Effects of mowing on N 2 O emission from a temperate grassland in Inner Mongolia, Northern China

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1 Biogeosciences Discuss.,, , 13 doi:.194/gd Author(s) 13. CC Attriution 3. License. Biogeosciences Discussions This discussion pper is/hs een under review for the journl Biogeosciences (BG). Plese refer to the corresponding finl pper in BG if ville. Effects of mowing on N 2 O emission from temperte grsslnd in Inner Mongoli, Northern Chin L. Zhng 1, Q. Wng 1, H. J. Lnroek 2,3, C. Wng 1, D. Guo 4, nd L. Li 1 1 Stte Key Lortory of Vegettion nd Environmentl Chnge, Institute of Botny, Chinese Acdemy of Sciences, Beijing, 93, Chin 2 Deprtment of Microil Ecology, Netherlnds Institute of Ecology (NIOO-KNAW), Wgeningen, the Netherlnds 3 Institute of Environmentl Biology, Utrecht University, Utrecht, the Netherlnds 4 Shndong Norml University, Jinn, 14, Chin Received: Octoer 13 Accepted: 27 Novemer 13 Pulished: 9 Decemer 13 Correspondence to: Q. Wng (qwng@ics.c.cn) Pulished y Copernicus Pulictions on ehlf of the Europen Geosciences Union Open Access Astrct Grzing nd mowing re two common prctices for grsslnd mngement. Mowing is now recommended s n lterntive to trditionl grzing for grsslnd conservtion in Inner Mongoli, northern Chin. Mny studies hve reveled tht oth mowing nd grzing my lter ecosystem properties in vrious wys. However, little ttention hs een pid to the effect of mowing on trce gs emissions, especilly on N 2 O flux. In this study, we conducted n experiment to investigte the effects of mowing on N 2 O fluxes from semirid grsslnd in Inner Mongoli. The mowing experiment, which strted in 3, comprised four mowing intensity tretments, i.e. mowing heights t 2,, nd cm ove the soil surfce, respectively, nd control of non-mowing, with five replictes. Gs fluxes were mesured through closed sttic chmer technique during the growing sesons (usully from My to Septemer, depending on locl climte t the time) of 8 nd 9, respectively. Our results showed tht mowing decresed N 2 O emissions, ove-ground iomss nd totl litter production. N 2 O emissions were greter in My nd June thn in other smpling periods, regrdless of tretments. A co-reltionship nlysis suggested tht vritions in sesonl N 2 O fluxes were minly driven y vritions in soil moisture nd microil iomss nitrogen, except in July nd August. In July nd August, ove-ground plnt iomss nd soil totl nitrogen ecme the mjor drivers of N 2 O fluxes under the soil tempertures etween 16 C nd 18 C. Overll, our study indicted tht the introduction of mowing s mngement prctice might decrese N 2 O emissions in grsslnds, nd oth mowing height nd soil properties ffected the mgnitude of the reduction. Our findings imply tht grsslnds, long with proper mngement prctices, cn e N 2 O sink mitigting the rise of N 2 O in the tmosphere. 192

2 1 Introduction The temperte steppe in northern Chin is typicl vegettion type on the Eursin continent nd is sensitive to nthropogenic disturnces nd climte chnges (Christensen et l., 4; Niu et l., 9). Both mowing nd grzing re previling mngement prctices in these res (Tix, ). Recently, mowing ws highly recommended for sustinle grsslnd mngement in ntionl project clled Grin for Green, which ims to restore the degrded ecosystems in western Chin (Liu et l., 9). Mowing, the removl of prt of plnt shoot tissue, hs negtive effects on overll plnt growth nd cron lloction (Ferrro, 2), which cn influence the root cron exudtion nd the rhizosphere orgnisms tht rely on the nitrogen relesed from the plnt roots (Hmilton et l., 8). The removl of some plnts y mowing inevitly leds to the djustment of the size of the root system nd thus cuses the deth nd decy of the roots nd nodules, followed y decomposition, minerliztion of nitrogen, nitrifiction nd denitrifiction. Mowing lso reduces the input of ove-ground litter into the soil (Vlko et l., 12), nd consequently decreses the mount of corse orgnic mtter in the soil (Mikol et l., 9) nd relted gs emissions from the soil, including nitrous oxide (N 2 O). N 2 O is vitl greenhouse gs, nd it contriutes pproximtely 6 % to the nticipted glol wrming (IPCC, 7). The glol tmospheric N 2 O concentrtion incresed from preindustril vlue of 27 to 322 pp in 8 (IPCC, 7). N 2 O emitted from soils is considered s one of the mjor contriutors to this rise (Wrge et l., 1). Denitrifiction is key ecologicl process tht determines N 2 O production in n ecosystem. Relted studies suggest tht N 2 O emissions would e determined y soil properties nd processes including soil temperture, soil