Light Distribution Pattern Research Articles

Photosynthetic responses to light variation in rainforest species : II. Carbon gain and photosynthetic efficiency during lightflecks.

The dependence of net carbon gain during lightflecks (artificial sunflecks) on leaf induction state, lightfleck duration, lightfleck photosynthetic photon flux density (PFD), and the previous light environment were investigated in A. macrorrhiza and T. australis, two Australian rainforest species. The photosynthetic efficiency during lightflecks was also investigated by comparing observed values of carbon gain with predicted values based on steady-state CO2 assimilation rates. In both species, carbon gain and photosynthetic efficiency increased during a series of five 30-or 60-s lightflecks that followed a long period of low light; efficiency was linearly related to leaf induction state.In fully-induced leaves of both species, efficiency decreased and carbon gain increased with lightfleck duration. Low-light grown A. macrorrhiza had greater efficiency than predicted based on steady-state rates (above 100%) for lightflecks less than 40 s long, whereas leaves grown in high light had efficiencies exceeding 100% only during 5-s lightflecks. The efficiency of leaves of T. australis ranged from 58% for 40-s lightflecks to 96% for 5-s lightflecks.In low-light grown leaves of A. macrorrhiza, photosynthetic responses to lightflecks below 120 μmol m-2 s-1 were not affected significantly by the previous light level. However, during lightflecks at 530 μmol m-2 s-1, net carbon gain and photosynthetic efficiency of leaves previously exposed to low light levels were significantly reduced relative to those of leaves previously exposed to 120 and 530 μmol m-2 s-1.These results indicate that, in shade-tolerant species, net carbon gain during sunflecks can be enhanced over values predicted from steady-state CO2 assimilation rates. The degree of enhancement, if any, will depend on sunfleck duration, previous light environment, and sunfleck PFD. In forest understory environments, the temporal pattern of light distribution may have far greater consequences for leaf carbon gain than the total integrated PFD.

Origin, Migration, and Entrapment of Natural Gas in Alberta Deep Basin: Part 1: ABSTRACT

The Alberta Deep basin, situated along the northeastern front of the Rocky Mountain belt, is the deepest part of the Alberta synclinal sedimentary basin. This trough-shaped deep basin, extending across northwestern Alberta and into northeastern British Columbia, covers an area of 65,000 km2 (25,000 mi2). Enormous volumes of natural gas have been found in recent years within the thick, clastic Mesozoic sediments which partly fill the deep basin. These sediments exceed 3,100 m (10,200 ft) in total thickness. Based on detailed geochemical analyses of more than 300 rock samples (mainly cutting samples) from several wells in the Elmworth gas field, information was obtained on the hydrocarbon source strata and the generation and redistribution of hydrocarbons. The clastic Mesozoic rock section contains numerous shaly zones which are very rich in organic matter, and also a suite of coal strata. This section, containing mainly type III kerogen, is the ideal gas generator. Maturity ranges from about 0.5% vitrinite reflectance to about 2.0% in the deeper part of the section. Maturity has also been defined in terms of the Methylphenanthrene Index which is based on aromatic hydrocarbons. Apparently the mature section is still in an active phase of hydrocarbon generation. Due to the tightness of the rocks, hydrocarbon transport mechanisms seem to be dominated by diffusion processes. The light hydrocarbon distribution patterns observed throughout the wells suggest a dynamic trapping mechanism. Light hydrocarbons are lost at the top of the mature ydrocarbon generating zone and are replenished in the middle part of the section where rich source rocks are found. End_of_Article - Last_Page 642------------

Lighting systems in major New Zealand controlled environment facilities

The lighting systems used in New Zealand in the Department of Scientific and Industrial Research (DSIR) Climate Laboratory controlled environment rooms, the Forest Research Institute (FRI) tree growth rooms, and the DSIR-designed reach-in controlled environment chambers are described. All lighting systems are based on high-pressure discharge lamps which can be used with varying amounts of incandescent light supplementation. The main lighting type used in the Climate Laboratory controlled environment rooms is the high-pressure metal halide lamp, that in the FRI rooms the high-pressure mercury-vapour fluorescent lamp with internal reflector, and that in the reach-in chambers a high-pressure mercury halide lamp. Details of lighting rig design, of irradiance levels obtainable, vertical and horizontal light distribution patterns and spectral quality are presented for each system. The photosynthetic irradiance levels available at 2–3 m below the lighting systems in all of these controlled environment systems are high (180–200 W m −2 PAR). In the Climate Laboratory and FRI growth rooms peak sunlight values of approximately 400 W m −2 PAR (approximately 10,000 ft.c.) have been achieved. A discussion of the performance of these systems is also presented.

