redox potential. microbial communitystructure, Key words: abundances andcommunitystructures. paddy fields affects rice yield, soil nutrients, microbial In conclusion,openingadrainageditchincoldwaterlogged abundant anaerobicbacteriawereobservedatthe25m-site. wereobservedatthe5m-and15m-site,incontrast, microbial communitystructures. The abundantaerobic shaping in factors significant were substances reducing total redundancy analysisrevealedthatsoilredoxpotentialand group andsamplesof25m-sitewasanothergroup.Moreover, groups, samplesof5m-and15m-siteclusteredintoone microbial communitystructuresweredividedintotwomajor abundances. The Bray-Curtis distance demonstrated that microbial community compositions butwithdifferent relative and samples were ditch. The most abundant bacterial phyla acrossall soil decreased sharplywithincreasingdistancefromthedrainage gene did not exhibit a regular pattern but fungal abundance however, 25m-sitehadlowervalues.Bacterial16SrRNA nutrients,ditch suchas5m-sitehadhigheryieldandsoil physicochemical properties.Samplingsitesnearthedrainage effectdrainage ditchhadasignificant soil onthericeyieldand 25 m were investigated. The results showed that opening a different distances from a drainage ditch including 5, 15 and with treatments three has which field, paddy waterlogged cold abundances andcommunitystructuresinthesurfacesoilofa sativa ameliorating waterlogged soil. Inthe present study, rice ( However, little has been done on the role of a drainage ditch in improve waterloggedpaddysoilandtoincreasethericeyield. soil, andopeningadrainageditchhasbeensuggestedto Cold waterloggedpaddyfieldisatypeoflow-yield ABSTRACT doi:10.4067/S0718-58392017000100011 Accepted: 21November2016. Received: 13June2016. * Fuzhou, Fujian,350003,China. 1 Yu Fang drainage ditch paddy fieldto different distances from a Microbial responses inacoldwaterlogged Corresponding author([email protected]). Soil andFertilizer Institute, Fujian Academy of Agricultural Sciences, CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY L.)yield,soilphysicochemicalproperties,microbial 1 , Fei Wang and Cold waterlogged paddy field, drainage ditch, . Abundant fungalphylawere 1 , JichenChen CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY , . Three treatmentshadsimilar Oryza sativa 1 , ChengLin , , real-timePCR, Oryza Oryza 1 , andXinjianLin - , MARCH 2017 management is important for selecting suitable management tothedrainage response soil microbialcommunity and its ditches on the paddy soil microorganisms. Understanding the relatively fewresearchershave studiedtheeffect ofdrainage could resultinshiftingthe microbial communities.However, agriculture for improving the soil physical properties, which 2014). Drainage is an important water management strategy in communities (Li et al., 2012; Yuan et al., 2013; Zhao et al., irrigation pattern) largely determine the structures of microbial management practices(e.g.,fertilizationregimes,croprotations, (DeAngelis et al.,2010). Itiswell knownthatagricultural strategies forrespondingtochangingenvironmentalconditions are dynamic assemblages of populations with different soil aggregate(Kamaaetal.,2011). Soilmicrobialcommunities soil nutrients,decompositionoforganic matterandformationof ecosystems astheymediatemanyprocessesincludingcycling of agricultural landscapes(Needelmanetal.,2007). groundwater toallowforcropproductioninpoorlydrained drainage ditches areessential forremovalofsurface waterand drainage ditch, mole drainage and tile drainage. Agricultural have employed some techniques forland drainage, such as can increasetheiryieldthroughproperdrainage.Chinesefarmers CWPF matter.Therefore, organic of oxidation the accelerate and after drainage,whichcouldimprovethesoilaerationcondition removed rapidly be could field in water Excess potential. fertility inherent higher have CWPF Consequently, conditions. reducing easily subjected to accumulate rather than decompose because of are CWPF in matters Organic important. increasingly becoming is field paddy low-yield of productivity of improvement China, in demand food increasing the With nutrients. available of contents physical characteristics,excessivereducingsubstancesandlow table, poor drainage conditions, low soil temperature, poorsoil groundwater high to attributed is CWPF of productivity low water accumulation in the soil surface (Xie et al., 2015). The of local microclimate and topographical features resulting in are formedwhenthegroundwaterlevelrisesduetoimpact the low-yield paddy area in China.Coldwaterlogged paddy soils occupy15.07%ofthetotalpaddyareaand44.2% ha which 000 460 3 have CWPF China. southern in dams of downstream valleys, low-lying lands of hills, plains and lakes, and yield paddysoils which aremainly distributed inmountain low- of type main a are (CWPF) fields paddy waterlogged Cold INTRODUCTION Soil microorganisms areimportantcomponentsofagricultural 1* - MARCH 2017

