even enhance soil fertility. However, the influence of application rate of crop residues on denitrification and its related gaseous N emissions is not fully understood. We conducted a fully robotized continuous flow incubation experiment using a Helium/Oxygen atmosphere over 30 days to examine the effect of maize straw application rate on: i) the rate of denitrification, ii) denitrification product stoichiometry N2O/(N2O+N2), and iii) the contribution of fungal denitrification to N2O fluxes. Five treatments were established using sieved, repacked sandy textured soil; i) non-amended control, ii) nitrate only, iii) low rate of straw + nitrate, iv) medium rate of straw + nitrate, and iv) high rate of straw + nitrate (n = 3). We simultaneously measured NO, N2O as well as direct N2 emissions and used the N2O 15N site preference signatures of soil-emitted N2O to distinguish N2O production from fungal and bacterial denitrification. Uniquely, soil NO3− measurements were also made throughout the incubation. Emissions of N2O during the initial phase of the experiment (0–13 days) increased almost linearly with increasing rate of straw incorporation and with (almost) no N2 production. However, the rate of straw amendment was negatively correlated with N2O, but positively correlated with N2 fluxes later in the experimental period (13–30 days). Soil NO3− content, in all treatments, was identified as the main factor responsible for the shift from N2O production to N2O reduction. Straw amendment immediately lowered the proportion of N2O from bacterial denitrification, thus implying that more of the N2O emitted was derived from fungi (18 ± 0.7% in control and up to 40 ± 3.0% in high straw treatments during the first 13 days). However, after day 15 when soil NO3− content decreased to <40 mg NO3−-N kg−1 soil, the N2O 15N site preference values of the N2O produced in the medium straw rate treatment showed a sharp declining trend 15 days after onset of experiment thereby indicating a clear shift towards a more dominant bacterial source of N2O. Our study singularly highlights the complex interrelationship between soil NO3− kinetics, crop residue incorporation, fungal denitrification and N2O/(N2O + N2) ratio. Overall we found that the effect of crop residue applications on soil N2O and N2 emissions depends mainly on soil NO3− content, as NO3− was the primary regulator of the N2O/(N2O + N2) product ratio of denitrification. Furthermore, the application of straw residue enhanced fungal denitrification, but only when the soil NO3− content was sufficient to supply enough electron acceptors to the denitrifiers

Tardive Dyskinesia and Treatment Approaches

Tardive dyskinesia is an iatrogenic movement disorder with an incompletely determined etiology. Involuntary movements can effect oral, lingual, facial, corporal muscles and can be permanent. Tardive dyskinesia is one of the most important side effects of long term antipsychotic use. There is some decrease in tardive dyskinesia rates after common use of second generation antipsychotics but tardive dyskinesia can be seen even after use of second generation antipsychotics. There are some treatment options from drug-free observation to deep brain stimulation in tardive dyskinesia. The aim of this article is to review epidemiology, etiology, risk factors, pathophysiology and treatment options of tardive dyskinesia

N-Umsatz und Spurengasemissionen typischer Biomassefruchtfolgen zur Biogaserzeugung in Norddeutschland

Im Rahmen des Verbundprojektes Biogas-Expert an der CAU-Kiel wurden an zwei Standorten Schleswig-Holsteins veschiedene Fruchtfolgen zur Bereitstellung von Biogassubstraten unter Verwendung von Biogasgüllen als N-Dünger durchgeführt. Maismonokultur wies die höchsten Trockenmasseerträge auf, wobei keine signifikanten Unterschiede in den Erträgen zwischen Biogasgärresten, organischen N-Düngern und mineralischen Düngern ermittelt wurden. Während in Bezug auf die N-Düngeform bei N2O- und Nitratauswaschungsverlusten kein Einfluss der N-Form auf die Höhe der Verluste festgestellt wurde, war die Düngung mit Biogasgüllen mit signifikant erhöhten NH3-Verlusten verknüpft. Eine abschließende Bewertung der Produktionssysteme ist erst durch Analyse der experimentellen Ergebnisse mit einem Systemmodell möglich

Optimization of potassium supply under osmotic stress mitigates oxidative damage in barley

