Effect Of Long-term Fertilization On Greenhouse Gases Emission,Soil Microbes And Extracellular Enzymes In Paddy Soil

Methane and nitrous oxide are the two most effective greenhouse gases,and agricultural soils are one of the primary sources of these atmospheric gases.Soil microbial activities are consistently restricted not only by phosphorus availability but also by microbial carbon requirements.Soil microbes play an important role in the mechanisms of the nutrient cycle in agroecosystems because of their role in nutrient storage and formation in soil.To understand the interaction of microbial biomass stoichiometry,it is also very important to understand the nutrient cycling in agroecosystems in response to long-term fertilization.This research study was divided into four different sections.The objectives of the first study were to investigate the sole and combined effects of phosphorus and glucose on CH₄and N₂O emissions and also to determine their effect on soil microbial biomass activity in phosphorus-deficient and phosphorus-adequate soils.The second study monitored how different moisture regimes influence microbial biomass stoichiometry,enzymatic activity,and greenhouse gas emissions under paddy soils.In the third and fourth studies,we examine the effect of microbial community structural and soil microbial biomass stoichiometry under long-term inorganic fertilization combined with organic fertilization in paddy soil.For the first study,soils were selected from Qiyang long term experimental field（38 years）,which is under a rice-rice rotation system.The treatments consisted of CK（no fertilizer）,NPK（chemical fertilizer）,and NPKM（chemical fertilizer and cow manure）.Collected soils were treated with two levels of phosphorus(0 and 20 mg P kg^-1soil)with or without glucose(Glu,400 mg C kg^-1soil)and mixed well.We applied phosphorus as monopotassium phosphate（KH₂PO₄）as a phosphorus source.This was an incubation experiment,and the soil was analyzed for the determination of CH₄,N₂O emission,soil microbial biomass carbon,phosphorus,and soil properties.For the second study,soil was selected from Qiyang on the same field with the same treatment as a first study.In this study,we apply two moisture levels:60%and flooding（100%）moisture conditions.This is also an incubation experiment,in which we determine CH₄,N₂O emission,soil microbial biomass C,N,P stoichiometry,and enzymatic activity under long-term paddy soil.In the third study,soil was selected from Jinxian long term experimental field,which is a rice-rice rotation system.The selected treatments were CK,N（chemical nitrogen fertilizer）,NP（chemical nitrogen and phosphorus）,and NPKM.Soil samples for the fourth study were collected from a long term experiment in Hefei under a wheat-rice cropping system.Treatment selection for this study was CK,NPK,and NPKS（chemical fertilizer and wheat straw）.In third and fourth studies,we measure soil properties,microbial biomass stoichiometry,relative abundance of individual and total PLFA,and its activity.In the first study,the results revealed that high N₂O emissions were 17.44μg kg^–1measured in phosphorus-deficient soil with the addition of glucose.In phosphorus-adequate soils,the peaks of N₂O emission values in the glucose addition treatment were 20.8μg kg^–1,and 24.7μg kg^–1,which were higher than without glucose-added treatments.CH₄emissions were higher with glucose addition at 1.9μg kg^–1in phosphorus-deficient soil and 1.52μg kg^–1and 2.6μg kg^–1in two phosphorus-adequate soils,respectively.Phosphorus addition to deficient and adequate soil were significantly increased the cumulative CH₄and N₂O emissions compared to solely glucose added soil and the combination of glucose with phosphorus.Glucose addition significantly increased microbial biomass carbon（MBC）but decreased microbial biomass phosphorus（MBP）,especially the phosphorus-adequate soil.For MBC,the highest value obtained was 175.8 mg kg^–1in NPKM,which was determined under glucose addition in phosphorus-adequate soil.The soil p H increased with glucose addition but decreased with phosphorus addition in phosphorus-deficient soil.The soil organic carbon content was significantly affected by glucose addition in the phosphorus deficient soil.Available phosphorus was highly influenced by phosphorus addition but did not appear to be affected by glucose addition.In the second study,the results showed that 60%of water-filled pore spaces produced a higher amount of N₂O than flooded soil,while flooded soil significantly stimulated CH₄than 60%WFPS.The high N₂O flux values of 2.3,3.1,and 3.5μg kg^-1were recorded in 60%of WFPS under CK,NPK,and NPKM treatments.In flooded soil,the highest CH₄flux values were recorded at 1.7,3.2,and 3.8μg kg^-1in CK,NPK,and NPKM treatments,respectively.Dissolved organic carbon was increased by15–27%under high moisture content.The highest MBC was recorded in flooded condition,which is8–12%higher than 60%WFPS.The