Effect of habitable space on substrate selection by Paragnetina media (Walker) (Plecoptera: Perlidae)

A biological measure of space available within substrates was used as an index to examine substrate selection by the stonefly nymph Paragnetina media (Walker). Physical measures, such as total surface area of substrate, have not worked well in the past in explaining distribution of aquatic invertebrates. Although analysis of habitable space within substrate did not explain selection completely, the technique provided a precise measure and might be a more rigorous means by which substrate selection could be examined.     

人体急性缺氧性意识障碍

实验分为低压组(低压舱7,000米)与常压组(吸入7.6％低氧混合气),每组受试者各为12名,有7名参加了两组实验。每组各有4名平均经15分23秒发生了意识模糊或丧失(通称意识障碍)。障碍者的肺泡氧分压为29.9±0.8mmHg。障碍发生前,呈现严重无力,觉醒度降低,反应迟钝,脑波特征是高幅6波(100-300μV)占优势。障碍发生时,高幅δ波丧失节律,幅度衰减,波型不规则,额枕失同步;呼吸循环代偿功能增强程度明显高于障碍前。本工作对于预测和评价人体急性缺氧引起的意识障碍有意义。     

夏季高温对水牛瘤胃代谢的影响

利用南京地区夏季炎热的自然条件,连续两年在高温季节(7—8月)进行实验。第一年(系列Ⅰ)的实验动物为四头装置瘤胃瘘管的空怀母水牛,研究高温初期(27.5～33.4℃)和持续高温期(28.0～35℃)对水牛瘤胃消化代谢的影响。第二年实验(系列Ⅱ)利用三头装置瘤胃瘘管的海仔母水牛重复高温(26～35.3℃)实验。 夏季高温期间,实验水牛的呼吸率、瘤胃温度和直肠温度升高,采食量减少,饮水量增加,瘤胃液流速减缓。高温初期出现瘤胃代谢升高[总挥发性脂肪酸(TVFA)和氨氮(NH_3-N)浓度及乙酸/丙酸(A/P)比率升高]。但在持续高温情况下,水牛的采食和瘤胃代谢均明显抑制。采取瘤胃内降温措施(投入冰袋)或冷水淋浴,均能迅速降低呼吸率、直肠和瘤胃温度,恢复采食和反刍,并缓解瘤胃代谢的抑制。提示动物机体参与调节瘤胃代谢的变化,并为改善水牛夏季的饲养管理提供生理学依据。     

Effects of irradiation level on leaf growth of sunflower

Sunflower, Helianthus annuus L. cv. INRA 6501, plants were grown in a gravel culture subirrigated with Hoagland nutrient solution, at photosynthetically active radiation levels of 15, 30 and 60 W m^-2 at a daylength of 16 h, a temperature of 20°C and a relative humidity of 60% throughout. Development of the plant and growth of the leaves were measured. High irradiance accelerated development proportionally in all phases from germination, through leaf initiation, primordial flower formation and the maturation of all plant organs until anthesis. High irradiance levels stimulated the expansion of the growing shoot, which produced more and larger primordia. Under constant conditions the ratio between leaf initiation rate and mature length of a leaf remained constant, although the growth patterns [relationship between relative growth rate (RGR) and organ age] of successive leaves were not similar. Consequently, it may be assumed that, as in poplar, the increasing size of the growing shoot reflects the increase of the vascular system of sunflower. The growth patterns of the leaves depend on the developmental stage of the plant and, in the young primordial stage, also on irradiance level. In the linear phase of growth the growth pattern is independent of irradiance level.     

Senescence of attached leaves: Regulation by developing pods

Analysis of total nitrogen, chlorophyll content, ribulose-1,5-bisphosphate carboxylase/oxygenase activity and net photosynthesis rate was carried out on the leaves that support the developing pods in pigeon pea [ Cajanus cajan (L.) Millsp. cv. Prabhat] at several stages during pod filling. A continuous loss in all the above-mentioned parameters was observed during the course of pod development. When no pods were allowed to develop by continuous flower removal treatment, there was a considerable delay in loss of all these metabolic parameters. Excision of pods after their mid-development resulted not only in no further loss, but also in a significant recovery both of total nitrogen and of other investigated characteristics.     