Potassium (K) is the most abundant cation in plants, playing an important role in osmoregulation. Little is known about the effect of genotypic variation in the tolerance to osmotic stress under different K treatments in barley. In this study, we measured the interactive effects of osmotic stress and K supply on growth and stress responses of two barley cultivars (Hordeum vulgare L.) and monitored reactive oxygen species (ROS) along with enzymatic antioxidant activity and their respective gene expression level. The selected cultivars (cv. Milford and cv. Sahin-91Sahin-91) were exposed to osmotic stress (−0.7 MPa) induced by polyethylene glycol 6000 (PEG) under low (0.04 mM) and adequate (0.8 mM) K levels in the nutrient solution. Leaf samples were collected and analyzed for levels of K, ROS, kinetic activity of antioxidants enzymes and expression levels of respective genes during the stress period. The results showed that optimal K supply under osmotic stress significantly decreases ROS production and adjusts antioxidant activity, leading to the reduction of oxidative stress in the studied plants. The cultivar Milford had a lower ROS level and a better tolerance to stress compared to the cultivar Sahin-91. We conclude that optimized K supply is of great importance in mitigating ROS-related damage induced by osmotic stress, specifically in drought-sensitive barley cultivars

Greenhouse gas emissions in biogas production systems

There is growing concern that greenhouse gas (GHG) emissions during agricultural energy crop production might negate GHG emission savings. Here a study is presented evaluating two favourable biogas crops in two agro-ecological regions of Northern Germany for their productivity and GHG emissions. A 2-year field experiment was conducted at two sites with different soil type but similar temperate maritime climate. We compared silage maize which is currently the standard crop grown for biogas fermentation purposes to an alternative bioenergy crop at each site. Three forms of fertilizers/manures were given: calcium ammonium nitrate, cattle / pig slurry, biogas waste. GHG emissions of all biogas crops were strongly dominated by N2O emissions. There were very short CH4 emission events immediately after application of slurry and biogas waste. N2O flux patterns usually followed fertilizer application events in all crops and at both sites. Flux patterns indicated pronounced effects of soil moisture which was also seen as responsible for the 20–30 % higher N2O fluxes in maize compared to the other tested crops. Overall, N2O emissions at the loamy soil site were at least 3 times higher than in all crops examined at the site with sandy soil. The present study provides a very good basis for the assessment of direct emissions of greenhouse gases from relevant biogas crops in North-West Europe. It is intended to use measured and simulated data on soil moisture and the N/C inputs by fertilizer/manure application as drivers for a nitrification/denitrification module linked to a crop growth model

Optimized potassium nutrition improves plant-water-relations of barley under PEG-induced osmotic stress

Water use efficiency (WUE) of crop plants is an important plant trait for maintaining high yield in water limited areas. By influencing osmoregulation of plants, potassium (K) plays a critical role in stress avoidance and adaptation. However, whole plant physiological mechanisms modulated by K supply in respect of plant drought tolerance and water use efficiency are not well understood. In the present study, growth, development and transpiration dynamics of two barley cultivars were evaluated with and without PEG-induced osmotic stress using an automated balance system and image based leaf area determination. Experiments were conducted to study the effects of varied K supply under different osmotic stress treatments on a wide range of morphological, biochemical and physiological characteristics of barley plants such as leaf area development, daily whole plant transpiration rate (DTR), stomatal conductance (g(s)), assimilation rate (A(N)), biomass and leaf water use efficiency (WUE) as well as foliar abscisic acid (ABA) concentrations. Two barley cultivars (cv. Sahin-91 and cv. Milford) were treated with two K supply levels (0.04 and 0.8 mM K) and osmotic stress induced by polyethylene glycol 6000 (PEG) for a period of 9 days (in total 48 days experiment) in the hydroponic plant culture (non-PEG and + 20% PEG ). Without PEG, low-K supply depressed dry matter (DM) by almost 60% averaged across both cultivars. Under osmotic stress (+PEG), total leaf area was reduced by almost 70% in low-K compared to adequate-K plants. Low K concentration under PEG stress was correlated with higher ABA concentration and was correlated with lower leaf- and whole plant transpiration rate. Biomass-WUE under low K supply decreased significantly in both barley cultivars, to a greater extent in cv. Milford under osmotic stress. However, leaf-WUE was not affected by K supply in the absence of osmotic stress. It was suggested that reduced biomass-WUE in low-K treated barley plants was not related to inefficient stomatal control under K deficiency, but instead due to reduced assimilation rate. It was further hypothesized that under low K supply, a number of energy consuming activities reduce biomass-WUE, which are not distinguished by measuring leaf-WUE. This study showed that low K supply under osmotic stress increases foliar ABA concentration thereby decreasing plant transpiration

Rhizosphere processes in nitrate-rich barley soil tripled both N2O and N2 losses due to enhanced bacterial and fungal denitrification

