Nitrogen mineralization and water-table height in oligotrophic deep peat

Summary Peat cores, 0–60 cm depth, were taken on 14 occasions from three experimental plots where the water levels in the surrounding ditches had been artificially controlled for 14 years at 0, 20 and 50 cm below the surface. Numbers of aerobic and anaerobic ammonifying bacteria in the profile were significantly increased (P< 0.05) by lowering the water level from 0 to 50 cm. These increases occurred mainly in the surface 20 cm horizon, where 80%–90% of the ammonifying bacteria in the profile occurred. Mineral N in fresh samples, which was present almost entirely as ammonium, decreased sharply with depth below 20 cm, and on two occasions concentrations were significantly greater (P<0.05) in plots with water levels at 20 and 50 cm than in the flooded peat. Readily mineralized N, produced during waterlogged incubation at 30°C for 9 weeks, was significantly greater (P<0.05) on eight occasions in samples from plots with water levels at 20 or 50 cm than in those where the water level was at the surface. Calculations showed that the increases in N availability as a result of lowering the water-table could be attributed mainly to deeper rooting.     

Influence of hydrological fluxes on the structure of nitrate-reducing bacteria communities in a peatland

Factors influencing nitrate dynamics and nitrate-reducing bacteria in peat soil in the field, were investigated in laboratory experiments. A previous study had indicated that the on-site effects of redox conditions and nutrient fluxes on microbial activity were influenced by hydrological conditions. However, the laboratory experiments indicated that peat samples from sites under different hydrological regimes exhibited different microbial activities independently of oxygenation conditions. The effects of redox conditions and nutrient fluxes (i.e. influence of NO₃⁻ and O₂ concentration) on the nitrate reducer community were therefore assessed. Microbial community structures in peat samples from sites under different hydrologic regimes were compared using Terminal-Restriction Fragment Length Polymorphism diversity signatures of the narG gene. This gene encodes the catalytic subunit of the nitrate reductase. Unexpectedly, the nitrate reducer communities were very similar at the beginning of the experiment whatever the peatland soil analysed. However, a strong structuration and divergence within the nitrate reducer communities, that was site-dependent, was evident after 76 h of incubation. These modifications within the microbial communities seemed to be due to differences in peat saturation at the sampling sites resulting from the different hydrological regimes. Of the forcing variables tested, oxygenation had a slight effect on the composition of the nitrate-reducers' community whereas nitrate addition had no effect. This study shows that a physical constraint such as hydrological regime might be considered important in microbial community composition.     

缺氧土壤中硝态氮还原菌的生理生化特征

综述国内外有关硝态氮还原菌生理生化方面的研究进展 ,包括同化还原、硝酸异化还原成铵、呼吸反硝化和非呼吸性反硝化 ,侧重于电子传递系统