Light attenuation in a 14-year-old loblolly pine stand as influenced by fertilization and irrigation

 We examined empirical and simulated estimates of canopy light attenuation at SETRES (Southeast Tree Research and Education Site), a 2×2 factorial study of water and nutrients. Fertilized plots had significantly lower under-canopy PAR transmittance (T_C) when compared to non-fertilized plots. Light interception efficiency, as measured by the canopy cosine-corrected light extinction coefficient, G, was significantly lower in irrigated plots for all dates examined. Estimates of G ranged from a low of 0.36 in irrigated plots in September to a high of 0.64 in March for control plots. Study-wide analyses indicate that a G of 0.50 and a k (uncorrected light extinction coefficient) of 0.69 may be reasonable parameter estimates of canopy light extinction in intermediate-aged loblolly pine plantations across a range of stand conditions and seasons when site-specific data are unavailable. Simulated T_C from our version of the BIOMASS model corresponded well to the empirical estimates. Varying the vertical distribution of foliage in simulations (from 10:60:30 to 40:40:10% in the upper, middle, and lower canopy positions, respectively) resulted in only a ±7% change in total PAR intercepted, whereas varying G from 0.3 to 0.7 resulted in a 67% and 31% increase in light intercepted for control and fertilized plots, respectively. Decreased G resulted in an increased proportion of beam radiation intercepted – 63–67% of total PAR intercepted – by the middle canopy where 55–60% of the foliage was found. We hypothesize that proportionally increased productivity observed in irrigated treatments may be attributed to increased beam radiation intercepted deeper into the canopy by a greater foliage area. Received: 23 April 1998 / Accepted: 17 June 1998     

Light climate and energy flow in the seagrass canopy of Amphibolis griffithii (J.M. Black) den Hartog

 Absorption of light and radiation use efficiency (RUE) were measured in a dense stand of the seagrass Amphibolis griffithii in Warnbro Sound, a temperate marine embayment in southern Western Australia. Total light intercepted by the canopy was measured and compared with dry weight leaf production, under both summer and winter conditions. RUE was found to be higher in winter (1.56 g MJ^–1) than summer (1.01 g MJ^–1). These values are very similar to values measured for annual crop plants and emphasise the value of applying theory developed for terrestrial crop plants to seagrasses. Canopy extinction coefficients were 0.93 m^–1 in winter and 0.44 m^–1 in summer. There were large differences in hours above saturating irradiance (H _sat) between the top (H_sat = 5 h 14 min) and base (18 min) of the canopy in winter. Energy flows in A. griffithii suggest that this species is highly susceptible to short-term perturbations in incident irradience during the winter period as the energy stored within the rhizomes is small relative to daily respiratory demands. Received: 5 October 1995 / Accepted: 14 August 1996     

The response of Ceratophyllum demersum L. and Myriophyllum spicatum L. to reduced, ambient, and enhanced ultraviolet-B radiation

The response of Ceratophyllum demersum and Myriophyllum spicatum to three levels of UV-B radiation – reduced (ca. 50% reduction), ambient and enhanced UV-B radiation, simulating 17% ozone depletion – is discussed. The research revealed that UV-B stimulated the production of UV-B absorbing compounds in C. demersum, but not in M. spicatum. The relative amount of UV-B absorbing compounds was about four times lower in C. demersum. Enhanced UV-B also affected respiratory potential in C. demersum (on average 3.7 mg O₂/gDM/h), but no effect on M. spicatum (on average 5.5 mg O₂/gDM/h) was detected. Increased need for energy revealed that UV-B radiation exerted stress in C. demersum. No changes in chlorophyll a and no disturbance to photochemical efficiency due to UV-B were observed in either species.     

