Effects of Flooded Rice Cultivation on Soil Organic Carbon and Active Organic Carbon Content: A Microcosm Experiment

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1 Journl of Agriulturl Siene; Vol. 7, No. 7; 2015 ISSN E-ISSN Pulished y Cndin Center of Siene nd Edution Effets of Flooded Rie Cultivtion on Soil Orgni Cron nd Ative Orgni Cron Content: A Miroosm Experiment Bingjie Shen 1,2, Zhenke Zhu 2, Hongzho Yun 2, Jiurong Wng 2, Tid Ge 2, Mingli Chen 1, Xiofu Wu 1 & Jinshui Wu 2 1 College of Environmentl Siene nd Tehnology, Centrl South University of Forestry nd Tehnology, Chngsh, Chin 2 Key Lortory of Agro-eologil Proesses in Sutropil Region, Institute of Sutropil Agriulture, Chinese Ademy of Sienes, Chngsh, Chin Correspondene: Mingli Chen, College of Environmentl Siene nd Tehnology, Centrl South University of Forestry nd Tehnology, Chngsh , Chin. Tel: E-mil: hml18@163.om Reeived: April 21, 2015 Aepted: My 28, 2015 Online Pulished: June 15, 2015 doi: /js.v7n7p196 URL: Astrt Informtion on ron (C) dynmis nd llotion in plnt soil system is essentil to understnd the terrestril C yle. Our ims were to determine the effets of rie growth on soil orgni ron (SOC), dissolved orgni ron (DOC) nd miroil iomss ron (MBC) ontent. For this pot miroosm experiment in growth hmer ws onduted with soils plnted or unplnted with rie. The experiment lsted for 80 dys. The SOC ontent inresed oth in unplnted nd rie-plnted soils over the inution period. The inresing mount of SOC in rie-plnted soil ws lrger thn tht of in unplnted soil, inditing tht growing rie on ulk soil enhned the funtion of soil s ron poo1. The DOC enhned signifintly (P < 0.05) ompred to the zero time (Dy 0 (CK)) oth in plnted soils nd unplnted soils during 80 dys of inution. The DOC onentrtions in plnted soils were muh lrger thn tht of unplnted soils, suggesting the relese of solule root exudtes from rie roots. However, MBC delined oth in unplnted soil nd rie-plnted soil fter inution for 80 dys, ompred with the strt of experiment. The results suggest tht MBC dynmis in rie soil re lrgely ontrolled y orgni sustnes relesed from rie roots. Keywords: rie growth, soil orgni ron, dissolved orgni ron, miroil iomss ron, ron pool 1. Introdution Orgni ron (C) sequestrtion of ropping soils provides potentil sink for tmospheri CO 2, with n nnul rte of Gt C glolly (Ll, 2004). Understnding the intertions etween plnt roots, miroorgnisms nd soil orgni C pools provides key to the proesses ontrolling C fluxes etween plnt roots, miroil iomss, soil nd tmosphere (Yevdokimov et l., 2006; Kumr et l., 2014). Almost 10% of the tmosphere s CO 2 psses through soils eh yer (Rih & Tufekioglu, 2000), whih hs een driven y photosynthesis nd respirtions. Pddy soils glolly over totl re of out km 2, whih ounts for out 22% of the glol ropping re (Knner et l., 2010). Also, it is ommonly epted tht pddy soils were possily n importnt C sink (Ll, 2002). However, the pity of plnt-photosynthesized C, espeilly through root elution, entering into soil hs, so fr, not een quntified. Therefore, understnding the C yle of the mjor pddies of the world is neessry for developing urte nd preditive glol C yle models. The trnsporttion of plnt-photosynthesized C into the soil ours rpidly nd influenes soil tive orgni C pools in the soil (Kštovská & Šntrůčková, 2007; Rjesh et l., 2003). Root-derived mterils re n importnt DOC soure in soil (Lu et l., 2005). Aout 30 to 60% of the net photosynthesized C is lloted elow ground prts, nd s muh s 40 to 90% of this frtion enters the soil in the forms of root exudtes, muilge, sloughed-off ells nd deying roots (Lynh & Whipps, 1990). Kuzykov et l. (2006) hve demonstrted tht the mjority of root-derived C of plnt-photosynthesized C is represented y root exudtes, whih re dominted y low-moleulr-weight ompounds suh s rohydrtes (e.g., gluose, surose), mino ids (e.g., glutmte, glyine), nd orgni ids (e.g., itrte, ltte). These ompounds re n importnt DOC soure nd they re most ville for soil miroorgnisms (Lu et l., 2002; Chintl et l., 2014). The rhizodeposition ours ontinuously in the form of root exudtes, muilge, sloughed-off ells nd litter within the growing seson of 196

