Minimum Light Levels Research Articles

Determinants of whole‐plant light requirements in Bornean rain forest tree saplings

1 Shade tolerance, defined as the ability to survive and grow under low light, varies markedly among tree species. However, the role of low-light growth responses in determining shade tolerance is unclear, as are the effects of non-light resources such as soil nutrients. 2 A conceptually simple field measure of shade tolerance is the whole-plant light compensation point (WPLCP), evaluated as the x-intercept of the relationship between growth and incident light integrated over a long time interval. Here we compare WPLCP for growth and survivorship of saplings of Bornean tree species differing in shade tolerance, and evaluate the importance of various physiological and morphological traits in predicting WPLCP. We also examine both phenotypic and evolved differences in WPLCP between tree saplings growing on two distinct soil types at Sepilok Forest Reserve, Sabah, Malaysia. 3 Growth-based estimates of WPLCP showed essentially a 1 : 1 correspondence to threshold light levels for survivorship. At higher light, more light-demanding species showed higher growth, resulting in a steeper slope of the relationship between relative growth rate (RGR) and light availability than in more shade-tolerant species. This resulted in significant crossovers in the RGR–light relationship among species. 4 Dark respiration (Rd) was the single best predictor of WPLCP; other leaf traits such as leaf nitrogen and photosynthetic capacity were correlated with, but excluded as predictors of, WPLCP in multiple regression analyses. 5 Although soil type had no consistent phenotypic effect on WPLCP, evolved responses among species were pronounced: species associated with the nutrient-poor, drought-prone, sandstone-derived soils had higher WPLCP values than alluvial soil specialists in phylogenetically controlled comparisons. 6 Our results indicate that minimum light levels for growth do not diverge from those for survivorship, and do not support the view that low-light survivorship solely determines shade tolerance. Our analyses also suggest that Rd is the strongest determinant of whole-plant light requirements in tropical tree saplings, and thus may be an easily measured surrogate of WPLCP and shade tolerance. 7 Prediction of tree species resource requirements is crucial for understanding forest dynamics and promoting ecology-based forest management and restoration, particularly in diverse tropical forests where data on the resource requirements of most species are not available. Easily measured surrogates of resource requirements (e.g. Rdas a predictor of shade tolerance) will contribute to this goal, as will an improved understanding of the interactive effects of multiple resources on tree performance.

Lighting Levels in the Dwellings of Homebound Older Adults

Although poor lighting in the dwellings of older adults has been associated with falls, depression, and reduced visual performance, there has been little measurement of actual light levels in their homes. Knowing the interior light levels and preferences of older adults, especially the homebound, will be of value to service providers and designers in targeting effective interventions. This pilot study measured light levels in the apartments of 40 homebound older adults in New York City, and compared them with industry standard minimum light levels. Nearly all participants had inadequate light levels, yet rated their lighting conditions as adequate. Further research is needed on optimal light levels for improved health, safety, and quality of life.

Optical sources of ignition in hazardous areas

Interest in the possibility of igniting flammable gases and dust by using light gained momentum some 25 years ago when the use of fibre-optic transmission and laser techniques began to be explored. Since that time, there has been a considerable amount of work exploring the various mechanisms for ignition that can occur. Inevitably the challenge has been to find the minimum light levels that can cause ignition and some generally accepted results have emerged. The remaining task is to convert these results into a code of practice, which will allow the techniques to be used safely.

Resource allocation and sucrose mobilization in light-limited eelgrass Zostera marina

