Total Photosynthesis Research Articles

Limited effect of ozone reductions on the 20-year photosynthesis trend at Harvard forest.

Ozone (O3 ) damage to leaves can reduce plant photosynthesis, which suggests that declines in ambient O3 concentrations ([O3 ]) in the United States may have helped increase gross primary production (GPP) in recent decades. Here, we assess the effect of long-term changes in ambient [O3 ] using 20years of observations at Harvard forest. Using artificial neural networks, we found that the effect of the inclusion of [O3 ] as a predictor was slight, and independent of O3 concentrations, which suggests limited high-frequency O3 inhibition of GPP at this site. Simulations with a terrestrial biosphere model, however, suggest an average long-term O3 inhibition of 10.4% for 1992-2011. A decline of [O3 ] over the measurement period resulted in moderate predicted GPP trends of 0.02-0.04μmolCm-2 s-1 yr-1 , which is negligible relative to the total observed GPP trend of 0.41μmolCm-2 s-1 yr-1 . A similar conclusion is achieved with the widely used AOT40 metric. Combined, our results suggest that ozone reductions at Harvard forest are unlikely to have had a large impact on the photosynthesis trend over the past 20years. Such limited effects are mainly related to the slow responses of photosynthesis to changes in [O3 ]. Furthermore, we estimate that 40% of photosynthesis happens in the shade, where stomatal conductance and thus [O3 ] deposition is lower than for sunlit leaves. This portion of GPP remains unaffected by [O3 ], thus helping to buffer the changes of total photosynthesis due to varied [O3 ]. Our analyses suggest that current ozone reductions, although significant, cannot substantially alleviate the damages to forest ecosystems.

Inhibitory activity of different medicinal extracts from Thuja leaves, ginger roots, Harmal seeds and turmeric rhizomes against Fig leaf mottle-associated virus 1 (FLMaV-1) infecting figs in Mecca region.

Fig leaf mottle-associated virus-1 (FLMaV-1) is a closterovirus newly identified in fig trees, in the Mecca region, suffering from mosaic disease symptoms and apparently is compromising the fig plantation in the country. In the present study, we demonstrated the efficiency of two in vivo experiments including pre and post treatments using Thuja leaf, ginger roots, Harmal seeds and turmeric rhizome extracts on symptoms expression of rooted cuttings infected with FLMaV-1- and their impact on virus multiplication. Results showed that individual treatments with ginger roots and turmeric rhizomes in pre-grafting experiments and Thuja extract following Harmal seeds in post grafting experiments were efficient against symptom development. In addition, results showed that the total photosynthesis pigments; total soluble intracellular proteins and total phenol contents were higher in infected treated cuttings compared with healthy ones, thus it was taken as evidence on a mutual interaction between these extracts and virus multiplication.

Microbial processes and factors controlling their activities in alkaline lakes of the Mongolian plateau

A striking feature of the Mongolian plateau is the wide range of air temperatures during a year, -30 to 30°C. High summer temperatures, atmospheric weathering and the arid climate lead to formation of numerous alkaline soda lakes that are covered by ice during 6–7 months per year. During the study period, the lakes had pH values between 8.1 to 10.4 and salinity between 1.8 and 360 g/L. According to chemical composition, the lakes belong to sodium carbonate, sodium chloride-carbonate and sodium sulfate-carbonate types. This paper presents the data on the water chemical composition, results of the determination of the rates of microbial processes in microbial mats and sediments in the lakes studied, and the results of a Principal Component Analysis of environmental variables and microbial activity data. Temperature was the most important factor that influenced both chemical composition and microbial activity. pH and salinity are also important factors for the microbial processes. Dark CO2 fixation is impacted mostly by salinity and the chemical composition of the lake water. Total photosynthesis and sulfate-reduction are impacted mostly by pH. Photosynthesis is the dominant process of primary production, but the highest rate (386 mg C/(L∙d)) determined in the lakes studied were 2–3 times lower than in microbial mats of lakes located in tropical zones. This can be explained by the relatively short warm period that lasts only 3–4 months per year. The highest measured rate of dark CO2 assimilation (59.8 mg C/(L∙d)) was much lower than photosynthesis. The highest rate of sulfate reduction was 60 mg S/(L∙d), while that of methanogenesis was 75.6 μL СН4/(L∙d) in the alkaline lakes of Mongolian plateau. The rate of organic matter consumption during sulfate reduction was 3–4 orders of magnitude higher than that associated with methanogenesis.

