Changes of CO 2 emission and labile organic carbon as influenced by rice straw and different water regimes

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1 Int. J. Environ. Si. Thnol. (2015) 12: DOI /s ORIGINAL PAPER Chngs o CO 2 mission n lil orgni ron s inlun y ri strw n irnt wtr rgims M. Irhim C.-G. Co M. Zhn C.-F. Li J. Iql Riv: 2 Frury 2013 / Rvis: 26 July 2013 / Apt: 2 Novmr 2013 / Pulish onlin: 20 Dmr 2013 Ó Islmi Az Univrsity (IAU) 2013 Astrt Crop rsius unr irnt wtr rgims n us signiint ltrtions in soil orgni ron rtions, n in turn, soil-tmosphri ron ioxi (CO 2 ) missions. To vlut th t o ri strw pplition on CO 2 missions n lil orgni ron rtions unr irnt wtr rgims, n inution xprimnt ws onut or 90 ys. Tn trtmnts wr vlop rom th intrtion twn iv wtr lvls (100, 85, 70, 55, n 40 % o wtr-holing pity (WHC)) with n without inorportion o ri strw. Pks o CO 2 luxs wr osrv tr 13 ys o ri strw inorportion, whih rs grully till th n o th inution prio. Th inorportion o ri strw us signiint inrss in CO 2 luxs y tims rom th py soil. In th prsn o ri strw, th highst CO 2 luxs wr gnrlly osrv t W3 (70 % o WHC), whrs th lowst luxs wr ourr t W1 (100 % o WHC). Aition o ri strw unr rng o wtr rgims mrkly improv th trnsormtion o soil orgni ron n lil orgni ron pools suh s M. Irhim C.-G. Co M. Zhn (&) C.-F. Li MOA Ky Lortory o Crop Eophysiology n Frming Systm in th Mil Rhs o th Yngtz Rivr, Collg o Plnt Sin n Thnology, Huzhong Agriulturl Univrsity, Wuhn , Hui, Popl s Rpuli o Chin -mil: soillkhors@gmil.om M. Irhim Soil Sin Dprtmnt, Fulty o Agriultur, Bnh Univrsity, Moshtohor, Toukh, Klyoui 13736, Egypt J. Iql Dprtmnt o Agronomy, Iow Stt Univrsity, Ams, IA 50011, USA issolv orgni ron, miroil iomss ron, light rtion orgni ron, prtiult orgni ron, n prmngnt oxiizl ron. Th signiint orrltions twn ll lil soil orgni ron rtions n CO 2 onntrtions onirm thir importnt rols in th mission o CO 2 rom th py soil. In summry, th rsults suggst tht light rtion orgni ron, prtiult orgni ron, n prmngnt oxiizl ron wr mor snsitiv initors or CO 2 missions n orgni mttr ltrtions s ompr to othr ron rtions. Kywors Cron ioxi mission Lil orgni ron rtions Wtr rgims Ri strw Introution Inorportion o rop rsius in griulturl soils is onsir s goo mtho or prsrving n improving soil qulity. In Chin, thr r out 13 million htrs ount or ri wht ropping systm, n most o ths rs r lot in our provins (Anhui, Hui, Jingsu, n Sihun) roun th Yngtz Rivr vlly (Huk t l. 1993). This hs l to high proution n umultion o ri strw (200 million tons) vry yr in Chin (Hn t l. 2002). Thus, ri strw hs om on o th min orgni mnmnts in py soils, n its inorportion into ths soils n l to inrss in soil orgni mttr ontnts n rop yils. Th rmrs hv thr irnt mthos to rturn th ri strw to soils prior to rop ultivtion. Ths wys r urning, mulhing on soils, n inorporting into soils (M t l. 2010). Th urning o ri strw is nvironmntlly unptl n illgl, n hs n xtnsiv t on glol limt hng n

2 264 Int. J. Environ. Si. Thnol. (2015) 12: osystm proprtis through th rls o som grnhous gss (GHG) suh s ron ioxi (CO 2 ), mthn (CH 4 ), n nitrous oxi (N 2 O) to th tmosphr (Pthk t l. 2006; M t l. 2010). Cron ioxi (CO 2 ) is onsir s on o th most importnt n unnt GHG in th tmosphr n ontriuts out 50 % to th glol wrming, n its onntrtion hs n inrsing t rt o 0.5 % nnully (Ll t l. 1995). Th onntrtion o CO 2 in th tmosphr is prit to rh high lvl ( ppm) in 2050 (Bouwmn 1990; Ohl n Vourlitis 1994). Inrss in CO 2 missions r minly rsulting rom th us o ul omustion, inustril tivitis, n intnsiv griulturl prtis (Mstgh t l. 2002). Orgni mttr (OM) hs n ssntil rol in improving physil, hmil, n iologil proprtis o soils, n it is onsir s on o th most