Effect of gradient of temperature upon flows in the whole maize plant

Transport of ions in young maize plants was affected by the temperature gradient (gradT). This influence was dependent on the age of plants and the solute concentrations in compartments at the two sides of plants. When gradT was increased, current, volume and heat flows rose during 20 min and then declined. On the other hand, the diffusive flow only declined. The character of the flow changes was given by the changes in permeability and reflection coefficients. In young plants under low solute concentration on both sides of plants, the permeability of the plant tissues shifted from positive to negative values. Under higher solute concentrations on both sides of the plants such phenomenon was not observed. At high gradT the reflection coefficients of the plant tissues were low, but they rose during levelling the temperature in the two compartments.     

Non-marital pregnancies in New Zealand since the Second World War

The % of illegitimate births in New Zealand more than doubled from 1951 to 1976. Through 1971 most of this increase was due to an increase in nonmarital fertility rates. After 1971 most of this increase was due to a decrease in marital fertility rates. The % of pregnant brides in New Zealand increased from the beginning of available statistics in 1940, leveled off in the early and mid 1960s, and has been declining since then. This is not a measure of premarital sexual activity in the population. But the declining trend is mainly due to the declining probability of marriage when nonmaritally pregnant and the rising probability of marrying when not pregnant. Nonmarital pregnancy rates increased from 1940 to the mid 1960s before levelling off and dropping sharply during the 1970s. The increase is believed to be be due to an increase in premarital sex. The levelling off reflects the advent of the pill. The declining rate is probably due to the increased availability of abortion. A greater openness about premarital sexuality leading to an increase in the use of contraceptives also could have been a contributing factor. Data is divided into non-Maori and total population.     

A network thermodynamic model of kidney perfusion with a cryoprotective agent

A network thermodynamic model has been devised to describe the coupled movement of water and a permeable additive within a kidney during perfusion under the combined action of diffusive, hydrodynamic, and mechanical processes. The model has been validated by simulating perfusions with Me2SO, glycerol, and sucrose and comparing predicted weight and vascular resistance with experimental results obtained by Pegg (1993). The flows of CPA, water, colloid, and cellular impermeants are governed by a combination of the individual osmotic potential and pressure differences between compartments of the kidney, the viscoelastic behavior of the tissue, and the momentum transferred between the flows. The model developed in this study presents an analytical tool for understanding the dynamics of the perfused kidney system and for modifying perfusion protocols to minimize the changes in cell volume, internal pressure build-up, and increases in vascular resistance that currently present barriers to the successful perfusion of organs.     

Trends in the Supply and Distribution of Physicians in Saskatchewan: January 1962 to June 1964

Using all the readily available sources of information, a study was designed to describe the changes in supply and distribution of physicians in Saskatchewan during the inception of the Province''s controversial Medical Care Insurance Act. Baselines were obtained in January 1962, and comparisons made in June 1963 and June 1964. The physician:population ratio was 1:1037 in January 1962 and 1:980 in June 1964. The average yearly physician turnover rate of 10% was exceeded in 1960 and in 1961 and then levelled off. The levelling off continued from January 1962 to June 1963. But between June 1963 and June 1964 the total number of physicians was sufficient both to re-establish the rising trend of the previous decade and to offset some of the losses of 1960-1962.     

Alternative explanations for rising dissolved organic carbon export from organic soils

Since 1988, there has been, on average, a 91% increase in dissolved organic carbon (DOC) concentrations of UK lakes and streams in the Acid Waters Monitoring Network (AWMN). Similar DOC increases have been observed in surface waters across much of Europe and North America. Much of the debate about the causes of rising DOC has, as in other studies relating to the carbon cycle, focused on factors related to climate change. Data from our peat‐core experiments support an influence of climate on DOC, notably an increase in production with temperature under aerobic, and to a lesser extent anaerobic, conditions. However, we argue that climatic factors may not be the dominant drivers of DOC change. DOC solubility is suppressed by high soil water acidity and ionic strength, both of which have decreased as a result of declining sulphur deposition since the 1980s, augmented during the 1990s in the United Kingdom by a cyclical decline in sea‐salt deposition. Our observational and experimental data demonstrate a clear, inverse and quantitatively important link between DOC and sulphate concentrations in soil solution. Statistical analysis of 11 AWMN lakes suggests that rising temperature, declining sulphur deposition and changing sea‐salt loading can account for the majority of the observed DOC trend. This combination of evidence points to the changing chemical composition of atmospheric deposition, particularly the substantial reduction in anthropogenic sulphur emissions during the last 20 years, as a key cause of rising DOC. The implications of rising DOC export for the carbon cycle will be very different if linked primarily to decreasing acid deposition, rather than to changes in climate, suggesting that these systems may be recovering rather than destabilising.     

