First record of naturalization of Erechtites hieraciifolius (L.) Raf. ex DC. (Asteraceae) in Italy

The plant species Erechtites hieraciifolius (Asteraceae) is here reported for the first time in Italy as a naturalized neophyte in the Classical Karst. The species was observed in 2023 in post-fire forest areas burnt by wildfires in the summer 2022. The features of findings suggest for a naturalization of the species with putative invasive character. This novel occurrence highlights the need for additional research to better understand its colonization and expansion, suggesting the need of early eradication actions

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

Green roof irrigation management based on substrate water potential assures water saving without affecting plant physiological performance

Irrigation management in extensive green roofs (EGRs) is crucial in Mediterranean and semi-arid climates, as it should guarantee efficient water use while ensuring plant survival and vegetation cover. However, benefits of maintaining moderately low substrate water potential (psi(s)) have not been adequately investigated to date. An irrigation control unit based on psi(s) thresholds for irrigation (MediWater Safe [MWS]) was compared to a common irrigation timer maintaining psi(s) similar to 0 MPa (CTR) in shrub-vegetated Mediterranean EGR modules. The effect of the different irrigation regimes on substrate temperature, plant water relations (leaf conductance to water vapour, midday water potential and turgor loss point) and root vulnerability to heat stress via electrolyte leakage was tested in four shrub species. Decreasing psi(s) thresholds to -0.4 MPa reduced irrigation volumes by 68% in 3 summer months. However, the MWS unit neither influenced plant water status and vegetation cover nor induced physiological acclimation responses. Brief irrigation cycles imposed by MWS in the warmest hours reduced substrate surface temperature by 3 degrees C compared to CTR. Plant water status dynamics and root vulnerability to heat were species specific. Progressive stomatal closure and plant decline occurred only in Ceanothus thyrsiflorus and were associated to high root vulnerability to heat. Mortality occurred only in some Ceanothus plants in the CTR module, where higher psi(s) favoured the expansion of Hyperucum x moserianum. The results suggest that selecting proper psi(s) thresholds for irrigation could optimize EGR benefits, guaranteeing substantial water savings and proper plant establishment. Moreover, we claim root resistance to heat as a key parameter for plant selection in Mediterranean EGRs

Stem photosynthetic efficiency across woody angiosperms and gymnosperms with contrasting drought tolerance

Key messageStem photosynthesis seems to play an adaptive role for woody plants that prosper in hot and dry ecosystems.Stem photosynthesis is thought to be involved in tree resistance/resilience to water shortage. Recent studies have focused on the coordination between stem photosynthesis and hydraulics, but the generality of association of stem photosynthetic efficiency with species-specific adaptation to drought is still unclear. We quantified bark and wood chlorophyll a fluorescence (in terms of F-v/F-m) in current-year, 1-year and 2-year-old stems of several woody species harvested in diverse habitats. We ranked species in terms of relative drought tolerance on the basis of their vulnerability to xylem embolism (P-50), and compared stem photosynthetic efficiency of drought-tolerant vs drought-sensitive species. F-v/F-m values decreased with increasing stem age, and were generally higher for Angiosperms than Gymnosperms. F-v/F-m both at the bark and wood level was higher for drought-tolerant Angiosperms compared to drought-sensitive ones. Our results highlight the potential adaptive role of stem photosynthesis in drought-tolerant species, thriving under arid conditions likely leading to prolonged stomatal closure and halt of leaf-level carbon gain

Drivers of distance-decay in bryophyte assemblages at multiple spatial scales: Dispersal limitations or environmental control?

Questions: Despite the increasing scientific interest in distance decay of compositional similarity in ecology, the scale dependence of geographical versus environmental control on distance decay of biological communities has not been properly addressed so far. The present work highlights the relative importance of niche-based processes versus dispersal limitations on distance decay patterns of epilithic bryophyte assemblages at different spatial scales. Location: Serra de Sintra, central Portugal. Methods: We adopted a nested sampling design with 32 selected sampling sites in each of which two clusters, each with five rocks, were surveyed. Each cluster was characterized by a set of 15 macroscale variables, which were divided into environmental and anthropogenic. For each rock eight microscale variables were recorded. Partial Mantel tests were used to assess the relative importance of geographical and environmental distance on community dissimilarity for each grain size (site, cluster, rock). Quantile regressions were used to describe the decay patterns of community similarity with respect to geographical and environmental distances. Ordination analyses and variation partitioning techniques were applied to assess the pure and shared effects of measured variables on bryophyte community composition. Results: Environmental distance based upon macroscale predictors was significantly correlated to community similarity, while no significant correlation was found for ecological distance calculated for microscale predictors, except at the largest grain size. The decrease of community similarity with geographical and environmental distance was thus consistently strengthened with increasing sample grain. Compositional variation was best explained by anthropogenic variables. Conclusions: The relative importance of environmental versus geographical distance on compositional similarity in epilithic bryophyte communities varies with the spatial scale of the predictors and with the sample grain. The decrease of similarity with increasing distance is related to changes in habitat features, especially those driven by human disturbance, while it is weakly affected by variations in substrate features

