Root Exudates Mediated Belowground Chemical Interactions Between Plants

Plant-plant interactions are always fundamental problems in ecology research.In particular,much attention is focused on plant-plant chemical interactions.Root exudates play a crucial role in building associations of plants on the belowground.In the present study,perennial tree(Chinese fir(Cunninghamia lanceolata)-Michelia macclurei)and annual herbaceous plant(wheats(Triticum aestivum)-heterogeneous neighbors)were choosen as a mixture research system.Biomass,root morphology,root behavior pattern,and allelochemical content as evaluation indicators were adopted through a series of field,pot and root box experiments for investigating the interspecific and chemical interactions on the belowground mediated by root exudates and trying to find potential and key components.This study can provide a theoretical basis on studying the chemical mechanism of interspecific plant-plant interactions mediated by root exudates.(1)A broadleaf species M.macclurei facilitated the performance of an autotoxic conifer Chinese fir through belowground ecological process mediated by root exudates.Mixedculture treatments improved the nutrients content(P)in soils,and rehabilitated a microbial community which was different from a pure plantation and benifical to Chinese fir growth.Not only M.macclurei root exudates as well as root rhizosphere soil stimulated the Chinese fir growth,but also the change of soil microbial community was mediated by M.macclurei root exudates indirectly.The presence of M.macclurei root exudates induced horizontal and vertical distribution change of Chinese fir roots buffered belowground competition.However,in the case of co-ourrence with Chinese fir,the biomass,root morphology and behavior of M.macclurei never changed.Through further analyze the composition and content of Chinese fir and M.macclurei root exudates,the results were obviously different.(2)Root exudates mediated the root interactions between wheats and heterospecific plants.Plants could detect neighboring plants identities,and response to multiple strategies though setting different co-ocurrence patterns(63 heterospecific species co-ocurred with conspecific neighbors(no wheat),wheats co-ocurred with 63 heterospecific species,wheats co-ocurred with conspecific neighbors).There were several predominant behavioural strategies in a mixture system:biomass,root morphology and rooting patterns.Responses in wheat root morphology were functionally mediated by phylogenetical identities of heterospecific co-ocurrence plants.The differences in responses of root morphology including the change of root system area,total root length and maxim root amplitude were found in cotyledons types,family properties.The discrepancy of plant roots in horizon levels of roots allocation showed that three rooting development patterns(unresponse,avoidance,intrusive)were found in mixture system.Root exudates could mediate the root interactions between wheats and heterospecific neighbours,with important impacts on root development patterns.Compared to control,the horizontal asymmetry of root length in adding activated carbon conditions was from avoidance,intrusive pattern to unresponse pattern.(3)The potential chemical signals in root exudates mediated chemical communication between wheats and associated plants.The DIMBOA concentration in wheat roots was affected by species and concentration of plant root exudates.When highest root exudates of associated plants were added into the soils,DIMBOA concentration was increased.This adding would reduce biomass of wheats in a long term.Judgment of six chemicals(jasmonic acid,salicylic acid,maltol,(-)loliolide,veratric acid,luteolin)in tooking part in chemical communication was conducted between wheats and associated plants.The results showed that all of six chemicals could induce the increase of wheat root DIMBOA.Jasmonic acid,salicylic acid and(-)loliolide were commom in eleven plant tissues,root exudates and rhisophere soils.The concentration of(-)loliolide in root exudates was positive correlation with induced DIMBOA concentration in wheat roots.Jasmonic acid,salicylic acid,and(-)loliolide generally existed in plant tissues of 100 large species samples.