祁连山大野口流域青海云杉林苔藓枯落物及其土壤水热特征分析

为探讨森林生态系统中苔藓枯落物的生态属性与其下层土壤水热之间的关系,采用样地调查法及特征描述统计、相关系数等分析法,对祁连山大野口流域49块样地的青海云杉林苔藓枯落物及其土壤水热特征进行分析.结果表明:苔藓枯落物平均厚度(6.0±0.3)cm,平均含水率为(101.9±6.3)%;0~10、10~20、20~40、40~60、60~80cm土层深的土壤含水率平均值分别为(66.24±4.22)%、(57.62±3.23)%、(48.44±3.21)%、(42.81±6.48)%、25.89%,各土层温度平均值分别为(7.2±0.26)(5.2±0.27)(2.8±0.29)(2.0±0.61)(1.6±0.95)℃;苔藓枯落物厚度与海拔、坡向、坡度、胸径、树高、冠长、冠幅、郁闭度、土壤各层含水率和温度等因子均极弱相关,甚至认为不相关;苔藓枯落物含水率与海拔为中度正相关(P<0.05),与40~60cm深的土壤含水率存在显著正相关,与其温度成中度负相关.     

基于SVM的加工番茄早疫病叶氮素含量光谱反演

采用支持向量机(SVM)模型,对新疆加工番茄早疫病病害植株的叶片氮素含量进行光谱反演。分析不同病害严重度的病叶氮素含量的光谱特征,发现在218~357 nm、384~587 nm、1 033~1 141 nm、1 499~2 500 nm,氮素含量与光谱反射率的相关系数的绝对值大于0.7,在227~353 nm的相关系数大于0.8,表明不同病害严重度的病叶氮素含量与光谱反射率呈强相关。利用K层交叉检验(K-CV)方法验证、优选出SR705、ND705、GMI-2、RI-half、PTEBc等5种光谱指数,作为SVM模型的输入变量;同时,分别建立线性核、多项式核、径向基核和Sigmoid核的SVM模型,通过模型拟合比较,得出最佳模型为径向基核的SVM模型。采用径向基核的SVM模型对病叶氮素含量进行光谱反演,结果表明:径向基核的SVM模型氮素含量反演的真实值与预测值的MSE为0.012 4,相关系数R为85.916%,平均相对误差为0.175,结合多光谱指数的SVM模型提高了加工番茄早疫病病害叶片氮素含量的反演精度。     

海洋沉积物中重金属含量测定样品前处理方法研究

采用正交设计试验法对测定海洋沉积物中重金属含量的样品前处理方法进行了比较研究。结果表明。在王水、氢氟酸、高氯酸消解体系下，采用微波消解一原子吸收分光光度法测定重金属含量，省时，试剂用量少，结果准确，重现性好。     

Artificial induction of maturation and fertilization in the Japanese eel, Anguilla japonica

Repeated injections of salmon pituitary extract (20 mg per fish per week) induced vitellogenesis in feminized, cultivated Japanese eels (Anguilla japonica). Oocytes were attained at the migratory nucleus stage after 11 or 12 injections. Addition of 17,20-dihydroxy-4-pregnen-3-one (DHP) into the incubation medium induced germinal vesicle breakdown (GVBD) in the oocytes at the migratory nucleus stage. An injection of DHP (2 µg g^-1 BW), given 24h after an injection of salmon pituitary extract (20 mg fish^-1), succeeded in inducing maturation and ovulation in females which contained occytes at the migratory nucleus stage. Most fish ovulated 15–18h following the DHP injection. Eggs that were ovulated within 15h after the DHP injection showed high fertility and hatchability, but eggs ovulated 18 or 21h after the DHP injection, showed considerably lower fertility and hatchability. A delay between ovulation and stripping of the eggs rapidly decreased both the fertility and hatchability within 6–9h after ovulation, indicating that artificial fertilization must be carried out immediately after ovulation. Repeated injections of human chorionic gonadotropin (hCG) at a concentration of 1 IU g^-1 BW week^-1 induced spermatogenesis, spermiation, and the acquisition of potential for sperm motility in cultivated males. Most males spermiated after the fifth or sixth injection of hCG, and the milt weight gradually increased and remained constant (1–2 g) from the 11th to 31th injection. Sperm motility peaked 24h after each weekly injection, and decreased from the 3^rd day after the injection. Potassium ions are an essential constituent for the maintenance of motility in the eel spermatozoa. Artificial seminal plasma containing 15.2 mM KCl is applicable as a milt diluent. Using these techniques developed for female and male eels, we have succeeded in obtaining many fertilized eggs from cultivated eels.     