Simulation of Photosynthetic Capacity of Strawberry Plants at Different Leaf Ages

A mathematical simulation was carried out to study the photosynthetic capacity of strawberry plants (Fragaria X ananassa Duch., Benihoppe) at different leaf ages. It also compared the differences in chlorophyll and protein contents in the leaves in order to provide a theoretical basis for the cultivation of high-quality and high-yield strawberry plants. Our results indicated that the chlorophyll content in the functional leaves was 67 and 46% higher than in the new and old leaves and that the soluble protein content in the functional leaves was 21 and 13% higher than in the new and old leaves. Strawberry leaves at different leaf ages had a significantly different maximum photosynthetic rate; the maximum photosynthetic rate of the functional leaves was generally 1.5 times greater than the new leaves and more than 80% greater than the old leaves. The difference in the photosynthetic capacity of the leaves at different leaf ages was consistent with the difference in leaf structure and chlorophyll content. The simulation indicated that the total net photosynthesis of the new and old leaves was approximately 131 mmol/m/d and 140 mmol/m/d on clear days, only 62 and 67% the rate of the functional leaves.

A bioenergetic assessment of photosynthetic growth of Synechocystis sp. PCC 6803 in continuous cultures.

BackgroundSynechocystis sp. PCC 6803, a model organism used for bioenergy and bioplastic production, was grown in continuous culture to assess its most important bioenergetic parameters.ResultsBiomass yield on light energy of 1.237 g mol photons−1 and maintenance energy requirement of 0.00312 mol photons g−1 h−1 were calculated. This corresponded to a light conversion efficiency of 12.5 %, based on the model of Pirt which was about 35 % lower than the theoretical one based on the stoichiometric equation for the formation of biomass on carbon dioxide, water, and nitrate. The maximum Fv/Fm ratio recorded in the Synechocystis cultures was 0.57; it progressively declined to 0.45 as the dilution rate increased. An over-reduction of reaction centers at a high dilution rate was also recorded, together with an increased VJ phase for the chlorophyll fluorescence transient. In contrast, the chlorophyll optical cross section increased by about 40 % at the fastest dilution rate, and compensated for the decline in Fv/Fm, thus resulting in a constant total photosynthesis rate (photosynthesis plus respiration). Chlorophyll content was maximum at the lowest dilution rate and was 48 % lower at the highest one, while phycocyanin, and total carotenoids decreased by about 42 % and 37 %, respectively. Carotenoid analysis revealed increased echinenone, zeaxanthin, and myxoxanthophyll contents as the dilution rate increased (40.6, 63.8 and 35.5 %, respectively, at the fastest dilution rate). A biochemical analysis of the biomass harvested at each different dilution rates showed no changes in the lipid content (averaging 11.2 ± 0.6 % of the dry weight), while the protein content decreased as the dilution rate increased, ranging between 60.7 ± 1.1 and 72.6 ± 0.6 %. Amino acids pattern did not vary with the dilution rate. Carbohydrate content ranged from 9.4 to 16.2 % with a mean value of 11.2 ± 1.4 %.ConclusionsThe present work provides useful information on the threshold of light conversion efficiency in Synechocystis, as well as basic bioenergetic parameters that will be helpful for future studies related to its genetic transformation and metabolic network reconstruction.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0319-7) contains supplementary material, which is available to authorized users.

