Stream acidification increases nitrogen uptake by leaf biofilms: Implications at the ecosystem scale

Damon T. Ely, Daniel Von Schiller, H. Maurice Valett

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11 Scopus citations


While anthropogenic stream acidification is known to lower species diversity and impair decomposition, its effects on nutrient cycling remain unclear. The influence of acid-stress on microbial physiology can have implications for carbon (C) and nitrogen (N) cycles, linking environmental conditions to ecosystem processes. We collected leaf biofilms from streams spanning a gradient of pH (5.1-6.7), related to chronic acidification, to investigate the relationship between qCO2 (biomass-specific respiration; mg CO2-C g-1 fungal C h-1), a known indicator of stress, and biomass-specific N uptake (μg NH4-N mg-1 fungal biomass h-1) at two levels of N availability (25 and 100 μg NH4-N L-1) in experimental microcosms. Strong patterns of increasing qCO2 (i.e. increasing stress) and increasing microbial N uptake were observed with a decrease in ambient (i.e. chronic) stream pH at both levels of N availability. However, fungal biomass was lower on leaves from more acidic streams, resulting in lower overall respiration and N uptake when rates were standardized by leaf biomass. Results suggest that chronic acidification decreases fungal metabolic efficiency because, under acid conditions, these organisms allocate more resources to maintenance and survival and increase their removal of N, possibly via increased exoenzyme production. At the same time, greater N availability enhanced N uptake without influencing CO2 production, implying increased growth efficiency.5. At the ecosystem level, reductions in growth because of chronic acidification reduce microbial biomass and may impair decomposition and N uptake; however, in systems where N is initially scarce, increased N availability may alleviate these effects. Ecosystem response to chronic stressors may be better understood by a greater focus on microbial physiology, coupled elemental cycling, and responses across several scales of investigation.

Original languageEnglish
Pages (from-to)1337-1348
Number of pages12
JournalFreshwater Biology
Issue number6
StatePublished - Jun 2010


  • Aquatic fungi
  • Nitrogen uptake
  • QCO2
  • Respiration
  • Stream acidification
  • Stress


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