Westem Wildlife Vol4, No. 3 LEGUMESIN NATIVEBUSH AND AGRICULTURE:POTENTIAL ROLES IN FIXATIONAND CYCLINGOF NITROGEN? by John S. Pate \tr /FEI.IE\CR onesees a prolific form nodules in the presenceof Y Y crop o[ lupins,peas, faba appropriatebacteria, while members beansorchickpeas, or apasture rich of the thjrd groupcannot. in clover or serradella,one Even then,inspection ofroots of immediatelythinks of bacterial- native members of Fabaceaeand inducedroot nodulesand their Mimosaceae(peas and wattles) will capacityto supply legumeswith often fail to show presence of fixedatmosphericnitrogen. Indeed, nodules, especially when dealing withoutinputs from suchcrop and withrelatively oldplants.However, pasturelegumes, broadacre farming stands of seedlingsof shortlived in mostregions of Australiawould legumes (eg Eossiaea, Acacia, be disastrouslyunprofitable, since Gompholobium, Sesbania) it is uneconomicalfor mostfarmers recruiting after recent fires would to replacethe free source ofnitrogen be expected to be well. nodulated from legumes with expensive and can be shown by various nitrogenfertilisers. chemically-based assays to be Nevertheless, it must be currently fixing appreciable rememberedthat our agricultural amountsof nitrogen. However, as systern operatesuccessfully only these stands age, nodulation through continued application of becomesmuch lessprolific or even superphosphateand, in certain totally absent.Our interpretationof circumstances,any of a numberof this phenomenonis thatthe element otherpotentiaily limiting nutrients phosphorous,normally theprincipal suchas potassium, sulphur, copper, limiting nutrient in our ecosystems, zinc,manganese, molybdenum and that suchlegumes are nodulated and, becomestransiently availableafter cobalt. By correctingsuch if so, do they fix nitrogen as a fire in the form ofdepositedash or deficiencies,a situationis created effectively as in our ameliorated releasedfrom plants killed in the in which legumes flourish and agricultural systems? fire. On the other hand, most competesuccessfully with non- As a further issue, arethere other nitrogen of above-groundbiomass fixing speciesin low nitrogensoils. classesof plant in nativevegetation is lost to the atmosphereas gaseous Additionally,where a cerealfollows which are able to engagein ammonia and oxides of nitrogen a previouslegume crop or pasture, symbiotic nitrogen fixation in a during the fire, and so under the theyield of thecereal is noticeably manner akin to legumes? The ensuing nitrogen-limited: phos- benefitedby nitrogenreleased rn remainder of this short article will phorous-sufficientconditions well- decompositionof residuesof the attempt to answer these and other nodulatedlegumes will flourish and legumesconcerned. questions,mostlyusing information compete particularly effectively Butwhat aboutnitrogen fixation which the authorand his colleagues with non-legumes. The pre- in theoriginal bushlands from which have gathered from a range of dominance of shrub legumes in ourartificial agrosystemshave been ecosystemsin southwest WA over many post fire understoreysin our created? In virtualiy all cases the past years. forest and woodland ecosystems legumesare