importnt initors in vluting soil qulity n hlth (Brhim t l. 2011;Vughn t l. 2011; Ghosh t l. 2012). Th ition o orgni mnmnts in ri gro-osystms (py soils) n rsponsil or lrg umultions in soil orgni ron n nhnmnts in rop proutivity. This in turn rsults in high inrss in CO 2 missions rom ri-soil systms (Zou t l. 2004; Lou t l. 2007; Iql t l. 2009; Bhtthryy t l. 2012; Wu t l. 2013). Th inrs o soil orgni ron lvls r irtly rlt to th mount n qulity o OM to soils (Lmk t l. 2010). So, th soils n on o th si sours o CO 2 proutions. It ws rport tht soils n ontriut out % to th totl CO 2 missions (Duxury t l. 1993) n ount or pt grm (Pg) CO 2 -C yr -1, whih minly rsults rom th rspirtion o plnt roots, soil mirolor, n un, n lso rom th omposition o OM (Lou t l. 2007). Th xhng pross o CO 2 twn th tmosphr n th soil is vitl prt o th ron yl, n ontrolling this pross n t its onntrtion in th nvironmnt (Ussiri n Ll 2009). Th smll vritions o soil orgni ron pools my potntilly us ritil hngs in CO 2 onntrtions in th tmosphr (Eswrn t l. 1995; Flloon t l. 1998; Dvison t l. 2000). Th missions o CO 2 rom soils pn on mny tors, inluing th quntity n qulity o orgni mtrils, vilility o nutrints, soil moistur (roi n nroi onitions), tmprtur, ph, rtiliztion, ln us, n mngmnt prtis (Mosir 1998; Lou t l. 2003; Mjumr t l. 2006). Lil rtions o orgni ron suh s miroil iomss ron (MBC), issolv orgni C (DOC), prtiult orgni ron (POC), n sily oxiizl ron (EOC) hv n us s initors or soil qulity (Cmrll n Elliott 1992; Blir t l. 1995; Bolinr t l. 1999). It ws mntion tht MBC onsists o 1 5 % o totl orgni ron (TOC), n it n us s rptiv mrkr to vlut th nvironmntl impts suh s inrsing onntrtions o GHG in py soils (Hoqu t l. 2001). Th DOC is omplx mixtur o orgni ompouns, whih plys ky tsk in trrstril osystms n ts s mjor nrgy sour or soil iot (Thurmn 1985; Stvnson 1994). Although th onntrtion o DOC usully rprsnts out 2 % o totl orgni ron in griulturl soils, it is otn onsir s th most ynmi n vill C rtions (Mrshnr n Klitz 2003). Prtiult orgni ron (POC) ounts or 10 % o th soil C n onsists minly o smiompos orgni mtrils with rognizl strutur smllr thn 2 mm n grtr thn 50 lm in siz (sn-siz prtils) (Crtr t l. 1994; Grgorih t l. 1994). Th POC is mor snsitiv to mngmnt prtis s ompr to totl soil orgni ron n hs n importnt rol in nutrint rls n miroil tivitis u to its rily omposition y miroorgnisms (Cmrll n Elliott 1992; Gl n Cmrll 2000; Stll-Koutik t l. 2008). Th sily oxiizl ron (EOC) ounts or 5 30 % o TOC n inlus orgni omponnts, whih n spily oxiiz y potssium prmngnt (KMnO 4 ) (Blir t l. 1995). Thr hv n lot o invstigtions point out tht MBC, DOC, EOC, n POC wr snsitiv n rpi initors or hngs in soil orgni ron (Bolinr t l. 1999; Grgorih n Crtr 1997; Wnr n Birt 2000; Stll-Koutik t l. 2008). Py soils in Chin oupy 25 % o totl rl lns. Th us o irnt wtr rgims in ths soils n hv signiint impt on soil orgni ron rtions, n in turn, soil-tmosphr CO 2 missions. Although mny xprimnts hv n onut to stuy th t o wtr rgims or orgni mnmnts suh s ri strw on luxs o CO 2 (Lou t l. 2003; Dong t l. 2009; Iql t l. 2009; Bhtthryy t l. 2012), no ttntion hs n pi to xmin th omintion t o wtr rgims n ri strw on CO 2 missions n lil orgni ron rtions in py soils. Aoringly, th stuy o CO 2 luxs in rspons to lil orgni ron rtions is vry importnt in ths soils. So, th min ojtivs o this stuy r to (1) trmin th mission o CO 2 n th trnsormtion o lil soil orgni ron rtions in py soil trt with ri strw unr irnt wtr rgims, n (2) to signiy th t o lil orgni ron rtions on CO 2 missions rom Chins py soils. To prorm this stuy, th soil smpls wr inut uring Mrh Jun 2012 in limti int t Huzhong Agriulturl Univrsity, Wuhn City, Hui Provin, P.R. Chin.

