| Excessive application of phosphate fertilizer may change the physical,chemical and biological properties of soil,affect the migration and transformation of soil water and nutrients,and directly affect related nitrogen transforming microorganisms,thus regulate the whole processes of nitrogen cycle.Previous researches on soil nitrogen transformation under fertilization conditions mostly focus on organic fertilizer and nitrogen fertilizer,and there were few reports on the impact of phosphate fertilizer on it.In this study,we used soil from the long-term phosphate fertilization field and soil with phosphorus addition in the laboratory.The nitrifying and denitrifying microbial abundance and community structure were determined by molecular biology methods,and the soil nitrification,denitrification and N2O emission were monitored based on microcosmic culture experiments.The rates of key processes in nitrogen cycle were deterrmined based on the 15N isotope labeling test.The soil water transport law was determined by one-dimnsional vertical water infiltration test.The mechanisms of long-term and short-term impact of phosphate fertilizer application type and different phosphorus application rates on soil water transport and nitrogen conversion were clarified,in order to provide a theoretical basis for nitrogen and phosphorus reduction and greenhouse gas emission reduction.The main results of this study are as follows:(1)The effects of long-term combined application of phosphorus fertilizer on nitri fication,N2O emission,and related microbial functional gene abundance were significantly different.Compared with no fertilization(CK),phosphorus fertilization alone(P)significantly promoted the nitrification reaction,and the N2O accumulation increased by 45.10%under aerobic culture,the N2O accumulation decreased by 40.58%under anaerobic culture,the functional gene abundance of AOA-amoA and denitrifying bacteria nosZ decreased by 35.71%and 34.32%,respectively,and there was no significant difference in the abundance of other functional genes.Compared with organic fertilizer(M)alone,the combined application of phosphorus organic fertilizer(MP)significantly promoted the nitrification reaction and denitrification reaction,and the accumulation of N2O increased by 46,50%and decreased by 29.25%under anaerobic conditions,and the abundance of functional genes such as ammonia-oxidizing bacteria AOB-amoA and denitrifying bacteria nirK,nirS and nosZ increased by 191.77%,97.72%,64.96%and 36.30%,respectively.Compared with single nitrogen fertilizer(N),nitrogen and phosphorus combined application(NP)significantly inhibited the nitrification reaction,and the accumulation of N2O decreased by 15.1 3%and 9.18%under anaerobic conditions,except for AOB-amoA,the abundance of functional genes such as AOA-amoA,nirK,nirS and nosZ increased by 76.25%,109.07%,56.01%and 82.03%,respectively.Compared with the combined application of nitrogen and phosphorus(NMP),the accumulation of N2O increased by 10.75%～15.53%under aerobic conditions,and there was no significant difference under anaerobic conditions,and the abundance of functional genes of AOA-amoA,AOB-amoA nirK,nirS and nosZ decreased by 29.16%,53.21%,41.05%,49.40%and 50.90%.(2)Long-term application of phosphorus fertilizer with different gradients significantly improved organic nitrogen mineralization and microbial assimilation ability,promoted N2O emission,and changed the functional activities and community structure of ammonia oxidation and denitrification microorganisms Phosphorus application can significantly promote the mineralization and microbial assimilation of organic nitrogen,promote N2O emissions,and change the functional activity and community structure of ammonia oxidation and denitrification microorganisms.Compared with CK treatment,the mineralization rate(0～24 h)of P2 treatment(100 kg P2O5/ha)increased by 5.73%,and the NO3-assimilation rate(24～48 h)of P1 treatment(50 kg P2O5/ha)increased by 19.4%,and there was no significant difference between the other treatments.The N2O accumulation showed a trend of first increasing and then decreasing with the phosphorus application rate,and the N2O accumulation under P3 treatment(150 kg P2O5/ha)was the largest,which was increased by 15.18%compared with CK treatment,and the N2O accumulation of P3 treatment at the end of culture was increased by 15.18%.Compared with CK treatment,the abundance of AOA-amoA,narG,nirK and nosZ functional genes treated with P2 increased by 27 03%,37.79%,40.72%and 26 76%,and the abundances of AOB-amoA and nirS functional genes were not significant.Based on the diversity of ammonia oxidation and denitrifying microorganisms,the diversity of ammonia oxidation and denitrifying microorganisms a showed that phosphorus application could significantly increase the species richness of AOB,nirK and nirS denitrifying bacteria.Except for the enhancement of community diversity of nirK denitrifying bacteria,phosphorus application measures reduced the community diversity of ammonia oxidation and denitrify ing microorganisms.(3)From the effect of phosphorus addition of different gradients on soil water and nitrogen transport and transformation,phosphorus application with water had no significant effect on soil infiltration characteristics during infiltration.Compared with the control CK,the cumulative infiltration capacity of P1,P2,P3 and P4 increased by 7.82%,8.85%,9.82%and 11,21%,respectively,and the corresponding infiltration time decreased by 7.77%,14,56%,22.33%and 27.18%,respectively.The cumulative infiltration rate and wetted front migration velocity increased with the increase of phosphorus gradient,and the infiltration parameters in the fitted Kostiakov,Philip formula and wetted front migration distance-time formnula showed a good linear relationship with phosphorus concentration.After phosphorus culture,the composition of soil aggregates was changed to affect the water infiltration process,and the proportion of 0.25～2 mm granular aggregates in IP3 and IP4 treatment was significantly higher than that of the control CK without phosphorus,which increased by 35.9%and 51.28%,respectively,compared with CK.Compared with CIC treatment,short-term phosphorus addition promoted soil mineralization,nitrification and NH4+ assimilation.In summary,long-term application of phosphorus can increase the richness of nitrification and denitrifying microbial species and the abundance of related nitrogen conversion functional genes,and promote the nitrification and denitrification processes,but there are great differences in the combined application of different phosphate fertilizers.To select suitable phosphorus fertilizer application mode and the amount of phosphorus fertilizer can effectively reduce N2O emissions.It is speculated that the application of phosphorus fertilizer within a certain range can promote the formation of large soil aggregates,promote soil water and fertilizer retention,and provide a good soil environment for crops. |
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