87 RESEARCHRESEARCH CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY sample was partitioned into three subsamples: one stored bags andtransportedonicetothelaboratory. Eachsoil obtained. The fresh samples were sealed in sterilized plastic were obtained. Therefore, ninecompositesampleswere composite samples at different sites from the same distance randomly collected and composited. Similarly, two other were diameter) cm (5 cores soil five site, each At distance. Three samplingsiteswererandomlyselectedateach urea, superphosphate and potassium chloride, respectively. kg Nha cultivation). The amounts ofchemical fertilizers were 120 were collected in August 2014(tillering stage during rice from Qiuetal.,2013).Surfacesoilsamples(0-20cm) as “A”,“B”and“C”,respectively(Figure1,minorrevision the drainageditch,paralleltoditchandmarked for soilsampling,whichwerelocatedat5,15and25mfrom selected were distances Three field. paddy a of middle the in (200 m length, 30 cm width and 1 m depth) was established ditch drainage a field, in water excess remove To(USDA). Anthrosols Gleyi-Stagnic as classified is soil The mm. 1691 average temperatureof18.5°Candannualprecipitation has a subtropical monsoon humid climate with an annual (26º42’ N,117º42’ E),FujianProvince,China. This region The experimentwasestablishedin1979atShunchangcounty Experimental designandsoilsampling MATERIALS ANDMETHODS changes inthestructuresofmicrobialcommunities. and identify theenvironmental variables that correlated to bacterial andfungalcommunityatthe different distances; abundance, taxonomic diversity and compositions of California, USA). ditch on the Illumina Miseq platform (Illumina, San Diego, paddy soils at the different distances from the drainage fungal communitieswereexaminedinacoldwaterlogged study, thecompositionandstructureofsoilbacterial to determinethesuitabledrainagepractice.Inpresent drainage ditch onthemicrobial communities shouldhelp us Therefore, experiments examining the effect ofthe practice toimprove soil function and increasericeyield. cold waterloggedpaddyfieldandsamplingsites. Figure 1. Vertical sectionofanopening drainage ditchina The objectivesofthisstudywere to determinethe -1 , 48 kgP ha -1 , 84kgKha -1 peryearintheformof - MARCH 2017 reducing substances. remaining subsample was stored at 4 °C for determining passed througha2-mm sieve for chemical analysis and the at -20 °CforDNA extraction, the second was air-dried and 1 ×10 sequencing wascarriedouton theIllumina Miseq platform 1990). al., et (White region Amplicon ITS fungal amplify to (5’-GCTGCGTTCTTCATCGATGC-3’)used 2043R were ITS2- (5’-GGAAGTAAAAGTCGTAACAAGG-3’)and ITS5-1737F primers Fungi-specific (2011). al. et Caporaso DNA wasamplifiedfollowingthe protocoldescribedby unique to each sample for the subsequent identification. was designed to have a 6-bperror-correcting barcodes rRNA gene(Bergmann etal.,2011). The reverseprimer 16S bacterial of region hypervariable V4 the amplify to (5’-GGACTACHVGGGTWTCTAAT-3’)employed were 806R and (5’-GTGCCAGCMGCCGCGGTAA-3’) 515F spacer (ITS)regionamplification.Bacterialprimers template in 16S rRNA gene and internal transcribed of interest. known copynumbersofplasmidDNA possessingthegenes Delaware, USA). 2000(NanoDrop NanoDrop Technologies Inc., Wilmington, DNA concentrationandqualitywere determined using a Fragment Purification Kit (TaKaRa, Dalian, China). method (Zhouetal.,1996)andthenpurifiedbyDNA by Lu(2000). Soil organic matter(OM) was determined by the K extraction Soil chemicalanalysis andsoilDNA by melting curve.Standard curves ranging from 1×10 confirmed was specificity amplification The °C. 72 at s 30 °C, followedby40cyclesof5sat953055°Cand under thefollowingthermalcycleconditions:30sat95 USA) Massachusetts, Scientific, Waltham, Fisher (Thermo in triplicateusingan ABI 7500Real-timePCRSystems diluted extractedDNA.Real-timePCRwascarriedout Dalian, China),0.2µMofeachprimerand 2 µL 10-fold (TakaRa,mix PCR I Green SYBR µL 10 using µL 20 total Bouré etal.,2011). The PCRmixturewaspreparedina primers 338F/518RandFF390/FR1,respectively(Prévost- Abundances ofbacteriaandfungiwereperformedusing Real-time PCR andMiSeqsequencing Fe Aurora, Illinois, USA). Total reducing substances (TRS), indicator SpectrumIQ150(Spectrum Technologies Inc., Eh using field the in cm 5 of depth a at measured was (Eh) Shanghai-Spectrum, Shanghai, China).Soilredoxpotential using atomic absorption spectrometer (AAS,SP-3801, methods, respectively. Available K(AK)wasdetermined were determinedbyNaOHhydrolyzableandmolybdenum oxidation method. Available N(AN)and available P (AP) 2+ DNA extractedfromeachsoilsampleservedasa Soil totalDNA wasextractedbytheSDS-based andMn 9 copieswerepreparedby10-foldserialdilutionof 2+ weremeasured using themethodsdescribed 2 Cr 4 2 to O 7