3 Int. J. Environ. Si. Thnol. (2015) 12: Mtrils n mthos Sit sription Soil smpls wr ollt rom th sur lyr (0 15 m) o py soil (nthrosol, riv rom Qutrnry yllow simnt) t Wuxu City, Hui Provin, Chin ( N, E; 20 m ov s lvl). This rgion is hrtriz y humi mi-sutropil monsoon limt with n vrg nnul tmprtur o 16.8 C. Th mn nnul pripittion is 1,360 mm, whih mostly ours twn April n August. Soil n ri strw Th soil smpls wr ir-ri or 7 ys n groun to pss through 2-mm siv prior to strt o th xprimnt. Th txtur o th invstigt soil ws silty ly lom with 5.45 % sn, % ly, n % silt. Ri strw (RS) ws otin rom n xprimntl rm tr th hrvst o ri plnts. Th RS ws ovn-ri t C n thn rush to smll pis y grinr milling mhin. Th us RS ws hrtriz y 9.23 % moistur, % orgni mttr, 0.79 % N, 0.18 % P, n 0.94 % K. Exprimntl sign An inution xprimnt ws li in ompltly rnomiz lok sign with thr rplits. Air-ri soil smpls (900 g) wr put in plsti pots (17 m with 9 8 m hight), n th RS ws mix thoroughly toso1.5%(w/w)nwttyivwtrlvls (40, 55, 70, 85, n 100 % o wtr-holing pity (WHC)) using th istill wtr. Tn trtmnts wr vlop rom th omintion o wtr rgims (W) with ri strw (RS): W1(100 % WHC), W2 (85 % WHC), W3 (70 % WHC), W4 (55 % WHC), W5 (40 % WHC), W1RS (100 % WHC? 1.5 % RS), W2RS (85 % WHC? 1.5 % RS), W3RS (70 % WHC? 1.5 % RS), W4RS (55 % WHC? 1.5 % RS), n W5RS (40 % WHC? 1.5 % RS). All xprimntl pots wr ovr with in polythyln with smll hols to llow gsous xhng n minimiz th moistur loss. Th pots wr inut t onstnt tmprtur o 25 C n wight vry 2 ys to just th moistur t us lvls. Th soil smpls wr ollt our tims tr 15, 30, 60, n 90 ys, n sprt into two susmpls. Th irst susmpl ws kpt in rrigrtor t 4 C in orr to trmin issolv n miroil iomss ron, whil th son susmpl ws ir-ri n kpt in polythyln gs to msur othr orgni ron rtions (totl orgni ron, prmngnt oxiizl ron n light rtion, n prtiult orgni ron). Bsi soil n ri strw nlyss Dri soil smpls wr groun n siv through 2.00 n 0.15 mm sivs to trmin th ollowing proprtis. Soil ph ws msur in suspnsion o 1:2.5 (w/v) soil/wtr rtio tr shking or 1 h, using ph mtr. Th intrntionl piptt mtho ws us to vlut th soil prtil-siz istriution (Shlrik n Wng 1993). Totl soil orgni ron ws trmin y potssium ihromt (K 2 Cr 2 O 7 ) oxition t C ollow y titrtion with 0.5 mol l -1 rrous sult (Wlkly n Blk 1934). Th orgni mttr ontnt o ri strw ws trmin y th omustion mtho in mul urn t 600 C or 6 h (Golin 1987). Th orgni mttr ontnt ws trmin through th mss irn or n tr th omustion pross. Th totl nitrogn (N) n phosphorus (P) ontnts o soil n strw wr xmin y th FIA-str 5000 nlyzr mtho tr H 2 SO 4 / HClO 4 (2:1 rtio) igstion. Th totl potssium (K) o soil n strw wr nlyz using th lm photomtr pprtus. Soil vill N ws msur y Kjlhl mtho tr its xtrtion y KCl (2 mol l -1 ), whil th vill K ontnt ws stimt y th lm photomtr tr its xtrtion y NH 4 COO CH 3 (1 mol l -1,pH7)(Jkson 1973). Avill soil P ws xtrt y NHCO 3 (0.5 mol l -1, ph 8.5) n nlyz using th sptrophotomtr (Olsn n Sommrs 1982). Rsults o som hmil n physil proprtis o soil r prsnt in Tl 1. Cron ioxi (CO 2 ) mission Th mission o CO 2 rom th soil ws stimt ollowing th soil rspirtion mtho sri y Prkinson (1981). Brily, th xprimntl pot with 0.9 kg soil ws put in Tl 1 Chmil proprtis o th us py soil Proprtis Vlus ph 5.95 Totl orgni ron (g kg -1 ) Light rtion o orgni ron (g kg -1 ) 0.91 Prtiult orgni ron (g kg -1 ) 2.50 Esily oxiizl orgni ron (g kg -1 ) 1.14 Dissolv orgni ron (mg kg -1 ) Miroil iomss ron (mg kg -1 ) Totl N (g kg -1 ) 1.25 Totl P (g kg -1 ) 0.84 Totl K (g kg -1 ) Avill N (mg kg -1 ) Avill P (mg kg -1 ) 7.39 Avill K (mg kg -1 )

