Assessing changes in microbial respiration, bacterial growth efficiency, and bacterial production with nutrient addition to batch cultures

Abstract

Dissolved organic carbon (DOC) provides an important source of energy in lotic systems that can regulate food chain dynamics. It is thought that inorganic nutrient addition to stream culture samples will increase microbial respiration and bacterial growth efficiency (BGE). Nutrient limitation may prevent microbial communities from reaching their full potential in terms of biomass and efficiency, which could limit organisms at higher trophic levels. This study utilized batch cultures to assess changes across a variety of water quality and nutrient parameters in an effort to assess the role of inorganic nutrient addition in regulating microbial activity in headwater streams. Treatments of phosphorus addition (þP) and nitrogen plus phosphorus addition (þNþP) were used to assess changes in microbial activity in samples collected from forested and agricultural headwater streams. Phosphorus limitation was observed only at a single site, suggesting that a secondary limiting nutrient (e.g. nitrogen) may affect microbial activity at the other sites. Combined phosphorous and nitrogen additions demonstrated that nitrogen did limit microbial respiration at many of the study sites. BGE was highly variable and did not seem to be controlled by inorganic nutrient concentration. We did observe increased carbon production with nutrient addition at some of the study sites. The results of this study indicate that small streams could export more carbon through respiration rather than by incorporating available DOC into biomass.

Distinct patterns of microbial metabolism associated to riverine dissolved organic carbon of different source and quality

“…Our results show clear patterns in metabolism across all the rivers studied, but distinct microbial metabolic patterns were also evident when rivers were grouped according to the categories that emerged from the PCA (Figure 2). For example, in line with previous reports [Berggren et al, 2007;Dempsey et al, 2013], BGE…”

“…Our results show clear patterns in metabolism across all the rivers studied, but distinct microbial metabolic patterns were also evident when rivers were grouped according to the categories that emerged from the PCA (Figure ). For example, in line with previous reports [ Berggren et al ., ; Dempsey et al ., ], BGE was relatively high in all forested brown‐water catchments and forest headwaters were associated with significantly higher BGE than peat bog‐influenced streams and rivers (Figure ). BR, on the other hand, was significantly higher in clear nonheadwater mountain rivers than in all other catchments, especially in comparison with the forest headwaters.…”