Accuracy of the AVHRR vegetation index as a predictor of biomass,primary productivity and net CO2 flux

The Normalized Difference Vegetation Index (NDVI) or greenness index, based on the Advanced Very High Resolution Radiometer (AVHRR) aboard the NOAA-7 satellite, has been widely interpreted as a measure of regional to global vegetation patterns. This study provides the first rigorous, quantitative evaluation of global relationships between the NDVI and geographically representative vegetation data-bases, including field metabolic measurements and carbon-balance results from global simulation models. Geographic reliability of the NDVI is judged by comparing NDVI values for different surface types with a general global trend and by statistical analysis of relationships to biomass amounts, net and gross primary productivity, and actual evapotranspiration. NDVI data appear to be relatively reliable predictors of primary productivity except in areas of complex terrain, for seasonal values at high latitudes, and in extreme deserts. The strength of the NDVI-productivity relationship seems comparable to that of earlier climate-based productivity models. Little consistent relationship was found, across different vegetation types, between NDVI and biomass amounts or net biospheric CO₂ flux.Abbreviations AET= Actual Evapotranspiration - AVHRR= Advanced Very High Resolution Radiometer - GPP= Gross Primary Production - GVI= Global Vegetation Index - NDVI= Normalized Difference Vegetation Index - NPP= Net Primary Production     

Nitrogen and Carbon Concentrations, and Stable Isotope Ratios in Mediterranean Shrubs Growing in the Proximity of a CO2 spring

Seasonal changes in foliage nitrogen (N) and carbon (C) concentrations and δ¹⁵N and δ¹³C ratios were monitored during a year in Erica arborea, Myrtus communis and Juniperus communis co-occurring at a natural CO₂ spring (elevated [CO₂], about 700 μmol mol⁻¹) and at a nearby control site (ambient [CO₂], 360 μmol mol⁻¹) in a Mediterranean environment. Leaf N concentration was lower in elevated [CO₂] than in ambient [CO₂] for M. communis, higher for J. communis, and dependent on the season for E. arborea. Leaf C concentration was negatively affected by atmospheric CO₂ enrichment, regardless of the species. C/N ratio varied concomitantly to N. Leaves in elevated [CO₂] showed lower δ¹³C, and therefore likely lower water use efficiencies than leaves at the control site, regardless of the species, suggesting substantial photosynthetic acclimation under long-term CO₂-enriched atmosphere. Leaves of E. arborea showed lower values of δ¹⁵N under elevated [CO₂], but this was not the case of M. communis and J. communis foliage. The use of the resources and leaf chemical composition are affected by elevated [CO₂], but such an effect varies during the year, and is species-dependent. The seasonal dependency and species specificity suggest that plants are able to exploit different available water and N resources within Mediterranean sites. This revised version was published online in July 2006 with corrections to the Cover Date.     

The fate of nitrogen from winter-frozen rapeseed leaves: mineralization,fluxes to the environment and uptake by rapeseed crop in spring

For environmental purposes, very early sowing of winter rapeseed may reduce winter nitrate leaching thanks to the high N uptake capacities of rapeseed in autumn. However, freezing could lead to high losses of leaf nitrogen, amounting to more than 100 kg N ha^-1 (Dejoux et al., 1999). Here we investigated the agronomic and environmental consequences of the decomposition of fallen leaves, based on field and laboratory studies with ¹⁵N labeled leaves (C:N=9). The potential kinetics of decomposition of leaves were measured by incubation in the laboratory. In the field, all leaves were removed at beginning of winter and replaced by labeled leaves, artificially frozen at −15°C , which were laid on the soil surface. Compared on a thermal time basis, decomposition proceeded as quickly in the field as in the incubations and was complete after 116 normalized days at 15 °C. The proportion of ¹⁵N derived from labeled leaves, absorbed again by the rape plants, was 28% at flowering and 24% at harvest. This high N recovery is assumed to result from the synchronization of leaves decomposition and active N absorption by rape in spring. Leaf N mineralization did not increase soil N mineral content at flowering or at harvest, but we observed a 40% loss of ¹⁵N. As no leaching was simulated, this loss was supposed to be gaseous. Such a high percentage could be explained by the fact that the decomposing leaves lay on the soil surface, and by climatic conditions conducive to such emissions. For environmental purposes, the quantity and nature of these gaseous N emissions have to be studied for other climatic conditions and types of leaves. As a proportion of N is reabsorbed, N fertilizer application rates could be reduced accordingly. This revised version was published online in August 2006 with corrections to the Cover Date.     

