Programma della conferenza

Mountain regions are recognised as climate change hotspots. Increasing evidence from observations and model studies indicates that warming rates depend on elevation and often intensify with elevation, causing high-altitude environments to experience more rapid temperature changes than lower elevations. This phenomenon, known as Elevation-Dependent Warming, has been extensively studied due to its potential to accelerate transformations in mountain ecosystems, cryospheric systems, hydrological regimes, and biodiversity. However, fewer studies have examined the elevation-dependent changes of other climate variables, such as precipitation and its extremes (Elevation-Dependent Precipitation Change), that are as important as the temperature for high-altitude environments and downstream. Precipitation is crucial for mountain hydrological resources as its study in the context of climate change. Elevation and complex terrain significantly influence precipitation formation, contributing to the increase of extreme precipitation events. In this contribution, we present an analysis of the changes in mean precipitation and its extremes in ERA5 global reanalysis data in key mountain areas of the globe, along with their elevational dependence, from 1951 to 2020. The areas include the Tibetan Plateau, the US Rocky Mountains, the Greater Alpine Region, and the Andes, as representative of different latitudes and climatic influences. Our analysis reveals common patterns of elevation-dependent change in precipitation and its extremes in most of the mountainous areas, which emerge beyond their geographical differences. A positive elevational gradient of extreme precipitation trends is found in the Tibetan Plateau, the Greater Alpine Region, and the subtropical Andes, highlighting a wetting effect (positive trends) at very high elevations. In contrast, the Rocky Mountains exhibit a negative elevational gradient, with a drying effect (negative trends) increasing with the elevation. Mean precipitation, heavy (≥10 mm/day) precipitation and the length of consecutive wet days show a consistent elevation-dependent stratification within each of the study areas, suggesting possible common driving mechanisms.

Climate change affects natural and semi-natural ecosystems worldwide, with mountains experiencing even more drastic impacts due to elevation-dependent warming. High-elevation grasslands and alpine tundra act as regulators of the hydrological cycle, stabilise slopes and have a paramount role in nitrogen and carbon cycling. Owing to the very short snow-free season and the consequent adaptation of alpine plant to fast growth, alpine ecosystems mainly act as carbon sinks, with primary production usually exceeding ecosystems respiration. Combining timeseries of field (CO₂ fluxes and environmental variables; 3,590 single measurements - 5 sites), weather (daily precipitation and temperature), vegetation (PFT classification - 653 images) and remotely sensed data (CLr, NDSI, DEM) in the Nivolet area (Gran Paradiso NP, Italy), we investigated the environmental and climate controls on ecosystem respiration and primary production using structural equation modelling. We found GDD₀ (growing degree days since snowmelt) exerting a strong control on both respiration and production. The effect of GDD₀ on production is both direct, possibly reflecting the importance of cumulated heat on vegetation height, and mediated by the seasonal trend in greening (proxied by CLr). While greening had no effect on respiration, GDD₀ had a direct effect, supporting the view that ecosystem respiration was mainly microbial-driven and temperature-related. Summer cumulative precipitation proved to promote both respiration and production, at least until the phenological peak. Surprisingly, winter cumulative precipitation had no effect on production, and a negative effect on soil respiration, suggesting a direct effect on the cycling of organic matter rather than a contribution to the spring/summer water balance. Other variables (i.e., radiation, air temperature, soil moisture, PFT, topography) all supported our a-priori expectations or had no significant effect. Our results contribute to identify the causal relationships between climate and carbon cycling, allowing for a deeper understanding of the effects of climate changes on alpine ecosystems.

Spontaneous afforestation of formerly man-used land has increasingly been considered as a Nature-Based Solution to mitigate climate change. Besides obvious C sink above ground, afforestation leads to low soil pH, high C:N ratios and changes in litter and soil organic matter (SOM) quality with beneficial implications for soil carbon sequestration. However, less is known about the effects on soil microbial communities, which may play a crucial role as a controlling factor for nutrient cycling, SOM stabilization and soil fertility. The aim of this study, within the framework of Task 4.2.1 of Spoke 4 of the National Biodiversity Future Centre (NBFC), is to investigate the dynamics of carbon stocks and soil microbial diversity following afforestation in Julian Pre-Alps (Taipana, UD) using a space-for-time approach. Orthophotos were used to identify and date the successional stages spanning 70 years from grassland to forest.Organic C pools including soil, living trees, standing and lying dead wood and litter, as well as main physical-chemical properties including fine C molecular composition by 13C-CPMAS NMR, were measured, and fungi and bacteria community diversity was assessed by soil DNA metabarcoding.Aboveground C stock increased from 8.42 ± 0.91 tC ha^-1 in grassland, to 158.98 ± 23.85 tC ha^-1 in the oldest stands. Soil C stock, after initially decreasing from 63.62 ± 15.4 tC ha^-1 in grasslands to 47.74 ± 3.34 tC ha^-1 in shrubby sites, significantly increased along the successional process, reaching 78.44 ± 19.42 tC ha^-1 in mature forest. Microbial α-diversity substantially differed between bacterial and fungal communities, with the formers progressively declining while fungi showed a bell-shaped response peaking at intermediate successional stage (34 years).These findings open interesting perspectives for the management of rewilding dynamics suggesting alternative scenarios targeting either climate change mitigation and/or ecosystem resilience, with the latter strictly associated to the functional redundancy of microbial diversity.

Cryoconite holes are small depressions (from millimeters to tens of centimeters) in the ice surface of glaciers, filled with water and sediment at the hole base. The term ‘cryoconite’ refers to the granular sediment comprising mineral (e.g. soil or dust) and biological material. The cryoconite holes can cover a large portion of a glacier and are now recognized as an important microbial habitat and a major element of supraglacial ecosystems. Their autotrophic component plays an essential role in maintaining the whole cryoconite food chain, decreasing the albedo of glaciers, and representing a source of organisms for the emergent new ice-free area. However, the study of photoautotroph community in cryoconite ecosystems is complex, because the presence of dark sediment and the difficult cultivation of organisms make both molecular analyses and standard microscopic approaches complex. Here, we aim to gain insights into the diversity and composition of microalgae and Cyanobacteria in cryoconite holes from different glacial locations. Based on an innovative methodology, we provide a highly comprehensive description of the phenotypic characteristics, abundance, and structure of the autotrophic community in these extreme environments. The study poses the basis for the taxonomy of photoautotrophs in glacial habitats and their ecological role in cryoconite systems.

Alpine high-mountain lakes, often considered scenic marvels, play critical roles as indicators of global environmental change, repositories of geological history, and vital freshwater sources. Despite their pristine and remote locations, these lakes face significant threats that modify their ecological equilibrium. Climate change, primarily through glacier retreats, shifts in water temperatures, and heightened UV radiation levels, poses a substantial risk. Furthermore, pollutants transported over long distances, the introduction of invasive species, rising water demand from Alpine storage power stations, and expanding tourism and recreational activities further heighten vulnerability, exacerbating habitat disturbance and environmental degradation.

This study underscores the crucial importance of Alpine high-mountain lakes, emphasizing the urgent need to address both established and emerging threats. It outlines future research priorities focused on developing comprehensive monitoring programs and proactive conservation measures, highlighting the necessity of understanding the ecological health of these ecosystems, evaluating environmental impacts, and formulating effective strategies. Integrating interdisciplinary approaches is essential to deepen our understanding and mitigate threats to high-mountain lakes, ensuring the preservation of their ecological integrity and natural heritage for future generations. Engaging local communities and citizen scientists enhances data collection, promotes stewardship, enriches scientific knowledge, and fosters community involvement in environmental conservation.