The effect of nitrogen fertilization and no‐till duration on soil nitrogen supply power and post–spring thaw greenhouse‐gas emissions

With a world population now > 7 billion, it is imperative to conserve the arable land base, which is increasingly being leveraged by global demands for producing food, feed, fiber, fuel, and facilities (i.e., infra‐structure needs). The objective of this study was to determine the effect of varying fertilizer‐N rates on soil N availability, mineralization, and CO₂ and N₂O emissions of soils collected at adjacent locations with contrasting management histories: native prairie, short‐term (10 y), and long‐term (32 y) no‐till continuous‐cropping systems receiving five fertilizer‐N rates (0, 30, 60, 90, and 120 kg N ha^–1) for the previous 9 y on the same plots. Intact soil cores were collected from each site after snowmelt, maintained at field capacity, and incubated at 20°C for 6 weeks. Weekly assessments of soil nutrient availability along with CO₂ and N₂O emissions were completed. There was no difference in cumulative soil N supply between the unfertilized long‐term no‐till and native prairie soils, while annual fertilizer‐N additions of 120 kg N ha^–1 were required to restore the N‐supplying power of the short‐term no‐till soil to that of the undisturbed native prairie soil. The estimated cumulative CO₂‐C and N₂O‐N emissions among soils ranged from 231.8–474.7 g m^–2 to 183.9–862.5 mg m^–2, respectively. Highest CO₂ fluxes from the native prairie soil are consistent with its high organic matter content, elevated microbial activity, and contributions from root respiration. Repeated applications of ≥ 60 kg N ha^–1 resulted in greater residual inorganic‐N levels in the long‐term no‐till soil, which supported larger N₂O fluxes compared to the unfertilized control. The native prairie soil N₂O emissions were equal to those from both short‐ and long‐term no‐till soils receiving repeated fertilizer‐N applications at typical agronomic rates (e.g., 90 kg N ha^–1). Eighty‐eight percent of the native soil N₂O flux was emitted during the first 2 weeks and is probably characteristic of rapid denitrification rates during the dormant vegetative period after snowmelt within temperate native grasslands. There was a strong correlation (R² 0.64; p < 0.03) between measured soil Fe‐supply rate and N₂O flux, presumably due to anoxic microsites within soil aggregates resulting from increased microbial activity. The use of modern no‐till continuous diversified cropping systems, along with application of fertilizer N, enhances the soil N‐supplying power over the long‐term through the build‐up of mineralizable N and appears to be an effective management strategy for improving degraded soils, thus enhancing the productive capacity of agricultural ecosystems. However, accounting for N₂O emissions concomitant with repeated fertilizer‐N applications is imperative for properly assessing the net global warming potential of any land‐management system.     

Effects of exogenous enzyme supplementation in diets on growth and feed utilization in tilapia, Oreochromis niloticus x O. aureus

A 12‐week feeding trial was conducted to investigate the effects of supplemental exogenous enzyme on growth performance in juvenile hybrid tilapia Oreochromis niloticus×O. aureus (18 g, average initial weight). A commercial enzyme complex (neutral protease, β‐glucanase and xylanase) was included at the level of 0.0 (control group), 1.0 and 1.5 g kg⁻¹ diet in three test diets. Each diet was fed to triplicate tanks of the juvenile three times a day at 4–6% of wet body weight, and each tank was stocked with 50 fish. The results showed that specific growth rate and feed efficiency ratio significantly increased (P<0.05) with increasing dietary enzyme levels. The highest feed intake was recorded in the group fed the control diet (P<0.05). The highest apparent protein retention was observed in fish fed the diet containing the 1.5 g kg⁻¹diet (P<0.05). No significant differences were observed in the apparent digestibilities (ADC) of protein, lipid and gross energy among dietary treatments (P>0.05). However, the ADC of dry matter in fish fed high supplementation (1.5 g kg⁻¹) was significantly higher than the control and low supplementation (P<0.05). There were no significant differences in condition factor, whole body moisture, protein, lipid and ash among dietary treatments. Viscera ratio, hepatosomatic index and the liver lipid decreased significantly with increasing enzyme (P<0.05). Both protease and amylase activities in the intestine and the hepatopancreas of juvenile hybrid tilapia significantly increased (P<0.05) with increasing dietary enzyme levels. The results suggested that enzyme supplementation can significantly improve growth performance and feed utilization in juvenile hybrid tilapia.     

