Relationship between ecosystem productivity and photosynthetically-active radiation for northern peatlands

We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe. NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola (NEE = α PPFD Pmax/(α PPFD + Pmax) + R) better described the NEE-PPFD relationship than did a linear fit (NEE = β PPFD + R). Poor and rich fens generally had similar NEE-PPFD relationships, while bogs had lower respiration rates (R = −2.0μmol m−2s−1 for bogs and −2.7 μmol m−2s−1 for fens) and lower NEE at moderate and high light levels (Pmax = 5.2 μmol m−2s−1 for bogs and 10.8 μmol m−2s−1 for fens). As a single class, northern peatlands had much smaller ecosystem respiration (R = −2.4 μmol m−2s−1) and NEE rates (α = 0.020 and Pmax = 9.2μmol m−2s−1) than the upland ecosystems (closed canopy forest, grassland, and cropland) summarized by Ruimy et al. [1995]. Despite this low productivity, northern peatland soil carbon pools are generally 5–50 times larger than upland ecosystems because of slow rates of decomposition caused by litter quality and anaerobic, cold soils

Condensation in a square minichannel: application of the VOF method

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.A number of steady-state simulations of condensation of R134a at mass fluxes G=100 kg m-2s-1 and G=800 kg m-2s-1 inside a square cross section minichannel (Dh=1mm) are here proposed and compared against similar simulations in a circular cross section channel with same diameter. The VOF (Volume Of Fluid) method is used to track the vapour-liquid interface and the effects of interfacial shear stress and surface tension are both taken into account. A uniform wall temperature is fixed as boundary condition. At G=100 kg m-2s-1 the liquid film is assumed laminar and the vapour flow is turbulent; turbulence is handled by a low-Reynolds number form of the standard k-w model (Wilcox, 1998), which was modified in order to suppress the turbulent viscosity inside the liquid phase. At G=800 kg m-2s-1 a low Re form of the SST k-w model (Menter, 1994) has been used for turbulence modeling through both the liquid and vapour phases. Numerical simulations are validated against experimental data. The present paper looks at the effect of surface tension. Its influence on the shape of the vapour-liquid interface provides some heat transfer enhancement in non-circular minichannels. In circular minichannels, the overall effect of surface tension is shown to be not significant. On the contrary, the effect of surface tension in square channels provides a large enhancement at low mass flux

Efecto de la irradiancia en el crecimiento, fotosíntesis, contenido pigmentario y consumo de nutrientes en cultivos densos de Rhodomonas salina (Wislouch) (Cryptophyceae)

12 páginas, 5 figuras, 2 tablas.[EN] The effects of different incident irradiances on growth, photosynthesis, pigment content and nutrient uptake were studied in dense cultures of the cryptophyte Rhodomonas salina (Wislouch) Hill y Wetherbee. Cells were grown for ten days at different incident irradiances: 11, 33, 75, 260 and 320 ?mol photon m-2s-1. The average pigment content (phycoerythrin and chlorophyll a) was lower when cells were grown at high irradiances (260 and 320 ?mol photon m-2s-1) compared with cells grown under low irradiances (11, 33 and 75 ?mol photon m-2s-1).The maximum photosynthetic rate (Pmax) was maximal at 75 ?mol photon m-2s-1 , decreasing considerably at the highest irradiance in which apparent photosynthetic efficiency per cell and per chlorophyll a unit (ᣥll and ᣨla) also decreased. Results showed that dense cultures of R. salina grew optimally in a range between 75 and 260 ?mol photon m-2s-1 with optimal photosynthetic performance at 75 ?mol photon m-2s-1. Nitrogen and phosphorus depletion occurred as a consequence of the exponential growth, except under the lowest and the highest irradiances (11 and 320 ?mol photon m-2s-1, respectively). Associated to N-limitation, phycoerythrin (PE) and chlorophyll a decreased considerably. It is suggested that R.salina responds to nitrogen-depleted conditions by mobilizing nitrogen from PE, this behaviour being modelled by a relationship between external nitrogen availability and PE mobilization.[ES] En este trabajo se analizan los efectos que diferentes irradiancias incidentes tienen en el crecimiento, características fotosintéticas, contenido pigmentario e incorporación de nutrientes en cultivos densos de la criptofita Rhodomonas salina (Wislouch) Hill y Wetherbee. Con tal fin, se mantuvieron cultivos durante diez días bajo distintas condiciones de luz incidente: 11, 33, 75, 260 y 320 µmol fotón m-2s-1. El contenido pigmentario promedio (ficoeritrina y clorofila a) fue menor en células adaptadas a las mayores irradiancias (260 y 320 µmol fotón m-2s-1) en comparación con las adaptadas a las irradiancias menores (11, 33 y 75 µmol fotón m-2s-1). El valor máximo de fotosíntesis (Pmax) se obtuvo para las células adaptadas a 75 µmol fotón m-2s-1, decreciendo considerablemente para la irradiancia máxima ensayada en la que también la eficiencia fotosintética (ácel. and ácla) fue menor. Los resultados muestran que esta criptofita crece óptimamente en cultivos densos en un rango de irradiancias incidentes entre 75 y 260 µmol fotón m-2s-1, con una actividad fotosintética óptima a 75 µmol fotón m-2s-1. Como consecuencia del crecimiento exponencial de los cultivos, se produjo una desaparición paulatina y prácticamente total del nitrógeno y el fósforo del medio, excepto en los cultivos adaptados a las irradiancias máxima (320 µmol fotón m-2s-1) y minima (11 µmol fotón m-2s-1) empleadas. Asociada a tales condiciones de limitación de nitrógeno se observó una disminución del contenido celular de ficoeritrina y clorofila a, definiéndose una clara relación entre la disponibilidad de nitrógeno externo y la tasa de desaparición de ficoeritrina. Estos resultados sugieren que Rhodomonas salina es capaz de movilizar el nitrógeno asociado a la ficoeritrina como respuesta ante condiciones de baja disponibilidad de dicho nutriente.Este trabajo ha sido financiado por un proyecto CICYT (AMB-0684-CO2-01) del Ministerio de Educación y Cultura, España.Peer reviewe