moisture, sustrte vilility (Wrge et l., 1), soil diffusive chrcteristics, ir-fillled porosity (Neftel et l., ), the ctivity of nitrifying/denitrifying microil communities (Steenwerth, 8) nd concurrent N 2 O consumption processes in the soil (Cvigelli, 1). The complexity of these fctors, which regultes N 2 O production, consumption nd emission, results in considerle uncertinties in estimting ctul N 2 O exchnge rtes for given mngement scenrios. Both grzing nd mowing lter soil properties in grsslnds, susequently ffecting the grsslnd N cycle, including soil N 2 O emission. Wolf et l. () found tht grzing decresed grsslnd N 2 O relese vi chnging soil nd environmentl conditions. Sørensen et l. (8) reported tht mowing ltered N cycling y decresing soil N minerliztion. Other spects of grzing, such s rndom urine nd feces deposit of livestock, incresed N 2 O emissions (Ynulki et l., 1998). Therefore, it is necessry to quntify the chnges in N 2 O emission cused y mowing to fully understnd the regionl udget of trce gses. However, there is no informtion ville on how mowing ffects N 2 O emission (Clnc et l., 1), nd findings from grzing mngement cnnot e extrpolted to those from mowing, s defolition y grzing is more frequent nd not comprle to mowing. To quntify N 2 O fluxes in response to different mowing intensities, we conducted n experiment setup in 3 with different mowing heights in steppe ecosystem in Inner Mongoli of northern Chin. Here, we present results of N 2 O fluxes over the two growing sesons (from My to Septemer) of 8 nd 9, nlysing the reltion etween N 2 O emission nd iotic nd iotic fctors to identify the controls of the emission. We hypothesize tht (1) mowing will decrese N 2 O emission due to the removl of prt of plnts ove the soil surfce, which cn result in continuous decreses in the vilility of sustrte nd nutrient for N 2 O production (Berliner, 1999) nd the relted soil microes; (2) oth soil iotic nd iotic fctors ply importnt roles in underlying mowing effects on N 2 O flux

3 2 Mteril nd methods 2.1 Study site This study ws crried out t the Duolun Restortion Ecology Reserch Sttion, Institute of Botny, Chinese Acdemy of Sciences (IBCAS), which is locted in Duolun County ( E, 42 2 N) in Inner Mongoli, Chin. The re is situted in semirid, middle temperte zone nd chrcterized y continentl monsoon climte. The men nnul ir temperture is round 2.1 C, with monthly men tempertures rnging from 17. C in Jnury to 18.9 C in July. The men nnul precipittion is pproximtely 38 mm, with 8 % of precipittion occurring from mid-june to lte Septemer. The topogrphy is fetured y low foothills t elevtions of 1 18 m. The soil t the study site is clssified s chestnut soil in the Chinese soil clssifiction, contining 62.7 ±.4 % snd,.3 ±.1 % silt nd 16.9 ±.1 % cly, with men soil ulk density of 1.31 gcm 3 nd ph vlue of The dominnt plnt species in the temperte grsslnd re Stip krylovii Roshev., Cleistogenes squrros (Trin.) Keng., Artemisi frigid Willd, Potentill culis L., Allium identtum Fisch. Ex Prokh. nd Agropyron cristtum (L.) Gertn. 2.2 Experimentl design Mowing experiment ws set up in 3 nd consists of one control nd four mowing height tretments: non-mowing control (M ck ), mowing heights t 2 cm (M 2 ), cm (M ), cm (M ) nd cm (M ) ove the soil surfce, respectively, in complete rndomized lock design, with five replictes. The five tretments were rndomly ssigned to the five plots of m m, eing prt of lock design (i.e. five in totl), where djcent locks were seprted y 4 m. Any djcent locks nd plots within lock were 4 m prt from ech other. Mowing with complete removl of the plnt cuttings ws crried out in lte August ech yer strting in 3. The mient precipittion dt from 8 to 9 were provided y meteorologicl sttion in n open field, which is pproximtely 2 km wy from the experimentl site nd run y the Duolun Restortion Ecology Reserch Sttion, IBCAS. Prior to the setup of the experiment, the site hd een kept free from disturnce nd lrge niml grzing y fencing since N 2 O flux mesurements N 2 O fluxes were mesured y sttic chmer technique following Zhng et l. (7). Briefly, the chmer consists of stinless steel permnent se (cm cm 12cm) nd stinless steel top (cm cm cm). The se, with 3 cm-deep groove on the upper side for wter seling, ws driven into soil down to 12 cm ech yer pproximtely month efore the mesurement strted in ech plot (Song et l., 9). The top is covered y het-isolting nd light-impenetrle mterils outside nd equipped with one ruer sept for gs smpling nd two electric fns inside for mixing the ir in the