Progression age enhanced backward bifurcation in an epidemic model with super-infection

 We consider a model for a disease with a progressing and a quiescent exposed class and variable susceptibility to super-infection. The model exhibits backward bifurcations under certain conditions, which allow for both stable and unstable endemic states when the basic reproduction number is smaller than one. Received: 11 October 2001 / Revised version: 17 September 2002 / Published online: 17 January 2003 Present address: Department of Biological Statistics and Computational Biology, 434 Warren Hall, Cornell University, Ithaca, NY 14853-7801 This author was visiting Arizona State University when most of the research was done. Research partially supported by NSF grant DMS-0137687. This author's research was partially supported by NSF grant DMS-9706787. Key words or phrases: Backward bifurcation – Multiple endemic equilibria – Alternating stability – Break-point density – Super-infection – Dose-dependent latent period – Progressive and quiescent latent stages – Progression age structure – Threshold type disease activation – Operator semigroups – Hille-Yosida operators – Dynamical systems – Persistence – Global compact attractor     

Comparison of surface potentials due to several singularity representations of the human heart

In electrocardiography the electrical potentials due to the heart actions can be analyzed by assuming the human body to be a conductor of homogeneous medium and the heart to be a combination of singularities within it. For a spherical conductor the “interior sphere theorem” of G. Ludford, J. Martinek, and G. Yeh (Proc. Cambridge Phil. Soc.,51, 389–93, 1955) renders potential expressions due to any singularity. For a conductor of prolate spheroidal shape the potential expressions due to a source-sink pair and a general dipole have been given by J. R. Wait (Jour. App. Physics,24, 496–97, 1953) and the authors (paper at the Conference on the Electrophysiology of the Heart, Feb. 16–17, 1956, in New York, to appear in theAnn. N. Y. Acad. Sciences) respectively. (A theorem which applies to any singularity inside a prolate or oblate spheroid will be published by the authors soon). This paper presents numerical and graphical results of potentials on the surfaces of a prolate spheroid and a sphere due to source-sink pairs and dipoles of several locations and directions and compares the various representations. A discussion on the judicious choice of heart models concludes the paper. This investigation was supported by The National Heart Institute under a research grant H-2263.     

Somatic embryogenesis and in vitro rosmarinic acid accumulation in Salvia officinalis and S. fruticosa leaf callus cultures

The effect of explant age, plant growth regulators and culture conditions on somatic embryogenesis and rosmarinic acid production from leaf explants of Salvia officinalis and S. fruticosa plants collected in Greece was investigated. Embryogenic callus with numerous spherical somatic embryos could be induced on explants derived from both species and cultured for 3 weeks on a Murashige and Skoog (MS) medium supplemented with 1.8–18 μm 2,4-dichlorophenoxyacetic acid (2,4-D) and kinetin (Kin) or 10.5–21 μm 1-naphthalenacetic acid and 6-benzyladenine. Only explants from young plants (with six to eight leaves) responded to the culture treatments and, in general, low light intensities (50 μmol m^–2 s^–1) favoured callus formation and induction of somatic embryos. Somatic embryos were further developed on the same medium. Heart- and torpedo-shaped embryos (1–2 mm long) were subcultured on a growth-regulator-free MS medium for maturation. Maximum rosmarinic acid accumulation in S. officinalis and S. fruticosa callus cultured on 4.5 μm 2,4-D and 4.5 μm Kin was 25.9 and 29.0 g/l, respectively. Received: 17 January 1997 / Revision received: 26 May 1997 / Accepted: 30 June 1997     

Highly regenerative tissue cultures from axillary tiller buds of sexually mature oat plants (Avena sativa L.)

Summary Competent tissue cultures were initiated from axillary tiller buds and immature leaves of two cultivars ofAvena sativa L. and cultured on agar nutrient medium containing 2 mg/l of 2,4-dichlorophenoxyacetic acid and 1 mg/l benzyladenine. Using a technique of selective excision and subculturing of the shoot-forming tissues and rejecting the root-froming tissues, we regenerated numerous plants either on hormone-free medium or by allowing the subculture with hormone to age under usual culture-room light conditions. This research was supported in part through a grant to A. W. G. from BARD (Binational Agricultural Research and Development Foundation). N. S. S. is grateful to the Ministry of Education and Culture, Government of India, New Delhi, for the award of a National Scholarship for study abroad 1980–81.     