4 266 Int. J. Environ. Si. Thnol. (2015) 12: nothr plsti pot with imtr o 40 m whih ontin istill wtr. Atrwr, plsti ylinr hmr o 20 m in imtr ws put roun th xprimntl pot, n thn, th lux o CO 2 ws msur with LI 8100-A portl inrr nlyzr (LICOR In., Linoln, NE, USA). Th CO 2 luxs wr trmin 16 tims t 3, 6, 10, 13, 16, 22, 25, 28, 31, 35, 41, 50, 56, 65, 73, n 85 ys rom th xprimnt ginning (Mrh 2012). Thr rings o CO 2 missions wr ror or h xprimntl pot t h smpling tim. All th msurmnts wr rri out in th morning (09:00 11:00.m.) to gt rprsnttiv ily soil CO 2 luxs (Lou t l. 2003). Th t o CO 2 luxs wr xprss s mg CO 2 kg -1 soil h -1. Th CO 2 luxs n umultiv missions wr lult s sri y Li t l. (2012). Miroil iomss ron Miroil iomss ron (MBC) ws trmin using th hloroorm umigtion xtrtion mtho (Vn t l. 1987). In ri, 10 g rsh soil smpl ws xtrt y 40 ml o 0.5 MK 2 SO 4 (non-umigt). Anothr 10 g rsh soil smpl ws umigt with hloroorm or 24 h t 25 C n thn xtrt y 0.5 MK 2 SO 4 (umigt). Th non-umigt n umigt soil smpls wr shkn or 60 min t 200 rpm n thn iltr using Whtmn 42 ppr. Th onntrtions o C in xtrts wr msur y totl orgni ron (TOC) nlyzr (Multi N/C 2100, Jn, Grmny). Th vlus o MBC wr lult rom th irn twn th vlus o C in umigt n non-umigt smpls n ivi y 0.45 (Wu t l. 1990). Dissolv orgni ron Dissolv orgni ron (DOC) ws xtrt rom 10 g rsh soil using 40 ml istill wtr oring to th mtho o Zsolny (2003). Th soil smpls wr shkn or 30 min t sp o 250 r min -1. Th suprntnt ws ntriug or 10 min t 15,000 r min -1 n iltr y 0.45-lm llulos str iltrs. Th xtrts wr nlyz or C using TOC nlyzr (Multi N/C 2100, Jn, Grmny). Light rtion n prtiult orgni ron Light rtion orgni ron (LFOC) ws xtrt rom th soil using th mtho sri y Grgorih n Ellrt (1993). Dri soil susmpls (25 g) wr pl into ntriug tus with 50 ml NI solution n nsity o 1.70 g m -3. Th tu ws shkn or 1 h t 200 rv min -1 n ntriug t 1,000g or 15 min. Th xtrtion pross o LFOC ws rpt thr tims. Th loting mtril ws trnsrr to iltr ppr, wsh vry tim with 0.01 MCCl 2 n istill wtr, n inlly ri or 48 h t 60 C. Prtiult orgni ron (POC) ws xmin y using th mtho o Cmrll n Elliott (1992). A portion o th ri soil smpl (i.., 10 g) ws isprs in 30 ml o soium hxmtphospht (5 g l -1 ) n pl on riproting shkr (90 r min -1 ) or 18 h. Th soil suspnsion ws nt ovr 53-lm siv unr low o istill wtr to nsur sprtion. Th rmining soil on th siv ws trnsrr to glss ish, ri t C or 48 h n groun to powr y ll mill. Th onntrtions o orgni ron in LFOC n POC wr stimt y th wt oxition mtho using potssium ihromt (Wlkly n Blk 1934). Prmngnt oxiizl ron Th vlus o prmngnt oxiizl ron (PMOC) wr trmin using th mtho o Blir t l. (1995). Brily, soil smpls ontining out 15 mg C wr wigh n pl into plsti ntriug tus. Th smpls wr shkn with 25 ml o 333 mm KMnO 4 or 1 h t 12 rpm. Th lnk smpl ws run unr th sm onition without ny soil. Th suspnsions wr ntriug or 5 min t 2,000 rpm, n th iltrts ilut t 1:250 with ioniz wtr. Th onntrtions o PMOC wr msur y sptrophotomtr t wv lngth o 565 nm. Sttistil nlysis Th xprimntl t wr orgniz in triplit, n th mn vlus wr onsir or th sttistil nlysis. A on-wy ANOVA ws prorm using th sotwr o SPSS 12.0 (SPSS In., Chigo, USA) to stimt th t o ri strw n wtr rgims on CO 2 mission n lil soil ron rtion. A Prson s orrltion nlysis ws onut to vlut th rltionships twn CO 2 mission n lil soil ron rtions. Th Dunn s multipl rng tst s on lst signiint irn (LSD) vlus t lvl o p \ 0.05 ws us to nlyz th signiint vrition twn trtmnts. Rsults n isussion Et o ri strw n wtr rgims on missions o CO 2 Fluxs o CO 2 wr signiintly inlun y th ition o ri strw n wtr rgims (Fig. 1,). In gnrl, th