Background and aimsPlants can directly affect nitrogen (N) transformation processes at the micro-ecological scale when soil comes into contact with roots. Due to the methodological limitations in measuring direct N2 losses in plant-soil systems, however, the effect of rhizosphere processes on N2O production and reduction to N2 has rarely been quantified.MethodsFor the first time, we developed a robotic continuous flow plant-soil incubation system (using a He+O2 + CO2) combined with N2O 15N site preference approach to examine the effect of plant root activity (barley – Hordeum vulgare L.) on: i) soil-borne N2O and N2 emissions, ii) the specific contribution of different pathways to N2O fluxes in moist soils (85% water holding capacity) receiving different inorganic N forms.ResultsOur results showed that when a nitrate-based N fertiliser was applied, the presence of plants tripled both N2O and N2 losses during the growth period but did not alter the N2O/(N2O + N2) product ratio. The 15N site preference data indicated that bacterial denitrification was the dominant source contributing to the observed N2O fluxes in both nitrate and ammonium treated soils, whereas the presence of barley increased the contribution of fungal N2O in the nitrate treated soils. During the post-harvest period, N2O and N2 emissions significantly increased in the ammonium-fertilised treatment, being more pronounced in the soil with a senescing root system.ConclusionOverall, our study showed a significant interaction between rhizosphere processes and N forms on the magnitude, patterns, and sources of soil borne N2O and N2 emissions in moist agricultural soils

Soil NO3− level and O2 availability are key factors in controlling N2O reduction to N2 following long-term liming of an acidic sandy soil

Liming of acidic soils has been suggested as a strategy to enhance N2O reduction to N2 during heterotrophic denitrification, and mitigate N2O emission from N fertilised soils. However, the mechanisms involved and possible interactions of key soil parameters (NO3− and O2) still need to be clarified. To explore to what extent soil pH controls N2O emissions and the associated N2O/(N2O + N2) product ratio in an acidic sandy soil, we set-up three sequential incubation experiments using an unlimed control (pH 4.1) and a limed soil (pH 6.9) collected from a 50-year liming experiment. Interactions between different NO3− concentrations, N forms (ammonium- and nitrate) and oxygen levels (oxic and anoxic) on the liming effect of N2O emission and reduction were tested in these two sandy soils via direct N2 and N2O measurements.Our results showed 50-year liming caused a significant increase in denitrification and soil respiration rate of the acidic sandy soil. High concentrations of NO3− in soil (>10 mM N in soil solution, equivalent to 44.9 mg N kg−1 soil) almost completely inhibited N2O reduction to N2 (>90%) regardless of the soil pH value. With decreasing NO3− application rate, N2O reduction rate increased in both soils with the effect being more pronounced in the limed soil. Complete N2O reduction to N2 in the low pH sandy soil was also observed when soil NO3− concentration decreased below 0.2 mM NO3−. Furthermore, liming evidently increased both N2O emissions and the N2O/(N2+N2O) product ratio under oxic conditions when supplied with ammonium-based fertiliser, possibly due to the coupled impact of stimulated nitrification and denitrification.Overall, our data suggest that long-term liming has the potential to both increase and decrease N2O emissions, depending on the soil NO3− level, with high soil NO3− levels overriding the assumed direct pH effect on N2O/(N2+N2O) product ratio

Isotope fractionations factors of N2O production and reduction by denitrification derived from laboratory incubation studies and modeling

Quantifying denitrification in arable soils is crucial in predicting the microbial consumption of nitrogen fertilizers as well as N2O emissions. Stable isotopologue analyses of denitrification substrates (15NNO3, 18ONO3) and products (15NN2O, 18ON2O and SPN2O =Site Preference, i.e. difference in δ15N between the central and peripheral N positions of the asymmetric N2O molecule) can help to distinguish production pathways and to identify N2O reduction to N2. However, such interpretations are often ambiguous due to insufficient knowledge on isotopic fractionation mechanisms and wide differences in isotope fractionation factors determined by various studies for N2O production and reduction. Here we present results from laboratory incubations of soils and aquifer material to determine the net isotopic effect (η of N2O production (ηNO3-N2O) and N2O reduction to N2 (ηN2O-N2) during denitrification. ηNO3-N2O for 18O, 15Nbulk and SP was obtained by anaerobic incubation of NO3- amended soils when N2O reduction was inhibited by 10 kPa acetylene. ηN2O-N2 of the respective signatures was derived by comparing treatments with and without inhibition of N2O reduction. Furthermore, we present an original approach to determine ηprod and ηred by modeling. This determination is based on simultaneous modeling of both reaction steps (N2O production and reduction) and comparison of the results with experimental data from a laboratory incubation experiment carried out under N2-free atmosphere. For two analyzed arable soils (clay and sandy loam), the isotopic fractionation factors were very consistent. For N2O production mean net isotope effects of η15NNO3-N2O ~ -41‰, ηSPNO3-N2O ~ 2‰ and η18OH2O-N2O ~ +40‰ have been found. For N2O reduction mean net isotope effects of η15NN2O-N2 ~ +1‰, ηSPN2O-N2 ~ -7‰ and η18ON2O-N2 ~ -5‰ have been found