The growing difference between limnology and aquatic ecology

Research objectives of ecology and limnology differ: in the first emphasis is on the species approach and in the second on the ecosystem approach. It is stressed that the formation of compartments in ecosystem studies leads to a loss of information essential to the understanding of ecosystem functioning. The disciplines differ in yet another respect, namely the predominance of biotic factors in ecological research and of abiotic factors in limnological research. The research of aquatic ecologists is mostly species oriented thus compares better with ecology than with limnology. The raised points of discussion are illustrated with examples from studies of the author and his co-workers into diel vertical migration of zooplankton. As a final conclusion, it is suggested that feedback information flows regulate quantities of compartments and material flows. A picture in which material flows between compartments is combined with immaterial flows of information is presented. Last but not least, the increasing attention of limnologists, especially in The Netherlands, to applied research is considered a danger for the development of limnology as a science and for the education of students. Thus a plea is made to concentrate on fundamental research at least by those at universities and research institutes originally established with the aim to do pure science.     

蚜虫(Aphis medicaginis Koch)危害胁迫对不同苜蓿品种体内丙二醛含量及防御性酶活性的影响

研究了蚜虫危害胁迫后不同抗蚜性苜蓿品种叶片内丙二醛含量及防御性酶活性的动态变化。结果表明：在蚜虫刺吸诱导的过程中,高感品种的MDA含量始终高于高抗品种,并且高感和高抗品种均保持上升的趋势;高感品种的SOD、POD和PAL活性始终低于高抗品种,其中高感和高抗品种的SOD和POD活性均表现先上升后下降的趋势,而PAL活性上升到高峰后均趋于稳定;CAT活性在高感和高抗品种间表现为交替的上升下降;高抗品种的PPO活性前期低于高感品种,而后期高于高感品种。由此可见,在蚜虫危害胁迫下,高感和高抗品种间MDA、SOD、POD、PAL和PPO活性的变化与苜蓿的抗蚜性密切相关,均可作为苜蓿抗蚜性鉴定的生理指标,而CAT活性变化与苜蓿抗蚜性的联系有待进一步研究。     

Soil water balance in rainfed vineyards of the Penedès region (Northeastern Spain) affected by rainfall characteristics and land levelling: influence on grape yield

Rainfed agriculture has experienced important transformations in the Mediterranean area over the last decades. This is particularly true for traditional vineyards which have been restructured after levelling operations designed to facilitate the use of machinery. Levelling operations change soil properties and structure, negatively affecting soil hydrological processes, decreasing soil water intake and storage in the soil profile. This effect may become exacerbated under a climate change scenario as a result of increased water losses due to runoff after high intensity events and the resulting decrease in water availability for crops. This paper examines the effects of land levelling, carried out before the establishment of new vineyards, on soil water availability for vineyards in a Mediterranean climate area. These effects have been analysed taking into account the different rainfall distribution patterns in the study area, including extreme events. Soil moisture was analysed at depths of from 0 to 80 cm, for a 12 year period, in areas with different degrees of disturbance as a result of land levelling operations. Simulated rainfall was applied at the same points to evaluate the steady infiltration rate and to estimate runoff rates. Precipitation, runoff, crop evapotranspiration and changes in soil moisture were assessed for each crop stage and year for the vine varieties Macabeo, Chardonnay and Parellada. Precipitation was not enough to satisfy crop water requirements in many years, particularly during the bloom–veraison and ripening stages. Soil water content had a significant effect on grape yield, particularly the available water content during the budburst–bloom and bloom–veraison stages. Differences in yield of about 50% between years and of over 28% between levelled and non-levelled areas under similar management practices were observed.     