Acclimation of brown algal photosynthesis to ultraviolet radiation in Arctic coastal waters (Spitsbergen, Norway)

In field studies conducted at the Kongsfjord (Spitsbergen) changes of the irradiance in the atmosphere and the sublittoral zone were monitored from the beginning of June until the end of August 1997, to register the minimum and maximum fluxes of ultraviolet and photosynthetically active radiation and to characterise the underwater light climate. Measurements of photosynthesis in three abundant brown algal species (Alaria esculenta, Laminaria saccharina, Saccorhiza dermatodea) were conducted to test whether their photosynthetic performance reflects changing light climate in accordance with depth. Plants sampled at various depths were exposed to controlled fluence rates of photosynthetically active radiation (400–700 nm), UV-A (320–400 nm) and UV-B (280–320 nm). Changes in photosynthetic performance during the treatments were monitored by measuring variable chlorophyll fluorescence of photosystem II. In each species, the degree of inhibition of photosynthesis was related to the original collection depth, i.e. shallow-water isolates were more resistant than plants from deeper waters. The results show that macroalgae acclimate effectively to increasing irradiance levels for both photosynthetically active and ultraviolet radiation. However, the kinetics of acclimation are different within the different species. It is shown that one important strategy to cope with higher irradiance levels in shallow waters is the capability for a faster recovery from high light stress compared to isolates from deeper waters. Received: 13 March 1998 / Accepted: 16 May 1998     

Partitioning of biologically active radiation in plant canopies

 Plant germination, growth, maturation, and productivity are heavily influenced by the quality and quantity of the light in its environment. The light environment has traditionally been quantified in terms of radiant heat energy and available photosynthetic radiation (PAR), but detailed spectral irradiance or photon flux distributions have rarely been studied. This information is needed to translate the research that plant photobiologists and photochemists have been conducting with regard to understanding the light controls on plant physiology in the field environment of plant canopies. More interest has recently been generated as the potential impacts of global climate changes on intensively managed and natural terrestrial ecosystems are identified and evaluated. Linkages between the identified impacts of various wavelengths of light on plant physiology and the light environment of the plant canopy are identified, with detailed discussion concerning the impacts of plant canopy structure on the plant light response. Solar radiation in the ultraviolet-B (280–320 nm), ultraviolet-A and blue (350–500 nm), PAR (400–700 nm), blue (400–500 nm), green (500–600 nm) red (600–700 nm), far red (700–800 nm) and near infrared (800–1100 nm) is followed from the top of the plant canopy to the photoreceptor at the cellular level within the plant phytoelement.     

<Emphasis Type="Italic">Isatis indigotica</Emphasis> seedlings derived from laser stimulated seeds showed improved resistance to elevated UV-B

Sterilized seeds of Isatis indigotica (Brassicacae) were divided into four groups based on irradiation pretreatments. These control groups (C) were non irradiated, He–Ne laser treated seeds (L), UV-B treated seeds (B) and He–Ne laser followed by UV-B radiation treated seeds (LB). Laser radiation was provided by He–Ne laser, UV-B radiation was provided by filtered Qin brand 30 W fluorescent sun lamps. Malondialdehyde (MDA), proline, UV-B absorbing compounds and ascorbic acid (AsA) concentrations, as well as, the activities of superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) were measured in the cotyledons of seedlings from all the four irradiation treatments. The result indicate that UV-B radiation enhanced the concentration of MDA while decreasing the activities of SOD, CAT, POD and the concentration of AsA in the seedlings compared with the controls. The concentration of MDA decreased, while the activities of SOD, CAT, POD and the concentration of AsA increased in seedling treated with He–Ne laser and UV-B compared to UV-B alone. The concentration of proline and UV absorbing compounds increased progressively with treatments i.e. UV-B irradiation, He–Ne laser irradiation, and He–Ne laser irradiation followed by UV-B irradiation compared to the controls. The present data suggest that Isatis indigotica seedlings derived from laser stimulated seeds showed improved resistance to elevated UV-B.     

Cattaneo models for chemosensitive movement

 We derive models for chemosensitive movement based on Cattaneo's law of heat propagation with finite speed. We apply the model to pattern formation as observed in experiments with Dictyostelium discoideum, with Salmonella typhimurium and with Escherichia coli. For Salmonella typhimurium we make predictions on pattern formation which can be tested in experiments. We discuss the relations of the Cattaneo models to classical models and we develop an effective numerical scheme. Received: 8 October 2001 / Revised version: 2 August 2002 / Published online: 19 November 2002 Key words or phrases: Chemotaxis – Aggregation – Cattaneo model – Numerical schemes Acknowledgements. We are very grateful for comments of S. Noelle concerning the numerical scheme. We thank K.P. Hadeler and C. Schmeiser for helpful remarks. The research was supported by the Deutsche Forschungsgemeinschaft, research project ANumE and the Austrian Science Foundation, grant no. W008.     

