Simulated and measured nitrogen conditions in a manured and fertilised soil

The governing factors for soil nitrogen dynamics were identified with a simulation model. In addition, the model was used to interpret measurements from a plot fertilisation experiment in southwest Sweden.Simulated moisture and temperature conditions were the driving variables for the simulation of soil nitrogen dynamics and leaching during a 6-year period. The results of the simulation were compared with monthly observations on two plots with grain crops, one with liquid manure and commercial fertilisers applied and one with commercial fertilisers only.Simulated temporal variations of the nitrate and ammonium storages generally agreed with observations. The dominant role of the crops as a determinant of soil nitrogen conditions was demonstrated. A higher leaching loss from the plot with application of commerical fertilisers only occurred both in simulations and measurements compared to the plot with application of both commercial fertilisers and manure. The main reason was the higher N-application in the former treatment.The effect of water flows in macropores was interpreted as a delay of simulated leaching compared to observed leaching on some occasions in summer and early autumn. No direct effect of the macropores on the yearly rates of leaching could be seen.     

Seasonal nitrogen and carbon concentrations in white,brown and woody fine roots of sugar maple (Acer saccharum Marsh)

Small diameter (<1.0-mm) Acer saccharum Marsh roots were separated into white, brown and woody development state classes and analyzed for total N and C concentrations in April, July and October of 1988. White roots had greater concentrations of N and C than either brown or woody roots at each sampling date, and the N concentration of brown roots was consistently greater than that of woody roots. There were no temporal changes in N concentrations in any of the roots. C was slightly elevated in mid-summer in all three classes of roots. The data suggest the possible existence of an N translocation mechanism in ageing and developing fine roots. More research should be undertaken to establish the mechanisms of N loss in developing fine roots.     

Rhizosphere pH along different root zones of Douglas-fir (Pseudotsuga menziesii), as affected by source of nitrogen

Douglas-fir, grown on strongly acid soil (pH-H₂O 3.87), was fertilized with ammonium, nitrate or ammonium nitrate as N-source. Rhizosphere pH along the root axis was measured with microelectrodes. Pure ammonium supply resulted in acidification of the rhizosphere, almost along the entire root axis; only the extreme root tip was slightly alkaline compared with the bulk soil. With nitrate supply, the alkalization of the rhizosphere at the root tip was considerably stronger than with ammonium supply and the length of the alkalization zone greater, extending over the entire growth zone of the root. Acidification of the rhizosphere along the older parts of the root was less pronounced in the case of nitrate. It is concluded that nitrate nutrition enables the plant to protect its most essential root zone from the adverse effects of strong acidity by locally raising the rhizosphere pH.     

Effect of various irradiation treatments of plant protoplasts on the transformation rates after direct gene transfer

Summary In P. hybrida and B. nigra an enhancement of transformation rates (direct gene transfer) of about six to seven-fold was obtained after irradiation of protoplasts with 12.5 Gy (X-ray). The effect of protoplast irradiation was similar in experiments where protoplasts were irradiated 1h before transformation (X-ray/DNA) or 1h after completion of the transformation procedure (DNA/X-ray). Increased X-ray doses up to 62.5 Gy resulted in further enhancement of percentages of transformed colonies, indicating a correlation between relative transformation frequencies (RTF) and the doses applied. Estimation of degradation rates of plasmid sequences in plant protoplasts yielded a reduction of plasmid concentration to 50% 8–12 h after transformation. In 1-day-old protoplasts, the level of plasmid fragments dropped to 0%–10% compared to 1h after transformation. The results demonstrate that the integration rates of plasmid sequences into the plant genome may in part be governed by DNA repair mechanisms. This could be an explanation for the observed genotypic dependence of transformation rates in different plant species and plant genotypes. Gene copy number reconstructions revealed enhanced integration rates of plasmid sequences in transformed colonies derived from irradiated protoplasts.     

Energy expenditure and locomotor activity in mice selected for food intake adjusted for body weight

Summary The aim of this study was to examine the differences in physical activity and their contribution to differences in energy utilization in mice, selected either high or low for food intake, adjusted for body weight, which show correlated responses in lean content and metabolic rate. Simultaneous measurements of fasting metabolic rate and activity were made in lines of mice selected at either: a young age, 4-to 6-week food intake corrected for 4-week body weight; or an older age, 8- to 10-week food intake corrected for mean weight at 8 and 10 weeks of age. Correlated response in metabolic rate was found to have been accompanied by changes in locomotor activity near the ages at selection in both sets of lines. Activity, however, accounted for only a small proportion of variation in fasting heat production, generally less than 5%, although a highly positive correlation (r=0.63) between the two traits was found. It was concluded that selection for food intake adjusted for body weight has led to correlated response in physical activity. In consequence, mice selected in the upward direction expend some of the excess energy intake rather than assimilating it as body mass and are, therefore, slightly leaner than their counterparts selected in the downward direction.     

