1 research outputs found
Biofilm growth and nitrogen uptake responses to increases in nitrate and ammonium availability
13 páginas, 4 tablas, 5 figurasNitrate (NO3
-) and ammonium (NH4
+) are the
two major dissolved inorganic nitrogen (DIN) species
available in streams. Human activities increase stream DIN
concentrations and modify the NO3
-:NH4
+ ratio. However,
few studies have examined biofilm responses to
enrichment of both DIN species. We examined biofilm
responses to variation in ambient concentrations and
enrichments in either NO3
- or NH4
+. We incubated
nutrient diffusing substrata (NDS) bioassays with three
treatments (DIN-free, +NO3
- and +NH4
+) in five streams.
Biomass-specific uptake rates (Uspec) of NO3
- and NH4
+
were then measured using in situ additions of 15N-labeled
NO3
- and NH4
+. Biomass (estimated from changes in
carbon content) and algal accrual rates, as well as Uspec-
NO3
- of biofilms in DIN-free treatments varied among the
streams in which the NDS had been incubated. Higher
ambient DIN concentrations were only correlated with
enhanced biofilm growth rates. Uspec-NO3
- was one order
of magnitude greater and more variable than Uspec-NH4
+,
however similar relative preference index (RPI) suggested
that biofilms did not show a clear preference for either DIN
species. Biofilm growth and DIN uptake in DIN-amended
NDS (i.e., +NO3
- and +NH4
+) were consistently lower
than in DIN-free NDS (i.e., control). Lower values in
controls with respect to amended NDS were consistently
more pronounced for algal accrual rates and Uspec-NO3
-
and for the +NH4
+ than for the +NO3
- treatments. In
particular, enrichment with NH4
+ reduced biofilm Uspec-
NO3
- uptake, which has important implications for N
cycling in high NH4
+ streams.This study was funded by the Spanish
Ministry of Education and Science through NICON project (ref:
CGL2005-7362). MR was supported by a contract with the Spanish
Ministry of Science and Innovation through the MED_FORSTREAM
project (CGL2011-30590-C02-02). DvS’s work was also funded by a
Juan de la Cierva postdoctoral contract (JCI-2010-06397) from the
Spanish Ministry of Science and Innovation.Peer reviewe