5 Int. J. Environ. Si. Thnol. (2015) 12: Fig. 1 Emissions o CO 2 in ontrol py soil () n in ri strw-trt soil () unr irnt wtr rgims. Th rror rs rprsnt th stnr vitions o thr rplits A CO2 Fluxs (mg kg -1 soil h -1 ) W1RS W2RS W3RS W4RS W5RS Inution tim (y) B 6.0 W1 W2 W3 W4 W5 CO2 Fluxs (mg kg -1 soil h -1 ) Inution tim (ys) rs in soil wtr rgims l to notil inrss in CO 2 rls in th prsn n sn o ri strw. Ri strw pplition us highr missions in CO 2 t ll wtr rgims n inution tim s ompr to ontrol (no strw). Th CO 2 mission rts rh thir pks tr 13 ys rom th strt o inution n thn grully rs to lowr vlus till th n o inution in oth non-mn n ri strw-mn soils. In irst 13 ys o inution, th onntrtion o CO 2 vri rom 3.26 to 4.49 mg kg -1 soil h -1 in non-mn soil n rom to mg kg -1 soil h -1 in ri strw trtmnts. Morovr, th highst vlus o CO 2 luxs wr n mg kg -1 soil h -1 t W2 (80 % WHC) n W3 (70 % WHC) whn th soil riv ri strw. Howvr, in th s o no ri strw, th highst rlss o CO 2 wr 4.49 n 4.14 mg kg -1 soil h -1 t W3 (70 % WHC) n W4 (55 % WHC). Similr rsults otin y Lou t l. (2007) who osrv tht th ition o ri strw inrs th missions o CO 2 s ompr with ontrol in n inution xprimnt wr onut on py soil ollt rom Yingtn City, Jingxi Provin, Chin. Thy lso oun tht soil CO 2 luxs rpily inrs n rh thir highst vlus within 10 ys, n thn grully rs to th lowr vlus nr to th ontrol. This oul xplin y th st CO 2 missions t th rly stg might prou u to th inrs in ron supply n othr sustrts, whih might stimult oth miroil tivitis n ommunitis tr th inorportion o ri strw. In nothr stuy, th mximum CO 2

6 268 Int. J. Environ. Si. Thnol. (2015) 12: Fig. 2 Et o ri strw on soil totl SOC t irnt wtr rgims. SOC soil orgni ron, W wtr rgim, n RS ri strw. Dirnt lttrs on rs init signiint irn twn trtmnts t p \ Th rror rs rprsnt th stnr vitions o thr rplits proution ourr immitly tr 1 y o th strt o inution with wht strw t os o 2 % (w/w) in sny lom soil (r hromosol) o nturl ushln in Monrto, South Austrli (Duong t l. 2009). Ths uthors illustrt this phnomnon with th high rspirtion rts t th prliminry tim u to th rkown o sily vill orgni ompouns whn wht strw rsius wr ppli on. Furthrmor, thy mntion tht th rspirtion rts oul hv iminish tr th xhustion o sy minrlizl sustrts. On th othr hn, thy rport tht th inrs in inution prios us low CO 2 rls us o th hr omposition pross in th prsn o rlitrnt ompouns suh s lignin llulos n othr mromoluls. Th highr inrs in orgni ron inputs u to th inorportion o ri strw (Fig. 2) might us to luit th lrgr CO 2 luxs in ri strw-mn soil thn in th ontrol (no strw). It ws ror tht th high vilility o C n N sustrts, n miroil tivitis oul ountl or th lrg inrs in CO 2 missions tr ri strw ition (Iql t l. 2009; Vughn t l. 2011; Bhtthryy t l. 2012). Th grtr missions o CO 2 rom W3 n W4 trtmnts thn rom othr trtmnts oul rsult rom thir lrgr DOC n MBC ontnts (Figs. 3 n 4), whih oul simult th omposition o ri strw n th rls o CO 2. Th rol o soil moistur in CO 2 luxs rom soils might hv rsult rom its t on miroil tivity (Smith t l. 2003). It ws ror y Xu n Qi (2001) n Ry t l. (2002) tht missions o CO2 om mor notil whn th soil moistur ws lowr thn 60 % o wtr-ill por sp (WFPS). Dong t l. (2009) oun tht th inrs in soil wtr ontnts l to mrk rutions in th rls o CO 2 rom slit lom soil t Lunhng County, Hi Provin, Chin. Morovr, Iql t l. (2009) noti tht highst missions o CO 2 wr ror t 60 % o WHC t 25 C n30 C, whrs lowst missions wr ror t 20 n 100 % o WHC in n inution xprimnt on py soil otin rom Xinning County, Hui Provin, Southrn Chin. Ding t l. (2010) show tht CO 2 luxs wr xtrmly low whn th soil moistur ws t 85 % o WFPS, whrs th mission signiintly linrly inrs or rhing th soil moistur t 70 % o