Study On The Process And Mechanisms Of Soil Nitrogen Transformation In The Vegetation Restoration Of Farmland Abandonment In The Chinese Loess Plateau

Soil microbial communities,the engine of soil nitrogen cycle,play an important role in the function restoration of ecosystem.The purpose of this study was to study the evolution characteristics of soil microbial communities,the mechanisms of potential N₂O emission form denitrification and supply of soil inorganic nitrogen in the vegetation restoration from farmland.This study aimed to provide theoretical support for soil nutrient restoration and conservation of degraded ecosystem in the Chinese Loess Plateau.Therefore,we utilized natural restoration grasslands and artificial forests,through soil samping in the field,anaerobic incubation experiments and field continuous culture experiment,combined with Quantitative polymerase chain reaction?Q-PCR?and Illumina MiSeq high-throughput sequencing,to analysis the evolution of soil microbial communities,the risk of soil N₂O emission and the supply level of soil inorganic nitrogen.Furthermore,we reveal the major effecting factors and the mechanisms about the N₂O emission and the supply level of inorganic nitrogen.The main conclusions are as follows:1.The species numbers,diversities and composition of the soil microbial communities in the vegetation restoration process were presented as bacteria>fungi and archaea,and the bacterial community responded more rapidly to the changes of soil nutrients.The natural restoration process was more conducive to the increase of the species numbers and diversities in soil microbial communities,while the artificial restoration process had a greater impact on the compositions of soil microbial communities.Soil microbial communities were influenced by soil properties and plant diversities,and the dominant environmental factors of soil microbial communities in the two vegetation restoration patterns were different.2.The potential N₂O emission rates decreased from the farmland to the plant communities,indicated that the vegetation testoration could decrease the N₂O emission.In the later stage of vegetation restoration the N₂O emission rates increased,showed that the risk of N₂O increased.The denitrifying functional microorganisms had an increased trend in the abundance and diversities,including Protenbacteria and Acidobacteria.The increase of?nirK+nirS?/?napA+narG?and nosZ/nirK ratios would reduce N₂O emission,while the increase of qnorB/nosZ ratio would increase N₂O emission.The increase of plant diversity index can promote the recovery and development of denitrifying functionl microorganism.3.Soil inorganic nitrogen is in a balance state in the vegetation restoration.However,the farmland and June to July were in a nitrogen linmitation phenomenon.The mineralizing functional microorganisms were mainly Proteobacteria,and had the same patterns with plant communities in vegetation restoration.The decrease of soil mineralizing functional microorganism's species numbers and ACE diversity index and the differentiation of community structure would increase the supply level of soil ammonium nitrogen,while the differentiation of community structure and the increase of species numbers could increase the supply level of soil nitrate nitrogen.Failly,soil pH,organic carbon,total nitrogen,total phosphorus contents and buik density were correlated significantly with soil mineralizing functional microorganism.