88 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY C (25m) increasing distancefromthedrainageditch.Riceyield of opening a drainage ditch gradually weakened with could improvesoilnutrientcontents,buttheeffectiveness a drainageditchinthecoldwaterloggedpaddyfield samples. Soil chemical measurements showed that opening all across observed was OM soil in difference significant and Mn B (15m) A (5m) Table 1.Soilproperties andriceyieldacross different distances. m-site had thehighest rice yield, about 10 160kgha affected bythedistancefromdrainageditch. The 5 and rice yield arelisted in Table 1.Riceyield washighly The effect ofdrainageditchonthepaddysoilcharacteristics characteristics across different distances Variations inriceyieldandsoil RESULTS Wageningen, The Netherlands). Research, and University (Wageningen 4.5 Canoco the and redundancyanalysis(RDA)wereconductedusing microbial diversity, principalcomponentanalysis(PCA) OTU and identify environmental factors influencing community structuresacrossallsamplesbasedonthe mothur (Schlossetal.,2009). To comparemicrobial processing, OTU-basedanalysiswereperformedusing The communityrichnessindex,diversity data Statistical analysis and SRA310798,respectively. Read Archive (SRA)underaccessionnumbersSRA307922 Bacterial and fungal sequences were submitted to Short taxonomic datausingtheRDP classifier(Wang etal.,2007). a representativesequencewasselectedandusedtoassign taxonomic units(OTUs)at97%similarity. ForeachOTU, operational pick UPARSE to Then used filters. was pipeline al., 2010). The reads were first filtered by QIIME quality Microbial Ecology) and UPARSE pipeline (Caporaso et QIIME software package (Quantitative Insights Into barcode ofeach sample. Sequences were analyzed with reads wasassignedtoeachsampleaccording to theunique on themethodbyMagocandSalzberg (2011). Sequencing reads from the original DNA fragments were merged based at theNovogene Technology Co.(Beijing,China).Pairsof was also observed in the soil Eh. The minimum TRS, Fe TRS, minimum was alsoobservedinthesoilEh. The AP, AK decreased(P kg ha lowest riceyield wasobservedatthe25m-sitewith8460 P <0.01accordingtoLSD test,respectively. 3. = Valuesn SD, ± means the are Data differencesdifferent significant the indicate at lower-casewith letters and column uppercase 0.05 same and < the P in site Sampling With increasing distance from the drainage ditch, AN, ditch, drainage the from distance increasing With -1 . 2+ were observedat the 5m-site. However, no 3.55 ±0.01a 3.76 ±0.19a 3.59 ±0.01a gkg Organic matter -1

