Changes In Light Quality Research Articles

Stratospheric ozone depletion and plantinsect interactions: Effects of UVB radiation on foliage quality ofCitrus jambhiri forTrichoplusia ni

Projected decreases in stratospheric ozone may result in increases in shortwave ultraviolet (UVB) irradiation at the earth's surface. Furanocoumarins, phototoxic compounds found inCitrus jambhiri foliage, increase in concentration when these plants are grown under enhanced UVB. Survivorship schedules ofTrichoplusia ni (Lepidoptera: Noctuidae) caterpillars reared on plants in the presence and absence of enhanced UVB regimes differ significantly; larvae develop more slowly in early life when reared on plants exposed to increased UVB. This same developmental pattern is observed whenT. ni larvae are reared on artificial diets amended with ecologically appropriate amounts of furanocoumarins. Thus, anthropogenically derived changes in stratospheric ozone and concomitant changes in UV light quality at the earth's surface may influence ecological interactions between insects and their host plants by altering secondary metabolism and hence foliage quality for herbivores.

Action spectra of microalgal photosynthesis and depth distribution of spectral scalar irradiance in a coastal marine sediment of Limfjorden, Denmark

The role of complementary spectral utilization of light for the zonation of different groups of oxygenic phototrophic organisms in sediments was studied. The marine sediment was covered by a dense population of diatoms with an underlying population of cyanobacteria. Action spectra for photosynthesis and spectral scalar irradiance, E0, were measured directly in the sediment at a spatial resolution of 0.1 mm by the use of oxygen and light microsensors. The action spectrum for the diatoms was similar to the attenuation spectrum of the scalar irradiance, K0, in the diatom layer with Chl. a and carotenoids being the major photosynthetic pigments. The action spectrum of the cyanobacteria showed photosynthesis maxima at the absorption regions of Chl. a and phycocyanin. The measured depth distribution of spectral scalar irradiance and the action spectra of diatoms and cyanobacteria were used to calculate the spectral quality for photosynthesis of the 400–700 nm light to which the two populations were exposed. This spectral quality was compared to that of the light incident on the sediment surface. Due to preferential extinction of wavelengths, at which their photosynthetically active pigments had maximal absorption, the relative light quality for diatoms was reduced to 85% of the quality of incident light at a similar total quantum flux. This effect was partly due to spectral alterations of light backscattered from the underlying sediment with cyanobacteria. The cyanobacteria at the bottom of the euphotic zone, in contrast, experienced a light spectrum which was favorably altered, to 107% in quality, due to absorption by the overlying diatoms. It was concluded that these changes in spectral light quality can be considered as only one of more factors explaining the zonation of the two phototrophic populations, and that total light intensity and the chemical microenvironment are probably more important factors.

Action spectra of microalgal photosynthesis and depth distribution of spectral scalar irradiance in a coastal marine sediment of Limfjorden, Denmark

The role of complementary spectral utilization of light for the zonation of different groups of oxygenic phototrophic organisms in sediments was studied. The marine sediment was covered by a dense population of diatoms with an underlying population of cyanobacteria. Action spectra for photosynthesis and spectral scalar irradiance, E0, were measured directly in the sediment at a spatial resolution of 0.1 mm by the use of oxygen and light microsensors. The action spectrum for the diatoms was similar to the attenuation spectrum of the scalar irradiance, K0, in the diatom layer with Chl.a. and carotenoids being the major photosynthetic pigments. The action spectrum of the cyanobacteria showed photosynthesis maxima at the absorption regions of Chl.a. and phycocyanin. The measured depth distribution of spectral scalar irradiance and the action spectra of diatoms and cyanobacteria were used to calculate the spectral quality for photosynthesis of the 400–700 nm light to which the two populations were exposed. This spectral quality was compared to that of the light incident on the sediment surface. Due to preferential extinction of wavelengths, at which their photosynthetically active pigments had maximal absorption, the relative light quality for diatoms was reduced to 85% of the quality of d incident light at a similar total quantum flux. This effect was partly due to spectral alterations of light backscattered from the underlying sediment with cyanobacteria. The cyanobacteria at the bottom of the euphotic zone, in contrast, experienced a light spectrum which was favorably altered, to 10% in quality, due to absorption by the overlying diatoms. It was concluded that these changes in spectral light quality can be considered as only one of more factors explaining the zonation of the two phototrophic populations, and that total light intensity and the chemical microenvironment are probably more important factors.