microbial biomass nitrogen（MBN）was 14–21%higher in flooded soil as compared to 60%WFPS.The MBP was 4–22%high in flooded soil instead of 60%WFPS.The urease activity was significantly increased by 42–54%in flooded soil compared to 60%WFPS.In long-term fertilization,the NPKM treatment significantly increasedβglycosidase and acid phosphatase enzyme activities,whereas the moisture content showed 1.2–6.1%and 2–6.6%effect on BG and AP.DOC,MBC,and p H showed a significant positive relationship with cumulative CH₄,while DOC showed a significant relationship with cumulative N₂O.In the random forest model,soil moisture,MBC,DOC,p H,and enzymatic activities were the most significant factors for greenhouse gas emissions.The partial least squares path model showed that soil properties and enzymatic activities had a significantly positive direct effect on CH₄and N₂O emissions,while soil microbial biomasses had a highly positive indirect effect on CH₄and N₂O emissions.The third study indicated that nitrogen fertilization significantly decreased soil p H compared to control and chemical fertilizers combined with manure application.Soil organic carbon was significantly increased by 17%,6.5%,and 48%under N,NP,and NPKM treatment as compared to control.Total phosphorus was significantly higher in the NPKM treatment as compared to N,NP,while lower total phosphorus was noticed in sole nitrogen treatment as compared to control.Total nitrogen was increased 35%,30%,53%,under N,NP,and NPKM treatment compared to control.The available phosphorus content was significantly increased in application of inorganic fertilizers combine with manure.Available nitrogen was noticed 22%,28%,and 49%under long-term N,NP,and NPKM treatments.The MBC and MBN in NP treatment was increased 12%and 14%,respectively as compared to control.The MBC and MBN were higher,reaching 69%and 72%,respectively.High MBP was noticed at range 35%and 65%in NP and NPKM treatments.MBP were decreased 45%in N treatment as compared to other treatments.The order of relative abundance of individual phospholipid fatty acids was:Gram negative bacteria>Gram positive bacteria>Actinomycetes>AM Fungi>All Fungi>Eukaryotes.Total phospholipid fatty acid concentration was increased by 10%and 22%under NP and NPKM treatments,while its concentration was decreased by 15%under long-term sole N treatment.The fourth study examines whether long-term chemical fertilization significantly decreased soil p H,while inorganic fertilizers combined with straw increased soil p H compared to control.SOC was significantly increased by 34%and 48%under long-term NPK and NPKS treatments,respectively,as compared to CK.Total phosphorus was increased in NPKS and NPK treatments by up to 30%and 52%,respectively,as compared to CK.Soil available phosphorus was increased ranged 63%and 84%under NPK and NPKS treatments as compared to CK.Total nitrogen and available nitrogen were increased by48%and 55%under NPK and 58%and 75%in NPKS treatment compared to control.The MBC in NPK and NPKS treatments was 55%and 64%higher,respectively,as compared to CK.The MBN was highly increased in NPKS treatment up to 48%and 30%in NPK treatment as compared to CK.High MBP was noticed in NPKS treatment,which was 51%,while in NPK,microbial phosphorous was 39%as compared to CK.There was no significant difference in the soil microbial biomass ratio among all the fertilization treatments.The enzymatic activity was significantly increased when chemical fertilizer was combined with straw.The urease enzyme was increased by 49%and 56%in NPK and NPKS treatment as compared to control.β-glycosidase activity was also increased by 26%in NPK treatment and 42%in NPKS treatment as compared to CK.The abundance of Gram-negative bacteria was increased by 42%and 55%under NPK and NPKS treatment.In NPK and NPKS significantly increase the individual abundance of Gram-negative bacteria by 31%and 45%,respectively,as compared to CK.Actinomycetes abundance was increase in both NPK and NPKS treatments by 41%and 49%as compared to CK.Eukaryotes were increased by 32%and 50%under NPK and NPKS treatments as compared to CK.AM fungi and all fungi were increased in NPK treatment by 43%and 53%while they were increased by 55%and 63%in NPKS treatment as compared to CK.The concentration of total PLFAs was increased by 36%and 52%under NPK and NPKS treatments as compared to CK.From the current studies,we concluded that sole phosphorus and glucose addition increase CH₄and N₂O emissions in phosphorus-deficient and also in phosphorus-adequate paddy soils.The findings revealed that moisture has a significant impact on N₂O emissions.Flooded soil resulted in lower N₂O emissions than the 60%WFPS,while long term organic and inorganic treatment showed higher emissions in both water regimes.Long-term application of inorganic fertilizers and their combination with organics changed microbial C:N:P stoichiometry,enzyme activities,and microbial community structure.