Linking the grass-endophyte symbiosis to symbiotic nitrogen-fixing bacteria of legumes and ecosystem processes

GARCIA PARISI, PABLO ADRIÁN; GRIMOLDI, AGUSTÍN ALBERTO; LATTANZI, FERNANDO; OMACINI, MARINA

Cracovia

Congreso; 7th International Symbiosis Society Congress; 2012

International Symbiosis Society

&amp;amp;lt;!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --&amp;a <!-- @page { margin: 2cm } P { margin-bottom: 0.21cm } --> There is currently much interest in understanding how symbiosis affects ecosystems functioning, but few studies have evaluated how ecosystem processes change in response to multiple symbioses. Asexual endophytic fungi (Neotyphodium spp, Clavicipitaceae) often inhabit healthy aerial tissues of cool-seasongrasses, conferring benefits such as biotic and abiotic stress tolerance, growth enhancement, and increased reproductive success. Ouraims were(1)toidentifythe impact of the grass-endophyte symbiosis ontherelationshipbetweena neighbouring legumeanditsnitrogen-fixingsymbiont,and(2)to assess the effect ofbothsymbioseson the aboveground net primary productivity(NPP).Weperformedan outdoors experimentinN-limitedmicrocosmswhere4plantsof the legumeTrifoliumrepens(Tr) grewsurroundedby16plantsof the annual grass Loliummultiflorum (Lm). Tr seedswere either inoculatedwithRhizobiumleguminosarumornot,whileLmplantspresentedhighorlowproportionofendophyte-symbioticindividuals(Lm+orLm-respectively). Lm+ plants reduced the number of nodules in Tr plants (LRT, χ22=6.38, p=0.04), but did not affect the amount of nitrogen fixed (Anova, Endophyte: F1,20=0.22, p=0.64). However, the apparenttransferoffixednitrogenfrom the legumetothegrasswas slightly higher in Lm+ than Lm- plants (F1,20=28.77, p<0.01). The presence of each symbiontincreased host plant NPP irrespectiveofitsneighbours symbioticstatus(Rhizobiumfor Tr:F1,20=16.6,p<0.01,EndophyteforLm:F1,19=15,3,p<0.01). Microcosm NPP also increasedwhen both symbiontswere present (Rhizobium:F1,20=10.76,p<0.01;Endophyte:F1,20=5.54,p=0.02). However, nor was this effect cumulative (RhizobiumxEndophyteinteraction:F1,20=0.01,p=0.92),nor did symbioticplants affect the NPP of the neighbouringplants. Instead,LmplantswerebenefitedfromsymbioticTrplantsbecauseof nitrogen transfer.Theseresultssuggest,forthefirsttime,apossible synergistic impactofbothsymbiosesinthefunctionofthewholecommunity.