Comparison of two bidirectional atmosphere-surface exchange models for elemental mercury

This study compared two bidirectional atmosphere-surface exchange models by Wang et al. (2014) and Wright & Zhang (2015) for one monitoring site in the state of Georgia in the United States of evergreen needleleaf forest and deciduous broadleaf forest in summer and winter. Input data includes observed GEM concentrations and simulated meteorological data from June 2010 to September 2010 and from December 2010 to March 2011. For evergreen needleleaf forest in summer, the net emission flux estimated by Wang’s model was greater than that by Wright & Zhang’s (0.5 pg m-2s-1 vs. 0.18 pg m-2s-1). For deciduous broadleaf forest in summer, the net emission flux predicted by Wang’s model was smaller than that by Wright & Zhang’s (0.1 pg m-2s-1 vs. 0.29 pg m-2s-1). However, regardless of land cover in winter, the net flux produced by Wang’s model was emission flux (0.21 pg m-2s-1 for evergreen needleleaf forest and 0.18 pg m-2s-1 for deciduous broadleaf forest) while that simulated by Wright & Zhang’s model was deposition flux (0.59 pg m-2s-1 for evergreen needleleaf forest and 0.49 pg m-2s-1 for deciduous broadleaf forest). Additionally, stomata resistance, in-canopy aerodynamic resistance, stomata emission velocity, GEM compensation point concentration in stomata, GEM compensation point concentration in soil, stomata emission flux, soil emission flux, and net flux had large differences (≥100%) between the two models. The dominant factors resulting in these differences were identified. Wright & Zhang’s model is more appropriate for simulating GEM exchange flux in winter when a net deposition flux is expected

Laju Fotosintesis Jenis-jenis Pohon Pionir Hutan Sekunder Di Taman Nasional Gunung Halimun-salak Jawa Barat

Tree growth is closely related to the process of photosynthesis. So far the rate of photosynthesis in elements of secondary forests has not been known, especially in pioneer species. At the same height of the place and micro-climate conditions, the rate of photosynthesis of pioneer species of secondary forest has a different rate of photosynthesis. This study aims to determine the ability of the rate of photosynthesis of some secondary forest pioneer tree species in order to support reforestation efforts on degraded forests and at the same time looking for the kinds of pioneers who have a high absorption of CO2 gas in an effort to reduce global warming caused by emissions CO2 gas in the air. The survey results noted there are 6 common pioneer tree species grow at the sites. Trema orientalis had the highest CO2 assimilation value which is equal to 20,350 μmol m-2s-1, followed by the Macaranga triloba (17,198 μmol m-2s-1), Omalanthus populneus (14,097 μmol m-2s-1), Mallotus paniculatus (13,118 μmol m-2s-1), Macaranga tanarius (12,862 μmol m-2s-1) and Weinmannia blumei (10,058 μmol m-2s-1). Research conducted during the rainy season (September 2010). During measurement, the light radiation in the upper leaf surface between 63,583 to 363,750 μmol m-2s-1, air temperature 21,8 to 26,70C, air humidity 75,8-89,8%, light intensity 2483,3 to 28701,7 Lux, soil pH 5,8 to 6,3 and soil moisture between 50,7 to 71,7%

Influence of varying light regimes on photosynthesis and related variables on tree seedlings of Warburgia ugandensis Sprague and Polyscias fulva (Hiern) harms

