Average Photon Flux Research Articles

Factors Intrinsic to the Axillary Bud Determine Topophysic Effects on Bud and Shoot Growth and Flower Development inRosa hybrida

Topophysis (the influence of the position of axillary buds along the shoot on bud and shoot growth, fresh biomass accumulation, and flower development) were studied in Rosa hybrida L. Single-node cuttings with five-leaflet leaves were excised from nine stem positions and grown as single-stemmed rose plants. Plants were grown at 20-h photoperiods, 22 degrees C average air temperature, and an average photosynthetic photon flux density of 228 µmol m-2 s-1. Generally, onset of axillary bud growth and initial shoot growth were promoted, and flower height and bloom quality were reduced in plants from apical bud positions. Stem diameter, stem growth rate, and biomass buildup were greatest from medial bud positions; the plastochron was greater, and stems and internodes were longer, from basal bud positions. Flower diameter and cut flower vase life were not significantly influenced by topophysis. The results demonstrate that topophysis can determine the potential for plant development and flowering in R. hybrida and that this knowledge may be used to regulate plant growth. Results also indicate intrinsic mechanisms determining axillary bud growth, but the physiology of topophysis is presently unclear. A probable role of cytokinins in the topophysic prevention of growth observed is discussed.

Evaluation of laser-irradiated Ar clusters as a source for time-resolved x-ray studies

We have measured the absolute average photon flux, the spectral characteristics, and the time structure of x rays emitted from Ar clusters which were irradiated by a 100 fs laser with an intensity of 1017 W/cm2. The measured photon flux was 107 photons per shot in the Kα (at 3 keV) line in a 4π sr solid angle. The temporal structure was measured using a streak camera with a 10 ps time resolution. It was found that less than 1% of the photons were emitted within the 10 ps time-response function of the streak camera. The emission profile is roughly exponential with a time constant of 3 ns.

BUSH LUPINE MORTALITY, ALTERED RESOURCE AVAILABILITY, AND ALTERNATIVE VEGETATION STATES

Nitrogen-fixing plants, by altering the availability of soil N, potentially facilitate plant invasion. Here we describe how herbivore-driven mortality of a native N-fixing shrub, bush lupine (Lupinus arboreus), increases soil N and light availability, which promotes invasion by introduced grasses to the detriment of a native plant community. Soils under live and dead lupine stands contained large amounts of total N, averaging 3.14 mg N/g dry mass of soil (398 g/m2) and 3.45 mg N/g dry mass of soil (438 g/m2), respectively, over four years. In contrast, similar lupine-free soil was low in N and averaged only 1.66 mg N/g dry mass of soil (211 g/m2) over three years. The addition of N fertilizer to lupine-free soil produced an 81% increase in aboveground plant biomass compared to plots unamended with N. Mean rates of net N mineralization were higher under live lupine and where mass die-off of lupine had occurred compared to soils free of bush lupine. At all sites, only 2.5–4.2% of the total soil N pool was mineralized annually. Soil enriched by lupine is not available to colonists while lupines are alive. The dense canopy of lupine shades soil under shrubs, reducing average photon-flux density in late spring from 1725 μmol·m−2·s−1 (full sunlight) to 13 μmol·m−2·s−1 (underneath shrubs). Stand die-off due to insect herbivory exposed this bare, enriched soil. In January, when annual plants are establishing, average photon-flux density under dead lupines killed by insect herbivores was 370 μmol·m−2·s−1, compared to the photon-flux density under live lupines of the same age, which averaged 83 μmol·m−2·s−1. The availability of bare, N-rich patches of soil enabled nonnative annuals (primarily Lolium multiflorum and Bromus diandrus) to colonize sites, grow rapidly, and dominate the plant assemblage until lupines reestablished after several years. The N content of these grasses was significantly greater than the N content of the mostly native plants that occupied adjacent coastal prairie devoid of bush lupine. Between 57 and 70% of the net amount of N mineralized annually was taken up by introduced grasses and subsequently returned to the soil upon the death of these annuals. Even in the absence of further N inputs, we estimate that it would take at least 25 yr to reduce the soil N pool by 50%, indicating that the reestablishment of the native prairie flora is likely to be long term.

