Regulatory Effects And Mechanisms Of Different Components Of Decomposed Straw On Phosphorus Availability In Calcareous Soil

The limited availability of phosphorus poses a significant challenge to agricultural productivity in calcareous soils.The addition of exogenous organic matter has been shown to facilitate the transformation of inactive phosphorus into an active form in the soil.However,the properties of organic matter are dependent on their source,and their composition and structure can vary based on treatment methods,resulting in different effects on the regulation of soil phosphorus conversion.This study aims to investigate the response of changes in phosphorus availability and fractions to exogenous organic matter from different and identical sources using the"carbon supply results in phosphorus activation"approach.The research was conducted in two common calcareous soils（lime concretion black soil and fluvo-aquic soil）in the Huang-Huai-Hai Plain using five treatments:blank control（CK）,decomposed straw（S）,decomposed straw+ferrihydrite（SF）,decomposed straw+goethite（SG）,and decomposed straw+hematite（SH）.The preliminary experiment indicated that the activation effect of phosphorus in the lime concretion black soil was more significant when different sources of decomposed straw were used.Therefore,this soil was selected for further testing,using dissolved organic matter（DOM）extracted from straw at different decomposition periods as the exogenous organic matter.Three treatments were established:blank control（CK）,DOM extracted from 30 days of decomposed straw（DOM1）,and DOM extracted from 90 days of decomposed straw（DOM2）,to investigate whether differences in organic fractions were the primary factors regulating soil phosphorus availability.The results of this study provide a scientific basis for the use of exogenous organic matter as a means to enhance phosphorus availability in calcareous soils.The main findings are as follows:（1）The conversion of different phosphorus fractions and their relationship with soil physicochemical properties were analyzed to evaluate the effects of the application of the decomposed straw with different iron oxides on phosphorus availability in lime concretion black soil and fluvo-aquic soil.The results showed that（1）the application of decomposed straw significantly increased the available phosphorus contents in two soils（P<0.05）.After 60 days of incubation,the available phosphorus content increased by 10.2%-14.8%and 24.7%-35.0%respectively in lime concretion black soil and fluvo-aquic soil,and the increased of phosphorus content by the four treatments of decomposed straw application in lime concretion black soil and fluvo-aquic soil were in order of S>SG>SH>SF and SF>S>SG>SH,respectively.（2）The relative contents of active and moderately stable phosphorus pools increased while the relative contents of stable phosphorus pool decreased in lime concretion black soil with the application of decomposed straw.After 60 days of incubation,the accumulation of active phosphorus in SG treatment was significantly higher than those in other treatments（P<0.05）,which increased by 19.8%compared with CK.In fluvo-aquic soil,the relative content of the active phosphorus pool increased,while the relative contents of moderately stable phosphorus（except SG treatment）and stable phosphorus pools（except S and SH treatments）decreased.After 60 days of incubation,the accumulation of active phosphorus in SF treatment was significantly higher than those in other treatments（P<0.05）,which increased by 11.4%compared with CK.（3）Correlation and redundancy analyses showed that the available phosphorus contents in two soils were significantly positively correlated with soil organic matter content,and the transformation of phosphorus fractions was significantly influenced by soil p H in lime concretion black soil,and by soil alkaline phosphatase activity in fluvo-aquic soil.The application of decomposed straw significantly enhanced the phosphorus effectiveness,which mainly promote the conversion of inactive phosphorus to active phosphorus in two soils.And the application of decomposed straw with goethite was more effective in lime concretion black soil,while the application of decomposed straw with ferrihydrite was more effective in fluvo-aquic soil.（2）There were three treatments:blank control（CK）,DOM of 30-day decomposed straw addition（DOM1）and DOM of 90-day decomposed straw addition（DOM2）,were used to investigate the characteristics of phosphorus availability and fractions in response to the chemodiversity of exogenous DOM in lime concretion black soil.The results showed that DOM treatment increased the soil effective phosphorus content by 17.3%～54.3%and0.6%～18.2%,respectively,compared to CK,but there was no significant change in total soil phosphorus.The Tiessen sequential phosphorus extraction results indicated that the active phosphorus fraction increased by 12.4%～20.4%and 0.8%～8.3%,respectively.The Na OH-Pi in the medium-stable phosphorus fraction increased by 13.3%～15.0%and3.3%～10.0%and Na OH-Po decreased by 5.7%～17.2%and 0.8%～9.3%,respectively,compared to CK,while the stable phosphorus fraction decreased by 1.6%～2.6%and0.5%～3.7%,respectively.3D-EEM fluorescence spectroscopy results revealed more protein-like material in DOM1（46.2%）,while DOM2 had the largest percentage of humic-like material（41.4%）.Compared with DOM2,the addition of DOM1 significantly reduced soil p H and DOC and significantly enhanced soil Ca-ex content.High-throughput sequencing results indicated that the addition of DOM1 stimulated the growth of phosphate-solubilizing microorganisms such as Arthrobacter and Penicillium,and further analysis by Mantel test showed that soil properties had the strongest correlation with microbial communities in DOM1 treatment.In addition,MBP showed significant positive correlations with AP,H₂O-P,and Na HCO₃-Pi in DOM treatments.Random forest analysis revealed that MBP was a key factor driving changes in soil available phosphorus content.Therefore,the addition of DOM was able to enhance the soil available phosphorus content,and the simple composition DOM1 stimulated microbial activity and changed key phosphorus-related physicochemical factors more than the complex composition DOM2,which led to the increase of soil phosphorus content.The results of this study may provide new insights into the sustainable management of phosphorus in agroecosystems.In summary,the application of decomposed straw from different sources increased the content of available phosphorus in calcareous soils.In the lime concretion black soils,decomposed straw+goethite was more effective than other treatments,while the application of decomposed straw+ferrihydrite was more effective in fluvo-aquic soil.In addition,the decomposed straw of the same source had different effects on the regulation of soil phosphorus availability.The exogenous DOM with simple composition activated soil phosphorus significantly compared to exogenous DOM with complex composition.Therefore,the regulatory effect of organic matter on soil phosphorus conversion may be influenced by the differences in its components,which in turn may lead to different effects on the increase of soil phosphorus availability.This study provides a theoretical reference for the rational agricultural use of decomposed straw to soil phosphorus management.