利用ECMWF再分析数据验证PRECIS对中国区域气候的模拟能力

本文利用1979～1983年的ECMWF再分析数据作为准观测侧边界条件驱动Hadley气候预测和研究中心的区域气候模式系统PRECIS，验证PRECIS对中国区域的气候模拟能力。选择典型的观测站点北京模拟的日最高，最低气温、太阳短波总辐射和月均降水量与观测结果进行直接比较，显示：PRECIS具有很强的模拟地面气候季节变化的能力。全国740个台站的观测与模拟值的统计分析表明：尽管模拟的最高，最低气温在0℃附近有一‘锯齿’状的偏差，PRECIS能够很好地模拟全国范围最高，最低气温的型态分布特征；从全国范围看，模拟的降水值偏高，但显示出很强的模拟极端降水事件的能力；模拟的地面太阳短波总辐射与全国122个台站的观测结果的比较显示：PRECIS模拟的辐射值偏高，全国范围内约高22％。因此，当应用PRECIS输出结果进行气候变化的影响评价时，需要对模式的输出结果进行订正。     

Kinetics of soil microbial uptake of free amino acids

 Amino acids and proteins typically form the biggest input of organic-N into most soils and provide a readily available source of C and N for soil microorganisms. Amino acids can also be taken up directly by plant roots, providing an alternative source of available soil N. However, the degree to which plants can compete against the soil microbial population for amino acids in soil solution remains poorly understood. The aim of this study was to measure the rate of microbial uptake of three contrastingly charged ¹⁴C-labelled amino acids (glutamate^1–, glycine⁰, lysine^0.9+) over a wide concentration range (0.1–5 mM) and in two contrastingly managed soils varying in their degree of erosion, organic-C content and microbial biomass. Amino acid uptake was concentration dependent and conformed to a single Michaelis-Menten equation. The mean maximum amino acid uptake rate (V _max) for the non-eroded (control) soil (high organic-C, high biomass) was 0.13±0.02 mmol kg^–1 h^–1, while half maximal uptake occurred at a concentration (K _m) of 2.63±0.07 mM. Typically, V _max was fourfold lower and K _m twofold lower in the eroded soil (low available organic-C, low biomass) compared to the non-eroded (control) soil. Amino acid substrate concentration had little effect on the proportion of amino acid utilized in catabolic versus anabolic metabolism and was similar for both. While the results obtained here represent the summation of kinetics for a mixed soil population, they indicate that amino acid uptake is saturated at concentrations within the millimolar range. Because the affinity constants also were similar to those described for plant roots, we hypothesized that competition for amino acids between plants and microbes will be strong in soil but highly dependent upon the spatial distribution of roots and microbes in soil. Received: 2 March 2000     

Natal homing in a marine fish metapopulation

Identifying natal origins of marine fishes is challenging because of difficulties in conducting mark-recapture studies in marine systems. We used natural geochemical signatures in otoliths (ear bones) to determine natal sources in weakfish (Cynoscion regalis), an estuarine-spawning marine fish, in eastern North America. Spawning site fidelity ranged from 60 to 81%, comparable to estimates of natal homing in birds and anadromous fishes. These data were in contrast to genetic analyses of population structure in weakfish. Our findings highlight the need for consideration of spatial processes in fisheries models and have implications for the design of marine reserves in coastal regions.     

Plasma concentrations of cortisol, testosterone, glucose and blood gases in male goats during anaesthesia with pentobarbitone sodium

Fasting for 24 h had no statistically significant effect on cortisol, glucose or testosterone concentrations. A dose of pentobarbitone sodium which induced light anaesthesia resulted in an immediate decrease in cortisol values from 5.0-11.1 ng/ml to 2.2-3.6 ng/ml until waking-this latter event was accompanied by an excessive release of cortisol (up to 16.6 ng/ml). In two out of three goats testosterone concentrations decreased from 4.0-9.0 ng/ml to less than 0.5 ng/ml after pentobarbitone; low values were maintained for 4.5-6 hours. Glucose concentrations were unaffected. Precise doses of pentobarbitone (20 mg/kg or 30 mg/kg) resulted in similar cortisol profiles as above but with higher concentrations achieved upon waking from the higher dose of pentobarbitone. On two out of nine occasions increased PCO2 values were recorded concurrently with increased cortisol concentrations during the period of anaesthesia, suggesting that a sufficiently strong stressful stimulus can break through the pentobarbitone blockade.     

Effects of xylazine on the stress response to transport in male goats.

A 20-min van journey increased plasma cortisol concentrations to 15-25 ng/ml in male goats, blood glucose concentrations were not affected, but respiratory rates and heart rates were increased, the latter by 40 beats per min. A 2-h van journey increased plasma cortisol to greater than 25 ng/ml and blood glucose to greater than 5 mmol/l. Respiratory rates were increased to greater than 40 breaths per min and heart rates by greater than 100 beats per min. Xylazine alone (0.01 mg/kg) suppressed resting plasma cortisol concentrations, increased blood glucose concentrations to 4.5 +/- 0.8 mmol/l and suppressed respiratory rates by 5-10 breaths per min and heart rates by 20 beats per min. Cortisol concentrations were suppressed by xylazine treatment if given before a 20-min van journey, and for approximately 60 min if given 20 min after the start of a 2-h journey. When combined with transport, xylazine caused an additive effect on glucose concentrations, but suppressed respiratory and heart rates. However, for the latter criteria the timing of suppression was different depending on the time of onset and duration of the stressor. Injection of 50 micrograms ovine corticotrophin releasing factor (CRF) caused an immediate elevation of cortisol concentrations (but not glucose) which lasted for at least 6 h compared with the return to baseline within 60 min after either length of journey. Xylazine pretreatment did not alter the cortisol response to CRF, suggesting that xylazine must act centrally above pituitary level when blocking the cortisol response to transport. It is proposed that under resting conditions the hypothalamus is under alpha 2-adrenergic suppression. Stimulation of cortisol secretion in response to a stressor can be inhibited by an alpha 2-adrenergic agonist.     