Observed change of the standardized precipitation index, its potential cause and implications to future climate change in the Amazon region

Observations show that the standard precipitation index (SPI) over the southern Amazon region decreased in the period of 1970-1999 by 0.32 per decade, indicating an increase in dry conditions. Simulations of constant pre-industrial climate with recent climate models indicate a low probability (p=0%) that the trends are due to internal climate variability. When the 23 models are forced with either anthropogenic factors or both anthropogenic and external natural factors, approximately 13% of sampled 30-year SPI trends from the models are found to be within the range of the observed SPI trend at 95% confidence level. This suggests a possibility of anthropogenic and external forcing of climate change in the southern Amazon. On average, the models project no changes in the frequency of occurrence of low SPI values in the future; however, those models which produce more realistic SPI climatology, variability and trend over the period 1970-1999 show more of a tendency towards more negative values of SPI in the future. The analysis presented here suggests a potential anthropogenic influence on Amazon drying, which warrants future, more in-depth, study.     

Heavy metals in the Rosetta estuary of the Nile and the adjoining Mediterranean waters: evidence of removal of dissolved heavy metals from waters as a result of possible binding to suspended matter

The Rosetta estuary was partially separated from the Rosetta branch of the Nile by Edfina Barrage, which controls the Nile discharge into the Mediterranean Sea. The study area covers the Rosetta estuary (lotic environment) and the adjoining seawaters (lentic environment) to investigate the local and seasonal distribution of dissolved and particulate copper and zinc, as well as dissolved cadmium in this estuary and to illustrate its influence on the distribution of these metal forms in the inshore seawaters. Besides, emphasis on the removal of dissolved heavy metals from waters by their adsorption onto suspended matter (SM) was also considered. Contrary to particulate copper (PCu), the vertical values of dissolved copper (DCu) decreased generally with depth. Planktonic scavenging and regeneration processes might determine the vertical profiles of the copper forms. The copper data suggest that the surface sources of DCu exceeded the bottom sources, contrary to the sources of PCu. The markedly high and maximum seasonal averages of DCu in the estuary and inshore seawater in July inspite of the high uptake in summer possibly reflect higher amounts of humic materials. The lowest seasonal average value of DCu in the inshore seawater in January suggests removal of copper in presence of maximum value of SM during highest discharge. The highest regional average of DCu at the estuarine mouth coincided with desorption process during mixing of the fresh and salt waters. The vertical values of dissolved zinc (DZn) and particulate zinc (PZn) showed irregular variations and their high concentrations in the surface of the estuarine and inshore seawater indicate possible land-based sources. The high bottom DZn values, however, resulted from its contribution from the interstitial water of the sediments. The data suggest that the surface sources of DZn exceeded the bottom sources and PZn showed the opposite trend in the open sea area. In the estuary, the maximum seasonal average value of DZn accompanied by the lowest seasonal average of PZn in April inspite of the high uptake in spring suggest that desorption was the dominant process. The minimum regional averages of both zinc forms at the estuarine opening and the highest average of PZn near Edfina Barage are correlated with the amounts of SM, which decreased toward the estuarine mouth. The vertical values of dissolved cadmium (DCd) were much lower in the estuary than the other metals. They showed in both environments irregular variations with depth. The bottom maximum value of DCd can be attributed mainly to contamination from the sediments. There was a distinct seasonal variation of DCd. The minimum seasonal average value of DCd in the estuary in April seems to be caused by its specific binding to living plankton found in abundance. The minimum regional average of DCd value was found at the estuarine mouth. The decrease in Cd concentration due to removal from dissolved state is most pronounced in the early stage of mixing. The correlation coefficients of DCd were positive with salinity and negative with SM, indicating that Cd increased seaward. Statistical correlation between Cd and Zn concludes that the factors affecting their distribution are generally the same.     

