scholarly journals What limits photosynthetic energy conversion efficiency in nature? Lessons from the oceans

2017 ◽  
Vol 372 (1730) ◽  
pp. 20160376 ◽  
Author(s):  
Paul G. Falkowski ◽  
Hanzhi Lin ◽  
Maxim Y. Gorbunov
Keyword(s):  
Quantum Yield ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Surface Waters ◽  
Phytoplankton Community ◽  
Inorganic Nitrogen ◽  
Photosynthetic Apparatus ◽  
Energy Conversion Efficiency ◽  
Thermal Dissipation ◽  
Essential Components

Constraining photosynthetic energy conversion efficiency in nature is challenging. In principle, two yield measurements must be made simultaneously: photochemistry, fluorescence and/or thermal dissipation. We constructed two different, extremely sensitive and precise active fluorometers: one measures the quantum yield of photochemistry from changes in variable fluorescence, the other measures fluorescence lifetimes in the picosecond time domain. By deploying the pair of instruments on eight transoceanic cruises over six years, we obtained over 200 000 measurements of fluorescence yields and lifetimes from surface waters in five ocean basins. Our results revealed that the average quantum yield of photochemistry was approximately 0.35 while the average quantum yield of fluorescence was approximately 0.07. Thus, closure on the energy budget suggests that, on average, approximately 58% of the photons absorbed by phytoplankton in the world oceans are dissipated as heat. This extraordinary inefficiency is associated with the paucity of nutrients in the upper ocean, especially dissolved inorganic nitrogen and iron. Our results strongly suggest that, in nature, most of the time, most of the phytoplankton community operates at approximately half of its maximal photosynthetic energy conversion efficiency because nutrients limit the synthesis or function of essential components in the photosynthetic apparatus. This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement’.

First-principles study on the electronic and optical properties of the orthorhombic CsPbBr3 and CsPbI3 with Cmcm space group

2021 ◽  
Author(s):  
Xianhao Zhao ◽  
Tianyu Tang ◽  
Quan Xie ◽  
like gao ◽  
Limin Lu ◽  
...  
Keyword(s):  
Optical Properties ◽  
Solar Cells ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
First Principles ◽  
Energy Conversion Efficiency ◽  
Space Group ◽  
Absorbing Materials ◽  
Halide Perovskites ◽  
Lead Halide

The cesium lead halide perovskites are regarded as effective candidates for light-absorbing materials in solar cells, which have shown excellent performances in experiments such as promising energy conversion efficiency. In...

Metal-like electrical conductivity in LaxSr2−xTiMoO6 oxides for high temperature thermoelectric power generation

2017 ◽  
Vol 46 (18) ◽  
pp. 5872-5879 ◽  
Author(s):  
Mandvi Saxena ◽  
Tanmoy Maiti
Keyword(s):  
Power Generation ◽  
Electrical Conductivity ◽  
High Temperature ◽  
Energy Conversion ◽  
Thermoelectric Power ◽  
Conversion Efficiency ◽  
Energy Conversion Efficiency ◽  
Power Generators ◽  
Thermoelectric Power Generation

Increasing electrical conductivity in oxides, which are inherently insulators, can be a potential route in developing oxide-based thermoelectric power generators with higher energy conversion efficiency.

Fluorescence as a tool in photosynthesis research: application in studies of photoinhibition, cold acclimation and freezing stress

1989 ◽  
Vol 323 (1216) ◽  
pp. 281-293 ◽  
Keyword(s):  
Quantum Yield ◽  
Cold Acclimation ◽  
Spinacia Oleracea ◽  
Photosynthetic Apparatus ◽  
Fluorescence Induction ◽  
High Light ◽  
Thermal Dissipation ◽  
Freezing Stress ◽  
Chlorophyll Fluorescence Induction ◽  
Freezing And Thawing