chmer hedspce continuously nd thoroughly (Wng nd Wng, 3). During the mesurements, the top ws instlled over the se, with downsides into the groove. The grooves were filled with wter to sel the chmer. Gs smples were collected t min intervls for 3 min (i.e.,, nd 3 min) through the sept using 6 l syringes with irtight stopcocks. All gs smples were rought to lortory t the reserch sttion for N 2 O nlyses within 12 h fter smpling. N 2 O concentrtion ws nlysed using gs chromtogrph (HP 86, Agilent Technologies). N 2 O flux ws clculted from the liner slope of the mixing rtio chnges in the four smples tken t,, nd 3 min fter the chmer ws closed. The N 2 O flux ws mesured weekly from June to Septemer in 8 nd iweekly from My to Septemer in 9. Concurrent with the N 2 O flux smpling, ir temperture in the chmer, soil temperture nd soil moisture next to the chmers were mesured using portle digitl thermometer. Air temperture ws mesured t 4 cm height ove the soil surfce, nd soil temperture ws mesured t cm depth

4 2.4 Mesurements of vegettion nd soil Prior to experiments in 8 nd 9, vegettion vriles were mesured once t pek iomss (i.e. August). A 1m 1m frme with eqully distriuted grids of cm cm ws put ove the cnopy djcent to the flux chmers in ech m m plot. The coverge of ech species ws visully estimted following Yng et l. (11) in ll the grids, nd then summed s the totl coverge for the qudrt. After the mesurement of the coverge, ll plnts were clipped t ground level within the qudrt of 1 m 2 nd seprted into living vegettion s totl iomss (i.e. ove-ground iomss, ANPP; see lso Zhng et l., 12) nd ded plnt mterils s stnding litter. The totl litter ws the sum of the stnding litter nd litter collected on the surfce within the qudrt. All plnt mterils smpled were oven dried t 7 C for 48 h nd weighed. Soil smples ( cm lyer) were collected monthly during the 9 growing seson using soil corer ( cm dimeter) t the time of the fourth gs smpling. At ech soil smpling, three soil cores were tken rndomly t ech plot nd mixed evenly. These smples were seprted into two set of su-smples: one set ws stored t 4 C for microil nlysis, nd the other ws ir-dried for soil orgnic cron (SOC), totl nitrogen (TN) nd totl phosphorus (TP) nlyses s well s soil temperture (ST), soil moisture (SM), soil microil iomss cron (MBC) nd microil iomss nitrogen (MBN) for identifying the controls of N 2 O fluxes (for detils see Zhng et l., 12). 2. Sttisticl nlysis A repeted mesure nlysis of vrince (ANOVA) ws performed to exmine internnul vriility in SOC, TN nd TP with the pooled dt of ll tretments during the growing seson. Between-suject effects were evluted s mowing effects nd within-suject effects were the time-of-seson. Regression nlyses were mde etween N 2 O fluxes nd the mesured vriles (e.g. ST, SM, SOC, TN, TP, MBC, MBN nd ANPP, totl litter, totl coverge). Becuse some prmeters were mesured t 192 different times, we used the mens of the whole growing seson. Therefore, every vrile hd five replictes nd five tretments. Differences in sesonl cumultive N 2 O flux, totl litter nd ANPP mong tretments were determined y nlysis of simple one-wy ANOVA. To exmine which vrile hd the most importnt effect on N 2 O fluxes, stepwise multiple regression nlysis ws pplied etween the whole growing seson men N 2 O fluxes (s n independent vrile) nd the mesured vriles (s dependent vriles). All sttisticl nlyses were conducted with the SAS 8. softwre pckge (SAS Institute Inc., Cry, NC, USA). 3 Results 3.1 Climte The study re received 37 mm nd 18 mm of rin for 8 nd 9, respectively, nd showed gret vritions in temporl distriution (Fig. 1). Most of the rin fell over the summer months (from June to August), which ccounts for 9 % of the nnul totl precipittion in the two yers. Soil temperture nd moisture vried sesonlly t this site (see Zhng et l., 12). Briefly, soil temperture t cm depth rnged from 13.1 to 31.1 C with n verge of 22.3 C in 8, nd 8. to 27.9 C with n verge of 18.1 C in 9. The temperture lso generlly correlted negtively with mowing height. Soil moisture peked in July nd hd similr temporl fluctution ptterns over the two growing sesons, lthough the rinfll tht occurred in this re ws sustntilly different during the sme period. However, no consistent reltionship ws oserved etween soil moisture nd mowing height. 3.2 Effect of mowing on totl coverge, ove-ground iomss nd litter Totl coverge, ove-ground iomss nd litter mesure in 9 (prior to the N 2 O experiment) re presented in Tle 1. The mowing tretments did not significntly ffect plnt coverge, regrdless of mowing heights (P >.). The ove-ground iomss 19226

