The Influence Of Typical Environmental Factors On Nitrification And Physiological Ecology Of Ammonia-oxidizers

Nitrification is an important process in global nitrogen cycling. It includes ammoxidation which oxidizes ammonia to nitrite and nitrozation which oxidizes nitrite to nitrate, and ammoxidation is the rate-limiting step of nitrification and the key point of study. N itrification is mainly performed by ammonia oxid izers, and environmental factors effect nitrification by impacting physiological activity of ammonia oxidizers. Researches show changes of environmental factors like ammonia concentration, temperature, fertilization, agrotype, heavy metal stress, moisture, and oxygen concentration, produce influence on community abundance, structure and activity of microoganism. It has been research hotspot that explore the influence of environmental factors on ammonia oxidizers.Water is the basic material of life existence and continuation, and changes of moisture in soil certainly have influence on microoganism. Water flooding generally leads to organic matter accumulating, redox capacity increasing, pH rising. There has good correlation among organic matter, redox capacity and ammonia-oxidizing archaea activity. pH is one of the important factors which influence the activity, structure, and relative abundance of ammonia oxidizers. It is stated that the optimal p H of ammonia-oxidizing bacteria is 6.6-8.0, or even higher. In most study, ammonia-oxidizing bacteria manage ammoxidation in neutral and alkaline soil. In soil with low p H, there are few ammonia-oxidizing bacteria relatively, and ammonia-oxidizing archaea are domain which have more affinity for ammonia. O xygen is the matrix of nitrification, and its concentration impacts on ammonia-oxidizers’ niche. In dynamic researches, it has been discovered ammonia-oxidizing archaea have a lower semi-saturation constant to oxygen than bacteria, thus, have advantages in low oxygen condition.Marine archaea and soil arhaea are important branches of ammonia-oxidizing archaea, and exploring their competition between each other and adaption to environment is significant for ammonia-oxidizing archaea’s study.By using molecular techniques, such as PCR, qPCR, DGGE, clone library construction and sequencing, 454 high troughput pyrosequencing co mbined with DNA-SIP, this study explored the influence of typical environmental factors(moisture, pH, oxygen) on nitrification as well as its active ammonia oxidizers and their ecophysiological characteristics, and also examined the effect of typical environmental factors(moisture, p H, oxygen) on ammonia oxidizing microorganisms and investigated niche specialization of ammonia-oxidizing archaea or bacteria communities in response to the typical factors in complex environments under in situ condition. The main research and conclusions are as follow:Soil samples used in this study were collected at three altitudes in regions of Wan-Zhou, Feng-Du and C hang-Shou, representing 8, 5 and 0 times flooding-drying management, respectively. Soil physiochemical properties were analyzed and microcosms were constructed to monitor nitrification activity by fertilizing soils with ammonium substrate. Real-time PC R was employed to quantify the population size of ammonia-oxidizing archaea(AOA) and bacteria(AO B). DGGE fingerprints and clone libraries were conducted to investigate the shift of AO A and AOB compositions in nitrifying soils. Among the physiochemical characteristics of the soils, soil organic matter and total phosphates increased along with cycle increasing. After incubation for 13 days, the net nitrification rates of the samples with 8 cycles exceeded those with 5 cycles. The quantities of both AOA and AOB have increased during the incubation. Phylogenetic analysis showed that AOA were placed within the soil Group 1.1b and soil Group 1.1a, while bacterial ammonia oxidizers were closely related to Nitrosospiraand Cluster 0. Periodical flooding-drying increased soil organic matter, enhanced soil nitrification activity and likely played important roles in shaping community structures of soil ammonia oxidizers.This study mix acidic forest soil which active ammonia oxidizers are marine arhaea Group 1.1a-associated lineage and alkaline paddy soil which active ammonia oxidizers are soil arhaea Group 1.1b lineage with equa l dry weight, regulate pH and oxygen of the mixed soil. The result of incubation experiment shows nitrification rarely occurred in low pH soil, while nitrification activity was significantly stimulated by urea fertilization in pH6.0 and 7.6 soil. N itrification rate in high O2 environment is higher than low O2 environment. By using qPCR technique, it shows ammonia-oxidizing archaea obviously increase during the incubation with adding urea. By 454 high troughput pyrosequencing combined with DNA-SIP, it indicates active ammoniaoxidizers are almost soil archaea lineage Group 1.1b. The results suggest that pH not oxygen is the main effect factor of nitrification, oxygen has a certain influence on nitrification as well; in neutral and alkaline soil, soil archaea lineage have activity in high O2 and low O2 environment and have more adaptive capacity than marine lineage.Taken together, the study of the influence of typical factors on nitrification can be summarized into three points:(1) Periodical flooding-dryingenhanced soil nitrification activity and likely played important roles in shaping community structures of soil ammonia oxidizers;(2) pH has more influence than oxygen on nitrification.(3) soil archaea lineage have activity in high O2 and low O2 environment of neutral and alkaline soil and have more adaptive capacity than marine lineage.