Genotype dependent variation in mycorrhizal colonization and response to inoculation of pearl millet

Summary Genotypes of pearl millet (Pennisetum americanum L. Leeke) were examined for differences in vesicular-arbuscular mycorrhizal (VAM) colonization and response to inoculation. For thirty genotypes tested across three field locations there was a range of mycorrhizal colonization intensity between 25 and 56%. In another experiment with two male-sterile lines, restorer lines and their derived crosses, grown in pots filled with non-sterilized soil there were significant differences between genotypes for colonization by mycorrhiza. This showed hostgenotype dependence for mycorrhizal colonization.Root growth rates, mycorrhizal root length, percentage root colonization and plant growth and P uptake were studied in ten genotypes. A set of 3 genotypes with similar root lengths varied significantly with regard to mycorrhizal root length and the percentage colonization. This supports the suggestion that VAM colonization and spread is dependent on the host genotype. The growth responses differed significantly between the genotypes and they also differed in their responses to P uptake and VAM inoculation. The utility of host-genotype dependent differences in VAM symbiosis in plant breeding is discussed.Journal Article No. 453     

Response of potatoes to N fertilizer: Quantitative relations for components of growth

Summary Quantitative relationships for key processes influencing N response were derived from measurements of inorganic N in soil, the weights and N contents of foliage and tubers made at intervals during growth of maincrop potatoes in 11 N fertilizer experiments.Apparent mineralization rates (calculated from measurements of N uptake and inorganic N in the top metre and averaged over the growth period) were remarkably similar from site to site despite wide differences in the textures, water contents and organic matter contents of the soils. They were mostly about 0.78 kg N ha^–1 m^–1 d^–1.Inorganic N in the top 50 cm of soil was rapidly removed by the crop until it fell on all sites to a low value (about 4 g N cm^–3) which was maintained for the remainder of the growth period. When N fertilizer was applied, growth rate until at least the end of July was always well defined by a single coefficient in a previously derived equation. Average values of this coefficient for each of the soil types and for each of the years in which the experiments were carried out were within 20% of each other.The minimum %N in the dry matter needed to permit maximum growth rate declined with increase in plant weight in a similar manner to that previously found for other crops.Equations were found for the partition of assimilate and of nitrogen between the foliage and tubers. The coefficients in them were little affected by whether or not N fertilizer was applied.According to these relationships the maximum potential dry weight yield of tubers is 20 t ha^–1 and requires the crop to contain at least 290 kg N ha^–1.     

Aspects of the numerical and functional respones of the aphid parasite, Aphidius sonchi, in the laboratory

The fecundity, reproductive rates, and adult survival of Aphidius sonchi Marshall (Hymenoptera: Aphidiidae) parasitizing second and third instar nymphs of the sowthistle aphid, Hyperomyzus lactucae (L.) (Homoptera: Aphididae) were measured at six different host densities under constant laboratory conditions. At host densities of less than 50 aphids per flowering shoot per female per day, oviposition constraints resulting from the lack of hosts reduced the number of eggs laid, enhanced the extent of superparasitization and, as a result, effectively lowered the fecundity and reproductive rates of the parasites. Above this host density the parasites laid on average 220–230 eggs, but the effective fecundity and reproductive rates continued to increase with the host density. By contrast, the survivorship of the parasites seemed unaffected by host density, with an average adult life span of 4–5 days at all densities. Analysis of the data showed that the intrinsic rate of increase (r_m) of the parasite varied with the host density and could reach values higher than that of the host under identical conditions. The response of r_m to changes in host density and parasite sex ratio is illustrated.Overall, A. sonchi showed a typical convex functional response, to host density. However, the response showed obvious changes through the parasite's adult life and, furthermore, the rates of changes were not consistent at all host densities. The frequency distributions of parasite eggs were generally indistinguishable from random, and the number of hosts parasitized were predicted satisfactorily by the random oviposition equation.

