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PhD Project

Responses of litter decomposition and associated microbial
activity to simulated global warming and nitrogen enrichment:
disentangling direct environmental and litter quality effects

Decomposition processes are often influenced by litter chemistry, which
potentially can be influenced by both, increasing temperature and N
enrichment. In this chapter we investigated the potentially changed litter
quality (by warming and N enrichment) on decomposition processes
influenced by warming and N enrichment. To this end, we measured
litter mass loss, chemical litter properties, microbial respiration and
growth rates, bacterial and fungal biomass and production rates. Litter
decomposition over 225 days was slightly accelerated at elevated
temperature and bacterial biomass associated with the litter was
significantly increased in response to both warming and, less clearly to
nitrogen enrichment. In contrast, respiration rates and growth
efficiencies of the microorganisms were unaffected by any of the
treatment factors, and bacterial and fungal growth or production rates
responded negatively to warming and were unaffected by N
enrichment. Warming during plant growth increased N and P contents
of dead brown leaves at the time of collection from shoots, but did not
affect contents of acid-detergent fiber (ADF), cellulose or proximate
lignin. Nitrogen enrichment during plant growth had no effect on any of
the litter constituents measured. Likewise, no clear effects on litter
quality were mediated by either warming or N enrichment during
decomposition. Together this data suggests that (i) impacts of
moderate global change are strongest on bacterial and fungal growth,
(ii) impacts are more important when acting during decomposition than
during plant growth, and (iii) temperature effects are more important
than N enrichment effects, including effects on litter nutrient contents as
a result of altered environmental conditions during plant growth.