A comparison of several methods for estimating light under a paper birch mixedwood stand

In 1996 we initiated a study to evaluate several techniques for measuring light under broadleaf canopies. Hourly average photosynthetic photon flux density and percent transmittance were measured 1 m above the ground at four points in each of three canopy densities created by a spacing experiment in a 35-year-old paper birch (Betula papyrifera Marsh.) dominated stand located near Prince George, B.C. At each point, fisheye photographs were taken and LAI-2000 plant canopy analyzer (LAI-2000), spherical densiometer, and competition index (Lorimer's index) measurements were made. Percent transmittance measurements on an overcast day (1-h average), transmittance measured over periods of 3 h or longer on a clear day, LAI-2000 diffuse noninterceptance measurements, and gap light index determined from fisheye photographs were strongly correlated with growing season percent transmittance (r2>= 0.96) as was competition index (r2 = 0.928). Concave spherical densiometer measurements and midday percent transmittance measurements on clear days were also well correlated with measured percent transmittance (r2>= 0.89). Estimates of understory light by the LITE model were strongly correlated with growing season percent transmittance. Correlations improved with increasing length of the period simulated (r2 = 0.755 for a point measurement on a clear day; r2 = 0.936 for an entire sunny day; and, r2 = 0.953 for the entire growing season). However, this version of the model underestimated percent transmittance in these spaced birch stands by 34-90%.

A comparison of several methods for estimating light under a paper birch mixedwood stand

In 1996 we initiated a study to evaluate several techniques for measuring light under broadleaf canopies. Hourly average photosynthetic photon flux density and percent transmittance were measured 1 m above the ground at four points in each of three canopy densities created by a spacing experiment in a 35-year-old paper birch (Betula papyrifera Marsh.) dominated stand located near Prince George, B.C. At each point, fisheye photographs were taken and LAI-2000 plant canopy analyzer (LAI-2000), spherical densiometer, and competition index (Lorimer's index) measurements were made. Percent transmittance measurements on an overcast day (1-h average), transmittance measured over periods of 3 h or longer on a clear day, LAI-2000 diffuse noninterceptance measurements, and gap light index determined from fisheye photographs were strongly correlated with growing season percent transmittance (r2>= 0.96) as was competition index (r2 = 0.928). Concave spherical densiometer measurements and midday percent transmittance measurements on clear days were also well correlated with measured percent transmittance (r2>= 0.89). Estimates of understory light by the LITE model were strongly correlated with growing season percent transmittance. Correlations improved with increasing length of the period simulated (r2 = 0.755 for a point measurement on a clear day; r2 = 0.936 for an entire sunny day; and, r2 = 0.953 for the entire growing season). However, this version of the model underestimated percent transmittance in these spaced birch stands by 34-90%.

Modeling Carbon Cell Quota in Light-limited Phytoplankton

The carbon cell quota of light-limited microalgae often increases with average photon flux density. Models of light-limited microalgal growth do not account for this phenomenon, however. In this paper we present a model of the carbon budget of phytoplankton, which accounts for the variation in carbon cell quota with photon flux density. We distinguish two components in the cell, permanent biovolume and a transient carbon pool. Furthermore, we distinguish three processes: assimilation, maintenance and growth. Assimilation acts to increase the transient carbon pool, whereas maintenance and growth both act to decrease it. Maintenance represents a sink of carbon; in contrast, growth leads to an increase of permanent biovolume. We derive equations describing the carbon cell quota, the specific growth rate, photosynthesis and dark respiration. The model accurately describes data on the complete carbon budget of three widely different phytoplankton species. We show that the model is a generalization of the well-known Droop model for nutrient limited growth. This result indicates that light and nutrient limited growth may be less dissimilar than is generally thought.

EXCYSTMENT AND GROWTH OF CHRYSOPHYTES AND DINOFLAGELLATES AT LOW TEMPERATURES AND HIGH SALINITIES IN ANTARCTIC SEA‐ICE1

ABSTRACTExtreme environmental conditions have been thought to limit algal growth in the upper sea‐ice. In McMurdo Sound, Antarctica, chrysophyte statocysts (stomatocysts) and dinoflagellate hypnozygotes (resting cysts) overwinter in first‐ and second‐year land‐fast sea‐ice exposed to temperatures of ‐20° C or lower. In early November, when temperatures in the upper ice are < −8°C and brine salinities are >126 psu, dinoflagellate cysts activate and shortly thereafter excyst. During early November, chrysophyte statocysts also begin to excyst. Net daily primary production occurs in the sea‐ice brine at temperatures as low as −7.1° C, at brine salinities as high as 129 psu, and at average photon flux densities as low as 5 μmol photons.m−2.s−1. Dinoflagellate densities were >106 vegetative cells.L−1 of ice while temperatures in the upper ice were between −6.8 and −5.8° C and brine salinities were ∼100 psu. Chrysophyte densities reached >106.L−1 of ice by early December. High densities of physiologically active clyo‐ and halotolerant algae can occur in the upper land‐fast sea‐ice under extreme conditions of temperature and salinity.

