SOIL ORGANISMS Volume 81 (2) 2009 pp

SOIL ORGANISMS Volume 81 (2) 2009 pp. 225 236 ISSN: 1864-6417 Response of enhytrei worm popultions to ifferent forms of nitrogen (mmoni, mmonium, n nitrte) eposition Mirn Prenergst-Miller 1*, Vlerie Stnen 2, In D. Leith 3 & Luy J. Sheppr 3 1Cruikshnk Builing, Institute of Biologil n Environmentl Sienes, University of Abereen, St Mhr Drive, Abereen, Sotln, AB24 3UU, 2University of Durhm, Shool of Biologil Sienes, Engln, DH1 3LE, 3Centre for Eology n Hyrology, Peniuik Bush Estte, Einburgh, Sotln, EH26 0QB; e-mil: m.t.prenergst@bn..uk *Corresponing uthor Abstrt The hnges to eosystems n eosystem funtioning inue by nthropogeni retive nitrogen eposition ontinue to be stuie in rnge of hbitts. In semi-nturl hbitts, these effets n be pronoune, often with negtive impts on the ntive flor. An experimentl site estblishe on n ombrotrophi bog provies unique opportunity for the stuy of the effet of long-term simulte N eposition. The response of enhytrei worms to ifferent forms of nitrogen eposition (s mmoni, mmonium or nitrte) ws ssesse t this site, whih hs been reeiving N tretments sine 2002: previous stuies on the site hve shown tht high N eposition (64 kg N h -1 yr -1 ) hs hnge the bovegroun vegettion. In this stuy, the below-groun response of enhytreis to N tretment ws shown to be epenent on site wetness. Uner fvourble site onitions, i.e. when the pet moisture ontent ws high, enhytrei bunne ws negtively ffete by N eposition in the form of mmoni or nitrte, wheres ition of mmonium, mmonium plus PK (=K 2 HPO 4 ), n to lesser extent, nitrte plus PK, ppere to inrese enhytrei bunne. However, when the bog ws rier, enhytrei numbers were similr ross ll tretments n ppere to be insensitive to N. Keywors: Oligohet, enhytreis, ombrotrophi bog, oxiise N, reue N 1. Introution Atmospheri nitrogen (N) eposition in vrious forms (oxiise n reue, wet n ry) to semi-nturl hbitts, suh s ombrotrophi bogs, ontinues to ffet vegettion over, plnt speies iversity n eosystem funtioning, often resulting in negtive effets on the more N-sensitive plnt speies (Aerts et l. 1992, Bobbink et l. 1998, Lmers et l. 2000, Gllowy et l. 2008). Ombrotrophi bogs re hrterise by speilise plnt ommunities tht re pte to low nutrient onitions, n s these hbitts rely solely on tmospheri nutrient inputs, they re prtiulrly sensitive to inrese N eposition. Enhytrei worms re foun in wie rnge of hbitts. Together with their high