Source and sink carbon dynamics and carbon allocation in the Amazon basin

AbstractChanges to the carbon cycle in tropical forests could affect global climate, but predicting such changes has been previously limited by lack of field‐based data. Here we show seasonal cycles of the complete carbon cycle for 14, 1 ha intensive carbon cycling plots which we separate into three regions: humid lowland, highlands, and dry lowlands. Our data highlight three trends: (1) there is differing seasonality of total net primary productivity (NPP) with the highlands and dry lowlands peaking in the dry season and the humid lowland sites peaking in the wet season, (2) seasonal reductions in wood NPP are not driven by reductions in total NPP but by carbon during the dry season being preferentially allocated toward either roots or canopy NPP, and (3) there is a temporal decoupling between total photosynthesis and total carbon usage (plant carbon expenditure). This decoupling indicates the presence of nonstructural carbohydrates which may allow growth and carbon to be allocated when it is most ecologically beneficial rather than when it is most environmentally available.

Spatial variability of water use efficiency in China's terrestrial ecosystems

Water use efficiency (WUE) reflects the coupling of carbon and water cycles. Analyzing the spatial variability of WUE can improve our understanding on the interaction between carbon and water cycles at a large scale, which also provides a basis for improving the regional carbon budget assessment. Based on China's eddy covariance measurements, we examined the spatial variation of China's WUE and its affecting factors. WUE showed a decreasing trend with the increasing altitude, which was the result of ecosystem type distribution resulting from the climatic gradient. After fully considering the vertical variation of WUE, we found that not only mean annual air temperature (MAT), mean annual precipitation (MAP), and mean leaf area index (MLAI) but also mean annual total photosynthesis active radiation (MAR) affected the spatial variation of WUE. With the increasing MAT, MAP, and MLAI, WUE increased significantly but the increasing MAR decreased WUE. The spatial variation of WUE could be directly depicted by MLAI and altitude, the equation including which explained 65% of the spatial variation of WUE. The effects of MAT and MAP on the spatial variation of WUE may be achieved through altering MLAI, while the mechanism underlying the effect of MAR on the spatial variation of WUE was still unclear, which should be the subject of future investigations. This study reveals the vertical variation of WUE and provides a new approach to generate the spatial variation in WUE, which will benefit the regional carbon budget assessment.

Analysis of photosynthetic capacity of four apple canopy structures in China

光合作用是影响果树生长发育的重要因素, 果实的产量和品质主要取决于树冠内叶片的光合作用分布。本研究主要目的是利用三维树冠光合耦合模型模拟比较我国4种主要苹果树形(小冠疏层形、疏散分层形、纺锤形和开心形)光合能力的三维分布和日变化。试验于2010-2012年在富士苹果(<i>Malus domestica</i> Borkh. cv. "Fuji")园进行, 通过实测确定三维树冠内叶片和辐射分布, 根据不同辐射下叶片最大光合速率经验公式计算叶片净光合速率(<i>P</i>n)在三维树冠空间内的分布。结果表明, <i>P</i>n的三维分布和相对辐射相似, 在树冠上部变化平缓, 在树冠内随辐射的降低而急剧减少; 光合总量的分布主要取决于叶面积密度。通过对4种主要苹果树形光合能力分析研究发现, 当PAR=1 500 μmol·m^-2·s^-1时, 4种树形的Pn分别为: 小冠疏层形6.72 μmol·m^-2·s^-1、疏散分层形7.52 μmol·m^-2·s^-1、纺锤形7.24 μmol·m^-2·s^-1、开心形9.88 μmol·m^-2·s^-1。不同树形日光合总量的差异主要与叶面积指数相关; 在晴天, 单位地面上4种树形的日光合总量分别为: 小冠疏层形665.5 mmol·m^-2·d^-1、疏散分层形791.7 mmol·m^-2·d^-1、纺锤形752.6 mmol·m^-2·d^-1、开心形601.1 mmol·m^-2·d^-1。研究表明, 4种苹果树形中开心形树冠<i>P</i>n高, 有利于提高果实品质; 而其他3种树形的光合总量大, 有利于提高果实产量。