トウモロコシ葉の気孔コンダクタンスの変動に関する向軸面と背軸面の比較

We compared the variability of stomatal conductance between adaxial and abaxial surfaces of maize leaf in different environmental conditions, and addressed stomatal response to environmental factors, such as soil moisture.The stomatal conductance (G) for each of adaxial (gstd) and abaxial (gstb) surfaces and both surfaces combined (Gst) of a leaf varied significantly during the measurement. Diurnal changes of gstd, gstb and Gst were similar showing either unimodal, bimodal, or fluctuating patterns which depended on the environmental regimes of the measurement days. The gstb was larger than gstd, ratio (α) of gstb to gstd was not constant, the α varied with change in the environmental conditions during the measurement. Meanwhile, the stomatal conductance (gstd) (ZS), gstb (ZS), Gst (ZS) in different leaf positions (ZS, distance from the top of stem) on the stem decreased from upper leaf to lower leaf with quadratic functions, but the ratio of stomatal conductance on the two surfaces (α) in different leaf positions on the stem showed no specific pattern of changes.Effect of soil water content (θS, on mass basis) on the stomatal conductance (G) was expressed as G=GMax(1-θS0/θS), where G represented either gstd, gstb, or Gst; GMax was the maximum of G; θS0 was the soil water content when G=0. The relationships between the daytime average of the ratio α and the average photosynthetic photon flux density, saturation deficit and air temperature were expressed by quadratic functions, but the relationship between the average α and the mean of soil water content on mass basis was linear.

環境変数を用いたトウモロコシ葉の気孔コンダクタンスのモデリング

In the present paper, we attempted to use the average photosynthetic photon flux density (Qp), saturation deficit (De), leaf water potential (ΨL) and leaf temperature (TL) in the canopy as environmental variables (X) to optimize Jarvis' environmental variable model for estimating stomatal conductance (Gst) of a leaf in the maize canopy. The data, measured in the field in 1992-1994, were separated into three sets of short time period as one-year and a set of long time period as three-year. Therefore, the optimized models (*G(X)) to the each data set were selected through comparison of the coefficient of determinations (R2) of models with different numbers (from 1 to 4) of variable, respectively. The problems of application of the models on different period scale were also discussed.In the case of a short time period of one year, a relatively high estimated precision of Gst(R2=0.57-0.75) was obtained with the two-variable model *G(Qp, De) or *G(Qp, ΨL). However, in the long time period of three years, it was necessary that the model was constructed with three variables at least. The R2 of three-variable model *G(Qp, De, ΨL) was 0.43, and even if the model was constructed with four variables the R2 of model *G(Qp, De, ΨL, TL) was only 0.45.

Biological efficiency of supplementary lighting on cut roses the year round

The average monthly supplementary photosynthetic photon flux density (PPFD) effects on yield and energy consumption were studied for two cut rose cultivars using results from 2 years experiments with supplementary lighting. The effect of supplementary PPFD on rose yield lasted all through the year, and the extra yield due to extra PPFD tended to be lower around the equinox for both cultivars. The biological efficiency ((marketable) yield divided by kilowatt-hours or moles) of supplementary PPFD persisted year-round. However, for both cultivars the biological efficiency of supplementary lighting was higher in the summer than in the winter; e.g. in June and July the biological efficiency was about twice as high as in December and January. Since the photoperiods were equal, the increased light sum, which caused elevated average air and leaf temperatures, enhanced leaf expansion and increased light interception, and thereby increased growth vigour, may account for the higher summer efficiency of the supplementary PPFD. For the cut rose industry in northern countries, year-round use may prove advantageous when added to the general increase in yield and quality resulting from the use of supplementary lighting.

