Firefly shows bioluminescence by "luciferin-luciferase" (L-L) reaction using luciferin, luciferase, ATP and O2. The chemical photon generation by an enzymatic reaction is widely utilized for ...analytical methods including biological imaging in the life science fields. To expand photondetecting analyses with firefly bioluminescence, it is important for users to understand the chemical basis of the L-L reaction. In particular, the emission color variation of the L-L reaction is one of the distinguishing characteristics for multicolor luciferase assay and in vivo imaging. From the viewpoint of fundamental chemistry, this review explains the recent progress in the studies on the molecular mechanism of emission color variation after showing the outline of the reaction mechanism of the whole L-L reaction. On the basis of the mechanism, the progresses in organic synthesis of luciferin analogs modulating their emission colors are also presented to support further developments of red/near infrared in vivo biological imaging utility of firefly bioluminescence.
In Southeast Asia, a huge amount of peat has accumulated under swamp forests over millennia. Fires have been widely used for land clearing after timber extraction, thus land conversion and land ...management with logging and drainage are strongly associated with fire activity. During recent El Niño years, tropical peatlands have been severely fire‐affected and peatland fires enlarged. To investigate the impact of peat fires on the regional and global carbon balances, it is crucial to assess not only direct carbon emissions through peat combustion but also oxidative peat decomposition after fires. However, there is little information on the carbon dynamics of tropical peat damaged by fires. Therefore, we continuously measured soil CO2 efflux peat respiration (RP) through oxidative peat decomposition using six automated chambers on a burnt peat area, from which about 0.7 m of the upper peat had been lost during two fires, in Central Kalimantan, Indonesia. The RP showed a clear seasonal variation with higher values in the dry season. The RP increased logarithmically as groundwater level (GWL) lowered. Temperature sensitivity or Q10 of RP decreased as GWL lowered, mainly because the vertical distribution of RP would shift downward with the expansion of an unsaturated soil zone. Although soil temperature at the burnt open area was higher than that in a near peat swamp forest, model simulation suggests that the effect of temperature rise on RP is small. Annual gap‐filled RP was 382 ± 82 (the mean ± 1 SD of six chambers) and 362 ± 74 gC m−2 yr−1 during 2004–2005 and during 2005–2006 years, respectively. Simulated RP showed a significant negative relationship with GWL on an annual basis, which suggests that every GWL lowering by 0.1 m causes additional RP of 89 gC m−2 yr−1. The RP accounted for 21–24% of ecosystem respiration on an annual basis.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Data on ecosystem‐scale methane (CH4) fluxes in tropical peatlands are currently lacking in the global CH4 budget. Although the waterlogged Indonesian peatlands contain the largest share of peat ...carbon in South‐East Asia, ecosystem‐scale CH4 budgets have not yet been reported, although these peatlands have the potential to emit CH4. We observed 1‐year variations in the ecosystem‐scale CH4 flux in an undrained secondary peat swamp forest in central Kalimantan, Indonesia, using the eddy covariance method. We found that the peat swamp forest switched from being a CH4 sink during the dry season (as low as −8.9 mg C m−2 day−1) to a source of CH4 during the wet season (up to 10.7 mg C m−2 day−1), and this was dependent on changes in the groundwater level (GWL). The high GWL during the wet season enhanced the anaerobic CH4 production in the surface layer that had more labile organic matter. However, the CH4 emission also increased when the GWL dropped during dry spells in the wet season. The annual CH4 budget in the studied tropical peat swamp forest (0.09–0.17 g C m−2 year−1) was much lower than that in northern, temperate, and subtropical wetlands. We found that CH4 fluxes had almost no effect on the global warming gas budget of the peat swamp forest, and values were only a few percent less than the CO2 fluxes at the same site. In addition, we conducted anaerobic soil incubation experiments to examine the effect of land‐use change on CH4 production. The results indicated much higher CH4 production potential in undrained forest soil than in drained or drained and burned ex‐forest soils. However, although CH4 production decreased in drained soils relative to undrained soils, conserving pristine peat swamp forests with high GWLs is important to suppress global warming because CO2 emissions increase in drained peatlands.
Annual variations in daily average and standard error of ecosystem‐scale net ecosystem exchange of methane (NEE) and groundwater level (GWL) between June 1, 2016, and May 31, 2017. The gray‐shaded areas indicate periods when methane emission increased despite GWL declining. Annual methane budget was neutral, ranging from 0.09 to 0.17 g C m−2 year−1.