226 Mirn Prenergst-Miller et l. bunne n speies iversity, they oul provie sensitive brometer for ssessing the effets of nthropogeni tivities on soil (Dien & Römbke 2001). In ii, pety soils, the enhytreis re importnt orgnisms, mking up 75 % of the totl mesofun. The enhytreis re the keystone speies in these soils, responsible for orgni mtter eomposition n nutrient yling (Stnen 1978, Lkso & Setälä 1999, Cole et l. 2000, Cole et l. 2002, vn Vliet et l. 2004). The effet of inrese N on enhytreis hs been stuie in grsslns n upln pets, often following the pplition of N to smll plots (e.g. Coulson & Butterfiel 1978, Yesmin et l. 1995, Thompson 2003). However, the effet of N on enhytreis hs not been fully investigte in simultions of N eposition proesses uner rel worl onitions, where N itions reflet UK-wie N eposition n where pplition rtes re ouple to lol meteorologil onitions (e.g. rinfll n win spee n iretion). The min mehnism ontrolling the enhytrei response is still unertin ue to ontrsting n vrible results, where high N eposition hs been shown to both inrese (Coulson & Butterfiel 1978) n reue enhytrei numbers (Yesmin et l. 1995). Enhytreis re likely to respon to N eposition vi iniret effets to their foo soure (e.g. eomposing litter, bteri n fungi) n soil ph (Stnen 1982). A previous stuy onute in 2005 on n ombrotrophi bog (Prenergst-Miller et l. 2008) investigte the effet of the ry N eposition tretments (s mmoni gs) on enhytrei bunne t n experimentl site. The stuy foun tht within three yers of exposure to ry N eposition, there were eresing grients in pet N ontent (s mmonium n nitrte onentrtions) n pet ph, with inresing istne from the mmoni soure. Above-groun, Cllun N onentrtions were signifintly inrese, n within 8 m of the point soure Cllun ws more suseptible to frost mge (Sheppr et l. 2008). In ontrst, enhytrei bunne showe no response to inrese N eposition n ws highly vrible. This lk of response ws ttribute to the reltively longer time (> 3 yr) require for bove-groun folir N to beome inorporte into the litter lyer (Thompson 2003). Here we report on n ssessment of enhytrei bunne me fter six yers of N tretment of ifferent forms (s mmonium, nitrte or mmoni), to exmine the effet of both wet n ry eposition on the enhytreis. In orer to etet whether ny hnge ws ourring in the enhytreis, we ompre bunne in ontrol plots (reeiving mbient N eposition, ~ 8 kg N h -1 yr -1 ) with tht from plots reeiving the highest N eposition s mmonium, nitrte or mmoni. This ws to test the hypothesis tht the enhytreis woul show positive response to N eposition meite through the hnges in lef n litter N ontent whih woul be expete fter six yers. 2. Mterils n methos 2.1 Site esription Whim Moss in the Sottish Borers (3 16 W n 55 46 N) is n experimentl site estblishe in 2002 on n ombrotrophi bog, s prt of the UK Nturl Environment Reserh Counil s GANE (Globl Atmospheri Nitrogen Enrihment) progrmme. The mnipultion experiment ws estblishe to stuy the long-term effets of simulte N eposition s mmoni, mmonium or nitrte to semi-nturl hbitt. The Whim Moss vegettion is lssifie s M19 (Cllun vulgris Eriophorum vgintum mire) (Rowell 1991). The vegettion is mosi of Sphgnum mosses, with Cllun vulgris (L.) Hull, Eriophorum vgintum (L.), n some Cloni lihen speies. The site is unmnge, but is impte by

Response of enhytreis to nitrogen eposition 227 rbbits. The N tretments re pplie to the site in rel-time epening on the lol meteorologil onitions, s the utomte relese system ensures tht the tretments re only pplie when ertin threshol prmeters re met, suh s win spee n iretion. This provies unique opportunity to observe n ompre the effets of ifferent forms of N eposition (wet vs. ry, oxiise vs. reue) bove- n below-groun. The site is ivie into two res to stuy the effets of (1) wet eposition s mmonium or nitrte sprye in solutions (me from rinwter ollete t the site) over irulr plots (4 m imeter), n (2) ry eposition, s mmoni gs (NH 3 ) relese over 60 m trnset. Full esriptions of the tretments n mnipultions re given in Sheppr et l. (2004) n Leith et l. (2004). The wet tretments (reue (NH 4 Cl) or oxiise N (NNO 3 )) re provie s fine spry of rinwter mixe with three oses of N (8, 24 or 56 kg N h -1 yr -1 ), with n without phosphorus (P) n potssium (K). The ontrol plots reeive only mbient N eposition, with no itionl rinwter (~ 8 kg N h -1 yr -1 ). The tretments re pplie over the plots when the win spee is < 5 m s -1, n not when the groun is frozen (Sheppr et l. 2004). At the ry eposition re, whih simultes N eposition from point soure suh s lrge poultry frm, the mmoni gs relese system is tivte whenever the win spee is > 2.5 m s -1 n within the 180 215 esignte setor of the trnset (Leith et l. 2004). Therefore, the frequeny of N ition to the respetive plots vries between the ifferent forms of N, n pplition my be more thn one y, or even none t ll over ry summer or uring winter. The stuy presente here fouse on the high N tretments from the wet eposition plots (reeiving 64 kg N h -1 yr -1 s mmonium or nitrte) n the ry eposition trnset (8 m from the mmoni relese pipe, where eposition is 64 kg N h -1 yr -1 ), in orer to ientify if ny effet on the enhytreis ws ourring. Smples were tken in June 2008 from the selete N tretments shown in Tb. 1. Smples were tken gin in Otober from the sme plots to etermine if the effets shown erlier in the yer were still present. Tb. 1 Selete tretments (Control, wet n ry N eposition) smple t Whim Moss for ssessment of enhytrei bunne. Tretment Number of plots Annul eposition (kg N h -1 yr -1 ) Control (no e nutrients) 4 8 (mbient) Wet eposition plots Ammonium (NH 4 Cl) 4 64 (mbient + 56) Ammonium + PK (NH 4 Cl + K 2 HPO 4 ) 4 64 (mbient + 56) (NNO 3 ) 4 64 (mbient + 56) + PK (NNO 3 + K 4 HPO 4 ) 4 64 (mbient + 56) Dry eposition trnset Ammoni (NH 3 ) gs (8 m from point soure) 1 64 (mbient + 56)