Development of an emulsion prepared with lipophilized gelatin and its application for hormone administration in the Japanese eel Anguilla japonica

A new water-in-oil-in-water (W/O/W) type emulsion using lipophilized gelatin (LG) and cotton-seed oil was developed for a novel method of hormone administration in fishes. LG was prepared by attaching palmitic anhydride to gelatin. The best conditions for preparing stable emulsions were determined where the final concentrations of LG in the emulsion and the volume ratio of LG solution to cotton-seed oil were 2% and 1:2, respectively. Hormone releasing properties of LG emulsion were compared with a water-in-oil (W/O) type emulsion prepared with Freund's incomplete adjuvant (FIA) and saline solution by monitoring plasma profiles of salmon gonadotropin (sGtH) II in the Japanese eel. sGtH II is gradually released from the LG emulsion. LG emulsion had hormone-releasing properties different from those of the saline solution and the FIA emulsion. Immature female Japanese eel (BW, 566 to 1017 g) received a weekly intramuscular injections (total of 10 injections) of the LG emulsion, the FIA emulsion or the saline solution, each of which contained sGtH fraction. The LG emulsion was found to be more effective in inducing ovarian maturation. In mature eel, final maturation and ovulation could be induced by simultaneous administration of sGtH fraction and 17ORDER="0">-hydroxyprogesterone using LG W/O/W emulsion.     

Does urea reabsorption occur via the glucose pathway in the kidney of the freshwater rainbow trout?

This study tested the hypothesis that the renal reabsorption of urea occurs via the glucose transport pathway in the freshwater rainbow trout (Oncorhynchus mykiss). The relationship between glucose transport and urea transport was examined by experimentally elevating the rate of renal glucose reabsorption via infusion of the fish with exogenous glucose, and by inactivating the glucose transporters via the administration of phlorizin. Under all treatments, urea was reabsorbed against a concentration gradient, with plasma levels of urea being higher than urine levels. Glucose was almost completely reabsorbed (88%) whereas urea was reabsorbed less efficiently (47%) but to a greater extent than water (22%). Glucose and urea reabsorption were both found to be correlated with Na⁺ and Cl^– reabsorption, though the latter were 20 fold and 200–300 fold higher than glucose and urea transport rates, respectively. Glucose infusions greatly increased glucose reabsorption but urea reabsorption was unaffected. Phlorizin treatment completely blocked glucose reabsorption, but urea reabsorption was again unaffected. We conclude that there is no relationship between glucose and urea handling in the trout kidney, thus disproving the hypothesis.     

Effects of cyanide exposure on Dascyllus aruanus, a tropical marine fish species: lethality, anaesthesia and physiological effects

The lethality, anaesthetic and physiological effects of ORDER="0">pulsedORDER="0"> cyanide (CN-) exposures to a common tropical marine fish Dascyllus aruanus were assessed. Cyanide (25 and 50 mg l-1) was applied as pulses (10, 60 and 120 s) to fish under non-stressed and stressed (by chasing and/or placing fish under hypoxic stress) conditions. Following treatment, the time until recovery and the percent survival were determined. The fish were allowed a 2.5 week recovery period from the treatments at which time four physiological end-points were measured: (1) the blood haemoglobin content, (2) the percent blood O-2 content, (3) the liver rhodonase activity and (4) the liver O2 consumption rate. The greater the CN- concentration and exposure time, the longer the recovery time. Non-stressed fish exposed to 10 s pulses of 25 mg l-1 of CN- fully recovered within 4 min whereas fish exposed for 60 s and 50 mg l-1 of CN- required up to 50 min for full recovery. Exposure for 120 s at 25 and 50 mg l-1 of CN- proved lethal. Under stressed conditions, previously non-lethal exposures (60 s and 50 mg l-1) were lethal. Of the physiological end-points, only the liver O2 consumption rate was indicative of previous CN- exposure. Under non-stressed conditions, pulsed exposures at 25 and 50 mg l-1 of CN- for 10 and 60 s significantly reduced the liver O2 consumption rates (ANOVA; p < 0.05). Under stressed conditions, the liver O2 consumption rates were significantly greater (maximum rates up to 17-fold greater) than the control fish (ANOVA; p < 0.05). We conclude, therefore, that environmentally relevant exposures of CN- can adversely effect fish and this affect can be measured 2.5 weeks post-exposure. Importantly, the combined effects of exposure and stress both increased the mortality and placed an appreciable metabolic load on the fish as indicated by the elevated liver O2 consumption rates. Handling stress in combination with anaesthetic CN- doses could in part explain the delayed mortality reportedly associated with CN- use in the tropical fish trade. The significance of the elevated liver O2 consumption rates on the survival of CN--exposed fish is unknown     

A simple test to estimate the salinity resistance of fish with specific application to O. niloticus and S. melanotheron

