The Multi-Compartment Perspective

The shift of community ecology from taxonomic focuses to process-oriented perspective is a re-discovery of the integrative essence of Ecology. The bloom of plant-soil or plant-herbivore ecological fields are example of the recent steps toward better integrative consideration for the different compartments of the ecosystem interacting at the local scale. My research follows a similar path.

Interactions among atmosphere-plant-soil complex at the edge of severity gradient

Severe environments are appropriate to explore some dark aspects of local interactions highlighted by the environmental constraints. For instance, on high mountain cliffs, plant communities are structured in biotic islands around key stone species with cascading but poorly known effects on the rest of the ecosystem. The multidisciplinary ECOVER project explored in these natural mesocosms the structure of communities associated to Silene acaulis cushions along altitudinal and substrate cross-gradients (Fig. 2d). First results revealed contrasted engineer effects of the cushion plants on the underneath microbial communities. The cushions modulated the abiotic filtering of bacterial communities and provided suitable conditions for fungi establishment [44] (Fig. 15). Strong linkage between the plant genotype and the fungal community composition was also detected suggesting probable feedback mechanisms between beneficiary and facilitators [45].

Though a large part of vegetation studies focuses on the growing season, in cold ecosystems, winter processes can represent the majority of fluxes and interactions as subnivean litter decomposition. Winter ecological background from arctic and alpine systems underlines the importance of plant functional attributes for litter decomposition. However, the cool snow-covered system as represented by subalpine south-exposed slopes in the French Alps could illustrate the future conditions of colder areas. The accurate monitoring of plant litter decomposition from contrasted species under contrasted snowpack during a winter showed that the temporal (permanence) and physical (thermal resistance) dimensions of the snowpack on top of thickness are crucial parameters, far more important than the litter quality in our study, to consider in the physical modelling of cold ecosystem functioning [46] (Fig. 16 a, b, d). Interestingly, N-related microbial activities over the winter showed unexpected patterns: higher activity in the most exposed community as if freeze-thaw cyclic microclimate under thin snowpack favoured both nutrient release from soil organic and inorganic compounds and psychrophilic bacterial abundance and activity [47] (Fig. 16 c).

Opposed to long-term approaches on the spatiotemporal spectrum, the fine exploration of local interactions appears to be an indispensable element to a better understanding of the ecosystem functioning. These investigations on the subnivean biogeochemical activity or high-altitude biotic islands highlighted different poorly known aspects of the functioning of these systems contributing to a better general mechanistic understanding. This is one of the bases of a project as MicroClim combining the statistical analysis of long-term monitoring to a quasi-exhaustive investigation of the micro-habitats at the scale of a mountain (Mt Schrankogel, Tyrol), a transplant experiment and a sampling design to address the potential buffering effect of microclimate heterogeneity for the alpine vegetation facing climate changes [48,49,26]. In a related field, the SoilTemp initiative gathers at the global scale soil temperature time series as well as associated biodiversity and environmental information [50]. Such improvement in the resolution of investigations allows the consideration of more realistic climatic conditions in our modelling effort of biotic communities functioning [51].

Toward Multi-compartment exploration of local interactions

My research with the Czech Centre for Polar Ecology constitutes another step toward the integration of different aspects of local interactions in larger framework where the multi-trophic analysis of these interactions directly integrates a better understanding of the ecosystem services. TRAPA project explores the functional links among plant, soil invertebrate and microbial communities, and the C biogeochemical cycle along environmental gradients in different valleys of central Svalbard. The project is rooted at the intersection among the Global Change question of the C sink role of Arctic soils, the Response-Effect model and the concept of Integrated Community. More particularly, the project aims at linking the functional diversity of biotic communities [52] to the stabilisation of organic carbon in the soils [53] (Fig. 17) along environmental gradients through the multi-trophic response-effect model [54] applied to terrestrial arctic ecosystems (Fig. 18). This project embraces the holistic aspect of the ecosystems seeking for emergent properties through a multi-trophic perspective. It combines large sampling and manipulatives designs along environmental gradients allowing both the characterisation of the links among the ecosystem compartments and testing their resistance to environmental changes and risk of disruption.

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