压力、温度对穿心莲内酯超临界CO2萃取-结晶的影响

以穿心莲浸膏为原料，进行了穿心莲内酯的超临界CO₂萃取结晶分离纯化。考察了单因素参数压力、温度对穿心莲内酯纯度、结晶量等的影响。结果表明：超临界CO₂萃取结晶穿心莲内酯的纯度在结晶板上呈梯度分布；在25 MPa以下，压力升高，结晶板上部晶体纯度升高，而结晶量先增后减；在结晶板下部穿心莲内酯的纯度和结晶量都是先升高后降低；温度在一定范围内能提高晶体纯度，且有利于缩短萃取结晶时间。     

响应曲面法建立超临界CO2萃取结晶穿心莲内酯工艺模型

以穿心莲内酯含量为30%的穿心莲浸膏为试验原料，采用响应曲面分析法(Response Surface Methodology，RSM)建立了超临界CO₂萃取结晶穿心莲内酯结晶率的二次多项数学模型，验证了数学模型的有效性，并探讨了萃取结晶压力、温度、时间对结晶率的作用规律。根据该模型进行了工艺参数的优选，以结晶率为指标，试验所得穿心莲内酯超临界CO₂萃取结晶优化工艺条件为：压力20.88 MPa，温度50.27℃，时间97.02 min，该条件下结晶率高达74.77%。     

穿心莲内酯超临界CO2重结晶工艺初探

采用单因素实验法探讨超临界CO2重结晶压力、温度、时间对穿心莲内酯的纯度和结晶率的影响,并借助扫描电镜进行晶体形貌考察,利用高效液相色谱仪进行纯度检测.结果表明,采用超临界CO2重结晶技术得到的穿心莲内酯晶体形貌更加细小,并呈絮状分布在结晶板上;选择较佳纯化工艺参数为重结晶压力14 MPa,温度55℃,时间60 min,CO2流量20 L/min时,得到的穿心莲内酯纯度达90%以上,结晶率超过45%.     

夹带剂对超临界CO2萃取结晶穿心莲内酯的影响

以穿心莲内酯粗品和高纯品(纯度分别为30%和95%)为原料，采用超临界CO₂萃取结晶法，考察了乙醇、丙酮、异丙醇与乙酸乙酯四种夹带剂对超临界CO₂萃取结晶穿心莲内酯的结晶率、纯度、晶型和形貌等的作用规律。结果：因乙酸乙酯分离纯化综合效果较好，且既能与前处理工序中选择的浸提溶剂相统一，减少采用多种溶剂存在的污染，又能保持晶体优良晶型和结晶品质，所以优先选择了乙酸乙酯为夹带剂。     

超临界CO2萃取万寿菊花中叶黄素的研究

采用超临界CO₂萃取技术,研究了从万寿菊花中萃取叶黄素的工艺条件。对影响超临界CO₂萃取叶黄素的各种因素,包括分离参数、原料含水率、粉碎粒径，超临界萃取温度、压力、流速、时间等因素进行了考察,得到较佳的萃取工艺条件为:原料含水率10.92％，粒径40目，萃取温度60℃，压力30 MPa，CO₂流速15 L/h，分离釜Ⅰ温度40℃，压力6 MPa，分离釜Ⅱ温度20℃，时间为6 h。     

压力、温度对穿心莲内酯超临界CO2萃取-结晶的影响

以穿心莲浸膏为原料,进行了穿心莲内酯的超临界CO2萃取结晶分离纯化.考察了单因素参数压力、温度对穿心莲内酯纯度、结晶量等的影响.结果表明:超临界CO2萃取结晶穿心莲内酯的纯度在结晶板上呈梯度分布;在25 MPa以下,压力升高,结晶板上部晶体纯度升高,而结晶量先增后减;在结晶板下部穿心莲内酯的纯度和结晶量都是先升高后降低;温度在一定范围内能提高晶体纯度,且有利于缩短萃取结晶时间.     