Action spectra of microalgal photosynthesis and depth distribution of spectral scalar irradiance in a coastal marine sediment of Limfjorden, Denmark

The role of complementary spectral utilization of light for the zonation of different groups of oxygenic phototrophic organisms in sediments was studied. The marine sediment was covered by a dense population of diatoms with an underlying population of cyanobacteria. Action spectra for photosynthesis and spectral scalar irradiance, E 0, were measured directly in the sediment at a spatial resolution of 0.1 mm by the use of oxygen and light microsensors. The action spectrum for the diatoms was similar to the attenuation spectrum of the scalar irradiance, K 0, in the diatom layer with Chl. a. and carotenoids being the major photosynthetic pigments. The action spectrum of the cyanobacteria showed photosynthesis maxima at the absorption regions of Chl. a. and phycocyanin. The measured depth distribution of spectral scalar irradiance and the action spectra of diatoms and cyanobacteria were used to calculate the spectral quality for photosynthesis of the 400–700 nm light to which the two populations were exposed. This spectral quality was compared to that of the light incident on the sediment surface. Due to preferential extinction of wavelengths, at which their photosynthetically active pigments had maximal absorption, the relative light quality for diatoms was reduced to 85% of the quality of d incident light at a similar total quantum flux. This effect was partly due to spectral alterations of light backscattered from the underlying sediment with cyanobacteria. The cyanobacteria at the bottom of the euphotic zone, in contrast, experienced a light spectrum which was favorably altered, to 10% in quality, due to absorption by the overlying diatoms. It was concluded that these changes in spectral light quality can be considered as only one of more factors explaining the zonation of the two phototrophic populations, and that total light intensity and the chemical microenvironment are probably more important factors.

Light Quality and Vernalization Interact in Controlling Late Flowering in Arabidopsis Ecotypes and Mutants

The late flowering ecotypes of Arabidopsis thaliana L. (Heyn.) Eifel, Pitztal and Innsbruck responded to 10 d vernalization (cold treatment) by flowering earlier with less with less than half the number of leaves of non-induced plants. The vernalization response was cumulative: increased numbers of days of vernalization induced earlier flowering up to an apparent saturation in response after 30 to 40 d. The ratio of red:far-red (R:FR) light also affected non-vernalized time-to-flower. When grown under fluorescent plus incandescent lamps (R:FR = 1·0), time-to-flower was approximately half that required by plants grown under fluorescent lamps (R:FR = 5·8) at the same photon flux density and photoperiod. Leaf production rate was unaffected by either vernalization or light quality changes and time-to-flower and leaf number were highly correlated (r2 = 0·973).The late flowering mutants of Landsberg erecta were grown under lighting which displayed a gradient of R:FR. Some mutants like co, flowered at the same time in all R:FR treatment, while other like fca took nearly twice as long to flower, with double the number of leaves at R:FR ratio of 5·8 compared with the R:FR = 1 treatment. The ranking of the response from least to most responsive was co, fe, gi, WT, fd, fwa, ft, fha, fpa, fy, fve and fca.Vernalization of these Landsberg mutants always resulted in earlier flowering, although only fca, fve, fy and fpa were significantly more sensitive to thermoinduction than the wild type parent. There was a high correlation (r2 = 0·89 between the response to thermoinduction and to R:FR ratio. Vernalization of fca for 24 d largely eliminated the R:FR time-to-flower response. Vernalization and photoinduction similarly affect late flowering and can substitute for each another.

The dynamics of photosynthetic acclimation to changes in light quanlity and quality in three Australian rainforest tree species.

