Effects Of Inorganic Carbon On Microbial Iron Reduction Process In Paddy Soil

In terms of the iron-reducing bacteria, using of carbon source mainly focus on organiccarbon sources, which includes glucose, lactate, acetate, etc. However, there are fewer reportsabout inorganic carbon sources compared with organic carbon. Besides, inorganic carbon pooland its dynamic changes have an important effect on global climate in the whole world scale.Since soil inorganic concentration is affected by tillage methods, long term agriculturalproduction and change of land use have profound impacts on soil carbon cycle. Soilimprovement often involves using of carbonates because of low production of low pH soil. Asthe important composition in alkaline soils, carbonates play a crucial role in microbialphysical activities. Hence, studying of impacts of carbonates on microbial iron reductionprocess is of critical theoretical sense and practical meaning. In order to explore interactionsbetween iron reduction processes and concentration of carbonates in different paddy soils,slurry and mixed culture systems were used in the study. The main conclusions are following:(1) Iron reduction potential and maximum reaction rates increased significantly in BDand DN paddy soils, but the time to maximum reaction rates decreased with adding carbonate.However, iron reduction potential and maximum reaction rates in SR and HZ paddy soilswere decreased significantly when adding higher concentration carbonate. Maximum reactionrates increased in lower concentration carbonate but decreased in higher concentrationcarbonate, though there was no significant effect on iron reduction potential in FH strongacidic paddy soils. In comparison, iron reduction potential in strong alkaline paddy soildecreased while maximum reaction rates increased in SY. As a whole, effects of carbonate oniron reduction in acidic paddy soils were lower than that in alkaline paddy soils. Canonicalcorrespondence analysis showed that adding carbonate enhanced contribution of organicmatters to iron reduction potential, but weakened contribution of Amorphous and Free iron tomaximum reaction rates. Both iron reduction potential and maximum reaction rate had closedconnection with soil organic matters and pH.(2) Adding carbonate and bicarbonate in BD soils was able to increase its the iron reduction potential for more than7%. However, iron reduction potential decreased withadding carbonate, but there was no significant change of iron reduction potential in SR paddysoil. The maximum reduction rate had a obvious increase when adding carbonate in BD soil,which massively increased by148.6%and384.2%in BD(-Fe) treatment and BD(+Fe)treatment respectively. The maximum reduction rate significantly decreased when addingcarbonate in SR paddy soil, massively decreased by46.3%and54.5%in SR(-Fe) treatmentand SR(+Fe) treatment respectively. To some degree, adding bicarbonate into BD decreasedcould decrease the maximum reduction rate. In the condition of adding carbonate orbicarbonate in soils, iron reduction potential would increase when adding synthetic Fe(OH)3in slurry system.(3) Adding oxalate was able to increase iron reduction potential and maximum reactionrate and decrease time of maximum reaction rate in BD paddy soil. Precisely, iron reductionpotential and maximum reaction rate of BD(-Fe) treatment increased by52.7%and157.5%,respectively. Iron reduction potential and maximum reaction rate of BD(+Fe) treatmentincreased by80.3%and485.6%, respectively. The time of maximum reaction rate decreasedby32.6%and65.8%for treatment of BD(-Fe) and BD(+Fe). As for SR soil, iron reductionpotential and maximum reaction rate in SR(-Fe) decreased31.3%and47.5%, respectively.While iron reduction potential and maximum reaction rate in SR(+Fe) decreased34.4%and56.7%, respectively. Under the condition of adding oxalate, iron reduction potential increasedwith adding synthetic Fe(OH)3.(4) Adding NH4HCO3in SR soil had certain stimulative effects on iron reductionpotential, but there was no obvious effect on maximum reduction rate and its time. However,iron reduction potential and maximum reduction rate decreased by82.5%and93.3%withadding NH4Cl in SR soil, while time of maximum reduction rate decreased97.2%significantly.(5) Iron-reducing bacteria in BD and SR could not use bicarbonate as carbon source inabsence of organic carbon source. Iron reduction was suppressed when adding bicarbonate inmixture system, but the inhibited effect in lower concentration treatment was stronger thanthat in higher concentration. Adding carbonate inhibited the iron reduction in mixture culture,but the inhibited effect in higher concentration treatment was weaker than that in lowerconcentration. Under the condition of adding200mmol·L-1bicarbonate, improving glucoseconcentration in mixture system promoted iron reduction when glucose concentration wasless than40mmol·L-1. Moreover, iron reduction rate would be more larger with higherconcentration of glucose.