Full Solar Exposure Research Articles

Incidencia del sombreado, biorreguladores y bioestimulante en el desarrollo y rendimiento del pasto Mombaza (Panicum maximum Jacq.)

Shading (S), bioregulators (BR) and biostimulants (BS) techniques are alternatives that promote sprouting and production of grass. The objective was to evaluate the effect of S, BR and BSt on the growth and yield of Mombaza grass in Ecuador. A complete randomized block design, with split plot arrangement and three replications, was used, the main plot represented by condition S (S1: full solar exposure, S2: shade of trees) and secondary one by BR and BS application (A0: control; A1: minimum doses of BR, 250 mL.ha-1 Cytokin + 10 g.ha-1 New Gibb 10 %; A2: maximum doses of BR, 500 mL.ha-1 Cytokin + 20 g.ha-1 New Gibb 10 %; A3: commercial dose of BS Algamar, seaweed, 750 g.ha-1). Three cuts of grass were made, 35 days after staring experiment; in each one, tiller height (TH), number of tillersm-2 (NTM) and stemstiller-1 (NST), and dry matter yield (DMY) were evaluated. It is found effects (P<0.05) of S on the four variables in each cut; and application of BR and BS on TH in cuts 1, period of least precipitation. It is concluded that the grass cultivated in S1 increased the growth and DMY in cuts 1, 2 and 3 (0.180, 0.300 y 0.398 kg.m-2). NTM was stimulated with S2 and TH with the minimum dose of BR.

Microscale Variability in Biomass and Photosynthetic Activity of Microphytobenthos During a Spring-Neap Tidal Cycle

Carbon fixation by microphytobenthic algae of intertidal flats often dominates the total primary production of turbid, temperate estuaries. Whilst remote sensing can accurately measure the spatial distribution of photosynthetic biofilms at the mesoscale (1-300 m), variability at smaller scales requires in-situ investigation. Here, changes in biomass and photosynthetic activity of microphytobenthos (MPB) at the micro-scale (<1 m) were investigated. Biomass of MPB was estimated from repeated high resolution spectral measurements carried out at intervals along a short transect. Whilst the mean concentration of MPB remained constant over time, considerable variability in the spatial and temporal dimensions was measured. The biofilm grew and diminished along the transect over time, and net growth and loss rates could be established under natural conditions. Daily vertical migration was observed for the first time in an undisturbed sediment, and was modelled as a function of solar elevation and tidal angle. Top down factors such as grazing, or physical disturbance, play an important role in the changes in biomass. Photosynthetic activity was measured with portable fluorometers: one device used an artificial light source, the other measured the effective photosystem-II quantum efficiency (ΔF/Fm’) in-situ with solar irradiance. No evidence was found for photoinhibition, with Fv/Fm values consistently high, indicating an ability of the diatom biofilm to remain productive under periods of high irradiance. The maximum rate of photosynthesis reached artificial light was rarely achieved in-situ, even with full solar exposure. There was however a very good agreement between the predicted rate at ambient irradiance, and that actually measured. Composite photosynthesis-irradiance curves over the whole experimental period were similar, and showed the same initial slopes, but the maximum rate of relative photosynthetic electron transport (rETRm) based on the in-situ measurement was lower. When total depth-averaged primary production during low tide was calculated, the differences between methods varied between 5-13%, and were smallest when surface irradiance values were higher. These results show that the protocol used to measure the photosynthetic activity of the MPB had only minor importance on the overall productivity estimate compared to accurate knowledge of photosynthetically-active biomass and irradiance.

Quieting a noisy antenna reproduces photosynthetic light-harvesting spectra.

Photosynthesis achieves near unity light-harvesting quantum efficiency yet it remains unknown whether there exists a fundamental organizing principle giving rise to robust light harvesting in the presence of dynamic light conditions and noisy physiological environments. Here, we present a noise-canceling network model that relates noisy physiological conditions, power conversion efficiency, and the resulting absorption spectra of photosynthetic organisms. Using light conditions in full solar exposure, light filtered by oxygenic phototrophs, and light filtered under seawater, we derived optimal absorption characteristics for efficient solar power conversion. We show how light-harvesting antennae can be tuned to maximize power conversion efficiency by minimizing excitation noise, thus providing a unified theoretical basis for the observed wavelength dependence of absorption in green plants, purple bacteria, and green sulfur bacteria.

Atenuación de la temperatura y radiación UV de la vegetación en entornos urbanos de ciudades ribereñas y su demanda hídrica.