Subject index

One of the major challenges facing rice breeding is to produce ideotype or ideal plant architecture (IPA) to improve canopy radiation use efficiency and hence grain yield. The hybrid japonica rice Jiayou Zhongke 6 (JYZK-6) is one of the benchmark cultivars with IPA characteristics, but the physio-ecological foundation of its high yield potential is still imperfectly understood. In this study, two-year field experiments were conducted using four japonica rice cultivars including JYZK-6 with contrasting canopy structures. A dynamic canopy light interception simulating device was constructed to capture canopy images representing the diurnal dynamics of solar angles throughout the grain-filling stage. Subsequently, leaf to panicle ratio (LPR), a newly developed physiological trait indicative of source-sink relations, was exploited to quantify the light distribution pattern within the rice canopy. The LPRs with high spatio-temporal resolution clearly showed the diurnal changes of light interception within the rice canopy. Genotypic differences in diurnal pattern of LPR were detected among the tested cultivars in both growing seasons, with the amplitude varying with grain-filling stages. Notably, LPR of the IPA cultivar JYZK-6 and its analogue WYJ-29, had a pattern of a V-shaped graph, peaking at sunrise and sunset while dropping to the lowest at noon during middle and late stages. Morphological measurement showed that the V-shaped pattern was associated with the height difference between flag leaf and panicle, panicle curvature, ratio of leaf area to panicle area, as well as the changing solar angles along with the progression of growth stage. This distinguishing feature of light pattern indicates that within the canopy of IPA cultivars, the leaf receives more light in the morning and afternoon whereas the panicle harvests more light at noon. It is inferred that such novel characteristics may provide the IPA cultivar with advantages of reducing midday suppression over the conventional cultivars, while more work is needed to verify this hypothesis. In summary, findings of this study offer a deeper insight into the physio-ecological processes underpinning radiation use efficiency at canopy level, and hence are valuable for breeding programs for ideotype cultivars.

Light scattering from optical fibers with arbitrary refractive-index distributions

A scattering theory is presented, which is capable of predicting the light-distribution pattern that arises when a clad optical fiber of arbitrary core refractive-index distribution is illuminated by a laser beam perpendicular to its axis. Theoretical predictions are compared to experimental results in the backscattering direction, with excellent agreement for fibers of practical interest having core and cladding diameters on the order to 50 and 150 μm, respectively. Considerable sensitivity to parameter variations has been observed and implications for diameter and refractive-index distribution determinations are discussed.

Fine Structural Effects of Intrauterine Contraceptives on the Human Endometrium

Of 198 endometrial biopsies performed on 82 women with Lippes loops in situ for 6 weeks to 40 months 124 were proliferative and 74 were secretory. Samples were obtained from immediately beneath the device between the loops and from areas remote from the device. Specimens of basal endometrium lower segment or endocervix were excluded. Control tissue was obtained before insertion of the device. Slides were prepared for electron microscopy. No consistent generalized pathologic change was observed in either proliferative or secretory endometria. The stroma immediately beneath the loop appeared compressed and fibrotic throughout the cycle. Proliferative epithelium maintained the normal pattern of juxtaposed light and dark (electron-dense) cells mitotic activity and distribution of microvilli and cilia. No progression of epithelial ultrastructural differences occurrred after their first appearance in the second month after IUD insertion. Precocious changes in epithelial ultrastructure included 1) the appearance of a nucleolar channel system normally considered indicative of ovulation or exogenously administered hormones in 15-29% of endometria judged to be preovulatory; 2) numerous large mitochondria usually associated with the postovulatory phase in the late-proliferative endometrium and occasionally as early as in the midproliferative; and 3) the development of confluent fields of glycogen at the end of the proliferative phase a few days earlier than in controls. The premenstrual endometrium resembled the contrl of this stage; scarcity of microvilli and other characteristic ultrastructural traits of regression were noted. Ultrastructural changes in the proliferative stroma were observed first about 1 day preovulatory when the cytoplasm appeared better differentiated than in the controls. The stromal cells were highly differentiated at the end of the first postovulatory week; the cytoplasmic complexity at Days 19 or 20 often resembled that of Day 25 controls. Premature and asynchronous development of the endometrium may affect the correlation with ovular development which is a prerequisite for normal implantation. Since the IUD creates an unfavorable environment for blastocystic attachment but does not dislodge the implanted ovum its action is considered contraceptive rather than abortifacient in the usual sense.