Gonadotropins I and II do not stimulate thein vitro secretion of 17α,20β-dihydroxy-4-pregnen-3-one 20-sulphate by rainbow trout gonads during final sexual maturation

Thein vitro secretion of 17,20-dihydroxy-4-pregnen-3-one 20-sulphate (17,20-P-sulphate) and the free steroid 17,20-dihydroxy-4-pregnen-3-one (17,20-P), by rainbow trout (Oncorhynchus mykiss) gonads, in response to gonadotropin (GTH) I and GTH II, were studied during the final stages of sexual maturation. Substantial amounts of 17,20-P-sulphate were produced, by both mature ovaries and testes, indicating considerable 20-hydroxysteroid sulphotransferase (20-HST) activity within these tissues. In the post-ovulatory ovary the level of 17,20-P-sulphate (36.6 ng ml^–1) greatly exceeded that of 17,20-P (8.59 ng ml^–1). The amount of 17,20-P-sulphate produced in incubations of both mature ovary and testes was unaffected by either GTH I or GTH II treatment at physiological concentrations up to 100 ng ml^–1. Similarly, incubations of maturing ovary and testes, treated with GTH I or GTH II, in the presence of added 17,20-P at 100 ng ml^–1 of medium, produced levels of 17,20-P-sulphate that were similar to those of the controls. In incubations of mature ovarian follicles at the stages of germinal vesicle breakdown and preovulation, both GTHs significantly stimulated secretion of 17,20-P, although GTH II was always more potent than GTH I. GTH II significantly elevated the levels of 17,20-P in testicular incubations from mature males more than 4-fold relative to GTH I and controls, which did not differ from one another.In conclusion, 20-HST, the enzyme responsible for the sulphate conjugation of 17,20-P, was found to be active in the ovaries and testes of rainbow troutin vitro. However, the levels of this enzyme do not appear to be regulated by either GTH I or GTH II.     

Feed preferences in juvenile cod estimated by inert lanthanid markers – effects of moisture content in the feed

There are indications that low ingestion ratesof formulated feed may limit the growth ofearly juvenile fish, including cod. This hasparticularly been observed during the weaningperiod, when the fish must change from apresumably palatable live prey to usually a drydiet. The study of the physical properties ofthe diet seems to be an underestimated area ofresearch, compared to studies on thenutritional properties of the diet. In thisstudy we used lanthanide markers as a tool inestimating diet preferences for examining theeffect of dietary moisture content on ingestionrates in juvenile cod (0.8 g). Fishmeal-baseddiets were produced with five levels of water,giving diets with 35, 42, 54, 65 or 95% dryweight. Each diet was marked with a smallamount of a lanthanide or yttrium oxide. Thefish were hand fed on a mixture of these fivediets. Ingestion rates where then estimated bykilling 1/2 of the fish after one day and therest after four days of feeding. The whole fishwith gut content was homogenized and markercontent was measured by ICP-MS. The amountingested of each of the five diets could thenbe calculated from these figures. Despite thehigh variation in diet selection betweenindividuals the results clearly indicate ahigher intake of moist feed. This could becaused by a better palatability or to a higheravailability caused by a lower sinking rate ofthe moist feed.     

Influence of nutrition on the lipid quality of pond fish: common carp (Cyprinus carpio) and tench (Tinca tinca)

Like marine fish freshwater fish are an important source of essential fatty acids for human nutrition. However, the fatty acid composition of pond fish can vary considerably and strongly depends on that of the ingested food. Investigations on the fatty acid composition of common carp (Cyprinus carpio) and tench (Tinca tinca) have shown that different methods of rearing and feeding cause substantial variations in the proportions of the n-6 and n-3 polyunsaturated fatty acids of these fish species. Carp reared on the basis of natural food in ponds exhibit high contents of n-6 as well as n-3 fatty acids in their muscle triacylglycerols. On the other hand carp fed supplementary wheat in ponds resulted in somewhat lower levels of these essential fatty acids. High amounts of n-3 fatty acids can be found in carp fed high-energy diets containing high levels of fish oil. Analogous results were obtained in experiments with tench reared under different nutritional conditions. While rearing on the basis of only natural food in ponds as well as feeding supplementary wheat yielded in similar levels of n-3 and n-6 polyunsaturated fatty acids, higher contents of n-3 fatty acids were recorded in tench fed pellets. High levels of n-3 polyunsaturated fatty acids in foodstuffs have positive effects on human health. Experiments with different cultured fish species proved that the fatty acid composition of the edible parts can be influenced by the diet. Therefore, a finishing diet with a suitable fatty acid profile can be used to improve the nutritional quality of fish products of farmed origin.     

