Sunlight Environments Research Articles

Concentration of photosynthetic pigments and chlorophyll fluorescence of mahogany and tonka bean under two light environments

This study was carried out in a plantation of a degraded area in Central Amazon, Brazil, in order to assess environmental light effects on leaf pigment concentrations and chlorophyll a fluorescence in mahogany (Swietenia macrophylla King) and tonka bean (Dipteryx odorata Aubl. Willd). Three-year old saplings were grown in an open site (sun) with maximum radiation of approximately 2000 mumol m-2 s-1 and under the shade of a Ochroma pyramidale (Cav. ex Lam. Urb) canopy. A leaf area index of 2.46 was optically determined for the Ochroma foliage with 13% of full sunlight (maximum radiation about 260 mumol m-2 s-1). Carotenoid and chlorophyll concentrations were spectrophotometrically determined. Initial (Fo), maximum (Fm) and variable fluorescence (Fv) were determined with a portable fluorometer. Chlorophyll concentrations (Chl a, Chl b and Chl tot) on a fresh mass basis were greater in shade leaves than in sun acclimated leaves in both species. On the other hand, when comparisons were made on a per area basis, Chl a concentrations were greater in the sun than in shade leaves of tonka bean. In contrast, Chl b concentrations were higher in the shade environment for this species. No differences were observed in Chl concentrations per unit area in mahogany leaves. Carotenoid concentrations were higher for sun-acclimated leaves of mahogany, both on a per unit area and on a fresh mass basis. In tonka bean, higher carotenoid concentrations in shade leaves were only observed on a fresh weight basis. No differences were found between environments when carotenoid concentrations were expressed as a function of leaf area. Fluorescence variables (Fo, Fm, and Fv) were greater in sun leaves than in shade leaves of mahogany. In contrast, Fv and Fm, but not Fo, values were higher in shade acclimated leaves than in full sunlight-adapted leaves of tonka bean. However, there was a higher Fv/Fm ratio value for tonka bean in sunlight environments. We conclude that these species, classified as mid and late successional species, differ markedly regarding the utilization of photosynthetic pigments, increasing either light harvesting efficiency at low irradiance or protection against photosynthetic machinery damage in higher solar radiation environments.

Differences in Tillering of Long‐ and Short‐Leaved Perennial Ryegrass Genetic Lines under Full Light and Shade Treatments

There is uncertainty among plant breeders as to which characteristics to select for to optimize grass growth dynamics. The objective was to study the relationship between leaf length and tillering in perennial ryegrass (Lolium perenne L.). Two long‐leaved and two short‐leaved genetic lines were grown in simulated shade and near‐full sunlight (control) environments. The genetic lines were New Zealand cultivars Ellett (long‐leaved) and Grasslands Ruanui (short‐leaved), both early flowering. The other two were late‐flowering divergent selections ‘LL’ (long‐leaved) and ‘SL’ (short‐leaved). Differences between genetic lines in leaf length were attributable mainly to higher leaf elongation rate (LER) in the two long‐leaved genetic lines, and leaf elongation duration (LED) did not differ significantly between genetic lines. Grasslands Ruanui had a higher tiller number per plant than Ellett in both light environments, explained by higher site filling but similar leaf appearance rate (AL). In contrast, LL had a higher tiller number per plant than SL, arising from a higher AL in LL. This difference decreased during the experiment under the control treatment because SL tended to have a higher site filling ratio than LL. However, in the shade treatment, differences in tiller number between LL and SL were more mediated by AL than site filling. Therefore, selection for high LER and long lamina length, even though associated with reduced site filling in all treatments, did not necessarily result in reduced tiller number per plant.

Photosynthesis and respiration in Alocasia macrorrhiza following transfers to high and low light.