present in significant Is it correct to assumethat all attestto this. amount in terms of numbers of legumes are capable of forming Eventually, however, once speciesand the collective biomass nodules and therefore fixing phosphorousavailability declines, which they represent.In fact in nitrogen? Legumescomprise three bothlegumes and non-legumes have some cases,such as mulga and groups, the pea family (Fabaceae), to investincreasingly in specialised certainheathland systems, legumes the acacias and their allies feeding roots and symbiotic such as wattles (Acacia spp) may (Mirnosaceae)and the cassiasand associationswith mycorrhizalfungi comprise major componentsof their allies (Caesalpiniaceae). to access insoluble forms of vegetation.Yet, is thereevidence Membersof thefirsttwo groupscan phosphorous.Ability to fix nitrogen co inued on page 9 6/ aStd uo ?anuuuor qlnos uaaqa,,ruq ,{eru faqt ]eql?urtseSSns ,{qpacuauadxe sessa:ls e:ntereduel aJB SuOrlrpuocvAA ]sa,|A pa^rl seruoloc elruJal ur?lJa3 ,{\oleq q?rqpue 1q?no:plEuos?as aql uroq sB .rEJSB'pue tJoqs .'{11ecrd,{1 a:e seun3al patooJ-,^.olleqs Iroseql ur el?.rlruJo suorl?.nuaJuo:) pelcalo:d arc selnpouasaql a1r;o:d lsorx 'eJouuaqunC q8rq tcatep u?a euo yos eqlgo sgedlsrour ,{lsnonurluoc uo selnpoN sloor sll uI selnpou 'deep 'uorlexrJ ueSorlru luarualdrur ur pelecolSu Lag (sua/?|otd Surpug lou Jo srseqeql uo fydrurs rg-ua8or1ruur ol srcBns 3urp 1er.{-,{3:e ue snsU,I'Jat2u.lotlJ)alsrse8zl erun8el uonex IeuoIlJunJ qtrm:ellelaql ?urpr,ro:dsrustueS:o ee:t reppoJ eq! pue (dds Dlaospof -uou su eurn8al e Suturuapuoc -oJcru raruJoJeql qlr^\'slna 'ou?4osnnotVBa) serun?eya,lqeu ajoJaq lnJaJeJeq ol sEq auo 'soJIJ Jlaql ur BUatJBqSurxg-ua3o:1tu umuao Jo stoor del Surle:leued 0AISSeCJnS aq1urqtrni pu? 3ur s o dut o r ep - s s o 1n 11e c ,{1deepaqt 8urlc:rcue qldep utt uaa,trlaque1s.{socs luared Soruoloc3^€q ol u,^^oqsuesq -l le selnpoupruuarad ,{pue:uddr ltlrdec ueSorlru Jo aou€uelureul JO 'apeu aABq selrurJalJslrold 'soruoloo pue paleSuolea3:21 go srelsnlc spre,nol Surlnqr:tuoJsnqt elrurel ,{q fltuet:odru1 e:o ur paJatuno3uof lluece.r 6Aeq e,\\ eq ol N pexlJ Jo stndut snonurtuoc 'aJurtsur {lqrssodpuesrsruc uaqcrluteu:: {q rod sasud:nsdn Suuq ol pue luror;ru8rstcedxa p1no,uauo epeurBuraq su palucrpur e:a.t slndut sanuuuoJr{c:eesed,{11n;sseconssarunBelpa.t r1-3uo1 f puep,a.rnba puu 'e?1nur eurn8ayuouo^oq€ eqlJo eseJ uorlexry ;o sluauodruoc etulnpou ot a:rnba: .{eqt qorq,u sarceds lue1d-rolzru eqr ur .,:runBel,{q e ets?q Jo sur?.rlsaqt Jo poepur eqt u1 uorlcnpo:dalpaonpur-erlJ ur 'serun3a1 pue ,{\eu qsng E uouexguaSolrulo s3xssqe ;c::ue? rou e^ltuu rno go ,{ueur 3ur3e3ua seteel Jo aql otldsap',{11e1ueptcu1ua?o.rlru go saqrcedtcSutxg uoSo4rupue Surcnpordtue1d aqt qtr.u Surprcutoc 'arrJ paxrJ uo luepuedep ,{1,tesq eq snlelsuortelnpou eql SurprzSe: aptq rege e,r.r1ce,{1re1ncr1:ed ot:nbruq:olf,e:se adotost rno,{q .