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11.
Dale D. Brown Ronald G. Knowlton Joseph Hamill Teresa L. Schneider Ronald K. Hetzler 《European journal of applied physiology and occupational physiology》1990,60(3):179-182
The purpose of this study was to compare the physiological and biomechanical responses of wheelchair-dependent persons (WCD) to able-bodied persons (AB) during manual wheelchair ergometry. Five WCD and five AB performed a discontinuous wheelchair ergometer test starting at 12.8 W at 30 rev.min-1 (57 m.min-1) with increments of 7.0 W at 6-min intervals. Biomechanical data were collected 3.5 min into each stage followed by the collection of physiological data. After the fifth stage, peak oxygen consumption was determined by having the subject work against a resistance of 14.7-19.6 N at 30 rev.min-1. The WCD had significantly higher net mechanical efficiency at 26.7, 33.6 and 40.6 W in comparison to the AB. The WCD had significantly greater shoulder extension at the point of initial wheel contact as measured by the shoulder angle, while the AB had significantly greater shoulder range of motion at all work rates in comparison to the WCD. The results demonstrate that a significant physiological difference exists in the manner by which WCD and AB accomplish wheelchair ergometry. The biomechanical differences between AB and WCD were found to be a prominent factor contributing to the higher mechanical efficiency of WCD over AB. It was concluded that basic physiological and biomechanical differences exist between WCD and AB in manual wheelchair locomotion and that these differences are important considerations to the interpretation of data in wheelchair ergometry studies. 相似文献
12.
A field study with barley was conducted in 1984 and 1985 to provide data on uptake rates of N, P, K and Mg and their variation as the growing season progressed. Two varieties were grown: Galt in 1984 and Otal in 1985. Soil fertility was maintained at or near optimum conditions. Samples were obtained approximately every 10 days for shoot dry weight, nutrient content and root length measurements. The approximate method (Williams, 1948) traditionally used for calculating uptake rates was found to be invalid for most of the nutrients studied. The method used for measuring uptake rates was the functional approach proposed by Hunt (1973). Inflow,i.e. uptake rate per unit root length, of plant nutrients, decreased with time. However, maximum uptake rates measured in kg ha–1d–1 occurred at about 50 days from sowing because of increasing root length density with time. Inflow or uptake rates were low in 1985 because of moisture deficiency, and grain yield (0.89 t ha–1) was severely depressed. This study demonstrated that Hunt's method is superior and more advantageous than the traditional, approximate method. 相似文献
13.
Rice cultivar evaluation for phosphorus use efficiency 总被引:12,自引:1,他引:11
Phosphorus deficiency is one of the most growth-limiting factors in acid soils in various parts of the world. The objective of this study was to screen 25 rice cultivars (Oryza sativa L.) at low, medium, and high levels of soil P. Number of tillers, root length, plant height, root dry weight and shoot dry weight were related to tissue P concentrations, P uptake and P-use efficiency. Shoot weight was found to be the plant parameter most sensitive to P deficiency. Significant cultivar differences in P use efficiency were found. Phosphorus use efficiency was higher in roots than shoots and decreased with increasing levels of soil P. Positive correlations were found among growth parameters such as plant height, tillers, root and shoot weight, and P content of roots and shoots. These results indicate selection of rice cultivars for satisfactory performance under low P availability can be carried out using shoot and root dry weight as criteria. 相似文献
14.
Summary Two alternative estimators of individual tree leaf area (A1) area are used to derive estimates of leaf-area index (L) for 40 plots in Pinus contorta Dougl. stands. One estimator of A1 is based on the common assumption of a constant ratio between A1 and sapwood cross-sectional area at breast height (As). The second estimator of A1 accounts for tree-to-tree variation in the relation between A1 and As. The apparent relationship between stand growth and leaf-area index is strongly dependent on the way leaf area is estimated. When L is derived from a constant A1As ratio, stand growth appears to be strongly correlated with L. However, when L is based on estmates of A1 that account for tree-to-tree variation in the A1 — As relation, stand growth is seen to be only weakly related to L. Stand structure, quantified as percent live-crown, accounts for a great deal of the observed variation in leaf-area efficiency. These contrasting relationships illustrate the importance of unbiased estimates of L in interpreting the link between stand-level processes and leaf area.Utah Aggriculural Experiment Station Journal Paper No. 3333 相似文献
15.