In order to develop a simple and accurate index of the salinity resistance of tilapia, batches of 10 juveniles (5 to 20 g) of two different species Oreochromis niloticus and Sarotherodon melanotheron reared in freshwater were subjected to gradual increases in salinity until 100% mortality. Seven daily increments of salinity were tested with 4 replicates: 2, 4, 6, 8, 10, 12 and 14 g l⁻¹ day⁻¹, while control batches were kept in fresh water. The temperature was maintained at 27 °C. The concentration of oxygen, ammonia and the pH were not limiting factors. The mortality, monitored on a daily basis, appeared after 2–51 days and was spread out over 1–20 days, depending on the increment of salinity. The higher the daily rate in salinity increase, then the shorter the time lapse before total mortality occurred. The cumulative mortality as a function of salinity fit well with simple linear regressions. The criterion of the resistance to salinity was the index MLS (median lethal salinity) defined at each daily rate as the salinity at which 50% of fish died. For S. melanotheron, the mean MLS was 123.7±3.5 g l⁻¹ whatever the daily rate in salinity. For O. niloticus, the MLS was 46.3±3.4 g l⁻¹ for daily increases in salinity ranging from 2 to 8 g l⁻¹ day⁻¹ and decreased significantly (P<0.05) above this level. The MLS-8 g l⁻¹ day⁻¹ ,which takes into account the full capacity of the fish to adapt to the increasing salinity, appeared to be a simple, optimized and efficient criterion for assessing the resistance to salinity for O. niloticus and S. melanotheron. This criterion can be a useful tool for ranking the different parental strains and hybrids of different genus and species of tilapia used in programmes of genetic selection for growth and salinity tolerance.     

脂肪组织冰冻切片油红O滴染法的建立

为了提高脂肪组织冰冻切片的染色效果和效率,将传统的脂肪组织石蜡切片油红O染色法改进为冰冻切片油红O滴染法,以用于冰冻脂肪组织脂肪细胞增殖、分化的研究和脂肪相关疾病快速病理诊断。新鲜脂肪组织液氮冷冻后转入-20℃冰箱缓冲30min,在-33℃或-34℃时进行冰冻切片,组织染色采用油红O微量滴染法。本改良的油红O滴染法能应用于冰冻脂肪组织切片染色,清楚地显示脂肪细胞的形态和脂滴的分布,有助于脂肪组织增值分化的研究和相关疾病病理切片分析。该方法快速高效、染色清晰、不易脱片,效果良好,可明显缩短实验周期和减少试剂成本,可使脂肪组织冰冻切片和油红O染色技术更广泛的应用于脂肪组织相关的科学研究和病理诊断。     

旱耕人为土N2O排放动力学特征及其影响因素

以黄土高原南部典型旱耕地—休闲地土壤为对象 ,研究了中等水分条件下 (6 5 %的田间持水量 )土壤 N2 O排放的动力学特征 ,以及土壤深度和氮磷营养因子对 N2 O排放量的影响。结果表明 ,施肥和未施肥处理 ,土壤 N2 O排放累积量随时间 t的变化均符合修正的 Elovich方程 y=bln(t) +a。反应初始浓度 (a)和表观反应速率(dy/ dt)大多数随土壤深度增加而递增 ,但 15℃时以 10 cm深处反应初始浓度最大 ;2 5℃时 ,表观反应速率以 15cm深处最高 ,即在中等水分条件下 ,随温度升高 ,试验土壤 10～ 15 cm深处为 N2 O产生的活跃场所。磷素对土壤N2 O的减排效应不仅表现在排放总量上 ,也存在于动力学参数初始浓度和表观反应速率之中。     

中国南方山地羊消化道线虫体外发育的研究

本文检测中国南方亚热带山地环境因素（温度，相对湿度和降雨量）变化对羊捻转血矛线虫、环纹奥斯特线虫和粗纹食道口线虫体外发育的影响规律：捻转血矛线虫由卵至Ⅰ、Ⅱ和Ⅲ期幼虫的最高育成率均在６月；育成期分别是３、５和７ｄ。环纹奥斯特线虫卵至Ⅰ、Ⅱ和Ⅲ期幼虫育成率在５～７月均较高，其中Ⅰ和Ⅱ期幼虫最高育成率在６月，而Ⅲ期幼虫最高育成率在５月；育成期分别是３、５和１１ｄ。粗纹食道口线虫卵至Ⅰ、Ⅱ和Ⅲ期幼虫的最高育成率均在７月；育成期分别是６、７和９ｄ。１１月至次年３月间三线虫均不能发育，而且粗纹食道口线虫于１０月停止发育。文中还讨论了三线虫的防治措施。     

16O8+注入小麦种子胚乳引起M1代幼苗可溶性蛋白质的变化

通过控制单核能大小,将^16O离子注入小麦种子胚乳,结果引起M1代幼苗可溶性蛋白质的较大变化。可溶性蛋白质电泳凝胶胶片的扫描曲线显示：1）在高剂量的处理中,有的峰消失;有的峰高于对照,中、高剂量值呈升高趋势;有的峰低于对照,中、高剂量值呈下降趋势。2）按分子量的大小将可溶性蛋白质分成5个区段,并计算不同区段蛋白质组分的相对含量。结果表明,同对照相比,第2区段的相对含量降低（分子量较大区段）,而第5区段相对含量升高（分子量最小区段）。3）同时也表明,低剂量效应表现异常。本文也讨论了诱变胚乳对胚作用的可能机理。