Introducción. Este trabajo de investigación se realizó en la Ciudad de Honda, Colombia. Identificó el efecto de la sombra de los árboles en la atenuación de la temperatura, humedad relativa, temperatura de superficie del suelo, radiación solar y ultravioleta (UV) y determinó requerimientos de agua para la vegetación arbórea. Metodología. Se tomaron datos de temperatura del aire y de superficie de suelo, humedad relativa del aire, radiaciones solares y UV bajo la sombra de árboles y a plena exposición. Resultados. Se encontró que la temperatura del aire osciló entre 50ºC a plena exposición solar y 41ºC bajo sombra. La temperatura de superficie presentó a plena exposición solar valores de 66.8ºC y 42.6ºC bajo sombra. La variación de la radiación solar registrada ofreció un valor de 17.13 mW/cm2 a plena exposición solar y 1.69 mW/cm2 bajo sombra. La radiación UV presentó valores de 8 a plena exposición solar y 5 bajo sombra. La demanda hídrica por planta/día varió entre 5 y más de 500 litros, siendo la demanda diaria cercana a 2500 m3 . Conclusiones. En la ciudad no se realiza riego a los árboles, lo que conduce a que se produzca un déficit hídrico evidenciado por la pérdida de follaje ocasionando mínimas atenuaciones a la radiación UV. Las especies más relevantes respecto a la sombra son almendro (Terminalia cattapa), Pallandé (Pitecellobium dulce), naranjuelo (Capparis odoratissima), guayacán carrapo (Bulnesia carrapo), chirlobirlo (Tecoma stands), cumulá (Aspidosperma polyneuron) y mango (Manguifera indica). Los árboles pueden generar un buen servicio ecosistémico por la sombra, este servicio está mediado por la selección de la especie y el manejo de que son objeto los árboles.

Topical shading substantially inhibits vegetative branching by altering leaf photosynthesis and hormone contents of cotton plants

Cotton plants have complex branching patterns formed by distal fruiting branches (FB) and basal vegetative branches (VB). Our prior study showed that cotton’s vegetative branching was considerably inhibited under high plant density via altered hormone contents in VB tips and photosynthetic production in VB leaves. Here, our current objective was to determine whether or not shading of VB reduced vegetative branching, and whether this effect was elicited via a similar mechanism(s) as that under high plant density. To this end, cotton was planted on 76-cm row widths at a moderate density (5 plants m−2). Vegetative branches of cotton plants were shaded to approximate 60% of full solar exposure by using polyethylene nets during squaring; those without shading served as the control. The growth and development of VB, as well as underlying agronomic, physiological and molecular events of both shaded and control plants were examined. Shading VB reduced its numbers by 56.2%; its length by 88.8% and the ratio of VB biomass to total biomass by 91.3%, but it increased FB biomass by 30.8%, compared with the control at 69 days after seeding. Compared with control, shading did not reduce seedcotton yield, suggesting a yield stability similar to that found previously under high plant density. The net photosynthetic rate, chlorophyll content and ribulose-1,5-bisphosphate carboxylase activity in VB leaves were considerably decreased by shading. The sucrose biosynthesis gene GhCYFBP in leaves and GhphyB gene in tips of VB were down-regulated under its shading, followed by lower soluble sugar and starch contents. Suppressed photosynthetic production in leaves of VB was a key reason for poor vegetative branching under shaded conditions. Shading diminished both the auxin (IAA) content and auxin transport from VB tips by decreasing the expression of corresponding genes for auxin biosynthesis (GhYUC5) and transport (GhPIN1and GhPIN5). This treatment also reduced the content of cytokinins (CTKs) in the VB tips by decreasing the expression of the CTKs biosynthesis gene, GhIPT3. By contrast, the SL receptor gene, GhD14 was upregulated in the VB tips, followed by a greater content of strigolactones (SLs). We proposed that lower IAA, CTKs and brassinosteroid contents plus higher SLs content due to differential expression of hormone-related genes in the VB tips suppressed vegetative branching when shaded. Our results suggest this mechanism is not unlike how high plant density inhibits vegetative branching in cotton.

Light shading improves the yield and quality of seed in oil-seed peony (Paeonia ostii Feng Dan)