< 0.05).Similar decreasing pattern 142.30 ±0.57B 173.65 ±2.93A 177.80 ±12.29A Available N

4.68 ±0.45b 7.96 ±1.47a 5.11 ±1.13b Available P mg kg -1 38.51 ±1.96B 45.70 ±3.97B 57.22 ±6.77A Available K - MARCH 2017 -1 . The 2+

29.77 ±1.04C 41.93 ±0.46B 51.30 ±0.95A drainage ditch. the from distances different across gene rRNA 18S fungal Figure 2. Abundance ofsoil bacterial 16SrRNA gene and < 0.01,respectively. P differences at significant indicate letters uppercase and case lower- Different 3). = (n deviations standard to correspond Verticalbars abundance withconcentrationsofFe revealed positive correlations between the bacterial 18S rRNA geneatthesamedistance.Spearman’s analysis bacterial 16SrRNA genewashigherthanthatoffungal and 5m-site had the highest value. The copy number of with thetotal reducing substances (r=-0.891**)andFe (r =0.723*)and AK (r=0.854**)andnegatively correlated positivelycorrelated with thesoilEh(r=0.899**), was AP was alsoobserved(r=-0.695*). fungalabundanceand negative correlationbetween TRS between fungalabundanceand AK (r=0.683*),anda (r =0.667*).Moreover, therewasapositivecorrelation × 10 The bacterial16SrRNA geneabundancerangedfrom0.46 abundance Differentiations inthebacterial andfungal 18S rRNA geneabundancerangedfrom1.75×10 observed atthe15m-and5m-site,respectively. Fungal and lowestbacterial16SrRNA geneabundanceswere × 10 content (r=-0.695*). potential Redox mV 10

9 copiesg to3.34×10

Total reducing 0.37 ±0.06a 0.27 ±0.02b 0.20 ±0.04b substances cmol kg -1 soilacrossdifferent distances(Figure2b) 10 -1 copies g copies 100.38 ±3.35a 100.98 ±4.01a 91.32 ±1.85b Fe -1 2+ soil (Figure 2a). (Figure soil The highest mg kg 10.70 ±3.11a -1 4.50 ±0.94b 6.11 ±0.88b 2+ (r=0.833**),Mn Mn 2+ 10160 ±55A

8460 ±96C 8894 ±144B < 0.05andP Rice yield 9 kg ha to6.12 -1 2+ 2+

89 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY Fungi Bacteria Table 2.Operationaltaxonomicunits(OTU)numbersanddiversity indexesofbacteriaandfungiacross different distances. surface soilacross different distances. Figure 3. Proteobacteria of eachphylumvaried(Figure3a).Inallsamples, among nine samples weresimilar, while the distribution UPARSE program. The overall bacterial compositions All index amongallsamples. Shannon the in difference significant no was There 0.05). < the 5m-and15siteswerehigherthan25m-site(P increasing distance from thedrainage ditch. Chao1indexat (P <0.01). The number of OTUsstrikingly decreased with difference inthenumberofOTUsamongthreedistances to 63721amongthetreatments. There wasasignificant total numberofsequencespersamplerangedfrom40 471 Bacterial diversityandrichnessareshownin Table 2. The different distances Analysis ofbacterial communitiesacross LSD test,respectively. to according 0.01 < and P 0.05 < at P differences significant indicate letters uppercase Values3. and lower-casedifferent= with n SD, ± means the are Data standard deviations(n=3). to correspond Verticalbars phyla. fungal dominant the of abundance a. Relative abundance ofthe dominant bacterial phyla; b.Relative community Microbial

sequences wereclassifiedinto57phylabythe

Bacterial and fungal community distribution in the in distribution community fungal and Bacterial Sampling site C (25m) B (15m) C (25m) B (15m) A (5m) A (5m) wasthemostabundantphylum. 98.44 ±0.14a 98.26 ±0.00a 98.77 ±0.72a 96.33 ±0.52a 95.89 ±0.16a 95.63 ±0.26a Coverage (%) - MARCH 2017

