The mid-Holocene extinction of silver fir ( Abies alba ) in the Southern Alps: a consequence of forest fires? Palaeobotanical records and forest simulations

Pollen records suggest that Abies alba played a dominating role in both the montane and lowland forests at the border of the Southern Alps between ca. 8500 and 5700 years ago. Two major declines in fir, at about 7300-7000 cal b.p. and at ca. 6000 cal b.p., followed by the local extinction of the species are characteristic of the area below ca. 1000 m a.s.l. In order to test the impact of fire on the population dynamics of silver fir, a dynamic model (DisCForm) with a fire module was applied to simulate the early- and mid-Holocene forest development. Simulation outputs based on different fire scenarios were compared with the pollen record from Lago di Annone (226ma.s.l.). The marked Abies decreases shown in the pollen record can be simulated with very intensive fire scenarios, but they do not result in an extinction of silver fir in the model. Low charcoal influx values related to the Abies declines in the palaeobotanical record suggest that fire was not the only reason for the extinction of silver fir. Human impact, as well as Holocene climatic changes leading to temporary moisture deficits and reduced adaptability due to low genetic variation may have had a significant impact on the Abies forest

Cryo Electron Tomography of Herpes Simplex Virus during Axonal Transport and Secondary Envelopment in Primary Neurons

During herpes simplex virus 1 (HSV1) egress in neurons, viral particles travel from the neuronal cell body along the axon towards the synapse. Whether HSV1 particles are transported as enveloped virions as proposed by the ‘married’ model or as non-enveloped capsids suggested by the ‘separate’ model is controversial. Specific viral proteins may form a recruitment platform for microtubule motors that catalyze such transport. However, their subviral location has remained elusive. Here we established a system to analyze herpesvirus egress by cryo electron tomography. At 16 h post infection, we observed intra-axonal transport of progeny HSV1 viral particles in dissociated hippocampal neurons by live-cell fluorescence microscopy. Cryo electron tomography of frozen-hydrated neurons revealed that most egressing capsids were transported independently of the viral envelope. Unexpectedly, we found not only DNA-containing capsids (cytosolic C-capsids), but also capsids lacking DNA (cytosolic A-/B-capsids) in mid-axon regions. Subvolume averaging revealed lower amounts of tegument on cytosolic A-/B-capsids than on C-capsids. Nevertheless, all capsid types underwent active axonal transport. Therefore, even few tegument proteins on the capsid vertices seemed to suffice for transport. Secondary envelopment of capsids was observed at axon terminals. On their luminal face, the enveloping vesicles were studded with typical glycoprotein-like spikes. Furthermore, we noted an accretion of tegument density at the concave cytosolic face of the vesicle membrane in close proximity to the capsids. Three-dimensional analysis revealed that these assembly sites lacked cytoskeletal elements, but that filamentous actin surrounded them and formed an assembly compartment. Our data support the ‘separate model’ for HSV1 egress, i.e. progeny herpes viruses being transported along axons as subassemblies and not as complete virions within transport vesicles

Wissenswert: Ein Kosmos voller Pflanzen Alexander von Humboldt und die Botanik

hr-iNFO-Wissenswert widmet sich zum Humboldt-Jubiläum einem Aspekt, der bislang meist im Schatten stand: Humboldts Wirken als Botaniker. Nicht nur, dass er zahlreiche Pflanzenarten als erster beschrieb. Er inspirierte auch Maler zur wissenschaftlich präzisen Dokumentation von Pflanzen. Er begründete die Pflanzengeographie als Kunde von der Verbreitung und Ausbreitung der Pflanzen. Und er erkannte, wie der Mensch die Natur durch seine Eingriffe nachhaltig verändert

"Botanik in Bewegung" - Humboldt und die Wissenschaft der Pflanzen. Adrian Möhl und Oliver Lubrich im Radio-Interview von Sabine Frank.

Alexander von Humboldt entwickelte eine neue Sicht auf die Pflanzenwelt. Der Botaniker Adrian Möhl und der Literaturwissenschaftler Oliver Lubrich erzählen davon in ihrem neuen Buch. Ein Gespräch mit Sabine Frank

Botanik in Bewegung. Alexander von Humboldt und die Wissenschaft der Pflanzen. Ein interdisziplinärer Parcours

Alexander von Humboldt als Begründer einer neuen Sicht auf die Pflanzenwelt: ein bisher wenig beleuchteter Aspekt. Einzigartiges, zum Teil erstmals gezeigtes Bildmaterial. Alexander von Humboldt versetzte die Botanik in einem doppelten Sinn «in Bewegung»: Er erforschte Pflanzen auf seinen Expeditionen, im «Feld», in freier Natur. Und er dynamisierte das System der Naturgeschichte nach Carl von Linné, indem er nicht mehr nur einzelne Arten klassifizierte, sondern ihrer Verteilung über die Erde folgte und sie im Kontext ihrer Umwelt betrachtete. Er machte die Pflanzenwissenschaft auch zu einer Migrationskunde und – avant la lettre – zur Ökologie. «Botanik in Bewegung» erzählt Humboldts Leben als Botaniker in vier Kapiteln: «Träumen», «Beobachten», «Auswerten» und «Nachwirken». Wir folgen seinen wichtigsten Stationen inmitten einheimischer und exotischer Pflanzen: von Berlin und Paris nach Teneriffa, Havanna und Quito, St. Petersburg und Sibirien. Dieses reich bebilderte Buch liefert aber nicht nur eine Erzählung von Alexander von Humboldts botanischem Schaffen, sondern es setzt dieses auch ins Verhältnis zur modernen Pflanzenwissenschaft

Factors Controlling Species Richness in Alpine Plant Communities: An Assessment of the Importance of Stress and Disturbance

This study explores whether the high variability of vascular plant diversity among alpine plant communities can be explained by stress and/or disturbance intensities. Species numbers of 14 alpine plant communities were sampled in the Swiss Alps. To quantify the intensity of 13 stress and 6 disturbance factors potentially controlling plant life in these communities, a survey was conducted by asking numerous specialists in alpine vegetation to assess the importance of the different factors for each community. The estimated values were combined in stress- and disturbance-indices which were compared with diversity according to the Intermediate Stress Hypothesis, the Intermediate Disturbance Hypothesis, and the Dynamic Equilibrium Model, respectively. Each of these theories explained a part of the variability in the species richness, but only the Dynamic Equilibrium Model provided a complete and consistent explanation. The last model suggests that community species richness within the alpine life zone is generally controlled by stress intensity. Disturbance and competition seem to play a secondary role by fine-tuning diversity in specific communities. As diversity is primarily limited by stress, a moderation of temperature-related stress factors, as a result of global warming, may cause a shift of the equilibrium between stress, disturbance, and competition in alpine ecosystems