Carbon sequestration and noise attenuation provided by hedges in Rome: the contribution of hedge traits in decreasing pollution levels

Hedges are ubiquitous green elements in many European cities. The selection of hedge types characterized by different traits can be suggested for urban greening projects to decrease pollution levels. At this end, carbon dioxide (CO2) sequestration and noise attenuation capability were analyzed in the following hedge types: Laurus nobilis, Nerium oleander, Pittosporum tobira and Pyracantha coccinea, largely used as green infrastructure in Rome (Italy). Representative hedges for each species were selected from high level traffic streets in the city centre (P sites). Traffic density (TD) was monitored simultaneously with CO2 concentration and noise level (N) in each of the considered P sites. The monthly CO2 sequestration capability (MSC) was calculated multiplying the total photosynthesis per hedge by the total photosynthetic activity time (in hours) per month. The multiple regression analysis predicted noise attenuation (ΔN) by a linear combination of total leaf area (TLA), total leaf density (TLD) and leaf mass area (LMA) of the considered hedge types. All the considered species, being evergreens, were active all year long, including winter, when CO2 emissions from road transport peaked. Nevertheless, among the considered hedge types, P. tobira and L. nobilis were the most efficient species in both MSC (31.6±2.8 and 25.4±2.4 kg CO2 month–1, respectively) and ΔN (15±1%, mean value). The results give insight on the use of hedges to mitigate pollution effects. Moreover, this method can be used to monitor hedge contribution to air quality, in relation to various elements in the city (i.e. traffic density, new cars produced, application of management projects, local laws). These results might be available for projects based on the use of vegetation in order to improve environmental quality in urban areas.

三种温带树种叶片呼吸的时间动态及其影响因子

为认知叶片呼吸(<em>R</em>_L)的季节变化格局及其影响因子,以东北东部山区3个主要树种(红松 <em>Pinus koraiensis</em>、樟子松 <em>P.sylvestris</em> var. <em>mongolica</em>和白桦 <em>Betula platyphylla</em>)为对象,采用红外气体分析法在2011年生长季(常绿树4月至10月;落叶树6月至9月)测定了自然条件下叶片气体交换及其相关生理特征的季节变化,探索了<em>R</em>_L与空气温度(<em>T</em>_air)和相关叶片特征之间的关系。结果表明:红松和樟子松基于叶面积的<em>R</em>_L(<em>R</em>_L-area)表现为生长季初期和末期较大,而白桦<em>R</em>_L-area则随生长季进程而逐渐减小。在生长季中,<em>R</em>_L-area与叶片总光合之比的时间动态明显。红松、樟子松<em>R</em>_L-area与<em>T</em>_air关系显著,而白桦<em>R</em>_L-area与<em>T</em>_air关系不显著;但3种树种基于叶质量的<em>R</em>_L(<em>R</em>_L-mass)与<em>T</em>_air均呈显著的指数函数关系。叶片特征(包括可溶性糖、淀粉、氮、比叶面积等参数)也有明显的季节变化。影响<em>R</em>_L的叶片特征参数因树种而异,其中可溶性糖浓度对3种树种的<em>R</em>_L均有显著影响。可见,<em>R</em>_L的季节变化格局受树木的生长节律、温度和叶片特征的联合控制。;To understand the factors influencing seasonal variation in leaf respiration (<em>R</em>_L), the leaf gas exchange characteristics and related leaf traits were examined for three tree species in northeastern China. The species were Korean pine (<em>Pinus koraiensis</em>), Mongolian pine (<em>P. sylvestris</em> var. <em>mongolica</em>) and white birch (<em>Betula platyphylla</em>). The <em>R</em>_L, net photosynthetic rate, and air temperature (<em>T</em>_air) were measured <em>in situ</em> with an infrared gas exchange analyzer (LI-6400 IRGA) twice per month throughout the growing season in 2011 (from April to October for the pines; from June to September for the birch). Specific leaf area (<em>SLA</em>) was calculated from oven-dried leaf weight and projected leaf area; nonstructural carbohydrates (<em>NSC</em>) concentrations were determined by a modified phenol-sulfuric acid method; and leaf nitrogen concentrations were measured by the Kjeldahl method. A stepwise multiple regression procedure was applied to explore the relationships between <em>R</em>_L and leaf traits. The area-based <em>R</em>_L (<em>R</em>_L-area) of Korean pine and Mongolian pine peaked in early and late growing seasons, while the <em>R</em>_L-area of white birch declined gradually with the growing season proceeding. The ratio of <em>R</em>_L-area to total photosynthesis and leaf trait parameters (i.e., soluble sugar concentration, starch concentration, <em>SLA</em>, leaf nitrogen concentration) also exhibited seasonal variations for the three species. The <em>R</em>_L-area of pines were positively correlated with <em>T</em>_air, while that of the birch was not. The mass-based <em>R</em>_L (<em>R</em>_L-mass) of the three tree species, however, were all positively related with <em>T</em>_air in an exponential function. The leaf trait parameters affecting the <em>R</em>_L varied with species, and the soluble sugars concentration significantly influenced the <em>R</em>_L for all the species. These results suggest that seasonal variation in <em>R</em>_L jointly controlled by growth rhythm, temperature and leaf traits.

