• Energy Research

The synergistic activity between plants and microorganisms may contribute to the implementation of proactive management strategies in the stabilization of contaminated sites, although heavy metals, such as cadmium (Cd), are potentially toxic to them. The aim of this study was to evaluate the degree of tolerance to Cd contamination (supplying twice 40 mg kg(-1) of Cd) in poplar cuttings [clone I-214, P. × euramericana (Dode) Guinier] inoculated or not with two concentrations of Serratia marcescens strain (1 × 10(7) CFU/g and 2 × 10(7) CFU/g of potting mix). The response of the plant-bacteria system to excess Cd was investigated with special reference to the structural traits of plants and the functional efficiency of bacteria. Bacterial colonization and substrate components were previously assessed in order to define the best solution for formulating the experimental plant growth media. The tested plant-bacteria association, especially when bacteria were provided in double concentration, stimulated specific tolerance mechanisms to Cd through the promotion of the poplar growth. Inoculated plants produced larger leaves and increased stem diameter, while roots grew longer and wider in Cd-treated plants. The effect of bacterial inoculum on plant growth traits and metal partitioning in plant organs was assessed in order to define the potential of this poplar clone to be a suitable candidate for phytostabilization of Cd-contaminated soil. The final effect of the inoculation with bacteria, which alleviated the metal load and Cd phytotoxicity due to their bioaccumulation ability, suggests promising phytostabilization potential of these plant-bacteria associations.

ABSTRACTXylem phenology has been widely recognised as an ecological indicator of the impact of environmental changes on forest ecosystems, especially at the edge of a species distribution. We investigated xylem phenology of silver fir (Abies alba Mill.) in three sites in Italy, between the 38th and 46th parallels. The phases of xylem phenology were assessed weekly on wood microcores collected from March to November 2015 to calculate timing and duration of xylem cell production. The effect of temperature and precipitation on xylem phenology were sequentially included in stepwise regressions and used to predict the duration of each phenological phase under three future climatic scenarios at different concentrations of greenhouse gases (RCP 2.6; 4. 5; 8. 5). A growing season of 163 days was detected in the southern site that was longer compared to the central (132 days) and northern (120 days) sites. A longer duration of xylogenesis was mostly related to a delayed completion of xylem differentiation in autumn rather than an earlier onset of cambium reactivation in spring. Overall, 67–76% of the duration of phenological phases was controlled by growing season precipitation, while 24 –33% was influenced by minimum temperature. Inclusion of both the above factors in the modelling exercise simulated a lengthening of the silver fir growing season during the 21st century. A longer duration of xylogenesis was envisaged in the scenario RCP 8. 5, especially in the central site. Population and climate gradients need to be considered when addressing phenological shifts and growth dynamics of silver fir in Mediterranean mountains.

Cudlín, Pavel et. al.- 16 páginas.- Ilustraciones.- Se acompaña suplemento de 3 páginas.- © The autors 2017. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are unrestricted. Authors and original publication must be credited. A growing body of evidence suggests that processes of upward treeline expansion and shifts in vegetation zones may occur in response to climate change. However, such shifts can be limited by a variety of non-climatic factors, such as nutrient availability, soil conditions, landscape fragmentation and some species-specific traits. Many changes in species distributions have been observed, although no evidence of complete community replacement has been registered yet. Climatic signals are often confounded with the effects of human activity, for example, forest encroachment at the treeline owing to the coupled effect of climate change and highland pasture abandonment. Data on the treeline ecotone, barriers to the expected treeline or dominant tree species shifts due to climate and land use change, and their possible impacts on biodiversity in 11 mountain areas of interest, from Italy to Norway and from Spain to Bulgaria, are reported. We investigated the role of environmental conditions on treeline ecotone features with a focus on treeline shift. The results showed that treeline altitude and the altitudinal width of the treeline ecotone, as well as the significance of climatic and soil parameters as barriers against tree species shift, significantly decreased with increasing latitude. However, the largest part of the commonly observed variability in mountain vegetation near the treeline in Europe seems to be caused by geomorphological, geological, pedological and microclimatic variability in combination with different land use history and present socio-economic relations. This paper is based firstly upon work from the COST Action ES 1203 SENSFOR, supported by COST (European Cooperation in Science and Technology; www.cost.eu). This international work was further supported by projects granted by the Ministry of Education Youth and Sports of the Czech Republic, grant NPU I LO1415 and LD 14039, by the agency APVV SR under projects APVV-14-0086 and APVV-15-0270. We acknowledge the E-OBS dataset from the EU-FP6 project ENSEMBLES (http://ensembles-eu.metoffice.com) and the data providers in the ECA&D project (www.ecad.eu) Peer reviewed