Photochemical degradation of chromophoric-dissolved organic matter exposed to simulated UV-B and natural solar radiation

Photochemical degradation of chromophoric-dissolved organic matter (CDOM) by UV-B radiation decreases CDOM absorption in the UV region and fluorescence intensity, and alters CDOM composition. CDOM absorption, fluorescence, and the spectral slope indicating the CDOM composition were studied using 0.22-μm-filtered samples of Meiliang Bay water from Lake Taihu that were exposed to short-term (0–12 h) simulated UV-B radiation and long-term (0–12 days) natural solar radiation in summer. CDOM absorption coefficient and fluorescence decreased with increasing exposure time, which relates to the amounts of absorbed light energy. The decreases of CDOM absorption and normalized fluorescence corresponded to first order kinetics reactions. Different decreases of CDOM absorption and fluorescence at different wavelengths suggested that the composition of CDOM changed when it absorbed ultraviolet radiation. Photochemical degradation increased the spectral slope during 275–295 nm region (S _275–295) but decreased the spectral slope during 275–295 nm region (S _350–400). The slope ratio S _R (S _275–295:S _350–400) increased in the photochemical process, which could be used as an indicator of photobleaching and composition change of CDOM. Our results show that photochemical degradation is important in the cycling of CDOM, which indicated change in the composition of CDOM. Handling editor: Luigi Naselli-Flores     

Thallus morphology and optical characteristics affect growth and DNA damage by UV radiation in juvenile Arctic Laminaria sporophytes

Growth of young sporophytes of the brown algae Laminaria digitata, L. saccharina and L. solidungula from Spitsbergen were measured in the laboratory after being exposed for 21 days to either photosynthetically active radiation (PAR=P) or to full light spectrum (PAR + UV-A + UV-B=PAB) using of cutoff glass filters. The plants were grown at 8±2°C and 16 h light : 8 h dark cycles with 6 h additional ultraviolet radiation (UVR) exposure in the middle of the light period. Growth was measured every 10 min using growth chambers with online video measuring technique. Tissue morphology and absorption spectra were measured in untreated young sporophytes while chlorophyll (Chl) a content and DNA damage were measured in treated thalli at the end of the experiment. In all species, growth rates were significantly higher in sporophytes exposed to P alone compared to sporophytes exposed to PAB. Tissue DNA damage is dependent on thallus thickness and absorption spectra characteristics of pigments and UV-absorbing compounds. In sporophytes exposed to UVR, energy demands for repair of DNA damage and synthesis of UV-absorbing compounds for protection effectively diverts photosynthate at the expense of growth. Photosynthetic pigment was not significantly different between treatments suggesting a capacity for acclimation to moderate UVR fluence. The general growth pattern in sporophytes exposed to P alone showed an increasing growth rate from the onset of light (0500–0900 hours) to a peak at the middle of the light phase (0900–1500 hours), a decline towards the end of the light phase (1500–2100 hours) and a minimum “low” growth in the dark (2100–0500 hours) relative to growth during the entire light phase. Under PAB, different growth patterns were observed such as growth compensation at night in L. digitata, delayed growth recovery in L. saccharina and minimal but continuous growth in L. solidungula. Growth as an integrative parameter of all physiological processes showed that the effect of UVR is correlated to the depth distribution of these species.     