Stipules are the Principal Photosynthetic Organs in the Papilionoid Species Lathyrus aphaca

Occurrence of stipules of different shapes, sizes and varying configurations, has been reported in species of many angiosperm families. However, the functions of stipules in the biology of plants that carry them remain to be understood. There is perception that stipules that have the green coloration of chlorophyll are photosynthetically active. Here, total photosynthesis in the stipules and leaves of Lathyrus aphaca was investigated, together with the nature of heteroblasty and relative morphology and anatomy of stipules and leaves in this species. At each of the hundreds of nodes in the extensively branched post-flowering stage plants of L. aphaca, more than 95 % of photosynthesis occurred in the foliaceous stipules. The leaves in the form of simple tendrils at the nodes accounted for <5 % of photosynthesis. The stipules of L. aphaca were about as effective in photosynthesis as the foliaceous stipules of af and AF pea (Pisum sativum) plants. The L. aphaca stipules possessed all the cells/tissues that characterized photosynthetic leaves, stomata in epidermis, palisade and spongy mesophyll parenchyma, and vascular bundles. The tendrilled leaves were devoid of palisade tissue. The embryonic nodes bore stipule pairs of small size and compound leaves comprising of a pair of leaflets. Several nodes, above the embryonic nodes, bore fully developed stipule pairs but vestigial leaves (tendrils). It was concluded that stipules are the principal photosynthetic organs in L. aphaca.

Evaluation of flooding tolerance in cuttings of Populus clones used for forestation at the Paraná River Delta, Argentina

We analysed the responses to flooding of 14 poplar clones used for forestation at the Paraná River Delta, Argentina. Some are commercial clones planted in the area, and others belong to a poplar breeding program from the National Institute of Agricultural Technology (INTA) in Argentina. Potted plants of 60 cm high growing in a greenhouse were watered (control) or submerged in water 10 cm above soil level (flooding treatment) for 35 d. Flooding reduced growth in height and diameter (combined as the volume index), total leaf area, photosynthesis (measured as electron transport rate) and stomatal conductance. In flooded plants, the number and area of newly formed leaves were also reduced. In some clones, flooding accelerated the senescence of basal leaves and induced the development of adventitious roots. A hierarchical cluster analysis was performed to classify the responses of the clones to flooding. Evaluating flooding tolerance as less reduction in growth and retention of a higher leaf area under flooding conditions, three groups with different degrees of flooding tolerance were identified: clone Alton was the most tolerant; clones A129-60, A106-60, SIA 22-85, Catfish 2 and 150-82 showed intermediate tolerance; and the remainder of the clones had low flooding tolerance. This information will be useful to recommend clones to be planted in flood-prone areas, and to select parents to be used in breeding programs.

