苜蓿种植年限对土壤硝化潜势和氨氧化微生物丰度的影响

依托布设在黄土高原半干旱区的长期定位试验,通过高通量测序研究不同种植年限（L2003、L2005和L2012）苜蓿土壤氨氧化古菌(AOA)和氨氧化细菌(AOB)丰度,并分析揭示了影响氨氧化微生物丰度的环境因子。研究结果表明,土壤硝化潜势随苜蓿种植年限延长逐渐下降,其中,L2012、L2005和L2003处理的硝化潜势分别为0.05、0.04、0.04 μg·g^-1·h^-1,且处理间差异显著(P<0.05);土壤全氮含量随苜蓿种植年限延长逐渐增加,其中,L2012、L2005和L2003处理的全氮含量分别为1.02、1.14、1.18 g·kg^-1,且处理间差异显著(P<0.05),L2003和L2005处理的全氮含量分别比L2012高15.69%和11.76%;土壤硝态氮含量表现为随种植年限延长显著增加(P<0.05),L2003处理和L2005处理硝态氮含量分别比L2012处理提高59.73%和33.62%。高通量测序发现,AOA amoA基因拷贝数为9.75×10⁶~12.68×10⁶个·g^-1,明显高于AOB的5.01×10⁶~7.70×10⁶<个·g^-1,AOA丰度随苜蓿种植年限延长显著增加(P<0.05),但AOB丰度表现出随种植年限延长先升高后降低的趋势,这表明黄土高原半干旱区苜蓿土壤氨氧化微生物以AOA占主导地位。相关分析表明,AOA丰度与土壤全氮（r=0.853）和硝态氮（r=0.833）均呈极显著正相关,但与硝化潜势（r=-0.802）呈极显著负相关,AOB丰度与土壤氮素含量和硝化潜势没有明显相关性。由此可见,黄土高原半干旱区苜蓿土壤氨氧化微生物以AOA为优势类群,且对苜蓿种植年限有更强烈的响应,但其并未主导土壤硝化过程。     

Inhibitory effect of zacopride on ouabain-induced arrhythmias in adult rats

AIM: To investigate the effect of zacopride, an inward rectifier potassium channel agonist, on ouabain-induced arrhythmias in adult rats, and to explore the underlying electrophysiological mechanism.METHODS: Using ouabain to establish in vitro and in vivo arrhythmic rat models, the effects of zacopride on ouabain-induced arrhythmias were observed. The technique of whole-cell patch clamp was used to observe the effects of zacopride on inward rectifier potassium current (I_K1), resting membrane potential (RMP) and delayed afterdepolarizations (DADs) in single rat ventricular myocyte. RESULTS: Zacopride at 1 μmol/L significantly reduced total number of premature ventricular beats, and the duration and incidence of ventricular tachycardia and ventricular fibrillation induced by ouabain in rat hearts in vitro (P<0.05). In anesthetized rats, zacopride at 15 μg/kg significantly reduced total number of premature ventricular beats, and the duration and incidence of ventricular tachycardia and ventricular fibrillation induced by ouabain (P<0.05). I_K1 was significantly inhibited by ouabain (P<0.05), which was partially and even completely reversed by zacopride at 0.1~10 μmol/L. RMP value was significantly reduced by ouabain (P<0.05), and then increased to different levels after treatment with zacopride (0.1~10 μmol/L). Zacopride at 1 μmol/L showed its maximal effect and RMP was restored to normal level. Moreover, zacopride at 1 μmol/L markedly suppressed ouabain-induced DADs in single rat ventricular myocyte. The incidence of DADs decreased from 91.67% to 12.50% after zacopride was applied (P<0.05), and this effect was abolished by 1 μmol/L BaCl₂. CONCLUSION: Inward rectifier potassium channel agonist zacopride significantly inhibits ouabain-induced ventricular arrhythmias in adult rats. The mechanism is related to increased RMP level and inhibition of DADs by activation of I_K1 channel.     