The physiology of seedlings of Warburgia ugandensis and Polyscias fulva were studied at varying light levels. Photosynthesis was significantly higher in P. fulva (1.4 µmols CO2 m-2 s-1) than in W. ugandensis (0.3 µmols CO2 m-2s-1) when grown in full sunlight. However, photosynthesis was not significantly (P > 0.05) different under moderate and dense shades (PPFD about 600 µmols m-2s-1 and 350 µmols m-2s-1 respectively) for both species (and ranged between 0.4 and 0.5 µmols CO2 m-2s-1). Generally, P. fulva seedlings had significantly (P < 0.05) greater reductions (from 1.0 to 0.4 µmols CO2 m-2s-1) in photosynthetic rates in response to increasing shade than did W. ugandensis (0.6 to 0.4 µmols CO2 m-2s-1). However, W. ugandensis attained significantly (P < 0.05) higher photosynthetic rates under shade conditions (0.6 µmols CO2 m-2s-1) than full sunlight conditions (0.3 µmols CO2 m-2s-1). Leaf temperatures were highest (30°C) in full sunlight and lowest (27°C) in dense shade for both species. Generally, stomatal conductance, transpiration and water use efficiency showed significantly (P < 0.05) higher values for shade grown W. ugandensis and full sunlight grown P. fulva. Water use efficiency for P. fulva (2.3 µmols CO2 µmol-1 H2O) was significantly (P < 0.05) higher that for W. ugandensis (1.5 µmols CO2 µmol-1 H2O) in full sunlight than. It was concluded that P. fulva was also less adapted to growth at low light intensity while W. ugandensis was better adapted to growth at low light levels because of its significantly greater ability to maintain higher rates of photosynthesis in low light intensity. Therefore in East Africa P fulva can be a better agroforestry species than W. ugandensis.Key words: Net carbon exchange, forest tree seedlings, shade, Warburgia ugandensis, Polyscias fulv

Synthesis of phenolics and flavonoids in ginger (Zingiber officinale Roscoe) and their effects on photosynthesis rate

The relationship between phenolics and flavonoids synthesis/accumulation and photosynthesis rate was investigated for two Malaysian ginger (Zingiber officinale) varieties grown under four levels of glasshouse light intensity, namely 310, 460, 630 and 790 μmol m 2s 1. High performance liquid chromatography (HPLC) was employed to identify and quantify the polyphenolic components. The results of HPLC analysis indicated that synthesis and partitioning of quercetin, rutin, catechin, epicatechin and naringenin were high in plants grown under 310 μmol m 2s 1. The average value of flavonoids synthesis in leaves for both varieties increased (Halia Bentong 26.1%; Halia Bara 19.5%) when light intensity decreased. Photosynthetic rate and plant biomass increased in both varieties with increasing light intensity. More specifically, a high photosynthesis rate (12.25 μmol CO 2 m 2s 1 in Halia Bara) and plant biomass (79.47 g in Halia Bentong) were observed at 790 μmol m 2s 1. Furthermore, plants with the lowest rate of photosynthesis had highest flavonoids content. Previous studies have shown that quercetin inhibits and salicylic acid induces the electron transport rate in photosynthesis photosystems. In the current study, quercetin was an abundant flavonoid in both ginger varieties. Moreover, higher concentration of quercetin (1.12 mg/g dry weight) was found in Halia Bara leaves grown under 310 μmol m 2s 1 with a low photosynthesis rate. Furthermore, a high content of salicylic acid (0.673 mg/g dry weight) was detected in Halia Bara leaves exposed under 790 μmol m 2s 1 with a high photosynthesis rate. No salicylic acid was detected in gingers grown under 310 μmol m 2s 1. Ginger is a semi-shade loving plant that does not require high light intensity for photosynthesis. Different photosynthesis rates at different light intensities may be related to the absence or presence of some flavonoid and phenolic compounds

The hypothesis of path integral duality II: corrections to quantum field theoretic results

In the path integral expression for a Feynman propagator of a spinless particle of mass $m$, the path integral amplitude for a path of proper length ${\cal R}(x,x'| g_{\mu\nu})$ connecting events $x$ and $x'$ in a spacetime described by the metric tensor $g_{\mu\nu}$ is $\exp-[m {\cal R}(x,x'| g_{\mu\nu})]$. In a recent paper, assuming the path integral amplitude to be invariant under the duality transformation ${\cal R} \to (L_P^2/{\cal R})$, Padmanabhan has evaluated the modified Feynman propagator in an arbitrary curved spacetime. He finds that the essential feature of this `principle of path integral duality' is that the Euclidean proper distance $(\Delta x)^2$ between two infinitesimally separated spacetime events is replaced by $[(\Delta x)^2 + 4L_P^2 ]$. In other words, under the duality principle the spacetime behaves as though it has a `zero-point length' $L_P$, a feature that is expected to arise in a quantum theory of gravity. In the Schwinger's proper time description of the Feynman propagator, the weightage factor for a path with a proper time $s$ is $\exp-(m^2s)$. Invoking Padmanabhan's `principle of path integral duality' corresponds to modifying the weightage factor $\exp-(m^2s)$ to $\exp-[m^2s + (L_P^2/s)]$. In this paper, we use this modified weightage factor in Schwinger's proper time formalism to evaluate the quantum gravitational corrections to some of the standard quantum field theoretic results in flat and curved spacetimes. We find that the extra factor $\exp-(L_P^2/s)$ acts as a regulator at the Planck scale thereby `removing' the divergences that otherwise appear in the theory. Finally, we discuss the wider implications of our analysis.Comment: 26 pages, Revte