Photosynthesis of barley awns does not play a significant role in grain yield under terminal drought

In order to determine the importance of awn photosynthesis on grain yield under terminal drought, six two-rowed cultivars of barley representing high yielding commercial releases from 1961 to 2006 were studied in a glasshouse experiment at CSIRO, Western Australia. The cultivars were grown with and without watering from anthesis. Detailed measurements of plant water status, awn, flag and penultimate leaf photosynthetic rate were made from anthesis. At final harvest, biomass, yield and yield components were measured. Awn net photosynthesis rate (Pn) was lower than penultimate and flag leaf and decreased gradually after anthesis. The rate of decreasing Pn was rapid under terminal drought. There was no difference in awn Pn among cultivars under well-watered conditions, but under terminal drought the awn Pn of barley cultivars Baudin and Clipper decreased faster than Vlaming, Gairdner and Stirling. Surface area of awns in each cultivar was higher than the flag and penultimate leaf. Thus, total awn photosynthesis under both well-watered and terminal drought conditions was higher than flag leaf photosynthesis. In Vlaming, total awn photosynthesis was higher than penultimate leaf photosynthesis. Grain yield of the cultivars Baudin, Covette and Gairdner was affected by terminal drought, but grain yield did not correlate with awn total photosynthesis. Under well-watered conditions awn Pn had a significant negative correlation with ear weight. We suggest that under terminal drought, higher awn area does not lead to higher grain yield because sink size may be the factor limiting grain yield in barley.

Reduction of photosynthesis before midday depression occurred: leaf photosynthesis of Fagus crenata in a temperate forest in relation to canopy position and a number of days after rainfall

We investigated an effect of canopy position and a number of days after rainfall on reduction of photosynthetic rate in a Fagus crenata forest in summer 2008, during days when midday depression was not apparent. We compared in situ photosynthetic rate and photosynthetic rate that was calculated by photosynthetic light response curves measured in the morning. The ratio, in situ photosynthesis divided by the curve-estimated value, declined towards the end of each day for the upper leaves, but not for the lower leaves. Total photosynthesis was reduced only for the upper leaves by 12% during 5 days after the rainfall.

Energy Budget for the Cultured, Zooxanthellate Octocoral Sinularia flexibilis

The zooxanthellate octocoral Sinularia flexibilis is a producer of potential pharmaceutically important metabolites such as antimicrobial and cytotoxic substances. Controlled rearing of the coral, as an alternative for commercial exploitation of these compounds, requires the study of species-specific growth requirements. In this study, phototrophic vs. heterotrophic daily energy demands of S. flexibilis was investigated through light and Artemia feeding trials in the laboratory. Rate of photosynthetic oxygen by zooxanthellae in light (≈200 μmol quanta m⁻² s⁻¹) was measured for the coral colonies with and without feeding on Artemia nauplii. Respiratory oxygen was measured in the dark, again with and without Artemia nauplii. Photosynthesis-irradiance curve at light intensities of 0, 50, 100, 200, and 400 μmol quanta m⁻² s⁻¹ showed an increase in photosynthetic oxygen production up to a light intensity between 100 and 200 μmol quanta m⁻² s⁻¹. The photosynthesis to respiration ratio (P/R > 1) confirmed phototrophy of S. flexibilis. Both fed and non-fed colonies in the light showed high carbon contribution by zooxanthellae to animal (host) respiration values of 111-127%. Carbon energy equivalents allocated to the coral growth averaged 6-12% of total photosynthesis energy (mg C g⁻¹ buoyant weight day⁻¹ and about 0.02% of the total daily radiant energy. "Light utilization efficiency (ε)" estimated an average ε value of 75% 12 h⁻¹ for coral practical energetics. This study shows that besides a fundamental role of phototrophy vs. heterotrophy in daily energy budget of S. flexibilis, an efficient fraction of irradiance is converted to useable energy.