1021 ±76a 2807 ±30.95C 2899 ±31.75B 2961 ±18.71A 955 ±135a 834 ±331a OTUs Acidobacteria genera suchas m-site and lowestat the 5 m-site.Likewise, other anaerobic relative abundance ofgenus respiration bacterial species. It wasobserved that the aerobic bacteria such as genus showed a similar pattern. In contrast, relative abundance of low. m- and15sites, although their relative abundances were m- sites (Table 3). For example,oneanaerobic bacteria wereobservedatthe25m-sitethan5m-and15 In particular, ahigherrelativeabundanceofanaerobic ofotherphylaamongallsamples.the relativeabundances 1.11%) (P the 5m-site(1.98%)than15m-and25sites(1.40% 0.01). A higherabundance of phylum m- sites(10.34%and8.20%)than25m-site(3.99%)(P Phylum than 5 m- and 15 m- sites (0.80% and 0.96%) (P opposite pattern, being higher at the25m-site (1.69%) (15.22%), whilephylum 15 m-sites (20.57%and 19.56%) compared to 25m-site of phylum above 1% inat least one treatment. The relative abundance were the dominantphylawithrelative abundances m- and15sites. implicating little shift of microbial communities between 5 replicates of5m-and15sitesoverlappedeachother treatment of 25 m-site (Figure 5a). More importantly, the treatments of5m-and15sites,anotherfrom communities were partitioned into two clusters: one from m-site) and C3 (the third replicate of 25 m-site), bacterial communities. ExceptforB3(thethirdreplicateof15 distance wasusedtocomparetherelatednessofbacterial and 15m-siteswererelativelysimilar. The Bray-Curtis demonstrating thecommunitycompositions of 5m- 5 m-,15m-and25sitesalongthefirstprincipalaxis Bacterial communitycompositionsshiftgreatlybetween explain 69.6%ofthe total variation among all samples. (Figure 4a). The firsttwoprincipalcomponentscould distances, PCA wasconducted based onthebacterial OTUs richer atthe5m-and15sitesthan25m-site. To compare the microbiota across three different Geobacter Planctomycetes

< 0.05). There were no significant differences in differences significant no were There 0.05). < Acidobacteria was strikingly higheratthe25m-sitethan5 strikingly was , Planctomycetes is agenusof Syntrophobacter , , 3354.69 ±169.58b 3694.13 ±160.27a 3831.41 ±169.90a Chlorobi 801.65 ±54.51b 928.65 ±35.09a 859.85 ±8.70ab wasalsohigheratthe5m-and15 Chao1 Geobacter were higheratthe5m-and Proteobacteria , , Planctomyces Chloroflexi Bacteroidetes and WS3 was richestatthe25 Desulfobacterium , , was observedat exhibited the , was strikingly

, an anaerobic WS3 4.58 ±0.34a 4.60 ±0.36a 5.16 ±0.30a 9.99 ±0.09a 9.89 ±0.10a 9.94 ±0.06a Shannon

