Combined effects of eutrophication and climate change on fen meadows

Nitrogen (N) and sulphur (S) deposition, as
well as altered soil moisture dynamics due to climate
change can have large effects on fen meadow biogeochemistry
and vegetation. Their combined effects may
differ strongly from their separate effects, since each
process affects different nutrients through different
mechanisms. However, the impacts of these environmental
problems are rarely studied in combination. We
therefore investigated the separate and interactive
effects of current levels of N- and S-deposition and
changes in soil moisture dynamics on fen meadow
vegetation. We focused on vegetation biomass and N:P
stoichiometry, including access to soil P through root
surface phosphatase activity, in a 3-year factorial addition
experiment in an N-limited rich fen meadow in the
Biebrza valley in Poland. We applied 29.5 kg N ha-1
year-1 and 32.1 kg S ha-1 year-1
, which correspond
to current deposition levels in Western Europe.
Changes in soil moisture dynamics due to climate
change were mimicked by amplified drying of the soil
in summer. This level of N-deposition had limited
effects on plant biomass production in this rich fen,
despite low foliar N:P ratios that suggest N limitation.
This level of S-deposition, however, resulted in
decreased vegetation P-uptake and biomass. We also
showed that increased summer drought resulted in
considerable increases in vegetation biomass. We found
no interactive effects on vegetation biomass or N:P
stoichiometry, possibly as a result of the limited main
effects of the separate processes.