Photosynthetic capacities and respiration rates of Alocasia macrorrhiza leaves were measured for 4 weeks following reciprocal transfers between high (20% of full sun) and low (1% of full sun) light environments. Photosynthetic capacities and respiration rates of mature, high-light leaves were 1.7 and 4.5 times those of low-light leaves, respectively. Following transfer, respiration rates adjusted within 1 week to those characteristic of plants grown in the new environment. By contrast, photosynthetic capacities either did not adjust or changed only slowly following transfer. Most of the difference in respiration between high- and low-light leaves was related to the carbohydrate status as determined by the daily PFD and little was directly related to the maintenance costs of the photosynthetic apparatus. Leaf construction cost was directly proportional to maximum photosynthetic capacity. Consequently, although daily carbon gain per unit leaf area was the same for low-light and high to low-light transferred plants within a week after transfer, the carbon return per unit of carbon investment in the leaves remained lower in the high to low transfer plants throughout the 4 week measurement period. Conversely, in high-light, the low leaf construction cost of the low to high-light transferred plants resulted in carbon gain per unit investment just as high as that of the high-light plants.

Failure of environmental lighting to influence dental caries rate.

Two experiments involving littermate cotton rats were conducted to determine the effect of cool-white fluorescent versus artificial sunlight environments on caries incidence. There were no significant differences in either the incidence or extent of caries associated with the different types of lighting. This contradicts our previous observations (1) with this species using identical experimentation and calls for a retraction. It is suggested that the difference is due primarily to the application of an inappropriate statistical approach in the earlier work.

Significant effect of environmental lighting on caries incidence in the cotton rat.

The effect of differences in environmental lighting on dental caries in the cotton rat was studied. The animals were exposed to either incandescent, cool-white fluorescent, or artificial sunlight environments over an 18-day period while ingesting a diet containing approximately 6% sucrose. Both the incidence and extent of caries were significantly (P < 0.001) higher in animals housed under cool-white fluorescent lighting than for either of the other two groups.

High Temperature Elastomeric Compounds and Polymers

Abstract While special purpose elastomers for high temperature applications have been available since the introduction of the polyacrylates and silicones in the early 1940's, the intensive development and study of such materials really began in the early 1950's. Prior to that period, the major effort in the field of synthetic elastomers was directed toward development of general purpose polymers, principally for such applications as military and civilian tires, wire and cable, and other large volume uses. The extensive synthetic rubber development program sponsored by the U. S. Government during and following World War II is a matter of common knowledge to every rubber technologist and is well covered by Whitby. However, less well known because of restrictions on distribution of reports and technical data are the history and accomplishments of programs sponsored or motivated primarily by the Department of Defense on development of special purpose elastomers for varied and critical high temperature applications. This review will emphasize current knowledge on these specialty elastomers and will attempt to summarize the general limitations of the more common commercially available elastomers when exposed to high temperature environments. for the reader interested in a comprehensive review of this latter subject, Firestone Tire and Rubber Company prepared an outstanding summary of available information prior to initiating an Air Force sponsored research program on high temperature rubber compounds in 1956. Arbitrary definition of what constitutes a high temperature elastomer will naturally provide for many areas of controversy. To the metallurgist, organic polymers in general are not considered high temperature materials, yet in certain applications, such as ablation materials for missile nose cones or rocket nozzles, these polymers will exceed the performance of the most advanced alloys, and are actually considered useful at temperatures above 4000° F. On the other hand, commercial polymer manufacturers publish volumes of data to show that their particular polymer will withstand prolonged aging periods at temperatures of 200–250° F and thereby claim high temperature performances. Obviously, when considering the entire field of elastomeric polymers, no fine line can be drawn between those which may be considered suitable for high temperature applications and those which should be excluded from such applications. Further complicating any generalizations regarding high temperature usefulness is the fact that the high temperature environment is rarely the only environment to be considered in any given application for elastomers. Effect of fuels, lubricants, hydraulic fluids, special chemicals, ozone, sunlight, nuclear radiations, and other adverse environments must usually be considered, singly or in combination, along with the heat effects. Finally, in any given application, consideration of a specific physical property, or combination of properties, is essential for satisfactory performance. These properties include, but are certainly not limited to, tensile strength, elongation, stress relaxation, compression modulus, hardness, abrasion, permeability, lubricity, resilience, tear, cut growth, adhesion, and many others which can have a major influence on the performance or service life of an elastomeric component. Control of these properties over a broad temperature range is the real challenge to today's rubber technologists, and the constant broadening of the temperature range, from extremely low (below −300° F) to extremely high (above 1000° F), will continue to be the basis for special purpose polymer and elastomer development in the years ahead.