Stoichiometric traits of Microbial species and communities for predicting freshwater ecosystem responses to global changes – StoichioMic

In ecosystems, plants and microbial decomposers are generally considered as the two most important biological components of ecosystems, plants furnishing organic carbon and energy to all food webs components, and decomposers permitting to recycle, through their mineralization activity, dead organic matter. Despite its fundamental importance for ecosystem functioning, microbial mineralization of detritus remains hardly predictable, most probably because microbial decomposers are also able, depending on environmental conditions, to immobilize inorganic nutrients from their environment to fulfill their nutrient stoichiometric demand. To date, most models aimed at understanding or predicting nutrient recycling ensured by microbial decomposers have considered fixed decomposers’ elemental ratios. Yet, several studies showed that many decomposer species (including both bacteria and fungi) are largely variable in their elemental contents. In this context, determining the balance between nutrient immobilization and mineralization of microbial communities appears far from being trivial. The development of approaches based upon stoichiometric traits of microbial species and communities might represent a promising way to solve this question.
Focusing on stream microbial decomposers of leaf litter (firstly aquatic hyphomycetes, then more complex, natural communities), the StoichioMic project first aims at understanding in further details the elemental plasticity of microbial decomposers, at the specific and at the community level, and its consequences on the balance between nutrient immobilization and nutrient recycling (Task 1). In a second step, StoichioMic will furnish important data for understanding and predicting the response of microbial decomposers elemental plasticity to a selection of global change parameters and, in turn, consequences on nutrient immobilization and recycling (Task 2). Among these parameters, temperature increase, changes in carbon quality, and occurrence of contaminants will be specifically investigated, these stressors being certainly among the most important currently impacting microbial processes. Finally, StoichioMic will permit to investigate how these responses are modulated by the presence of competitors (plants) and predators (detritivores), rendering the results of the project more transposable to field situations (Task 3).
StoichioMic will bring new insights into the understanding of microbial ecology and, in particular, on the determinism of microbial community structure and on ecological processes ensured by microorganisms. In particular, StoichioMic should give experimental and theoretical evidences of the importance of microorganisms’ elemental plasticity on the intensity of nutrient mineralization and immobilization. These parameters should be of particular interest for predicting ecosystem services ensured by microorganisms in ecosystems, in particular nutrient retention and recycling. StoichioMic should also give some practical information for ecosystem managers, such as a new potential bioindicator of nitrogen and phosphorus bioavailability in streams, and information concerning the nature of the leaf litter species maximizing nutrient retention in streams. StoichioMic will also give fundamental information for predicting the consequences of diverse global change parameters, including climate change, eutrophication, and contaminations, on microbial communities and C, N and P biogeochemical cycles in ecosystems. This ambitious and original project will be included in the well-established Ecological Stoichiometry conceptual framework that permits to relate organism physiology to community structures and explicitly considers organisms’ elemental contents and requirements for predicting consequences on C, N and P biogeochemical cycles.