2 plnts. Witt et l. (2000) reported tht MBC deresed with plnt growth nd there ws no differene etween plnted nd unplnted soils in flooded onditions. On the other hnd, Reihrdt et l. (1997) oserved deline of totl miroil iomss ut n inrese in neroi popultions towrd the mturtion stge of rie. However, the influene of plnt growth on miroil dynmis, however, is omplex nd poorly understood in rie soils. Therefore, informtion of root-derived DOC nd MBC is essentil to understnd the proesses, suh s miroil tivity nd soil respirtions, whih is importnt for further insight into C yling in the plnt-soil system. We hypothesized tht the dynmis of SOC, DOC nd MBC in flooded rie soil were signifintly influened y plnt growth. The ojetive of this study therefore ws to evlute the soil SOC nd tive orgni C pools (DOC nd MBC) during rie growth in hmer. 2. Method 2.1 Soil Preprtion Three middle of sutropil red pddy soils (P1, P2, P3) developed from quternry red-erth prent mteril in Chin under doule-ropping rie ultivtion systems in Chngsh City, Hunn Provine, Chin were used in this study. All soil smples were olleted from the plough lyer (0-20 m) using 5.5 m dimeter stinless steel orer fter rie hrvest. Bulk soil ws immeditely pled in gs-permele plsti ox fter removing orse plnt residues. The properties of the soil ( quternry red-erth developing towrds typil Ultisol t ll sites) re shown in Tle 1. Soil ph ws determined in 1:2.5 (w/v) soil to H 2 O rtio extrts using ph meter. Soil texture (ly ontent) ws determined using the pipette method (Müller & Höper, 2004). Contents of SOC nd totl N were mesured y dry omustion in C/N (Vrio MAX C/N, Elementr, Germny) uto-nlyzers (Chintl et l., 2013). Ction exhnge pity (CEC) were mesured y the proedure of Brue nd Ryment (Brue & Ryment, 1982). Tle 1. Seleted properties of the surfe (0-20 m) from three ontrsting pddy soils used in this study Soil ultivtion systems Site/Position SOC (g kg -1 ) TN (g kg -1 ) ph C:N Cly ontent (%) CEC ( mol kg -1 ) P1 doule-ropping rie E ; N ± ± ± ± ± ±0.04 P2 doule-ropping rie E ; N ± ± ± ± ± ±0.04 P3 doule-ropping rie E ; N ± ± ± ± ± ±0.00 Note. All vlues represent mens ± SD (n = 3). All vlues re expressed on soil dry weight sis nd represent the men of three determintions. In the sme olumn, different letters re signifintly different y Dunn test (P < 0.05), the sme s elow. SOC, TN, CEC indites soil orgni ron, totl nitrogen nd tion exhnge pity, respetively. 2.2 Tretments The experiment hd two prinipl tretments, nmely: (1) unplnted pddy soil with 12 h photoperiod; nd (2) rie-plnted pddy soil with 12 h photoperiod. The experiment ws rried out with four replitions nd rrnged in ompletely rndomized design, resulting 24 miroosms. 2.3 Rie Growth Briefly, the soils were given n initil sl fertilizer pplition, onsisting of NH 4 SO 4, lium super-phosphte nd KCl t the rtes of 40 mg N, 20 mg P nd 80 mg K kg -1 soil for eh tretment. One kilogrm of the fertilized soil smple ws filled into PVC tues (10 m inner dimeter nd 20 m height). Three 25-dy-old rie seedlings (Oryz stiv L. v. Zhongyou 169 from Hunn Seedling Compny, verge dry weight of the rie seedling ws 0.16 g plnt -1 ) were trnsplnted to eh pot on 19 June 2009, just one dy fter the sumergene of soil. Soil pots were irrigted with deionized wter, with 2-3 m wter lyer mintined on the soil surfe throughout the growing period. 2.4 Smpling nd Anlyze After 80-d growth, whih inluded the vigorous growth period of the rie, inluding the entire tillering stge, the 197