5 nd totl litter decresed progressively s cutting height decresed from cm to 2 cm, except for the ove-ground iomss of M in 8, nd significntly lower litter mss ws found for the M 2 nd M tretments (P <.1). This ws lso oserved for ANPP, indicting tht cutting height > cm hs little effect on net primry productivity. Aove-ground iomss nd totl litter were mrkedly lower in 8 compred with 9, except for the M 2 tretment in ANPP. These results indicted tht the effects of higher cutting heights (M nd M ) on net primry production were limited in this grsslnd ecosystem. We lso oserved tht the ove-ground iomss nd totl litter were significnt differences in the two yers, except for the ove-ground iomss of tretment M 2, suggesting tht significnt yer effect existed in the grsslnd (Tle 1). In ddition, the iomss of Artemisi frigid, species with low height, contriuted most of the totl iomss of M 2 nd M plots reltive to tht of the control, M nd M plots (dt not shown). 3.3 Temporl dynmics in N 2 O fluxes Men N 2 O emission rtes from the different mowing tretments vried in rnge of 31.7 to 67.2 µgn 2 Om 2 h 1, with mens of 12.7, 4.2, 4.8,.2 nd 4.1 µgn 2 Om 2 h 1 for tretments of M ck, M, M, M, nd M 2, respectively, over the growing seson of 8, nd mens of 13.6, 9., 3.7, 2.9 nd. µgn 2 Om 2 h 1 for M ck, M, M, M, nd M 2, respectively, in 9 (Fig. 2). The vrition of N 2 O fluxes ws reltively nrrow in the dry yer (9) compred with the wet yer (8) (Fig. 2). The higher vrition in N 2 O emission rte resulted in high vrition in the monthly cumultive N 2 O flux, with rnge of.48 to.3 kgn 2 Oh 1 over the two growing sesons (Fig. 3). Figure 3 lso indictes tht the grsslnd could possily function s N 2 O source (positive vlue), ut tht it hs lso frequently cted s N 2 O sink (negtive flux vlues). Regrdless of the mowing heights, surprisingly, the monthly cumultive N 2 O flux ws negtive in July for most of the tretments, except for the controls oth in 8 nd 9 nd the M nd M 2 in 8 (Fig. 3) Effects of mowing on N 2 O fluxes Tle 1 presents the sesonl cumultive N 2 O emissions sed on liner interpoltion, sptilly verged, of dily or monthly men fluxes. Over the two growing sesons, n estimted mount of.22 kgn 2 Oh 1 per seson ws emitted in the control tretment, of which more thn 88 % occurred in My nd June. Occsionlly, negtive vlues were oserved in the control nd other mowing tretments (Fig. 2). The estimted sesonl cumultive emissions in the different tretments rnged from.8 kgn 2 Oh 1 to.1 kgn 2 Oh 1 in 8, wheres they fluctuted from.27 kgn 2 Oh 1 to.33 kgn 2 Oh 1 in 9 (Tle 1). M ck nd most of the mowing tretments cted s net sources of N 2 O, except for the M tretment, which promoted the grsslnd to uptke N 2 O from tmosphere, with n estimted cumultive flux of.8 kgn 2 Oh 1 (Tle 1) in oth 8 nd 9. For the totl fluxes over the two growing sesons, the vlue for M ws the only mowing tretment significntly different from tht of the control (p <.). Compred with the control, the M, M, M nd M 2 mowing tretments decresed N 2 O emission y 96, 4, 18 nd %, respectively, in 8 (Tle 1), nd y 182, 82, 124 nd 118 %, respectively, in 9 (Tle 1). Over the two-yer period, the M, M, M nd M 2 mowing tretments decresed the totl N 2 O emission y 9, 73, 36 nd 77 %, respectively, reltive to the control (Tle 1). 3. Controls of N 2 O fluxes The sesonl N 2 O flux incresed with incresing soil moisture content, indicting strong influence of soil moisture on sesonl N 2 O flux (Fig. 4). The results of regression nlyses showed tht the closest reltionship existed etween the N 2 O fluxes nd soil moisture (r 2 =.8, P <.1), followed y ove-ground plnt iomss (r 2 =.3, P =.2), nd microil iomss nitrogen (r 2 =.16, P =.14) in this experiment (Fig. 4,, nd d). A significnt liner reltionship etween N 2 O fluxes nd soil totl nitrogen ws only oserved within soil tempertures rnging from 16 to 18 C 19228

