Tesis doctoral de Joan Artigas Alejo
The microbial structure and metabolism of benthic microbial communities was analyzed over a hydrological year in a mediterranean forested stream (the fuirosos). Microbial heterotrophic biomass was generally higher than autotrophic biomass, except during short periods of high light availability in the spring and winter. During these periods, algal biomass and peptidase activity increased in benthic communities. Heterotrophic biomass and activity (polysaccharide and lignin degrading activities) showed a peak in autumn. The aquatic microfungi in the fuirosos mainly developed in leaves, but were also relevant in sand and gravel habitats. Microbial communities associated to leaves and branches showed higher c: n and lower n: p molar ratios and higher polysaccharide degrading activity. Instead, biofilms on sand and gravel, where algae accumulated and fine detritic materials were more available, showed lower c: n and higher n: p molar ratios, as well as higher ligninolytic and peptidase activity. a three-month litter breakdown experiment using two different leaf species (platanus acerifolia and populus nigra) revealed different patterns of fungal and bacterial biomass accumulation. Bacteria increased earlier than fungi in leaves, though fungi prevailed in terms of biomass and activity. The widest and fastest leaf structural changes and the maximum enzyme activities per unit of microbial carbon took place between the second and third week of experiment. In contrast to leaf communities, stream epilithic biofilms (communities growing on rocky substrata) are mainly colonized by algae, bacteria and protozoa. Patterns on epilithic biofilm formation in two streams (a central european, the walzbach and a mediterranean, the fuirosos) were related to environmental characteristics. Flooding episodes produced a drastic reset in diatom populations in the fuirosos. Overall, the higher structural complexity of the epilithic biofilms in the mediterranean stream (higher bacterial biodiversity and biomass and extracellular polysaccharide content) did not result on major enzyme activity efficiency per bacterial cell. Conversely, the environmental stability in the central european stream played an important role in shaping biofilm structure and in regulating a more efficient use of the organic matter resources. two nutrient enrichment experiments (nitrate and phosphate addition) were conducted on benthic microbial communities to determine: i) whether long- and short-term (1.5 years and 48h, respectively) nutrient enrichment affected sporulation and diversity of aquatic hyphomycetes, and ii) whether changes in total water nutrient concentration and n:p molar ratios affected epilithic biofilms integrity. Long-term nutrient additions did not affect potential sporulation rates, though short-term nutrient additions produced insignificant increases in these rates. However, long-term nutrient enrichment produced significant changes in the hyphomycetes community composition. Further, biofilms exposed to high water nutrient concentration showed higher n recycling (increase of peptidase activity) within the biofilm, and strong p limitation (n:p ratio of 56:1) mostly affected bacteria and stimulated eps accumulation and phosphatase activity. Results from both experiments revealed that stream benthic community is dynamic and sensitive to the changes in the water nutrient availability.
Datos académicos de la tesis doctoral «The role of fungi and bacteria on the organic matter decomposition process in streams: interaction and relevance in biofilms«
- Título de la tesis: The role of fungi and bacteria on the organic matter decomposition process in streams: interaction and relevance in biofilms
- Autor: Joan Artigas Alejo
- Universidad: Girona
- Fecha de lectura de la tesis: 19/12/2008
Dirección y tribunal
- Director de la tesis
- Sergi Sabater Cortés
- Tribunal
- Presidente del tribunal: Jesús Pozo Martinez
- arturo Elosegui irurtia (vocal)
- Manuel Graí§a (vocal)
- helmut Fischer (vocal)