Chlorophyll fluorescence induction (at 20 °C and 77 K) and quenching were analysed in relation to effects of environmental stresses imposed by chilling in high light and by freezing and thawing of spinach ( Spinacia oleracea L.) leaves. The data indicate that cold acclimation of spinach plants, which leads to increased frost tolerance of the leaves, results in decreased susceptibility to photoinhibition of photosynthesis at chilling temperatures. When plants acclimated to 18 °C and 260-300 µmol quanta m -2 s -1 were exposed to higher light (550 µmol quanta m -2 s -1 ) at 4 °C, they developed strong photoinhibition, as characterized by decreased quantum yield of O 2 evolution and decreased ratio of variable: maximum fluorescence (F V /F M ) of photosystem II. The decrease in F V /F M resulted from a decline in F V and an increase in F 0 . The F V /F M ratio was lowered to a significantly greater extent when induction was recorded at 20 °C, as compared with 77 K. The effects related to photoinhibition were fully reversible at 18 °C in dim light. Plants that had been cold-acclimated for 10 days exhibited slightly decreased quantum yield and lowered F V /F M ratio. However, they did not show further photoinhibition on exposure to 550 µmol quanta m -2 s -1 at 4 °C. The reversible photoinhibition is discussed as a protective pathway serving for thermal dissipation of excessive light energy. It is hypothesized that such a mechanism prevents destruction of the photosynthetic apparatus, until other means of protection become effective during long-term acclimation to high light. Inhibition of photosynthetic carbon assimilation caused by freezing and thawing of leaves in the dark was closely correlated with inhibition of photochemical fluorescence quenching (q Q ). As a sensitive response of the thylakoid membranes to freezing stress, the energy-dependent quenching, q E , was inhibited. Only more severe impact of freezing caused a significant decline in the F V /F M ratio. It is concluded that measurements of fluorescence induction signals ( F V /F M ratios) provide a sensitive tool with which to investigate photoinhibition, whereas freezing damage to the photosynthetic system can be detected more readily by the quenching coefficients q Q and q E than by F V /F M ratios.

Performance Improvements in Cooker-Top Gas Burners for Small Aspect Ratio Changes

2017 ◽  
Vol 9 (4) ◽  
Author(s):  
Robson L. Silva ◽  
Bruno V. Sant′Ana ◽  
José R. Patelli ◽  
Marcelo M. Vieira
Keyword(s):  
Energy Conversion ◽  
Fuel Consumption ◽  
Conversion Efficiency ◽  
Minimum Energy ◽  
Energy Conversion Efficiency ◽  
Energy Performance ◽  
Operating Conditions ◽  
Lower Fuel Consumption ◽  
Performance Improvements ◽  
Aspect Ratios

This paper aims to identify performance improvements in cooker-top gas burners for changes in its original geometry, with aspect ratios (ARs) ranging from 0.25 to 0.56 and from 0.28 to 0.64. It operates on liquefied petroleum gas (LPG) and five thermal power (TP) levels. Considering the large number of cooker-top burners currently being used, even slight improvements in thermal performance resulting from a better design and recommended operating condition will lead to a significant reduction of energy consumption and costs. Appropriate instrumentation was used to carry out the measurements and methodology applied was based on regulations from INMETRO (CONPET program for energy conversion efficiency in cook top and kilns), ABNT (Brazilian Technical Standards Normative) and ANP—National Agency of Petroleum, Natural Gas (NG) and Biofuels. The results allow subsidizing recommendations to minimum energy performance standards (MEPS) for residential use, providing also higher energy conversion efficiency and/or lower fuel consumption. Main conclusions are: (i) Smaller aspect ratios result in the same heating capacity and higher efficiency; (ii) higher aspect ratios (original burners) are fuel consuming and inefficient; (iii) operating conditions set on intermediate are lower fuel consumption without significant differences in temperature increases; (iv) Reynolds number lower than 500 provides higher efficiencies.

Improvement of energy-conversion efficiency from laser to proton beam in a laser-foil interaction

2008 ◽  
Vol 78 (4) ◽  
Author(s):  
Y. Nodera ◽  
S. Kawata ◽  
N. Onuma ◽  
J. Limpouch ◽  
O. Klimo ◽  
...  
Keyword(s):  
Energy Conversion ◽  
Proton Beam ◽  
Conversion Efficiency ◽  
Energy Conversion Efficiency
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