CO2 environment,microclimate and photosynthetic characteristics of the moss Hylocomium splendens in a subarctic habitat

Summary In order to document the natural CO₂ environment of the moss Hylocomium splendens, and ascertain whether or not the moss was adapted to this, and its interactions with other microenvironmental factors, two studies were carried out. Firstly, the seasonal variations of CO₂ concentration, photosynthetically active radiation (PAR), tissue water content and temperature were measured in the natural microenvironment of H. splendens in a subarctic forest during the summer period (July–September). Secondly, the photosynthetic responses of the species to controlled CO₂ concentrations, PAR, temperature, and hydration were measured in the laboratory. CO₂ concentrations around the upper parts of the plant, when PAR was above the compensation point (30 mol m^–2 s^–1), were mostly between 400 and 450 ppm. They occasionally increased up to 1143 ppm for short periods. PAR flux densities below saturating light levels for photosynthesis (100 mol m^–2 s^–1), occurred during 65% (July), 76% (August) and 96% (September) of the hours of the summer period. The temperature optimum of photosynthesis was 20° C: this temperature coincided with PAR above the compensation point during 5%, 6% and 0% of the time in July, August and September, respectively. Optimal hydration of tissues was infrequent. Hence PAR, temperature and water limit CO₂ uptake for most of the growing season. Our data suggest that the higher than normal ambient CO₂ concentration in the immediate environment of the plant counteracts some of the limitations in PAR supply that it experiences in its habitat. This species already experiences concentrations of atmospheric CO₂ predicted to occur over the next 50 years.     

Reduced N cycling in response to elevated CO2, warming,and drought in a Danish heathland: Synthesizing results of the CLIMAITE project after two years of treatments

Field‐scale experiments simulating realistic future climate scenarios are important tools for investigating the effects of current and future climate changes on ecosystem functioning and biogeochemical cycling. We exposed a seminatural Danish heathland ecosystem to elevated atmospheric carbon dioxide (CO₂), warming, and extended summer drought in all combinations. Here, we report on the short‐term responses of the nitrogen (N) cycle after 2 years of treatments. Elevated CO₂ significantly affected aboveground stoichiometry by increasing the carbon to nitrogen (C/N) ratios in the leaves of both co‐dominant species (Calluna vulgaris and Deschampsia flexuosa), as well as the C/N ratios of Calluna flowers and by reducing the N concentration of Deschampsia litter. Belowground, elevated CO₂ had only minor effects, whereas warming increased N turnover, as indicated by increased rates of microbial NH₄⁺ consumption, gross mineralization, potential nitrification, denitrification and N₂O emissions. Drought reduced belowground gross N mineralization and decreased fauna N mass and fauna N mineralization. Leaching was unaffected by treatments but was significantly higher across all treatments in the second year than in the much drier first year indicating that ecosystem N loss is highly sensitive to changes and variability in amount and timing of precipitation. Interactions between treatments were common and although some synergistic effects were observed, antagonism dominated the interactive responses in treatment combinations, i.e. responses were smaller in combinations than in single treatments. Nonetheless, increased C/N ratios of photosynthetic tissue in response to elevated CO₂, as well as drought‐induced decreases in litter N production and fauna N mineralization prevailed in the full treatment combination. Overall, the simulated future climate scenario therefore lead to reduced N turnover, which could act to reduce the potential growth response of plants to elevated atmospheric CO₂ concentration.     