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Borneo has accumulated an abundance of woody carbon in its forests and peat. However, agricultural land conversion accompanied by plantation development, dead wood burning, and peat drying from ...drainage are major challenges to climate change mitigation. This study aimed to develop a method of estimating carbon dioxide (CO
) emissions from land use change, forest and peat fires, and oxidative peat decomposition, and CO
uptake from biomass growth across Borneo using remote sensing data from 2001 to 2016. Although CO
uptake by biomass growth in vast forests has shown a significant increasing trend, an annual net release of 461.10 ± 436.51 (average ± 1 standard deviation) Tg CO
year
was observed. The estimated emissions were predominantly characterized by land use changes from 2001 to 2003, with the highest emissions in 2001. Land use change was evaluated from annual land use maps with an accuracy of 92.0 ± 1.0% (average ± 1 standard deviation). Forest and peat fires contributed higher emissions in 2002, 2006, 2009, 2014, and 2015 compared to other years and were strongly correlated with the Southern Oscillation Indexes. These results suggest that more CO
may have been released into the atmosphere than previously thought.
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In Southeast Asia, peatland is widely distributed and has accumulated a massive amount of soil carbon, coexisting with peat swamp forest (PSF). The peatland, however, has been rapidly degraded by ...deforestation, fires, and drainage for the last two decades. Such disturbances change hydrological conditions, typically groundwater level (GWL), and accelerate oxidative peat decomposition. Evapotranspiration (ET) is a major determinant of GWL, whereas information on the ET of PSF is limited. Therefore, we measured ET using the eddy covariance technique for 4–6 years between 2002 and 2009, including El Niño and La Niña events, at three sites in Central Kalimantan, Indonesia. The sites were different in disturbance degree: a PSF with little drainage (UF), a heavily drained PSF (DF), and a drained burnt ex‐PSF (DB); GWL was significantly lowered at DF, especially in the dry season. The ET showed a clear seasonal variation with a peak in the mid‐dry season and a large decrease in the late dry season, mainly following seasonal variation in net radiation (Rₙ). The Rₙdrastically decreased with dense smoke from peat fires in the late dry season. Annual ET forced to close energy balance for 4 years was 1636 ± 53, 1553 ± 117, and 1374 ± 75 mm yr⁻¹(mean ± 1 standard deviation), respectively, at UF, DF, and DB. The undrained PSF (UF) had high and rather stable annual ET, independently of El Niño and La Niña events, in comparison with other tropical rainforests. The minimum monthly‐mean GWL explained 80% of interannual variation in ET for the forest sites (UF and DF); the positive relationship between ET and GWL indicates that drainage by a canal decreased ET at DF through lowering GWL. In addition, ET was decreased by 16% at DB in comparison with UF chiefly because of vegetation loss through fires.
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•A simple CH4 model constrained by observed data with a Bayesian method was developed.•CH4 flux based on the eddy covariance method was partitioned in a cool temperate bog.•Ebullition and ...plant-mediated transport are important pathways.•The anoxic deep layer contributed more to the CH4 flux than the oxic surface layer.•Long-term data are indispensable for better constraining models.
The responses of CH4 fluxes to environmental drivers are known to be complex in wetlands and are not easily interpreted due to their nonlinear nature. To better understand the observed CH4 flux, we developed a method to partition this flux into CH4 production, oxidation, and three transport pathways. Based on a Bayesian method with six-year eddy covariance measurements from a cool temperate bog in northern Japan, we estimated the parameters of a simple two-layer model, which considered the processes in surface oxic and deep anoxic layers. The constrained model explained 87% of the variation in the observed CH4 flux at the daily to seasonal timescales. The model estimated that 64% of CH4 was transported by ebullition compared with 36% by plant-mediated transport during snow-free periods. The model predicted that CH4 was mostly emitted from the deep anoxic layer rather than from the surface layer. The model explained 56% of the interannual variations in the annual CH4 flux, which was mostly controlled by CH4 production. Posterior distributions of the parameters depended on the data coverage that constrained the model, strongly indicating that long-term data are indispensable for constraining process models. Even when using the six-year data, all parameters were not well constrained probably because the data did not contain enough information to constrain the processes. Thus, the method must be tested in various wetlands with additional long-term data to evaluate its applicability and limitations.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The carbon balance of tropical peatlands was investigated using measurements of gaseous fluxes of carbon dioxide (CO₂) and methane (CH₄) at several land-use types, including nondrained forest (NDF), ...drained forest (DF), drained regenerating forest (DRF) after clear cutting and agricultural land (AL) in Central Kalimantan, Indonesia. Soil greenhouse gas fluxes depended on land-use, water level (WL), microtopography, temperature and vegetation physiology, among which WL was the strongest driver. All sites were CH₄ sources on an annual basis and the emissions were higher in sites providing fresh litter deposition and water logged conditions. Soil CO₂ flux increased exponentially with soil temperature (T s) even within an amplitude of 4-5°C. In the NDF soil CO₂ flux sharply decreased when WLs rose above −0.2 and 0.1 m for hollows and hummocks, respectively. The sharp decrease suggests that the contribution of surface soil respiration (RS) to total soil CO₂ flux is large. In the DF soil CO₂ flux increased as WL decreased below −0.7 m probably because the fast aerobic decomposition continued in lower peat. Such an increase in CO₂ flux at low WLs was also found at the stand level of the DF. Soil CO₂ flux showed diurnal variation with a peak in the daytime, which would be caused by the circadian rhythm of root respiration. Among the land-use types, annual soil CO₂ flux was the largest in the DRF and the smallest in the AL. Overall, the global warming potential (GWP) of CO₂ emissions in these land-use types was much larger than that of CH₄ fluxes.
