| Soils harbor diverse microorganisms,which play an important role in the regulation of biogeochemical cycles and the maintaining of ecosystem function.Understanding the spatial distribution of microorganisms and its forming mechanisms will help us protect,manage and regulate the terrestrial ecosystems and cope with global environmental issues such as global warming.Nitrification,as a crucial component of the global nitrogen cycle,is of great importance to improve the utilization rate of nitrogen fertilizer.Researches about the effects of elevation and temperature on soil nitrification process can help us better understand the effects of climate change on nitrification and nitrifying microorganisms in paddy soils,thus providing a scientific basis for rational fertilization and nitrogen utilization.Therefore,this study,based on the biggest terrace in East China,Yunhe terrace,investigated the elevational distribution pattern of bacterial,archaeal and fungal diversity and community structure.At the same time,the differences of soil nitrification activity and active nitrifying microorganisms at different elevations as well as the effects of warming on soil nitrification were also explored.Main results are as follows:(1)The elevational distribution pattern of bacterial diversity and community compisiton in natural and paddy soils.The connectivity between bacterial communities in paddy soils is lower,and their response to environmental disturbances is slower than that of natural soils.Significant differences in bacterial community composition between natural and paddy soils were observed,and bacterial community composition differed significantly among the selected elevations in both natural and paddy soils.In natural soils,there was a monotonic decreasing trend of bacterial diversity and soil C/N ratio was the best predictor of both bacterial diversity and composition.In paddy soils,a Hump-Backed-like trend of bacterial species richness and diversity was found with a 'peak'appeared in elevation 500 m,and the bacterial diversity and composition were most strongly affected by soil available phosphorus(AP)content.There was a very significant positive correlation between the relative abundance of phosphate solubilizing bacteria and soil AP content,implying the great influence of phosphate solubilizing bacteria to the whole bacterial community.The historical effects persistent in soil microbial communities cannot be erased by contemporary disturbance even after a long-term rice cultivation process,although the contemporary factors(soil properties)were more important than the historical factors(elevation and geographic distance)in shaping bacterial community in both natural and paddy soils.(2)The elevational distribution pattern of archaeal diversity and community compisiton in natural and paddy soils.The connectivity between archaeal communities in paddy soils is higher,and their response to environmental disturbances is also faster than that of natural soils.Classes Nitrososphaeria associated with nitrification and Methanomicrobia associated with methane production dominated the archaeal communities in natural and paddy soils,respectively.The archaeal diversity increased with high elevation and also correlated with different soil properties in both kinds of soils.The contents of nitrate content and available phosphorus were the best predictor of archaeal diversity and community in natural and paddy soils,respectively.(3)The elevational distribution pattern of fungal diversity and community compisiton in natural and paddy soils.The relative abundance of Ascomycota increased while Basidiomycota decreased,and the co-occurence network of fungi in paddy soils were simpler compared with natural soils.In natural soils,the diversity of fungi decreased with elevation and was significantly negatively correlated with SOC and ammonium content,while positively correlated with soil nitrate content.In paddy soils,there was also a negative linear elevational distribution pattern of fungal diversity which was significantly correlated with soil nitrate content,CEC and soil texture.Soil C/N ratio and elevation was the best predictor for fungal community in natural and paddy soils,respectively.(4)Difference of nitrification and active nitrifiers in soils with different elevations.Nitrification activity increased from E200 to E600 and then to E1100,accompanied with significant growth of ammonia-oxidizing bacteria(AOB)over the 56-day incubation,while the abundance of archaeal amoA gene declined significantly in all soils during incubation.Active AOB outnumbered ammonia-oxidizing archaea(AOA)and were much more heavily labeled than AOA and nitrite-oxidizing bacteria(NOB)during the incubation,providing the unequivocal evidence for the significant contribution of AOB to nitrification in these acidic paddy soils using DNA-SIP.Active ammonia oxidizing microorganisms were dominated by group 1.1a associated cluster AOA and Nitrosospira cluster 3 AOB,and 13C-NOB was dominated by Nitrospira-like NOB,with distinct phylotypes in different soils,which was driven by soil properties.Soil physiochemical properties(e.g.,pH,available phosphorus(AP)and soil oxidation capacity(OXC))are of great significance in determining the composition of the active nitrifying populations.Soil nitrification activity was influenced by the differences in the relative abundance and community structure of active nitrifiers.(5)Influence of elevated temperature on nitrification and active nitrifiers.Nitrification activity greatly increased with increasing temperature,accompanied by increase in AOB abundance,while the abundance of AOA gradually decreased during incubation.AOA and AOB responded differently to elevated temperatures,and the dominant ammonia oxidizers changed from AOA to AOB with increasing temperature.Dominant 13C-NOB shifted from Nitrospira moscoviensis to Nitrospira japonica at elevated temperatures.Elevated temperature had significant direct and indirect impacts on soil nitrification which were driven by changes in AOA and AOB abundance,as well as the community structure of AOA and NOB,while the composition of AOB was more stable than AOA communities under elevated temperatures without shift. |
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