Leaf litter decomposition in Mediterranean streamsmicrobial processes and responses to drought under current global change scenario

Résumé

This thesis studied the principal environmental controlling factors and microbial mechanisms involved in leaf litter decomposition in Mediterranean intermittent streams. Additionally, drought disturbance in both Mediterranean intermittent and Atlantic permanent streams was also evaluated. At the Mediterranean intermittent stream leaf litter decomposition varied mainly related to seasonal variations in temperature, conductivity and current velocity. Drought clearly affected microbial assemblages and functioning in these ecosystems although this did not resulted in changes on breakdown rates. In permanent streams drought disturbance also affected microbial activity and structure, reducing breakdown velocity due to emersion of leaves. Microbial communities from nutrient enriched streams were more resistant to drought disturbance. Results suggest that under more extreme environmental variation and dry conditions expected with the global change, microbial decomposers will be severely affected. However consequences in carbon recycling will depend on to the type of drought-related disturbance, interaction with other stressors and previous communities dwelling in.