WFPS. In th prsnt stuy, th most wt (100 % o WHC) n ry (40 % o WHC) onitions h inhiition ts on CO 2 proution whn py soil i not riv ri strw. Howvr, in th prsn o ri strw, th highst wt (80 n 100 % o WHC) onitions only show lrgst rutions in missions o CO 2. This onorm tht th inorportion o ri strw h low t on CO 2 luxs rom py soils t wt onitions s ompr with ry onitions. Orgni ron pools trnsormtion Ri strw itions signiintly nhn th totl soil orgni ron (SOC) ontnts o th stui py soil unr ll wtr rgims (Fig. 2). Th totl SOC ontnts inrs y 1.98 n 2.15 tims tr 90 ys in W1 (100 % WHC) n W5 (40 % WHC), rsptivly. It ws ppr tht th pplition o ri strw t rt o 4.5 Mg h -1 l to signiint nhnmnt in SOC ontnts y 3.64 g kg -1 in py soil otin rom Jinji Township, Jingsu Provin, Chin (Pn t l. 2009). Soil wtr rgims h signiint ts on SOC n th

7 Int. J. Environ. Si. Thnol. (2015) 12: Fig. 3 Et o ri strw on soil DOC t irnt wtr rgims. DOC issolv orgni ron, W wtr rgim, n RS ri strw. Dirnt lttrs on rs init signiint irn twn trtmnts t p \ Th rror rs rprsnt th stnr vitions o thr rplits DOC (mg kg -1 ) W1 W2 W3 W4 W5 W1RS W2RS W3RS W4RS W5RS g g h i g h 0 15 ys 30 ys 60 ys 90 ys Inution tim Fig. 4 Et o ri strw on soil MBC t irnt wtr rgims. MBC miroil iomss ron, W wtr rgim, n RS ri strw. Dirnt lttrs on rs init signiint irn twn trtmnts t p \ Th rror rs rprsnt th stnr vitions o thr rplits MBC (mg kg -1 ) i g i W1 W2 W3 W4 W5 W1RS W2RS W3RS W4RS W5RS g i h j g h gh h g g g 0 15 ys 30 ys 60 ys 90 ys Inution tim rs o wtr lvls mrkly iminish th SOC in th invstigt soil. At ll inution tims (15, 30, 60, n 90 ys), th highst SOC vlus wr ror in W1 (100 % WHC), whrs th lowst wr osrv in W5 (40 % WHC). Th hng o soil wtr rgim is on o th most importnt tors in ontrolling th pross o SOC minrliztion n trnsormtion (Ho t l. 2011). Morovr, thy mntion tht th ily minrliztion o SOC ontnts unr th roi onition (60 % WHC) ws gnrlly highr thn unr th sumrg onition (soil/ wtr rtio o 1:1 w/w) uring th whol inution prio in py whit soil ollt rom Chngshu City, Jingsu Provin, Chin. Dt in Figs. 3 n 4 show tht th us o ri strw onsirly inrs th issolv orgni ron (DOC) n miroil iomss ron (MBC). In th prsn o ri strw, th highst DOC n MBC onntrtions (2,234.6 n mg kg -1, rsptivly) wr ror tr 60 ys t W4, whrs th lowst vlus ( n mg kg -1, rsptivly) wr noti tr 15 ys t W1 (100 % WHC). In th sn o ri strw, th s o soil wtr rgims gnrlly improv th vlus o DOC n MBC t 15, 30, n 60 ys only. Howvr, tr 90 ys, th mounts o DOC n MBC shrply lin with th rs in wtr rgims. Th rs in vill sustrts suh s solul ron n nitrogn might hv

8 270 Int. J. Environ. Si. Thnol. (2015) 12: Fig. 5 Et o ri strw on soil LFOC t irnt wtr rgims. LFOC light rtion o orgni ron, W wtr rgim, n RS ri strw. Dirnt lttrs on rs init signiint irn twn trtmnts t p \ Th rror rs rprsnt th stnr vitions o thr rplits LFOC (g kg -1 ) W1 W2 W3 W4 W5 W1RS W2RS W3RS W4RS W5RS ys 30 ys 60 ys 90 ys Inution tim Fig. 6 Et o ri strw on soil POC t irnt wtr rgims. POC prtiult orgni ron, W wtr rgim, n RS ri strw. Dirnt lttrs on rs init signiint irn twn trtmnts t p \ Th rror rs rprsnt th stnr vitions o thr rplits POC (g kg -1 ) W1 W2 W3 W4 W5 W1RS W2RS W3RS W4RS W5RS g g 0 15 ys 30 ys 60 ys 90 ys Inution tim n us s logil rson to xplin th lin o DOC n MBC with inrsing inution tim. Our rsults r omptil with th inings o Lou t l. (2007) who show tht th oth DOC n MBC rs signiintly with th inrs o inution tims rom zro to 60 ys in py soil trt with ri strw (0.1 %) t 60 % WHC. Thy lso oun tht th inorportion o ri strw l to highr DOC n MBC ontnts thn in th sn o ri strw. Th ition o ri strw to th py soil unr irnt