Effects Of Elevated Surface Ozone On Nitrogen Cycle And Related Functional Microbiology In Rice-Wheat Rotation Soil

An FACE (Free-air ozone concentration enrichment) system was used to investigate the effects of elevated surface O3concentration on rice and wheat N-uptake, soil total N and mineral N status, urease activity, and the population of nitrogen-fixing bacteria (NFB), ammonia-oxidizing bacteria (AOB), denitrifying bacteria (DNB), soil nitrification and denitrification potentials at different growth stages of rice and wheat. The main results were as following:1、When O3concentration elevated, N-uptake of individual wheat increased, while soil total N and mineral N decreased. At maturing stage of wheat, in FACE soil, total N and NH4+-N decreased significantly (p<0.05) by9%and71%, respectively, and soil N03--N decreased by36%than that of ambient soil. Elevated O3tended to enhance soil urease activity, which was significantly (p<0.05) higher than the ambient soil in jointing, heading and filling stages of wheat. Elevated O3also tended to increase the population of soil AOB and DNB, which were significantly (p<0.05) higher than the ambient soil at wheat maturing time, respectively. Although the specific nitrification potential of AOB tended to decrease, soil nitrification potential under elevated O3tended to increase owing to higher DNB population. Although the specific denitrification potential of DNB significantly (p<0.05) decreased, soil denitrification potential under elevated O3did not alter because of the high population. These results suggested that elevated O3accelerated wheat N-uptake, soil N transformation and urease activity, and increased the population of soil AOB and DNB with low metabolic activity.2、When O3concentration elevated, N-uptake of individual rice tended to increase, while soil total N tended to decrease. At maturing stage of rice, soil total N decreased averagely by9%in FACE soil than in ambient soil. Elevated O3tended to enhance soil urease activity, which averagely increased by13%at maturing stage of rice. During the whole growth stage of rice, the population of soil AOB and DNB showed increased first and then decreased, and both reached the peak at rice flowering stage, but increase more under the elevated O3. Elevated O3tended to decrease soil nitrification and denitrification potentials, which averagely decreased by17%and24%, respectively, owing to low specific nitrification potential of AOB and specific denitrification potential of DNB at rice maturing stage. These results suggested that under elevated O3, soil N transformation accelerated because of rice N-uptake increasing, the population of soil AOB and DNB tend to increase but their metabolic activity tended to decrease.3、When O3concentration elevated,the number of nitrogen-fixing bacteria (NFB) in rice soil, averagely decreased by26%in returning stage and7%in flowing stage. In wheat soil NFB averagely decreased by7%and7%in tillering stage and heading stage respectively.DGGE fingerprinting profile of DNB revealed that elevated O3changed the community structure of NFB. Most NFB belong to Azospirillum in experiment soil.In conslusions, elevated O3accelerated soil N transformation, increased the population of soil AOB and DNB with low metabolic activity, decreased the population of soil NFB as well as community structure of NFB.