Ted L. Gragson 《Human ecology: an interdisciplinary journal》1992,20(1):109-130
Information is presented on fishing effort, efficiency, techniques, and catch composition for Pumé men, women, and children along with a conceptual model of fishing as a food procurement strategy. The Pumé are a native lowland South American group living in the topical savanna region of southwestern Venezuela characterized by seasonal flooding. Results are discussed in relation to the Pumé environmental and social situation, and briefly compared with results from other lowland South American groups. 相似文献
16.
Synopsis Changes in the daily appetite and weekly growth rates of individual adult minnows,Phoxinus phoxinus, on ad libitum rations were recorded before and after they had experienced 4 or 16 days of food restriction. Feeding levels during the restriction periods were either starvation or a maintenance ration. The latter was estimated from a previously determined regression model. Water temperature was 15°C and the photoperiod 9L15D in all experiments. The mean weight of fish used ranged from 1.06 to 2.15 g. The 4 day restriction had no detectable effects on appetite or growth. After the 16 day restriction, the minnows showed hyperphagia and had increased specific growth rates and growth efficiencies compared with control fish. The compensatory increases in appetite and growth were not sustained and within three weeks had declined to levels not significantly different from those of the control fish. At the end of the experiments, there were no significant differences between the mean weights or cumulative food consumption of the restricted and control groups. The results suggest that adult minnows regulate their appetite and growth rate in relation to their previous nutritional history. 相似文献
17.
The feasibility of introducing foreign genes into the genomes of cattle, goats, pigs, and sheep has only recently been demonstrated. Studies have thus far focused on improving growth efficiency or directing expression of pharmaceutical proteins to the mammary glands of these species. The general strategy for producing transgenic livestock and mice is similar. In addition to the obvious difference in scale between mice and livestock experiments, there are noteworthy obstacles that significantly reduce the efficiency of producing transgenic livestock. Low embryo viability, low transgene integration rates, and high animal costs contribute to project costs that can easily exceed hundreds of thousands of dollars. A better understanding of the mechanisms that govern transgene integration should lead to improved efficiencies. But, the full potential of the transgenic livestock system will not be fully realized until: 1) gene constructs can be designed that function in a reproducible, predictable manner; and 2) the genetic control of physiological processes are more clearly elucidated. Newly emerging approaches may resolve at least some of these issues within the next decade. 相似文献
18.
ROGER T. KOIDE 《The New phytologist》1991,117(3):365-386
19.
Phosphorus efficiency of plants 总被引:1,自引:0,他引:1
Föhse et al. (1988) have shown that P influx per unit root length in seven plant species growing in a low-P soil varied from 0.6×10-14 to 4.8×10-14 mol cm-1s-1. The objective of this work was to investigate the reasons for these differences. No correlation was found between P influx and root radius, root hairs, cation-anion balance and Ca uptake. However, when root hairs were included in mathematical model calculations, the differences of P influx could be accounted for. These calculations have shown that in soils low in available P, contribution to P uptake by root hairs was up to 90% of total uptake. The large contribution of root hairs to P uptake was partly due to their surface area, which was similar to that of the root cylinder. However, the main reason for the high P uptake efficiency of root hairs was their small radius (approx. 5×10-4 cm) and their perpendicular growth into the soil from the root axis. Because of the small radius compared to root axes, P concentration at root hair surfaces decreased at a slower pace and therefore P influx remained higher. Under these conditions higher Imax (maximum influx) or smaller Km values (Michaelis constant) increased P influx. The main reasons for differences found in P influx among species were the size of Imax and the number and length of root hairs. In a soil low in available P, plant species having more root hairs were able to satisfy a higher proportion of their P demand required for maximum growth. 相似文献
20.
Elena Fernandez Garcia 《Entomologia Experimentalis et Applicata》1988,48(2):173-178
The suitability of different host plants for Pieris rapae L. in the South of the Iberian Peninsula, was studied in relation to host plant phenology, female behaviour, and larval development. Capparis spinosa is the only host plant available during the dry season of the year in the area studied. D. virgata, R. raphanistrum, H. incana and S. alba being suitable spring hosts. Comparative studies on mortality, larval development and larval growth between C. spinosa and the spring hosts revealed no significant differences.
Résumé L'adéquation de différentes plantes comme hôtes de P. rapae a été examinée en fonction de la phénologie des végétaux, du comportement de la femelle et du développement larvaire dans le sud de la péninsule ibérique. Pendant la saison sèche, C. spinosa est la seule plant convenable dans la zone étudiée. Diplotaxis virgata, Raphanus raphanistrum, Hirschfeldia incana et Sinapis alba sont des hôtes printaniers convenables. La mortalité, le développement et la croissance larvaires ne sont pas différentes sur C. spinosa et sur les hôtes de printemps.相似文献