228 Mirn Prenergst-Miller et l. 2.2 Pet smpling From the wet eposition site, 2 3 ores were tken from eh plot. On the mmoni trnset, 4 ores were tken within 8 m of the mmoni relese pipe. An itionl 4 ores were tken from the ontrol plots, whih reeive mbient N eposition with no itionl nutrients or wter. The ores were tken using 3 m imeter orer, n the pet ws smple to epth of 10 m. Smples were bgge in the fiel n returne to the lbortory where they were store t 4 C. The ores were ut vertilly in hlf: one portion ws use for ph (1:2 rtio of pet:eionise wter) n ry weight etermintion (oven-rie overnight t 105 C); the other hlf ws use for enhytrei extrtion. Cores from the sme plots were poole together. The enhytreis were extrte for 3 hr using Bermn funnels whih were set up uner bnk of lights (O Connor 1957). Enhytreis were ollete in smll glss vils tthe to the en of the funnels n immeitely ounte. As n inition of whether nutrient ition h ltere litter n pet qulity within the ssume enhytrei feeing epth, oven-rie surfe litter n pet (0 10 m epth) smples from the ontrol, mmonium n nitrte plots were nlyse on CN nlyser for totl rbon n nitrogen. Dt on preipittion n pet temperture (t epth of 10 m) re mesure utomtilly t the site, n these were use to lulte monthly mens between My n Otober 2008. 2.3 Sttistil nlysis To test for ifferenes between tretments in moisture ontent, ph n C:N rtios, t were nlyse by one-wy ANOVA; signifint ifferenes (P < 0.05) were etermine using postho Tukey s honestly signifint ifferene tests. T-tests were performe to test for ifferenes between months within the sme tretment. Non-prmetri tests were use to ompre tretments in eh month for enhytrei bunne s the t i not meet the requirements for equl vrine n normlity. All nlyses were performe on Minitb v.15. 3. Results 3.1 Moisture ontent The smples tken in June were signifintly wetter (men grvimetri wter ontent 9.2 g g -1 wt) thn the Otober smples (men grvimetri wter ontent 1.9 g g -1 wt) (Fig. 1; P < 0.001). This ws espite signifintly more rin flling in the month preeing Otober ompre to June (Fig. 2). The men monthly rinfll, mesure ily t the site, ws tully higher (P < 0.001) in Otober (5.45 mm) ompre to June (3.16 mm), n the men monthly

Response of enhytreis to nitrogen eposition 229 14 Grvimetri wter ontent (g g -1 ry wt) 12 10 8 6 4 2 Fig. 1 0 Control Ammoni Ammonium Ammonium + PK Tretment + PK Pet grvimetri wter ontent (men + s.e.m.) from ores smple in June (open brs) n Otober (she brs) 2008 (n = 4 per tretment). Refer to Tb. 1 for etils of the ifferent tretments. Fig. 2 Monthly rinfll (men + s.e.m.; she br) n pet temperture t 10 m epth (men ± s.e.m.) mesure t the site between My n Otober 2008.