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 187:121-131 (1999) - doi:10.3354/meps187121 Resource allocation and sucrose mobilization in light-limited eelgrass Zostera marina Teresa Alcoverro1,*, Richard C. Zimmerman2, Donald G. Kohrs2, Randall S. Alberte3 1Centre d'Estudis Avançats de Blanes (CSIC), Carretera Sta. Bàrbara s/n, 17300 Blanes, Girona, Spain 2Moss Landing Marine Laboratories, San Jose State University Foundation, PO Box 450, Moss Landing, California 95039, USA 3Areté Associates Inc. 1725 Jefferson Davis Hwy, Arlington, Virginia 22202, USA *E-mail: teresa@ceab.csic.es ABSTRACT: This study evaluated the ability of Zostera marina L. (eelgrass) to balance the daily photosynthetic deficit by mobilization of carbon reserves stored in below-ground tissues during a period of extreme winter light limitation. A quantitative understanding of the mobilization process and its limitations is essential to the development of robust models predicting minimum light levels required to maintain healthy seagrass populations. Plants were grown in running seawater tanks under 2 light regimes. One treatment was provided with 2 h irradiance-saturated photosynthesis (Hsat) to produce severe light limitation, while control plants were grown under 7 h Hsat, simulating the typical wintertime condition in Monterey Bay, California, USA. Although plants maintained under 2 h Hsat were more severely carbon limited than plants grown under 7 h Hsat, whole-plant carbon balance calculated from metabolic needs and growth rates was negative for both Hsat treatments. The eelgrass studied here responded to negative carbon balances by suppressing the production of new roots, depleting sucrose reserves, and effecting a gradual decrease in growth rate and an increase in the activity of sucrose synthase (SS, E.C. 2.4.1.13) in sink tissues in the terminal stages of carbon stress. The 7 h Hsat plants survived the 45 d course of the experiment while the plants grown under 2 h Hsat died within 30 d, even though one-third of their carbon reserves remained immobilized in the rhizome. Thus, extreme light limitation can prevent full mobilization of carbon reserves stored in below-ground tissues, probably through the effects of anoxia on translocation. Metabolic rates, particularly photosynthesis and respiration of the shoot, were unaffected by prolonged carbon limitation in both treatments. The patterns observed here can provide useful indices for assessing the state and fate of seagrass ecosystems in advance of catastrophic declines. KEY WORDS: Seagrass · Carbon balance · Resource allocation · Photosynthesis · Light Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 187. Publication date: October 14, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Effects of potential PAR on shoot extension in juveniles of the main tree species in a Japanese temperate forest

We studied the relationship between potential photosynthetically active radiation (PAR), estimated from hemispherical photographs, and shoot extension rates of juveniles of 12 seral tree species. We distinguished between direct light site factor (DIR), diffuse light site factor (DIF), and gap light index (GLI). We used a log‐linear model to relate growth to DIR, DIF and GLI. Potential PAR explained shoot growth rates significantly in 33 cases out of 36 (12 species × 3 PAR). DIF explained the shoot extension rates better than DIR and GLI for 10 of the 12 species. The mean values of maximum shoot extension rates of the tolerant, the intermediate and the intolerant species were 52.4 cm year–1, 64.3 cm year–1 and 87.7 cm year–1, respectively. The maximum shoot extension rates of the tolerant and the intolerant species were recorded in about 50% DIF and more than 70% DIF, respectively. The minimum light level for seedling establishment of the intermediate and intolerant species was more than 20% DIF. We explained distribution characteristics and shoot extension of the species in relation to light in terms of shade tolerance. Predictions based on light‐growth curves and maximum growth curves were similar to field observations made elsewhere, suggesting that these models may be useful to predict extension growth of juvenile trees in mixed species stands.

Evaluation of least-squares phase-diversity technique for space telescope wave-front sensing

Because of mechanical aspects of fabrication, launch, and operational environment, space telescope optics can suffer from unforeseen aberrations, detracting from their intended diffraction-limited performance goals. We give the results of simulation studies designed to explore how wave-front aberration information for such near-diffraction-limited telescopes can be estimated through a regularized, low-pass filtered version of the Gonsalves (least-squares) phase-diversity technique. We numerically simulate models of both monolithic and segmented space telescope mirrors; the segmented case is a simplified model of the proposed next generation space telescope. The simulation results quantify the accuracy of phase diversity as a wave-front sensing (WFS) technique in estimating the pupil phase map. The pupil phase is estimated from pairs of conventional and out-of-focus photon-limited point-source images. Image photon statistics are simulated for three different average light levels. Simulation results give an indication of the minimum light level required for reliable estimation of a large number of aberration parameters under the least-squares paradigm. For weak aberrations that average a 0.10lambda pupil rms, the average WFS estimation errors obtained here range from a worst case of 0.057lambda pupil rms to a best case of only 0.002lambda pupil rms, depending on the light level as well as on the types and degrees of freedom of the aberrations present.

