RECONSTRUCTING COMMUNITY DYNAMICS AND FUNCTIONS IN DEGLACIATED AREAS THROUGH AN AD HOC ENVIRONMENTAL DNA METABARCODING TECHNIQUE

Deglaciated areas are increasing worldwide due to the global glacier shrinkage and are undergoing rapid colonization by multiple lifeforms, thus representing experimental systems to study community dynamics and ecosystem functioning. Our understanding of biotic colonization after glacier retreat has greatly advanced in recent years thanks to the integration of methodological innovations and ecological theories. The development of standardized, robust and previously tested molecular tools can shed light on fundamental gaps in ecological research. Here, I show how classical approaches can be combined with environmental DNA (eDNA) metabarcoding and functional trait analysis to document the formation of multitrophic communities, improving our understanding of the biotic processes that occur following the retreat of glaciers. This work contributed to both a methodological advancement of the eDNA metabarcoding technique and a conceptual advancement in the understanding of the dynamics of communities in deglaciated areas. In the first half of my thesis, I show how some important methodological approaches can be optimized to improve the strength and reliability of datasets built using eDNA metabarcoding. Specifically, I compare several approaches to soil preservation, and show that both low temperature and desiccation can enable long-term soil conservation before eDNA extraction. Subsequently, I compare thresholds for the bioinformatics clustering of metabarcoding data, and evaluate how optimal thresholds can be defined on the basis of study aims and markers. In the second half of the thesis, I analyse how environmental factors influence the colonization of glacier forelands by several taxonomic groups (bacteria, fungi, microeukaryotes and animals). By using a multi-taxa approach, I investigate how soil depth and time since glacier retreat influence the colonization of ice-free areas, and show that different groups colonize the forelands in a similar way, with communities homogenizing through different depths with time. Finally, I evaluate how time since glacier retreat, soil features and climate interact in determining the velocity of colonization of nematodes, and show how they shape community structure and functionality through succession. Understanding how metabarcoding data can be properly used to assess the colonization of glacier forelands and how different factors influence this process is particularly important in the context of ongoing climate change and for the extrapolation of current observations to the future. Besides helping to understand the biological consequence of the retreat of glaciers, the advancements provided here may allow the development of scenarios on how mountain environments can change over the next century.