极化型静电分级机设计理论

通过极化型静电分级机的结构介绍及种子在静电场中的运动学特性分析,提出了有关种子和静电场的假说,建立了种子在静电场中的运动方程。通过对种子在静电场中的运动特性研究,发现种子的极化力质比是影响极化型静电分级机分离质量的重要因素,是设计极化型静电分级机的关键参数;应通过大量的试验来建立种子极化力质比数据库,满足极化型静电分级机设计的需求。     

长期施肥对棕壤氧化还原酶活性和动力学特征的影响

土壤质量与土壤的生物学性质密切相关,施肥制度对土壤生物学特性的影响研究对土壤质量管理具有重要的意义。本文以沈阳农业大学长期肥料定位试验为基地,研究长期不同施肥制度对土壤理化性质,过氧化氢酶、脱氢酶活性和动力学特征的影响。主要研究结果:施用化肥、有机肥配施化肥降低土壤pH值,提高4种土壤全量养分(全C、全P、全S、全N)含量,有机肥配施化肥提高土壤速效N含量;低量化肥配施有机肥显著提高土壤过氧化氢酶活性及Vmax/Km值和Vmax值,低量化肥配施有机肥显著提高脱氢酶活性及Vmax/Km值,降低脱氢酶Km值。本文的研究表明,合理的化肥施用量及配施有机肥是提高土壤生物学活性的有效手段。     

Role of nitrite and nitric oxide in the processes of nitrification and denitrification in soil: Results from N tracer experiments

Recent research has proven soil nitrite to be a key element in understanding N-gas production (NO, N₂O, N₂) in soils. NO is widely accepted to be an obligatory intermediate of N₂O formation in the denitrification pathway. However, studies with native soils could not confirm NO as a N₂O precursor, and field experiments mainly revealed ammonium nitrification as the source of NO. The hypothesis was constructed, that the limited diffusion of NO in soil is the reason for this contradiction. To test this diffusion limitation hypothesis and to verify nitrite and NO as free intermediates in native soils we conducted through-flow (He/O₂ atmosphere) ¹⁵N tracer experiments using black earth soil in an experimental set up free of diffusion limitation. All of the three relevant inorganic N soil pools (ammonium, nitrite, nitrate) were ¹⁵N labelled in separate incubation experiments lasting 81 h based on the kinetic isotope method. During the experiments the partial pressure of O₂ was decreased in four steps from 20% to about 0%. The net NO emission increased up to 3.7 μg N kg⁻¹ h⁻¹ with decreasing O₂ partial pressure. Due to the special experimental set up with little to no obstructions of gas diffusion, only very low N₂O emission could be observed. As expected the content of the substrates ammonium, nitrate and nitrite remained almost constant over the incubation time. The ¹⁵N abundance of nitrite revealed high turnover rates. The contribution of nitrification of ammonium to the total nitrite production was approx. 88% under strong aerobic soil conditions but quickly decreased to zero with declining O₂ partial pressure. It is remarkable that already under the high partial pressure of 20% O₂ 12 % of nitrite is generated by nitrate denitrification, and under strict anaerobic conditions it increases to 100%. Nitrite is present in two separate endogenous pools at least, each one fed by the nitrification of ammonium or the denitrification of nitrate. The experiments clearly revealed that nitrite is almost 100% the direct precursor of NO formation under anaerobic as well as aerobic conditions. Emitted N₂O only originated to about 100% from NO under strict anaerobic conditions (0-0.2% O₂), providing evidence that NO is a free intermediate of N₂O formation by denitrification. To the best of our knowledge this is the first time that NO has been detected in a native soil as a free intermediate product of N₂O formation at denitrification. These results clearly verify the “diffusion limitation” hypothesis.     

