Synergistic Effects Of Trichoderma Harziamum And Soil Minerals Mechanisms

Soil-borne diseases are considered to be one of the most difficult deseases to cure in the plant world.As a large country of agricultural products,vegetables,fruits and cash crops in China are often cultivated continuously in high density owing to high demand,leading to excessive consumption of soil fertility.In addition,large amounts of pesticides and fertilizers application further aggravate the deterioration of soil physical and chemical indicators,decrease soil beneficial microorganisms,and deteriorate soil self-remediation ability.Moreover,the cultivation of single plant species in the fields is serious,and multiple-cropping index is high,which provided a parasitic host and a breeding environment for native diseases and encouraged the accumulation of native diseases and diseases in the soil.At present,the methods of preventing and controlling soil-borne diseases are mainly chemical fungicides and biological fungicides.As chemical fungicides can cause serious environmental and food security problems,it is of great significance to study biological control by using biological fungicides.The objectives of this study were(ⅰ)to test whether fungal-derived iron minerals possess peroxidase-like activity,and(ⅱ)to explore the catalytic mechanisms of fungal-derived iron minerals.For these purposes,Trichoderma guizhouense NJAU4742 and iron minerals,including goethite,hematite and magnetite,were used as model fungus and mineral,respectively,due to their ubiquity in a wide range of environments and strong catalytic ability.Throughout our experiments,X-ray diffraction(XRD)、transmission electron microscope(TEM)、X-rayphotoelectron spectroscopy(XPS、high-performance liquid and synchrotron radiation techniques were integrated to identify the specific catalytic mechanisms that operate in these fungal-derived iron minerals.The effects of the interaction between trichoderma and iron mineral on the growth and reproduction of trichoderma,the generation of reactive oxygen species and the mechanism of action were also investigated.The main research results are listed as follows:(1)The addition of iron mineral did not have a significant effect on pH.Under the action of fungi,the pH of the system decreased significantly with time,and was negatively correlated with the production of soluble iron.Protons generated by the decrease of pH replaced oxygen to form proton-metal bonds with iron,which destroyed the mineral structure and promoted the dissolution of iron.Fungi-mineral interactions can significantly enhance Fe(Ⅱ)production.In comparison with biomineralization,there is no soluble iron and Fe(Ⅱ)formation in the nonbiomineralization group.The formation rates of soluble iron and Fe(Ⅱ)in different minerals are different.Moreover,different morphologies of the same mineral have significant effects on iron dissolution and Fe(Ⅱ)production,which are hematite>hematite nanocrystal>hematite nanorods,respectively.(2)The co-culture of fungus and iron mineral can significantly promote the production of hydrogen peroxide.Compared with the fungus culture treatment alone,the amount of hydrogen peroxide produced by the treatment with hydropyrite,goethite and hematite increased significantly,but the difference between different minerals was not obvious,indicating that iron mineral can promote the generation of hydrogen peroxide.Fungi can produce a large amount of superoxide,which can be converted into hydrogen peroxide under the action of superoxide dismutase,and react with iron mineral to produce Fe(Ⅱ)and hydroxyl radicals.The concentration of hydrogen peroxide was hematite nanoplate>hematite>hematite nanorods,indicating that the change of mineral surface structure could significantly affect the generation of hydrogen peroxide.The significant positive correlation between hydrogen peroxide and Fe(Ⅱ)indicated that fenton-like reaction occurred in the solution,which promoted the conversion of Fe(Ⅲ)to Fe(Ⅱ).(3)Iron oxides(hydroxides)interact with fungi to destroy the structure of the mineral itself and form mineral nanoparticles and new nano minerals.The average size of newly formed nanoparticles is less than 10nm.The formation of new biological nano mineral classes with internal activity of catalase,peroxidase activity within 72 hours after the initial is proportional to the discharge of hydroxyl radicals,nanometer mineral particles generated new catalytic decomposition of hydrogen peroxide,the hydroxyl free radicals,so that the hydrogen peroxide to maintain in the toxin levels,alleviate the pressure of the fungus to oxidative stress.Through XPS characterization,it was found that the oxygen vacancy of magnetite increased significantly after 120h of culture,which proved that oxygen vacancy promoted the magnetite nano-enzyme activity through electron transfer,and this catalytic mechanism proved that the mineral surface anion enhanced the catalytic activity of nano-enzyme.In summary,the interaction between trichoderma and iron mineral will lead to fenton-like reaction to promote the generation of a large number of hydroxyl radicals,which can effectively kill soil pathogens,and provide an advantageous means to resist native diseases.At the same time,the newly formed nano iron oxide nanoparticles have catalase activity,which can catalyze the decomposition of hydrogen peroxide,relieve the oxidative stress pressure of microorganisms in the soil,and further promote the generation of hydroxyl radicals,providing theoretical basis and technical support for biological control.In addition,the synergetic effect of trichoderma and iron minerals promotes the dissolution of iron minerals and the redox cycle of iron in the environment,releases the organic matters and trace elements fixed by iron minerals in the soil,and provides nutrients for the growth and reproduction of trichoderma and plants.