Shifts of nitrogen transforming microbial communities during paddy soil evolution.

The aim of this Ph.D. thesis was to investigate the consequences of land-use changes from tidal wetlands to paddy soils and long-term cultivation up to 2000 years for nitrogen transforming microbial communities. Nitrogen is important for rice growth, especially in flooded soils, which are known to be strongly nitrogen deficient. We sampled a paddy soil chronosequence in the Yangtze River Delta in China, where it is a common practice to do land reclamation by sea dyke building. Differences in nitrogen-fixing, nitrifying and denitrifying microbial community structure and function along the chronosequence could be observed, following alterations in soil physical and chemical properties. While abundances of nitrogen fixation and nitrification genes as well as diversity pattern changed soon after tidal wetland conversion, gene abundance pattern of denitrification showed only after 300 years of paddy soil development significant shifts