Analysis and modeling of gas exchange processes in Scaevola aemula

Scaevola aemula is a popular ornamental crop cultivated as a bedding plant or for hanging baskets. We characterized gas exchange properties of S. aemula ‘New Wonder’ in response to photosynthetically active radiation (PAR), carbon dioxide concentration, and leaf temperature. Net CO₂ assimilation rate (A) was responsive to CO₂, exhibiting a saturation when intercellular CO₂ concentration (C_i) was greater than 600 μmol mol⁻¹. Net CO₂ assimilation rate and dark respiration rate (R_d) were 23.1 and 2.3 μmol m⁻² s⁻¹, respectively, at 25 °C and PAR = 1500 μmol m⁻² s⁻¹. Net CO₂ assimilation rates were similar at leaf temperatures between 20 and 30 °C but significantly reduced at 15 °C. These gas exchange results were used to test the extendibility of a coupled gas exchange model previously developed for cut-roses. Utilizing the gas exchange data measured at 25 °C leaf temperature, several model parameters were independently determined for S. aemula. Model predictions were then compared with observations at different leaf temperatures. The model predicted the rates of net CO₂ assimilation and transpiration of S. aemula reasonably well. Without additional calibration, the model was capable of predicting the temperature dependence of net CO₂ assimilation and transpiration rates. Applying the model to predict the effects of supplemental lighting and CO₂ enrichment on canopy photosynthesis and transpiration rates, we show that this model could be a useful tool for examining environmental control options for S. aemula production in the greenhouse.     

Humoral and cellular immunoresponsiveness of stanchioned cattle infested with Psoroptes ovis

Bovine scabies in a clinical problem during the cool autumn and cold winter months. In south Texas it is necessary to stanchion animals in order to elicit patent infestation during summer months. Environmental factors and grooming have been purported to account for summer resistance to infestation. However, stanchioned animals exhibit varied levels of susceptibility to infestation, suggesting that the noted variability may be influenced by the host immune response. In this study, animals were infested with Psoroptes ovis while in stanchions. The development of anti-P. ovis antibody activity was measured by the enzyme-linked immunosorbent assay and cellular immune function was monitored with mitogens and P. ovis antigens. A correlation was noted between the development of anti-P. ovis antibody activity and the increase in mite numbers and dermatitis. Coincident with the developing infestation was a suppression of T-cell function that appeared to be stress-related as a result of stanchioning. A working hypothesis is presented that attempts to correlate the developing humoral response and the depressed T-cell response with both an increasing dermatitis and mite population.     

Effect of sodium bicarbonate on racing Standardbreds

Twenty-two Standardbred horses in race training were used in a crossover experiment to determine the effect of oral sodium bicarbonate (NaHCO3) administration on performance and metabolic responses to a 1.6-km (1-mile) race. Horses were paired and one horse in each pair was treated with either NaHCO3 (300 mg/kg BW) or a placebo, 2.5 h before they raced against each other. Each horse was scheduled to compete in two races, approximately 1 wk apart, one on each treatment. Horses always raced in the same pairs. Fourteen horses successfully completed both races. Jugular blood samples were obtained 1.5 h after treatment (rest), immediately before racing, 5 min post-race and 15 min post-race. In six horses, blood samples also were obtained 30 min post-race. Race times averaged 1.1 s faster after NaHCO3 treatment (P less than .1). Sodium bicarbonate treatment also elevated blood pH (P less than .05). In the horses sampled 15 and 30 min post-race, blood lactate disappearance was faster with the NaHCO3 treatment (P less than .05). The NaHCO3 may delay the fatigue precipitated by i.m. acidosis. Because other factors may limit performance (musculoskeletal soundness, cardiovascular and respiratory ability), NaHCO3 would not be expected to enhance the performance of all horses. However, the effect of NaHCO3 on lactate clearance may have implications for all intensively worked horses; because lactate and the associated hydrogen ions are believed to cause muscle damage and soreness, any mechanism to increase their removal rate could benefit the equine athlete.     

Relationship of blood corticosterone, immunoglobulin and haematological values in young crocodiles (Crocodylus porosus) to water temperature, clutch of origin and body weight

Objective To examine whether sub-optimal temperature induced stress and immunosuppression in farmed saltwater crocodile (Crocodylus porosus) hatchlings. Design A clinico-pathological study. Animals A total of 140 hatchlings were used. Procedure Body weight and length, plasma corticosterone and immunoglobulin concentrations and total and differential white blood cell counts were measured in 140 hatchlings from five clutches divided between five water temperature treatment groups. Initially all groups were housed at 32°C for 10 weeks, then two groups (L, LC) were changed to low temperature (28°C) and two groups (H, HC) to high temperature (36°C), while one group (C) remained at 32°C. The LC and HC groups were maintained at these temperatures for 10 days, after which the water temperature of both groups was returned to 32°C. Blood samples were collected twice (at 6 and 9 weeks of age) before the initial temperature change, and at 10 days and 4 weeks after the initial temperature change (at 11.5 and 14 weeks of age). Results Except for an increase in plasma corticosterone in the HC group and a decrease in the L group when the temperature change was first introduced, changes in plasma corticosterone were not significant. There were no significant changes in immunoglobulin concentrations. There were, however, significant decreases in the total white cell and lymphocyte counts in the LC group after the temperature was decreased to 28°C, and an increase in these counts after water temperature was returned to 32°C. Clutch of origin had significant effects on body weight and length gains, and there were negative relationships between body weight and corticosterone concentrations and between body weight and immunoglobulin concentrations. Conclusions As haematological changes indicative of stress were not associated with significant changes in serum corticosterone, immunosuppression in young crocodiles may be independent of the hypothalamic-pituitary-adrenal cortical axis.     

Evaluation of the efficacy of an epsiprantel/pyrantel combination against gastrointestinal helminths of dogs

Trials were conducted to evaluate the anthelmintic effect of a combination of epsiprantel at a dose rate of 5-5 mg/kg bodyweight and pyrantel pamoate at 5 mg pyrantel base/kg against Toxocara canis in prenatally infected unweaned greyhound pups, Toxascaris leonina, Uncinaria stenocephala, Trichuris vulpis and Dipylidium caninum in naturally infected adolescent greyhounds and Ancylostoma caninum, U stenocephala. Taenia hydatigena and Taenia pisiformis in artificially infected laboratory beagles. The product was well accepted and produced no obvious side effects. Percentage efficacy values based on post mortem worm counts were: T hydatigena 100; T pisiformis 100; D caninum 100; adult T canis 84-0; adult T leonina 96-5; immature T leonina 99-8; U stenocephala 99-0 and 87-7; A caninum 92-7; and T vulpis 43-3.     

森林经营中的地方分权和权力下放

一、引言 地方分权和权力下放，以及一系列相关的术语(如参与和权力)目前已被广泛用于有关林业政策的讨论中。但是这些术语过去常常被用来描述森林经营的各种方法和过程，并且常被错误地互换。本文的目的是界定这些术语和概念的含义；总结这些概念在实践中的应用方式，并依据已有的经验来指导将地方分权和权力下放这些概念应用于今后的森林经营实践。 二、定义和概念 地方分权和权力下放这两个术语常被互换，但区分二者之间的差别很重要。地方分权可以定义为：将地方的管理职能在当地进行重新分配，这并不一定意味着决策中心的改变或权力的…