Responses of fungal root colonization,plant cover and leaf nutrients to long‐term exposure to elevated atmospheric CO2 and warming in a subarctic birch forest understory

Responses of the mycorrhizal fungal community in terrestrial ecosystems to global change factors are not well understood. However, virtually all land plants form symbiotic associations with mycorrhizal fungi, with approximately 20% of the plants' net primary production transported down to the fungal symbionts. In this study, we investigated how ericoid mycorrhiza (ErM), fine endophytes (FE) and dark septate endophytes (DSE) in roots responded to elevated atmospheric CO₂ concentrations and warming in the dwarf shrub understory of a birch forest in the subarctic region of northern Sweden. To place the belowground results into an ecosystem context we also investigated how plant cover and nutrient concentrations in leaves responded to elevated atmospheric CO₂ concentrations and warming. The ErM colonization in ericaceous dwarf shrubs increased under elevated atmospheric CO₂ concentrations, but did not respond to warming following 6 years of treatment. This suggests that the higher ErM colonization under elevated CO₂ might be due to increased transport of carbon belowground to acquire limiting resources such as N, which was diluted in leaves of ericaceous plants under enhanced CO₂. The elevated CO₂ did not affect total plant cover but the plant cover was increased under warming, which might be due to increased N availability in soil. FE colonization in grass roots decreased under enhanced CO₂ and under warming, which might be due to increased root growth, to which the FE fungi could not keep up, resulting in proportionally lower colonization. However, no responses in aboveground cover of Deschampsia flexuosa were seen. DSE hyphal colonization in grass roots significantly increased under warmer conditions, but did not respond to elevated CO₂. This complex set of responses by mycorrhizal and other root‐associated fungi to global change factors of all the fungal types studied could have broad implications for plant community structure and biogeochemistry of subarctic ecosystems.     

Responses of the biting midge Culicoides impunctatus to acetone, CO2 and 1-octen-3-ol in a wind tunnel

Responses of host-seeking female Culicoides impunctatus (Goetghebuer) (Diptera: Ceratopogonidae) to acetone, carbon dioxide and 1-octen-3-ol were measured in a wind tunnel. Carbon dioxide, presented as a filamentous plume, increased upwind flight in a dose-dependent manner, up to 0.09% concentration. A homogenous CO2 plume elicited similar upwind responses at concentrations up to 0.09%, whereas higher plume concentrations (> 0.1%) induced erratic responses with a suppression of upwind flight. Bovine equivalent concentrations of acetone (1.5 x 10(-6)g/l) and 1-octen-3-ol (1.3 x 10(-8)g/) failed to induce any significant upwind response when tested alone. In the presence of CO2, however, 1-octen-3-ol showed highly significant increases in upwind responses at concentrations of 1.3 x 10(-1) - 10(-8)g/l. Mixtures of CO2+ acetone also enhanced upwind flight at 1.5 x 10(-9)g/l. High tunnel concentrations of both 1-octen-3-ol and acetone inhibited upwind responses. These findings are discussed in relation to host finding by C. impunctatus and known mechanisms by which upwind flight is initiated and arrested at high odour concentrations.     

The stunting effect of a high CO2 ocean on calcification and development in sea urchin larvae,a synthesis from the tropics to the poles

The stunting effect of ocean acidification on development of calcifying invertebrate larvae has emerged as a significant effect of global change. We assessed the arm growth response of sea urchin echinoplutei, here used as a proxy of larval calcification, to increased seawater acidity/pCO₂ and decreased carbonate mineral saturation in a global synthesis of data from 15 species. Phylogenetic relatedness did not influence the observed patterns. Regardless of habitat or latitude, ocean acidification impedes larval growth with a negative relationship between arm length and increased acidity/pCO₂ and decreased carbonate mineral saturation. In multiple linear regression models incorporating these highly correlated parameters, pCO₂ exerted the greatest influence on decreased arm growth in the global dataset and also in the data subsets for polar and subtidal species. Thus, reduced growth appears largely driven by organism hypercapnia. For tropical species, decreased carbonate mineral saturation was most important. No single parameter played a dominant role in arm size reduction in the temperate species. For intertidal species, the models were equivocal. Levels of acidification causing a significant (approx. 10–20+%) reduction in arm growth varied between species. In 13 species, reduction in length of arms and supporting skeletal rods was evident in larvae reared in near-future (pCO₂ 800+ µatm) conditions, whereas greater acidification (pCO₂ 1000+ µatm) reduced growth in all species. Although multi-stressor studies are few, when temperature is added to the stressor mix, near-future warming can reduce the negative effect of acidification on larval growth. Broadly speaking, responses of larvae from across world regions showed similar trends despite disparate phylogeny, environments and ecology. Larval success may be the bottleneck for species success with flow-on effects for sea urchin populations and marine ecosystems.     