Female choice impacts resident male takeover in golden snub-nosed monkeys(Rhinopithecus roxellana)

In primate species with social systems consisting of one-male breeding units(OMUs), resident male takeover represents a major challenge to individual reproductive success and mating strategies. The golden snub-nosed monkey(Rhinopithecus roxellana)is characterized by large multilevel societies(MLS)comprised of several OMUs and all-male units(AMUs);however, the factors and mechanisms associated with resident male takeover, which offer important insight into primate reproduction and social strategies, are still poorly understood. Based on 5-year monitoring data from a free-ranging herd of golden monkeys from the Qinling Mountains in China, we categorized three phases of an OMU, that is, a rising phase,developing phase, and declining phase. The rising and declining phases were unstable periods in which male takeover in an OMU might occur. Factors causing takeover, such as leader male rank, fighting ability, reproduction rate, and affiliation(proximity,allogrooming), were analyzed for males and females and for different OMUs. Results indicated that the new resident male's fighting ability was lower than that of the former resident male in 23 cases. After replacement, the rank order of the new resident male significantly declined. Females involved in a takeover increased their distance from the resident male and decreased mating frequency during the three months prior to takeover. Females with infants under one-year-old had a marked effect on the specific time of takeover occurrence. These results suggested that female choice was the main factor deciding whether a takeover attempt was successful. Furthermore, rather than male conflict, females more often initiated and affected takeover and outcome, implying that the social status and competitive ability of the males played lesser roles during takeover.     

Modeling the Values of Net Primary Production for the Zonal Vegetation of European Russia

Several modern approaches to the problem of estimating the net primary production of terrestrial ecosystems are discussed. A method for predicting the dynamics of this parameter as a function of radiation balance and annual evapotranspiration is described. The values of annual carbon by the zonal vegetation of European Russia are calculated in two ways: by methods based on the empirically determined relationships between the annual average values of climatic parameters and net primary production and on the basis of models describing carbon flows between the compartments of ecosystems. The model estimations of net primary production are compared with experimental data.     

Phosphate-limited continuous culture of Rhodotorula rubra: kinetics of transport, leakage, and growth.

The phosphate-limited growth kinetics of Rhodotorula rubra, a small yeast of marine origin, were examined by analysis of 32P distributions in continuous cultures. Isotope relaxation procedures were used to identify unidirectional flows of Pi and organic phosphate among compartments modeled during growth. The concentrations of phosphates in these compartments at various growth rates were used, together with attendant flows, to produce a mathematical model of growth. Both Pi and phosphate-containing metabolic intermediates leaked from cells during growth. Total leakage ranged from 4 to 10% of influx and was comprised mostly of Pi. Transport capacity was at least 10 times that required for growth at saturating Pi concentrations, so that influx was linear with concentration during growth. This led to the realization that the curvature of Monod plots (Kmu = 12 nM mumax = 0.18/h, and the threshold At = 2.5 nM) is due to change in yield with growth rate. Growth rate related to Pi by the affinity, aA (= 0.43 liter/mg of cells.h) of cells for Pi and the growth rate-dependent yield. It was also specified by a series of kinetic constants that specified flow among the various compartments and equilibrium compartment concentrations as they were set by extracellular Pi. The importance of leakage by healthy cells to the organic chemistry of aquatic systems is noted.     

A non-linear model of phosphorus flux in the phytoplankton of a temperate eutrophic reservoir

Phosphorus fluxes in phytoplankton, between intracellular andexternal compartments have been measured, in the epilimnion ofatemperate eutrophic reservoir, by means of phosphorusdepletionexperiments performed in situ. Flow rates betweencompartments were plotted against the phosphorus concentrationofthe compartments' origin of the flows and fitted to saturationfunctions.A value of phosphorus cell subsistence quota for the wholecommunity has been computed from the X-intercept values ofeveryfunction. The obtained figures are 10–100 times higher,dependingon the reference value, than those measured running theclassicalsingle species growth response experiments in chemostats.We propose a model using five compartments and a series offlowrates between them in order to simulate the general phosphoruscycling in freshwater phytoplankton. Short term simulation ofphosphorus content in every compartment shows a fluctuatingpatternaround rates of equilibrium, in agreement with the pattern ofvariation observed in situ for the selectedcompartments.     