< 0.05). , NC10

< , ,

90 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY Desulfobacterium units atadistanceof3%. taxonomic operational on based (b) communities fungal and (a) bacterial of (PCA) analysis component Principle 4. Figure Syntrophobacter (genus) Geobacter (genus) Planctomyces Spirochaetes Table 3.Relativeabundancesofselectedbacterialtaxashowingsignificantdifferences across different distances. distance Bray-Curtis using calculated was that matrix distance the on based trees cluster hierarchical (b) fungal and (a) Bacterial 5. Figure according toLSDtest,respectively. Data are the means ± SD, n = 3. Values in the same row with different lower-case and uppercase letters indicate significant differences at P < 0.05 and P < 0.01 Taxa . (phylum) (genus) (genus) A, B,Crepresent5 m-,15m-and25sites,respectively. 0.0015 ±0.0003b 0.0027 ±0.0003B 0.0044 ±0.0006b 0.0270 ±0.0062a 0.0021 ±0.0001C A (5m) - MARCH 2017 0.0023 ±0.0004b 0.0029 ±0.0002B 0.0059 ±0.0004ab 0.0184 ±0.0070a 0.0026 ±0.0001B B (15m) bacterial communitystructure(Figure5b). treatment of25m-site. This resultwassimilartothatof from treatments of 5m-and15sites, andanother from fungal communities were partitioned into two clusters: one of 5m-site) and C3(the third replicate of25m-site), could alsobeobserved.Exceptfor A3 (thethirdreplicate between 25m- and 5m-, 15m- sites along the first axis (Figure 4b).Similartothatofbacteria,aclearseparation fungal OTUs could explain 68.6% of the total variation highest valueand5m-sitehadthelowestvalue. three different distances(P <0.01),25m-sitehadthe phyla were significant differences in therelative abundances of m- siteswhileitwasstrikinglylowatthe25m-site. There 3b). Phylum 37.98%, 29.65%,9.41%,1.21%,0.62%,respectively(Figure sp WEF9 Ascomycota distances. differencessignificant different inShannonindexacross lowest valuewasobservedatthe25m-site. There wereno Chao1 at the 15m-site had the highest value andthe of sequencesper sample varied from 15 160 to 64253. in Fungal diversityindexesareshown Table 2. The number different distances Analysis offungal communitiesacross The first two principal components in the PCA targeted PCA the in components principal two first The The obtained fungalreadswereaffiliated to phyla Chytridiomycota , Chytridiomycota , Zygomycota Zygomycota 0.0033 ±0.0006a 0.0041 ±0.0002A 0.0070 ±0.0014a 0.0061 ±0.0021b 0.0032 ±0.0000A C (25m) and was dominant at the5m-and15 , withanaverageproportionof Basidiomycota Un-s-fungal spWEF9

, Obligate aerobe Un-s-fungal Anaerobe Anaerobe Anaerobe Anaerobe across

91 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY separate groupattributedtolowerEhandhigher TRS. bacterial and fungalcommunities ofthe25m-siteformeda respect tobacterialandfungalcommunities.Specifically, environmental variables in explaining the variance with was concluded that Eh and TRS were the most important it results, above From 6b). (Figure influential significantly = 3.571,P =0.036)andEh( (Figure 6a). For fungi, AN ( variation total the explaining in factors significant most the Bacterial community(a)andfungal(b). Figureanalysis 6.Redundancy increasing With characteristics. soil on impacts significant that openingadrainageditchinwaterloggedpaddysoilhas composition (Li et al., 2012). In present study, we found considered animportantfactorinfluencingsoilmicrobial on soiloxygenconcentrationandnutrientavailability, is Soil water content, which has direct and indirect effects ecosystems. paddy rice in factor major a is Water2015). al., et (Wang respectively sites, m- 25 and m- 15 m-, 5 March 2011 to April 2014were-16.7,-5.4and8.3cmat showed that the average underground water level from waterlogged paddyfields.Previousresearchbyourteam Drainage managementisanimportantpracticeincold relatively littleresearchondrainageditchhavebeendone. et al., 2012;Itohet 2013; Dong etal.,2014),however, community inagriculturalland(Lietal.,2012;Chaudhry use, irrigation patterns andwater management onmicrobial management practices such as fertilization regimes, land Previous researchesfocusedontheeffect of agricultural DISCUSSION = 4.780, P = 0.032) and TRS ( variables onmicrobial abundant phyla.Forbacteria, Eh ( RDA wasperformedtostudytheeffect ofenvironmental communities andenvironmental factors Relationships betweenthemicrobial ● OM: Organic matter; AN: available N; AP: availableP; AK: available K; TRS: total reducingsubstances;Eh:redoxpotential.

5 m-site,

▲ 15 m-site, F ( RDA) illustrating the relationship between microbial abundant phyla and environmentaland relationshipvariables: microbialphyla the between illustrating abundant RDA) F = 4.078,P =0.020), TRS ( F