Photosynthetic acclimation was studied in seedlings of three subtropical rainforest species representing early (Omalanthus populifolius), middle (Duboisia myoporoides) and late (Acmena ingens) successional stages in forest development. Changes in the photosynthetic characteristics of pre-existing leaves were observed following the transfer of plants between deep shade (1-5% of photosynthetically active radiation (PAR), selectively filtered to produce a red/far-red (R/FR) ratio of 0.1) and open glasshouse (60% PAR and a R/FR ratio of 1.1-1.2), and vice versa. The extent and rate of response of the photosynthetic characteristics of each species to changes in light environment were recorded in this simulation of gap formation and canopy closure/overtopping. The light regimes to which plants were exposed produced significant levels of acclimation in all the photosynthetic parameters examined. Following transfer from high to low light, the light-saturated rate of photosynthesis was maintained near pre-transfer levels for 7 days, after which it decreased to levels which closely approximated those in leaves which had developed in low light. The decrease in photosynthetic capacity was associated with lower apparent quantum yields and stomatal conductances. Dark respiration was the parameter most sensitive to changes in light environment, and responded significantly during the first 4-7 days after transfer. Acclimation of photosynthetic capacity to increases in irradiance was significant in two of the three species studied, but was clearly limited in comparison with that of new leaves produced in the high light conditions. This limitation was most pronounced in the early-successional-stage species, O. populifolius. It is likely that structural characteristics of the leaves, imposed at the time of leaf expansion, are largely responsible for the limitations in photosynthetic acclimation to increases in irradiance.

SENSITIVITY OF WATERMELON PLANT GROWTH TO PHOTOMORPHOGENIC SIGNALS DURING THE LIGHT OR DARK PHASE OF THE PHOTOPERIOD

Previous research has demonstrated that watermelon plants are sensitive to changes in light quality, as suggested by an individual treatment of plants with 15-min of end-of-day (EOD) red (R)and far-red (FR) light. FR-induced growth responses (i.e., petiole elongation, internode elongation, reduced petiole angles) were reversed by immediately following the FR light treatment with R light implicating phytochrome as the light quality perception mechanism. The objective of the present experiment was to determine the influence of individual and multiple FR light treatments (each treatment of 15-min duration) during the light and dark phase of the photoperiod on photomorphogenic growth responses of young watermelon plants. Light regulated growth responses of watermelon were influenced by the timing and the number of light quality exposures during the light or dark phase of the photoperiod. Individual FR treatments during the light phase except for the EOD exposure did not affect plant growth responses. In contrast, individual FR treatments at selected intervals during the dark period affected plant development. The most effective individual FR treatment to induce growth responses was at the beginning of the dark period, with decreasing responses as the FR treatment was delayed into the dark period. Multiple exposures of FR during the dark slightly increased growth responses as compared to a single EOD FR treatment.

The Ecophysiology of Veronica Chamaedrys, V. Montana and V. Officinalis. I. Light Quality and Light Quantity

In view of the contrasting ecologies of the closely related species Veronica chamaedrys, V. montana and V. officinalis, the morphological effects of changes in light quality and quantity were investigated using the technique of growth analysis. By definition, the term weight ratio refers to the quotient of the dry weight of a particular organ to the total dry weight of the plant. Three light climates were investigated: unshaded; muslin shaded (c. 37% full daylight, with no change in light quality); canopy shaded, using Ricinus zanzibariensis, also about 37% full daylight, but with lowered red:far-red (R:FR) ratio (...)

Assay of photosynthetic reaction centres by HPLC quantitation of chlorophyll a′ and pheophytin a. Application to the chromatic regulation of photosystem stoichiometry in cyanophytes

Higher plants, algae and cyanophytes contain two molecules of chlorophyll a′ per reaction centre (RC) I, and only one is extracted with chloroform. In contrast, two molecules of phenophytin a are associated with RC II. Therefore the RCs can be assayed by simple high performance liquid chromatography (HPLC) quantitation of these pigments. In view of this, the process of chromatic regulation in two cyanophyte species ( Synechocystis PCC 6714 and Anacystis nidulans R 2, in which the RC I to RC II molar ratio changes significantly with a change in light quality) has been studied by chloroform extraction and HPLC. The results agree well with the reported data acquired by quantitation of P700, cytochrome b-559 and/or molecular oxygen by flash illumination in the same species