Analysis of Voyager spectra of the beta Cephei star nu Eridani

view Abstract Citations (4) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Analysis of Voyager Spectra of the beta Cephei Star nu Eridani Porri, A. ; Stalio, R. ; Ali, B. ; Polidan, R. S. ; Morossi, C. Abstract Voyager 500-1700 A spectrophotometric observations of the beta Cephei star nu Eri are presented and discussed. The Voyager observations were obtained in 1981 and cover six pulsation cycles of the star. These data are supplemented with a set of nine International Ultraviolet Explorer (IUE) SWP high-resolution observations covering one, earlier epoch, pulsation cycle. Light curves are derived from the Voyager data at 1055 and 1425 A. These light curves are found to be consistent in both shape and period with published optical curves. The 1055 A light curve also exhibits a phenomenon not seen in the optical curves: a small but highly significant systematic increase in the flux of the maximum light phases while maintaining a constant minimum light level over the interval of observation. Substantially larger errors in the longer wavelength data preclude discussion of this phenomenon in the 1425 A light curve. Examination of the far-UV continuum in nu Eri during this period shows that the color temperature is lower for the brighter maxima. Analysis of the far-UV continuum at maximum and minimum light yields an effective temperature difference between these two phases of 2200 + or - 750 K. Spectroscopically, three prominent features are seen in the Voyager data: a feature at 985 A mostly due to a blend of C III 977 A, H I Ly gamma 972 A, and N III 990 A; a feature at 1030 A due to H I Ly beta 1026 A and C II 1037 A; and the Si IV resonance doublet near 1400 A. A comparison of the 912-1700 A spectral region in nu Eri with a set of standard, i.e., nonpulsating stars, shows that nu Eri closely resembles the standard both in continuum shape and spectral line strengths with the possible exception of a slight flux excess between 912 and 975 A. The equivalent width of the 985 A feature is shown to vary in strength over the pulsation cycle in antiphase with the light curve and variations seen in the C IV 1548-1551 lines from the IUE data. This behavior of the 985 A feature is most likely caused by variations in the strength of the Ly gamma component of the blend. Comparisons are also made between nu Eri and the only other beta Cephei star studied in the far-UV, BW Vul, with the most notable differences between the two stars being the much larger delta(Teff) for BW Vul and the almost total absence of abnormalities in observed spectrum of nu Eri. Publication: The Astrophysical Journal Pub Date: March 1994 DOI: 10.1086/173898 Bibcode: 1994ApJ...424..401P Keywords: Cepheid Variables; Light Curve; Pulse Duration; Radiative Heat Transfer; Stellar Spectra; Iue; Periodic Variations; Radial Velocity; Astrophysics; STARS: VARIABLES: CEPHEIDS; STARS: INDIVIDUAL CONSTELLATION NAME: NU ERIDANI full text sources ADS | data products SIMBAD (3) MAST (1)

Toward the Optimization of Lighting Equipment Location with Respect to Minimum Lighting Level Criterion

Toward the Optimization of Lighting Equipment Location with Respect to Minimum Lighting Level Criterion

Minimum Light Requirements for Substrate Colonization by Cladophora glomerata

Cladophora glomerata, an attached filamentous green alga that inhabits streams and lakes in North America, can produce large quantities of standing crop in areas of the Laurentian Great Lakes. An integrated laboratory and field survey approach was used to define the minimum light intensity required to support substrate colonization by Cladophora. In a laboratory light gradient experiment, negligible growth was observed at light intensities less than 29 μEm −2s −1. Field surveys of the vertical distribution of Cladophora were undertaken in western Lake Erie to determine if the minimum laboratory light intensity was also observed in nature. Surveys were conducted utilizing SCUBA techniques during the peak biomass periods in late June over 3 years. The depth of Cladophora colonization varied from site to site depending on light attenuation, with the maximum depth corresponding to areas having the highest Secchi transparencies and lowest light extinction coefficients. Paired observations of photosynthetically active radiation (PAR) profiles and Cladophora deepest depth of colonization indicated that average daily intensities below 28 μEm −2s −1 were limiting to Cladophora colonization. A model is presented that predicts the maximum depth of Cladophora colonization based on the laboratory minimum light level and site-specific field light attenuation coefficients.