3 miroosms were destrutively hrvested; the shoots were ut off t the stem se with sissors, llowing for seprtion of the roots, shoots, nd soil omponents. All roots, shoots, nd smll soil su-smple (out 20 g) were dried to onstnt weight in n oven t 70 C to nlyze for totl C. MBC ws determined y the differene etween K 2 SO 4 -extrtle C in CHCl 3 -fumigted nd non-fumigted soil using k ftor 0.45 (Wu et l., 1990). DOC ws diretly tken the vlues determined in the un-fumigted soil. Dt were nlyzed with SPSS 10.5 (SPSS In., Chigo, IL, USA) using the Post Ho method. 3. Results 3.1 Rie Growth At hrvest time (fter growth for 80 dys), the mount of rie totl plnt iomss nd shoot iomss C grown in P1 ws 6.41 nd 5.78 g pot -1, respetively, whih ws 0.91, 0.90 nd 0.58, 0.58 times lrger thn those of P2, P3, respetively (Tle 2). In omprison to P3, rie root iomss C showed signifint inrese (P < 0.05) when grown in P1 nd P2. However, there ws no signifint differene (P > 0.05) in totl iomss, shoot nd root iomss C etween whih grown in P1 nd P2. There ws no signifint differene (P > 0.05) in the shoot/root rtio growing in three tested pddy soils, illustrting little hnge in photosynthte prtitioning etween the oveground nd the elowground prts of plnts during the growing periods (Tle 2). Tle 2. Amounts of rie iomss C nd the rtio of root to shoot otined from three ontrsting pddy soils fter 80-d pot growth in limte-ontrolled growth hmer soil Totl iomss C (g plot -1 ) Shoot iomss C (g plot -1 ) Root iomss C (g plot -1 ) root/shoot P ± ± ± P ± ± ± P ± ± ± Note. Vlues represent men ± SD (n = 4). Different lowerse letters in eh olumn indite signifint differene mong tretments t the 0.05 level. 3.2 SOC Chnge etween Dy 0 nd Hrvest At the 80 dys of inution, the SOC mount in unplnted nd rie-plnted soils inresed over the period etween Dy 0 nd hrvest (Tle 3). ANOVA reveled tht rie growth hd no signifint impt (P > 0.05) on the ontent of SOC lthough generlly followed the series: rie plnted soil > Unplnted soil. However, signifint differene in SOC mount (P < 0.05) ws oserved mong three tested soils, nd generlly followed the series: P1 > P2 > P3 (Tle 3). This might e expeted euse of the different pity of rie produtivity nd ssimiltion in different pddy soils. Tle 3. The hnge of soil orgni ron (SOC) etween Dy 0 nd hrvest (in rie plnted nd unplnted soil) from three ontrsting pddy soils SOC (g kg -1 ) P1 P2 P3 Dy 0 (CK) 22.65± ± ±0.22 Unplnted soil 22.78± ± ±0.36 Rie-plnted soil 23.20± ± ± DOC Chnge etween Dy 0 nd Hrvest The dynmis of DOC differed signifintly etween plnted soils nd unplnted soils fter 80 dys of inution (Figure 1). In plnted soils, DOC onentrtions rnged from 63.8 to 69.8 mg kg -1 t hrvest in the studied soils, whih ws times lrger thn those of the strt of experiment (Dy 0). In unplnted soils, DOC onentrtions rnged from 40.1 to 56.6 mg kg -1 t hrvest, whih ws times higher thn those of Dy 0 (Figure 1). The men DOC onentrtions were 1.5 times higher in rie-plnted soils thn in unplnted soils. DOC ontent in P1 showed signifint higher (P < 0.05) thn oth in P2 nd P3, however, there ws no signifint differene etween in P2 nd P3. 198