The Response of Three Festuca rubra Clones to Changes in Light Quality and Plant Density

The influence of (a) plant density and (b) artificial canopy shading (reducing red/far-red ratio=R/FR) of only the basal parts of plants, on the growth of three morphologically different clones of Festuca rubra was investigated in field experiments and in a growth room. In all three clones both treatments resulted in lower tiller number, lower tiller natality and higher maximum height of tillers of treated plants. It seems that both responses may be elicited by a lower R/FR ratio of the light reaching the basal parts of the plant (...)

Control of Flowering in Arabidopsis thaliana by Light, Vernalisation and Gibberellins

The late flowering mutants of the Landsberg erecta race of Arabidopsis thaliana (L.) Heynh. were responsive to both vernalisation treatment and the ratio of red: far-red light (660 : 730 nm) with regard to time to flower and the numbers of leaves formed prior to flowering. The most vernalisation-sensitive mutants, fca, fve, fy and fpa, were also the most sensitive with regard to changes in the red:far-red light ratio. These responsive mutants flowered up to 40% earlier under lighting that included a greater proportion of far-red (730 nm) light from incandescent lamps compared with plants under light at the same photon flux density (PFD) with a greater proportion of energy from fluorescent lamps. Conversely, the mutants that were only slightly responsive to vernalisation (co, gi and fe) were also least responsive to changes in red:far-red ratio. The correlation between responsiveness to vernalisation and responsiveness to changes in red: far-red for the 11 mutants and Landsberg was highly significant (r2 = 0.88). Time to flower and leaf number at flowering were also markedly affected by changes in PFD in the vernalisation-sensitive mutants. Halving the PFD approximately doubled time-to-flower and leaf number of fca, the most responsive of the late flowering mutants, whereas there were only slight changes in the flowering responses of the parent Landsberg. Thus, these single point late flowering mutants are responsive not only to vernalisation but also to changes in light quality and PFD. These responses imply that both daylength perception and photosynthesis have been affected by the mutations. Gibberellins (GAS) induced earlier flowering not only in the late flowering mutant fca, but also in Landsberg, when that race was grown in short days. Dosages of 5 μg plant-1 of GA3, GA5 and GA9 were equaIly effective in promoting flowering of 15-day-old fca plants with subsequent flowering 9-13 days earlier with 4-6 fewer leaves. Photoperiodic sensitivity to a single long day 15 days after sowing showed Landsberg flowering 6 days earlier and with 1.4 fewer leaves than plants continuously in short days.

Germination and Population Dynamics of Cistus Species in Relation to Fire

1. The shrubs Cistus monspeliensis and C. albidus are obligate seeders which are often dominant in Mediterranean habitats degraded by recurrent fires. 2. To determine the role of fire in the regulation of the population dynamics of these species, the germination requirements and population age-structure have been examined for populations in the South of France. 3. Germination of both species was enhanced by a change in light quality (red/farred ratio) similar to that which occurs when fire removes the light-filtering green leaves, but to a lesser extent than by a heat pretreatment designed to simulate fire temperatures

Brookhaven national laboratory free‐air carbon dioxide enrichment facility

When evaluating the effects of gases on crops, forests or other ecosystems, the experimenter is faced with the problem of trying to produce an exposure regime in which only the variables chosen to be investigated are altered, while other features of the remaining edaphic environment remain in a natural state. This type of experiment has often been hampered by an inability to create an experimental environment free of artifacts introduced by the structures and equipment used to expose the target ecosystem to the test gas. These are generally described as {open_quotes}chamber effects{close_quotes} and include changes in wind velocity, humidity, temperature, light quality or intensity, and soil variables. In the quest for a more realistic experimental design, researchers have moved their plant fumigation studies from the highly controlled and unnatural environment of the greenhouse or growth chamber to open-top chambers. The primary benefit of this shift has been to reduce experimental artifacts associated with soil variables. Many of the other limitations of chambers have remained. 7 refs., 3 figs.