{ra,r.,troul ylrtsa,tr ,{lot?unuoJull serrtooeq uorlsxrJ ueBorltu 'uorlexg 'efixezurlspalle'Ja,ra,nog ueSo4tu u,roqs 0J0.4^puP palelnpou lle,\\ aq uaSo:1ruut ol lno peurnl serun8eleql uorlenlts alnpoueq1;o Suruoqcun3:edo:d o1 qlrmflsnonurluoc ssal:o aroru 1ue1d pnsnunsrqt ul slrlrqrq e31nrueq1 prluosselueu?rd adf l-urqolSoueeq lsoq aq13urpr,r.o:d sueS:o crlotqut,{s sarcedspa,t r JOeUO Ur elel e punoff pu?su,iAolq ;o acuesard sel?Jrpur srqJ luruue.red,{:rec 1 'sanss11 -?uo1esaq seSSnsserpnts' oryuDq -pur,trpagrsal Jo se8pr.rSuqrqequt ?urureluoc-eLrotoBqlzJlueJ suorleyndodeurn?e1 Surlseralut .rreqlur uortctuaru8rd>1urd:o pe:3o eteofurourtrr aql 3u1u reluoc poJeluno3uaeABq e,^^uorlualuoJ ecuese:d,(qpalecrpur lseq sr srqt pue solo:eqn11oo: 3ursn,{1:epurs e.a.eqaq srql ?uqroddns seltse81nur:no 1e fqlleaq aq ol a,teqplno,l,i peulocuoo \Dau un sDJ o / / v zu Lt071 szJ ) srtBoeqs serceceur Suruaddeqsr teq,^Asr srql selnpou eql 1ng qt,tror? poddns pur'(o/,(qdoaD'()) ee?1euaa:8 ,{lqrssodpue a1e:1ru.{q pelqlqul ol uaSo:lru pexrJ luercrllns qlr,r\ anlq ?urxr;-ua3o:1ru3ur:noq:uq prolleroJ pas ,(13uor1sere seurnSel1e.rn11ncq?e 31es1rSurpr,lo:d eq o1 pelcedra aq slooJ r1elcads -t aqt q?no:qtueSorlru xg ;o uoqexrgueSo4ru pue uowlnpou p1no,tr1ue1d sq1;o sseu aqlJo 060I ;o,{cua8u 'uels,{soaa DlttlDzolJqn) eruez rno S? leql u,roul llo,{\ sr tI ot Surlunorue,{1a,lr1re11ocselnpou Va/p21.1 aql sJetu,lapuno.t3puu go uoqelndod e uoseos 8ur,ro:3 qrns spec,{cleqt u,roul IIe,{\sr lI Jo lros 'alq?asrlou ur peJelunocue.{1pcrdf1 alerlru ;o eqt ?ur:np 3ur,{::er eq ot punoJ sacrnosere8rey aqt uo,{psoru 3ur,{1e: aurn8aye qurnqtgoelnr praua8 e sy ,{:a,r.aq ,{l:rusuoseas 8ur,ro11og eql ',{lnzdec aq o1 reedde sarcadsSurxrg-uou Surleynpouuo uowrxJoJur ra,'rossrcsds Suqqrs snourun8al-uou raqlo pue.{eqlleql pueluecgtu?rsut Surpeelsrru apr,ro:d plno,tt o1ua?or1ru go :agsu".rlsosec qcns uI areserceoe eqt f q uaSorlru;oslndur reururnsur suorl?AecxeoS q8H :tuaruqsrtq€tserroql petduo:d qJIq,l.r rrlorqu,{s l"ql pauJuuoJ e^Pq 3,r fye,rrssecxelou sre sa:nle:adurel luJ\JJrU:qt ratjcse:f gJ-9,{es '.{lsnouorqcu,{s '8ursnare saun8eluou Su4tqeqoc pue lslolx ere SIIOSuaq,Lr pOt:ed ssalro eJorrrJJo erp pue seurn8alesaql qcrq,r ue?o:1ru 3ur:ds7ra1ur,ngoqs e.ro;fpo a.trlre saurn8elqn:qs qcns;o suoneyndod '0JrJ Jo serJnoseql fesse o1 anbruqcal puelueserd f ypcrd.'(lare'pouJaruoc sasEsauos uI ur lsol sstJnossJ edolosreyqels pesrlerceds e Sutsn ueSo:tru Surqsrualde.r ur a1o: 'uorle1e?a,r ue ,{e1dpuI{ e^oqe Jo ss"lJ srql luegodurr aleuruop qJrq,{\ sBrsEr? eql Jo sauln8al ,{ero1s:epun os ro uezop aqt .{uB leqt pee:?e , 11e:eua8 Jpq Jo 'sreo^ uo salnpou purJ ol palruJ sr lr .rete1ur ua?o:lru e^sq a,4^aJaH 'srlEJ]snv Surxg ur f1r..t.r1cuSurulycep 'sseleq uJelses pue uJalsal!\ :raql atrdsap a^oN 'eleqdsoqd go uorlzla?e,r e31nur 3ut: tnbce ur 3ur1c,{cueSo:1ru ;o roJ srxsrueqreu Surpueruap -f3:aue serpnlslu63el Jno stuecuoJ Surl:oddns osle 'psurelqo ueaq sAeq alrq,4Aselnpou Jo uo[eurJo] s11nse:palcsdxeun qcrq,u o1 lcnpo.rd cl1aq1u,{soloqd grd ur alduexe JequnJ V JO eJJnOSeJrreqt ;o .IIOS 8uqo.a.ep;r paSelue^psspeq sarunSal'peepul oqt Jo sJe,{eloJeJJns reeu 11a,n1q8[u 'anssr u? .ro8uolou ueql st ur sged:elunoc1e:aruaqda I aSDdtuo4pan ruor aurps alllpt1/. lof put j aqt lo raptshaN 'sraelunlo^ /no +ouueeJo slllisuoero a,^ /,\//:d*- io uols!^ladns :e+lsqel puo uolloulprooo l3olord op!^otd 'ldoc u.rocAo/qoudn@slllIsr0 :lloLUa oslouoo a/r^puD on lsnlcul llD alo s3+Dl rnoi roJlZtO tee6 outd ' '090 toe€9e06 (80) xol