超临界CO2萃取大蒜精油及油树脂的研究

研究了大蒜精油及油树脂的超临界CO₂提取工艺，探讨了粒度，萃取及分离的温度、压力和时间对各萃取率的影响，建立了萃取温度、压力与各萃取率的数学模型。确定了超临界CO₂同时提取大蒜精油及油树脂的优化工艺条件。     

超临界CO2连续浓缩鱼油EPA和DHA的研究

为了克服鱼油有效组分超临界CO₂间歇萃取方法的缺点，设计建造了超临界CO₂在内径14 mm、填料高1.8 m的填料塔中连续萃取浓缩鱼油有效组分的流程。根据单因素试验的结果，对工艺参数进行优化。设计了4因素3水平并考虑部分交互作用的正交试验方案，以综合指标进行评价，得到了优化工艺参数为：填料塔压为12.5 MPa；CO₂流量为5L/min；鱼油进料流量为0.8 mL/min；塔的温度分布为40～85℃。经方差分析得知，温度分布的影响对综合指标高度显著，鱼油进料流量对综合指标的影响显著，试验范围内的压力、CO₂流量、压力和温度分布交互作用、温度分布和CO₂流量交互作用以及压力和CO₂流量交互作用对综合指标没有显著影响。     

超声强化超临界CO2萃取人参皂苷的研究

为了探讨超声波对超临界CO₂萃取(SCE)的影响，考察了在不同萃取温度、萃取压力、萃取时间和流体流量下，有、无超声时超临界CO₂萃取人参皂苷的萃取率。试验结果发现，超声强化超临界CO₂萃取(USCE)的合适萃取温度比没加超声(SCE)时的低10℃；在各自合适的萃取压力下，USCE的皂苷萃取率是SCE的1.64倍；CO₂流体的流量大更有利于USCE。在SCE中，超声的加入能明显提高产物的萃取率和生产效率，降低生产能耗和节     

响应曲面法建立超临界CO2萃取结晶穿心莲内酯工艺模型

以穿心莲内酯含量为30%的穿心莲浸膏为试验原料,采用响应曲面分析法(Response Surface Methodology,RSM)建立了超临界CO2萃取结晶穿心莲内酯结晶率的二次多项数学模型,验证了数学模型的有效性,并探讨了萃取结晶压力、温度、时间对结晶率的作用规律.根据该模型进行了工艺参数的优选,以结晶率为指标,试验所得穿心莲内酯超临界CO2萃取结晶优化工艺条件为:压力20.88 MPa,温度50.27℃,时间97.02 min,该条件下结晶率高达74.77%.     

氰在土壤中的吸附与转化

氰(C2N2)是一种具有替代溴甲烷潜力的新熏蒸剂,明确C2N2在土壤中的吸附与转化行为对C2N2的安全应用具有重要的意义.利用静态法研究了C2N2在土壤中的吸附与转化过程,土壤对C2N2的吸附速率与土壤的理化性质有关,受环境温度、土壤含水量和土壤生物的影响较少,与熏蒸浓度无关.采用气相色谱(GC)和流动注射分析仪(FIA)测定了土壤对C2N2的吸附率和C2N2在土壤中的可能转化产物.结果表明,土壤对C2N2的吸附能力很强,熏蒸2h吸附率在75％以上,熏蒸24 h吸附率在98％以上,并可快速转化为HCN、NH4+和NO3-.其中,大约20％的C2N2转化为NH4+和NO3-,13％的C2N2转化为HCN.熏蒸48 h未检测到NO2-.HCN在土壤中不稳定,可进一步转化为其他含氮化合物.     

