Alberi e pavimentazioni

La presentazione illustrer\ue0 gli effetti di una sperimentazione in corso dal 2011 finalizzata a studiare gli effetti di diverse tipologie di pavimentazioni sulla crescita e la fisiologia di due specie arboree, oltre che su alcuni parametri fisici del suolo. Verranno illustrate le principali problematiche derivanti dall'impermeabilizzazione del suolo e possibili metodo per porvi rimedio, tra cui pavimentazioni alternative e il verde urbano. Infine, sar\ue0 chiarito quali siano gli stress tipici che possono ridurre i servizi ecosistemici degli alberi in ambienti pavimentati

It’s not the size, it’s the relationship: from ‘small states’ to asymmetry

Debate about the definition of “small state” has produced more fragmentation than consensus, even as the literature has demonstrated its subjects’ roles in joining international organizations propagating norms, executing creative diplomacy, influencing allies, avoiding and joining conflicts, and building peace. However, work on small states has struggled to identify commonalities in these states’ international relations, to cumulate knowledge, or to impact broader IR theory. This paper advocates a changed conceptual and definitional framework. Analysis of “small states” should pivot to examine the dynamics of the asymmetrical relationships in which these states are engaged. Instead of seeking an overall metric for size as the relevant variable—falling victim in a different way Dahl’s “lump-of-power fallacy,” we can recognize the multifaceted, variegated nature of power, whether in war or peacetime

Can a K103N HIV strain stably overcome the wild type in the absence of non-nucleoside reverse transcriptase inhibitor selective pressure?

The impact of drug resistance mutations on viral fitness is one of the main issues being investigated in HIV therapy. Some, such as M184V, seem to reduce the replicative capacity of HIV, whereas others, such as thymidine analogue-related mutations, seem to potentiate virulence, and persist in the blood for years after the removal of selective pressure. We report a case of an HIV-infected patient whose prevalent viral population continued to carry the K103N mutation for more than 7 years after a 2-year treatment with zidovudine and lamivudine plus loviride despite subsequent changes in therapy with the absolute exclusion of non-nucleoside reverse transcriptase inhibitors (NNRTI)

Evaluating the effects of trenching on growth, physiology and uprooting resistance of two urban tree species over 51-months

Excavation within the root-zone of urban trees is increasing rapidly in compact cities for the installation and repair of belowground infrastructures, but research on excavation damages is mostly limited to the assessment of their effects on growth and dieback, while effects on physiology and long-term stability are still elusive. This experiment was aimed to understand long-term mechanisms of tree response to root severance. Two urban tree species (Aesculus hippocastanum and Tilia x europaea) were subjected to two different root damage intensities by digging either one, or two parallel (either side of the root flare) trenches. An equal number of trees were left undamaged as control. Shoot elongation and DBH growth were measured at the end of each growing season for four years after severance. Root system area was measured after the excavation and four years later. Leaf gas exchange, water relations, and chlorophyll fluorescence were assessed during the growing seasons over a 51-month period after severance. The effects on tree stability were evaluated 2 and 44 months after root severance by conducting pulling-tests and by calculating a theoretical uprooting resistance index based on the size of the root system. Results showed that, even at the most severe root damage treatments, which removed up to 70% of the root system, tree survival, growth and physiology were little affected. CO2 assimilation declined by 16-25%, mostly due to stomatal limitations, as also supported by a 0.7-1.9% decrease in the maximum quantum yield of PSII (Fv/Fm). Excavation reduced stem diameter growth rate by 16-28% and shoot elongation by 30-41%, compared to control. Although the disturbance to tree physiology induced by excavation had a moderate intensity, the ability to recover from such damage over a 51-month period was scarce, particularly in Aesculus. Results indicate that root damage acts as a predisposing factor which reduces in the long term the capacity of trees to withstand co-occurring stresses by decreasing carbon availability for growth and defence. Similarly, the ability of trees to withstand uprooting was reduced by excavation, and no full recovery occurred in the following 44 months, when uprooting resistance was still 20-66% lower in damaged plants compared to control, depending on the severity of the damage. A strong correlation (R2 = 0.822) was found between results of the pulling test and the uprooting resistance index. This study highlights the importance of integrating physiological parameters for a better prescription of tree preservation guidelines during excavation work