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The role of aquatic hyphomycete spores in headwater stream food webs: a food quality approach.

Periodic Reporting for period 1 - Spor-oikos (The role of aquatic hyphomycete spores in headwater stream food webs: a food quality approach.)

Reporting period: 2017-09-01 to 2019-08-31

The problem being investigated: Our aim was to understand a uninvestigated process on energy and nutrient flow in headwater streams: the fate of fungal spores. Headwater streams rely on allochthonous organic matter (mainly leaf litter and woody debris), which is used as energy source by aquatic hyphomycete decomposers. Fungal biomass may account for up to 8% of leaf litter mass in streams, and about 50% of their assimilated carbon (C) is converted into reproductive spores. The spores are a major component of fine particulate organic matter (FPOM), an important fraction of (C) fluxes in detritus-based systems. Yet, their role on headwater stream food webs has been overlooked, although they could be a non-negligible source of nutrients and essential molecules for aquatic filter feeder and collector consumers.

Why is it important for the society: This project brings new information on the relation between an anthropogenic constraint (nutrient loads) and the integrity (biotic and functional) of an essential component responsible of the mineralization of huge quantities of terrestrial carbon. Understanding how our activities are affecting natural nutrient cycles, and the responsible of these cycles contribute towards European policy objectives (biodiversity) and strategies (conservation).

Overall objectives:
1. Investigate the chemical factors controlling aquatic hyphomycetes' sporulation and deduce if global changes could modulate the sporulation process and the intrinsic quality of spores.
2. Study the role of aquatic hyphomycete spores as a resource for consumers in headwater streams by characterizing their elemental (C, N and P) and biochemical (FA and sterols) composition.

Conclusions of the action (achievements):
(1) Production of fungal mycelia without exposing it directly to the medium. (2) Demonstration that fungal mycelia produce spores differing in size when exposed to different nutrient ratios. This new finding has important implications in a global warming context where natural nutrient ratios are affected by anthropogenic activities. (3) Demonstration that certain stoichiometric ratios affect spores of mycelia exposed to different nutrient ratios. (4) Demonstration that the chemical complexity of essential nutrients (C, N and P) needs to be considered when studying the effect on biological traits. We showed that phosphorus chemical complexity can increase fungal spores biovolume, and the essential ratios CN and CP. This can have consequences in their potential trophic quality.
Work performed:
1. Obtention of fungal traits from several parts of the world and harvesting fungal spores without fungal mycelia (especial microcosm).
2. Experiments to elucidate if the investment of fungal mycelia on asexual spores could be affected by the quantity and the quality of the nutrients (i.e. treatment 1, 2, 3, 4 and 5 of phosphorus designed recalcitrant (PRec) and treatment 1, 2, 3, 4 and 5 of phosphorus designed labile (PLab)).
I tested two hypotheses (1) the mycelia exposed to nutrients would invest the energy in the production of spores as the conditions were favorable, increasing the chances of dispersion and colonization. (2) Fungal mycelia exposed to nutrients would invest on its biomass, maximizing the opportunity of having access to nutrients. In parallel we sampled spores of 4 oligotrophic and 4 eutrophic streams.Rationale: (a) The laboratory experiments investigated whether if it was possible to manipulate the elemental composition of the spores by exposing the mycelia to different nutrient ratios. (b) The field study aimed to investigate the elemental composition of spores coming from natural ecosystems.
3. Main scientific achievements and innovation output
(1) Production of fungal mycelium without exposing it directly to the medium. (2) Demosntration that fungal mycelium produce spores differing in size when exposed to different nutrient ratios. (3) Demonstrations that certain stoichiometric ratios could be affected in the spores of mycelia exposed to different nutrient ratios. (3) demonstration that essential nutrients (C, N and P) need to be considered when studying the effect on biological traits.
This projected address issued related to climate change. More precisely the project tried to understand how nutrient loads could affect the elemental composition of aquatic fungal spores. This approach, although specific, would help to better understand the flow of nutrients, from carbon to other essential nutrients, in a highly important and active component of running waters, microbial communities. The scientific achievements will bring new perspectives to the field of aquatic ecology and will be available for the scientific community offering hence the opportunity to increase the quality of models dealing with nutrients flows in continental aquatic systems.
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