Effects Of Long-Term Fertilization On Phosphorus Characteristic And Transformation In Black Soil And Its Aggregates

Retention and supply capacity of soil phosphorus are important foundation to maintain agricultural productivity and soil fertility.Soil organic phosphorus(OP)is the most active part of soil phosphorus,understanding the chemical composition of soil OP is the basis to understanding plant nutrition and soil biogeochemical cycles.However,OP remains poorly understood,especially the composition of OP in soil and its potential contribution to plant nutrition,despite constituting a large proportion of the total P in many soils,and providing a source of P for plant uptake.Long-term fertilisation influences soil nutrient cycling and nutrient availability by altering the physical,chemical and biological properties of soil,including effects on activity,biomass and composition of microbial communities responsible for soil functions.Based on longterm fertilization experiment station,0-20 cm soil samples were collected,including six treatments: CK(no fertilizer),NPK(chemical fertilizer alone),M₂CK(normal manure application),M₂NPK(the chemical fertilizer combined with normal manure rate),M₄CK(high quantity manure application),M₄NPK(the chemical fertilizer combined with high quantity manure rate).Aggregate wet sieve method,quantitative PCR(Q-PCR)and Illumina Miseq high-throughput sequencing were adopted to study the effects of different fertilization treatments on the phosphorus nutrient retention and supply characteristics of black soil and its aggregates,as well as the driving and regulating modes of phoD gene-encoding functional microorganisms in the transformation of organic phosphorus components,in order to explore the effect of long-term fertilization on the phosphorus cycle of black soil and reveal its specific action mode and path.The main results and conclusions are as follows:1.Long-term fertilization significantly affected the total amount of organic phosphorus and its fractions in black soil and aggregates.The effect of organic fertilizer was better than that of chemical fertilizer.The content of MLOP was the highest in soil and aggregates.L-OP,ML-OP,and MR-OP are mainly distributed in micro-aggregates,HR-OP is mainly distributed in macro-aggregates.2.Long-term organic fertilizer application significantly increased the content of total phosphorus,available phosphorus and activation coefficient of phosphorus in black soil and aggregates and improved the effectiveness of phosphorus in microaggregates.The contribution rate of total phosphorus and available phosphorus to soil phosphorus nutrient was higher in 2-0.25 mm and 0.25-0.053 mm aggregates.3.Organic manure combined inorganic fertilizer significantly increased the alkaline ALP activity of black soil.Long-term application of chemical fertilizer and organic fertilizer could improve the activity of ALP in soil,especially the combination of organic and inorganic fertilizer.ALP was significantly positively correlated with TP,AP,TOP and OP fractions.4.Single organic fertilizer application significantly increased phoD gene abundance in black soil and its aggregates,and phoD gene abundance were positively correlated with ALP,organic phosphorus fractions(except HR-OP).Compared with NPK,the effect of organic manure combined inorganic fertilizer on phoD gene abundance was not significant,although phoD gene abundance was increased.phoD gene abundance did not change under only fertilizer application in the black soil and its aggregates.Relative abundance of phoD gene copy numbers in the organic manure and inorganic fertilizer combination treatment was higher than that in the large aggregate,while in other treatments,the relative abundance of phoD gene copy numbers in the large aggregate was higher than that in the microaggregate.5.The dominant phyla of phoD gene were Proeobacteria,Acidobacteria,Actinobacteria and Cyanobacteria in black soil and aggregates.At the level of genus,the dominant bacteria in soil aggregate were different in aggregates.The availability of P in soil was mainly affected by Steroidobacter,Mesorhizobium and Rhizobium.The availability of P in macro-aggregates was mainly affect by Bradyrhizobium,Kribbella and Lechevalieria,but less affected by the abundance in microaggregates.The availability of phosphorus in soil can be improved by adjusting the abundance of microbial communities.The increase of organic carbon in the soil can significantly change the abundance of the microbial communities.Therefore,organic fertilizer application can regulate the structure of the microbial communities and thus improve the availability of phosphorus.