Managing biological variation in skin background colour along the postharvest chain of ‘Jonagold’ apples

Skin background colour is an important quality aspect in the grading of ‘Jonagold’ apples, with consumers usually preferring fruit with a green background colour. However, apple handlers are usually faced with large fruit-to-fruit variability of background colour within a population of fruit. In this study, a stochastic modelling approach was used to describe how the initial fruit-to-fruit variability in the background colour of ‘Jonagold’ apples present at harvest, propagates throughout the postharvest chain. Two hundred and twenty ‘Jonagold’ apple fruit were harvested and stored at 1 °C or 4 °C, under different controlled atmosphere (CA) conditions for 6 months, followed by 2 weeks exposure to shelf-life conditions, during which the background colour and ethylene production of the individual fruit were measured. A kinetic model was developed to describe the postharvest loss of skin greenness, by assuming that the loss was principally due to chlorophyll breakdown, the rate of which was dependent on the endogenous ethylene concentration. Stochastic model parameters were identified, and by treating these parameters as fruit-specific, the model could account for more than 95% of the variability of the data. By treating the stochastic model parameters as random factors, the Monte Carlo method was used to model and describe the propagation of the fruit-to-fruit variability of the background colour within a population of fruit. The model developed in this study might allow better management of variability in quality along the postharvest chain, by predicting how the initial fruit-to-fruit variability within a batch of apples will propagate throughout the postharvest chain, as a function of storage and shelf-life conditions.     

Oxidation of diazinon and malathion by myeloperoxidase

The aim of the work was to investigate the in vitro oxidation of diazinon and malathion, organophosphorous pesticides (OPs) containing phosphorthioate group, catalyzed by enzyme myeloperoxidase (MPO). The oxidation was performed in the presence of hydrogen peroxide. The products were identified as oxon derivatives (phosphates), where the sulfur atom from thioate group was substituted by an oxygen atom. No hydrolysis products were detected after enzyme - induced oxidation. The oxidation efficiency was controlled using acethylcholinesterase (AChE) bioassay for determination of oxon derivatives concentration. The influence of OPs concentration, incubation time of OPs with MPO, as well as MPO concentration on the yield of oxo forms was investigated. Kinetic constants of MPO in oxidation of malathion and diazinon were estimated. The maximum concentration of oxo forms was achieved after 10 min incubation of OPs in 50 mM phosphate buffer (pH 6.0) with 100 nM MPO.     

Release of sulphate-sulphur, potassium, calcium and magnesium from spent mushroom compost under field conditions

 The release of SO₄ ^2–-S, K⁺, Ca²⁺ and Mg²⁺ from soil amended with spent mushroom compost (SMC), a byproduct of mushroom production, was measured in leachate from field lysimeters for 30 weeks. Rates of application were 0 and 80 t ha^–1 moist SMC. The SMC contained 1.7% K, 6.5% Ca, 0.4% Mg and 1.2% S (of which 87% is SO₄ ^2–-S), and has a C : S ratio of 26. The break-through curves of ion leaching were polymodal indicating the preservation of soil structure in the lysimeters and its influence on leaching. SO₄ ^2–-S release from SMC was rapid (first-order exponential) and was very similar to the release from a laboratory incubation. The release of K⁺, Ca²⁺ and Mg²⁺ was described using first/zero-order models which were also used to describe their release in the laboratory. The rate and amount of Ca²⁺ release was similar in the field and laboratory, but the amount of K⁺ (and to a lesser extent Mg²⁺) release was less in the field than in the laboratory. Recoveries of SMC applied nutrients in leachate were 80% of S (263 kg ha^–1), 3% of K (14 kg ha^–1), 16% of Ca (284 kg ha^–1) and 37% of Mg (40 kg ha^–1). Little if any S was mineralised. Using SMC could provide plants with S, K, Ca and Mg but there is potential for SO₄ ^2–-S losses via leaching. Received: 7 April 1999     

Gymnastic Training of Hippotherapy Horses Benefits Gait Quality When Ridden by Riders with Different Body Weights

The objective was to evaluate the effects of gymnastic training on stride characteristics of walk and trot in therapy horses carrying riders of different weights. Eighteen horses used for therapeutic riding 5 days/week were randomly divided into 2 groups. Nine horses performed gymnastic (GYM) exercises after therapeutic riding on 4 days/week for 3 months, 9 horses did no additional exercises (SED). On days 0 and 90, an inertial sensor mounted to the girth on the ventral midline was used to evaluate stride characteristics when horses were ridden at walk (1.3 m/second) and trot (3.0 m/second) by able-bodied riders representing rider: horse body weight ratios (BWRs) 15%, 20%, and 25%. On day 0, the measured variables did not differ significantly between sedentary (SED) and GYM groups, but on day 90, the following statistically significant results were found: GYM-trained horses had higher regularity for all BWRs at walk and 15% and 20% BWRs at trot. Higher stride symmetry was found in GYM-trained horses carrying 25% BWRs at walk and all rider weights at trot. Dorsoventral displacement was higher in GYM-trained horses when carrying 20% and 25% BWRs at walk and 25% BWRs at trot. Dorsoventral power was lower in SED-trained versus GYM-trained horses carrying 15% BWR at walk and 20% BWR at trot. A more regular and symmetrical stride with a larger range of dorsoventral trunk motion is likely to provide a better therapeutic riding experience.     