4 DOC ontent (mg kg -1 ) Dy 0 (CK) Unplnted soil Rie-plnted soil 0 P1 P2 P3 Pddy soil Figure 1. The hnge of dissolved orgni ron (DOC) etween Dy 0 nd hrvest (in rie plnted nd unplnted soil) from three ontrsting pddy soils. Vlues represent men ± SD (n = 4). Different letters indite signifint differenes t the P < 0.05 level 3.4 MBC Chnge etween Dy 0 nd Hrvest The men of MBC deresed from 794±135 mg kg -1 soil t the strt of experiment (Dy 0 (CK)) to 555±51.3 in unplnted soil nd 434±16.1 mg kg -1 soil in rie-plnted soil, respetively, fter inution for 80 dys (Figure 2). In plnted soils, MBC onentrtions rnged from to mg kg -1 throughout the period in three seleted soils, whih ws times lower thn those of the strt of experiment (Dy 0). In unplnted soils, similrly, MBC onentrtions rnged from to mg kg -1 throughout the experimentl period, whih ws times smller thn those of Dy 0 (Figure 2). The men MBC onentrtions were 1.3 times lower in rie-plnted soils thn in unplnted soils. MBC ontent in P2 showed signifint higher (P < 0.05) thn oth in P1 nd P3, however, there ws no signifint differene etween in P1 nd P3 inuted in plnted nd unplnted soils (Figure 2). During 80-d of inution, MBC ws positively orrelted to DOC onentrtion (n = 6, r 2 = 0.88, P < 0.01). MBC ontent (mg kg -1 ) Dy 0 (CK) Unplnted soil Rie-plnted soil 0 P1 P2 P3 Pddy soil Figure 2. The hnge of miroil iomss ron (MBC) etween Dy 0 nd hrvest (in rie plnted nd unplnted soil) from three ontrsting pddy soils. Vlues represent men ± SD (n = 4). Different letters indite signifint differenes t the P < 0.05 level 4. Disussion The mount of SOC during inution vried from g kg -1 in unplnted soil nd g kg -1 in rie plnted soil, net inrese of % in unplnted soil nd % in rie-plnted soil (Tle 3). 199

5 This enhnement of SOC ws euse of the input of rie roots, root exudtes nd the involvement of the proess of the miroil ssimiltion of CO 2 y wide rnge of utotrophi nd phototrophi miroorgnisms. Through the use of isotopi tehniques, i.e. ontinuous, pulse-hse 13 C or 14 C leling nd 13 C nturl undne, reserhers hve mde onsiderle progress in determining the input nd prtitioning of plnt-photosynthesized C into plnt prts, elow-ground C trnslotion nd CO 2 emissions from soil (Kuzykov & Shnekenerger, 2004). Aout 40% of plnt-photosynthesized C input into the soil during the growing seson is dependent on the plnt speies nd environmentl onditions (Lynh & Whipps, 1990). Hütsh et l. (2002) showed tht the photosynthesized C input into the soil vried mong plnt speies nd tht the mximum proportion ws up to 20%, 64-86% of whih ws rpidly respired y soil miroorgnisms nd only 2-5% of whih ws inorported into SOC. Unfortuntely, in our study, the ontriution of rie-photosynthesized C nd miroil ssimiltion of tmospheri CO 2 to SOC ws unle to e quntified, euse it ws not lelled with 13 C or 14 C. Hene, quntifying the ontriution of rie-photosynthesized C nd soil ssimiltion C y miroorgnisms to SOC should lso tke into ount y isotope-lelling tehnique in the future studies. It should e noted, in this work, use of plnt pots nd n enlosed growth hmer my oth hve deresed plnt growth. Therefore, field-rie ould e expeted to input more C into the soil. The hypoxi nd noxi onditions in rie-pddy systems will solutely effet the SOC nd tive ron pool. The new SOC derived from roots in pddy soil is more stle euse root-derived orgni mtter my form omplexes with the tive iron oxide in the soil. It would then eome more stle nd prtiipte in the formtion of soil ggregtes ( mm) tht protet the newly root-derived SOC from deomposition. Root-derived C dependene on photosynthesized C trnsformtion ontriutes onsiderly to the soil C omponents, espeilly MBC nd DOC, whih re