The xylem is a complex system that includes a network of dead conduits ensuring long-distance water transport in plants. Under ongoing climate changes, xylem embolism is a major and recurrent cause of drought-induced tree mortality. Non-structural carbohydrates (NSC) play key roles in plant responses to drought and frost stress, and several studies putatively suggest their involvement in the regulation of xylem water transport. However, a clear picture on the roles of NSCs in plant hydraulics has not been drawn to date. We summarize the current knowledge on the involvement of NSCs during embolism formation and subsequent hydraulic recovery. Under drought, sugars are generally accumulated in xylem parenchyma and in xylem sap. At drought-relief, xylem functionality is putatively restored in an osmotically driven process involving wood parenchyma, xylem sap and phloem compartments. By analyzing the published data on stem hydraulics and NSC contents under drought/frost stress and subsequent stress relief, we found that embolism build-up positively correlated to stem NSC depletion, and that the magnitude of post-stress hydraulic recovery positively correlated to consumption of soluble sugars. These findings suggest a close relationship between hydraulics and carbohydrate dynamics. We call for more experiments on hydraulic and NSC dynamics in controlled and field conditions.

Summary The seedling stage is the most susceptible one during a tree′s life. Water relations may be crucial for seedlings due to their small roots, limited water buffers and the effects of drought on water transport. Despite obvious relevance, studies on seedling xylem hydraulics are scarce as respective methodical approaches are limited. Micro‐ CT scans of intact Acer pseudoplatanus and Fagus sylvatica seedlings dehydrated to different water potentials (Ψ) allowed the simultaneous observation of gas‐filled versus water‐filled conduits and the calculation of percentage loss of conductivity ( PLC ) in stems, roots and leaves (petioles or main veins). Additionally, anatomical analyses were performed and stem PLC measured with hydraulic techniques. In A. pseudoplatanus , petioles showed a higher Ψ at 50% PLC (Ψ 50 −1.13 MP a) than stems (−2.51 MP a) and roots (−1.78 MP a). The main leaf veins of F. sylvatica had similar Ψ 50 values (−2.26 MP a) to stems (−2.74 MP a) and roots (−2.75 MP a). In both species, no difference between root and stems was observed. Hydraulic measurements on stems closely matched the micro‐ CT based PLC calculations. Micro‐ CT analyses indicated a species‐specific hydraulic architecture. Vulnerability segmentation, enabling a disconnection of the hydraulic pathway upon drought, was observed in A. pseudoplatanus but not in the especially shade‐tolerant F. sylvatica . Hydraulic patterns could partly be related to xylem anatomical traits.

Questions: (a) Are there differences in abundance-weighted functional trait values between native and alien species in coastal plant communities? (b) Which functional traits are associated with a higher level of invasion in these communities? (c) Do functional diversity patterns differ between native and alien species? (d) Is alien species occurrence linked to small-scale functional homogenization effects on the resident native species? Location: N-Adriatic coastal ecosystems (Marano and Grado lagoon, Friuli Venezia Giulia region, Italy). Methods:We sampled coastal vegetation within two habitats (foredunes and saltmarshes) along nine belt transects in two sampling sites. Plant species richness and abundance were assessed in 128 plots along with a suite of plant functional traits.We tested for differences in community-weighted means between native and alien species within the two habitats, and Linear Mixed Models provided insights into traits fostering the invasion success among alien species. To check for potential functional homogenization driven by alien species invasion, we explored functional diversity patterns of native and alien species (β and γ functional diversity) and the relationship between α functional diversity and alien cover.Results: Alien species had lower functional diversity than natives and were characterized by lower leaf construction costs coupled with lower drought resistance and higher water transport efficiency. The most abundant aliens were the ones minimizing carbon investment for leaf construction. In addition, we also found evidence for small-scale functional homogenization driven by alien invasion. Conclusions:Our results suggested that native species adopt a resource conservative strategy whereas alien species are characterized by a higher resource acquisition capacity (i.e., acquisitive strategy). Our data also confirmed that alien species are less functionally diverse than natives, potentially driving the community towards small-scale functional homogenization, resulting in a loss of species and a reduction in the functional space. K E Y W O R D S biological invasion, community ecology, community weighted mean, functional homogenization, functional rarefaction, functional traits, functional uniqueness, quantitative methods | 499 Journal of Vegetation Science TORDONI eT al.

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Synchrotron X-ray computed micro-tomography (microCT) has emerged as a promising noninvasive technique for in vivo monitoring of xylem function, including embolism build-up under drought and hydraulic recovery following re-irrigation. Yet, the possible harmful effects of ionizing radiation on plant tissues have never been quantified. We specifically investigated the eventual damage suffered by stem living cells of three different species exposed to repeated microCT scans. Stem samples exposed to one, two or three scans were used to measure cell membrane and RNA integrity, and compared to controls never exposed to X-rays. Samples exposed to microCT scans suffered serious alterations to cell membranes, as revealed by marked increase in relative electrolyte leakage, and also underwent severe damage to RNA integrity. The negative effects of X-rays were apparent in all species tested, but the magnitude of damage and the minimum number of scans inducing negative effects were species-specific. Our data show that multiple microCT scans lead to disruption of fundamental cellular functions and processes. Hence, microCT investigation of phenomena that depend on physiological activity of living cells may produce erroneous results and lead to incorrect conclusions.

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Italy is among the European countries with the greatest plant diversity due to both a great environmental heterogeneity and a long history of man-environment interactions. Trait-based approaches to ecological studies have developed greatly over recent decades worldwide, although several issues concerning the relationships between plant functional traits and the environment still lack sufficient empirical evaluation. In order to draw insights on the association between plant functional traits and direct and indirect human and natural pressures on the environmental drivers, here we summarize the existing knowledge on this topic by reviewing the results of studies performed in Italy adopting a functional trait approach on vascular plants, briophytes and lichens. Although we recorded trait measurements for 1418 taxa, our review highlighted some major gaps in plant traits knowledge: Mediterranean ecosystems are poorly represented; traits related to belowground organs are still overlooked; traits measurements for bryophytes and lichens are lacking. Finally, intraspecific variation has been little studied at community level so far. We conclude highlighting the need of approaches evaluating trait-environment relationship at large spatial and temporal scales and the need of a more effective contribution to online databases to tie more firmly Italian researchers to international scientific networks on plant traits.

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