Mechanisms Of Soil Microbiome In Mediating Interspecific Interactions And Plant Diversity-Productivity Relationship

In both natural ecosystems and intercropping agroecosystems,plant community productivity generally enhances with increasing plant diversity.The mechanisms underlying this positive plant diversity-productivity relationship were mainly attributed to abiotic factors,including niche complementarity and interspecific facilitation.However,biotic factors,in particular soil microbes are still poorly understood.Plants and soil microorganisms are intimate and form complex interactions.Understanding the effect of soil microbiome on interspecific interactions and plant diversity-productivity relationship are crucial to optimize cropping systems,improve productivity and resources use efficiency,and promote sustainable development of agriculture and ecosystem services.In the present study,by applying the methodology of plant-soil feedbacks,we explored the effects of arbuscular mycorrhizal fungi(AMF),soil-borne pathogens or different soil microbiota in intercropping and the late-successional plant community.Our research included four aspects:(1)the role of AMF in regulating interspecific interactions and productivity of maize/faba bean intercropping under different levels of water and phosphorus(P);(2)In wheat/faba bean intercropping,the effect of dual inoculations of AMF and take-all disease(Gaeumannomyces graminis var.tritici)on interspecific interactions of wheat and faba bean as well as the growth of weed species(Chenopodium album Linn);(3)The contribution of plant-soil feedback of AMF and take-all on wheat/faba bean intercropping;(4)the influence of different soil microbiota(AMF,old field and remnant prairie soil)on plant-plant interactions and diversity-productivity relationship of late successional plant community.The main results were as follows:(1)Maize/faba bean biomass was higher in intercropping than in monoculture,resulted in intercropping advantage(overyielding).The inoculation of AMF(Funneliformis mosseae)had significant effect on intercropping,and total biomass was increased by 21.1%compared with monoculture.At low P level(10 mg kg-1),overyielding was mainly due to AMF mediated increase of maize biomass,while AMF showed no significant effect on faba bean biomass.At high P(100 mg kg-1),overyielding was found in all the treatments,regardless of AMF.AMF significantly improved water use efficiency(WUE)of maize monoculture and maize/faba bean intercropping,in particular at low P level.However,WUE of faba bean was not significantly affected by AMF.At low P level,AMF might be a prerequisite to overyielding as AMf mediated resource partitioning by asymmetrically improving growth and water uptake of maize plants but not faba bean.(2)The inoculation of take-all significantly reduced wheat biomass and N,P uptake.The effect was significant in wheat/faba bean and wheat/faba bea/Chenopodium album intercropping.By contrast,take-all indirectly improved faba bean biomass and nutrient uptake in intercropping.On average take-all reduced intercropped wheat biomass by 31.0%,while intercropped faba bean biomass was increased by 30.4%.Consequently,the asymmetric competition between wheat and faba bean caused by take-all maintained productivity of wheat/faba bean.In the absence of take-all,wheat showed competitive advantage against C.album,and was inferior to faba bean.However,the presence of take-all significantly decreased wheat competitive ability against those two species.Our results indicated that take-all sustained wheat/faba bean intercropping biomass by asymmetrically mediating competitive relationships between intercropped plants and neighbouring weeds.(3)In the plant-soil feedback experiment,both wheat and faba bean showed negative feedback effect.Negative feedback was present in the presence of take-all for wheat.Wheat biomass increased by an average of 6.6%in faba bean conditioned soil and 4.9%in intercropping conditioned soil,compared to soil conditioned by wheat.Faba bean showed negative feedback in all inoculation treatments.Faba bean biomass increased by an average of 3.7%and 8.2%in wheat and intercropping conditioned soil respectively,compared to that in faba bean conditioned soil.Both wheat and faba bean biomass were higher in intercropped than in monoculture soils,indicating positive legacy benefit of intercropping.Moreover,the legacy benefit of faba bean was larger than that of wheat.Intercropping advantage was mainly attributable to the decrease of negative effects caused by take-all on wheat and potential pathogens on faba bean,and simultaneously compensatively improving the growth of faba bean.(4)The growth of three late successional plants,Andropogon gerardii(grass),Amorpha canescens(legume),Liatris pycnostachya(forb)were dependent on soil microbes in the live soils(AMF,old field and remnant prairie),while plant biomass was significantly decreased in the sterilized soil.The positive relationship of plant diversity-productivity was observed in old field and remnant prairie soils,but not in the AMF treatment.Amorpha showed positive density-dependent effects.Shoot biomass was improved with the increase of plant density,while Andropogon and Liatris showed negative and neutral density-dependent.Andropogon grew better and attained more N and P in mixture than in monoculture,while the biomass of both Amorpha and Liatris was suppressed when in mixture with Andropogon.Compared with AMF treatment,soil fungal and AMF community structure were significantly different among three plant species in the old field and remnant prairie soils.The growth of Andropogon was worse in soils conditioned by conspecifics than by heterospecifics,showing negative plant-soil feedback,while Amorpha and Liatris showed positive and neutral feedbacks respectively.Further analysis indicated that the potential pathogen release and nutrient facilitation by other microbials(rhizobia and AMF)in mixture benefited Andropogon and resulted in overyielding of the plant diversity community.Overall,beneficial microorganisms(AMF and rhizobium)led to overyielding by mediating interspecific resources partitioning.Soil pathogens reduced host plants fitness and growth,while compensatively increased the growth of neighbor plants.In intercropping and natural ecosystems,negative plant-soil feedbacks caused by soil pathogens may enhance productivity of plant community.This dissertation provides theoretical evidence for screening suitable crop combinations,optimizing cultivation systems and maximizing the advantage of intercropping or rotation based on plant-soil-microbiome interactions.