Effects of photo-oxidative loss of FeNa2EDTA and of higher iron supply on chlorophyll content, growth and propagation rate in triploid watermelon cultures

Summary Triploid watermelon (Citrullus lanatus [Thunb.] Matsum. & Nakai) Arka Manik cultures exhibited a general pale color and yellowing of lower leaves by 3–4 wk following subculturing to fresh medium. Protecting the medium from light by covering the surface with sterile aluminum foil significantly improved leaf color and chlorophyll content by 50–60%. Raising the concentration of FeNa₂EDTA (Fe-EDTA) in the light-exposed medium from the normal level (100 μM) to 150 or 200 μM significantly increased the leaf chlorophyll two- to threefold, suggesting that the light-induced effect was mainly attributable to photo-oxidation of Fe-EDTA. Fe-EDTA supplementation also resulted in better expansion and lobe formation of upper leaves, a reduction in internode length, an increase in the number of nodes, and a significant improvement in propagation rate. There was also a reduction in axillary sprout growth at elevated Fe-EDTA levels, indicating a more prominent apical dominance effect and a reduction in the number and vigor of tendrils. Increasing the Fe-EDTA level in the medium to 150 μM is suggested for routine micropropagation of triploid watermelon, in order to compensate for the photo-oxidative loss of Fe-EDTA.     

Characterisation, prediction and relationships between different wavebands of solar radiation transmitted in the understorey of even-aged oak (Quercus petraea, Q. robur) stands

Solar radiation transmission in forest stands affects many processes, including biomass and diversity of understorey vegetation and tree seedling regeneration (growth and morphogenesis). However, understorey light availability is not easy for forest managers or scientists to measure. Therefore, different models have been developed to predict light transmission in forest stands according to tree or stand structure. However, these models are generally too complex to be used operationally. This paper reports the assessment of light transmission according to stand parameters commonly measured by foresters in inventories. We measured transmittance in 29 even-aged oak stands in France for various wavebands, total solar radiation (TSR, 300–3000 nm), PAR (400–700 nm), red (R, 660 nm) and far-red (FR, 730 nm), and demonstrated that transmittance in a given waveband can be predicted from the measurement of another waveband. The R:FR ratio can be predicted according to TSR or PAR transmittance, but the opposite is also true; PAR or TSR transmittance can be predicted from the R:FR ratio. Transmittance variability was characterised, and the variation coefficient ranged from 5 to 45% with a trend to increase with tree density. By analogy to Beer–Lambert's law, we established that mean daily transmittance for the different wavebands can be assessed according to stand basal area and stand age with good accuracy (R ²>0.74). Results are discussed in comparison with other models based on the principle of parsimony.     

Effect of low doses of UV-A and UV-B radiation on photosynthetic activities in<Emphasis Type="Italic">Phaseolus mungo</Emphasis> L.

The effect of low doses of UV-A (320–400 nm) and UV-B (280–320 nm) radiation on photosynthetic activities inPhaseolus mungo L. was investigated under field condition. Supplementation of UV-A enhanced the synthesis of chlorophyll and carotenoids than the UV-B supplemented plants. Significant increase was seen in the concentration of UV-B absorbing compounds of UV-B treated plants. Increase of PS 2 activity in UV-A treated plants was seen. Changes in photosynthetic activity were measured in terms of PS 2 mediated O₂ evolution and Chl a fluorescence.     

Combined effects of enhanced ultraviolet-B radiation and doubled CO2 concentration on growth, fruit quality and yield of tomato in winter plastic greenhouse

Five different doses of ultraviolet-B (UV-B) radiation were supplied to tomato (Lycopersicon esculeutum. Mill) with the doubled CO₂ concentration (700 μmol · mol⁻¹) in the winter plastic greenhouse. The influences on the seedling growth, fruit quality and yield of tomato were investigated. Results showed that the seedling growth, and the contents of UV absorbing compounds, soluble sugar, organic acid, vitamin C and lycopene of tomato fruits, and yield of tomato increased under doubled CO₂ concentration. Under the doubled CO₂ concentration the effects of lost doses of UV-B radiation could further promote the effects of doubled CO₂ concentration. However, there is no significant increase in yield of tomato. The best dose of UV-B radiation is about 1.163 kJ·m⁻². When the dose of UV-B radiation is more than it, the effects of UV-B will be reduced. __________ Translated from Journal of Wuhan Botanical Research, 2006, 24(1): 49–53 [译自: 武汉植物学研究]     