A high-resolution Lidar–Thomson scattering diagnostic for JET

A LIDAR–Thomson scattering system with better than 5 cm spatial resolution to resolve edge electron temperature and density gradients in H-mode operation in JET is needed. A dynamic range in measurable electron temperature of 0.1–1.5 keV and a minimum detectable electron density of 1019/m3 are required. To achieve these levels of performance, it is planned to use a modified section of the existing JET LIDAR–Thomson scattering system. A new detection system, consisting of a streak camera and an intensifier unit, will be used. Spectral dispersion is to be performed by a three-channel edge filter spectrometer. Recording and digitization of the scattered signal will be performed by a CCD camera read out by a personal computer. The system is described and results of experiments to determine the minimum visible light levels using a commercial streak camera, intensifier unit, and CCD camera and a pulsed laser diode light source are briefly presented. In addition, simulations of expected signal-to-noise ratio performance are discussed.

Physical control of the horizontal patchiness of sea-ice microalgae

Factors controlling the horizontal distribution of sea-ice microalgae were studied in Southeastern Hudson Bay and adjacent Manitounuk Sound (Canadian Arctic). Both large (-30 km) and small (0.3 to 500m) scales of variability were investigated. Results showed that salinity was the most important factor controlling large scale distribution of the ice-microalgal biomass, through its effect on the structure of the ice (surface available for colonization). Variation in the thickness of the snow-ice cover, which determines irradiance at the bottom of the ice, was the factor controlling distribution of the algal biomass at smaller scale (diameter of patches of microalgal biomass ranging between 20 and 90 m). The relation between ice-algal abundance and snow-ice thickness changed however over the season. At the beginning of the growing season (in April when the bottom-ice irradiance was higher than a minimum critical irradiance), maximum algal biomass was observed under areas covered by the smallest snow depths. Towards the end of the season, when light transmitted through the snow-lce cover increased, maximum algal biomass was observed under areas covered by the deepest snow. This suggests that ice algae have both minimum and maximum critical light levels. The minimum level is the irradiance below which there is no photosynthetic activity (Imi, 7.6 CL Einst m-2 S-') and the maximum level corresponds to the inhibiting light intensity, which may vary during the growth season. The horizontal heterogeneity of the snow-ice cover, whlch is influenced by wind at the air-ice interface, thus provides diversified bottom-ice habitats where irradiance is compatible or not with the physiological limits of the ice microalgals cells. This results in a strong patchiness in distribution of ice-bottom microalgae.

Agglomeration of magnetic fine particles in fluid dispersion

Agglomeration of γ-Fe2O3 acicular magnetic particles in concentrations of approximately 0.005% by weight in water was studied by measuring light transmission through the dispersions while they were subjected to a stepwise rotating magnetic field of 15-Oe magnitude. Transmitted light intensity varies synchronously with rotation, having its minimum when particles are aligned with their long axes parallel to the light and its maximum when particles are perpendicular to the beam. With time, the minimum light level diminishes, whereas the maximum light condition remains constant. This behavior is attributed to the formation and growth of particle chains. The chaining idea is supported by the observation that the response time of particles to the changing field increases with time and by other optical effects which are observed in high-speed rotation of the field. The effect of milling time on particle mobility is also observed. The observations are discussed in terms of a model of the attraction and attachment behavior of dilutely dispersed magnetic particles in a fluid.

Deepest Known Plant Life Discovered on an Uncharted Seamount

The discovery of abundant autotrophic macrophytes living below 200 meters indicates their importance to primary productivity, food webs, sedimentary processes, and as reef builders in clear oceanic waters. Estimates concerning minimum light levels for macroalgal photosynthesis and macrophytic contributions to the biology and geology of tropical insular and continental borderlands must now be revised.