The structure, biological activity and biogeochemistry of cryoconite aggregates upon an Arctic valley glacier: Longyearbreen, Svalbard

AbstractGlacier surfaces support unique microbial food webs dominated by organic and inorganic debris called ‘cryoconite’. Observations from Longyearbreen, Spitsbergen, show how these aggregate particles can develop an internal structure following the cementation of mineral grains (mostly quartz and dolomite) by filamentous microorganisms. Measurements of carbon and dissolved O2show that these microorganisms, mostly cyanobacteria, promote significant rates of photosynthesis (average 17 μgC g−1d−1) which assist aggregate growth by increasing the biomass and producing glue-like extracellular polymeric substances. The primary production takes place not only upon the surface of the aggregates but also just beneath, due to the translucence of the quartz particles. However, since total photosynthesis is matched by respiration (average 19 μgC g−1d−1), primary production does not contribute directly to cryoconite accumulation upon the glacier surface. The microorganisms therefore influence the surface albedo most by cementing dark particles and organic debris together, rather than simply growing over it. Time-lapse photographs show that cryoconite is likely to reside upon the glacier for years as a result of this aggregation. These observations therefore show that a better understanding of the relationship between supraglacial debris and ablation upon glaciers requires an appreciation of the biological processes that take place during summer.

Performance physiologique du génotype autotétraploïde induit de Trigonella foenum-graecum L. comparée aux génotypes diploïdes

Polyploid plants are distinguished from diploids by an improved photosynthetic capacity related to the increase of the photosynthetic enzymes and pigments quantities. The aim of this work was to study the physiological performances accompanying the experimental polyploidisation of Trigonella foenum- graecum by comparing the induced autotetraploid, the diploid resulting from the treated plants and the parent. Total chlorophylls content, photosynthesis rate, transpiration rate and stomatal conductance were measured for each genotype. Results showed highly significant variations (p < 0.01) between the different genotypes for the studied physiological characters. PCA and UPGMA method structured the genotypes in two groups. The first group is formed by the autotetraploids and the second is consisted by the parents and the diploids resulting from the treated plants.

Photosynthetic Characteristics and Photoprotective Mechanisms in Highland Barley

As a local crop of Qinghai-Tibet Plateau, highland barley (Hordeum vulgare L.) has acclimated to the typical habitat with strong light and low O2 to CO2 ratio. Low O2 to CO2 ratio may have a great influence on photorespiration which plays an important role in protecting photosynthetic apparatus against photoinhibition. In this study, we hope to know whether photorespiration plays an important role in photoprotection of highland barley and what are the main photoprotective mechanisms of high-land barley. Gas exchange, fluorescence quenching kinetics and reflectance spectrum were investigated to explore the photosynthetic characteristic and allocation of excitated energy in two highland barley cultivars. Results showed that light saturation point of highland barley was about 1 000 μmol m-2 s-1. Photorespiration rate (Pr) increased with light intensity increasing while it did not change significantly above 500 μmol m-2 s-1. The percentage of photorespiration to total photosynthesis (Pr/Pm) declined gradually with the increase of light intensity. The efficiency of open centers of photosystem II (Fv'/Fm'), actual photosystem II efficiency (ΦPSII) and photochemical quenching (qP) all declined with the increase of light intensity; non-photochemical quenching increased with light intensity increasing, indicating that more and more excited energy dissipated as thermal dissipation. Spectrum analysis showed that the change of photochemical reflectance index (△ PRI) increased significantly when fully dark-adapted plants were suddenly exposed to light. On these bases, we concluded that photorespiration is not the main pathway for highland barley to relieve strong light stress; thermal dissipation relying on xanthophyll cycle may play an important role in dissipating excessive excited energy in highland barley.