Acidosis, Acetazolamide, and Amiloride: Effects on 22Na Transfer Across the Blood-Brain and Blood-CSF Barriers

Sprague-Dawley rats were given treatments, known to decrease 22Na movement into choroid plexus and CSF, to investigate their effect on 22Na transfer across the cerebral capillaries. Acidic salts, acetazolamide, or amiloride was injected intraperitoneally into bilaterally nephrectomized rats, and the rate of 22Na uptake into parietal cortex, pons-medulla, and CSF was determined at 12, 18, and 24 min. Severe acidosis (arterial pH 7.2), produced by HCl injection, decreased the rate of 22Na entry into both brain regions and CSF by 25%, whereas mild acidosis (pH 7.3) from NH4Cl injection reduced brain entry by 18%, but CSF entry by only 10%. Like HCl acidosis, amiloride reduced transport into both brain and CSF by 22%. Penetration of 22Na into parietal cortex was unchanged by acetazolamide, but that into CSF was slowed 30%. Since uptake of 22Na into cortical regions is primarily movement of tracer across the cerebral capillaries when tracer uptake time is less than 30 min, the results indicate that both metabolic acidosis and amiloride decrease Na+ permeativity at the cerebral capillaries as well as at the choroid plexus. Acetazolamide, on the other hand, alters Na+ movement only across the choroidal epithelium.     

海南大田自然保护区海南坡鹿种群动态研究

笔者自1986年起对仅存于海南大田国家级保护区围栏内外两个坡鹿种群进行了连续4年追踪研究,就数量、年净增长率、年均增长率、年龄组成、性比、成幼比、母仔比、及补充率和死亡率进行了分析。围栏内外坡鹿年均增长率22.5％和10.6％,年净增长率逐年呈下降趋势。补充率下降是围栏内坡鹿年净增长率下降的主要原因,而这是由于密度过高、食物不足造成的;围栏外坡鹿年净增长率下降是死亡率增加的结果,偷猎是主要因素。对性比、成幼比、母仔比变化的分析也得出了同样的结论。本文最后提出了保护建议。     

Effect of cooling rate,cryoprotectant and holding time at different transfer temperatures on the survival of cryopreserved cell suspension culture (Puccinellia distans (L.) Parl.)

Reflexed saltmarsh-grass suspension cultures produced by seed callus were frozen to the liquid nitrogen temperature. Cooling rates, cryoprotectants and holding times were taken as a function of transfer temperatures. The highest survival of cells (45%) was found at a freezing rate of 1°C min^-1, without cryoprotectant treatments. The cryoprotectants (proline, dimethyl sulphoxide, glycerol), used at different concentrations and transfer temperatures, increased the survival rate. The maximum value was 78% at 12.5% (w/v) of proline with –30°C transfer temperature. Considerable improvement of viability (from 0% to 95%) among the 12.5 and 15.0% (v/v) dimethyl sulphoxide cryopreserved cells was achieved by holding them at – 20°C for 10–30 min before plunging into the liquid nitrogen. A 20 min holding time at 15.0% (v/v) glycerol level and – 30°C transfer temperature significantly enhanced the viability of the explants from 42% to 92%. Plants were successfully regenerated from cells cryopreserved with proline (w/v) and dimethyl sulfoxide (v/v) levels of 12.5 and 15.0%, respectively.     

Effect of harvest intensity and ground flora establishment on inorganic-N leaching from a Sitka spruce plantation in north Wales,UK

Inorganic-N concentrations in soil solution of whole tree harvest (WTH) and conventional fell (CF) plots were monitored for two years before felling and four years after felling. Concentrations in the mineral soil after felling were higher than in standing forest for up to 14 months in both felling treatments. In the WTH plots inorganic-N concentrations then dropped steadily until four years after felling they approached zero. In contrast, inorganic-N concentrations of the CF plots remained comparatively large. Inorganic-N was dominated by nitrate throughout the period of the study, and especially in the mineral horizons.Felling debris was not a source of inorganic-N, unless indirectly through release and mineralisation of soluble organic-N. Vegetation cover, biomass and N content were substantially greater in the WTH plots two to three years after felling, compared with the CF. Vegetation cover and brash cover (slash cover in N. America) were negatively correlated. There was also a negative correlation between inorganic-N concentration in soil water samplers and the vegetation cover within the collection area of, or a 1 m square surrounding, these samplers.Two factors are probably responsible for the reduction in inorganic-N concentrations after felling in the WTH — the rapid re-establishment of vegetation and the lack of a N source in felling debris. In the CF plots, brash prevents re-establishment of vegetation over wide areas for at least four years. However, brash is not directly a source of inorganic-N at this stage.     

The cumulative effect of wetlands on stream water quality and quantity. A landscape approach

A method was developed to evaluate the cumulative effect of wetland mosaics in the landscape on stream water quality and quantity in the nine-county region surrounding Minneapolis—St. Paul, Minnesota. A Geographic Information System (GIS) was used to record and measure 33 watershed variables derived from historical aerial photos. These watershed variables were then reduced to eight principal components which explained 86% of the variance. Relationships between stream water quality variables and the three wetland-related principal components were explored through stepwise multiple regression analysis. The proximity of wetlands to the sampling station was related to principal component two, which was associated with decreased annual concentrations of inorganic suspended solids, fecal coliform, nitrates, specific conductivity, flow-weighted NH₄ flow-weighted total P, and a decreased proportion of phosphorus in dissolved form(p < 0.05). Wetland extent was related to decreased specific conductivity, chloride, and lead concentrations. The wetland-related principal components were also associated with the seasonal export of organic matter, organic nitrogen, and orthophosphate. Relationships between water quality and wetlands components were different for time-weighted averages as compared to flow-weighted averages. This suggests that wetlands were more effective in removing suspended solids, total phosphorus, and ammonia during high flow periods but were more effective in removing nitrates during low flow periods.