Light Penetrating a Bahiagrass Canopy and Its Influence on Establishing Jointvetch1

AbstractBahiagrass (Paspalum notatum Flügge) is important in the southeastern USA and is Florida's major perennial grass, but low protein content and digestibility can limit cattle performance. Mixing bahiagrass with a legume such as jointvetch (Aeschynomene americana L.) would improve animal grazing performance. This 3‐year study was conducted at Ona, Fla. (27°25 N, 81°55 W) on a sandy, siliceous, hyperthermic Alfic Haplaquod to determine the effect of light on legume seedling establishment and yield to develop management guidelines that would enhance seeding success. Bahiagrass was treated each year by: i) spraying paraquat (1,1' dimethyl‐4,4' bipyridinium dichloride) at 0.56 a.i. kg. ha−1, desiccating for 72 h, then burning the residue and drilling seed into the sod; ii) disking sod three times followed by broadcasting seed; iii) grazing to 3 to 5 cm stubble, drilling seed and grazing until jointvetch was 2.5 cm tall; iv) spraying glyphosate [(N‐phosphonomethyl) glycine] at 0.84 a.i. kg. ha−1 in 15 cm wide bands, 22.9 cm apart, drilling seed; v) spraying dalapon (2,2 dichloropropionic acid) at 3.32 kg. −1 in 15 cm wide bands, drilling seed; vi) drilling seed in untreated hahiagrass (check). More light penetrated through the canopy of the paraquat‐burn (21 to 33 E m−2 day−1) and graze treated (20 to 30 E m−2 day−1) bahiagrass than in any other treatment. These treatments also had the greatest number of seedlings (3‐year average was 86 m−2), the highest dry matter yield of jointvetch (2,200 kg ha−1), and they produced the grass‐legume mixtures with the highest protein content (10.6%) and digestibility (49.1 %). Glyphosate treated sod allowed 17 to 24 E m−2 day−1 to penetrate the canopy, and good legume stands developed (80 seedlings m−2). The canopy from dalapon and check treatments was too dense (7 to 20 E m−2 day−1) to permit good legume establishment. Studies with saran shade screen indicated that 45% incident light, 20 E m−2 day−1, was the minimum light level for good jointvetch establishment. These data indicated that grazing was the most practical and successful method of removing and controlling the bahiagrass pasture canopy during legume establishment.

Designing for visual cues that enhance speech reception

Design guidelines which incorporate the visual contribution to speech are developed for maximum room size and speaker‐listener distance, and for minimum lighting level on the speaker, when unamplified speech level and background noise level are known. Room‐scale studies on speech intelligibility are conducted at different speech‐to‐noise ratios and different levels of visual acuity. Visual acuity has not been considered as a factor in earlier studies on the visual contribution to speech [W. H. Sumby and I. Pollack, J. Acoust. Soc. Am. 26, 212–215 (1954)]. The articulation index is evaluated on the basis of the modified rhyme test in accordance with the newly proposed international standard on speech intelligibility testing. The studies confirm the striking effect of speech‐to‐noise ratio on intelligibility. Also, the contribution of visual cues is shown to be very considerable, especially when the level of audible speech at the receiver is near the background noise level. The amount of improvement in speech intelligibility is shown to depend upon the illumination level on the speaker and the distance from the speaker.

The effects of physiology and behaviour on the near-bottom distributions of Kareniabrevis on the West Florida shelf: a numerical study

The distribution of near-bottom populations of Karenia brevis depends on both cell physiology and behaviour. The migration distance of cells, and the subsequent exposure to light, may vary as a result of the nocturnal uptake of nitrate. The adaptive advantage of higher nocturnal uptake rates and upward migration is evident in clear deep (90m) water columns as well as in shallower (30m), more turbid water columns. In deeper offshore environments, migrating cells with high nocturnal uptake rates are able to access light levels needed to compensate growth, whereas migrating cells with slow nocturnal uptake rates or non-migrating cells cannot access the minimum light levels needed for growth. In shallow, more turbid environments, migrating cells access between 35% and 67% of the light needed to saturate growth, whereas cells that do not migrate are only exposed to 6% of the light needed to saturate growth. Vertical migration may not only extend the depth distribution of K. brevis but also provide an adaptation to persist in more turbid nearshore waters.