Extracellular K+ and Ca2+ activities measured during the action of negative pressure under a suction electrode placed on the surface of frog heart ventricle

The application of negative pressure of -40 kPa (-300 mm Hg) for 10 min under a suction electrode placed on the surface of the spontaneously beating frog ventricle changed the extracellular potassium activity (aoK+) in three phases: a phase of rapidly rising aoK+, a slowly decaying phase and a phase of slowly rising aoK+. The changes reversed when suction was discontinued during the rapidly rising and decaying phase, but were not reversed during the slowly rising phase. Calcium extra-cellular activity (aoCa2+) decreased between -5 and -13 kPa, but increased during the higher pressures. The results indicated that injury of the ventricular tissue caused by a suction electrode elevated aoK+ and altered aoCa2+.     

Responses of luteinizing hormone (LH) and follicle-stimulating hormone levels to exogenous gonadotropin-releasing hormone during the estrogen-induced LH surge in the ovariectomized rhesus monkey

Experiments were performed to study the responsiveness of the pituitary to gonadotropin-releasing hormone (GnRH) during the dynamic changes in gonadotropin secretion associated with the estrogen-induced luteinizing hormone (LH) surge in the ovariectomized (OVX) rhesus monkey. Silastic capsules filled with estradiol-17-beta were implanted subcutaneously in ovariectomized rhesus monkeys, resulting in an initial lowering of circulating LH and follicle-stimulating hormone (FSH) concentrations followed by an LH-FSH surge. GnRH was injected intravenously just before estrogen implantation, during the negative feedback response and during the rising, the peak, and the declining phases of the LH surge. The LH and FSH responses during the negative feedback phase were as large as those before estrogen treatment (control responses). During the rising phase of the LH surge, the acute response to GnRH injection did not differ significantly from the control response, but the responses 60 and 120 min after injection were somewhat increased. During the declining phase of the LH surge, the pituitary was not responsive to exogenous GnRH, although LH probably continued to be secreted at this time since the LH surge decreased more slowly than predicted by the normal rate of disappearance of LH in the monkey. We conclude that an increased duration of response to GnRH may be an important part of the mechanism by which estrogen induces the LH surge, but we do not see evidence of increased sensitivity of the pituitary to GnRH as an acute releasing factor at that time.     

A stochastic compartmental model with continuous infusion

This paper deals with stochasticm-compartmental systems with continuous time-dependent infusions into all compartments and reversible time-independent flows between any two compartments. A methodology for the first two moments of the distribution of the number of units in the different compartments at any point in time is outlined without resorting to the usual techniques of generating functions and inverse Laplace transforms. A possible application to a systems analysis of the kidney transplant system is discussed.     

An Analysis of the Effects of Temperature and Light Integral on the Vegetative Growth of Pansy cv. Universal Violet (Violaxwittrockiana Gams.)

Pansies (Viola xwittrockiana Gams.) cv. Universal Violet weresown on five dates between Jul. and Dec. 1992 and placed insix temperature-controlled glasshouse compartments set to providemean temperatures between 6.5 and 30 °C. Shoot dry weightand leaf number were recorded. A model was constructed, to analysethe effects of light and temperature on dry matter accumulation,which assumed that relative growth rate (RGR) declined linearlywith thermal time accumulated from sowing, reflecting ontogeneticdrift. Furthermore, it assumed that RGR was a semi-ellipsoidfunction of temperature, rising to an optimum of 25.3 °Cand declining thereafter, and a positive linear function oflight integral. When fitted to data collected in this studythe model accounted for 94% of the variance in RGR. Independentvalidation using data from four further crops grown in glasshousecompartments at four different set point temperatures showedthat the model could also be used to predict plant dry weightaccurately (r ²=0.98). The rate of mainstem leaf productionwas also linearly related to both light integral and temperature. Pansy; Viola xwittrockiana ; temperature; light integral; dry weight; relative growth rate; leaf number     

