Impact of elevated CO2 on the metabolic diversity of microbial communities in N-limited grass swards

The impact of elevated atmospheric CO2 on qualitative and qua ntitative changes in rhizosphere carbon flow will have important consequences fo r nutrient cycling and storage in soil, through the effect on the activity, biom ass size and composition of soil microbial communities. We hypothesized that mic robial communities from the rhizosphere of Danthonia richardsonii, a n ative C3 Australian grass, growing at ambient and twice ambient CO2 a nd varying rates of low N application (20, 60, 180 kg N ha-1) will be different as a consequence of qualitative and quantitative change in rhizosphere carbon flow. We used the Biolog^TM system to construct sole carbon source utilisation profiles of these communities from the rhizosphere of D. richardsonii. Biolog^TM GN and MT plates, the latter to which more ecologically relevant root exudate carbon sources were added, were used to characterise the communities. Microbial communities from the rhizosphere of D. richardsonii grown for four years at twice ambient CO2 had significantly greater utilisation of all carbon sources except those with a low C:N ratio (neutral and acidic amino acids, amides, N-heterocycles, long chain aliphatic acids) than communities from plants grown at ambient CO2. This indicates a change in microbial community composition suggesting that under elevated CO2 compounds with a higher C:N ratio were exuded. Enumeration of microorganisms, using plate counts, indicated that there was a preferential stimulation of fungal growth at elevated CO2 and confirmed that bacterial metabolic activity (C utilisation rates), not population size (counts), were stimulated by additional C flow at elevated CO2. Nitrogen was an additional rate-limiting factor for microbial growth in soil and had a significant impact on the microbial response to elevated CO2. Microbial populations were higher in the rhizosphere of plants receiving the highest N application, but the communities receiving the lowest N application were most active. These results have important implications for carbon turnover and storage in soils where changes in soil microbial community structure and stimulation of the activity of microorganisms which prefer to grow on rhizodeposits may lead to a decrease in the composition of organic matter and result in an accumulation of soil carbon.     

Litter quality and decomposition in Danthonia richardsonii swards in response to CO2 and nitrogen supply over four years of growth

Litter quality parameters of Danthonia richardsonii grown under CO₂ concentrations of ≈ 359 & ≈ 719 μL L^{? 1} at three mineral N supply rates (2.2, 6.7 & 19.8 g m^{? 2} y^{? 1}) were determined. C:N ratio was increased in senesced leaf (enhancement ratios, R_e/c, of 1.25–1.67), surface litter (1.34–1.64) and root (1.13–1.30) by CO₂ enrichment. After 3 years of growth, nonstructural carbohydrate concentrations were reduced in senesced leaf lamina (avg. R_e/c= 0.84) but not in root in response to CO₂ enrichment. Cellulose concentrations increased slightly in senesced leaf (avg. R_e/c= 1.07) but not in root in response to CO₂ enrichment. Lignin and polyphenolic concentrations in senesced leaf and root were not changed by CO₂ enrichment. Decomposition, measured as cumulative respiration in standard conditions in vitro, was reduced in leaf litter grown under CO₂ enrichment. Root decomposition in vitro was lower in the material produced under CO₂ enrichment at the two higher rates of mineral N supply. Significant correlations between decomposition of leaf litter and initial %N, C:N ratio and lignin:N ratio were found. Decomposition in vivo, measured as carbon disappearance from the surface litter was not affected by CO₂ concentration. Arbuscular mycorrhizal infection was not changed by CO₂ enrichment. Microbial carbon was higher under CO₂ enrichment at the two higher rates of mineral N supply. Possible reasons for the lack of effect of changes in litter quality on in‐sward decomposition rates are discussed.     

Unique DNA repair properties of a xeroderma pigmentosum revertant.

A group A xeroderma pigmentosum revertant with normal sensitivity was created by chemical mutagenesis. It repaired (6-4) photoproducts normally but not pyrimidine dimers and had near normal levels of repair replication, sister chromatid exchange, and mutagenesis from UV light. The rate of UV-induced mutation in a shuttle vector, however, was as high as the rate in the parental xeroderma pigmentosum cell line.     

Kontrolle der Eiablage der Brachfliege (Leptohylemyia coarctata Fallén) als Voraussetzung für die Befallsprognose und Bekämpfung

Study of bean plants infected by tabacco mosaic virus and potato X virus was performed. Virus infection of bean plants induced the injury of structural state of photosynthetic apparatus, viz., the a/b chlorophyll ratio decreased and the main photosynthetic membrane lipid monogalactosyl diacylglycerol degradation took place with parallel accumulation of intermediate compound suggested to perform a signal function. Phospholipid and free sterol content increase pointed out on the changes of the membrane fluidity and permeability. Accumulation of sulphoquinovosyl diacylglycerol in infected plants evidences the probability of latter to play important roles in adaptive reactions of photosynthetic apparatus.     