6 (Fig. 4f). Our stepwise regression nlyses showed tht comintion of soil moisture (prtil R 2 =.42, P =.), soil temperture (prtil R 2 =.13, P =.2) nd totl phosphorus (prtil R 2 =.8, P =.47) explined 62. % of the vrition in the N 2 O fluxes (P <.) in My. Microil iomss nitrogen explined 21.2 % of the vrition in the N 2 O fluxes (P =.2) in June, nd soil moisture explined 21.4 % of the vrition (P =.2) in July. Other fctors did not contriute significntly to the explntion of the vrition in N 2 O fluxes in these summer months. In ddition, we did not find significnt correltion etween N 2 O fluxes nd ny other vriles mesured t P <. in August nd Septemer. Using the pooled dt of the whole growing seson in the different tretments, stepwise regression nlyses show tht microil iomss nitrogen ws mjor controlling fctor in N 2 O fluxes in the control nd the M 2 tretment, explining % nd 27 % of the vrition in the N 2 O fluxes, respectively (P =.1,P =.8). Microil iomss cron ws mjor controlling fctor in the M tretment, explining 23 % of the vrition in the N 2 O fluxes (P =.14), nd soil moisture ws the most importnt controlling fctor in the M tretment, explining 21 % of the vrition in the N 2 O fluxes (P =.2). 4 Discussion 4.1 Controls of chnges in N 2 O fluxes Our oservtions, showing decrese in N 2 O with mowing height, generlly supported the hypothesis tht mowing would decrese the grsslnd N 2 O emissions into the tmosphere. This ws in line with others, though the mowing effects were not sttisticlly significnt in most cses. In this experiment, these oservtions re in line with the results of nother similr investigtion lso conducted in grzed grsslnd in Inner Mongoli (Wolf et l., ), ut opposite to the findings in hevily grzed lpine grsslnd y Go et l. (8). Mowing not only led to lower N 2 O emission rtes, ut lso led to lower ove-ground plnt nd litter iomss s well s totl plnt cov erge (Tle 1), nd most likely removl of nitrogen from the system. Nitrifiction is commonly repressed y nitrogen limittion, which explins the decline in N 2 O with mowing height. Indeed, we oserved liner reltionship etween N 2 O fluxes nd totl soil nitrogen (Fig. 4f). However, this reltionship ws only found with soil tempertures rnging from 16 to 18 C. This ws in line with findings tht N minerliztion nd nitrifiction were repressed during the growing seson, ut incresed fter tht period (Both et l., 1992). In July of 8 nd 9, numer of wek N 2 O uptke peks occurred in some of the mowing tretments (Fig. 3 nd ), leding to significnt uptke of N 2 O on monthly sis (Fig. 3). Though the temperture ws fvourle in July, microil ctivity my decrese due to the low precipittion (Fig. 1). Additionlly, plnts strongly compete for the minerlized N, leving less N for nitrifying nd denitrifying cteri (Verhgen et l., 1994; Mikol et l., 9). This competition my e the reson for the N 2 O uptke oserved in grsslnds during July in our study. This result confirms tht grsslnd soils my ct s net sinks of tmospheric N 2 O under certin conditions due to high N 2 O reduction ctivity y denitrifying microorgnisms (Wrge et l., 4; Flechrd et l., ). N 2 O reduction y denitrifying microorgnisms is ound to reduced levels of oxygen, which is usully relted to incresed moisture content (Schlesinger, 13). Despite the different ptterns of N 2 O fluxes in July 8 nd 9, soil moisture content ws not very different etween these months (Zhng et l., 12). Hence, unknown soil fctors might hve een responsile for the oserved differences in the fluxes in July. In August, however, there ws net N 2 O emission (Fig. 3). At this time of the yer, the temperture is still high enough for soil microil ctivity (dt not shown). Therefore soil microes will decompose plnt mteril nd likely result in minerliztion of N. However, most of the plnts get senescent with more sustrte relesed into the soil, nd require fewer nutrients from the soil for growth t tht time; susequently the competition etween plnts nd microorgnisms for minerlized N will e reduced. The 1923

7 higher sustrte nd N vililities likely promote microil nitrifiction, leding to high N 2 O production. Using the pooled dt of the whole growing seson nd ll tretments, stepwise regression nlyses show tht soil moisture ws the most importnt controlling fctor in N 2 O fluxes, which explins 8 % of the oserved vritions in sesonl verge N 2 O fluxes (P <.1) t our study site (Fig. 4). Similr results were reported for grsslnds in Irelnd (Lehy et l., 4) nd New Zelnd (Müller et l., 4). Therefore, soil moisture could e considered s mjor control of sesonl N 2 O fluxes, nd determines microil N 2 O emissions (Merino et l., 1). In some griculturl regions, soil moisture ws lso found to e the controlling fctor in N 2 O fluxes (Izurrde et l., 4). Becuse soil moisture is the key determinnt of the microil processes tht consume or produce N 2 O, soil moisture shifts in rid nd semirid regions will likely ffect N 2 O fluxes. 