A major challenge in current Ecology is to determine how human activities affect the relationships between biodiversity and ecosystem functioning. The Functional Ecology team aims to understand the impacts of anthropogenic stressors on aquatic communities and ecosystem processes. Particular emphasis has been given to plant litter decomposition, a key ecosystem process that links riparian vegetation, physico-chemical environment and decomposer communities, namely invertebrates, fungi and bacteria.
Our studies in streams impacted by urbanization, agriculture and industrial activities showed that leaf breakdown rates and the associated decomposers respond to water quality degradation, supporting that leaf breakdown experiments are valuable to assess stream integrity. We found that metals and inorganic nutrients alone or in mixtures severely affect the structure and functions of aquatic microbes. Generally, pollution affected fungal diversity more than biomass and decomposition, suggesting that functional redundancy may occur among aquatic fungi. Data from manipulative experiments provide evidence of positive effects of fungal diversity on leaf decomposition and related ecosystem functions. The exposure to stressors (e.g., metals) decreased the positive diversity effects on leaf decomposition, indicating that biodiversity effects are modulated by the environmental context. Moreover, the variability of process rates (e.g., leaf decomposition) decreased with increasing fungal species richness, particularly under metal stress. These results were supported by transfer experiments in streams and suggest that biodiversity helps to buffer environmental change contributing to functional stability. We also found that species identity affect ecosystem function into a greater extent than species richness, probably because species do not equally contribute to ecological processes. Because traits that determine how species affect ecosystem processes may differ from those that determine how a species responds to stress, we also addressed the mechanisms underlying the resistance / tolerance of aquatic fungi to metal stress. Our results suggest that the tolerance of aquatic fungi to metals is associated with their ability to initiate an efficient antioxidant defense system and to undergo programmed cell death.
The work greatly beneficiate from our culture collection of aquatic fungi that comprises more than 550 isolates (about 65 species) collected from streams in Portugal, Spain, France, Italy and Switzerland.
Ongoing and future Work
The Functional Ecology team has been studying the impacts of anthropogenic activities on aquatic communities and stream ecosystem processes. Taking into account that freshwater biodiversity is highly endangered, understanding the mechanisms and the conditions under which diversity affects ecosystem processes, is of great priority. Our main goal is to better understand the role of biodiversity to sustain ecosystem processes and the services they provide. Particular emphasis has been given to plant litter decomposition and decomposer communities, namely invertebrates, fungi and bacteria. Most studies have been conducted by manipulating diversity at single trophic levels. We intend to examine diversity effects at multitrophic levels (e.g. fungi and invertebrates) and to scale up experiments across a range of spatial and temporal scales. This is crucial if we want to predict the consequences of species loss to ecosystem functioning and stability. Additional attention is now being given to climate change because is expected to have far reaching impacts on streams from altering temperature and runoff regimes.
In parallel, the effects of priority and emerging contaminants (e.g. metals, aromatic hydrocarbons and engineered nanoparticles) will be studied at the community, population and cellular level. Addressing impacts within and across different biological levels of organization pave the way to identify sensitive organisms, potential biomarkers, and to elucidate the action mechanism of contaminants in aquatic organisms, ultimately contributing to ecological risk assessment. Particular attention will continue to be given to fungi and invertebrates because they are important mediators of carbon transfer in aquatic food webs.
Pascoal, C., Cássio, F., Nikolcheva, L.G. and Bärlocher, F. 2010. Realized fungal diversity increases functional stability of leaf-litter decomposition under zinc stress. Microbial Ecology, 59:84–93.
Azevedo, M.-M., Almeida, B., Ludovico, P. and Cássio, F. 2009. Metal stress induces programmed cell death in aquatic fungi. Aquatic Toxicology, 92: 264–270.
Duarte, S., Pascoal, C., Garabetian, F., Cássio, F. and Charcosset, J.-Y. 2009. Microbial decomposer communities are mainly structured by the trophic status in circumneutral and alkaline streams. Applied and Environmental Microbiology, 75: 6211-6221.
Duarte, S., Pascoal, C., Alves, A., Correia, A. and Cássio, F. 2008. Copper and zinc mixtures induce shifts in microbial communities and reduce leaf litter decomposition in streams. Freshwater Biology, 53: 91-102.
Duarte, S., Pascoal, C. and Cássio, F. 2008. High diversity of fungi may mitigate the impact of pollution on plant litter decomposition in streams. Microbial Ecology, 66: 688-695.
Azevedo, M.-M., Carvalho, A., Pascoal, C., Rodrigues, F. and Cássio, F. 2007. Responses of antioxidant defenses to Cu and Zn stress in two aquatic fungi. Science of the Total Environment, 377: 233-243.