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Résumé L'étude a porté sure l'influence de 6 densités différentes d'Hyperomyzus lactucae (L.) (Homoptera: Aphididae), en conditions constantes de laboratoire, sur la fécondité, le taux de reproduction et la survie des adultes d'Aphidius sonchi Marshall (Hym. Aphidiidae, parasite des larves de 2e et 3e stades. A des densités inférieures à 50 pucerons par tige fleurie de Sonchus oleraceus L, par femelle et par jour, la limitation de la ponte due à l'absence d'hôtes a réduit le nombre d'oeufs émis, élevé le taux de superparasitisme et, en conséquence, diminué la fécondité et le taux de reproduction des parasites. Aux densités d'hôtes supérieures, les parasites ont pondu, en moyenne, 220 à 230 oeufs, mais la fécondité réelle et les taux de reproduction ont continué à augmenter avec la densité des pucerons. Par contre, la longévité des parasites n'a pas été affectée par la densité des hôtes, avec une durée moyenne de vie de 4 à 6 jours. L'analyse des données a montré que le taux d'accroissement intrinsèque (r_m) du parasite a changé avec la densité des hôtes, et pourrait atteindre des valeurs supérieures à celles de l'ôte sous des conditions identiques. Les réponses de r_m aux changements de densité des hôtes et au taux sexuel du parasite sont expliquées.Globalement, A. sonchi a présenté une réponse fonctionnelle convexe typique à la densité des hôtes. Cependant, cette réponse a changé au cours de la vie des images et, de plus, les taux de changement ne sont pas logiques à toutes les densités d'hôtes La fréquence de distribution des oeufs n'est généralement pas séparable d'une distribution au hasard, et le nombre d'hôtes parasites peut être prédit d'une façon satisfaisante en utilisant une équation de ponte au hasard.

     

Export of species to islands from sources of differing maturity

Export of species from sources (epicenters) of differing ages and complexities was examined using laboratory microcosms. Polyurethane foam (PF) artificial substrates were colonized by protozoans for different time periods in a small pond. Substrates were returned to the laboratory and used as epicenters for protozoan colonization of barren PF islands in initially sterile microcosms. Islands were exposed to epicenters for either 24 h or continuously for 28 d. Islands from pairs of microcosms exposed to epicenters of identical ages were sampled on 1, 3, 7, 14, 21, 28 and 46 d after initial epicenter exposure. Colonization parameters were estimated by fitting numbers of colonizing species to the MacArthur-Wilson equilibrium model. Islands exposed continuously to epicenters were colonized by significantly more species than those exposed for only 24 h. Islands exposed to immature, species poor epicenters were colonized by a greater proportion of the source community than those exposed to more mature, species rich epicenters. All islands were depauperate compared to epicenters except those exposed to the most immature (1 d old) epicenter. Colonization continued at a reduced rate in spite of the absence of the epicenter. Results from communities with rapid species turnover and rapidly reproducing species suggest that the continuous presence of a species source is less important for colonization of a new habitat. Dispersal of potential colonists occurs rapidly in these communities. Less mature communities dominated by pioneer forms are more effective at producing colonists than more mature communities.     

Clearance rates of sessile rotifers: in vitro determinations

We measured laboratory clearance rates of 10 rotifer and one unidentified bryozoan species from 3 different lakes using ³²P labeled algae (Chlamydomonas) or yeast (Rhodotorula). Clearance rates for all rotifers fed yeast ranged from < 2.0 to > 260 µl · animal^–1 · h^–1 depending on species. The in vitro clearance rates of two sessile rotifers (Ptygura crystallina and P. pilula) were not significantly different from previously measured in situ rates (Wallace and Starkweather 1983). Clearance rates for 5 rotifers fed algae ranged from < 5.0 to > 90.0 µl · animal^–1 · h^–1. Ptygura beauchampi, P. crystallina, P. pilula, Floscularia conifera, and F. melicerta ingested both cell types but their clearance rates varied substantially among species and between cell types. There was a substantial time-dependent loss of 32P from formalin-fixed animals (Sinantherina socialis) awaiting processing. This loss stabilized at approximately 20 hours and was estimated to be about 40% of the initial ingested label. Clearance rates for the bryozoan fed yeast or algae were highly variable, ranging from < 1.0 to > 3 000 µl · animal^–1 · h^–1.