4.2 Effect of mowing on N 2 O fluxes The reltionship etween N vilility nd N 2 O flux is commonly exmined for predicting N 2 O fluxes on lrge scles, nd Millr et l. () hd even reported tht N vilility is the only fctor ffecting N 2 O fluxes t metre scles. However, in our study, we did not find ny significnt correltion etween totl nitrogen nd N 2 O fluxes; coming with nother result, the mowing tretments did not lter the concentrtions of soil TN (including NH + 4 nd NO 3 ) (Tle 2), nd we my explin why there ws no significnt effect of mowing on the cumultive N 2 O fluxes in 8 in this study (Tle 1). Our other hypothesis is tht oth soil iotic nd iotic fctors ply importnt roles underlying mowing effects of decresing plnt iomss on N 2 O fluxes. Since the cumultive sesonl N 2 O fluxes were only slightly different mong different mowing tretments, nd no consistent chnges were found mong ny of the mowing tretments (Tle 1), we tested the effects of mowing on N 2 O fluxes y compring the pooled dt of ll the mowing tretments, including those of the control. The result suggests tht mowing might decrese N 2 O emissions y reducing plnt litter nd ove-ground iomss (Tle 1), since the decresed plnt litter nd iomss might result in decreses in the sustrtes supplied to microes, which re in chrge of nitrifiction nd denitrifiction processes. The ove finding grees with tht of some previous studies. Zou et l. () estlished positive liner reltionship etween ove-ground plnt iomss nd N 2 O emissions. Kmmnn et l. (1998) found tht incresing numers of cuts reduced N 2 O emissions. However, in other cses, for instnce, Beck nd Christensen (Beck, 1987) found tht N 2 O emissions incresed when ll ove-ground grss ws removed, nd Klumpp et l. (11) only oserved tht some smll peks of N 2 O emission occurred in response to cutting events. Further nlysis indictes tht there ws significnt effect of the differences in soil moisture on the N 2 O fluxes fter mowing (Fig. ), which explins 76 % of the vrition in the N 2 O emissions induced y mowing (P <.1). Similr results were found in study performed in grzed grsslnds y Wolf et l. (). Overll, our results showed tht the N 2 O emissions from the grsslnd mowed t plnt heights of cm were smller thn those from the grsslnds not mowed during the growing seson in Inner Mongoli. We my extrpolte from this finding tht y chnging grsslnd mngement, such s introducing proper mowing intensity, the greenhouse effects of N 2 O emission might e mitigted in the grsslnd. Thus, emission estimtes from grsslnds my need to tke into ccount more specific mngement prctices, for instnce, mowing intensity. The most significnt finding from this study is tht soil moisture plyed key role in the sesonl cumultive N 2 O fluxes. Acknowledgements. We thnk Shuxin Xu, Shihun Song, Xin Li nd Gungqun Wng for their help in setting up the field fcilities nd experimentl mesuring. This study ws supported y the Ntionl Nturl Science Foundtion of Chin ( , 4837), the Ntionl Bsic Reserch Progrm of Chin (973 progrm) (CB913), the Key Projects of the Knowledge Inititive Progrm of the Chinese Acdemy of Sciences (KZCX2-YW-JC44) nd the grnts from the Stte Key Lortory of Vegettion nd Environmentl Chnge, Institute of Botny, Chinese Acdemy of Sciences

8 Author contriutions Conceived nd designed the experiments: L. L. Performed the experiments: L. Z., Q. W., C. W., D. G. Anlysed the dt: L. Z., Q. W., H. J. L., L. L. Contriuted regents/mterils/nlysis tools: L. Z., L. L., C. W. Wrote the pper: L. Z., Q. W., H. J. L., L. L. References Beck, H. nd Christensen, S.: The effect of grss mturing nd root decy on N 2 O production in soil, Plnt Soil, 3, , Berliner, D. nd Kioko, J.: The effect of long-term mowing nd ungulte exclusion on grss species composition nd soil nutrient sttus on the Athi Kpiti plins, centrl Keny, Afr. J. Rnge For. Sci., 16, 62 7, Both, G. J., Gerrds, S., nd Lnroek, H. J.: Temporl nd sptil vrition in the nitriteoxidizing cteril community of grsslnd soil, FEMS Miroio. Ecol., 1, , Clnc, P., Neftel, A., nd Fuhrer, J.: N mngement of Europen grsslnds: cn the exchnge of gseous N species e influenced t the opertionl level?, Sci. World J., 3, 62 67, 1. Cvigelli, M. A. nd Roertson, G. P.: Role of denitrifier diversity in rtes of nitrous oxide consumption in terrestril ecosystem, Soil. Biol. Biochem., 33, 297 3, 1. Christensen, L., Coughenour, M. B., Ellis, J. E., nd Chen, Z. Z.: Vulnerility of the Asin typicl steppe to grzing nd climte chnge, Climtic Chnge, 63, , 4. Ferrro, D. O. nd Oesterheld, M.: Effect of defolition on grss growth. A quntittive review, Oikos, 98, 1 133, 2. Flechrd, C., Neftel, A., Jocher, M., Ammn, C., nd Fuhrer, J.: Bi-directionl soil/tmosphere N 2 O exchnge over two mown grsslnd systems with contrsting mngement prctices, Glo. Chnge Biol., 11, ,. Go, Y. H., Luo, P., Wu, N., Chen, H., nd