Prior stress exposure influences microbial community assembly and litter decomposition in headwater streams
Abstract
In the context of global change, headwater rivers face various anthropogenic and environmental stressors that impact biodiversity and ecosystem functions. This study evaluates how prior exposure of microbial communities (aquatic hyphomycetes and diatoms) to nutrient deficiency (nitrogen and phosphorus) or fungicide contamination (tebuconazole) influences their ability to colonize and decompose leaf litter. Aquatic hyphomycetes sporulation and diatom cultivation were conducted under two stressful conditions: nutrient deficiency or exposure to 10 µg.L-1 tebuconazole. Four microbial assemblages were then created under non-stressful conditions: (i) bacteria alone, (ii) bacteria + diatoms, (iii) bacteria + hyphomycetes, and (iv) bacteria + diatoms + hyphomycetes. These assemblages were placed in contact with sterile maple leaf discs for 1.5 days to allow colonization, then transferred to fresh medium for 30 days. Samples were collected at 1.5, 10, and 30 days to assess decomposition rates, stoichiometric composition (C:N:P), and microbial communities via qPCR. Initial results showed significant effect of microbial assemblage composition on decomposition, with increased efficiency when hyphomycetes and diatoms were associated, indicating that hyphomycetes are the primary contributors to litter decomposition and suggesting functional complementary between these groups. Stoichiometric analysis revealed differentiated effects of assemblages on nitrogen and phosphorus fixation dynamics in leaves. However, no significant treatment effects were detected, suggesting resilience of microbial communities or recovery mechanisms. qPCR analyses of microbial composition are ongoing to characterize microbial succession and identify mechanisms of differentiated colonization. These results will contribute to improving understanding of the links between microbial community structure and decomposition processes in an environmental stress context.