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1663. Plant diversity decrease and directional species turnover induced by shifting overstory dominance in the oak-hornbeam forest reserve over 50 yearsJanez Kermavnar, Lado Kutnar, 2025, izvirni znanstveni članek Povzetek: Due to a long history of various anthropogenic pressures, lowland forest reserves are scarce and lack historical datasets suitable for analysing long-term vegetation trends. This study investigated changes in plant diversity and species composition in the long-untouched Krakovo forest reserve, the only preserved remnant of lowland oak-hornbeam forests with primary status in Slovenia. The original vegetation sampling was conducted in the 1970s. In 2024, we resurveyed 30 semi-permanent plots capturing the natural variation in soil moisture gradient. We found the decline of Quercus robur in the upper tree layer and the expansion of shade-casting tree Carpinus betulus in the lower tree layer, a pattern mainly attributed to the lowering of the groundwater table. This shift in overstory dominance manifested in a directional change of herb-layer composition associated with high species turnover (61 %). The deterioration of light conditions at the forest floor resulted in significant decrease of species richness, accompanied by the process of taxonomic homogenization. The analysis of Ellenberg indicator values revealed a reorganization of the plant communities in response to the increasingly shaded and cooler understory environment, benefitting a limited number of perennial herbs preferring closed canopies. The change towards nutrient-demanding species was probably caused by improved litter quality, nitrogen input from agricultural areas and nutrient release from accumulated deadwood. In terms of soil moisture, the reserve still exhibits a mosaic of interchanging distribution between wetter and more mesic habitats. However, given that oak natural regeneration is very poor, we anticipate even more drastic vegetation changes in the future.
Ključne besede: lowland primary forest, Quercus robur dieback, Carpinus betulus, Light availability, taxonomic homogenization, semi-permanent plot
Objavljeno v DiRROS: 05.05.2025; Ogledov: 617; Prenosov: 263
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1670. Pressure-induced comproportionation in palladium trifluorideSylwia Olszewska, Sharad Babu Pillai, Deepak Upadhyay, Kinga Zdun, Jakub Drapała, Klemen Motaln, Mirela Dragomir, Matic Lozinšek, Dominik Kurzydłowski, 2025, izvirni znanstveni članek Povzetek: Despite its seeming simple stoichiometry, palladium trifluoride (PdF3) is a mixed-valent system better formulated as PdIIPdIVF6. In an attempt to verify whether the application of high pressure (P > 1 GPa) might force this compound to form a genuine palladium(III) fluoride (PdIIIF3), a joint theoretical and experimental study on its properties at large compression was performed. Indeed, hybrid density functional calculations predict the thermodynamic preference for single-valent (comproportionated) polymorphs at pressures exceeding 30 GPa. The ambient-pressure LiSbF6-type polymorph of R3̅ symmetry was experimentally observed to transform into a triclinic P1̅ phase above 42 GPa. While this polymorph is still a mixed-valent compound PdIIPdIVF6, another phase transition, commencing at ∼50 GPa, introduces a monoclinic C2/c phase containing genuine PdIII centers. Both high-pressure polymorphs of palladium trifluoride exhibit novel structure types. Moreover, preliminary data suggest that the C2/c comproportionated structure might host strong one-dimensional antiferromagnetic exchange interactions.
Ključne besede: palladium fluoride, high pressure, comproportionation, DFT calculations
Objavljeno v DiRROS: 05.05.2025; Ogledov: 706; Prenosov: 951
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