Round table : microbial processes in paddy fields

Bullerin of Japanese Society of?.licrobial Ecolog>~

I

Sol. 5. SO. 1. 15-27, 19S9

ious. 0.ur .ving being dent upon 1

1

1 I

ISME-5

[ -

i;?."&

Round table : Microbial processes in pzddy fields rhe' great !ni on Mii

Pierre Roger

,

.i gratirude

Commiitee -id ail the 2vored for

The round table c n "Microbial process in paddy fields" was lield fioin 19GO to 2100 his on August 25. Th2 session was chaired by Dr. T. Wetanabe. Xfier the inuoducrion of the parricipants (list annexed). DÍ. Watanabe indicated Thar ;he session \vas intended for E n informal exchange of ideas and opinions. He proposed io stzit the round table s%.ith 2 brieÎ introduction o n N cycle in wer!md ricefe!ds. rhea to place emphasis on ( I ) microbial biomass jn ï-icefields, (2) denitrification, (3) nierhane production. and finally to discuss

~

, .

othe: 'iopics OE Inïeresr to the periicipants. Afieï a brief sunmarization of ilie beneficial efecrs of 3,oodipg on rice soils ferdity, Dr. Roger presenred. IRRI's work on ihe role of the photosynthetic Lquaric biomass (algae and aquatic plants) on soil processes. I32 summarized recent I estimates of C a n d - N inputs by This biomass ( i n cluding photodependent biological N, fixation) and their ckniribution to the ' maintenance of microbial biomass and available h ' in soil. Data in 19% show rhar supprssing phoros~~nrheric activ1

.

..

. Fig.

1. Conceprual scheine of the pathnxys involved i n the replenishmenr of soil miciobial biomass i n wetland ricefields. -3

.

I -

Fonds Documentaire ORSTOM

36

-*

ROGER

iry in floodwater led, during the firsr ).ear, to an unsuitable for measuring biomass C in \ r x e r average decrease by 20-2596 of soil niicrobiai logged soil. Biomass N can be estimated by FE biomass (N fkuh). Dï. Roger ended his presentabut the comeision factor needs to be examined. tion Iviih a conceprual scheme of ihe role of soil , Dr. h u b u s h i also summarized his eariy srudiej microbial biomass in \verland s;il fertility and the -_ done at IRRI \vith Dr. Waranabe on parh:va);s invoivsd i n , its repienishnent (Fig. 1). changes in microbial biomass in thïee soil y p e s Dr. Watanabe comnienicd on rhe key role of soil during a crop cycle. This \vorkl \vidi 'jN-Iabeled soiI, quantified sui1 microbial bioinass and siic.xed microbid piomass :C.Ï rice production. Mos: of the N absorbed by the rice plant conies from the that during the second part of tge crop cycle. N soil a n d adequate meThodologies are needed for absÒrbed.by the rice planr came froín rhe soil and .. . . , . esiimaiiag miciobiai biomass in wer!ands. ,. h a d ' an .isotopic composition clcse to thar of &lethodologlcal aSpeCtS, of microbial biomass '. microbial biomass. . quaniificatidr, were pesenred by.Dr. Brookes and T h e pjjticipanis aiscussed hon. a rapid t u r n o \ - a .. ,. Dï. h u b u s h i who reporred rhe rqiïlts oï a labora- .' of microbiomass N in paddy soils is p o s s i 3 e tory study comparing f ~ ~ i g z t i o n - i n c u b a r i o(FI), n despite the apparently lo\v activiry sholvn .in Îuumigarjon-e..;c.action ( F E ) , and ATP to estimare adenylate energy. charge. Dr. Wata2abe pcinied inicrobial bioimss C in an upland teniperate .soil. -ou! thar the r'apid t x n o v e r in topical. riceFields and a \\-erland iemperare rice soil. Burh soils \\.ere may be due to teinperaiurz and \i'aier saturaiion. unplanted. Under aerobic condirions biomass C Dï.Jariya Bomjawar pointed out b a r . anaerobic estiniared. by FI, FEI and ATP changed liiile conditions may stimulare ammonium excretion. during an SO-da): incubation period and yere Dï. Kanazawa then prestnied ihe ïesule of a closely corre!a~ed. But when soil was waterstudy of enzyrnaiic [hydrases) activities in the logged, bioniass C estimared b y FE decreased by rhizosphere of rice. Results shon-e2 a decrease of i0-40%. ATP EISO decreased and the ' decrease. all tested aciivities under \raterlogged conditions. had 2 Îcsier rate i h m that of biomass C. Dr. u.hi!e microbial biomass and ,?TP co!ite;lt :I;Brookes indicxed that changes in the rota! pool of creased (Fig. 2). The discrepancy benveen Lbese edminc: niicleoiids (,4TPT,ADP+A31P) more resuiis a n d ihose of Dis. Brookes and h u b u s h i csn closely ;'olIo\.-.ed the decrease in biomass C esribe espiained by a replenishrnenr of soiï rnicrobiai i;la;ed b!? FE 2s compared Ivith .ATP. Adenylzie biomass by rlie rice rhizosphere and t k c ei;erg?- charge L(.iTP=0.5 ADP)/(.ATP ADP+ phorosyntheric aquatic biomass in rhe seid sampies ,ìJi? j: decxaser2 [ïom 0.75 i o 0.31 dilring ameï-. used by Dï. Kanaza\va. The r;l.eihods of .AT? .. . o z x J ~ C S ~ ~cf~ u2isnd O Z soil and from 0.75 to exrrzcrion used by Dr. Ksnazan.a and Ers. BroaC.5-i i n rice :oil. It \l.zj concluded that FI i s kes and Inubushi \vere also diSzrent Dr. IVatanabe poiilted OU: thar. \\-hereas dirsfr nerhods for e s h a t i n g Iota! N losses I5K bzìince) 2nd N losses by a n m o n i a ~olarilizarion(micro hereoroiogical method) me availab!e. there is szill no satisfxiory meihod for diïecr measurement of N losses by denitrification. None of :he participants could suggest a ne\v approach. or afi improvement of existing merhods. for such llle3surements. Fig. 2. Schemziic rcprcscniaiion of s e a s o n a l Dr. Kno\vles presenied daia slioiving $\,idence chsnges of microbis1 counts. ~iiicrobialbiomass, for nieth~anotrophicnitrification in an organic soil. s n d rnzyrnsric sciivi[ies i n rice ïhizosphere. '

