Microbial Response Characteristics Of Phosphorus Dynamics In Purple Soil And Nutrition Efficiency Of Maize Under Different Phosphorus Application Rates

Both the planting area and the production of maize,an important grain-feeding crop in Sichuan Province,is increasing in recent years.However,excessive phosphorus（P）application and low P fertilizer utilization rate are still the main problems in the maize production.In this study,we used spring maize Zhongyu 3 as the test material,and based on the 11-year long-term P application experiment located at the experimental station of Sichuan Agricultural University,Ya’an campus,and set five P application levels of 0（P0）,37.5（P37.5）,75（P75）,112.5（P112.5）and 150（P150）kg P₂O₅·hm^-2.The modified Hedley P classification method was used to study the content and transformation of different P fractions in soil.The contribution of different P fractions to the soil P activation coefficient（PAC）was evaluated by random forest model.The diversity,community structure and composition of soil bacteria and fungi were analyzed by Illumina Nova Seq sequencing technology,and combined with structural equation modeling（SEM）to explore the interaction mechanisms between soil chemical properties,bacterial and fungal community and transformation of different labile P fractions under long-term P application.At the same time,the growth and development,yield and P utilization efficiency of maize uhder different P level were investigated,so as to provide scientific application and efficient management for local P fertilizer and theoretical basis for exploring the potential of soil microbial P supply.The main results of this study are as follows:（1）Different P application treatments significantly affected the contents of soil biochemical properties and P fractions.Compared with no P application,P application affected soil nutrients and microbial biomass in different degrees,especially significantly increasing the contents of available P（AP）and total P（TP）in different soil layers,and decreasing soil N/P and C/P ratios.Among them,AP,TP and PAC all showed a trend of increasing and then leveling off with the increase of P application rate,while the trends of soil N/P and C/P ratios were opposite.The results of P fractions showed that,except for stable P（SP,c.HCl-Pi,c.HCl-Po and Residual-P）,the contents of labile P（LP,Resin-Pi,NaHCO₃-Pi and NaHCO₃-Po）,moderately labile P（MP,NaOH-Pi,NaOH-Po and d.HCl-Pi）all showed an increasing trend with the increase of P application and then leveled off.The proportion of MP gradually increased,while the proportion of SP gradually decreased with the increase of P application,and there was no significant change after the P application rate exceeded 75 kg·hm^-2.Except for SP,the correlations between different P fractions reached significant levels and were positively correlated with AP.NaHCO₃-Pi and Resin-Pi and d.HCl-Pi are the main P forms that affected the P availability of surface and deep soil,respectively.In addition,AP was significantly correlated with most of the soil nutrient indicators.Predicted by random forest model,soil inorganic P（NaOH-Pi、NaHCO₃-Pi、d.HCl-Pi and Resin-Pi）are the main determinants of PAC,which are important for the sustainable supply of P in soil.（2）The application of P fertilizer significantly decreased theα-diversity（Shannon index）and significantly altered theβ-diversity of soil bacteria and fungi.The community composition of soil bacteria and fungi was similar at different P application rates,but there were significant differences in the relative abundance of different classification levels.The bacterial Shannon index was positively correlated with soil p H and N/P ratio,and negatively correlated with SOC,AP,TN,TP,LP and MP.The fungal Shannon index was positively correlated with soil p H and N/P ratio,and negatively correlated with AP,TP,LP,MP and SP.Most of the dominant phyla and genera of bacteria and fungi were significantly correlated with soil nutrients and P fractions,and p H,SOC,AP,TN,TP,N/P ratio,LP and MP were the main environmental factors driving the changes of bacterial and fungal communities.The structural equation model showed that different P application mainly induced changes in bacterial and fungal diversity and community by reducing soil p H,N/P and C/P ratios,which in turn promoted the transformation of soil MP and SP to LP and affected soil P effectiveness.（3）P fertilization increased the plant height,ear height and ear height coefficient of maize,and the dry matter accumulations of maize shoot first increased with the P application level,reaching the maximum at the P application level of 75 kg·hm^-2.The root configuration of maize plants at R1 stage was significantly changed without P application,in which the total root length,root surface area and the proportion of 0-0.5 mm root diameter were significantly higher than those of other P treatments.Maize yield increased significantly with increasing P rates,but there was no significant difference when P application rates exceeded75 kg·hm^-2.According to the liner platform simulation,when the maize yield was the highest(9438.38 kg·hm^-2),the P fertilization was 84.65 kg·hm^-2.Appropriate P application significantly increased the P contents in maize leaves,leaf sheaths and bracts,and the N and K contents in grains,and the accumulation of N,P and K in maize.When the P fertilization exceeded 75 kg·hm^-2,there was no significant difference in N and P accumulation,but K accumulation decreased significantly.The d.HCl-Pi fraction was the most important factor affecting P accumulation in maize.The agronomic efficiency of P fertilizer,P fertilizer bias productivity,P uptake efficiency and P utilization efficiency all decreased significantly with the increase of P application rate.The apparent P utilization rate reached the maximum at 75kg·hm^-2,and the apparent P surplus was close to 0(-4.85 kg·hm^-2),which indicated that appropriate P application could significantly reduce soil P residue and increase P fertilizer utilization rate.In summary,excessive P application would lead to a large accumulation of different P forms in the soil and reduce P effectiveness.Appropriate P application could improve soil fertility and promote soil P activation and transformation of SP and MP to LP.Soil microbial processes were important factors leading to changes in soil P fraction,which could promote the effective transformation of active P pool.Appropriate P application promoted the growth and development of maize,promoted the accumulations of dry matter and nutrients,reduced the residual P in the soil,and improved the utilization rate of P fertilizer.Under the condition of this study,the suitable P fertilization rate for maize was 75-85 kg P₂O₅·hm^-2.