The Effect Of Soil PH And Land Use On Soil Nitrification And Nitrifying Microorganisms

Nitrogen?N?is an essential element of life on Earth.The soil nitrogen cycle consists of six different reaction processes that occur in an orderly manner.Nitrification,as the intermediate link between nitrogen fixation and denitrification,is the most critical part of the entire nitrogen cycle.The products of nitrification may cause water eutrophication to pollute water sources,increase the risk of greenhouse gas N₂O emissions,and cause soil acidification.Therefore,the study of nitrification is of great significance for improving soil nitrogen fertilizer utilization rate,reducing greenhouse gas emissions and environmental protection.Nitrification is a biochemical process that is highly sensitive to pH.pH not only affects the size of nitrification,but also affects the abundance and community structure of nitrifying microorganisms.Therefore,p H is considered to be one of the factors affecting nitrification and nitrifying microorganisms.Acid soils are widely distributed globally,accounting for about 30%of the surface of ice-free areas on land,including various ecosystems such as farmland,forests,and grasslands.The impact of land use change on the nitrogen cycle has always been a hotspot of soil science research.Therefore,it is of great significance to study the impact of different land use methods on nitrification in acid soils.It can not only help us formulate effective ecological management strategies to regulate plants and the nitrogen source availability of soil microorganisms can also provide an important reference for controlling greenhouse gas emissions and preventing environmental pollution caused by nitrate leaching.We explored the effect of pH on forest soil nitrification and nitrifying microorganisms in subtropical regions.The purple soil of different pH in the subtropical area was taken as the research object?acid forest soil,p H=3.63;neutral forest soil,pH=7.00;alkaline forest soil,pH=7.80?.The results are as follows:the nitrification potential and soil nitrite oxidation potential are affected by pH,and the nitrification potential of acid forest soil is significantly lower than that of neutral forest soil and alkaline forest soil.The nitrification potential of purple forest soil ranges from0.11 ug g^-1h^-11 to 0.35 ug g^-1h^-1.The nitrite oxidation potential of acid forest soil is significantly lower than that of neutral forest soil and alkaline forest soil.The nitrite oxidation potential of purple forest soil under subtropical evergreen tree vegetation ranges from 0.16 ug g^-1h^-11 to 0.45 ug g^-1h^-1.The abundance of nitrifying microorganisms has different responses to different p H.The abundance of AOA amoA gene in alkaline forest soil is significantly higher than that in neutral forest soil and acid forest soil?P<0.05?.The abundance of AOB amoA gene in alkaline forest soil was significantly higher than that in neutral forest soil?P<0.05?.AOB amoA gene abundance was not detected in acid forest soil.AOA amoA gene abundance was significantly higher than AOB amoA gene abundance?P<0.05?.As the pH continues to increase,the ratio of AOA:AOB continues to decrease,and AOA:AOB decreases as the pH increases,indicating that AOA is more suitable for living in an acidic environment.The abundance of Nitrobacter-like NOB nxrA gene in neutral forest soil was significantly higher than that in acid forest soil and alkaline forest soil?P<0.05?.The abundance of Nitrobacter-like NOB nxrB gene in alkaline forest soil was significantly higher than that in acid forest soil Nitrospira-Like NOB nxrB gene abundance and neutral forest soil Nitrospira-like NOB nxrB gene abundance.Nitrospira-like NOB nxrB gene abundance is higher than Nitrobacter-like NOB nxrA gene abundance in forest soils with different pH.The ratio of nxrB:nxrA gene abundance increases significantly with increasing pH,indicating that Nitrobacter-like NOB may be more suitable for living in an acid environment.Comammox clade A amo A gene abundance is between 2.03×10⁷ g^-11 dry soil?3.76×10⁷ g^-11 dry soil,Comammox clade B amoA gene abundance is 1.02×10⁶ g^-11 dry soil?2.52×10⁶ g^-11 dry soil between.Compared with the abundance of Comammox clade A amoA gene in alkaline and neutral forest soil,the abundance of Comammox clade A and clade B amo A gene in acid forest soil is significantly higher than that of both?P<0.05?.It is more suitable for survival in acid