wtr rgims rsult in highr onntrtions o light rtion orgni ron (LFOC) n prtiult orgni ron (POC) s ompr with ontrol (no strw) t ll inution prios (Figs. 5 n 6). Furthrmor, whn th soil ws mn with ri strw, LFOC n POC ontnts mrkly inrs with th rs o soil wtr rgim. Th highst vlus o LFOC n POC wr noti t W4 (55 % WHC), whil ing lowst t W1 (100 % WHC). In s o no strw ition, th lin o soil wtr ontnt us nonsigniint rss in LFOC n POC vlus t th irst our wtr rgims (W1, W2, W3, n W4). Howvr, th rs o LFOC n POC ontnts m mor ovious t W5. Unr ll wtr rgims n inution prios, th prmngnt oxiizl ron (PMOC) rtion onsirly

9 Int. J. Environ. Si. Thnol. (2015) 12: Fig. 7 Et o ri strw on soil PMOC t irnt wtr rgims. PMOC prmngnt oxiizl ron, W wtr rgim, n RS ri strw. Dirnt lttrs on rs init signiint irn twn trtmnts t p \ Th rror rs rprsnt th stnr vitions o thr rplits inrs in ri strw trtmnts s ompr to ontrol (Fig. 7). Morovr, th rs in soil wtr rgims l to mrk inrss in PMOC, th ontrol n ri strw trtmnts. Th highst vlus o PMOC (2.87 n 5.58 g kg -1 ) wr oun t W4 (55 % WHC) tr 90 ys, whrs th lowst mounts (1.39 n 3.31 g kg -1 ) wr noti t W1 (100 % WHC) tr 15 ys rom th strt o th xprimnt in th sn n prsn o ri strw, rsptivly. Our rsults wr onsistnt with prvious stuis, whih ror tht th input o orgni mtrils into soils oul inrs LFOC n POC rtions. For xmpl, Yn t l. (2007) show tht oth POC n LFOC wr inrs rom 4.88 n 1.44 to 5.28 n 1.96 g kg -1 tr th pplition o ri strw in prml py soil t Suzhou City, Jingsu Provin, Chin. In nothr stuy, Yng t l. (2012) show tht LFOC, POC, n PMOC wr improv y 2.25, 1.84, n 2.15 tims tr th ition o wht strw or miz stlk in silt ly lom soil ws lot in Yngling istrit, Shnxi Provin, Chin. Thy lso mntion tht PMOC ws highr in wht strw or miz stlk-mn soil thn th ontrol oul xplin y th highr lil orgni ron inputs, whih ssoit with th strw n stlk. Th highr onntrtions o LFOC n POC in W4 (55 % WHC) s ompr with othr wtr rgims wr possily rsult rom th grtr miroil proprtis suh s DOC n MBC (Figs. 3 n 4), whih oul simult th omposition o soil orgni mttr n thn umult n istriut th orgni ron in LFOC n POC rtions unr this wtr lvl. Morovr, th omposition pross o soil orgni mttr h ky rol in nhning soil PMOC vlus. It ws oun y Yng t l. (2005) tht soil PMOC, LFOC, n POC unr wtr rgim o ontinuous wtrlogging rs y 30.6, 8.3, n 10.6 % in wht strw trtmnt, rsptivly, s ompr to th wtr rgim o ltrntiv wtting n rying. This onirm tht th option o soil wtr rgims is n importnt tor to improv th trnsormtion o soil orgni ron pools tr th ition o ri strw. Et o lil orgni ron rtions on th mission o CO 2 Intrstingly, soil CO 2 luxs positivly orrlt with ll soil orgni ron rtions (SOC, MBC, DOC, LFOC, POC, n PMOC) in this stuy (Tl 2). Ths orrltions suggst tht lil orgni ron rtion (LFOC, MBC, DOC, LFOC, POC, n PMOC) h mor signiint ts on CO 2 luxs s ompr with th totl SOC in th py soil. Morovr, th highst orrltions (r = 0.97 n 0.98 t p \ 0.01) wr oun twn CO 2 missions n LFOC n POMC. Gnrlly, our rsults wr in grmnt with Lou t l. (2007) who oun tht soil CO 2 luxs positivly orrlt with DOC n MBC (r = n t p \ 0.05 n 0.01, rsptivly) tr 55 ys rom th xprimnt ginning. In nothr stuy, Iql t l. (2010) oun positiv rltionships twn CO 2 luxs n DOC n MBC (r = n t p \ 0.05) in il xprimnt whih ws onut on upln soil trnsrr rom py t th xprimntl sttion o Zigui County, Thr Gorgs Rsrvoir Ar, southrn Chin. Bhtthryy t l. (2012) lso oun signiint orrltions twn SOC, MBC, rily minrlizl ron (RMC), n CO 2 missions (r = 0.93, 0.92, n 0.96 t p \ 0.01, rsptivly) tr th pplition o ri strw n grn mnur in py sny ly lom soil in Cuttk City t th strn prt o Ini.