Drift patterns of particulate matter and organisms during artificial high flows in a large experimental channel

Using a large experimental channel, five artificial high flows with different flow regimes were launched to reveal the precise temporal sequences of drifting particulate matter and organisms during the high flows. Drifting fine particulate matter and organisms were collected by sampling bottles and a water pump, respectively. The peaks of drift abundance occurred before the peak discharges, and the abundance declined quickly within several minutes during the rising phase of high flows. The major determinant of drift abundance of particulate matter and organisms was periods of stable conditions before each high flow (tested by determination coefficients in a correlation analysis). The drift of macroscopic plant material also accelerated the drifts of epiphytic fauna and infauna, which drifted with plants and bed sediments. The magnitude (discharge and duration of peak flows) of high flows only slightly affected drift abundance. The fauna more resistant to high flows were invertebrates that fasten their cases or retreats by silk threads on the substrata. Invertebrate taxa having sucking apparatus or high swimming activity were also resistant to high flows.     

Ecosystem multifunctionality lowers as grasslands under restoration approach their target habitat type

Biodiversity is declining at a rapid pace and, with it, the ecosystem functions that support ecosystem services. To counter this, ecosystem restoration is necessary. While the relationship between biodiversity and ecosystem functioning has been studied in depth, the relationship between ecosystem restoration and ecosystem functioning is studied less. We performed an observational study in grasslands undergoing restoration management toward Nardus grassland. Eight ecosystem functions, representing flows of energy, matter or information between functional compartments, were measured across five successive restoration phases along the restoration gradient. The levels of functioning were then compared along the gradient for both the individual functions and a multifunctionality index. We hypothesized that plant richness increases when grasslands are more restored and this increase in biodiversity is paralleled by an increase in ecosystem functioning. In our study, the degraded grasslands, generally occurring on more nutrient-rich soils, were dominated by competitive fast-growing species, resulting in higher process rates and thus in higher, faster functioning. Likewise, more restored grasslands exhibited slower process rates and, thus, lower functioning. When studying ecosystem functioning, value judgments are easily made. Especially in a restoration context, high functioning does not necessarily equals well functioning, as this depends on the stakeholder perspective. We need to ask ourselves if a high functioning ecosystem is most desirable, especially in a restoration or conservation context. Policy frameworks will need to balance these goals.     

Seasonal Changes in Respiration, Photosynthesis, and Translocation of the 14C Labelled Products of Photosynthesis in Young Pinus strobus L. Plants

Three-year-old Pinus strobus plants, grown under conditionsof either high or low light intensities, were brought from thenursery to the laboratory every three to four weeks from themiddle of April 1961 until January 1962. Translocation, measuredas the amount of ¹⁴C recovered from the roots at the end ofseven hours of illumination following exposure of the shootto ¹⁴CO₂, was found to be high in the spring, dropping to negligibleamounts during June and July, increasing again in the autumnand declining after October. Seasonal variation in root respirationwas found to parallel that of translocation. Rates of apparentphotosynthesis were low during the spring, rising to a maximumduring September, and then declining over the winter. The respiration,photosynthesis, and translocation of the low-light grown plantsfollowed a similar pattern to those grown in high-light, exceptthat in general rates were of a lower order. In the high-light grown plants more than 90 per cent of theabsorbed carbon was present in the ethanol-soluble form, ofwhich sugars formed at least 90 per cent. This was even morepronounced in the case of low-light grown plants. The main sugarwas always sucrose. The raffinose content was found to decreaseduring the warmer months. The new needles, during their period of maximum growth, fixedcarbon dioxide photosynthetically at a rate comparable to thatof the old needles. The new stems also possessed a relativelyhigh carbon dioxide fixing ability. Shoot growth, as measured by the increase in length of the newleader stem and new needles, showed the typical patterns forpine species.