Understanding the role of soil microorganisms in sustainable agriculture

2019-09-29 In­ten­si­ve agri­cul­tu­re has led to over-uti­li­sa­ti­on of mi­ne­ral fer­ti­li­sers for in­cre­a­sing crop pro­duc­tivi­ty. Sub­se­quent­ly, this has re­sul­ted in huge eco­no­mic and en­vi­ron­men­tal costs as well as bio­di­ver­si­ty los­ses. Un­der­stan­ding and har­n­es­sing plant-mi­cro­be in­ter­ac­tions may lead to a much more ef­fec­tive fer­ti­li­ser use in agri­cul­tu­re.

Ac­cor­ding to cal­cu­la­ti­ons by the United Na­ti­ons, al­most ten bil­li­on peop­le will live on earth in 2050. To feed the world's po­pu­la­ti­on, agri­cul­tu­re nee­ds new ob­jec­tives. Mi­ne­ral fer­ti­li­sers used in mo­dern agro­eco­sys­tems are neit­her ef­fi­ci­ent nor sustainable: "Most plants only ab­sorb part of the fer­ti­li­ser ap­p­lied. The rest re­aches the ground­wa­ter, soils aci­di­fy and green­hou­se ga­ses are re­leased," ex­plains Dr. Amit Ku­mar. The eco­lo­gist of Prof. Vicky Tem­per­ton's re­se­arch group the­re­fo­re looks at na­tu­ral soil pro­ces­ses as part of the "IN­PLA­MINT" re­se­arch pro­ject wi­t­hin the BMBF Bo­den als Nach­hal­ti­ge Re­sour­ce (Bo­Na­Res) pro­gram­me. He finds them in the di­ver­si­ty of crops and in the soils them­sel­ves: "We want to bet­ter un­der­stand the plant-soil mi­cro­or­ga­nism’s in­ter­ac­tions in re­la­ti­on to fer­ti­li­sa­ti­on and crop im­pro­ve­ment. Soil mi­cro­or­ga­nisms have the po­ten­ti­al to im­pro­ve crop per­for­mance. We know that cer­tain bac­te­ria and fun­gi pro­mo­te or in­hi­bit the growth of plants, but we still don’t suf­fi­ci­ent­ly un­der­stand why. At the mo­ment it is of­ten a black box into which we reach and mea­su­re so­me­thing and we want to go much fur­ther than this." said Dr. Ku­mar. 

Fin­dings from the IN­PLA­MINT con­sor­ti­um, which in­clu­des part­ners stu­dy­ing agro­no­my, mi­cro­bio­lo­gy, ga­seous emis­si­ons and eco­sys­tem ser­vices, aim to pro­vi­de new agri­cul­tu­ral con­cepts for re­du­cing fer­ti­li­ser in­put whilst still ge­ne­ra­ting high agri­cul­tu­ral yiel­ds. For ex­amp­le, agri­cul­tu­ral prac­tices have pro­ven that gro­wing the same crop over and over again si­gni­fi­cant­ly re­du­ces the yield. The re­a­son be­hind this is that cer­tain soil pa­tho­gens ac­cu­mu­la­te if the same (host) crop is grown con­ti­nuous­ly in one lo­ca­ti­on. Is such plant- soil-feed­back ef­fect (PSF) stron­ger when more my­cor­r­hi­zal fun­gal spe­cies are in­vol­ved? To an­s­wer this Ku­mar and Tem­per­ton have set up a green­hou­se ex­pe­ri­ment with soils, which har­bour dis­tinct my­cor­r­hi­zal fun­gal di­ver­si­ty, from the In­den mine in Nord­rhein West­fa­len. They in­ves­ti­ga­te, whe­ther the soil mi­cro­bi­al le­ga­cy or the ef­fect of the cur­rent plant af­fects fu­ture plant per­for­mance on the same soil to a hig­her de­gree. “We collec­ted soils from the­re as they have a dif­fe­rent mi­cro­bi­al di­ver­si­ty and we want to see the ef­fects of this mi­cro­bi­al di­ver­si­ty on crop per­for­mance”, Ku­mar ex­plains.
Ku­mar has so far found that both soil le­ga­cy and the re­cent crop (faba bean or oats) have strong yet dis­tinct ef­fects on the sub­se­quent crop per­for­mance, and the­se fin­dings along with fur­ther ex­pe­ri­ments should al­low us to sug­gest new crop ro­ta­ti­on ma­nage­ment prac­tices that will be then fur­ther tested for their re­spec­tive eco­sys­tem ser­vice pro­vi­si­on. 

Re­se­arch in the field is com­plex, as the plant-mi­cro­bi­al in­ter­ac­tions un­der real far­ming con­di­ti­ons are of­ten af­fec­ted by the en­vi­ron­ment. Dr. Ku­mar, the­re­fo­re, also works in a re­gu­lar agri­cul­tu­ral field whe­re he grows dif­fe­rent crops in mo­no­cul­tu­res and in a ‘team of two’. The selec­tion of crops for this in­ter­crop­ping ex­pe­ri­ment is ba­sed on the crop’s mu­tua­lis­tic in­ter­ac­tions with cer­tain soil mi­cro­or­ga­nisms. This no­vel idea will lead us to know­ledge of the best com­bi­na­ti­ons of crops in mix­tu­res, which get the ma­xi­mum be­ne­fits from mo­bi­li­sa­ti­on of re­sour­ces through mu­tua­lism with be­ne­fi­ci­al soil mi­cro­or­ga­nisms.  

In ad­di­ti­on, Ku­mar looks at the ef­fects of soil nut­ri­ents on the hi­d­den half of the plant, its roots. Lon­ger, thin­ner roots are bet­ter sui­ted for ab­sor­bing nut­ri­ents than short, thick roots. He in­ves­ti­ga­tes how root growth re­s­pon­ses are af­fec­ted by cer­tain soil nut­ri­ents, which can la­ter be selec­ted as spe­ci­fic traits for ge­ne­tic plant bree­ders to de­ve­lop no­vel crop va­rie­ties. 
This se­cond pha­se of the IN­PLA­MINT pro­ject – in­cre­a­sing the ef­fi­ci­en­cy of agri­cul­tu­ral nut­ri­ent use by op­ti­mi­sing plant-soil-mi­cro­bi­al in­ter­ac­tions – is fun­ded by the BMBF with ap­pro­xi­mate­ly 317,000 eu­ros.

Amit Kumar ©Leuphana/Patrizia Jäger
Dr. Amit Ku­mar