losely relted to CO 2 nd CH 4 emissions (Ling et l., 2002). In the present study, DOC in the rie-plnted soil showed signifint inrese (Figure 1), in omprison to tht of the strt of experiment (Dy 0). Orgni mnure ws not pplied to soil in this experiment. This finding suggests tht root-derived DOC is ontrolled y the relese of orgni mterils originting from the roots. The inrese in DOC with plnt growth illustrted the inrese in C sustrtes, whih were redily ville for miroorgnisms. Previous work hs lso shown tht in rie ultivted pddy soil, the mount of DOC ws higher thn tht in unplnted soil, inresing grdully with rie growth, nd generlly orrelting with the root iomss inresing grdully with rie growth, nd generlly orrelting with the root iomss (Lu et l., 2002). This onfirms our suggestion presented ove. In ddition, the inresing in DOC from unplnted soil indite tht phototrophi-derived DOC is ontrolled y the relese of orgni mterils originting from the tmospheri CO2 ssimiltion y miroorgnisms. Previous work hs shown tht in rie-plnted soil, the mount of DOC ws higher thn tht in unplnted soil, inresing grdully with rie growth, nd generlly orrelting with the root iomss (Lu et l., 2002). The derese in MBC in rie-plnted nd unplnted soil during the 80-d inution period, ompred with the strt of the experiment, ws likely due to the hnge in the miroil ommunity struture in the spn of our experiment. This finding suggests tht rie-photosynthesized C input into the soil hs n effet on the dynmis of MBC, s supported y previous study (Witt et l., 2000). Lu et l. (2002) oserved sustntil derese in MBC during the erly periods nd slight inrese during the lte periods of rie growth. The level of derese in rie-plnted soil ws higher thn tht of unplnted soil, suggested tht plnt ompetition for nutrition resoures depressed miroil growth during the rie growth. Severl studies hve shown tht most of the reently photosynthesized C diretly lloted to the soil y the plnt roots is more rpidly lost through soil respirtion thn through miroil respirtion (Leke et l., 2006). The unplnted soil hs lso n effet the dynmis of MBC during the inution reveled some neroi miroes with photosynthesis funtion, So fr, it is unler wht the hrteristi nd eologil funtions of these soil miroes re ted s in pddy soil. 4. Conlusions The SOC ontent ws inresed oth in unplnted nd rie-plnted soil over the inution seson inditing tht growing rie nd ulk soil enhned the funtion of soil s ron poo1. DOC onentrtions in plnted soils were muh lrger thn tht of unplnted soils, refleting the relese of solule root exudtes from rie roots. MBC delined oth in unplnted soil nd rie-plnted soil fter inution for 80 dys, ompred with the strt of experiment. However, the informtion on input, distriution nd fte of photosynthesized ron (C) in rie-soil system, suh s the ontriution of rie growth on the soil C pools y using C isotope leling tehnique, the influene of photosynthesized C input on the deomposition of ntive soil orgni ron (SOC), is essentil for 200

6 understnding their nutrient nd C yle nd require further study. We elieve tht suh work is importnt for n understnding of the role of the elow-ground iomss in the storge nd dynmis of SOC in flooded rie-soil systems. Aknowledgements This work ws supported y the Ntionl Nturl Siene Foundtion of Chin ( ) nd The open fund projet of Key Lortory of the Edution Deprtment of Hunn provine (12K071). We thnk Editge for editoril ssistne. Referenes Brue, R. C., & Ryment, G. E. (1982). Anlytil Methods nd Interprettions Used y the Agriulturl Chemistry Brnh for Soil nd Lnd Use Surveys. Queenslnd Deprtment of Primry Industries