Light Distribution in Field Soybean Canopies1

AbstractA study was conducted to determine the pattern of light interception and distribution in a field soybean community. Light interception occurred primarily at the periphery of the canopy. When the open space between rows closed or when it was nearly closed, interception was primarily at the top of the canopy.The distribution of light through a soybean community could be approximated by an exponential distribution. The slope of the regression of the logarithm of percent light interception of leaf area index (LAI) above the point of light measurement was affected by the morphology of the community.From the distribution of percent light and cumulative LAI, an estimate of the “effective” LAI was determined. The large amount of self‐shading and predominant interception at the periphery of the canopy indicates that many lower leaves are not receiving adequate radiation. An increase in yield could possibly be achieved by selecting varieties whose natural inclination leads to deeper penetration of useful energy to a greater number of leaves.

A Study in Street Lighting Reflector Design

The solution to a problem in asymmetric reflector design for illumination is described. Working backward from a required rectangular and nonuniform light distribution pattern, the reflector geometry is arrived at by a combination of calculus and geometric construction. The central curve is computed from the general reflector equation lnR = tan (theta - d/2) dtheta, the integration being performed on an approximate matching function or graphically. The off-center contours are then obtained by means of an original drafting-board construction which is described, and the complete reflector shape is thus defined.

LIGHT RELATIONS OF TERRESTRIAL PLANT COMMUNITIES AND THEIR MEASUREMENT

Summary1. ‘Light’ covers a variety of related measures of radiant energy: the particular usage must be defined for each investigation.2. Light in the open varies in intensity and spectral composition, both with time and over space. These variations can usually be formulated mathematically and used to predict conditions in plant communities.3. Light may be measured directly with radiometric instruments, responding equally to all wavelengths within a certain waveband, or with photometric instruments, whose response approximates to that of the human eye. The use of the former is desirable whenever possible, as it simplifies subsequent interpretation of the results.4. Photographs covering an entire hemisphere can be used to estimate the contribution of diffuse and direct light separately under many circumstances. They are a great help with the interpretation of many forms of measurement.5. If the percentage of light transmitted by a plant community is to be treated as constant, diffuse and direct light must be treated separately. Even so, it is only the average transmission over considerable periods that is reasonably constant. The pattern of diffuse light distribution in the community is very different on clear and on cloudy days.6. In general, most diffuse light penetrates the plant community near the zenith. However, on clear days the aureole of light near the sun shining through a low‐altitude canopy gap may entirely alter this relationship.7. The distribution of direct light can be analysed from tracing the path of the sun across the canopy. The sun shines unobstructed through gaps of an angular width greater than 1/2.8. In some herbaceous communities the logarithm of relative intensity of diffuse light inside and outside the community is approximately proportional to the cumulative leaf area per unit area of ground above the level investigated. The relation varies with the angle of incidence of direct sunlight. The relation is not valid in all communities, and the errors involved in the assumption of its validity require further investigation.9. The leafy plant community reflects and transmits light selectively. It is important to allow for the interaction of changed spectral composition on the spectral sensitivity of the instrument when making estimates of albedo or percentage light transmission.10. Although the spectral characteristics of reflexion and transmission of individual leaves are nearly identical, this is not so for plant communities with a highly inhomo‐geneous structure.11. The percentage of total light transmitted usually increases with increasing cloud cover of the sky. The absolute intensity of diffuse light in the stand is usually higher when the sky is partly overcast than when the sky is entirely covered or clear. This is due to the increase of total light in the open with decrease of cloud cover, while the proportion of diffuse light in the total decreases with decrease in cloud cover. Provided the stand transmits more diffuse than direct light, the percentage transmission of the total will therefore fall as the total increases.12. Daily variation of diffuse light generally follows that in the open.13. In deciduous woods a light phase before leaf expansion and a shade phase after it can be distinguished. Each phase is characterized by a fairly constant percentage of diffuse light: that of direct light depends on daily and seasonal variation of solar altitude, increasing with increasing altitude.14. Light measurements given as percentages of that in the open may disguise important features of the variation of absolute amounts of light. Wherever possible these absolute quantities should be calculated. Where no direct meteorological data exist, it is often possible to make reasonable assumption from other data. The precise time, place and cloud conditions should be given for each measurement,15. Because of the great variety of instruments and techniques used, often inadequately described, comparison of results is nearly impossible. A thorough examination of the magnitude of the errors of each technique is badly needed.