Short-term immobilisation and crop uptake of fertiliser nitrogen applied to winter wheat: effect of date of application in spring

Previous studies on the fate of fertiliser nitrogen applied to winter wheat in temperate climates have shown that nitrogen (N) applied early, at tillering for wheat, was less efficiently taken up than N applied later in the growth cycle. We examined the extent to which the soil microbial N immobilisation varied during the wheat spring growth cycle and how microbial immobilisation and plant uptake competed for nitrogen. We set up a pulse-15N labelled field experiment in which N was applied at eight development stages from tillering (beginning of March) to anthesis (mid-June). Each application was 50 kg N ha-1 as 15N labelled urea except for the first application which was 25 kg N ha-1. The distribution of fertiliser 15N in shoots, roots, mineral and organic soil N was examined by destructive sampling 7 and 14 days after each 15N pulse. The inorganic 15N pool was almost depleted by day 14. The N uptake efficiency increased with later applications from 45% at tillering to 65% at flowering. N immobilisation was rather constant at 13–16% of N applied, whatever the date of application. The increase in plant 15N uptake resulted in an increase in the total 15N recovery in the plant-soil system (15N in soil +15N in plant), suggesting that gaseous losses were lower at the later application dates.     

Moderate exercise training does not worsen left ventricle remodeling and function in untreated severe hypertensive rats.

Exercise training and hypertension induced cardiac hypertrophy but modulate differently left ventricle (LV) function. This study set out to evaluate cardiac adaptations induced by moderate exercise training in normotensive and untreated severe hypertensive rats. Four groups of animals were studied: normotensive (Ctl) and severe hypertensive (HT) Wistar rats were assigned to be sedentary (Sed) or perform a moderate exercise training (Ex) over a 10-wk period. Severe hypertension was induced in rat by a two-kidney, one-clip model. At the end of the training period, hemodynamic parameters and LV morphology and function were assessed using catheterism and conventional pulsed Doppler echocardiography. LV histology was performed to study fibrosis infiltrations. Severe hypertension increased systolic blood pressure to 202 +/- 9 mmHg and induced pathological hypertrophy (LV hypertrophy index was 0.34 +/- 0.02 vs. 0.44 +/- 0.02 in Ctl-Sed and HT-Sed groups, respectively) with LV relaxation alteration (early-to-atrial wave ratio = 2.02 +/- 0.11 vs. 1.63 +/- 0.12). Blood pressure was not altered by exercise training, but arterial stiffness was reduced in trained hypertensive rats (pulse pressure was 75 +/- 7 vs. 62 +/- 3 mmHg in HT-Sed and HT-Ex groups, respectively). Exercise training induced eccentric hypertrophy in both Ex groups by increasing LV cavity without alteration of LV systolic function. However, LV hypertrophy index was significantly decreased in normotensive rats only (0.34 +/- 0.02 vs. 0.30 +/- 0.02 in Ctl-Sed and Ctl-Ex groups, respectively). Moreover, exercise training improved LV passive filling in Ctl-Ex rats but not in Ht-Ex rats. In this study, exercise training did not reduce blood pressure and induced an additional physiological hypertrophy in untreated HT rats, which was slightly blunted when compared with Ctl rats. However, cardiac function was not worsened by exercise training.     

The partitioning of fertilizer-N between soil and crop: Comparison of ammonium and nitrate applications

Field experiments were carried out in 1987 on winter wheat crops grown on three types of soil. ¹⁵N-labelled urea, ¹⁵NH₄NO₃ or NH₄ ¹⁵NO₃ (80 kg N ha^-1) was applied at tillering. The soils (chalky soil, hydromorphic loamy soil, sandy clay soil) were chosen to obtain a range of nitrogen dynamics, particularly nitrification. Soil microbial N immobilization and crop N uptake were measured at five dates. Shortly after fertilizer application (0–26 days), the amount of N immobilized in soil were markedly higher with labelled urea or ammonium than that with nitrate in all soils. During the same period, crop ¹⁵N uptake occurred preferentially at the expense of nitrate. Nitrification differed little between soils, the rates were 2.0 to 4.7 kg N ha^-1 day^-1 at 9°C daily mean temperature. The differences in immobilization and uptake had almost disappeared at flowering and harvest. ¹⁵N recovery in soil and crop varied between 50 and 100%. Gaseous losses probably occurred by volatilization in the chalky soil and denitrification in the hydromorphic loamy soil. These losses affected the NH₄ ⁺ and NO₃ ^- pools differently and determined the partitioning of fertilizer-N between immobilization and absorption.     

