- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Comprehensive Remote Sensing || Solar Induced Chlorophyll Fluorescence: Origins, Relation to Photosynthesis and Retrieval
摘要： Photosynthesis has been key to Earth’s habitability, especially since the evolution of oxygenic photosynthesis with the accompanying rise in atmospheric O2 starting in the Proterozoic era, around 2.5 billion years ago. The conversion of light to chemical energy enables higher life forms and the presence of reduced carbon stocks and molecular O2 (accumulated products of photosynthesis) provided the fossil fuels for the initiation of our industrialized society. As a visible indicator of photosynthesis, fluorescence emanating from chlorophyll molecules attracted interest more than 100 years ago. In 1874, red fluorescence from a green living leaf was observed to be weaker than from a dilute chlorophyll solution (Müller, 1874), indicating an alternate fate for energy absorbed by chlorophyll in vivo. More quantitative studies of chlorophyll a fluorescence go back to observations by Hans Kautsky and A. Hirsch in 1931 at the Chemical Institute at the University of Heidelberg, Germany (Kautsky, 1931). They discovered the so-called Kautsky effect, a decrease in Chl fluorescence following illumination of dark-adapted leaves. Both studies already indicated an important aspect of chlorophyll fluorescence, namely, that its yield can vary. This effect is caused by variation in the balance of pathways that compete with fluorescence for quenching of the excited chlorophyll state. The porphyrin ring of the chlorophyll molecule is the center of light absorption and fluorescence. In a dilute chlorophyll solution, where fluorescence is the only route for de-excitation, the fluorescence lifetime (sF) is about 6 ns and the fluorescence yield (FF) approaches 1. In vivo, the excited chlorophyll state can be quenched by other processes, most notably photosynthesis itself but also quenching to heat; FF is lower (1%–5%) and the sF proportionally shorter. Fluorescence in itself is not a significant route for de-excitation of chlorophyll but changes in FF or sF can be used to study how absorbed energy is used. On the other hand, when FF is constant, fluorescence can provide information on the total amount of light absorbed, as the amount emitted will be proportional to the total amount of photosynthetically active radiation (PAR) that is absorbed by chlorophyll and associated pigments. Fig. 1 shows an example of a typical fluorescence spectrum as well as the absorbance spectrum by chlorophyll.
关键词： Fluorescence Yield,Solar Induced Chlorophyll Fluorescence,Chlorophyll,Photosynthesis,Remote Sensing
更新于2025-09-04 15:30:14
-
A Mechanistic View of the Main Current Issues in Photocatalytic CO2 Reduction
摘要： After 40 years of research on photocatalytic CO2 reduction, there are still many unknowns about its mechanistic aspects even for the most common TiO2-based photocatalytic systems. These uncertainties include the pathways inducing visible-light activity in wide-band-gap semiconductors; the charge transfer between semiconductors and plasmonic metal nanoparticles; the unambiguous determination of the origin of C-bearing products; the very first step in the activation of the CO2 molecule; the factors determining the selectivity; the reasons of photocatalyst deactivation; the closure of the catalytic cycle by the hole-scavenging reagent; and the detailed reaction pathways and the most suitable techniques for their determination. This perspective discusses these controversial issues based on the most relevant investigations reported so far. For that purpose, we have tried to view the complex CO2 reduction in a holistic manner, considering today’s state-of-the-art approaches, strategies and techniques for the study of one of the hottest topics in energy research.
关键词： Advanced characterization techniques,CO2 reduction,Photocatalysis,Artificial photosynthesis,Reaction mechanism,Charge transfer
更新于2025-09-04 15:30:14
-
Airborne Hyperspectral Evaluation of Maximum Gross Photosynthesis, Gravimetric Water Content, and CO2 Uptake Efficiency of the Mer Bleue Ombrotrophic Peatland
摘要： Peatlands cover a large area in Canada and globally (12% and 3% of the landmass, respectively). These ecosystems play an important role in climate regulation through the sequestration of carbon dioxide from, and the release of methane to, the atmosphere. Monitoring approaches, required to understand the response of peatlands to climate change at large spatial scales, are challenged by their unique vegetation characteristics, intrinsic hydrological complexity, and rapid changes over short periods of time (e.g., seasonality). In this study, we demonstrate the use of multitemporal, high spatial resolution (1 m2) hyperspectral airborne imagery (Compact Airborne Spectrographic Imager (CASI) and Shortwave Airborne Spectrographic Imager (SASI) sensors) for assessing maximum instantaneous gross photosynthesis (PGmax) in hummocks, and gravimetric water content (GWC) and carbon uptake ef?ciency in hollows, at the Mer Bleue ombrotrophic bog. We applied empirical models (i.e., in situ data and spectral indices) and we derived spatial and temporal trends for the aforementioned variables. Our ?ndings revealed the distribution of hummocks (51.2%), hollows (12.7%), and tree cover (33.6%), which is the ?rst high spatial resolution map of this nature at Mer Bleue. For hummocks, we found growing season PGmax values between 8 μmol m?2 s?1 and 12 μmol m?2 s?1 were predominant (86.3% of the total area). For hollows, our results revealed, for the ?rst time, the spatial heterogeneity and seasonal trends for gravimetric water content and carbon uptake ef?ciency for the whole bog.
关键词： Shortwave Airborne Spectrographic Imager (SASI),Compact Airborne Spectrographic Imager (CASI),carbon uptake,gravimetric water content,normalized difference water index (NDWI),photosynthesis,airborne hyperspectral,bog,Mer Bleue,peatlands
更新于2025-09-04 15:30:14
-
Effects of UV-C radiation on common dandelion and purple coneflower: First results
摘要： Ultraviolet-C (UV-C) light (100 ≤ λ ≤ 280 nm) is a ionizing radiation that can damage living organisms. An experiment was conducted on plants of common dandelion (Taraxacum officinale Weber, T. Densleonis Desf.) and purple coneflower [Echinacea purpurea, (L.) Moench] irradiated with UV-C at different exposition times, under controlled conditions and grown in self-produced characterized compost, to assess the effect of different doses UV-C radiation on some physiological parameters. Trials have been carried out using a black chamber equipped with an UV-C lamp in which plants were divided in four groups on the basis of UV-C irradiation period (10, 30, 60, and 120 min). Non-irradiated plants were kept as controls. Plant photosynthetic performance, chlorophyll content (SPAD) and some morphologic traits were recorded before, immediately after irradiations and 20 days weeks later. The effects on photosynthetic performances and chlorophyll contents (SPAD) were evaluated and compared with data obtained in similar experiments where tomato plants were irradiated at different times with UV-C light. In both species, SPAD values decreased as the irradiation period became longer. The two species showed different gas exchange dynamics, depending on the UV-C exposure time. Two months after the UV-C irradiation, plant dry weight measured at 120-min UV-C exposure was significantly lower than the control.
关键词： photosynthesis,dry matter,gas exchange,chlorophyll content,ozone layer.
更新于2025-09-04 15:30:14