•Reduction of maximum foam volume linear with carbon content of reductant added.•O2 evolution suppressed in feeds with 3 wt% reductant addition.•Fe, Mn, Cr and Ce oxidation states explored by 57Fe ...Mössbauer and XANES during melting.•Highest theoretical O2 contribution from change in Mn oxidation state.
Foaming during vitrification of radioactive waste in Joule-Heated Ceramic Melters (JHCM) is exacerbated by trapping of evolving gases, such as CO2, NOx and O2, beneath a viscous reaction layer. Foaming restricts heat transfer during melting. Sucrose is employed as the baseline additive at the Hanford site in Washington State, USA to reduce foaming. Alternative carbon-based reductant additives were explored in simulated, inactive Hanford high-iron HLW-NG-Fe2 feeds, for both their effect on foaming and to give insight to the behaviour of multivalent species in glass melts under different redox conditions. Graphite, coke (93% C), formic acid and HEDTA additives were compared with sucrose, and a feed with no additive. Graphite and coke additions proved most effective in reducing the maximum foam volume by 51 ± 3% and 54 ± 2%, respectively, compared with 24 ± 5% for sucrose. Lower foaming could result in more efficient vitrification in JHCMs. Reductants also affected redox ratios in the multivalent species present in the feed. The order of reduction, Mn3+/Mn2+ > Cr6+/Cr3+ > Ce3+/Ce4+ > Fe3+/Fe2+ was as predicted on the basis of their redox potentials. There is less reduction overall, particularly in the Fe3+ → Fe2+, than predicted by the calculations, attributed to the oxygenated atmosphere of the experiments.
Key message
Enhanced levels of CO
2
affected both the nutrition and morphology of both species. The effect of interspecific competition was dependent on the species identity but not on the CO
2
...level.
The interest in adaptive forest strategies to overcome predicted scenarios of climate change is increasing worldwide. An example of these strategies is the introduction of native species into mono-specific plantations. However, to fully consider this option/strategy, a higher understanding of the responses of forest tree species to concurrent biotic and abiotic factors is needed. The aim of the present study was to assess nutritional and morphological adjustments of individuals of European beech (
Fagus sylvatica
L.) and Norway spruce
Picea
abies
(L.) Karst growing at enhanced levels of CO
2
and with different proportions of con-specific individuals in its vicinity. Individuals that grew at elevated CO
2
levels showed higher values of relative growth rate (RGR), total twig dry biomass and root biomass, and lower values of leaf area ratio, leaf N and Mg concentrations and soil nutrient concentrations. Individuals of Norway spruce growing in the vicinity of high proportions of European beech showed a reduction in the allocation of biomass to foliar tissue, and lower values of RGR and root biomass. European beech, by contrast, showed a limited response to Norway spruce presence and higher capacity in the exploitation of space both above- and below-ground. In conclusion, the lower response of European beech to both environmental factors suggests that the introduction of European beech into Norway spruce stands could be a feasible option in current forest transition strategies.
This study focused on the comparison of two contrasting forest regeneration types and their susceptibility to drought stress. Transpiration and biomass production were studied on young sessile oak ...trees Quercus petraea (Matt.) Liebl. regenerated as sprouts and seedlings, and grown in a coppice experimental site in the Czech Republic. Biomass production was estimated using destructive methods, while transpiration was derived from sap flow measurements and assessed according to the plant biometry and microclimatic conditions. Sprouts were characterized by a significantly higher diameter, height, leaf area and above-ground biomass and by a lower wood density as compared with seedlings of the same age. Moreover, the sap flow of sprouts was higher than that of seedlings, which was explained by the plant dimension. Transpiration, expressed as sap flow scaled to plant leaf area, did not differ between seedlings and sprouts when soil water was not limiting. However, during drought periods, when soil water potential dropped below -1.4 MPa, sprouts transpired significantly more than seedlings. Our results confirm that sprouts have access to a larger water pool via the old stump root system and are able to draw more water under drought. Moreover, sprouts seemed to be less susceptible to water limitations than seedlings of similar age. Less influence of drought on sprouts may partially explain their higher above-ground biomass production. Based on our results, coppice could be an appropriate management system to be adopted in sites characterized by frequent or extreme drought periods.
Elevated CO2 affects physiological, anatomical and morphological properties of plants, both directly and indirectly. Higher carbon gain corresponds with higher transpiration demands. Juvenile trees ...of Picea abies and Fagus sylvatica were planted under ambient (385 μmol CO2 mol-1) and elevated (700 μmol CO2 mol-1) concentration in semi-opened glass domes with adjustable windows. We have evaluated biomass allocation and transpiration of the studied species. No effect of elevated CO2 on Norway spruce was observed. European beech showed remarkable increase of root biomass and transpiration in elevated CO2. Reduction of the transpiration caused by the elevated CO2 was not observed.
The effect of different durations of the incubation wetting period on the infection of Dendrobium flowers by two serious pathogens—Alternaria alternata (Fr.) Keissl. 1912 and Curvularia eragrostidis ...(Henn.) J.A. Mey. 1959—was investigated. Cut orchid flowers of the genus Dendrobium were used for the inoculation. The courses of symptom development and mycelium growth were determined. The results indicate that the infection and the subsequent development of disease on the flowers occur rapidly even if the conditions favourable for pathogen germination on the plant tissues persist for only 2 h. However, the proportion of infected flowers was significantly higher after a longer incubation period (6 h). The mycelium growth of the pathogen was also significantly influenced by the length of the incubation period.
Long-term water use efficiency (WUE) describes water utilization by plants on different levels of biosphere organization. We have performed a WUE evaluation in two young spruce forests of different ...stand densities, sparse (FS) and dense (FD) from 1998 to 2003. WUE in this study was calculated as a ratio of total aboveground biomass increment (TB) and transpiration (T) on annual time scale. Two approaches were used for total biomass evaluation: i) TBI - from stem diameter at the breast height (DBH) increment dynamic and its allometry with TB, and ii) TBII - as a sum of leaf, branch and stem biomass. Growth dynamic of branch biomass was related to tree height increment and leaf biomass to the leaf area index. TBI was found significantly higher than TBII in FD. However, WUE was not significantly different among the stands and approaches. WUE with TBI (WUEI) used were 4.30 g/L and 4.68 g/L in FS and FD, WUE with use TBII (WUEII) 4.17 g/L and 4.14 g/L in FS and FD, respectively. WUE of FS and FD was similar due to the identical climate conditions, stand age and genetic origin of the trees. We can recommend TBI approach due to lower instrumentation demands and accurate results in the same time.
Coppice forest is an alternative to high forest mainly aimed at the production of firewood with a short rotation period. A new interest in this silvicultural system has arisen with the demand for ...renewable energy resources. Exploiting the existing root system of the stump, sprouts are advantaged over plants of seed origin, and this advantage could induce changes at the level of a photosynthetic apparatus, especially in young plants. This paper presents a comparison of the photosynthetic ability of young sprouts, young seedlings and mature trees of sessile oak (Quercus petraea (Matt.) Liebl.) growing in a forest stand managed as a coppice-with-standards in the southeast of the Czech Republic. The basic photosynthetic characteristics and transpiration rate at the leaf level were determined using gas-exchange measurement techniques. Data taken in non-limiting conditions were compared with those obtained under limiting soil moisture. The results revealed no differences between the measured parameters of sprouts, seedlings and old trees in non-limiting conditions. Contrastingly, sprouts had the highest photosynthetic capacity and transpiration during drought due to their ability to maintain a higher stomatal conductance as compared with seedlings and old trees. This suggests a better drought tolerance of sprouts compared to seedlings.
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