Bulletin. QB Chintl, R., Cly, D. E., Shumher, T. E., Mlo, D. D., & Julson, J. L. (2013). Optimiztion of oxygen prmeters for nlyzing ron nd nitrogen in iohr mterils. An Let, 46(3), Chintl, R., Shumher, T. E., Kumr, S., Mlo, D. D., Rie, J., Blekley, B.,... Gu, Z. R. (2014). Moleulr hrteriztion of iohr mterils nd their influene on miroiologil properties of soil. J Hz Mte, 279, Hütsh, B. W., Augustin, J., & Merh, W. (2002). Plnt rhizodeposition-n importnt soure for ron turnover in soils. J Plnt Nutr Soil Si, 165, Kštovská, E., & Šntrůčková, H. (2007). Fte nd dynmis of reently fixed C in psture plnt-soil system under field onditions. Plnt Soil, 300, Knner, I. K., Amelung, W., Co, Z., Fiedler, S., Frenzel, P., Jhn, R.,... Shloter, M. (2010). Biogeohemistry of pddy soils. Geoderm, 157, Kumr, S., Nkjim, T., Monimp, E. G., Gutm, S., Somireddy, U. R., Kdono, R. A.,... Fusey, N. (2014). Long-term tillge nd dringe influenes on soil orgni ron dynmis, ggregte stility, nd ron yield. Soil S Plnt Nutr, 60(1), Kuzykov, Y., & Jones, D. L. (2006). Gluose uptke y mize roots nd its trnsformtion in the rhizosphere. Soil Biol Biohem, 38, Kuzykov, Y., & Shnekenerger, K. (2004). Review of estimtion of plnt rhizodeposition nd their ontriution to soil orgni mtter formtion. Arh Agro Soil Si, 50, Ll, R. (2002). Soil ron sequestrtion in Chin through griulturl intensifition, nd restortion of degrded nd desertified eosystems. Lnd Degrd Dev, 13, Ll, R. (2004). Offsetting Chin s CO2 emissions y soil ron sequestrtion. Clim Chnge, 65, Leke, J. R., Ostle, N. J., Rngel-Cstro, J. I., & Johnson, D. (2006). Cron fluxes from plnts through soil orgnisms determined y field 13CO2 pulse-lelling in n uplnd grsslnd. Appl Soil Eol, 33, Ling, B. C., Wng, X. L., & M, B. L. (2002). Mize root-indued hnge in soil orgni ron pools. Soil. Si So Am J, 66, Lu, Y., Wtne, A., & Kimur, M. (2002). Contriution of plnt-derived ron to soil miroil iomss dynmis in pddy rie miroosm. Biol Fertil Soils, 36, Lu, Y., Wtne, A., & Kimur, M. (2002). Input nd distriution of photosynthesized ron in flooded rie soil. Glo Biogeohem Cyle, 16, Lu, Y., Wtne, A., & Kimur, M. (2005). Contriution of plnt photosynthtes to dissolved orgni ron in flooded rie soil. Biogeohemistry, 71, Lynh, J. M., & Whipps, J. M. (1990). Sustrte flow in the rhizosphere. Plnt Soil, 129,

7 Müller, T., & Höper, H. (2004). Soil orgni mtter turnover s funtion of the soil ly ontent: onsequenes for model pplitions. Soil Biol Biohem, 36, Rih, J. W., & Tufekioglu, A. (2000). Vegettion nd soil respirtion: orreltions nd ontrols. Biogeohemistry, 48, Rjesh, C. R., Reddy, K. S., Nidu, M. V. S., & Rmvtrm, N. (2003). Prodution nd evlution of ompost nd vermiompost from solid orgni wstes. Asin Journl of Miroiology, Biotehnology, nd Environmentl Siene, 5, Witt, C., Biker, U., Glii, C. C., & Ottow, J. C. G. (2000). Dynmis of soil miroil iomss nd nitrogen vilility in flooded rie soil mended with different C nd N soures. Biol Fertil Soils, 30, Wu, J., Joergensen, R. G., Pommerening, B., Chussod, R., & Brookes, P. C. (1990). Mesurement of soil miroil iomss C y fumigtion-extrtion-n utomted proedure. Soil Biol Biohem, 22, Yevdokimov, I., Ruser, R., Buegger, F., Mrx, M., & Munh, J. C. (2006). Miroil immoilistion of 13Crhizodeposits in rhizosphere nd root-free soil under ontinuous 13 C lelling of ots. Soil Biol Biohem, 38, Copyrights Copyright for this rtile is retined y the uthor(s), with first pulition rights grnted to the journl. This is n open-ess rtile distriuted under the terms nd onditions of the Cretive Commons Attriution liense ( 202

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