Denitrification potential in a grassland subsoil: effect of carbon substrates

We examined the potential of a subsoil to denitrify nitrate under optimal anaerobic conditions in a laboratory-based incubation when supplied with a range of C substrates of increasing recalcitrance. Both topsoil and its associated subsoil were supplied with nitrate and either glucose, starch or cellulose. Microbial respiration and the evolution of N₂O and N₂ were measured. The subsoil supported low amounts of microbial activity and responded only to the glucose treatment; with less than one-fifth of the N₂O production measured in the top soil. Overall, our findings demonstrated that the denitrification potential of this particular subsoil is relatively low and that only simple carbohydrates could be utilised readily by the resident microorganisms.     

Sulfur dioxide inhibition of photosynthesis at different CO2 and O2 concentrations in relation to photorespiration

The mechanism of SO₂ inhibition of photosynthesis in intact leaves of tomato and maze was studied to evaluate SO₂ inhibition of photorespiration. Leaf tissues were fumigated with SO₂ under photorespiratory (low CO, and/or high O, concentrations) and non-photo-respiratory conditions. When tomato leaf disks were fumigated with 10 ppm SO₂ at 2, 21 and 100° o O., SO₂ inhibited photosynthesis at 2% O₂ in the same degrees as at 21% O₂. SO₂ inhibition of photosynthesis was depressed at higher CO₂ concentrations when the disks were fumigated with SO₂ at different CO₂ concentrations. High CO₂ concentrations also reduced the photosynthesis inhibition of maize leaf disks. These results suggest that SO₂ inhibits photosynthesis through other mechanisms than photorespiration inhibition and confirm the view that SO₂ competes with CO₂ for the carboxylating enzymes in photosynthesis     

Availability and extractability of soil manganese in a liming experiment

Abstract

The availability of soil Mn to corn in relation to extractability of soil Mn by EDTA, Mg(NO₃)₂, CH₃COONH₄, hydroquinone, H₃PO₄, and NH₄H₂PO₄ as affected by liming was evaluated under field conditions on a single soil type. EDTA, Mg(NO₃)₂ and CH₃COONH₄‐extractable Mn were related inversely to available Mn. No useful relationships were found between hydroquinone, H₃PO₄, and NH₄H₂PO₄‐extractable soil Mn and Mn uptake by sweet corn.     

Developmental patterns of lamellae and stroma fractions of chloroplasts in rice plants

On examining the changes in lamellae and stroma nitrogen during leaf development, it is demonstrated that the lamellae and stroma fractions ofrice chloroplasts develop in quite different ways. In the case of stroma, the stroma materials existing in the leaf section which has just emerged from a leaf sheath are quite limited and the major part of this fraction is derived from the successive protein synthesis, i.e., the synthesis of this fraction was markedly increased during leaf expansion. This developmental pattern of the stroma coincided with the changes in the high-molecular-weight water soluble leaf protein, which seemed to be mainly composed of Fraction I protein. A rapid increase in stroma nitrogen was found to be a major cause for an increase in the leaf nitrogen content during leaf development.

On the other hand, the developmental pattern of the lamellae fraction was characterized by the fact that a considerable amount of this fraction had already been prepared when a leaf emerged from a leaf sheath and thereafter, no outstanding increase was seen compared to that of the stroma. This developmental pattern of the lamellae fraction resulted in a lowering of the proportion of lamellae nitrogen to the total leaf nitrogen during leaf development.

A great change in the lamellae-stroma composition of chloroplasts was observed. The proportion of stroma nitrogen to the total chloroplast nitrogen tended to increase as a leaf develops. Since the developmental stage varied according to the regions of a leaf, variation of the lamellaestroma composition was seen even within a leaf, i.e., the proportion of stroma nitrogen increased from base to tip.

In order to compare the synthetic rate of chlorophyll with those of the stroma and lamellae fractions, the changes in the ratios of stroma nitrogen/chlorophyll and lamellae nitrogen/chlorophyll were examined. The lamellae nitrogen/chlorophyll ratio decreased as a leaf developed, whereas the stroma nitrogen/chlorophyll ratio increased. Then the synthetic rates of these fractions during leaf development turned out to be of the same order as the stroma fraction, chlorophyll, lamellae fraction.     