+-

.I 3 in water-

,4 m i l e d bacierial consorrium. obtained from a humis01 and incubated \\,ich mechane and a~mnionium. shou ed nitrite production during methane consumption. This n a s folloned by nirrale formation. Dr. Knowles concluded rhar such interacrions could occur in cerrain aquaiic and cerresrial ecos:, stems. Dr. 34. Kimura presented a n elec:ron microscope

!aied by F E examined. 'zïl jT studies ?Ce

__

On

soil types :fN-labeled and showed sp cycle, N :he soil and io that OF 5

study of che microbial co!onizat~on of the rice rhizoplane and its decomposirion by bacteria. Different patterns of colonization and decomposition \vere o b c r \ s d for (1) the sites oflatera! rooi emergence. ( 2 ) rhe young roots \viih mucigel a n d hairs. and ( 3 ) old roots 1viLh precipitated ferric hydroxide CO\ er.

: i

c

i

-. . ,

!id turnover

is ? o A b l e cho\\in in !x pointed :I iicefields . . sa turati.on. . anaerobic SCI erion. ?s?llt? of a .: .. :nthe i decrease of zondiriow. 'onTeni in'.'?en rhese :bushi can zlcrobia! 3nd t h e id samples of ATP Drs. Broo-

...

'. : -

.

I

i!*. ;i

- '

I

12'anie

In reresi-

Jari) a Ijoonja\s.?t. Phil Brookes S. C h a Ú d h s i

Pl, fixarion in rice. rhizosphere Soil microbia! biomass Rice culture. N1,-flxarion b>j root association.

Tse- shu Chien

Soii microbjology microbiology of methane . ... .. . . . . . ._ . __ _. . . iermenrzrionDistriburion 5: chemical acriviv of soil microorganisms N,-fisink bacteria Microbial biomass in soils Su1fa:e reducers and anaerobes EKecrs of soil macroorganisms on microbes and soi! chemistry . Enzymaric activities i n rhizosphere Rhizosphere. Denitrifkarion in phycosph-ïe. . . . N metabolism Sr inerhanouophs z-.-.-

Choseki .Furusaka KI.\R. Japan h í l E Universic

T. Gamo K.lnubushi hi a fio io 1sh i moro Eisukis F;Ikuchi

1

Tohoku Universiry

I

'

i? ?!

1:

tj

.

,

S. Kanazsn.2 AI. Kimura Roger Ki:oivles

Soil microbial biomass $,-fixing bacreria S cycle and.phoros!.nrhetic.aquaric biomass in ri c=ik! ds ~. , vr.U1. soil rerriliry, ect. E c o l o g ~of soil borne'parhogen ECO IO^ of soil microorganisms&arion ., . . - . '_". ..-. -.-.-, Ecoior, or" soil microparhogen Biomass .C and O'turno\'er

J.X. Ocio

Hiroshi Oyaizu Pierre Roser hiasoi!ori Saito Moioaki Tojo Kaki Toyot2 .. . I K\Varanabe ~O h ii 1su o W ^c ia n a be Jinshui \Vu '

,

'

.

_ _ ..._.. ..

;; I!

_i I I

._ ,I . i

..

.1.,.:

1i

+;

,

,

e\-idence ganic soil.

i

,

!i

!;

.

i!

.Q

!! .

i

.

. .

l.