2 research outputs found
Macrophyte Complexity Controls Nutrient Uptake in Lowland Streams
18 páginas, 6 figuras, 6 tablas.Macrophytes act as ecosystem engineers in lowland
stream ecosystems, enhancing habitat complexity and
physical structure. Studies have demonstrated that
macrophyte abundance and growth form can dictate the
degree to which physical and biological stream characteristics
are altered. However, few studies have investigated
the influence of macrophytes and their speciesspecific
variation in morphological complexity on functional
processes, such as nutrient uptake. We injected
15N-labeled ammonium (15N-NH4
+) into four macrophyte-
rich lowland streams in Denmark to quantify the
uptake of NH4
+ by macrophytes, epiphytic biofilms,
benthic biofilms, and suspended particulate organic
matter in the water column. Overall, macrophytes and
their epiphytic biofilms accounted for 71–98% of the
reach-weighted uptake across the study streams. While
macrophytes had the highest rates of NH4
+ uptake
among the compartments we measured, the epiphytic
biofilms had the highest uptake efficiency, ranging from
0.06 to 0.6 mg N mg Nbiomass
-1 d-1. Among all compartments,
the uptake efficiency was inversely related to the
carbon-to-nitrogen ratio. Macrophyte complexity, expressed
as leaf perimeter-to-area ratio (P:A), varied
among the five species found in the study streams. The
uptake rates by macrophyte species with high leaf P:A
were, on average, an order ofmagnitude higher thanthe
rates for species with simple leaf morphology (430 vs.
49 mg N m-2 d-1). In summary, our results indicate
that macrophytes regulate stream function both via direct
uptake of NH4
+ from the water column and by
providing a substrate for epiphytic biofilms. Furthermore,
the effect of leaf architecture on nutrient uptake
rates provides evidence that physical complexity can
enhance ecosystem function.We are grateful to the
Danish Council for Independent Research and the
EU MARS Project (Contract #60337) for providing
funding to support our research and the kind land
owners who allowed us to access our field sites.Peer reviewe