Maltose fermentation to acetate,CO2 and H2 in the anaerobic hyperthermophilic archaeon Pyrococcus furiosus: evidence for the operation of a novel sugar fermentation pathway

The hyperthermophilic anaerobe Pyrococcus furiosus was grown on maltose as energy and carbon source. During growth 1 mol maltose was fermented to 3–4 mol acetate, 6–7 mol H₂ and 3–4 mol CO₂. The presence of the following enzyme activities in cell extracts of maltose-grown P. furiosus indicate that the sugar is degraded to pyruvate and H₂ by a modified non-phosphorylated Entner-Doudoroff-pathway (the values given in brackets are specific enzyme activities at 100 °C): Glucose: methyl viologen oxidoreductase (0.03 U/mg); 2-keto-3-deoxy-gluconate aldolase (0.03 U/mg); glyceraldehyde: benzyl viologen oxidoreductase (2.6 U/mg), glycerate kinase (2-phosphoglycerate forming) (0.48 U/mg), enolase (10.4 U/mg), pyruvate kinase (1.4 U/mg). Hexokinase, glucose-6-phosphate dehydrogenase, 2-keto-3-deoxy-6-phosphogluconate aldolase and phosphofructokinase could not be detected. Further conversion of pyruvate to acetate, CO₂ and H₂ involves pyruvate: ferredoxin oxidoreductase (0.4 U/mg; T=60°C with Clostridium pasteurianum ferredoxin as electron acceptor), hydrogen: methyl viologen ixodoreductase (3.4 U/mg) and ADP-dependent acetyl-CoA synthetase (1.9 U/mg). Phosphate acetyl transferase and acetate kinase could not be detected. The ADP-dependent acetyl-CoA synthetase catalyzes ATP synthesis via the mechanism of substrate level phosphorylation and apparently constitutes the only ATP conserving site during maltose catabolism in P. furiosus.This novel pathway of maltose fermentation to acetate, CO₂ and H₂ in the anaerobic archaeon P. furiosus may represent a phylogenetically ancient pathway of sugar fermentation.Non-standard abbreviations DTE dithioerythritol - MV methyl viologen - BV benzyl viologen - CHES cyclohexylamino-ethane sulfonic acid - ABTS 2,2-Azino-di-(3-ethylbenzthiazoliumsulfonate)     

Linear analysis applied to the comparative study of the I-D-P phase of chlorophyll fluorescence as induced by actinic PS-II light,PS-I light and changes in CO2-concentration

The investigation of the kinetics of chlorophyll-fluorescence under continuous background light enables the application of linearizing conditions. This approach, which provides a quantitative evaluation by means of curve-fitting routines, is applied to the investigation of the linear kinetics of the I-D-P phase. Using changes in PS II-light, PS I-light and in CO₂-concentration as input signals showed that a pool at the acceptor side of PS I, in addition to the plastoquinone pool, plays an essential role in the generation of the dip. The occurrence of the dip is related to the sign of the faster one of the two components related to the I-D and the D-P phase. This sign can be inverted by the ratio of PS I and PS II light. However, model calculations show that the change of this sign does not allow a decision which one of the two components is related to which one of the two pools. The dependence of the sign of the faster component on light conditions can generate different types of I-D-P transitions, namely nearly monophasic increases, sigmoid responses or dips. As these phenomena are already created by the linear responses, non-linear effects or additional loops between PS II and PS I are not required for the explanation of the basic features.Abbreviations ETC electron transfer chain - F fluorescence - PQ plastoquinone pool - PS Photosystem - X pool at the acceptor side of PS I     

The action of a range of supplementary ultraviolet (UV) wavelengths on photosynthesis in Brassica napus L. in the natural environment: effects on PS II,CO2 assimilation and level of chloroplast proteins

