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Drivers of bryophyte diversity allow implications for forest management with a focus on climate change

Understanding the major drivers of diversity in forests is crucial for ecologists, conservationists, and particularly forest managers. In most forested habitats, bryophytes are diverse and important primary producers. Here we report the first study of the relative importance of regional macroclimate as compared to local variables on abundance, species richness, and community composition of bryophytes growing in soil and in dead wood in a mountain temperate forest. Using PCA axes, we built predictor sets for macroclimate, microclimate, soil attributes, and dead wood availability. The explanatory power of each set was tested using variance partitioning. Abundance and species richness of soil bryophytes was best explained by microclimate, whereas the community composition did not distinctively differ between the environmental sets. In contrast, dead wood bryophyte abundance, species richness, and community composition was clearly driven by macroclimate. Among the single axes, the component represented best by soil moisture was the main driver for soil bryophyte abundance. In contrast, dead wood bryophyte abundance was mostly affected by components correlated with minimum global radiation and minimum temperatures as well as by the component represented by dead wood. The component represented by canopy openness was superior in explaining the community composition of both soil and dead wood bryophytes. We conclude that (1) dead wood amounts should be increased in closed stands to act as a buffer during climate changes, and (2) open canopy, which provides important habitats for soil-inhabiting bryophytes, should be provided by management with slow reforestation after natural or logging openings.     

Model studies on reactions occurring in oxidations of lignin with molecular oxygen in Alkaline Media

Basic reactions governing the degradation of lignin in oxidation with molecular oxygen are discussed emphasizing the radical (homolytic) or one-electron transfer-oxidations in the initial phase. The critical oxidation potentials (COP) according to Fieser were found to represent a useful measure for the ease of electron release from lignin-related phenolic models. At low alkalinity rough correlations were observed between the measured COPs and the initial oxygenation rates. The results obtained from quantum mechanical calculations of critical oxidation potentials are briefly discussed.The importance of phenoxy radicals and the hypothetical cyclohexadienone hydroperoxides as intermediates is outlined in view of such degradation reactions as oxidative side-chain eliminations, demethoxylations, and splitting of aromatic rings.Research performed at the Institute of Organic Chemistry, University of Vienna.     

Moderate nitrogen retention in temperate heath ecosystem after elevated CO2, drought and warming through 7 years

Nitrogen (N) dynamic is one of the main controlling factors of responses to climate change in N-limited terrestrial ecosystems, which rely on nutrient recycling and retention. In this study we investigate the N partitioning in ecosystem compartments of a grassland heath, and the impact of multiple climate change factors on long-term N retention after ¹⁵N pulse labelling. The impacts of elevated carbon dioxide (eCO₂), warming and drought and the treatments in combination on ecosystem N retention were investigated in a field scale manipulation experiment. A 6-year time-course was assessed by pulse-labelling with the stable N isotope ¹⁵N and by sampling after 1 day, 1 year and 6 years. After 6 years we observed that the total ecosystem retained 42% of the amended ¹⁵N across treatments (recovery of the amended ¹⁵N in the pool). The fate of the applied ¹⁵N was mainly stabilization in soil, with 36% ¹⁵N recovery in soil, while the plant compartment and microbial biomass each retained only 1%–2% of the added ¹⁵N. This suggests a moderate retention of N, for all treatments, as compared to similar long-term studies of forest ecosystems. A decreased ammonium and vegetation N pool combined with higher ¹⁵N retention in the soil under eCO₂ treatments suggests that eCO₂ promoted processes that immobilize N in soil, while warming counteracted this when combined with eCO₂. Drought treatments contrastingly increased the vegetation N pool. We conclude that as the organic soil layer has the main capacity for N storage in a temperate heathland-grassland, it is important for buffering nutrient availability and maintaining a resilient ecosystem. However, the full treatment combination of drought, warming and eCO₂ did not differ in ¹⁵N recovery from the control, suggesting unchanged long-term consequences of climate change on retention of pulse added N in this ecosystem.     

Use of a substrate/alliinase combination to generate antifungal activity in situ

Allicin, an active ingredient of garlic, possesses a range of antimicrobial properties. Unfortunately, certain properties of the compound, such as chemical instability and low miscibility with water, have hampered its practical use in the past. Here, we show that it is possible to use a binary system consisting of the plant enzyme alliinase and its substrate alliin to generate allicin, and hence antifungal activity, in situ. During application, the two inactive components generate compounds that inhibit growth and infection-related development of the rice blast fungus Magnaporthe grisea. It is therefore possible to "trigger" biological activity in a controlled, yet effective manner. Apart from circumventing many of the drawbacks of allicin, this binary system has additional important advantages, such as low toxicity of its individual components and selective activation. Importantly, alliinase is also able to use different substrates, therefore paving the way to a range of novel, binary antimicrobial systems with custom-made chemical and biochemical properties.     

Aluminium sulphate solubility in acid forest soils in Denmark

Ion leaching in 3 sandy spruce forest soils of different origin and pH was investigated in the laboratory. Zero-tension lysimeters containing undisturbed soil columns of varying soil depth were subjected to H₂SO₄ loadings for a period of 9 weeks. The analysis of the resulting leachate supports the hypothesis that Al-sulphate minerals may form in acidic soils when exposed to acid (H₂SO₄) deposition. In the B horizon of a glaciofluvial sandy soil (pH 4.2), both H⁺ and sulphate ions were retained to maintain 2pH + PSO₄ = 11.9 in the leachate solutions. This relation between H⁺ and sulphate activity may be due to an adsorption mechanism or a precipitation mechanism. The precipitation mechanism is favored by the good fit of leachate composition to the conditions for jurbanite [AlOHSO₄] formation from gibbsite [Al(OH)₃]. In the B horizon of a sandy till at pH 3.7, the Al in soil solution (0.5 mmol L^?1) was leached with sulphate. As the sulphate load was increased, some sulphate was retained. This may also be due to the dissolution and precipitation of an Al-sulphate mineral. The ion activity products of leachate solutions from the B horizon of this soil were close to the pK_s reported for jurbanite. The conditions for the possible existence and/or formation of Al-sulphate minerals in acidic soils are discussed.     

Lichen diversity in temperate montane forests is influenced by forest structure more than climate

Although the effect of forest management on lichens in temperate forests has been widely examined, little is known about the influence of management-related factors on their biodiversity relative to factors that cannot be altered by management. Here we determined whether forest structure or climate determines lichen diversity in the Bavarian Forest National Park in southeastern Germany, taking spatial variables into account. We investigated 517 single tree stems along 4 transects in 113 pre-stratified plots (8 m in diameter) in this montane forest. We grouped environmental variables into three sets: climate (macroclimate, non-manageable), forest structure (manageable), and space. The explanatory powers of these sets of variables for lichen diversity were compared using variance partitioning for the lichen community, species density, and threatened species density. The relationships of single characteristics of forest structure with lichen species diversity were analyzed using generalized linear models (GLM). Lichen diversity was better explained by stand structures than by climate. Spatial effects influenced the number of species per plot. Among the structural features, the availability of dead wood and sycamore maple as well as forest continuity were most important for the enhancement of lichen diversity. Open canopy structures affected the total diversity positively. Although the availability of large trees was not an influential factor in the GLM at the plot level, high diversity levels were generally associated with large stem diameters at the level of single stems. We provide recommendations for sustainable forest-management practices that aim at specifically enhancing lichen diversity in temperate areas experiencing low levels of air pollution.     

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