Swimming depth and thermal history of individual Atlantic salmon (Salmo salar L.) in production cages under different ambient temperature conditions

Salmon production cages at sites with a pronounced thermal stratification give individual fish an opportunity to choose their thermal environment. The behavioural responses of individual salmon to such stratification, however, are poorly documented. Information about spatial distributions and temperature experience of individual Atlantic salmon (initial weight 1.5 kg) was gathered over a period of 4 months (mid-August to early-December) using data storage tags. Fish were stocked at normal or high densities in triplicate 2000 m³ production cages at 5.6–14.5 (ND) or 15.7–32.1 (HD) kg m^− 3, and valid data were collected for 12 ND and 11 HD salmon. There were large inter- and intra-individual variations in swimming depth, with indications that the salmon performed behavioural thermoregulation in an attempt to maintain body temperature within the range of 8–20 °C. Stocking density influenced the average swimming depth and body temperature, indicating competition for preferred thermal space in periods of unfavourably high temperature (towards 20 °C) in large parts of the cage volume. Analysis of temporal behavioural patterns demonstrated a higher variability during day than night and that 60 to 70% of the individuals displayed cyclic diel patterns in either swimming depth or body temperature in at least one out of three sub-periods. The results are discussed in relation to bio-energetic and thermal stress theory and possible consequences for growth variation in salmon cages. Generally, this study suggests that individual swimming depth and body temperature is in part a response to available temperature interacting with stocking density and time of day, while some individual variation cannot be ascribed to the measured variables.     

Dormancy and germination in Rosa multibracteata Hemsl. & E. H. Wilson

Most of the achenes produced by Rosa multibracteata Hemsl. & E. H Wilson are dormant on maturity and require pretreatment to stimulate germination. To investigate the mechanism of dormancy and to develop effective methods of improving germination, roles of the pericarp, testa, and embryo of R. multibracteata in regulating dormancy were studied by investigating the effect of different pretreatments on germination. The effects of temperature and water stress were also tested with achenes treated by warm plus cold stratification. In freshly harvested achenes, pericarps are permeable and the embryo fully developed, which eliminates the possibility of physical, morphological, or morphophysiological dormancy. Germination percentage remained low (<5%) despite softening the pericarp or even removing it fully. However, fully removing the testa improved germination significantly (39%), indicating the possible presence of germination inhibitors in the testa. Dry storage, scarification with sulphuric acid (H₂SO₄), and warm stratification proved ineffective by themselves but when combined with cold stratification, improved germination and shortened the cold stratification period needed to break dormancy. Dry storage for 68 weeks followed by cold stratification for 16 or 24 weeks resulted in maximum germination (72–79%) among all the treatments. In achenes scarified with H₂SO₄, germination increased with an increase in the duration of cold stratification. Neither gibberellic acid (GA₃) nor ‘smoke water’ (water through which smoke had been bubbled for 2 h) had any positive effect on germination even on seeds that had been mechanically scarified or stratified. Both high temperature and water stress lowered germination in achenes treated with warm plus cold stratification. Our results suggest that R. multibracteata achenes have an intermediate physiological dormancy, and that dry storage for 68 weeks followed by cold stratification for 16 or 24 weeks is the best method for propagating R. multibracteata from seed.     

Thermal and hormonal regulation of the dormancy–germination transition in Amaranthus tuberculatus seeds

The transition from seed dormancy to germination is a multi‐step process. However, distinguishing between physiological processes involved in seed dormancy alleviation and those involved in germination has been difficult. We studied the seed dormancy alleviation process in Amaranthus tuberculatus, an important weed species in midwestern USA. Using three A. tuberculatus biotypes that differ in dormancy level, it was determined that stratification reduced seed dormancy from a high to a low level. Temperature alternation alleviated low seed dormancy and triggered germination. Exogenously applied abscisic acid (ABA) and gibberellic acid (GA) had no effect on seeds with high dormancy. However, ABA and paclobutrazol (a GA biosynthesis inhibitor) significantly reduced germination of seeds with low dormancy. Hormones could not replace the effects of stratification or temperature alternation on dormancy alleviation. Based on our results, we propose a seed dormancy–germination transition model in which the dormancy of A. tuberculatus seeds is progressively reduced from a high to a low level; but environmental conditions (i.e. stratification) can accelerate the dormancy alleviation process. Under low dormancy levels, the seed is more sensitive to environmental cues that are responsible for removing dormancy and triggering germination (i.e. temperature alternation). Finally, ABA and GA regulation occurs primarily during the final transition from low dormancy to germination rather than the alleviation of high dormancy.     

对红松种子混雪埋藏处理育苗效果分析

介绍了红松种子混雪埋藏育苗试验过程.从而得出结论,利用混雪埋藏技术育苗与用温水浸种催芽方法育苗相比,有许多优点,可使幼苗早出土、延长生长周期、增强苗木抗寒抗旱抗病虫能力.     