The effects of different wavebands of UV radiation on photosynthesis and the expression and abundance of photosynthetic proteins in oilseed rape (Brassica napus L. cv. Rebel) were investigated. Plants were grown outdoors under natural radiation (52° N, 0° E) supplemented with six wavebands of UV radiation (0.4 Wm⁻²) between 313 nm and 356 nm. A control treatment was centred at 343 nm. Exposure to supplementary UV-A radiation (320–400 nm) had no significant effects, however UV-B radiation, centred at 313 nm, caused a marked reduction in photosynthesis. This decrease was related to a reduction in the initial carboxylation velocity of Rubisco which was further correlated with a large reduction in the expression and abundance of both large and small subunits of Rubisco. These results indicate a molecular mechanism behind UV-B induced reductions in photosynthesis per unit area in plants grown under field conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Binding characteristics and sensitivity to endogenous dopamine of [11C]-(+)-PHNO, a new agonist radiotracer for imaging the high-affinity state of D2 receptors in vivo using positron emission tomography

[11C]-(+)-PHNO (4-propyl-9-hydroxynaphthoxazine) is a new agonist radioligand that provides a unique opportunity to measure the high-affinity states of the D2 receptors (D2-high) using positron emission tomography (PET). Here we report on the distribution, displaceablity, specificity and modeling of [11C]-(+)-PHNO and compare it with the well characterized antagonist D2 radioligand, [11C]raclopride, in cat. [11C]-(+)-PHNO displayed high uptake in striatum with a mean striatal binding potential (BP) of 3.95 +/- 0.85. Pre-treatment with specific D1 (SCH23390), D2 (raclopride, haloperidol) and D3 receptor (SB-277011) antagonists indicated that [11C]-(+)-PHNO binding in striatum is specific to D2 receptors. Within-subject comparisons showed that [11C]-(+)-PHNO BP in striatum was almost 2.5-fold higher than that measured with [11C]-(-)-NPA ([11C]-(-)-N-propyl-norapomorphine). Comparison of the dose-effect of amphetamine (0.1, 0.5 and 2 mg/kg; i.v.) showed that [11C]-(+)-PHNO was more sensitive to the dopamine releasing effect of amphetamine than [11C]raclopride. Amphetamine induced up to 83 +/- 4% inhibition of [11C]-(+)-PHNO BP and only up to 56 +/- 8% inhibition of [11C]raclopride BP. Scatchard analyses of [11C]-(+)-PHNO and [11C]raclopride bindings in two cats showed that the Bmax obtained with the agonist (29.6 and 32.9 pmol/mL) equalled that obtained with the antagonist (30.6 and 33.4 pmol/mL). The high penetration of [11C]-(+)-PHNO in brain, its high signal-to-noise ratio, its favorable in vivo kinetics and its high sensitivity to amphetamine shows that [11C]-(+)-PHNO has highly suitable characteristics for probing the D2-high with PET.     

Aggregates formed as a result of the expression of yeast <Emphasis Type="Italic">Met2</Emphasis> gene in transgenic tobacco plants,stimulate the production of stress-protective metabolites and increased the plants tolerance to heat stress

Methionine biosynthesis has taken different evolutionary pathways in bacteria, fungi and plants. To gain insight into these differences and to search for new ways of manipulating methionine biosynthesis in plants, the yeast (Saccharomyces cerevisiae) Met2 gene and the bacteria (Leptospira meyeri) MetX gene, both encoding homoserine O-acetyltransferase, were expressed in tobacco plants. We found protein aggregates in extracts of these transgenic plants, whose levels were much higher in plants grown at 35 °C than at 25 °C. It appears that the yeast and the bacterial proteins are heat labile and tend to change their intracellular conformation. These conformational changes of the transgenic proteins were more prominent at high temperature and most probably triggered aggregation of the yeast and the bacterial proteins. Moreover, plants expressing the yeast gene that grew at 35 °C over-accumulated stress-associated metabolites, such as phenolic compounds, including tannins, as well as the amino acid arginine. In addition, the transgenic plants expressing high levels of the foreign genes show growth retardation, which further suggests that, these plants suffer from internal stress. The changes in protein conformation and the consequent triggering of stress response may account for the ability of these transgenic plants to tolerate more extreme heat stress (60 °C) than the wild-type plants.