Tree peony seed is unique for its super-high content of unsaturated fatty acid and is thus considered as an important source of woody oil. However, photosynthetic production is greatly reduced under high light intensity and air temperature during the seed filling period, which negatively affects seed yield and quality. The objective of this study was to determine if appropriate shading improves yield and quality of seed in oilseed peony. In this study, oilseed peony trees were shaded by different density polyethylene nets from four weeks after flowering to harvest stages to form light, moderate, and severe shadings, equivalent to about 80, 40, and 20% of full solar exposure, respectively. The effects of different shadings on some physiological parameters, yield and yield components, and nutritional composition of seed were examined. Averaged across two years, light shading increased the actual net photosynthetic rate (Pn) by 16.8%, the maximum net photosynthetic rate (Pmax) by 81.4%, chlorophyll (Chl) content by 52.8%, auxin (IAA) content by 38.1%, and gibberellic acid (GA3) content in leaves by 6.3%; it decreased the accumulation of H2O2 in leaves by 24.8%, malondialdehyde (MDA) by 22%, and endogenous abscisic acid (ABA) by 8.8%, indicating that leaf senescence in late season was considerably delayed. Light shading increased seed yield, and contents of crude fat and unsaturated fatty acids by 9.7, 5.6, and 9.6%, respectively, while moderate or severe shading significantly reduced all the three parameters. Light shading increased seed weight, but moderate or severe shading reduced seed weight or follicle density. The improved seed yield under light shading was mainly due to increased seed weight, while the reduced seed yield under moderate or severe shading was mainly attributed to reduce follicle density and seed weight. The improved seed weight and content of unsaturated fatty acids under light shading was possibly due to the delayed leaf senescence. The overall results indicated that light shading is beneficial to yield and quality parameters of seed in oilseed peony. Cultivating oilseed peony under a light shading environments such as partially closed forests would better increase total output and income per unit land area than that under full solar exposure.

Domestication Performance of Indigenous Trees: A Decade of Rainforestation Experience in Degraded Karst Lands

This study tested the domestication potential of 43 indigenous timber species in 1.2-ha degraded karst land. Survival, height and diameter growth performance and site factors were periodically monitored. Results showed twenty-eight indigenous forest timber species thriving in an open karst area including 8 dipterocarps: narig, mayapis, white lauan, bagtikan, guisok-guisok, kalunti or manggasinoro, red lauan and yakal-kaliot. The non-dipterocarps include bitanghol &amp; kalingag. Species with 100% survival were aniam gubat, bayokbok, ipil, kalumpit, lamog, puso-puso, sagimsim and taluto. White lauan had a survival of 96% and molave had 92%. Kalumpit had the highest increment both in height and diameter. Kalumpit was followed by dao, duguan, milipili. Among the dipterocarps, white lauan got the highest diameter and height growth increment. Narig, with its waxy leaf surface of all the dipterocarps, was tolerant under full solar exposure. Domestication farms should include or integrate fruit trees, vegetable trees (like bago or Gnetum gnemon) and other economic plants. Domestication trials of barit, anislag, sudiang, other dipterocarps, bago, nito, sig-id, rattan and other sources of raw materials for handicrafts should also be tried.

Ionization mechanisms in CRRES chemical releases: 2. Strontium photoionization and Ba+/Sr+ collisional ionization cross‐section calculations

Two particular collision processes involving electron transfer are investigated that may have impact on the analyses of ion flux data obtained in the CRRES G‐1 and G‐11b, upper atmospheric chemical release experiments. Ion pair production (σIP) and charge exchange ionization (σCE) cross sections are calculated as a function of collision energy for reactions between Ba/Sr atoms and O atoms and O+ ions, respectively, using two‐state approximation theories. The cross sections for each process are calculated for both the ground and metastable states of the metal atoms. At a collision energy of 9.5 eV attained in the G‐1 and G‐11b CRRES releases, the calculations indicate that σIP = 1.3 × 10−16 cm2 and σCE = 2–6 × 10−16 cm2 for reactions involving Ba(1S0). The cross sections for the analogous Sr reactions are approximately 1.2 × 10−16 cm2 and 2–8 × 10−17 cm2, respectively. In addition, Sr photoionization from 3PJ metastable states is investigated. Although we calculate a 29‐s photoionization time constant from these states, a kinetic analysis indicates the metastable states cannot accumulate an appreciable equilibrium population in full solar exposure. Thus photoionization from the Sr 3PJ levels does not significantly contribute to the total ion inventory.

Winter protection of container-grown nursery stock as affected by container design, hardening-off time and solar exposure

The effects of container type (round vs. square), solar exposure (100% vs. 50%) and hardening-off time (0, 3 or 6 weeks) on winter damage to Ilex crenata Thumb. ‘Hetzii’ (Hetz Japanese holly) and Buxus sempervirens L. (common boxwood) were studied. Container type and hardening-off time had significant effects on plant viability of Ilex crenata ‘Hetzii’ after exposure to freezing temperatures. Plants in square containers achieved substantially higher viability ratings than plants in round containers after freezing. Buxus sempervirens was significantly affected by hardening-off time only. Plant viability increased greatly with 3 or 6 weeks of hardening-off as compared to no hardening-off. Common boxwood plants in square containers did not achieve the same level of growth as plants in round containers during the 1980 growing-season (before freezing). Optimum growth for Buxus sempervirens occurred under full solar exposure.