Photoperiod Influences Growth, Bud Dormancy, and Cold Acclimation in Vitis labruscana and V. riparia

The grape species Vitis labruscana Bailey and V. riparia Michx. were subjected to a decreasing photoperiod at constant moderate temperatures to determine whether acclimation occurred in response to a shortening photoperiod. Cane growth, periderm development, killing temperature of the primary bud, and bud dormancy were measured in vines receiving a natural photoperiod (ND), a simulated long photoperiod of 15 hours (LD), and shorter photoperiods of 14, 13, or 12 hours (SD). The LD treatment was effective at maintaining growth and inhibiting periderm development and the onset of bud dormancy in V. labruscana. Cane growth rate with all SD treatments decreased as compared to the LD regime. A significant increase in periderm development occurred with the 12-hour SD treatment. Similarly, the onset of bud dormancy was promoted by the 12-hour SD in V. labruscana. The primary bud killing temperature was 1C lower in V. labruscana under the 12-hour SD than under the LD treatment. In contrast, the LD treatment neither maintained growth nor fully inhibited periderm development and the onset of dormancy in V. riparia. The decrease in the cane growth rate upon exposure to SD was significantly greater in V. riparia than V. labruscana. Periderm development was observed in both the SD and its respective LD-treated V. riparia vines. However, the rate of periderm development was significantly greater in the SD vines than in the LD vines. The onset of bud dormancy was promoted by 13-hour SD in V. riparia. Similarly, the primary bud killing temperature was 2 to 3C lower in V. riparia upon exposure to SD. Vitis riparia has a longer critical photoperiod than V. labruscana and appears to be more sensitive to changes in light intensity or light quality. While the change in freezing tolerance in response to short photoperiods is small, the photoperiod response at a longer critical photoperiod, when combined with lower temperatures, will promote an earlier and possibly more rapid cold acclimation in V. riparia than in V. labruscana.

Ecological significance of light controlled seed germination in two contrasting tropical habitats

The effects of temperature, photoperiod, phytochrome photoreversion and the response to a R/FR ratio gradient were investigated in seeds of four species from two contrasting tropical habitats; two species from a rain forest (Cecropia obtusifolia and Piper umbellatum) and two from a high altitude lava field covered by low vegetation (Buddleja cordata and Chenopodium ambrosioides). In the rain forest seed species the photoblastic response seems to be adapted to light quality changes due to canopy destruction, on the other hand, the lava field seed species seem to be adapted to instantaneous light stimulus such as would be produced by the sudden exposure of a buried seed to the soil surface light environment.

Studies on the adaptation of intact leaves to changing light intensities by a kinetic analysis of chlorophyll fluorescence and oxygen evolution as measured by the photoacoustic signal

A detailed quantitative study of the kinetics of photochemical and non-photochemical quenching was achieved by a linear analysis of the yields of chlorophyll fluorescence and of oxygen evolution (as measured by the photoacoustic effect) by their responses to sinusoidal changes of actinic light. The results of this analysis were given in terms of the parameters of the kinetic phases obtained as a response to a step function change in the light intensity from a previous steady-state. Thus, it was possible to split the responses to a change in light intensity into six components which could be assigned to 6 time-constants (60 ms, 1.8 s, 2.5 s, 8 s, 150 s and 400 s). The comparison of the kinetics of responses induced by blue-light (approx. 400-500 nm) and by far-red (720 nm) light led to the assignment of the 1.8-s time-constant to the loading and discharge of the plastoquinone pool and of the 400-s time-constant to the state-transition controller which could be shown to be involved also in the adaptation to changes in light intensity and not only to changes in light quality (wavelength). The time-constant of 8 s, also occurring in 532-nm light-scattering was assigned to the "high-energy state" quenching (qE) of fluorescence. qE was paralleled by a decrease of the photoacoustic signal, demonstrating an "high-energy state" quenching of oxygen evolution as well. The 60-ms time-constant is suggested to be related to the redox state of the primary quinone acceptor of PS II, whereas the other two time-constants could not be identified. The calculation of the relative contributions of the photo-chemical and of the non-photochemical quenching in the individual components revealed that both quenching-mechanisms occur in all components except in the assumed fastest one.