Factors regulating acetylene reduction assay for measuring heterotrophic nitrogen fixation in water-logged soils

In the C₂H₂-C₂H₄ assay for measurement of heterotrophic N₂ fixation in water-logged soils, the diffusion of C₂H₂ into the soil and the recovery of C₂H₄ from it are critical factors regulating the assay result. To establish an C₂H₂-C₂H₄ assay technique suitable for waterlogged soils, the C₂H₂-reducing activities (ARA), assayed by varying the method of assay gas filling, the pC₂H₂ of the assay gas, the duration of assay incubation and of soil vibration before the gas sampling, were compared.

A maximum ARA was measured when the following set of procedures were applied to the soil sample in assay flasks: 1) a 4-fold repetition of I-min evacuation under 0.01 atmospheric pressure and the subsequent I-min filling under 1 atmospheric pressure with assay gas at pC₂H₂ of 0.1 atm, 2) an assay incubation for 3 hr, and 3) a sampling of an aliquot of the headspace gas after strongly vibrating the flask for 1 min.

The ARA measured by this technique was several times larger than those measured by the techniques hitherto applied, and corresponded to an almost 80% of the V _max of the sample. This technique was, therefore, proposed for the assay of heterotrophic N₂ fixation in waterlogged soils.

A striking depression of ARA in the soil sample prepared with agitation indicated that a microbial ecosystem established in the soil should be kept as undisturbed as possible throughout the C₂H₂-C₂H₄ assay.     

CO2, CH4 and N2O fluxes of upland black spruce (Picea mariana) forest soils after forest fires of different intensity in interior Alaska

Abstract

Forest fires can change the greenhouse gase (GHG) flux of borea forest soils. We measured carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) fluxes with different burn histories in black spruce (Picea mariana) stands in interior Alaska. The control forest (CF) burned in 1920; partially burned (PB) in 1999; and severely burned (SB1 and SB2) in 2004. The thickness of the organic layer was 22 ± 6 cm at CF, 28 ± 10 cm at PB, 12 ± 6 cm at SB1 and 4 ± 2 cm at SB2. The mean soil temperature during CO₂ flux measurement was 8.9 ± 3.1, 6.4 ± 2.1, 5.9 ± 3.4 and 5.0 ± 2.4°C at SB2, SB1, PB and CF, respectively, and differed significantly among the sites (P < 0.01). The mean CO₂ flux was highest at PB (128 ± 85 mg CO₂-C m^?2 h^?1) and lowest at SB1 (47 ± 19 mg CO₂-C m^?2 h^?1) (P < 0.01), and within each site it was positively correlated with soil temperature (P < 0.01). The CO₂ flux at SB2 was lower than that at CF when the soil temperature was high. We attributed the low CO₂ flux at SB1 and SB2 to low root respiration and organic matter decomposition rates due to the 2004 fire. The CH₄ uptake rate was highest at SB1 [–91 ± 21 μg CH₄-C m^?2 h^?1] (P < 0.01) and positively correlated with soil temperature (P < 0.01) but not soil moisture. The CH₄ uptake rate increased with increasing soil temperature because methanotroph activity increased. The N₂O flux was highest [3.6 ± 4.7 μg N₂O-N m^?2 h^?1] at PB (P < 0.01). Our findings suggest that the soil temperature and moisture are important factors of GHG dynamics in forest soils with different fire history.     