SUPPLEMENTAL IRRADIANCE DURING PRIMULA SEEDLING DEVELOPMENT

Seedlings of Primula malacoides Franch `Prima Carmine Red' and Primula vulgaris Huds.`Danova Lemon Yellow' received supplemental irradiance from high pressure sodium lamps for 2 weeks initiated at germination, 14 days after germination or 28 days after germination. The plants were grown at 15 ± 3C, 16 hours photoperiod and except during treatment, an average photosynthetic photon flux of 100 μmol·s-1m-2 (5.8 mol· day-1m-2). The irradiance levels during treatment were 200 or 300 μmol·s-1m-2 (11.5 or 17.3 mol·day-1m-2). There were no significant effects of supplemental irradiance on rate of flowering for P. malacoides, although the leaf number on the main shoot increased from 22 ± 4 leaves for control plants to 30 ± 3 leaves for plants receiving 300 μmol· s-1m-2. Flowering of P. malacoides averaged 100 ± 4 days from germination. Two weeks of 300 μmol· s-1m-2 initiated 4 weeks after germination resulted in an average plant dry weight of 0.56 ± 0.07 g compared to an average 0.39 ± 0.05 g for plants continuously grown at 100 μmol· s-1m-2.

Fast metastable defect-creation in amorphous silicon by femtosecond light pulses.

The creation of metastable dangling-bond defects in hydrogenated amorphous silicon subjected to short, intense laser pulses is investigated. It is found that pulse excitation leads to an order-of-magnitude increase in the defect creation rate compared to continuous illumination with the same average photon flux and photon energy. This implies that metastable-defect formation depends superlinearly on the density of photoexcited carriers. The much larger defect creation rate in the case of pulse excitation allows us to clarify the origin of saturation effects in the metastable-defect density, that are important for an assesment of the long-term conversion efficiency of amorphous-silicon solar cells.

Leaf Attributes as Indices of Fruit Quality in Prune Tree Canopies

Leaf dry weight per leaf area (LDW/LA); weight of leaf N per unit leaf area (LN/LA); leaf dry weight (LDW); and fruit quality, particularly sugar per fruit (SF); fruit fresh weight (FFW); and fruit dry weight (FDW) were measured over a range of daily average incident photosynthetic photon flux values (PPF) (50 to 1000 μmol·s-1·m-2) in 7-year-old prune (Prunus domestics L. syn. `Petite d'Agen') tree canopies. Linear or curvilinear relationships between these leaf attributes and fruit characteristics were significant over the PPF range. Analysis of LDW/LA or LN/LA may be used to indicate tree canopy locations in which fruit size and quality is limited by suboptimal PPF.

Photosynthetic Photon Flux Influences Macroelement Weight and Leaf Dry Weight per Unit of Leaf Area in Prune Tree Canopies

Abstract The relationship between canopy position and foliage concentrations of several phloem-mobile and -immobile essential nutrients was determined over a 20-fold range of average incident photosynthetic photon flux (PPF) (50 to 1000 μmol·s−1·m−2) in 7-year-old prune (Prunus domestica L., syn. ‘Prune d’Agen’) tree canopies. Mineral weight per unit of leaf area (LA) increased with increasing PPF within the canopy according to the relationship N > Ca > Mg > K > P. Dry weight per leaf area (DW/LA) increased 3-fold over the range of light exposures sampled. Leaf nutrient concentration expressed as percent dry matter (DM) did not vary with PPF. Both DW/LA and leaf N/LA appear to integrate the light microenvironment at the canopy coordinates of leaves sampled and may be correlated with photosynthetic capacity. Thus, these parameters may have diagnostic value in orchard management and crop production.

Effect of Light Level on Dinitrogen Fixation and Carbohydrate Distribution in Virginia Peanuts1

The peanut (Arachis hypogaea L.) is an important grain legume world‐wide, yet the N2 fixation capabilities of this crop have received minimal attention. An experiment was conducted to study the effects of radiant flux on peanut growth, N2 fixation, and the distribution of nonstructural carbohydrates among plant parts during vegetative and early‐reproductive growth stages. Two Virginia‐type cultivars, NC4 and NC6, were grown in controlled‐environment chambers under average photon flux treatments of 230 and 650 µimol photon m−2 s−1. Plants grown under the higher irradiance accumulated three times more dry matter, fixed three times more N2, and had greater reproductive potential than plants under the low irradiance. The greater fixation in plants under high light was attributed to an increased effective nodule mass in those plants and not to a greater efficiency of nodules to fix N2. There were no significant cultivar differences for dry matter or N accumulation, although NC4 was always slightly higher than NC6. Concentrations of nonstructural carbohydrates in peanut tissues varied depending on the growth stage. The content of carbohydrates in root, stem, and leaf tissues was greater in high‐light plants, compared with plants under low light. Within the high‐light treatment, carbohydrate content was greatest in tissues of NC4 plants. Carbohydrate concentration in nodules was not significantly different between light treatments.