A Satellite Approach to Estimate Land–Atmosphere $\hbox{CO}_{2}$ Exchange for Boreal and Arctic Biomes Using MODIS and AMSR-E

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Northern ecosystems are a major sink for atmospheric <formula formulatype="inline"><tex Notation="TeX">$\hbox{CO}_{2}$</tex> </formula> and contain much of the world's soil organic carbon (SOC) that is potentially reactive to near-term climate change. We introduce a simple terrestrial carbon flux (TCF) model driven by satellite remote sensing inputs from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Microwave Scanning Radiometer for EOS (AMSR-E) to estimate surface (<formula formulatype="inline"><tex Notation="TeX">$≪ 10$</tex></formula>-cm depth) SOC stocks, daily respiration, and net ecosystem carbon exchange (NEE). Soil temperature and moisture information from AMSR-E provide environmental constraints to soil heterotrophic respiration <formula formulatype="inline"><tex Notation="TeX">$(R_{h})$ </tex></formula>, while gross primary production (GPP) information from MODIS provides estimates of the total photosynthesis and autotrophic respiration. The model results were evaluated across a North American network of boreal forest, grassland, and tundra monitoring sites using alternative carbon measures derived from tower <formula formulatype="inline"><tex Notation="TeX">$\hbox{CO}_{2}$</tex></formula> flux measurements and BIOME-BGC model simulations. Root-mean-square-error (rmse) differences between TCF model estimates and tower observations were 1.2, 0.7, and 1.2 <formula formulatype="inline"><tex Notation="TeX">$\hbox{g} \cdot \hbox{C} \cdot \hbox{m}^{-2} \cdot \hbox{day}^{-1}$ </tex></formula> for GPP, ecosystem respiration <formula formulatype="inline"><tex Notation="TeX">$({\rm R}_{\rm tot})$</tex> </formula> and NEE, while mean residual differences were 43% of the rmse. Similar accuracies were observed for both TCF and BIOME-BGC model simulations relative to tower results. TCF-model-derived SOC was in general agreement with soil inventory data and indicates that the dominant SOC source for <formula formulatype="inline"><tex Notation="TeX">$R_{h}$</tex> </formula> has a mean residence time of less than five years, while <formula formulatype="inline"><tex Notation="TeX">$R_{h}$</tex> </formula> is approximately 43% and 55% of <formula formulatype="inline"><tex Notation="TeX">$R_{\rm tot}$</tex></formula> for respective summer and annual fluxes. An error sensitivity analysis determined that meaningful flux estimates could be derived under prevailing climatic conditions at the study locations, given documented error levels in the remote sensing inputs. </para>

Is ecosystem structure the target of concern in ecological effect assessments?

The species sensitivity distribution, a technique currently used to derive water-quality standards of chemicals, is associated with a set of inadequately tested assumptions. One of these assumptions is that ecosystem structure is as or more sensitive than ecosystem function, i.e., that structure is the target of concern. In this paper, we tested this assumption for a simple freshwater ecosystem exposed to different toxicants. Using an ecosystem model, we calculated no observed effect concentrations (NOECs) for ecosystem structure (ecosystem structure-NOECs) and function (ecosystem function-NOECs) for each of 1000 hypothetical toxicants. For 979 of these toxicants, the ecosystem structure-NOEC was lower than or equal to the ecosystem function-NOEC, indicating that the tested assumption can be considered valid. For 239 of these 979 toxicants, both NOECs were equal. For half of the 1000 toxicants, the structure of lower trophic levels (i.e., phytoplankton) appears to be more sensitive than the structure of higher trophic levels (i.e., fish). As such, ecosystem structure-NOECs are primarily determined by the sensitivity of the structure of lower trophic levels. In contrast, ecosystem functions associated with higher trophic levels (e.g., total ingestion by fish) are more sensitive than functions associated with lower trophic levels (e.g., total photosynthesis by phytoplankton) for 749 toxicants.