Wood growth is key to understanding the feedback of forest ecosystems to the ongoing climate warming. An increase in spatial synchrony (i.e., coincident changes in distant populations) of spring phenology is one of the most prominent climate responses of forest trees. However, whether temperature variability contributes to an increase in the spatial synchrony of spring phenology and its underlying mechanisms remains largely unknown. Here, we analyzed an extensive dataset of xylem phenology observations of 20 conifer species from 75 sites over the Northern Hemisphere. Along the gradient of increase in temperature variability in the 75 sites, we observed a convergence in the onset of cell enlargement roughly toward the 5th of June, with a convergence in the onset of cell wall thickening toward the summer solstice. The increase in rainfall since the 5th of June is favorable for cell division and expansion, and as the most hours of sunlight are received around the summer solstice, it allows the optimization of carbon assimilation for cell wall thickening. Hence, the convergences can be considered as the result of matching xylem phenological activities to favorable conditions in regions with high temperature variability. Yet, forest trees relying on such consistent seasonal cues for xylem growth could constrain their ability to respond to climate warming, with consequences for the potential growing season length and, ultimately, forest productivity and survival in the future.

AbstractDespite growing interest in predicting plant phenological shifts, advanced spring phenology by global climate change remains debated. Evidence documenting either small or large advancement of spring phenology to rising temperature over the spatio‐temporal scales implies a potential existence of a thermal threshold in the responses of forests to global warming. We collected a unique data set of xylem cell‐wall‐thickening onset dates in 20 coniferous species covering a broad mean annual temperature (MAT) gradient (−3.05 to 22.9°C) across the Northern Hemisphere (latitudes 23°–66° N). Along the MAT gradient, we identified a threshold temperature (using segmented regression) of 4.9 ± 1.1°C, above which the response of xylem phenology to rising temperatures significantly decline. This threshold separates the Northern Hemisphere conifers into cold and warm thermal niches, with MAT and spring forcing being the primary drivers for the onset dates (estimated by linear and Bayesian mixed‐effect models), respectively. The identified thermal threshold should be integrated into the Earth‐System‐Models for a better understanding of spring phenology in response to global warming and an improved prediction of global climate‐carbon feedbacks.

The dynamics of Pinus mugo krummholz during concomitant change in pastoral land use and climate in central Italy since the mid-20th century was investigated. Krummholz dynamics were detected using sequential aerial photography and fitted to a logistic regression model with elevation, grazing, proximity to beech forest, and proximity to krummholz as explanatory variables. Dendrochronological series were correlated with temperature and precipitation and fitted to a linear model. During this period krummholz doubled in extent and migrated 35–65 m upslope. Expansion was positively associated with krummholz proximity, residual pastoral grazing, and proximity to beech forest beyond 10 m and negatively associated with elevation and beech forest closer than 10 m. The logistic regression model forecasts krummholz migration by an additional 30 m upslope by 2060. During the 20th century, winter and spring minimum temperatures increased but did not result in increased radial stem growth of P. mugo. The combined evidence suggests that krummholz dynamics can be explained by the legacy of summer pastoralism and the dispersal limitations of P. mugo, rather than by climate change.

Global changes push to set up strategies able to mitigate and adapt agricultural and forest crops to environmental variability, and the sustainable intensification of production processes under agricultural and forestry systems is one of the approaches mainly supported. In Italy biomass and biogas are the renewable energy sources that have shown the greatest potential for growth in recent years. In this context, during the XV National Congress held in Bolzano in February 2018, the Italian Association of Agricultural Scientific Societies has promoted an analysis about potential and limits of the sustainable intensification of agricultural and forestry systems for bioenergy production. This document reports the outcome, in the form of a commented discussion on the main evidences and proposals from technical-scientific and operational points of view.