The relationship between reorientational molecular motions and phase transitions in [Mg(H2O)6](BF4)2, studied with the use of (1)H and (19)F NMR and FT-MIR.

A (1)H and (19)F nuclear magnetic resonance study of [Mg(H2O)6](BF4)2 has confirmed the existence of two phase transitions at Tc1 ≈ 257 K and Tc2 ≈ 142 K, detected earlier by the DSC method. These transitions were reflected by changes in the temperature dependences of both proton and fluorine of second moments M2 (H) and M2 (F) and of spin-lattice relaxation times T1 (H) and T1 (F). The study revealed anisotropic reorientations of whole [Mg(H2O)6](2+) cations, reorientations by 180° jumps of H2O ligands, and aniso- and isotropic reorientations of BF4 (-) anions. The activation parameters for these motions were obtained. It was found that the phase transition at Tc1 is associated with the reorientation of the cation as a whole unit around the C3 axis and that at Tc2 with isotropic reorientation of the BF4 (-) anions. The temperature dependence of the full width at half maximum value of the infrared band of ρt(H2O) mode (at ∼596 cm(-1)) indicated that in phases I and II, all H2O ligands in [Mg(H2O)6](2+) perform fast reorientational motions (180° jumps) with a mean value of activation energy equal to ca 10 kJ mole(-1), what is fully consistent with NMR results. The phase transition at Tc1 is associated with a sudden change of speed of fast (τR ≈ 10(-12) s) reorientational motions of H2O ligands. Below Tc2 (in phase III), the reorientations of certain part of the H2O ligands significantly slow down, while others continue their fast reorientation with an activation energy of ca 2 kJ mole(-1). This fast reorientation cannot be evidenced in NMR relaxation experiments. Splitting of certain IR bands connected with H2O ligands at the observed phase transitions suggests a reduction of the symmetry of the octahedral [Mg(H2O)6](2+) complex cation.

Climate, host and geography shape insect and fungal communities of trees.

Non-native pests, climate change, and their interactions are likely to alter relationships between trees and tree-associated organisms with consequences for forest health. To understand and predict such changes, factors structuring tree-associated communities need to be determined. Here, we analysed the data consisting of records of insects and fungi collected from dormant twigs from 155 tree species at 51 botanical gardens or arboreta in 32 countries. Generalized dissimilarity models revealed similar relative importance of studied climatic, host-related and geographic factors on differences in tree-associated communities. Mean annual temperature, phylogenetic distance between hosts and geographic distance between locations were the major drivers of dissimilarities. The increasing importance of high temperatures on differences in studied communities indicate that climate change could affect tree-associated organisms directly and indirectly through host range shifts. Insect and fungal communities were more similar between closely related vs. distant hosts suggesting that host range shifts may facilitate the emergence of new pests. Moreover, dissimilarities among tree-associated communities increased with geographic distance indicating that human-mediated transport may serve as a pathway of the introductions of new pests. The results of this study highlight the need to limit the establishment of tree pests and increase the resilience of forest ecosystems to changes in climate.

Worldwide diversity of endophytic fungi and insects associated with dormant tree twigs.

International trade in plants and climate change are two of the main factors causing damaging tree pests (i.e. fungi and insects) to spread into new areas. To mitigate these risks, a large-scale assessment of tree-associated fungi and insects is needed. We present records of endophytic fungi and insects in twigs of 17 angiosperm and gymnosperm genera, from 51 locations in 32 countries worldwide. Endophytic fungi were characterized by high-throughput sequencing of 352 samples from 145 tree species in 28 countries. Insects were reared from 227 samples of 109 tree species in 18 countries and sorted into taxonomic orders and feeding guilds. Herbivorous insects were grouped into morphospecies and were identified using molecular and morphological approaches. This dataset reveals the diversity of tree-associated taxa, as it contains 12,721 fungal Amplicon Sequence Variants and 208 herbivorous insect morphospecies, sampled across broad geographic and climatic gradients and for many tree species. This dataset will facilitate applied and fundamental studies on the distribution of fungal endophytes and insects in trees.

The genetic relationships within Apiognomonia errabunda and related species.

Species of Apiognomonia are some of the most ubiquitous leaf-associated fungi of broad-leaved trees of the northern temperate zone. Especially widespread and diverse is Apiognomonia errabunda, found mostly on beech, oak, and linden. This species and its closest relatives are known for their complicated phylogenetic relationships that have caused considerable confusion in the past. In the present paper, we describe the results of a three-gene-based reconstruction of phylogenetic relationships between A. errabunda, A. veneta, and A. hystrix for 373 isolates. Using combined information from the nuc rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS barcode) and intron regions of actin (ACT) and calmodulin (CAL) genes for 263 isolates, we confirmed the occurrence of host-associated lineages within A. errabunda. However, the clustering of isolates by host species was incomplete: some isolates occurred on the "wrong" hosts and a number of isolates carried mixed genetic profile, indicating substantial level of inter-host group recombination. In addition, a number of isolates were identified as putative, pending further verification, interspecies hybrids between the much more divergent A. errabunda and A. hystrix.