Interspecific differences in early life‐history traits in a species complex of stream‐resident galaxiids

Fish differentially provision resources to eggs and larvae to optimise survival during the critical early life‐history period. Resource allocation is limited by a trade‐off between egg size and fecundity, and the optimal strategy varies with habitat type. This study examines the consequences of egg size differences for the early life‐histories of four closely related galaxiid species which occur in contrasting habitat types on the South Island, New Zealand. Headwater species had substantially larger water‐hardened eggs, longer incubation times, and newly hatched larvae were on average up to 41% longer than lower catchment species. Significant interspecific differences in gape diameter, eye diameter and myomere depth were also observed. Swimming ability was positively associated with larval length at hatch. Interspecific differences in length and swimming ability were generally maintained throughout the larval period, despite larvae being reared under relatively benign conditions where many other studies suggest initial differences should disappear. These results demonstrate the consequences of differential maternal provisioning to the egg for larval traits. The larger larvae of headwater species are likely to be more resistant to starvation and have improved foraging ability compared to lower catchment species; traits which are likely to confer them survival advantages in the low productivity, food‐scarce environments they occupy. The smaller larvae of lower catchment species are likely to be a consequence of females investing in fecundity in these relatively resource‐rich streams.     

Nitrous oxide fluxes and denitrification sensitivity to temperature in Irish pasture soils

Nitrous oxide (N₂O) emissions from grazed pastures constitute approximately 28% of total global anthropogenic N₂O emissions. The aims of this study were to investigate the effect of inorganic N fertilizer application on fluxes of N₂O, quantify the emission factors (EFs) for a sandy loam soil which is typical of large areas in Ireland and to investigate denitrification sensitivity to temperature. Nitrous oxide flux measurements from a cut and grazed pasture field for 1 year and denitrification laboratory incubation were carried out. The soil pH was 7.3 and had a mean organic C and N content at 0–20 cm of 44.1 and 4.4 g/kg dry weight, respectively. The highest observed peaks of N₂O fluxes of 67 and 38.7 g N₂O‐N per hectare per day were associated with times of application of inorganic N fertilizer. Annual fluxes of N₂O from control and fertilized treatments were 1 and 2.4 kg N₂O‐N per hectare, respectively. Approximately 63% of the annual flux was associated with N fertilizer application. Multiple regression analysis revealed that soil nitrate and the interaction between soil nitrate and soil water content were the main factors controlling N₂O flux from the soil. The derived EF of 0.83% was approximately 66% of the IPCC default EF value of 1.25% as used by the Irish EPA to estimate greenhouse gases (GHGs) in Ireland. The IPCC‐revised EF value is 0.9%. A highly significant exponential regression (r² = 0.98) was found between denitrification and incubation temperature. The calculated Q₁₀ ranged from 4.4 to 6.2 for a temperature range of 10–25 °C and the activation energy was 47 kJ/mol. Our results show that denitrification is very sensitive to increasing temperature, suggesting that future global warming could lead to a significant increase in soil denitrification and consequently N₂O fluxes from soils.     

Effect of hydroxyethyl starch infusion on colloid oncotic pressure in hypoproteinemic horses

OBJECTIVE: To determine the effect of hydroxyethyl starch (HES) on colloid oncotic pressure (pi) during fluid resuscitation of hypoproteinemic horses and to evaluate the clinical usefulness of direct and indirect methods for determination of pi before and after infusion of a synthetic colloid. DESIGN: Prospective clinical study. ANIMALS: 11 hypoproteinemic horses. PROCEDURE: Horses received IV infusions of 8 to 10 ml of a 6% solution of HES/kg (3.6 to 4.5 ml/lb) of body weight during fluid resuscitation. Blood samples were obtained for determination of plasma measured colloid oncotic pressure (pi meas) and plasma total protein and albumin (A) concentrations. Plasma globulin concentration (G) was calculated as the difference between plasma total protein and albumin concentrations. Calculated values for colloid oncotic pressure (piA + G) were determined by use of a predictive nomogram previously developed for horses. RESULTS: There was no significant difference between the means of pi meas and piA + G at the beginning of HES infusion. After HES infusion, the mean of pi meas was increased significantly from baseline for 6 hours. Mean plasma total protein and albumin concentrations and piA + G were decreased significantly from baseline for 24 hours. Differences between mean pi meas and piA + G after HES infusion were significant for 24 hours. CONCLUSIONS AND CLINICAL RELEVANCE: There was good agreement between plasma pi meas and piA + G in blood samples obtained from hypoproteinemic horses immediately before infusion of HES. Use of a predictive nomogram did not, however, account for the oncotic effect of HES. Results of comparison of pi meas to piA + G after HES infusion suggest that a significant oncotic effect was maintained for 24 hours in the study horses.