春小麦蒸发蒸腾的调控

春小麦蒸发蒸腾受环境条件,土壤水分状况和小麦叶片气孔的综合调控。甘肃河西地区辐射强列,与春小麦蒸发蒸腾具有高度相关性（ｒ〉０．９５）,决定了该地区作物的高耗水特性。土壤水分条件在水势为－０．０１－－０．１ＭＰａ时,春小麦蒸发蒸腾受气象条件影响和小麦叶片气孔调节的作用较大;当土壤水势降至－０．３－－１．５ＭＰａ时,叶片气孔开始关闭,太阳辐射对春小麦蒸发蒸腾的作用明显减弱（相关系数ｒ〈０．３１）。土壤     

东北地区春玉米农业气候资源数值模拟

运用ＡＲＩＯ ＣＲＯＰ模型对东北三省春玉米气候生产力进行了数值模拟研究,给出了气候丰产力分布图,并指定模式水分因子为最适状态,计算了春玉米光温生产潜力分布状况,在此基础上给出了水分增产力分布图。研究表明,东北地区春玉米气候生产力大致由南向北递减,变幅在４．５￣２２．５ｔ／ｈｍ＾２之间,而光温生产力分布则主要表现为由西南向东北递增。水分增产力分析表明,对春玉米生产而言,东北地区中部水分条件最优,水分     

金沙江干热河谷农业自然资源现状和可持续发展潜力

从土地资源特征、气候资源特征、种质资源特征分析了金沙江干热河谷农业自然资源现状,提出发挥热区优势,坚持资源开发与治理保护相结合,深度开发与广度开发相统一,困地制宜,突出重点的持续农业发展途径。     

The Application of Microcomputer in Experiment on Demarcating Thermocouple

A traditional method of experiment on demarcating thermocouple is analyzed and its shortcoming is indicated.It is proposed that the experimental device for demarcating thermocouple should be advanced through application of a microcomputer.The timing for data sampling is carried out in a real time clock way and then the analogue signal is converted into digital information through a A/D converter.Finally, the results of demarcating thermocouple are audio-visually displayed on the screen in a graphic mode.     

Variational Method of Network Structure of Linear Hardening Materials

This paper developed out coordinate equations and equation of strain energy for suspensionand network structure made of linear hardening materials.Then displacements and horizontal forces ofthe network are determined by principle of minimum potential energy.     

Theoretical Analysis for the Performance of HVDC Grounds Electrodes and the Mathematical Modal

The performance of HVDC ground electrodes is analyzed in detail.On the basis of electromagnetic field theories and its assumptions,the mathematical model is built,the ground resistance,the distribution of potential and temperature are computed with the current field distributions of HVDC ground electrodes.     

Phosphorus mineralization and microbial biomass in a Florida Spodosol: effects of water potential, temperature and fertilizer application

 Phosphorus mineralization and microbial biomass were measured in the surface 5 cm of a Spodosol (sandy, siliceous hyperthermic Ultic Alaquod) from north-central Florida. Soils from fertilized and unfertilized plantations of loblolly pine (Pinus taeda L.) were incubated at a range of water potentials (∼0, –3, –8, –10 and –1500 kPa) and temperatures (15  °C, 25  °C and 38  °C) for 14 days and 42 days. Increasing water potential and temperature increased specific P mineralization (mineralization expressed as a percentage of total P) regardless of fertilizer treatment. An increase in water potential from –10 kPa to –0.1 kPa resulted in an increase of between 38% and 239% in the concentration of KCl-extractable inorganic P, depending on incubation temperature and time. An increase in incubation temperature from 15  °C to 38  °C resulted in an increase of between 13% and 53% in KCl-extractable inorganic P. Changes in specific P mineralization with change in water potential or temperature were not affected by fertilizer application. This suggests that, although specific P mineralization was greater in the fertilized soils, environmental control of P mineralization was the same for both treatments. Specific P mineralization was most sensitive when soils were at higher water potentials, and decreased logarithmically to water potentials of between –3 kPa and –8 kPa. Specific P mineralization was relatively insensitive to changes in water potential when water potential was lower than –8 kPa. Microbial biomass C showed no consistent responses to changes of temperature or water potential and was not significantly correlated with specific P mineralization. Our results suggest that field estimates of P mineralization in these Spodosols may be improved by accounting for changes in soil water potential and temperature. Received: 30 October 1997     

关于“恒电位表面”概念的讨论

长期以来,人们认为水合氧化物型表面（可变电荷表面）的定位离子是Ｈ＾＋和ＯＨ＾－,所以表面电位（Φ０）只是ｐＨ值的函数,而与电解质的浓度无关。所以反水合氧化物型表面又称恒电位表面。本文从理论上和实验上都表明,情况并非这样,可变电荷表面的电位强烈地依赖于电解质浓度,并且其表面电荷密度既依赖于溶液ｐＨ值也依赖于电解质浓度。所以,可变电荷表面并非恒电位表面。