Flow-microcalorimetry measurements of aerobic and anaerobic soil microbial activity

Heat output can be used as an indicator of microbial activity and is usually measured in a microcalorimeter with closed ampoules. In long-term experiments particularly, interpretation of the data is hindered by the changing environment in the closed ampoules because of O₂ consumption and CO₂ enrichment. We used a combination of a flow-microcalorimeter and a gas chromatograph to measure the heat flux and CO₂ and N₂O production rates under controlled conditions. Simultaneous detection of the heat output and CO₂ emission allowed calculation of the calorimetric: CO₂ (Cal/CO₂) ratio. A mean ratio of-435 kJ mol^-1 CO₂ was detected in six different soils amended with glucose and incubated under aerobic conditions. This ratio indicated that CO₂ was the end-product of catabolism. In wet 10–12 mm soil aggregates of a gleyic vertisol amended with glucose, values of-285 kJ mol^-1 CO₂ under an aerobic and-141 kJ mol^-1 CO₂ under a N₂ atmosphere was determined. These findings indicated that fermentative metabolism occurred. The Cal/CO₂ ratio was not affected when enough NO _inf3 ^sup- was available and denitrification processes (N₂O production) were possible.     

Perennial winged bean yield and nitrogen fixation improvement with soil fertility treatments of a typic eutrustox

The perennial legume, Winged Bean (Psophocarpus tetragonolobus (L) DC), has potential as a high protein food crop for the humid, tropical regions of the world. Edible seed pods, oil seed grain, leaves, flowers, and unique high protein tubers provide abundant nutritious components desirable for improved human diets. However, soil characteristics and fertility levels influence plant growth, yields and nitrogen fixation capability of this legume. Objectives of this study were to determine soil‐plant nutrient influences on vigorous regrowth, pod and tuber yields, nitrogenase (C₂H₂ red.) activity levels, and nodule cytosol components of the perennial Siempre cultivar grown on a Typic Eutrustox during three years, 1978–1980.

Available soil phosphorus was a first limiting plant nutrient during all three years of plant age. Effects of combined 100 mg P with 200 mg K/kg soil were highly significant for every parameter and plant age. Pod and seed yields more than doubled with PK addition compared to the check. Tuber growth, nodule mass and nitrogenase activity levels more than trebled with PK treatments as compared to the check. Both elemental P and K were significantly increased within the nodule cytosol of fertilized plants. Cytosol Na was significantly decreased with soil K additions. The best fit multiple regression was: nitrogenase = 1.99 nodule wt. + 6.34 tuber wt. + 0.39 tuber % N + 5.08 cytosol P + 1.55 cytosol K ‐ 0.45 cytosol Na, R² = 95.5, C.V. = 11.2%. The dominant nodule cytosol enzymes, aspartate aminotransferase (AST) and glutamine synthetase (GS), significantly increased with soil K additions regardless of P treatments. Glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) also contributed significantly with multiple regression for nitrogenase = 1.07 GS + 2.1 AST + 1.74 GOGAT ‐ 1.76 GDH + 12.89 Ureide, R² = .89, C.V. = 17.3%. Highly significant increases in nodule cytosol ureide composition with K soil additions has interest because of the role as a nitrogenous nonprotein component for many legumes. Increases in growth, nodulation and nitrogenase activity levels resulted with increased K levels of 0, 100, 200 and 300 mg K/kg soil when soil P and Ca were not limiting.     

Gaseous nitrogen losses from fertilized soil during nitrification and denitrification using the acetylene blockage technique

Summary A sandy soil amended with different forms and amounts of fertilizer nitrogen (urea, ammonium sulphate and potassium nitrate) was investigated in model experiments for N₂O emission, which may be evolved during both oxidation of ammonia to nitrate and anaerobic respiration of nitrate. Since C₂H₂ inhibits both nitrification and the reduction of N₂O to N₂ during denitrification, the amount of N₂O evolved in the presence and absence of C₂H₂ represents the nitrogen released through nitrification and denitrification.Results show that amounts of N₂O-N lost from soils incubated anaerobically with 0.1% C₂H₂ and treated with potassium nitrate (23.1 µg N-NO ₃ ^– /g dry soil) exceeded those from soils incubated in the presence of 20% oxygen and treated with even larger amounts of nitrogen as urea and ammonium sulphate. This indicates that nitrogen losses by denitrification may potentially be higher than those occurring through nitrification.