poor soil.The ratio of Comammox clade A amo A gene copy number to Comammox clade B amoA gene copy number keeps increasing with the increase of pH.It is speculated that Comammox clade B may be more suitable for acidic environment than Comammox clade A.In acid forest soil,the AOA amo A functional gene group is Group 1.1a associated,and the neutral and alkaline forest soil AOA amoA functional gene group is Group 1.1b.The AOB amoA functional gene group of neutral forest soil and alkaline forest soil belongs to Nitrosospira Cluster3a.1.The neutral forest soil has the highest AOA population richness and diversity.Compared with the acid forest soil AOA,the neutral and alkaline forest soil have similar community structure compositions.The Nitrospira-like NOB community structure of the neutral forest soil and alkaline forest soil is similar,and the Nitrobacter-like NOB population richness and diversity of the neutral forest soil are the highest.This article next explores the effects of different land use methods on soil nitrification and nitrifying microorganisms under acid soil conditions.The acid soil with the same parent material but different utilization methods was selected as the research object?primary forest soil,p H=4.13;returning farmland to forest soil,pH=4.83;cultivated soil,pH=4.10?.The results are as follows:The nitrification potential and nitrite oxidation potential of farmland soil were significantly higher than that of the virgin forest and the soil converted from farmland to forest,indicating that fertilization can improve soil nitrification.Compared with the virgin forest,the nitrite oxidation potential of the soil converted from farmland to forest was significantly increased?P<0.05?.Nitrifying microorganisms have different responses to different land use methods.The amoA gene abundance of returning farmland to forest is significantly higher than that of amoA gene in primary forest and farmland soil?P<0.05?.As for the amo A gene abundance of AOB,the amoA gene abundance of AOB in primitive forest is significantly lower than that of AOB returning farmland to forest and farmland soil?P<0.05?.The abundance of Nitrobacter-like NOB nxrA gene in converted farmland was significantly lower than that in primary forest and farmland?P<0.05?,while the abundance of Nitrospira-like NOB nxrB gene in converted farmland was significantly higher than that in primary forest and farmland,Nitrospira-like NOB nxrB gene abundance is higher than Nitrobacter-like NOB nxrA gene abundance?P<0.05?,the ratio of nxrB to nxr A gene abundance is the largest in soil converted from farmland to forest,indicating that Nitrospira-like NOB in soil converted from farmland to forest It has a more advantageous living environment than Nitrobacter-like NOB.Comammox clade A amoA gene abundance is between 1.27×10⁷ g^-11 dry soil?4.59×10⁷ g^-11 dry soil,Comammox clade B amo A gene abundance is 2.26×10⁴ g^-11 dry soil?5.37×10⁵ g^-11 dry soil between.The abundance of Comammox clade A amoA gene is highest in farmland?P<0.05?.It may be that adding fertilizer to acid soil is beneficial to the survival of Comammox clade A.Among the Comammox clade B amoA gene abundance,the Comammox clade B amoA gene abundance was significantly higher than that of the other two?P<0.05?,and the Comammox clade B amoA gene abundance was the lowest in farmland soil.In primitive forest soil and farmland soil,the copy number of amoA gene of Comammox is higher than that of AOA,while the ratio of Comammox/AOA in returning farmland to forest soil is less than 1,and the copy number of amoA gene of AOA is higher than Comammox.In primary forest soil and farmland soil,the dominant group of AOA amoA functional genes is Nitrosotalea subcluster 1,and the dominant group of AOA amoA functional genes in soil converted from farmland to forest is Nitrosotalea subcluster 2.The AOB amoA functional gene groups in primary forest treatment are Nitrosospira cluster 2 and Nitrosospira cluster 3a.1.In the treatment of returning farmland to forest,Nitrosospira cluster 1 has the highest relative abundance of 71.4%.Nitrosospira cluster 2 has the highest relative abundance of 36.3%in cultivated farmland soil,followed by Nitrosomonas cluster at 26.2%.Different land use pattern have a greater impact on the community structure of AOB amoA gene in acid yellow soil.Nitrospira-like NOB community structure composition is similar,Nitrobacter-like NOB community structure composition gap is large.