Comparative carbon dioxide exchange for two Populus clones grown in growth room, greenhouse, and field environments

Light-saturated net photosynthetic rates per unit leaf area were 1.6–2.1 times greater for the photosynthetically mature leaves of plants of two hybrid Populus clones (NC-5260, 'Tristis No.1' (Populustristis Fisch. × P. balsamifera L.); NC-5326, 'eugenei' (P. deltoides Bartr. ex Marsh. × P. nigra L.)) grown in pots in the field than in comparable plants from a controlled environment growth room and a winter greenhouse. Stomatal resistances to CO2 in the field trees were only 0.4–0.6 of those in growth room and greenhouse trees. Mesophyll (residual) resistances to CO2 in field trees were 0.4–0.8 of those in growth room and greenhouse trees. Field plants had specific leaf weights 1.5–1.8 times higher than growth room and greenhouse plants, likely primarily owing to the greater average photosynthetic photon flux density in the field (835, 225, and 142 μE m−2 s−1 for field, growth room, and greenhouse conditions, respectively). When net photosynthetic rates (Ps) were corrected for the differences in specific leaf weights to derive net photosynthetic rate per unit leaf dry weight, the values were similar for plants from the three environments (Ps in field trees was 0.9–1.2 times Ps in growth room and greenhouse trees); gross photosynthetic rates per unit leaf weight were even more similar. Internal leaf CO2 concentrations, and photorespiration and dark respiration rates per unit leaf area were not related to growth environment. However, photorespiration rate as a percentage of net photosynthetic rate was lower in the field trees (12–16% in field trees, 19–24% in growth room trees, and 23–39% in greenhouse trees). Net photosynthetic rate was shown to be under strong genetic control in these clones. The effects of growth environment on variables of carbon exchange are sensitive to the basis of expression of those variables.

Seasonal variation in light- and temperature-dependent growth of marine planktonic diatoms in in situ dialysis cultures in the Trondheimsfjord, norway (63°N)

Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from −1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m −2 · s −1 (0.5 m depth), and the length of the days ( I > 1 μE · m −2 · s −1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m −2 · s −1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day −1 (July, 15–16°C). The three species exhibit different ecological behaviour. Skeletonema is eurythermal ( Q 10 = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found.

FLUORESCENCE KINETICS OF SPINACH CHLOROPLASTS MEASURED WITH A PICOSECOND OPTICAL KERR GATE

Abstract. An overview of the reported chlorophyll a fluorescence lifetimes from green plant photosystems is presented and the problems encountered in the measurement of fluorescence lifetime using two currently available picosecond techniques are discussed.The fluorescence intensity of spinach chloroplasts exposed to 10 ps flashes was measured as a function of time after the flash and wavelength of observation by the ultrafast Kerr shutter technique. Using a train of 100 pulses separated by 6ns and with an average photon flux per pulse of ˜2 times 1014 photons/cm2, the fluorescence intensity at 685 nm (room temperature) was found to decay with two components, a fast one with a 56 ps lifetime, and a slow one with a 220 ps lifetime. The 730 nm fluorescence intensity at room temperature decays as a single exponential with a 100 ps lifetime. The 730 nm fluorescence lifetime was found to increase by a factor of 6 when the temperature was lowered from room temperature to 90 K while the lifetime of 685 and 695 nm fluorescence were unchanged. At room temperature, the fast and slow components at 685 nm are attributed to the emission from pigment system I (PS I) and PS II, respectively. It is likely that the absolute values of lifetimes, reported here, may increase if single ps low intensity flashes are used for these measurements.

Maximum likelihood estimate of target angles for a conical scan tracking system in the presence of speckle

The equation for the maximum likelihood estimate of target angle is derived for a conical scan tracking system when the target produces speckle and Gaussian noise is present. Operation with a direct detection receiver is assumed with the average photon flux large enough so that the discrete nature of photoelectric events may be ignored. For large average SNRs, the estimate is shown to be unbiased and the variance of the estimate limited by both the average SNR and the number of degrees of freedom of the detected field.

Search for point sources of high-energy cosmic gamma rays

A balloon-borne photographic spark chamber was flown at a pressure of 10 g cm−2 on 14 April 1966 from Holloman A.F.B., New Mexico. Upper limits were obtained on gamma-ray fluxes above 1 GeV from various discrete sources including Cyg A, Cas A, and the Crab nebula. Also a measurement was made on the average photon flux above 1 GeV from a portion of the galactic disk.