Substratum type and nutrient supply as modulating factors of organic matter by stream biofilms

ROMANI, A.; ADONIS GIORGI; ACUNA, V.; SABATER, S.

LIMNOLOGY AND OCEANOGRAPHY

ASLO

Año: 2004 vol. 49 p. 288 - 296

0024-3590

The microbial community which colonizes stream benthic substrates (sand, rocks) is build responding to micro and macro-scale physical and chemical characteristics. The especific biofilm structure and metabolism of each substrate might be determinant for the global stream C cycling. Rock and sand colonization and biofilm formation at two trophic conditions (oligotrophic and eutrophic) was intensively followed during 44 days. Structural (C: N and polysaccharide content, bacterial and chlorophyll density) and metabolic (b-glucosidase, peptidase and phosphatase enzyme activities) biofilm parameters were analysed along the colonization process. The episammic biofilm (grown on sand) was characterized by a constant and high C: N content (22.7) along colonization and a higher degradation activity of polysaccharides and organic phosphorus compounds was measured. The epilithic biofilm showed a high C: N content at the beginning of the colonization (43.2) but decrease to lower values at the end (10.5). The epilithic biofilm is a more structured (higher proportion of polysaccharides) biofilm, composed by fresh active organisms (lower C: N ratio) and with an important internal recycling of nitrogenous compounds (positive relationship between N biofilm content and peptidase activity per bacterial cell). The epipsammic biofilm is an important site for organic matter accumulation and degradation were heterotrophic activities are predominant. The different trophic conditions of the flowing water affect the epilithic biofilm in increasing bacterial and algal biomass and in the epipsammic a decrease in the phosphatase activity was observed. However, the structural parameters such as C: N content and polysaccharide content werre not affected by water nutrient content. The paper underlies the different but key functions of the benthic stream biofilms and the importance of the preservation of habitat diversity.