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Reconstructing community dynamics and ecosystem functioning after glacial retreat

Periodic Reporting for period 2 - IceCommunities (Reconstructing community dynamics and ecosystem functioning after glacial retreat)

Reporting period: 2019-10-01 to 2021-03-31

Glaciers are retreating all over the globe. Increasing areas are exposed and colonized by multiple organisms, but lack of global studies hampers a complete understanding of the future of recently deglaciated terrains. What will be the fate of these areas? How do animals, plants and microorganisms colonize them? How do they interact to perform successful colonization? Which are the processes determining colonization patterns? How does ecosystem functioning evolves through time? Until now, the complete reconstruction of soil communities was hampered by the complexity of identification of organisms, thus analyses at broad geographical and taxonomic scale have been so far impossible. IceCommunities combines innovative methods and a global approach to boost our understanding of the evolution of ecosystems in recently deglaciated areas. We are investigating chronosequences ranging from recently deglaciated terrains to late successional stages of soil pedogenesis, exploiting the power of environmental DNA metabarcoding.
IceCommunities identifies species is obtaining a complete reconstruction of biotic communities along glacier forelands over multiple mountain areas across the globe. This allows measuring the rate of colonization at an unprecedented taxonomic detail and completeness. Information on assemblages is combined with analyses of soil, landscape and climate to identify the drivers of community changes. Furthermore, IceCommunities assesses the impact of eco-geographical factors (climate, regional pool of potential colonizers) on colonization. Finally, the analysis of functional traits allows reconstructing how functional diversity emerges during community formation, and how it scales to the functioning of food webs.
Due to ongoing climate change, deglaciated areas are an increasingly important component of mountain and high-latitude ecosystems. Understanding the consequence of glacier retreat is thus a hot topic for both ecology and global change studies, with researchers trying to understand the consequence of retreat and to develop scenarios on how mountain environments may change over the next century. IceCommunities will help to predict the future development of these ecosystems, providing a supported rationale for their management.
- Through multiple field expeditions, we collected samples representative of glaciers all over the world (Fig. 1-3)

- We are exploiting the power of eDNA metabarcoding to measure soil biodiversity
Environmental DNA (eDNA) is the DNA that can be extracted from environmental samples (e.g. soil, water…) without isolating the remains of the organisms. A given environmental sample contains the eDNA of multiple organisms, that can be amplified, compared with reference databases and identified in a procedure named eDNA metabarcoding.
We extracted eDNA from >1200 soil samples, and amplified it using primes targeting multiple components of biodiversity: bacteria; fungi; eukaryotes, vascular plants, Annelida; Arthropoda; Collembola and Insecta.
We also compared the primers with the best resolution for the identification of animals (Ficetola et al. 2020), helping the advancement of the use of metabarcoding to assess biodiversity.

- We performed bioinformatic analyses: from sequences to biodiversity information.
Several methodological analyses enhanced the rigour of our study. We 1) compared the approaches for soil preservation in eDNA studies, demonstrating that we can obtain robust biodiversity estimates independently of the protocols used for soil storage (Guerrieri et al. 2020); 2) we developed optimal tools for the analysis of eDNA data with complex spatial structure, as the ones that are produced with IceCommunities (Chen and Ficetola 2019) and 3) we contributed to a major methodological essay, describing the best practices for biodiversity analyses using metabarcoding (Zinger et al. 2019).
The IceCommunities sequencing activities have generated an impressive amount of genomic information that require complex bioinformatics analyses, including filtering erroneous sequences and the assignation of sequences to molecular operational taxonomic units.

- We are analysing environmental variation in glacier forelands: climate, soil and vegetation.
To identify the drivers of community composition, we are performing a fine-scale reconstruction of the microclimate of glacier forelands. Fine-scale climatic data improve predictions of the impact of climate change in high-mountain environments (Feldmeier et al. 2020).
We performed pedological analyses (grain size, pH, organic matter, nitrates, phosphorous) on the soil samples, to measure properties that affect the development of communities, and confirmed the importance of these parameters for soil fauna (Rota et al. 2020). We also showed that soil organic matter increases with time in glacier forelands from all over the world (Khedim et al. in press; Fig. 4).

- We are using taxonomic information to measure functional diversity of communities.
Taxonomic information is now used to measure the functional traits of communities. We started with nematodes, which are among the most abundant soil animals. The richness of nematode communities shows a sharp increase after the retreat of glacier. The rise of taxonomic diversity is paralleled by an increase of functional diversity. Very long periods (>100 years) are required for the development of functional diversity.
- We analysed the broadest collection of samples from peri-glacier environments, covering all the continents and most of climatic regimes
- We helped to define the best-practices for the analysis of environmental DNA
- We showed that soil organic matter content increases with time in all the glacier forelands, and provide a first estimate of the amount of carbon sequestration as a consequence of glacier retreat, showing that SOM content increases faster in forelands experiencing warmer climates.
- we are producig global measures of biodiversity in peri-glacial environments. For the first time, high quality data are also available for multiple tropical mountains.
- we are showing that, during colonization after glacier retreat, taxonimic and functional diversity follow parallel trajectories. Both taxonomic and functional diversity continue to increase for long periods after the retreat of glaciers, highlighting the long time required for the recovery of ecosystem functions.

By the end of the project, our data will allow us to:
- obtain measures of taxonomic and functional diversity for all the taxonomic groups, from bacteria to plants to animals
- identify the drivers of community development along successions, teasing apart the role of 1) soil developent; 2) climate and 3) time since the retreat of glaciers
- complete the first reconstruction of how trophic webs change through time during the development of new ecosystems
Fig. 2 What is a chronosequence?
Fig. 3. Example of sampling activity
Fig. 1 Sampled glaciers all over the world
Fig. 4. The development of soils after the retreat of glaciers