230 Mirn Prenergst-Miller et l. pet temperture ws lower (P < 0.001) in Otober (Fig. 2). There were no ifferene in moisture ontent between the ifferent tretments in June or Otober. 3.2 Pet ph The ph from pet smples in June ws generlly higher thn the ph from the smples tken in Otober (P < 0.001). For the mmonium n nitrte plots ph i not hnge between smpling time. In both months, there ws tretment effet on pet ph (P < 0.001 for eh month; Fig. 3): in June, the ph from the mmoni n nitrte + PK tretments ws higher thn the ontrol n both mmonium tretments; in Otober, the ph of the ontrol n mmonium 4.5 b b 4.0 b pet ph 3.5 3.0 Fig. 3 2.5 Control Ammoni Ammonium Ammonium + PK Tretment + PK Pet ph (men + s.e.m.) from ores smple in June (open brs) n Otober (she brs) 2008 (n = 4 per tretment.). Brs with the sme letters in June or Otober re not signifintly ifferent (P > 0.05). Refer to Tb. 1 for etils of the ifferent tretments. + PK plots ws signifintly lower thn the mmoni n both nitrte tretments. There ws signifint orreltion between pet ph n grvimetri wter ontent in June (r = 0.474, P < 0.05) but not in Otober (r = 0.006, P > 0.05). 3.3. Surfe litter n pet C:N rtios Surfe litter n pet smples (0 10 m epth) from the ontrol n tretments reeiving the highest nutrient itions (without PK) were nlyse for totl rbon n nitrogen to provie n inition of whether high nutrient input h ltere litter n pet qulity. Lower C:N rtios ompre to the ontrol, ue to the higher N ontent, woul suggest improve substrte qulity. Although the surfe litter C:N rtios ppere to be lower in the mmonium

C:N rtio Response of enhytreis to nitrogen eposition 231 50 40 30 20 10 Fig. 4 0 Control Ammonium Tretment Tretment C:N rtios (men + s.e.m.) of surfe litter (open brs) n pet (0 10 m epth; she brs) smple from the ontrol, mmonium n nitrte plots (n = 4). Refer to Tb. 1 for etils of the ifferent tretments.. n nitrte plots, this ws not signifintly ifferent ompre to the C:N rtio of the ontrol plots (Fig. 4). Pet C:N rtios (0 10 m) were lso similr between tretments. There were no signifint ifferenes between surfe litter n pet C:N rtios for eh tretment. 3.4 Enhytrei bunne Overll enhytrei bunne ws greter in smples tken in June ompre to Otober, P < 0.005 (Fig. 5A). In the smples tken in June, mmonium + PK ition inrese enhytrei bunne ompre to the ontrol (P < 0.05). In ontrst, mmoni n nitrte itions ppere to lower enhytrei bunne. In Otober, no enhytreis were foun in the mmoni trete plots n there ws no ifferene in bunne between the ontrol n other tretments (P > 0.05). There were signifint negtive orreltions between pet ph n enhytrei bunne (r = 0.475, P < 0.05) n wter ontent n enhytrei bunne (r = 0.519, P < 0.01) in June. There were no orreltions between these vribles n enhytreis in Otober (ph: r = 0.343, P > 0.05; moisture ontent: r = 0.063, P > 0.05). Enhytrei bunne ws lso lulte per g ry wt of the pet smples (Fig. 5B) to reflet the ifferene in moisture ontent mesure in June n Otober. Here, there ws no

232 Mirn Prenergst-Miller et l. 60 50 A b Number per smple 40 30 20 Enhytrei bunne 10 0 8 B Number g -1 ry wt 6 4 2 0 b b Control Ammoni Ammonium Ammonium + PK Tretment + PK Fig. 5 Enhytrei bunne (men + s.e.m.) extrte from pet ores t eh tretment in June (open brs) n Otober (she brs) 2008; n = 4 per tretment. Enhytrei bunne is represente s number per smple (A) n number per g ry pet (B). Brs with the sme letters in June or Otober re not signifintly ifferent (P > 0.05). Refer to Tb. 1 for etils of the ifferent tretments.