酪氨酸酶的提取及其催化活性研究

［目的］进一步研究影响酪氨酸催化活性的因素，减少黑色素在生物体内的生成。［方法］以pH值7.2的Na2HPO4-HCl缓冲溶液为体系, 用分光光度计在480 nm处测定马铃薯提取液的吸光度,以吸光度对时间的变化率（ΔA/Δt） 为反应速率，建立多巴溶液的转换动力学曲线，从而可计算出酪氨酸酶的活性。［结果］结果显示，在480 nm波长下, 以pH值7.2的Na2HPO4-HCl缓冲溶液为体系，对测定体系干扰小, 所测数据波动小,酪氨酸酶的活性稳定性高，为进一步确定和研究影响酪氨酸酶活性的因素提供了理论依据。［结论］ 试验以缓冲溶液为底物研究和测定酪氨酸酶的催化活性，准确度高，效果佳。     

Maturity assessment at harvest and prediction of softening in a late maturing nectarine cultivar after cold storage

The absorption coefficient μ_a measured at 670 nm in fruit pulp at harvest by time-resolved reflectance spectroscopy (TRS) has been shown to be a good maturity index for early nectarine cultivars. By including individual fruit maturity as a biological shift factor (BSF) into a kinetic model for softening it is possible to select fruit with different shelf-life potential. The BSF approach combined with TRS measurement and kinetic modeling of firmness was applied to a late maturing nectarine cultivar (‘Morsiani 90’), ripened at 20 °C after harvest or after storage at 0 °C and 4 °C, the latter conditions inducing chilling injury. At harvest the absorption coefficient μ_a had low values and low variability, indicating advanced maturity, while firmness was similar to that of early cultivars. The softening model took into account these differences, showing parameters similar to those of the early cultivars with the exception of the softening rate which was 2-6 times lower, indicating a slower softening in ‘Morsiani 90’ fruit. Decay of μ_a at 20 °C was also slower. Softening continued during storage at 4 °C, but not at 0 °C. After storage at 0 °C softening was resumed similarly to non-stored fruit, but with much variability. Fruit stored at 4 °C, which showed chilling injury, had a softening rate at 20 °C significantly higher than that of 0 °C fruit. It is suggested that the same changes in cell wall metabolism which induce the appearance of chilling injury also affect firmness and increase softening rate.     

土壤非交换性钾释放动力学特征及其生物

采用生物耗竭法和0.2mol L-1的NaTPB化学浸提法,利用不同动力学方程对我国8种主要土壤非交换性钾的释钾特性及其生物有效性进行定量评估。结果表明,供试土壤非交换性钾释放分为快速释放和稳定释放两个阶段,一级动力学方程、Elovich 方程、双常数曲线方程和抛物线扩散方程均能描述土壤非交换性钾的释放过程。根据双常数方程中的参数（a）所表征的土壤非交换性钾释放速率常数,供试8种土壤的释钾能力按取土地区存在着自西向东、自北向南渐减的趋势。盆栽试验中,在累积释钾量高且释放速率快的土壤上,黑麦草累积生物量、累积吸钾量和相对含钾量较高,表现出强的供钾能力;与此相反,累积释放量低且释放速率慢的土壤上,黑麦草各项指标偏低,供钾能力较弱。以黑麦草钾素丰缺临界值34.00 mg kg-1 DW-1和土壤非交换性钾释放速率396.32 mg kg-1 h-1作为评价指标,供试8种土壤中,仅取自新疆石河子、陕西常武和黑龙江哈尔滨地区的土壤在短期不施用钾肥的情况下能保证黑麦草丰产且不出现缺钾症状。因此,为了维持土壤钾素平衡和保证作物高产稳产,在我国西北、东北地区耕地土壤中应加强秸秆的循环利用,而在华中和华东地区则需增施钾肥和有机肥。