Implications of productivity and nutrient requirements on greenhouse gas balance of annual and perennial bioenergy crops

Biomass from dedicated crops is expected to contribute significantly to the replacement of fossil resources. However, sustainable bioenergy cropping systems must provide high biomass production and low environmental impacts. This study aimed at quantifying biomass production, nutrient removal, expected ethanol production, and greenhouse gas (GHG) balance of six bioenergy crops: Miscanthus × giganteus, switchgrass, fescue, alfalfa, triticale, and fiber sorghum. Biomass production and N, P, K balances (input‐output) were measured during 4 years in a long‐term experiment, which included two nitrogen fertilization treatments. These results were used to calculate a posteriori ‘optimized’ fertilization practices, which would ensure a sustainable production with a nil balance of nutrients. A modified version of the cost/benefit approach proposed by Crutzen et al. (2008), comparing the GHG emissions resulting from N‐P‐K fertilization of bioenergy crops and the GHG emissions saved by replacing fossil fuel, was applied to these ‘optimized’ situations. Biomass production varied among crops between 10.0 (fescue) and 26.9 t DM ha^?1 yr^?1 (miscanthus harvested early) and the expected ethanol production between 1.3 (alfalfa) and 6.1 t ha^?1 yr^?1 (miscanthus harvested early). The cost/benefit ratio ranged from 0.10 (miscanthus harvested late) to 0.71 (fescue); it was closely correlated with the N/C ratio of the harvested biomass, except for alfalfa. The amount of saved CO₂ emissions varied from 1.0 (fescue) to 8.6 t CO₂eq ha^?1 yr^?1 (miscanthus harvested early or late). Due to its high biomass production, miscanthus was able to combine a high production of ethanol and a large saving of CO₂ emissions. Miscanthus and switchgrass harvested late gave the best compromise between low N‐P‐K requirements, high GHG saving per unit of biomass, and high productivity per hectare.     

Quality and decomposition in soil of rhizome, root and senescent leaf from Miscanthus x giganteus, as affected by harvest date and N fertilization

To predict the environmental benefits of energy crop production and use, the nature and fate of biomass residues in the soil need to be quantified. Our objective was to quantify Miscanthus x giganteus biomass recycling to soil and to assess how harvesting time and N fertilization affect their characteristics and subsequent biodegradability. The quantification of aerial and belowground biomass and their sampling were performed on 2- and 3-year-old Miscanthus stands, either fertilized with 120 kg N ha^?1 year^?1 or not fertilized, in autumn (maximal biomass production) and winter (maturity). Plant biomass was chemically characterized (total sugars, Klason lignin, C/N) and incubated in optimum decomposition conditions (15°C, ?80 kPa) for 263 days, for C and N mineralization. Accumulation of carbon in rhizomes and roots was 7.5 to 10 t C ha^?1 and represented about 50% of total plant biomass C. Senescent leaves represented about 1.5 t C ha^?1 year^?1. All residues, especially the roots, had high lignin contents, while the rhizomes also had a high soluble content due to their nutrient storage function. The C mineralization rates were closely related to the chemical characteristics of the residue, higher sugar and lower lignin contents leading to faster decomposition, as observed for rhizomes.     

Integrated Control of Nitrate Uptake by Crop Growth Rate and Soil Nitrate Availability under Field Conditions

There is still disagreement about whether crop growth rate orsoil nitrate concentration control nitrogen absorption by cropsunder field conditions. The influence of these factors on thecontrol of N uptake rate was examined in the absence of waterstress, using data on dry matter production, above-ground nitrogenaccumulation and soil nitrate concentration from several N-fertilizerexperiments on winter wheat, winter oilseed rape and maize.The results confirmed that crops can accumulate nitrogen farin excess of the ‘critical dilution curve’, whichdefines the minimum amount of nitrogen needed for maximal growthrate: the N concentration in plants could exceed the criticalN concentration by 70 to 80% for the three species studied.The nitrate uptake rate index (NUI) was calculated as the ratioof actual and critical N uptake rates, at intervals of 1 week.NUI varied with nitrate concentration in the 0–30 cm soillayer according to a Michaelis–Menten equation (with oneor two components). This response was compared with the kineticsof saturation of the nitrate uptake systems: the high affinitytransport system (HATS) and the low affinity transport system(LATS). As a result, it is proposed that there is a criticalN dilution curve delimiting two domains of N use by plants.This is linked to the two nitrate transport systems, with HATSworking at low nitrate concentrations, below the critical dilutioncurve, and LATS at high nitrate concentrations, above the curve.NUI provides another method for calculating the actual nitrateuptake rate, which depends on the maximal crop growth rate (withoutN deficiency) and on the external nitrate concentration. Copyright2000 Annals of Botany Company Nitrate, uptake rate, growth rate, wheat, maize, oilseed rape, soil N availability     