Response of enhytreis to nitrogen eposition 233 signifint ifferene in enhytrei bunne between the two smpling times. N tretment h no effet on bunne in Otober, but in June, the number of enhytries ws highest in the mmonium n mmonium + PK tretments (P < 0.05). 4. Disussion This pper hs resse the question of enhytrei sensitivity (bunne) to N form n other rivers, using N mnipultion experiment on n ombrotrophi pet bog, Whim Moss, to etermine if high N eposition (in the form of reue n oxiise, wet n ry N) hs ffete the enhytreis. The results, with lower numbers in Otober when the pet ws rier, inite tht pet moisture ontent is the min ftor ontrolling enhytrei bunne. Uner wetter onitions, enhytreis respone to ition of N s mmonium + PK n the results suggest tht enhytreis were negtively ffete by mmoni, nitrte, n to lesser extent by nitrte + PK. Aitions of the ifferent N forms h signifint effet on soil ph n it seems likely tht the enhytrei response to the ifferent N itions reflets these ph hnges, rther thn hnges in litter or pet N sttus. 4.1 Site onitions Pet moisture n temperture re importnt ftors ontrolling enhytrei bunne, n in the UK, enhytreis re most bunnt uring the summer months with numbers elining in winter (Pehey 1963, Cole et l. 2002). Here lso, enhytrei bunne ws highest in June, implying more fvourble environmentl onitions thn in Otober when pet temperture ws lower. However, pet smples were only tken to epth of 10 m, n it is possible tht the enhytreis h migrte eeper into the pet prior to the Otober smpling to voi esition (Springett et l. 1970). The wek orreltion between pet moisture n ph suggests tht lower pet moisture my lso hve ffete the pet ph, whih ws lower in Otober ompre to June. This mens tht site wetness, s n importnt regultor of enhytrei bunne, will etermine whether ny response to hbitt perturbtion n be iserne; this highlights the nee for regulr smpling. 4.2 Effet of N eposition on enhytreis High N eposition in ifferent forms (mmoni vs. mmonium or nitrte) hs h vrible effets on the vegettion t Whim Moss (Crfre et l. 2005, Sheppr et l. 2008). After four yers of tretment (2002 2006), high N eposition s ry mmoni eposition, hs h mrke effet on the ominnt erioi Cllun; folir N onentrtions hve inrese n the plnts re more sensitive to stresses from rought, frost n pthogens (Sheppr et l. 2008). The istribution of sensitive moss n lihen speies hs lso been negtively ffete t high mmoni onentrtions. The effet on the vegettion is lerly seen lose to the point soure, where the Cllun hs been blehe. However, on the wet eposition plots, reue N (s mmonium) n oxiise N (s nitrte) t equivlent N oses hve proue only smll

234 Mirn Prenergst-Miller et l. inreses in folir N onentrtions n inrese Cllun over (Sheppr et l. 2008). Anlysis of surfe litter n pet smples from the ontrol n wet eposition plots (Fig. 4) showe no signifint effet of N eposition, suggesting the response shown by the enhytreis in these plots to N tretment ws not meite vi substrte qulity. Below-groun, high N eposition hs ffete pet hemistry. Compre to the mbient (ontrol) site, mmoni n nitrte eposition hve inrese the pet ph, n these trens i not hnge with rier pet onitions. In ontrst, there hs been no signifint hnge in the ph of the mmonium plots. At the high mmoni site, the higher ph (ph 4.2), ompre to the ontrol plot (ph 3.6), now exees the rnge tolerte by Cognetti sphgnetorum (ph 2.7 to 3.8 (Yesmin et l. 1995)), n this oul explin the very low numbers reore from this plot, even though the pet moisture ontent here ws high in June. On the wet eposition plots, the form of N hs h ontrsting effets: eposition s mmonium inrese enhytrei numbers, wheres numbers re lower on the nitrte plots, whih hve higher ph (ph 3.8). These observtions strongly suggest tht the ifferent N forms re ffeting enhytrei bunne vi soil ph. In orer to test the effet of N form lone, we woul nee to ountert the ph effet. The inlusion of itionl nutrients (phosphorus n potssium) hs slightly inrese enhytrei bunne in both the mmonium n nitrte PK tretments. The higher bunne from the nitrte + PK tretment suggests tht the extr nutrients n meliorte the negtive effet of nitrte on its own. Therefore, these essentil elements my be limiting enhytrei bunne t the site, s the enhytreis pper to nee PK to inrese their bunne. 4.3 Long-term N eposition reues speies iversity Despite the inrese in enhytrei numbers from the mmonium plots, the speies iversity t the site hs been lowere. In April 2002, survey of enhytreis from ross the site foun five enhytrei speies, ominte by C. sphgnetorum with 83 % bunne (V. Stnen pers. omm.). Other speies foun were Mesenhytreus snguineus, M. flvus, Cernosvitoviell spp., n Mrionin lvt. In the 2005 stuy, only three speies were ientifie: C. sphgnetorum, M. snguineus, n Cernosvitoviell spp. (Prenergst-Miller et l. 2008). In this stuy, only C. sphgnetorum ws ientifie. Thompson (2003) suggeste tht n improvement in N onitions woul result in the replement of C. sphgnetorum with other enhytrei speies tht prefer less ii onitions. Our results from smples tken fter six yers of elevte N eposition suggest tht high N eposition is hving negtive impt on speies iversity. However, given the ontrol plots lso h only one speies, it is possible tht other environmentl ftors hve ontribute to the loss of speies iversity. 4.4. Conlusions The results inite tht the form of N shoul be tken into ount when investigting N eposition effets on enhytrei bunne. The reson for this ppers to be linke to the effet of N on pet ph, rther thn through eutrophition effets. On the sme site, mmoni, mmonium n nitrte re hving ontrsting effets on enhytrei bunne. This observtion points to the nee to monitor more frequently to ppreite the signifine of environmentl influenes (espeilly moisture ontent) on enhytrei bunne in orer to

