Less safety for more efficiency: water relations and hydraulics of the invasive tree Ailanthus altissima (Mill.) Swingle compared with native Fraxinus ornus L.

Invasion of natural habitats by alien trees is a threat to forest conservation. Our understanding of fundamental ecophysiological mechanisms promoting plant invasions is still limited, and hydraulic and water relation traits have been only seldom included in studies comparing native and invasive trees. We compared several leaf and wood functional and mechanistic traits in co-occurring Ailanthus altissima (Mill.) Swingle (Aa) and Fraxinus ornus L. (Fo). Aa is one of the most invasive woody species in Europe and North America, currently outcompeting several native trees including Fo. We aimed at quantifying inter-specific differences in terms of: (i) performance in resource use and acquisition; (ii) hydraulic efficiency and safety; (iii) carbon costs associated to leaf and wood construction; and (iv) plasticity of functional and mechanistic traits in response to light availability. Traits related to leaf and wood construction and drought resistance significantly differed between the two species. Fo sustained higher structural costs than Aa, but was more resistant to drought. The lower resistance to drought stress of Aa was counterbalanced by higher water transport efficiency, but possibly required mechanisms of resilience to drought-induced hydraulic damage. Larger phenotypic plasticity of Aa in response to light availability could also promote the invasive potential of the species.

A comparison between two moss species used as transplants for airborne trace element biomonitoring in NE Italy.

Transplants of the mosses Hypnum cupressiforme and Pseudoscleropodium purum used as active biomonitors of airborne trace elements were compared in a survey carried out at Trieste (NE Italy). Twelve elements were considered: Al, As, Cd, Cr, Cu, Fe, Hg, Mn, Pb, Ti, V, Zn. Water-washed materials of H. cupressiforme and P. purum, collected in a remote area to prepare transplants, showed comparable content of all elements, excluding Pb. Transplants of P. purum showed a significantly higher accumulation of Al, Fe, Pb and Ti; higher levels of Cu and V were accumulated in H. cupressiforme. Losses of some elements occurred in some samples of both species; the most consistent losses regarded Cr and Mn. Accumulation data of Al, As, Cd, Hg, Zn found in the two transplanted sets were not correlated. Differences in element uptake in the two mosses are likely to depend mainly on morphology, and probably on the different forms of emission and deposition types of the elements. The two mosses showed an overall accordance in discriminating sites highly and scarcely affected by trace element depositions, although they accumulated some elements, in particular Hg and Zn, in different ways. P. purum proved to be a better accumulator than H. cupressiforme, showing similar or higher accumulation and lower loss of almost all elements, especially those related to particulate, dry depositions; H. cupressiforme could be effective in detecting large-scale patterns, related to wet depositions. These results indicate that these mosses cannot be used interchangeably for monitoring particular elements, and are able to provide complementary information on different, local and long-range deposition patterns.

Evaluation of lichen diversity as an indicator of environmental quality in the North Adriatic submediterranean region.

In 2000, a standardized sampling protocol was developed by a group of European researchers to provide a repeatable and objective strategy for mapping lichen diversity as an indicator of environmental changes; this protocol is nowadays adopted in the guidelines to air quality bioindication in Italy. The present paper shows the results of a study of epiphytic lichen diversity performed according to both the new protocol and the standard methodology previously used in Italy; diversity values are based on frequency counts of all lichen species within particular sampling grids positioned on the trunks and divided in subunits. The survey was carried out in 61 sampling sites of two areas of the Friuli Venezia Giulia region (Italy) and Slovenia, characterized by similar climatic conditions and a wide range of anthropic pressure. Biodiversity values obtained following the two sampling methods are highly statistically correlated; this suggests an interpretative continuity of lichen diversity data for biomonitoring purposes. Lichen communities and diversity values occurring in natural areas, far from heavy human influences, are investigated by means of multivariate analysis of floristic releves of 11 sites. Diversity values scored in natural areas are rather variable, and are mainly influenced by the different vegetation types, Parmelion communities having lower diversity values than communities with Xanthorion elements. Evaluation scales of environmental alteration based on lichen diversity in the North Adriatic submediterranean bioclimatic area are provided. Some critical aspects of the sampling strategies are discussed.