▼ = 3.255,P =0.044)were = 4.093, P = 0.048) were 25m-site. - MARCH 2017 F F like Fe positively correlatedwiththecontentsofreducingsubstrates were higherthanin5m-site,butbacterialabundances number ofbacterial16SrRNA genein15m-and25sites between bacterial abundance andthe distance. The copy its effect on soil microorganisms. There was no correlation ditch inacoldwaterloggedpaddysoilwasselectedtostudy Xiang etal.,2008).Inthepresentstudy, openingadrainage 2008; al., et (Gorden content water soil to respond microbes which wasalsodemonstratedbyHussonetal.(2001). study, riceyielddecreasedsharplywhenEh agriculture asitplaysanimpactoncropyields.Inpresent Soil redox potential is offundamental importance for soil propertiesandprocesses(Tokarz andUrban,2015). reduction potentialisassociated withthemostimportant than15m-and25m-sites. nutrients The oxidation- 2009). Therefore, inourstudy, 5m-sitehadthe higher mineralization (Xiang et al., 2008; Borken andMatzner, enzymatic activities, which in turn increase nutrient intracellular osmolytesandenhancingmetabolic mobilizing Cphysicallyprotectedinaggregates,releasing rewetting conditionledtoacascadeofresponsesincluding to thedecomposers(Oretal.,2007). Then thesubsequent reduces solute, enzyme mobility and the substrate supply m- sitesaremostlybelowthegroundlevel.Soildrying rewetting condition but the water level of 15m- and 25 showed that5 m-site isobviouslyunderfluctuating dry- 2015) al., et (Wang team our by research Previous 2000). observed inprevious study (LuedersandFriedrich, such asmetalreductionprogressedsequentially, asalso and Ehdecreasedgraduallyanaerobicprocesses distance fromthedrainageditch,soilavailablenutrients ditch andwerenegativelycorrelatedwiththe TRS. Above decreased sharplywithincreasingdistancefromthedrainage Previously, various studies have examined how soil 2+ andMn 2+ . Incontrasttobacteria,fungalabundances

92 CHILEAN JOURNAL OF AGRICULTURAL RESEARCH 77(1)JANUARY communities (Husson,2013). that soilEhwasanimportantfactorinshapingbacterial previousstudies,whichdemonstratedwere consistentwith affecting microbialcommunitystructures. These results that Eh and TRS were the common predominant factors 2012; Liuetal.,2014;2015). The RDA analysissuggested could shape microbial community structures (Brockett et al., aerobic toanaerobicbacteria. decreases; accordingly, microbial populations switch from soil pores,andtheoxygensuppliedfromatmosphere Excess water at 25 m-site replaces the gaseous phase in the and 15m-sitesweremoresimilarascomparedto25m-site. m- 5 at structures community microbial that reflect clearly based onsoilmicrobial OTUs at 5 m-,15m-and25m-sites Bergmann, G.T.,Bergmann, S.T.,Caporaso, Lauber,Bates, C.L., K.G., Eilers, REFERENCES experiments. Ltd. (Beijing,China)fortheirhelpwiththesequencing Co.,TechnologyNovogene thankWe (201003059). Agroscientific Research in the Public Interest, China This research was fundedbytheSpecial Fundfor ACKNOWLEDGEMENTS could resultinlowersoilnutrientsandriceyield. our studyisabout15m.Severeanaerobic conditions insoil the distancefromdrainageditchandeffectiveness in microbial abundanceandcommunitystructuresdependon effects of drainage practice on the soil chemical properties, practice in improving soil nutrients and rice yield. The a coldwaterloggedpaddyfieldisanefficient agricultural Our study has documented that opening a drainage ditch in CONCLUSIONS m-site may result in much higher Fe higher abundanceoftheknownFereducers relative abundances ofanaerobic bacteria. The relatively m-sites than25m-site,incontrast,m-sitehadhigher of aerobicbacteriawerestrikinglyhigherat5m-and15 waterlogged paddy field. Moreover, relative abundances were rathersensitivetoopeningadrainageditchincold Acidobacteria phyla, dominant the among that found have Wedistances. acrossdifferentbut withabundance-dependentshifts taxonomic groupsdetectedwerepresentedinallsamples exhibit thebestdevelopmentonlyatEh>250mV. reported thatfungipreferweaklyreducingconditionsand under strongly reducing condition. Seo and DeLaune (2010) results demonstratedthatfungalgrowthwereeasilyinhibited and Biochemistry 43:1450-1455. of J.G. Walters, W.A.2011.al. et under-recognized dominance The Many studies haveshownthat environmental factors The sequenceanalysisrevealedthatthemajorityof Verrucomicrobia , Planctomycetes insoilbacterialcommunities.Soil , Bacteroidetes 2+ concentration. PCA Geobacter and - MARCH 2017 at 25 at 25 WS3

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