The Interaction Between Soil PH And Carbon,Nitrogen Mineralization In Acid Soil

In recent decades,soil acidification has become an increasingly serious issue,which raises widespread concern.Therefore,the amelioration of acid soil is an important research area.In order to investigate the effect of amelioration of acid soils by effective ameliorants(biochar,lime and organic fertilizer)and their combinations,an acid red soil in Quzhou was selected to carry out a field trail.The study investigated,in laboratory investigations,how the soil basic physicochemical properties(pH and dissolved organic C(DOC))changed after incorporation of organic materials(maize flour and maize straw)into a soil previously amended with three field treatments,i.e.,unamended,treated with wheat biochar and organic fertilizer.The relative contributions of soil pH and substrate availability to bacterial community changes in amended soil were also assessed in other laboratory trials.The main results were as follows:(1)The field experiment investigated the effect of application of biochars(10.0 t/ha),lime(2.0t/ha),organic fertilizer(10.0 t/ha),and their combinations on acid soil.Soil pH was increased by all of the ameliorants.Wheat biochar produced the largest increase,of approximately 2 pH units,and a mixed treatment(one third rice husk biochar,one third lime,and one third organic fertilizer)also caused large increases,of almost 1 pH unit.In general,the basic cations(Ca2+,Mg2+ and K+)of the ameliorants were the main factors contributing to the increase of soil pH,while N mineralization(mainly nitrification)made a relatively small contribution to the pH decrease.(2)There was strong evidence that the ratio of ammonia-oxidizing archaea(AOA)to ammonia oxidizing bacteria(AOB)abundance greatly increased with decreased soil pH,indicating that soil pH was an important factor affecting the abundance of AOB.High-throughput MiSeq sequencing showed that the soil ameliorants significantly increased the relative abundances of Nitrosomonas and Nitrospira.Soil pH was an important determinant of the bacterial community composition and diversity.The ameliorants(biochar,lime,organic fertilizer,and their combinations)change soil nitrification by altering nitrifying bacteria abundance,diversity,and composition,caused by the changed soil pH.(3)Maize flour mineralized more rapidly than maize straw in the soils of different pHs(4.63 to 6.32),and fastest at the highest pH(6.3).After incorporation of maize flour(5 mg C g-1 soil),soil pH increased during the first day,then decreased consistently.The main factors causing soil pH changes are the interactions between the release of alkalinity from the decomposition of organic materials and nitrification.Compared to the control soil,maize flour made a more significant contribution to soil pH and increased microbial biomass more than maize straw.High-throughput MiSeq sequencing showed that the bacterial communities differed remarkably along the different treatments,and there were significant relationships between community structure and soil pH,microbial biomass 13C derived from added substrate and soil organic matter mineralization,respectively.The relative abundances of Alphaproteobacteria,Betaproteobacteria and Saprospirae were positively correlated but those of Acidobacteria,Gammaproteobacteria and Ktedonobacteria were negatively related to soil pH.The addition of substrates significant increased the relative abundance of proteobacteria(Betaproteobacteria and Gammaproteobacteria),but decrease the relative abundance of Ktedonobacteria.However,there is no significant relationship between TOC and dominant class of bacteria.It also showed that bacterial community structure and composition was influenced more by soil pH than by the input of organic substrates.