Projections of leaf turgor loss point shifts under future climate change scenarios

Predicting the consequences of climate change is of utmost importance to mitigate impacts on vulnerable ecosystems; plant hydraulic traits are particularly useful proxies for predicting functional disruptions potentially occurring in the near future. This study assessed the current and future regional patterns of leaf water potential at turgor loss point (Ψtlp) by measuring and projecting the Ψtlp of 166 vascular plant species (159 angiosperms and 7 gymnosperms) across a large climatic range spanning from alpine to Mediterranean areas in NE Italy. For angiosperms, random forest models predicted a consistent shift toward more negative values in low-elevation areas, whereas for gymnosperms the pattern was more variable, particularly in the alpine sector (i.e., Alps and Prealps). Simulations were also developed to evaluate the number of threatened species under two Ψtlp plasticity scenarios (low vs. high plasticity), and it was found that in the worst-case scenario approximately 72% of the angiosperm species and 68% of gymnosperms within a location were at risk to exceed their physiological plasticity. The different responses to climate change by specific clades might produce reassembly in natural communities, undermining the resilience of natural ecosystems to climate change

Using spectral diversity and heterogeneity measures to map habitat mosaics: An example from the Classical Karst

Questions: Can we map complex habitat mosaics from remote-­sensing data? In doing this, are measures of spectral heterogeneity useful to improve image classification performance? Which measures are the most important? How can multitemporal data be integrated in a robust framework? Location: Classical Karst (NE Italy). Methods: First, a habitat map was produced from field surveys. Then, a collection of 12 monthly Sentinel-­2 images was retrieved. Vegetation and spectral heterogeneity (SH) indices were computed and aggregated in four combinations: (1) monthly layers of vegetation and SH indices; (2) seasonal layers of vegetation and SH indices; (3) yearly layers of SH indices computed across the months; and (4) yearly layers of SH indices computed across the seasons. For each combination, a Random Forest clas- sification was performed, first with the complete set of input layers and then with a subset obtained by recursive feature elimination. Training and validation points were independently extracted from field data. Results: The maximum overall accuracy (0.72) was achieved by using seasonally ag- gregated vegetation and SH indices, after the number of vegetation types was re- duced by aggregation from 26 to 11. The use of SH measures significantly increased the overall accuracy of the classification. The spectral β-­diversity was the most im- portant variable in most cases, while the spectral α-­diversity and Rao's Q had a low relative importance, possibly because some habitat patches were small compared to the window used to compute the indices. Conclusions: The results are promising and suggest that image classification frame- works could benefit from the inclusion of SH measures, rarely included before. Habitat mapping in complex landscapes can thus be improved in a cost-­and time-­effective way, suitable for monitoring applications

Stem photosynthesis contributes to non-structural carbohydrate pool and modulates xylem vulnerability to embolism in Fraxinus ornus L

Stem photosynthesis can significantly contribute to the carbon budget of woody plants, providing an extra carbon gain that might be crucial under drought stress causing leaf photosynthesis impairment and/or a reduced phloem transport.Stems of Fraxinus ornus L. saplings were covered with aluminum foil to test the impact of inhibition of stem photosynthesis on plant vulnerability to drought. Plants were water-stressed to target xylem water potential of-3.5 MPa and were then re-irrigated to field capacity to quantify their recovery capacity. Vulnerability to xylem embolism was assessed in light-exposed and stem-shaded saplings with both the hydraulic method and in vivo with X-ray phase contrast micro-computed tomography. We also measured non-structural carbohydrate (NSC) concentration and osmotic potential in bark and wood, separately.Stem shading increased xylem vulnerability to embolism formation under drought but did not influence the recovery phase. This difference was coupled with modification of the NSC pool and impaired osmoregulation, in particular in the wood of stem-shaded saplings compared to control ones.Our results indicate stem photosynthesis as an important source of local NSCs, directly or indirectly involved in osmoregulation processes, which could be crucial to enhance the hydraulic resistance to embolism formation and to endure drought