| In the context of the current low utilization rate of phosphorus fertilizer in farmland soils in the current season,with most phosphorus lost or fixed by the soil,field and indoor experiments were conducted to control fertilization,soil temperature,water content,and exogenous organic carbon addition on soil microorganisms,phosphorus availability,and increase soil available phosphorus content in paddy soil in the Jianghan Plain.In order to explore the impact of long-term phosphorus deficiency on the yield,soil properties,and microbial community of rice rape rotation,four treatments were selected:applying phosphorus and potassium fertilizer without nitrogen fertilizer（PK）,applying nitrogen and potassium fertilizer without phosphorus fertilizer（NK）,applying nitrogen and phosphorus fertilizer without potassium fertilizer（NP）,and applying nitrogen,phosphorus and potassium fertilizer（NPK）.The crop yield of each treatment was measured at maturity,and the soil of each treatment was collected,Amplification and sequencing of bacterial 16S r DNA and fungal ITS in soil samples based on Illumina Miseq high throughput sequencing technology,and analysis of bacterial and fungal community composition and diversity in soil using bioinformatics.The results reveal that long-term phosphorus deficiency can significantly affect crop morphology and yield,change the composition and diversity of bacterial and fungal communities in cultivated soil,and indicate that field hydrothermal conditions can significantly affect the phosphorus supply capacity of rice fields.In order to further clarify the impact of hydrothermal conditions on phosphorus in paddy soil,indoor simulation studies were conducted.Firstly,soil samples of four land use types in Jianghan Plain,including paddy field,dry land,vegetable field,and forest land,were collected as objects,and three water（W）gradients were set:40%,70%,and 100%soil mass and water content,respectively recorded as W40,W70,and W100;The three temperature（T）gradients:15,25℃and 35℃are recorded as T15,T25 and T35,respectively.Secondly,the effects of straw carbon addition（low and high biomass carbon:1%and 2%,recorded as SC1and SC2,respectively）and biochar addition（low and high biomass carbon:1%and 2%,recorded as BC1 and BC2,respectively）on soil phosphorus speciation were compared through indoor culture and the classification method of soil phosphorus bioavailability（BBP）and Hedley phosphorus speciation classification method,and the soil p H,available phosphorus（Olsen-P）,total nitrogen（TN）Total phosphorus（TP）,soluble organic carbon（DOC）,readily oxidizable organic carbon（ROC）,free iron（Fe-d）,and amorphous iron（Fe-o）contents were analyzed to determine the effects of soil moisture,temperature,exogenous organic carbon addition,and other physical and chemical properties on soil phosphorus availability.Finally,based on high throughput sequencing techniques for functional gene and microbial diversity,the effects of four treatments,namely,dry land（D）,dry land with straw（DS）,paddy field（W）,and paddy field with straw（WS）,on phosphorus related functional gene diversity,community composition,and diversity of soil bacteria and fungi were compared and analyzed to clarify the biochemical mechanism of the effective effects of water heat coupling and organic carbon field on phosphorus in paddy field soil.The main research results are as follows:1)Under long-term field trial conditions,compared with NPK treatment,the annual average yield decline rates of rice and rape under PK,NK,and NP treatments were 12.5%,18.1%,6.4%,and 33.1%,54.8%,and 16.0%,respectively.Under NK treatment,compared with the rice season,the root system of rape in the dry season is significantly underdeveloped,the plant is short,and the yield is lower.Compared with NPK fertilization,NK treatment increased the composition and diversity of soil microbial communities,while PK and NP treatments had opposite effects.Available potassium,p H,and slowly available potassium are closely related to changes in dominant bacterial communities;In contrast,Olsen-P,slow-acting potassium,and p H were significantly correlated with fungal communities.Fertilization leads to differences in soil properties that have a more direct impact on crop yields than microbial communities.It can be seen that soil phosphorus availability plays an important role in stabilizing crop yields,maintaining farmland microbial ecosystems,and maintaining soil nutrient balance.2)Under indoor cultivation conditions,increasing soil water content can increase the amounts of HCl-P,Citrate-P,Enzyme-P,and Olsen-P in paddy,dry,vegetable,and forest soils.Increasing soil temperature can help increase the amount of HCl-P and Olsen-P,and reduce the amount of Citrate-P.The amount of Ca Cl2-P and the amount of Enzyme-P in paddy field,dry land,vegetable land,and forest land soils were significantly affected by the interaction of water and heat.Within a certain range of soil temperature and water,temperature and water have a positive coupling effect on phosphorus bioavailability components in different types of soil,and significantly affect soil phosphorus supply capacity.3)Under indoor cultivation conditions,adding an appropriate amount of straw can help improve soil phosphorus availability and increase soil Olsen-P content.Flooding is beneficial for soil inorganic phosphorus activation;Moderate increase in soil temperature can enhance the dissolution of inorganic phosphorus and mineralization of organic phosphorus in the soil.The changes in the content of soluble organic carbon（DOC）,easily oxidizable organic carbon（ROC）,amorphous iron（Fe-o）,and free iron（Fe-d）in soil indirectly affect the changes in Olsen-P content in the soil.Under simulated paddy field conditions,adding biochar to the soil had a more significant effect on increasing Olsen-P content,while adding straw to dryland soil had an advantage in increasing Olsen-P content.After adding biochar and returning straw to the field,the middle active phosphorus（HCl-P and Na OH-P）accounted for the highest proportion of total phosphorus in paddy soil,while water-soluble inorganic phosphorus（H2O-P）and active phosphorus（Na HCO3-P）only accounted for a small portion of total phosphorus in the soil.The content of various forms of phosphorus in the soil,from high to low,is HCl-P>Na OH-P>Na HCO3-P>H2O-P.The addition of biochar increased soil p H,total nitrogen（TN）,soluble organic carbon（DOC）,and organic carbon（SOC）content;The addition of straw carbon increased the content of total phosphorus（TP）,soluble organic carbon（DOC）,and organic carbon（SOC）in the soil.In biochar treated soil,the Olsen-P content is significantly positively correlated with the contents of H2O-P,Na HCO3-P,SOC,and NH4+-N.The Olsen-P content in soil treated with straw addition was significantly positively correlated with the contents of Na OH-P,HCl-P,TN,and NH4+-N.It can be seen that under different hydrothermal environments,biochar and straw carbon also have significant differences in the effectiveness of phosphorus in paddy soil.4)Under indoor cultivation conditions,the richness and diversity of bacterial communities in simulated dry land treated soil were higher than those in paddy field;The richness and diversity of fungal communities in simulated paddy field soil were higher than those in dry land.Redundancy analysis showed that water had a significant impact on soil bacterial community structure;The addition of straw carbon has a significant impact on the structure of soil fungal communities.The classification level of soil bacteria and fungi is not affected by water content and straw addition.The dominant bacteria in the soil bacterial community of each treatment are Proteobacteria and Actinobacteria（relative abundance>15.0%）;The dominant fungi in the fungal community are Ascomycete and Basidiobolomycete（relative abundance>5.0%）.Adding straw carbon can help increase the richness and diversity of microbial communities with pho D functional genes in soil,promote the regulatory role of microbial communities with pho D genes in organic phosphorus mineralization,and thereby enhance the content of available phosphorus in soil. |