Response of enhytreis to nitrogen eposition 235 be ble to seprte these effets from those of nthropogeni influenes. The signifine of N eposition for enhytreis is still not resolve, lthough this experiment suggests tht in bogs PK vilbility my lso be limiting, n thus moifying the N response. 5. Aknowlegements Funing ws provie by DEFRA n CEH. The uthors woul like to thnk CEH Lnster for CN nlysis n Anni Vuohelinen for smple preprtion. 6. Referenes Aerts, R., B. Wllen & N. Mlmer (1992): Growth-limiting nutrients in Sphgnum-ominte bogs subjet to low n high tmospheri nitrogen supply. Journl of Eology 80: 131 140. Bobbink, R., M. Hornung & J. G. M. Roelofs (1998): The effets of ir-borne nitrogen pollutnts on speies iversity in nturl n semi-nturl Europen vegettion. Journl of Eology 86: 717 738. Crfre, J. A., L. J. Sheppr, J. A. Rven, I. Leith, W. Stein, A. Crossley & M. Theobl (2005): Erly effets of tmospheri mmoni eposition on Cllun vulgris (L.) Hull growing on n ombrotrophi pet bog. Wter, Air, n Soil Pollution: Fous 4: 229 239. Cole, L., R. D. Brgett & P. Ineson (2000): Enhytrei worms (Oligohet) enhne minerliztion of rbon in orgni upln soils. Europen Journl of Soil Siene 51: 185 192. Cole, L., R. D. Brgett, P. Ineson & J. K. Amson (2002): Reltionships between enhytrei worms (Oligohet), limte hnge, n the relese of issolve orgni rbon from blnket pet in northern Engln. Soil Biology n Biohemistry 34: 599 607. Coulson, J. C. & J. Butterfiel (1978): An investigtion of the bioti ftors etermining the rtes of plnt eomposition on blnket bog. Journl of Eology 66: 631 650. Dien, W. & J. Römbke (2001): Enhytreis s initor orgnisms for hemil stress in terrestril eosystems. Eotoxiology n Environmentl Sfety 50: 25 43. Gllowy, J. N., A. R. Townsen, J. W. Erismn, M. Bekun, Z. Ci, J. R. Freney, L. A. Mrtinelli, S. P. Seitzinger & M. A. Sutton (2008): Trnsformtion of the nitrogen yle: Reent trens, questions, n potentil solutions. Siene 320: 889 892. Lkso, J. & H. Setälä (1999): Sensitivity of primry proution to hnges in the rhiteture of belowgroun foo webs. Oikos 87: 57 64. Lmers, L. P. M., R. Bobbink & J. G. M. Roelofs (2000): Nturl nitrogen filter fils in pollute rise bogs. Globl Chnge Biology 6: 583 586. Leith, I. D., L. J. Sheppr, D. Fowler, J. N. Cpe, M. Jones, A. Crossley, K. J. Hrgreves, Y. S. Tng, M. Theobl & M. A. Sutton (2004): Quntifying ry NH 3 eposition to n ombrotrophi bog from n utomte NH 3 fiel relese system. Wter, Air, n Soil Pollution: Fous 4: 207 218. O Connor, F. B. (1957): An eologil stuy of the enhytrei worm popultion of oniferous forest soil. Oikos 8: 161 199. Pehey, J. E. (1963): Stuies on the Enhytreie (Oligohet) of moorln soil. Peobiologi 2: 81 95. Prenergst-Miller, M., L. Cole, V. Stnen, R. Rees, J. Prker, I. Leith & L. Sheppr (2008): Are enhytrei worms (Oligohet) sensitive initors of mmoni-n impts on n ombrotrophi bog? Europen Journl of Soil Biology 44: 101 108. Rowell, J. S. (1991): British plnt ommunities. Volume 2: mires n heths. Cmbrige University Press, Cmbrige, (Engln); New York: 640 pp.

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