Wng, G. X.: Impcts of grzing intensity on nitrogen pools nd nitrogen cycle in n lpine medow on the estern Tietn Plteu, Appl. Ecol. Environ. Res., 6, 69 79, Hmilton, E. W. III, Frnk, D. A., Hinchey, P. M., nd Murry, T. R.: Defolition induces root exudtion nd triggers positive rhizospheric feedcks in temperte grsslnd, Soil Biol. Biochem., 4, , 8. IPCC: Climte Chnge 7: The Physicl Science Bsis. Contriution of Working Group I to the Fourth Assessment Report of the Intergovernmentl Pnel on Climte Chnge (IPCC), edited y: Solomon, S., Qin, D., Mnning, M., Mrquis, M., Averyt, K., Tignor, M. M. B., Le Roy Miller Jr., H., nd Chen Z., Cmridge University Press, Cmridge, UK, 94 pp., 7. Izurrde, R. C., Lemke, R. L., Goddrd, T. W., McConkey, B., nd Zhng, Z.: Nitrous oxide emissions from griculturl topo sequences in Alert nd Ssktchewn, Soil Sci. Soc. Am. J., 68, , 4. Kmmnn, C., Grunhge, L., Muller, C., Jcoi, S., nd Jger, H. J.: Sesonl vriility nd mitigtion options for N 2 O emissions from differently mnged grsslnds, Environ. Pollut., 2, , Klumpp, K., Bloor, J. M. G., Amus, P., nd Soussn, J. F.: Effects of clover density on N 2 O emissions nd plnt-soil N trnsfers in fertilized uplnd psture, Plnt Soil, 343, 97 7, 11. Lehy, P., Kiely, G., nd Scnlon, T. M.: Mnged grsslnds: greenhouse gs sink or source?, Geophys. Res. Lett., 31, L7, doi:.29/4gl21161, 4. Liu, X. Y., Ling, T. G., Long, R. J., nd Guo, Z. G.: Clssifiction mngement mechnisms for grsslnd resources nd sustinle development strtegies in Northern Chin, Act Ecol. Sinic, 29, 81 89, 9. Merino, P., Estvillo, J. M., Pinto, M., Rodríguez, M., nd Duñeiti, M. K.: Nitrous oxide emissions from grsslnd in n intensive diry frm in the Bsque Country of Spin, Soil Use Mnge., 17, , 1. Millr, N., Roertson, G. P., Grce, P. R., Gehl, R. J., nd Hoen, J. P.: Nitrogen fertilizer mn- gement for nitrous oxide (N 2 O) mitigtion in intensive corn (Mize) production: n emissions reduction protocol for US Midwest griculture, Mitig. Adpt. Strteg. Glo. Chnge,, 18 4,. Mikol, J., Setälä, H., Virkjärvi, P., Srijärvi, K., nd Ilmrinen, K.: Defolition nd ptchy nutrient return drive grzing effects on plnt soil properties in diry cow psture, Ecol. Monogr., 79, ,

9 3 Müller, C. nd Sherlock, R. R.: Nitrous oxide emissions from temperte grsslnd ecosystems in the Northern nd Southern Hemispheres, Glol Biogeochem. Cy., 18, GB4, doi:.29/3gb217, 4. Neftel, A., Bltter, A., Schmid, M., Lehmnn, B., nd Trknov, S. V.: An experimentl determintion of the scle length of N 2 O in the soil of grsslnd, J. Geophys. Res.,, ,. Niu, S., Wu, M., Hn, Y., Xi, J., Zhng, Z., nd Wn, S.: Nitrogen effects on net ecosystem cron exchnge in temperte steppe, Glo. Chnge Biol., 16, 144, 9. Schlesinger, W. H.: An estimte of the glol sink for nitrous oxide in soils, Glo. Chnge Biol., 19, , 13. Song, C., Xu, X., Tin, H., nd Wng, Y.: Ecosystem tmosphere exchnge of CH 4 nd N 2 O nd ecosystem respirtion in wetlnds in the Snjing Plin, northestern Chin, Glo. Chnge Biol.,, 692 7, 9. Sørensen, L. I., Kytoviit, M. M., Olofsson, J., nd Mikol, J.: Soil feedck on plnt growth in su-rctic grsslnd s result of repeted defolition, Soil Biol. Biochem., 4, , 8. Steenwerth, K. nd Belin, K. M.: Cover crops nd cultivtion: impcts on soil N dynmics nd microiologicl function in Mediterrnen vineyrd groecosystem, Appl. Soil Ecol., 4, 37 38, 8. Tix, D. nd Chrvt, I.: Aoveground iomss removl y urning nd rking increses produc- tivity in tllgrss pririe, Restor. Ecol., 13, 28,. Vlko, O., Torok, P., Mtus, G., nd Tothmeresz, B.: Is regulr mowing the most pproprite nd cost-effective mngement mintining diversity nd iomss of trget fors in mountin hy medows?, Flor, 7, 33 39, 12. Verhgen, F. J. M., Hgemn, P. E. J., Woldendorp, J. W., nd Lnroek, H. J.: Competition for mmonium etween nitrifying cteri nd plnt roots in soil in pots: effects of grzing y flgelltes nd fertiliztion, Soil Biol. Biochem., 26, 89 96, Wng, Y. S. nd Wng, Y. H.: Quick mesurement of CH 4, CO 2 nd N 2 O emissions from shortplnt ecosystems, Adv. Atmos. Sci.,, , 3. Wolf, B., Zheng, X., Bruggemnn, N., Chen, W., nd Dnnenmnn, M.: Grzing-induced reduc- tion of nturl nitrous oxide relese from continentl steppe, Nture, 464, ,. Wrge, N., Velthof, G. L., vn Beusichem, M., nd Oenem, O.: Role of nitrifier denitrifiction in the production of nitrous oxide, Soil Biol. Biochem., 33, , Wrge, N., Luf, J., del Prdo, A., Pinto, M., nd Pietrzk, S.: Distinguishing sources of N 2 O in Europen grsslnds y stle isotope nlysis, Rpid Commun. Mss Sp., 18, 11 17, 4. Ymulki, S., Jrvis, S. C., nd Owen, P.: Nitrous