Recently, the effect of large-scale fires on the global environment has attracted attention. Satellite observation data are used for global estimation of fire CO2 emissions, and available data ...sources are increasing. Although several CO2 emission inventories have already been released, various remote sensing data were used to create the inventories depend on the studies. We created eight global CO2 emission inventories through fires from 2001 to 2020 by combining input data sources, compared them with previous studies, and evaluated the effect of input sources on CO2 emission estimation. CO2 emissions were estimated using a method that combines the biomass density change (by the repeated fires) with the general burned area approach. The average annual CO2 emissions of the created eight inventories were 8.40 ± 0.70 Pg CO2 year−1 (±1 standard deviation), and the minimum and maximum emissions were 3.60 ± 0.67 and 14.5 ± 0.83 Pg CO2 year−1, respectively, indicating high uncertainty. CO2 Emissions obtained from four previous inventories were within ±1 standard deviation in the eight inventories created in this study. Input datasets, especially biomass density, affected CO2 emission estimation. The global annual CO2 emissions from two biomass maps differed by 60% (Maximum). This study assesses the performance of climate and fire models by revealing the uncertainty of fire emission estimation from the input sources.
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Tropical peatlands have accumulated huge soil carbon over millennia. However, the carbon pool is presently disturbed on a large scale by land development and management, and consequently has become ...vulnerable. Peat degradation occurs most rapidly and massively in Indonesia, because of fires, drainage, and deforestation of swamp forests coexisting with tropical peat. Peat burning releases carbon dioxide (CO2) intensively but occasionally, whereas drainage increases CO2 emission steadily through the acceleration of aerobic peat decomposition. Therefore, tropical peatlands present the threat of switching from a carbon sink to a carbon source to the atmosphere. However, the ecosystem‐scale carbon exchange is still not known in tropical peatlands. A long‐term field experiment in Central Kalimantan, Indonesia showed that tropical peat ecosystems, including a relatively intact peat swamp forest with little drainage (UF), a drained swamp forest (DF), and a drained burnt swamp forest (DB), functioned as net carbon sources. Mean annual net ecosystem CO2 exchange (NEE) (± a standard deviation) for 4 years from July 2004 to July 2008 was 174 ± 203, 328 ± 204 and 499 ± 72 gC m−2 yr−1, respectively, for the UF, DF, and DB sites. The carbon emissions increased according to disturbance degrees. We found that the carbon balance of each ecosystem was chiefly controlled by groundwater level (GWL). The NEE showed a linear relationship with GWL on an annual basis. The relationships suggest that annual CO2 emissions increase by 79–238 gC m−2 every 0.1 m of GWL lowering probably because of the enhancement of oxidative peat decomposition. In addition, CO2 uptake by vegetation photosynthesis was reduced by shading due to dense smoke from peat fires ignited accidentally or for agricultural practices. Our results may indicate that tropical peatland ecosystems are no longer a carbon sink under the pressure of human activities.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The present study describes a color-tunable imaging portfolio together with twelve novel coelenterazine (CTZ) analogues. The three groups of CTZ analogues create diverse hues of bioluminescence (BL) ...ranging from blue to far red with marine luciferases. We found that the hue completes the whole color palette in the visible region and shows red-shifted BL with a marine luciferase: for example, Renilla luciferase 8 (RLuc8) and Artificial Luciferase 16 (ALuc16) show 187 nm- and 105 nm-redshifted spectra, respectively, by simply replacing the substrate CTZ with 1d. The optical properties of the new CTZ analogues were investigated such as the kinetic parameters, dose dependency, and luciferase specificity. The 2-series CTZ analogues interestingly have specificity to ALucs and are completely dark with RLuc derivatives, and 3d is highly specific to only NanoLuc. We further determined the theoretical background of the red-shifted BL maximum wavelengths (λ
) values according to the extended π conjugation of the CTZ backbone using Density Functional Theory (DFT) calculations. This color-tunable BL imaging system provides a useful multicolor imaging portfolio that efficiently images molecular events in mammalian cells.
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