Effect of tillage intensity on population densities of Heterodera glycines in intensive soybean production systems

The effects of tillage on Heterodera glycines, the most important yield-reducing pathogen of soybean in the U.S., were examined in a long-term tillage and crop sequence study initiated in 1975 on a mollisol at Purdue University. Population densities of H. glycines were monitored under corn–soybean rotation and soybean monoculture in 2003 and 2004. Tillage treatments included: (A) fall moldboard plow + spring secondary tillage; (B) fall chisel plow + spring secondary tillage; (C) ridge tillage; and (D) no-tillage. In both years in the rotational plots, final population densities of H. glycines were proportional to tillage intensity. Under both soybean and corn rotation crops, highest population densities were observed with plowing + secondary tillage and lowest population densities were detected under no-tillage. In 2004, population densities in monoculture soybean soil declined with depth intervals in layers of 0–10, 10–20, and 20–30-cm depth under no-till, but not in plowed plots. Multiple regression analysis determined that the stratification of nematode population densities was strongly correlated to penetrometer resistance and potassium concentration of the soil. Tillage seemed to affect population densities of H. glycines by modification of the soil physical parameters in corn–soybean rotation plots. Reducing tillage intensity was beneficial in reducing population densities of H. glycines in rotational soils. Thus, the choice of tillage system can reduce the risk for damage by this widely distributed pathogen.     

"需要层次理论"在图书馆年轻职工管理中的应用

在当今大多数图书馆队伍中,年轻职工所占的比例越来越大,发挥着越来越重要的作用。文章首先分析了图书馆中年轻职工的特点及存在的问题,然后根据“需要层次理论”,阐述了如何提高对年轻职工的管理水平,从而最大限度地调动年轻职工的积极性,为图书馆的改革与发展注入新的活力。     

几个灌木树种种子处理及苗木年生长过程的研究

本文概述了胡枝子、杭子梢、花木兰、荆条、伞花胡颓子等5个树种的种子休眠类型。通过实验,找到了热水浸种最适温度、硫酸浸种最佳时间和层积催芽最适天数。观测了这几个树种的苗木年生长过程,划分了生育阶段。     

Serial Estimation of Survival Prediction Indices Does Not Improve Outcome Prediction in Critically III Dogs with Naturally Occurring Disease

Objective: The objectives of this study were to test the value of adding serial measurements to the Survival Prediction Index (SPI 2), and to investigate whether time trajectories add predictive information beyond measurements at a single point in time.
Design: Prospective clinical trial.
Setting: Intensive care unit at a Veterinary Teaching Hospital.
Animals: 63 critically ill dogs
Interventions: Physiologic data were collected within 24 hours of admission to the ICU (Day 1), and again on Day 3 of hospitalization.
Measurements: The first analysis applied the SPI 2 equation on Day 1 and again on Day3. Then a prediction model was re-estimated using Day 1 measurements, and the incremental predictive value of adding Day 1 to Day 3 change scores was evaluated. the third analysis tested the incremental predictive value of change scores in models containing only one prognostic variable. The final analysis compared the re-estimated Day 1 model to an analogously re-estimated Day 3 model.
Main Results: Using the SPI 2 equation, the AUC was 7.7% higher using Day 3 measurements than that obtained using Day 1 measurements (P = 0.515). Starting with the re-estimated Day 1 model (AUC = 0.925), forward stepwise addition of the difference score for each variable did not result in an improvement in the AUC. The AUC for the re-estimated Day 1 model was not statistially different from that of the re-estimated model using Day 3 measurements.
Conculusion: This study shows no benefit to repeated calculation of the SPI 2 later in hospitalization.     

Physical characteristics of gastrointestinal content of llama (Lama glama)

Changes in digesta dry matter (DM) and mean digesta particle size (MPS) along the gastrointestinal tract are well known in ruminants, but not in camelids. We collected digesta from the dorsal (d) and ventral (v) first forestomach compartment (C1), the second forestomach compartment (C2), three proximal segments and the subsequent glandular part of the third compartment (C3A‐D), the caecum and the faeces twelve llamas (Lama glama). DM analysis indicates the presence of digesta stratification in the C1, the presence of fluid in the C2 to facilitate the sorting function of this compartment, the fluid‐absorbing function of the proximal parts of the C3, the secretion of enzymes and digestive acids in the C3D, and the water‐resorbing function of the lower intestinal tract. These findings illustrate the functional resemblance between the gastrointestinal tract of camelids and cattle‐like ruminants (C1 equivalent to the rumen with stratified contents, C2 to the reticulum, C3A/B/C to the omasum and C3D to the abomasum). MPS analysis revealed a progressive reduction in MPS from the C1 to the distal C3. This gradual transition is different from the clear‐cut threshold in ruminants between the reticulum and the omasum and had so far only been described in dromedaries (Camelus dromedarius). These findings indicate that regardless of the convergent property of rumination and resemblance of general mechanisms involved in contents stratification and particle sorting, differences between ruminants and camelids exist that could be interpreted as a more efficient functionality of the ruminant forestomach.     

低温层积对纳罗克非洲狗尾草种子酶活性及其萌发的影响

为探究低温层积对纳罗克非洲狗尾草(Setaria sphacelata cv.Narok)种子酶活性及其萌发的影响,将一年龄纳罗克非洲狗尾草生产的种子进行低温(4℃)层积不同时间处理,并测定在不同处理下种子的酶活性、发芽率及活力水平。结果表明:纳罗克非洲狗尾草种子在低温层积处理最佳时间为30 d,在此处理条件下,种子休眠已完全解除,此时种子的发芽率和各项活力指数分别达到75%和0.0263,是对照(低温层积处理0d)的2.08倍和2.27倍,差异达到极显著水平(P0.01);种子超氧化物歧化酶(SOD)活性,呈先下降后升高并逐渐稳定的趋势,低温层积60 d降至最低水平650.800 U/g FW·h,较对照降低了9.07倍;过氧化物酶(POD)活性随时间的推移波动变化,但变化不明显(P0.05);过氧化氢酶(CAT)活性在层积处理90 d前无显著变化(P0.05),之后逐渐下降。