Nitrogen Cycling With The Distribution And Activity Of Novel Processes Microorganisms In Upland Soils

In biological cycle of the earth,nitrogen is an important element,biological nitrogen cycle is closely related with the carbon cycle through variety of ways.In recent years,new nitrogen cycle process was found,such as anaerobic ammonium oxidation?anammox?and nitrite-dependent anaerobic methane oxidation?n-damo?.The new theoretical system of nitrogen and carbon cycle continues to be improved.However,there are still many vacancies in the understanding of nitrogen cycling so far.The study about anammox and n-damo is also focused on aquatic ecosystems,the role in upland soil is not yet well explored.Here,we studied the step process of soil nitrogen cycle and investigated the distribution and activity of anammox and n-damo bacteria in upland soils.We also expored the interaction between nitrogen cycle microorganisms?ammonia-oxidizing archaea,ammonia oxidation bacteria,denitrifying bacteria,anammox bacteria and n-damo bacteria?.Evidence was obtained with molecular biology methods,environmental factors analysis and stable isotope-tracing technique.Based on the study of different types of upland soil cores,the following results were obtained:In different types of upland soil cores,the rate of aerobic ammonia oxidation?NH₄⁺-NO₂^-?was 0.16-124.93 times of nitrite oxidation rate?NO₂^--NO₃^-?.Nitrification should not be regarded as a single reaction,it included two separate steps of ammonia oxidation reaction and nitrite oxidation reaction.Similar to the nitrification process,there was no rate synchronization between nitrate reduction?NO₃^--NO₂^-?and nitrite reduction?NO₂^--N₂?during denitrification,the denitrification process also included two separate steps.In addition,the sources of NO₂^-came from different process of nitrogen cycle in the upland soils.The reaction of nitrification and denitrification could dominate nitrogen cycle respectively in different types of soils.As the main consumption of NO₂^-,the role of nitrite oxidation,nitrite reduction,anammox and dissimilatory nitrite reduction to ammonium was diversity in different types of upland soils.The abundance and activity of anammox bacteria was both low in the upland soils,the abundance was 5.93×10³-2.60×10⁵ copies g^-1 and the activity was 0.002-0.52 nmol N g^-1 h^-1.The distribution of anammox in the vertical soils was unbalanced.The activity of anammox near water level was the highest,which consistented with the region where the highest value of abundance appeared.The rate of anammox in the vicinity of water level was significantly higher than denitrification rate and occupied the dominant position of soil nitrogen loss.In addition,the source of NO₂^-substrate for anammox bacteria was determined by the dominant process of soil nitrogen cycling.If the nitrification process controled nitrogen cycling,the NO₂^-substrate came from aerobic ammonia oxidation reaction.And if the soil nitrogen cycle was dominated by the denitrification process,the nitrate reduction reaction provided NO₂^-substrate for anammox bacteria.We found the anammox bacteria from the agricultural upland in Beili River showed apparent spatial heterogeneity and the biodiversity was high.‘Brocadia',‘Kuenenia' and ‘Jettenia' existed here and the highest biodiversity appeared in the subsurface soil.The spatial heterogeneity of n-damo bacteria here was also apparent,while its biodiversity was very low.Moreover,the non-continues vertical distribution showed the preferred habitats of n-damo bacteria in upland soil might restrict to certain depths.It might be an integrated effect of substrate shortage and the competition with denitrification bacteria in natural environments manipulating the non-continuous distribution of n-damo bacteria in the upland soil ecosystems.In surface soil?0-20 cm?,denitrification?NO₂^--N₂?contributed 85.0-99.0% of N loss with rate of 1.23–2.73 nmol N g^-1 h^-1,which was significantly higher than that of anammox rate(0.01–0.46 nmol N g^-1 h^-1,1.0-14.4 %)and n-damo rate(0.02 nmol N g^-1h^-1,0.6 %).The contribution of N loss from denitrification,anammox and n-damo process was 40.23-89.07 g N m^-2 yr-1,0.41-15.07 g N m^-2 yr-1 and 40.65 g N m^-2 yr-1,so denitrification was the main contributor to N-loss in surface soil.However,in subsurface and deep soil?20-300 cm?where no n-damo rate was detected,the anammox rate(0.00005-0.18 nmol N g^-1 h^-1,51.4-89.5%)was higher than the denitrification rate(0.00001-0.06 nmol N g^-1 h^-1,10.5-48.6 %).The contribution of N loss from denitrification and anammox process was 0.00028-1.88 g N m^-2 yr-1 and 0.0015-5.78 g N m^-2 yr-1.Anammox dominated the N loss in the deeper soil core.The studies about step process of soil nitrogen cycling and new nitrogen cycle microorganism are changing our understanding of the nitrogen cycle,providing new insight about soil nitrogen loads and nitrogen cycle fluxes.As a key factor affecting the global nitrogen cycle model,the new nitrogen cycle process will improve our understanding of nitrogen balance constantly.