Nutrient limitation of epilithic and epixylic biofilms in ten North American streams

Abstract

SUMMARY 1. Nutrient diffusing substrata were used to determine the effect of added inorganic nitrogen (N) and phosphorus (P) on the development of epilithic and epixylic biofilms in 10 North American streams. Four treatments of diffusing substrata were used: Control (agar only), N addition (0.5 m NaNO3), P addition (0.5 m KH2PO4), and N + P combined (0.5 m NaNO3 + 0.5 m KH2PO4). Agar surfaces were covered with glass fibre filters (for epilithon) or discs of untreated white oak wood veneer (for epixylon). 2. We found that if algae showed significant response to nutrient addition, N limitation (either N alone or N with P) was the most frequent response both on GF/F filters and on wood. Despite the low dissolved nutrient concentrations in our study streams, more than a third of the streams did not show any response to N or P addition. In fact, P was never the sole limiting nutrient for algal biofilms in this study. 3. Nutrient addition influenced algal colonisation of inorganic versus organic substrata in different ways. The presence of other biofilm constituents (e.g. fungi or bacteria) may influence whether algal biomass on wood increased in response to nutrient addition. Algae on organic and inorganic substrata responded similarly to nutrient addition in only one stream. 4. Fungal biomass on wood was nutrient limited in six of 10 study streams. N limitation of fungal biomass (with or without secondary P limitation) was most frequent, but P limitation did occur in two streams. 5. Our results show that biomass responses to nutrient addition by the heterotrophic and autotrophic components of the epixylic biofilm were different, though both experienced the same stream nutrient conditions. For algae and fungi growing on wood, limiting nutrients were rarely similar. Only three of nine streams showed the same biomass response to nutrient addition, including two that showed no significant change in biomass despite added nutrients.

High habitat-specificity in fungal communities in oligo-mesotrophic, temperate Lake Stechlin (North-East Germany)

“…These autotrophic lake biofilms seem to be a rich source of fungal biodiversity and pose promising target habitats for future studies. Biofilms (in our case mainly littoral periphyton and epilithic biofilms) have been rarely examined for fungi, and only a few studies on stream ecosystems have investigated the fungal occurrence (measured as ergosterol) on substrates other than leaves (Tank and Dodds 2003;Artigas et al 2004;Aguilera et al 2007;Frossard et al 2012). In lakes and streams, periphyton can contribute substantially to the primary production of the whole ecosystem (Lalonde et al 1991;Vadeboncoeur et al 2007 and references therein; Vis et al 2007) and can be the primary food source for macrozoobenthic grazers (Cattaneo and Mousseau 1995).…”

Transformations in DOC along a source to sea continuum; impacts of photo-degradation, biological processes and mixing

“…The combined solar radiation and biofilm treatments did not lead to an overall increase in DO 14 C removal in the 'Peatland + Mountain' mix, but resulted in around 50% more removal in the 'Peatland + Agricultural' mix. This suggests that biofilm activity may be nutrient-limited, and therefore that they are more able to utilise peatderived DOC (either directly, or by utilising organic matter which has been partially broken down by photo-degradation) in the presence of elevated nutrients from agricultural runoff (Tank and Dodds 2003). It is worth noting that the amount of biofilm used in these experiments may represent upper limits for field conditions, because biofilm surface area to water volume ratios were relatively high, and contact times relatively long.…”

Nutrient Uptake and Mineralization during Leaf Decay in Streams – a Model Simulation

“…Results from previous studies suggest that autotrophic biofilms are stoichiometrically plastic since biomass N : P for a given biofilm composition can vary with environmental conditions (FRANCOEUR, 2001;TANK and DODDS, 2003;DODDS et al, 2004) while elemental composition of heterotrophic bacteria and fungi are more homeostatic (STERNER and ELSER, 2002;MAKINO et al, 2003). However, a few studies have observed limited elemental plasticity of aquatic bacteria (e.g., TEZUKA, 1990;CHRZANOWSKI and KYLE, 1996), and there is some evidence that fungi respond to low phosphorus by storing phosphorus in polyphosphate granules, reducing the phosphorus content of cell walls, and partially replacing phospholipid with phosphorus-free lipid (BEEVER and BURNS, 1980;JENNINGS, 1995).…”