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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. |
An example of a mesocosm. |
Phragmites australis leaves |
Syber Green stained Bacteria |
Aquatic fungi |