An assessment of photosynthetic light use efficiency from space: Modeling the atmospheric and directional impacts on PRI reflectance

Estimation of photosynthetic light use efficiency (ε) from satellite observations is an important component of climate change research. The photochemical reflectance index, a narrow waveband index based on the reflectance at 531 and 570 nm, allows sampling of the photosynthetic activity of leaves; upscaling of these measurements to landscape and global scales, however, remains challenging. Only a few studies have used spaceborne observations of PRI so far, and research has largely focused on the MODIS sensor. Its daily global coverage and the capacity to detect a narrow reflectance band at 531 nm make it the best available choice for sensing ε from space. Previous results however, have identified a number of key issues with MODIS-based observations of PRI. First, the differences between the footprint of eddy covariance (EC) measurements and the MODIS footprint, which is determined by the sensor's observation geometry make a direct comparison between both data sources challenging and second, the PRI reflectance bands are affected by atmospheric scattering effects confounding the existing physiological signal. In this study we introduce a new approach for upscaling EC based ε measurements to MODIS. First, EC-measured ε values were “translated” into a tower-level optical PRI signal using AMSPEC, an automated multi-angular, tower-based spectroradiometer instrument. AMSPEC enabled us to adjust tower-measured PRI values to the individual viewing geometry of each MODIS overpass. Second, MODIS data were atmospherically corrected using a Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, which uses a time series approach and an image-based rather than pixel-based processing for simultaneous retrievals of atmospheric aerosol and surface bidirectional reflectance (BRDF). Using this approach, we found a strong relationship between tower-based and spaceborne reflectance measurements (r² = 0.74, p < 0.01) throughout the vegetation period of 2006. Swath (non-gridded) observations yielded stronger correlations than gridded data (r² = 0.58, p < 0.01) both of which included forward and backscatter observations. Spaceborne PRI values were strongly related to canopy shadow fractions and varied with different levels of ε. We conclude that MAIAC-corrected MODIS observations were able to track the site-level physiological changes from space throughout the observation period.     

A functional test platform for the Community Land Model

The realistic representation of key biogeophysical and biogeochemical functions is the fundamental of process-based ecosystem models. A functional test platform is designed to create direct linkages between site measurements and the process-based ecosystem model within the Community Earth System Models (CESM). The platform consists of three major parts: 1) interactive user interfaces, 2) functional test models and 3) observational datasets. It provides much needed integration interfaces for both field experimentalists and ecosystem modelers to improve the model's representation of ecosystem processes within the CESM framework without large software overhead.     

多效唑浸种对盐胁迫下麻疯树幼苗光合作用的影响

研究了200mmol.L-1NaCl处理（10d）下不同浓度（0、200、400、600、800、1 000mg.L-1）多效唑（PP333）浸种处理对麻疯树南油1号幼苗生长和光合作用的影响。结果表明：在盐胁迫下,不同浓度的PP333浸种处理均显著提高了盐胁迫下的植株干物质积累速率、根冠比和叶绿素含量,提高了净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（Tr）和气孔限制值（Ls）,降低了细胞间隙CO2浓度（Ci）,其中600mg.L-1PP333浸种处理效果最好。可见,多效唑浸种能促进盐胁迫下麻疯树南油1号幼苗的生长,缓解盐胁迫对麻疯树幼苗的非气孔限制,改善光合作用,减缓盐胁迫的伤害。     

基于模糊神经网络的温室二氧化碳控制

在温室蔬菜大棚控制技术的科技改造中,智能控制将成为温室控制的关键技术.二氧化碳是农作物进行光合作用的主要原料之一,温室大棚由于其封闭性,随着农作物光合作用的进行,如果没有新的二氧化碳气体注入的话,会造成室内二氧化碳浓度远低于室外,不利于农作物生长.本文提出一种利用BP神经网络结合模糊控制的方法,对温室二氧化碳的输入量进行控制.这种方法克服了现有控制方法需要大量的数据传输、准确的数学模型等缺陷,并使用Matlab进行了仿真,仿真结果表明该方法有效.     

Seasonal and diurnal variations of temperature, pH and dissolved oxygen in advanced integrated wastewater pond system treating tannery effluent

Seasonal and diurnal fluctuations of pH, dissolved oxygen (DO) and temperature were investigated in a pilot-scale advanced integrated wastewater pond system (AIWPS) treating tannery effluent. The AIWPS was comprised of advanced facultative pond (AFP), secondary facultative pond (SFP) and maturation pond (MP) all arranged in series. The variations of pH, DO and temperature in the SFP and MP followed the diurnal cycle of sunlight intensity. Algal photosynthesis being dependent on sunlight radiation, its activity reached climax at early afternoons with DO saturation in the SFP and MP in excess of over 300% and pH in the range of 8.6-9.4. The SFP and MP were thermally stratified with gradients of 3-5 degrees C/m, especially, during the time of peak photosynthesis. The thermal gradient in the AFP was moderated by convective internal currents set in motion as a result of water temperature differences between the influent wastewater and contents of the reactor. In conclusion, the AFP possessed remarkable ability to attenuate process variability with better removal efficiencies than SFP and MP. Hence its use as a lead treatment unit, in a train of ponds treating tannery wastewaters, should always be considered.     