Variationsstatistik und Ökologie bei rezenten Foraminiferen

The variability in the characteristics of three recentBolivina-species in different environments has been statistically investigated with 6600 measurements. Bolivina argentea develops all transitions between slender and less sculptured types in low-oxygen basinwaters or broader, costate tests in watermasses, which are richer in their oxygen contents. Similar trends are indicated byBolivina pseudobeyrichi. Bolivina spissa develops slender forms in colder water exceeding 1000 meters in depth; whereas it creates broader and more sculptured tests in more shallow warmer water between 300 and 500 meters in depth. There is a gradual change between these two extreme-types in this case too. With the application of variation-statistics it has been possible for the first time to establish these ecotypical modifications with a sufficient degree of certainty. A direct application of the results in paleoecology doesn't seem to be justified in spite of several similar trends obtained with fossil foraminifers. By comparing the fossil relations with lithological data and indications from other elements of the fauna it should be possible to develop with variation-statistics a new important tool for the ecological interpretation of fossil sediments.     

Hageman factor deficiency (factor XII)--hemorrhage or thrombosis?

Four generations of a kin with congenital Factor XII deficiency were examined for coagulation and fibrinolysis, with the homozygous female carrier of features with a Factor XII below 1% also revealing certain indications of a disturbed fibrinolysis. The other members of the family had to be evaluated as heterozygous ones, showing values of Factor XII between 40 and 60%. The findings are discussed by referring to data from literature.     

Global atmospheric change effects on terrestrial carbon sequestration: Exploration with a global C- and N-cycle model (CQUESTN)

A model of the interacting global carbon and nitrogen cycles (CQUESTN) is developed to explore the possible history of C-sequestration into the terrestrial biosphere in response to the global increases (past and possible future) in atmospheric CO₂ concentration, temperature and N-deposition. The model is based on published estimates of pre-industrial C and N pools and fluxes into vegetation, litter and soil compartments. It was found necessary to assign low estimates of N pools and fluxes to be compatible with the more firmly established C-cycle data. Net primary production was made responsive to phytomass N level, and to CO₂ and temperature deviation from preindustrial values with sensitivities covering the ranges in the literature. Biological N-fixation could be made either unresponsive to soil C:N ratio, or could act to tend to restore the preindustrial C:N of humus with different N-fixation intensities. As for all such simulation models, uncertainties in both data and functional relationships render it more useful for qualitative evaluation than for quantitative prediction.With the N-fixation response turned off, the historic CO₂ increase led to standard-model sequestration into terrestrial ecosystems in 1995AD of 1.8 Gt C yr^–1. With N-fixation restoring humus C:N strongly, C sequestration was 3 Gt yr^–1 in 1995. In both cases C:N of phytomass and litter increased with time and these increases were plausible when compared with experimental data on CO₂ effects. The temperature increase also caused net C sequestration in the model biosphere because decrease in soil organic matter was more than offset by the increase in phytomass deriving from the extra N mineralised. For temperature increase to reduce system C pool size, the biosphere leakiness to N would have to increase substantially with temperature. Assuming a constant N-loss coefficient, the historic temperature increase alone caused standard-model net C sequestration to be about 0.6 Gt C in 1995. Given the disparity of plant and microbial C:N, the modelled impact of anthropogenic N-deposition on C-sequestration depends substantially on whether the deposited N is initially taken up by plants or by soil microorganisms. Assuming the latter, standard-model net sequestration in 1995 was 0.2 Gt C in 1995 from the N-deposition effect alone. Combining the effects of the historic courses of CO₂, temperature and N-deposition, the standard-model gave C-sequestration of 3.5 Gt in 1995. This involved an assumed weak response of biological N-fixation to the increased carbon status of the ecosystem. For N-fixation to track ecosystem C-fixation in the long term however, more phosphorus must enter the biological cycle. New experimental evidence shows that plants in elevated CO₂ have the capacity to mobilize more phosphorus from so-called unavailable sources using mechanisms involving exudation of organic acids and phosphatases.     

Elevated atmospheric [CO2] promotes frost damage in evergreen tree seedlings

Growth under elevated [CO₂] promoted spring frost damage in field grown seedlings of snow gum ( Eucalyptus pauciflora Sieb. ex Spreng.), one of the most frost tolerant of eucalypts. Freezing began in the leaf midvein, consistent with it being a major site of frost damage under field conditions. The average ice nucleation temperature was higher in leaves grown under elevated [CO₂] (– 5·7 °C versus – 4·3 °C), consistent with the greater incidence of frost damage in these leaves (34% versus 68% of leaves damaged). These results have major implications for agriculture, forestry and vegetation dynamics, as an increase in frost susceptibility may reduce potential gains in productivity from CO₂ fertilization and may affect predictions of vegetation change based on increasing temperature.