Effects Of Fertilization On Soil Ammonia Oxidizers:Relationships With Bulk Soil Environmental Variables And Plant Community

Alpine meadow is a very important ecosystem in Qing-hai Tibet plateau,but it is sensitive to global changes because of its long-term low temperature and high radiation.In recent years,anthropogenic disturbance and climate change have caused the ecosystem to experience a series of serious problems,such as the decline of biodiversity,primary productivity and ecological stability.Fertilization,as an important land management mode,can effectively increase the availability of soil resources and thus change the aboveground plant community and the belowground functional microbial community.AOM is a key microorganism driving nitrification process and plays an important role in soil nitrogen conversion.Therefore,the response of AOM community structure,diversity and plant-AOM-soil coupling relationship to fertilization was studied in depth,which provide theoretical basis for maintaining the functional stability of the alpine meadow ecosystem on the Qing-hai Tibet plateau.The abundance,community structure and diversity of AOM were determined by qPCR and Illumina MiSeq high-throughput sequencing.At the same time,the above-ground plant community and underground soil were measured.To study the effects of different gradient nitrogen?N?,phosphorus?P?and nitrogen and phosphorus?NP?on AOM community,the relative influence of soil environmental variables and plant richness to drive AOM abundance in alpine meadow of Qing-hai Tibet plateau and the coupling relationship of plant-AOM-soil with different fertilizer gradients was determined by SEM.The research results are as follows:1.Influence of fertilization on soil AOM community structure and diversityIllumina MiSeq high-throughput sequencing results showed that there were385,822 AOA sequences ranked to 30 OTUs and 409,385 AOB sequences ranked to287 OUTs.Phylogenetic analysis results showed that the dominant OUTs of AOA?relative abundance of>0.1%?belonged to the Group1.1b and cluster?dominated in all treatments;the dominant OUTs of AOB?relative abundance>0.1%?belonged to Nitrosospira and cluster 3a and cluster 4 were the dominant groups of AOB.AOA community structure changed in NP fertilization and its diversity decreased gradually,while N fertilization significantly affected AOB community structure,and its diversity decreased with the increase of nitrogen concentration.The results showed that AOA community had obvious response to NP fertilization,while AOB community was more sensitive to N fertilization.2.Impact of resource availability and plant richness on AOM OUTs richnessResearch on AOA OUTs richness showed:AOA OUTs richness had a significant linear fitting relationship with soil pH?R²=0.24,P=0.002?,and the richness of AOA OUTs increased gradually with the soil pH increasing;plant species richness was no relationship with AOA OUTs richness.During N fertilization,soil pH was the only driving factor of AOA OUTs richness.There were not found biotic and abiotic factors driving of AOA OTUs richness in P and NP treatments.The results showed that soil resource availability?soil NH₄⁺and AP?and plant richness did not affect AOA OTUs richness,and soil acidification caused by fertilization was the only soil factor driving changes in AOA OUTs richness.Research on AOB OUTs richness showed:soil NH₄⁺had a nonlinear relationship with AOB OUTs richness.With the increase of soil NH₄⁺,AOB OUTs richness first increased and then decreased?R²=0.14,P=0.03?.Similarly,with the increase of AP content in soil,the richness of AOB OUTs showed a marginal significant decline trend?R²=0.11,P=0.06?,plant species richness significantly increased AOB OUTs richness?R²=0.38,P<0.001?.SEM results showed that soil AP had different effects on AOB OUTs richness when N and NP fertilization,N fertilization was a positive effect and NP treatment was a negative effect.3.Plant-ammonia oxidation microbial-soil linkagesThe growth of AOA under N fertilization was mainly affected by plant biomass??=0.66?,while AOB was directly affected by soil pH??=-0.72?.When P was added,soil AP had an indirect effect on plant biomass??=-0.31?,resulting in an increase in AOA abundance??=0.52?,and there was a significant negative correlation between AOA and AOB??=-0.60?.When NP addition,soil NH₄⁺directly promoted the growth of AOA??=0.51?,while soil AP inhibited the growth of AOB??=-0.55?by increasing plant biomass??=0.53?.The results showed that different type of fertilizations change the coupling relationships among plant-AOM-soil.