Effects of dietary lipid level and vegetable oil on fatty acid metabolism in Atlantic salmon (Salmo salar L.) over the whole production cycle

Changes in fatty acid metabolism in Atlantic salmon (Salmo salar) induced by vegetable oil (VO) replacement of fish oil (FO) and high dietary oil in aquaculture diets can have negative impacts on the nutritional quality of the product for the human consumer, including altered flesh fatty acid composition and lipid content. A dietary trial was designed to investigate the twin problems of FO replacement and high energy diets in salmon throughout the entire production cycle. Salmon were grown from first feeding to around 2 kg on diets in which FO was completely replaced by a 1:1 blend of linseed and rapeseed oils at low (14–17%) and high (25–35%) dietary oil levels. This paper reports specifically on the influence of diet on various aspects of fatty acid metabolism. Fatty acid compositions of liver, intestinal tissue and gill were altered by the diets with increased proportions of C₁₈ polyunsaturated fatty acids and decreased proportions of n-3 highly unsaturated fatty acids (HUFA) in fish fed VO compared to fish fed FO. HUFA synthesis in hepatocytes and enterocytes was significantly higher in fish fed VO, whereas β-oxidation was unaltered by either dietary oil content or type. Over the entire production cycle, HUFA synthesis in hepatocytes showed a decreasing trend with age interrupted by a large peak in activity at seawater transfer. Gill cell prostaglandin (PG) production showed a possible seasonal trend, with peak activities in winter and low activities in summer and at seawater transfer. PG production in seawater was lower in fish fed the high oil diets with the lowest PG production generally observed in fish fed high VO. The changes in fatty acid metabolism induced by high dietary oil and VO replacement contribute to altered flesh lipid content and fatty acid compositions, and so merit continued investigation to minimize any negative impacts that sustainable, environmentally-friendly and cost-effective aquaculture diets could have in the future. Abbreviations: FO - fish oil; HUFA - highly unsaturated fatty acids acids (carbon chain length ≥C ₂₀ with ≥3 double bonds); LO - linseed oil; RO - rapeseed oil; VO - vegetable oil. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of melatonin,p-chlorophenylalanine,and α-methylparatyrosine on plasma gonadotropin level and ovarian activity in the catfish,Heteropneustes fossilis: A study correlating changes in hypothalamic monoamines

The effects of (ip, 10 injections over 20 days) of melatonin (75 g 100 g^–1 BW), the serotonin (5-HT)-synthesis blocker, para-cholorophenylalanine (p-CPA, 10 mg 100g^{–1 BW}) and the catecholamine-synthesis blocker, -methylparatyrosine (-MPT, 10 mg 100 g^–1 BW) on gonadotropin (GTH) secretion and ovarian activity were studied in ^{Heteropneustes fossilis} during late preparatory to early prespawning (April–May). The treatments resulted in significant reductions of plasma GTH and estradiol-17 levels, the gonadosomatic index, frequency distribution of vitellogenic and postvitellogenic oocytes, and ovarian and serum ³²p-labelled alkali-labile phosphoprotein (a marker of vitellogenic activity). Most of the oocytes were nonvitellogenic or had undergone atretic changes. The hepatic ³²-phosphoprotein content increased significantly over the saline control value. The effects were similar and pronounced in the p-CPA and melatonin-treated groups but were moderate in the -MPT-treated group. Hypothalamic 5-HT content and turnover were significantly inhibited in the p-CPA and melatonin-treated groups but the content and turnover of catecholamines were not. The -MPT treatment decreased significantly the content and turnover of dopamine (DA), noradrenaline (NA), and adrenaline (A) but did not influence the 5-HT content or turnover. These results suggest that 5-HT, NA and A are stimulatory to GTH secretion and that melatonin may act on the serotonergic system to inhibit the pituitary-gonadal axis.to whom correspondence should be addressed.A part of the results was presented at the International Workshop on Pineal gland: Its molecular signals and published as an abstract in Neuroendocrinol. Lett. 14: 399 pp., 1992.     

The effects of hypoxia,in vivo,on red blood cell β-adrenoceptors in the rainbow trout,Oncorhynchus mykiss

Rainbow trout, Oncorhynchus mykiss, were exposed to 48h of environmental hypoxia (water partial pressure of oxygen = 8.0 kPa) at either 5 or 15°C. Blood was sampled during hypoxia via a dorsal aorta cannula to measure arterial blood partial pressure of oxygen and plasma catecholamine concentrations. After 48h, the number (B_max) and dissociation constant (K_d) of red blood cell surface -adrenoceptors were determined using a radioligand-displacement binding assay. At 5°C, plasma catecholamine levels were elevated at 24h whereas at 15°C, levels were elevated at 48h. At either temperature, following 48h of hypoxia, there was no change in B_max or K_d of red blood cell surface -adrenoceptors, compared to normoxic control fish. This study demonstrates that chronic exposure to moderate hypoxia does not affect the number or affinity of cell surface -adrenoceptors on trout red blood cells.