Stomatal and non‐stomatal limitations to carbon assimilation: an evaluation of the path‐dependent method

Abstract Environmental stresses can decrease photosynthesis by a direct effect on photosynthetic capacity of the mesophyll or by a CO2 limitation resulting from stomatal closure. In the present study, a ‘path‐dependent method’ (Jones, 1985) for the partitioning of a stress‐related decline in assimilation rate between non‐stomatal and stomatal factors was evaluated, using light quality as a ‘stress’. Kinetic data on assimilation rate and conductance of Phragmipedium longifolium following a change in light quality from 95 μmol m−2s−1 white light to 95 μmol m−2s−1 red light failed to generate a smooth response curve for conductance. Partitioning of limitations on assimilation by a path‐dependent method that utilizes the actual trajectories of conductance and assimilation was therefore not feasible. A simplified path‐dependent method (Jones, 1985) which assumes that either mesophyll cells or guard cells respond first to a stress was applied to steady‐state measurements of assimilation and conductance under red and white illumination. Either 5% or 23% of the observed reduction in assimilation rate under white light was attributable to stomatal factors, depending on whether the ‘stomatal first’ or the ‘mesophyll first’ path was assumed. In the absence of additional information indicating the appropriate choice of path, arbitrary choice may therefore lead to widely divergent estimates, and potentially erroneous conclusions. An alternative approach to the evaluation of the importance to carbon assimilation of stomatal and non‐stomatal factors is suggested.

Effects of intensity and height of shading on the tiller initiation of six grass species from the Highland sourveld of Natal

Grass species of the conservation areas of the Natal Drakensberg are divided into two ecological groups. Decreaser species are those which decrease with over- or under-utilization, while increaser I species are those which increase with under-utilization. The effect of intensity and height of shading on decreaser species (Themeda triandra, Heteropogon contortus and Trachypogon spicatus) and increaser species (Tristachya leucothrix, Harpochloa falx and Alloteropsis semialata) was determined in potted plant trials. Results of this study support the hypothesis that decreaser species were more sensitive to low light intensities (30% full sunlight) than increaser species. These two species groups did not, however, differ in their response to height of shading. The results suggest that different fire regimes resulting in changes in canopy cover and light quality are important mechanisms in regulating tiller initiation in perennial grasses.

Modifications to the photosynthetic apparatus of higher plants in response to changes in the light environment

A brief review of the photosynthetic apparatus of higher plants is given, followed by a consideration of the modifications induced in this apparatus by changes in light intensity and light quality. Possible strategies by which plants may optimize photosynthetic activity by both long- and short-term modifications of their photosynthetic apparatus in response to changing light regimes are discussed.

Photosynthetic and pigment responses of sea-ice microalgae to changes in light intensity and quality

Responses of sea-ice microalgae to changes in light intensity and quality were studied from March to May 1983 on the first-year ice of southeastern Hudson Bay (Canadian Arctic). Photosynthetic parameters P B max , α B and β B of the ice algae progressively increased throughout the sampling season. This increase paralleled the under-ice irradiance; it also paralleled the progressive increase of the diatom Nitzschia frigida in the population, from ≈45% of the cells at the end of March to almost 100% in May. The photosynthetic efficiency ( α B ) and several other photosynthetic parameters doubled when the algae were incubated under blue light, as compared with white light. This result stresses the importance of considering the photosynthetically usable radiant energy (PUR) rather than the photosynthetically available radiation (PAR), when measuring photosynthetic responses to light colour. Ice algae generally had high concentrations of chlorophyll c, which could be an adaptive response to their blue-green light environment. When incubated under white illumination, which corresponded to widening the light spectrum, the algae responded by increasing their proportions of carotenoids and chlorophyll c. These changes were in agreement with the theory of complementary chromatic adaptation. The bottom ice environment of Hudson Bay being limited by light intensity and nutrient resources, the ability to chromatically adapt may become a critical factor in species competition.