Chlorophyll assembled electrode for photovoltaic conversion device

Chlorophyll-a (Chl-a) assembled in hydrophobic domain by fatty acid with long alkyl hydrocarbon chain such as myristic acid (Myr), stearic acid (Ste) and cholic acid (Cho) modified onto nanocrystalline TiO₂ electrode is prepared and the photovoltaic properties of the nanocrystalline TiO₂ film by Chl-a are studied. Incident photon to current efficiency (IPCE) value at 660 nm in photocurrent action spectrum of Chl-a/Ste-TiO₂, Chl-a/Myr-TiO₂ and Chl-a/Cho-TiO₂ electrodes are 5.0%, 4.1% and 4.1%, respectively. Thus, the IPCE is maximum using Chl-a/Ste-TiO₂ electrode. From the results of photocurrent responses with light intensity of 100 mW cm⁻² irradiation or monochromatic light with 660 nm, generated photocurrent increases using Chl-a/Ste-TiO₂ electrode compared with the other Chl-a assembled TiO₂ electrodes. These results show that the hydrophobic domain formed by stearic acid with long alkyl hydrocarbon chain is suitable for fixation of Chl-a onto TiO₂ film electrodes and photovoltaic performance is improved using Chl-a onto Ste-TiO₂ film electrode.     

Metabolic flux analysis of the hydrogen production potential in Synechocystis sp. PCC6803

Hydrogen is a promising energy vector; however, finding methods to produce it from renewable sources is essential to allow its wide-scale use. In that line, biological hydrogen production, although it is considered as a possible alternative, requires substantial improvements to overcome its present low yields. In that direction, genetic manipulation probably will play a central role and from that point of view metabolic flux analysis (MFA) constitutes an important tool to guide a priori most suitable genetic modifications oriented to a hydrogen yield increase.In this work MFA has been applied to analyze hydrogen photoproduction of Synechocystis sp. PCC6803. Flux analysis was carried out based on literature data and several basic fluxes were estimated in different growing conditions of the system. From this analysis, an upper limit for hydrogen photoproduction has been determined indicating a wide margin for improvement. MFA was also used to find a feasible operating space for hydrogen production, which avoids oxygen inhibition, one of the most important limitations to make hydrogen production cost effective. In addition, a set of biotechnological strategies are proposed that would be consistent with the performed mathematical analysis.     

Assessment of the technological development and economic potential of photobioreactors

In this paper, we investigate the development and economic potential of the photobioreactor (PBR) technology for energy purposes, i.e. production of hydrogen or biofuels. The approach adopted is to consider the technology, its expected costs and revenues, and related risks from an investor perspective. To this end we develop an investment model that is used to calculate the economic feasibility of PBRs for different scenarios, including a best-case scenario, with plenty of sunlight and water, inexpensive nutrients, high prices for hydrogen and biomass, and low other costs. The best-case scenario is compared to a scenario with less favorable boundary conditions. We find that PBR efficiencies will likely be less than 10%, with typical values between 1.8% and 5.6%. We also find that hydrogen production costs would be lower than those for biodiesel or biogas from solid biomass produced in PBRs. Compared to biofuels from traditional agriculture there is a great advantage for the PBR technology if land is scarce, because land is used more efficiently. Since PBRs can be designed as a closed system they can be applied in very dry regions. In the long term this might enable this promising concept to penetrate the energy supply market.     

螺旋藻的脉冲激光光声研究

用脉冲激光及液体光声传感器研究了螺旋藻的光声谱及入射能量与光声信号之间的关系,并比较了正常状态与在 DCMU 存在下螺旋藻光声图谱的变化。     

盐胁迫对黑麦草幼苗生长的影响及磷肥的缓解作用

采用盆栽试验和生理生化分析方法研究了盐胁迫对黑麦草幼苗生长的影响以及施用磷肥(过磷酸钙)对盐胁迫下黑麦草幼苗生长的缓解作用。结果表明,盐胁迫下黑麦草幼苗干物质积累下降;增施磷肥能促进黑麦草幼苗生长,增加干物质积累,增强黑麦草对Na 、K 吸收的选择性,促进K 的吸收和向叶片运输;能提高叶片叶绿素含量,增强叶片净光合速率和气孔导度,增加可溶性蛋白、可溶性糖及脯氨酸含量,从而增强黑麦草幼苗对盐胁迫的适应能力。