Discovery of (S,E)-3-(2-fluorophenyl)-N-(1-(3-(pyridin-3-yloxy)phenyl)ethyl)-acrylamide as a potent and efficacious KCNQ2 (Kv7.2) opener for the treatment of neuropathic pain

Acrylamide (S)-6, a potent and efficacious KCNQ2 (Kv7.2) opener, demonstrated significant activity in two models of neuropathic pain and in the formalin test, suggesting that KCNQ2 openers may be useful in the treatment of neuropathic pain including diabetic neuropathy.     

Determination of a Critical Nitrogen Dilution Curve for Winter Wheat Crops

A set of N-fertilization field experiments was used to determinethe 'critical nitrogen concentration', i.e, the minimal concentrationof total N in shoots that produced the maximum aerial dry matter,at a given time and field situation. A unique 'critical nitrogendilution curve' was obtained by plotting these concentrationsN_ct (% DM) vs. accumulated shoot biomass DM (t ha^-1). It couldbe described by the equation: N_ct = 5·35DM^-0·442 when shoot biomass was between 1·55 and 12 t ha^-1. Anexcellent fit was obtained between model and data (r² = 0·98,15 d.f.). A very close relationship was found using reducedN instead of total N, because the nitrate concentrations inshoots corresponding to critical points were small. The criticalcurve was rather close to those reported by Greenwood et al.(1990) for C₃ plants. However, this equation did not apply whenshoot biomass was less than 1·55 t ha^-1. In this case,the critical N concentration was independent of shoot biomass:the constant critical value N_ct = 4·4% is suggested forreduced-N. The model was validated in all the experimental situations,in spite of large differences in growth rate, cultivar, soiland climatic conditions; shoot biomass varying from 0·2to 14 t ha^-1. Plant N concentration was found to vary by a factor of fourat a given shoot biomass level. In the heavily fertilized treatments,shoot N concentration could be 60% higher than the criticalconcentration. Most (on average 80%) of the extra N accumulatedwas in the form of reduced N. The proportion of nitrate to totalN in shoot mainly depended on the crop stage of development.It was independent of the nitrogen nutrition level.Copyright1994, 1999 Academic Press Winter wheat, Triticum aestivum, arable crops, plant N concentration, aerial biomass, critical nitrogen, dilution curve, fertilization, reduced N, nitrate     

Doppler tissue imaging in assessment of pulmonary hypertension-induced right ventricle dysfunction

We aimed to assess the accuracy of Doppler tissue imaging (DTI) in detecting right ventricle (RV) dysfunction and electromechanical coupling alteration following pulmonary hypertension (PHT) in rat. PHT was induced by chronic hypoxia exposure (hypoxic PHT) or monocrotaline treatment (monocrotaline PHT). In both PHT models, we observed transparietal RV pressure increase and remodeling, including hypertrophy and dilation. Conventional echocardiography provided evidence for pulmonary outflow impairment with midsystolic notch and acceleration time decrease in PHT groups (21.7 +/- 1.6 and 13.2 +/- 2.9 ms in hypoxic and monocrotaline PHT groups vs. 28.1 +/- 1.0 ms in control). RV shortening fraction was decreased in the monocrotaline PHT group compared with the hypoxic PHT and control groups. Combining conventional Doppler and DTI was more helpful to detect RV diastolic dysfunction in the monocrotaline PHT group (E/Ea ratio = 17.0 +/- 1.4) compared with the hypoxic PHT and control groups (11.5 +/- 0.7 and 10.2 +/- 0.4, respectively). Tei index measured using DTI highlighted global RV dysfunction in the monocrotaline PHT group (1.36 +/- 0.24 vs. 0.92 +/- 0.05 and 0.86 +/- 0.05 in the hypoxic PHT and control groups, respectively). Q-Sm time measured from the onset of Q wave to the onset of DTI Sm wave was increased in both PHT groups. PHT-induced electromechanical coupling alteration was confirmed by in vitro activation-contraction delay measurements on isolated RV papillary muscle, and both Q-Sm time and activation-contraction delay were correlated with PHT severity. We demonstrated that Q-Sm time measured in DTI was an easily and convenient index to detect early RV electromechanical coupling alteration in both moderate and severe PHT.