Visual behaviour of neonata larvae of the light brown apple moth

When neonate larvae of a leafroller moth,Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae) were released into the middle of a circular arena with blue paper on one side of the arena and apple foliage on the other side, more larvae walked towards the apple foliage. These oriented responses were enhanced, in terms of the number of larvae responding, by increasing the amount of light reflected from or transmitted through apple foliage. Larvae also responded to painted targets, and specifically to targets reflecting light in the region of 470–570 nm (green-yellow region to the human eye). When the amount of 470–570 nm reflected from targets was reduced, numbers of larvae responding to targets decreased. The addition of 400–500 nm reflected light to 470–570 nm reflected light also resulted in a reduction of oriented responses to targets. Tests using neutral colours (white, black, and a series of greys) indicated that, in the absence of targets reflecting primarily in the 470–570 nm region, larvae oriented towards targets with low levels of reflectance. When the orientation of walking larvae was measured at various distances from targets of different colours or diameters, targets subtending 5–8 degrees elicited responses from 50% of all larvae. Behaviour other than walking was also influenced by visual stimuli: fewer larvae spun down on a silken thread when blue paper was placed beneath a walking platform than when brown or green papers were present.     

Isolation,callus formation and plantlet regeneration from mesophyll protoplasts of <Emphasis Type="Italic">Tylophora indica</Emphasis> (Burm. f.) Merrill: an important medicinal plant

Protoplast culture and plant regeneration of an important medicinal plant Tylophora indica were achieved through callus regeneration. Protoplasts were isolated from leaf mesophyll cells and cultured at a density of 5 × 10⁵ protoplasts per gram fresh weight, which is required for the highest frequency of protoplast division (33.7%) and plating efficiency (9.3%). The first division was observed 2 d after plating and the second division after 4 d. Culture medium consists of Murashige and Skoog (MS) liquid medium with 4 μM 2,4-D, 0.4 M mannitol and 3% (w/v) sucrose with pH adjusted to 5.8. After 45 d of culture at 25°C in the dark, protoplasts formed colonies consisting of about 100 cells. The protoplast-derived microcalli were visible to the naked eye within 60 d of culture and reached a size of 0.2–0.4 mm in diameter after 90 d. Calli of 0.2–0.4-mm size were transferred to MS medium supplemented with 2,4-D (4 μM), 3% (w/v) sucrose and 0.8% (w/v) agar, formed friable organogenic calli (7-8 mm size) after 8 wk under incubation in normal light period supplemented with 200 μmol m⁻² S⁻¹ of day light fluorescent illumination. The calli were transferred to MS medium supplemented with thidiazuron (TDZ) (1–7 μM) and naphthalene acetic acid (NAA) (0.2–0.4 μM) for regeneration. The calli developed shoot buds after 3–4 wk, and the frequencies of calli-forming shoots varied from 5% to 44%. Optimum shoot regeneration occurred on MS medium supplemented with 5 μM TDZ and 0.4 μM NAA. On this medium, 44% cultures responded with an average number of 12 shoots per callus. Whole plants were recovered following rooting of shoots in 1/2 MS medium supplemented with 3 μM indole 3-butyric acid.     

Regeneration of plantlets from mature embryos of western larch

Summary Larix occidentalis Nutt. can be micropropagated using whole excised mature embryos. The basal medium for induction (over 70% response) was half-strength Quoirin and LePoivre salts with Schenk and Hildebrandt organics and N⁶-benzyladenine singly or with kinetin at a final concentration of 10μM. Bud elongation was best on half-strength Schenk and Hildebrandt or Bornman’s mineral salts, and elongated shoots could be maintained on either half-strength Quoirin and LePoivre or Schenk and Hildebrandt formulations containing 0.05% activated charcoal, 2% sucrose, and 0.7% agar. Axillary buds developed naturally on elongating juvenile shoots, but a high sucrose treatment (6%) for 2 wk enhanced the number produced. Very good rooting (80 to 100%) was obtained by pulsing shoots for 2 to 3 h in a solution of indole butyric acid (1 mM, pH 4.5–5.0), or by planting shoots in peat-vermiculite moistened with basal medium containing 5μM α-naphthalene acetic acid, pH 5.0. Rooted shoots were hardened before transfer to the greenhouse, and initially were kept at low light and high humidity after transfer to ex vitro conditions. This research was supported initially by a National Research Council of Canada, Division of Energy Contract, and subsequently by a Natural Sciences and Engineering Research Council of Canada strategic grant to T. A. Thorpe.