oxide emissions from excret pplied in simulted grzing pttern, Soil Biol. Biochem., 3, 491, Yng, H., Wu, M., Liu, W., Zhng, Z., nd Zhng, N.: Community structure nd composition in response to climte chnge in temperte steppe, Glo. Chnge Biol., 17, 42 46, doi:.1111/j x, 11. Zhng, L. H., Song, C. C., nd Wng, D. X.: Effects of exogenous nitrogen on freshwter mrsh plnt growth nd N 2 O fluxes in Snjing Plin, northest Chin, Atmos. Environ., 41, 8 9, 7. Zhng, L. H., Guo, G. F., Niu, S. L., Wng, C. H., Sho, C. L., nd Li, L. L.: Effects of mowing on methne uptke in semirid grsslnd in northern Chin, Plos ONE, 7, e392, doi:.1371/journl.pone.392, 12. Zou, J., Hung, Y., Sun, W., Zheng, X., nd Wng, Y.: Contriution of plnts to N 2 O emissions in soil-winter whet ecosystem: pot nd field experiments, Plnt Soil, 269, 211,

10 Tle 1. Mens of totl plnt litter (gm 2 ), ove-ground plnt iomss (gm 2 ), totl plnt coverge (%), nd cumultive N 2 O emission/uptke (kgh 1 ) under different mowing tretments in steppe ecosystem in Inner Mongoli, northern Chin. Tretment Totl litter Aove-ground Totl coverge Soil moisture Cumulted N 2 O iomss (kgh 1 ) M ck M M c M c M c Zhng et l. (12). Vlues represent the men of five replictes. Different letters in column indicte significnt difference etween tretments t P <.. M ck represent the no-mowing control. M, M, M nd M 2 represent the tretments of plnts mowed t heights of cm, cm, cm nd 2 cm ove the soil surfce, respectively Tle 2. P vlues of repeted mesures ANOVAs on the effects of mowing (M), smpling dte (D) nd their interctions on C/N rtio, soil orgnic cron (SOC), totl nitrogen (TN) nd totl phosphorus (TP) under different mowing tretments. Dt with indicte significnt difference t the P <. level. Tretment C/N SOC TN TP M M M M 2 D M D M D M D M D M D M D M D M

11 Precipittion (mm) Jn Fe Mr Apr My Jun Jul 31 Fig. 1. Monthly precipittion in 8 nd 9 in the study re. 32 Figure 2 Temporl vritions in N 2 O fluxes under different mowing tretments in 8 (left) nd Aug Sep Oct Nov (right). Pnels A nd B represent the no-mowing control (Mck). Pnels C nd D, pnels E nd F, pnels G nd H, pnels I nd J represent the tretments of plnt mowed t heights of cm Dec 3 (M ), cm (M ), cm (M ) nd 2 cm (M 2 ) ove soil surfce, respectively. Dt re men ±SE 36 (n=) N2O fluxes (ug m -2 h -1 ) Jun 1 A C E I G Jun 19 Jun 24 Jul 1 Jul 6 Jul 11 8 Jul 17 Jul 23 Aug 1 Aug 9 Aug 29 Mowing Dte Sep 11 Sep 24 Sep 3 Smpling Dte Fig. 2. Temporl vritions in N 2 O fluxes under different mowing tretments in 8 (left) nd 9 (right). (A) nd heights. (B) represent Vlues re men the ± SE (n=). no-mowing Different letters control represent sttisticlly (M ck ). significnt (C) nd differences (D), (E) nd (F), (G) nd (H), nd (I) nd (J) represent the tretments of plnts mowed t heights of cm (M ), 4 mong tretments in the sme month t P<.. cm (M ), cm (M ) nd 2 cm (M 2 ) ove the soil surfce, respectively. Dt re men ± SE (n = ) My B D J F H My 23 Jun Jun 23 Jul 9 9 Jul Aug 8 Aug Sep 7 Mowing Dte Figure 3 Monthly cumultive N2O fluxes in 8 (A) nd 9 (B) under different mowing 1924 Sep 22 Sep 3 28

12 41 Monthly cumultive N 2 O fluxes (kg N 2 O h -1 ) A 8 Jun Jul Aug Sep M ck M M M M 2 c B c 9 c My Jun Jul Aug Sep Fig Monthly cumultive N 2 O fluxes in 8 (A) nd 9 (B) under different mowing heights. Vlues re men ± SE (n = ). Different letters represent sttisticlly significnt differences etween 43 tretments in the sme month t P < c Fig Figure 4 Reltionships etween Soil moisture N 2 O fluxes nd soil moisture Soil (%, microil A), microil nitrogen iomss nitrogen 3 3 N2O fluxes ( g m-2 h-1) C A (mg kg -1, B), totl soil phosphorus (g kg -1, C), ove-ground plnt iomss (g m -2, D), totl soil cron (g kg -1, E), totl soil nitrogen (g kg -1, F). Solid circles in F only plotted from the dt E Soil totl phosphorus Soil totl cron r 2 =.8, p< B D B Aove-ground plnt iomss F r 2 =.34, p= Soil totl nitrogen Fig. 4. Reltionships etween N 2 O fluxes nd soil moisture (%, A), microil iomss nitrogen (mgkg 1, B), totl soil phosphorus (gkg 1, C), ove-ground plnt iomss (gm 2, D), totl soil cron (gkg 1, E), totl soil nitrogen (gkg 1, F). Solid circles in (F) only plotted from the dt otined t soil tempertures etween 16 nd 18, while the open circles represent those vlues mesured outside of the temperture rnge

13 62 Figure The reltionship etween soil moisture nd N 2 O fluxes t sites fter mowing. N2O flux chnges induced y mowing ( g m -2 h-1 ) r 2 =.7, p< Soil moisture vrition fter mowing (%) 64 Fig.. The reltionship etween soil moisture nd N 2 O fluxes t sites fter mowing