10 272 Int. J. Environ. Si. Thnol. (2015) 12: Tl 2 Prson s orrltion oiints (r) twn mns o CO 2 luxs n orgni ron rtions (n = 10) CO 2 SOC LFOC POC EOC DOC MBC CO TOC 0.87** 1.00 LFOC 0.97** 0.91** 1.00 POC 0.95** 0.96** 0.99** 1.00 EOC 0.98** 0.87* 0.97** 0.95** 1.00 DOC 0.93* 0.74** 0.94** 0.88** 0.94** 1.00 MBC 0.94** 0.78** 0.95** 0.91** 0.97** 0.99** 1.00 SOC soil orgni ron, LFOC light rtion o orgni ron, POC prtiult orgni ron, PMOC prmngnt oxiizl ron, DOC issolv orgni ron, n MBC miroil iomss ron ** p \ 0.01, rsptivly In this stuy, LFOC ompr to othr ron rtions ppr to th most snsitiv initor o CO 2 missions rom th py soil (r = 0.97 t p \ 0.01). Th LFOC h highr t on CO 2 luxs s ompr with POC us LFOC mostly onsists o orgni mtrils in rsh s or in n rly stg o th omposition pross or short prio (Mullr t l. 1998), n lso, it is mor lil thn POC (Grgorih n Jnzn 1996). Ovrll, it is worthwhil to mntion rom our inings tht th high iint ts o ri strw on LFOC, POC, n PMOC (Figs. 5, 6, 7) oul us s n vn illustrtion or th high missions o CO 2 rom th py soil. Rltionships twn soil orgni ron rtions Th orrltions twn ll soil orgni ron rtions wr signiintly positiv (Tl 2). Th totl SOC h highr links with LFOC (r = 0.91) n POC (r = 0.96) thn with PMOC (r = 0.87, DOC (r = 0.74) n MBC (r = 0.78) t p \ Th orrltions o DOC n MBC with LFOC (r = 0.94 n 0.95) n PMOC (r = 0.94 n 0.97) t p \ 0.01 wr highr thn thos with POC (r = 0.88 n 0.91) t p \ Th lrgst orrltions wr oun twn LFOC n POC (r = 0.99), n DOC n MBC (r = 0.99) t p \ Similr rsults h n ror y Yn t l. (2007), Dou t l. (2008), Chn t l. (2009), Lou t l. (2011), Li t l. (2012), Wng t l. (2012), n Yng t l. (2012) who osrv positiv orrltions twn LFOC, POC, PMOC, MBC, DOC, n SOC. It ws suggst y Yng t l. (2012) tht th signiint rltionships twn SOC n LFOC, POC, MBC, n PMOC onirm th mjor rol o SOC in th quntity n qulity o lil orgni ron rtions. Th high orrltions twn DOC n MBC n othr lil orgni ron rtions (LFOC, POC, n PMOC) might us to show how LFOC, POC, n PMOC wr signiintly t y th soil miroil proprtis. Morovr, th st orrltions o SOC with LFOC n POC init thir ynmi rsponsiility in th ltrtion rts o SOC in th invstigt py soil. Conlusion Th hngs o soil wtr rgims h n importnt t on th mission o CO 2 with n without inorportion o ri strw into th py soil. Th ition o ri strw rsult in highr CO 2 luxs rom th py soil s ompr to ontrol (no strw), spilly in W3 (70 % WHC) n W4 (55 % WHC). Th t o wtr rgims on CO 2 luxs rom th py soil ws mor notil in th prsn o ri strw thn in th sn o ri strw. All vlut lil orgni ron rtions, issolv orgni ron (DOC), miroil iomss ron (MBC), light rtion orgni ron (LFOC), prtiult orgni ron (POC), n prmngnt oxiizl ron (PMOC) wr signiintly inrs tr th inorportion o ri strw in th py soil. Gnrlly, th hngs o soil wtr rgims h no mrk t on DOC, MBC, LFOC, POC, n POMC in th sn o ri strw. Th rsults init tht th mission o CO 2 rom th stui py soil ws highly t y DOC, MBC, LFOC, POC, n PMOC. Th highr positiv orrltions twn totl SOC n LFOC n POC s ompr with othr lil orgni ron rtions rlt thir lrgr rols in soil orgni mttr ltrtions in th py soil. Furthr, short- n long-trm stuis r n to improv our knowlg out th rltionships twn missions o CO 2 or othr grnhous gss suh s CH 4 n N 2 O rom py soils n lil orgni ron rtions unr il onitions s t y irnt orgni wsts. Aknowlgmnts This stuy ws innilly support y th Ntionl Nturl Sin Fountion o Chin ( ), th Ntionl Thnology Projt or High Foo Yil o Chin (2011BAD16B02). Th irst uthor is vry thnkul to th mmrs o Soil Sin Dprtmnt, Fulty o Agriultur (

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