Study On Microbial Degradation Of Crop Stalks

The work was microbial degradation of the stalks for restoring the degenerated black soil. Return of the stalks degraded by microorganisms to the field benefit not only to the environments but also to the restoration of the degenerated black soil, it benefit to the development of green agriculture and continuation development of agriculture. The main content of the work was screening microorganisms that could both degrade stalks and promote crop growth. Following work included: isolation of fungi, bacteria and actinomycetes that could degrade stalks; measurement of the capability and rough extent of the degradation; evaluation of the effects of the addings to the degradation; tests of the effects of the degradation inoculated with mixed microorganisms and the competition between the microorganisms; tests of the effects of inoculation with selected filamentous fungi that could degrade stalks on the growth and germination of maize seedling in the potted trials; evaluation of solid fermentation of the stalks using chosed microorgansms. Some strains of microorganisms that could both degrade stalks and promote maize growth were got, programmed degradation of the stalks using microorganisms was put forward. The detailed methods and contents of the research work could be seen as following:A new simple method to isolate filamentous fungi that could degrade stalks was built. Fifty-six strains of fungi include 46 strains of filamentous fungi were isolated from the black soil in the northeast in China by the method. The isolation method could be summarized as: Stalks were nearly rotten after being covered with soil or compost suspension for a few days, ethanol were used to disinfect the surface of the stalks, the culture medium (Potato Dextrose Agar,PDA) were used to isolate the microorganisms in the stalks, most of the microorganisms isolated by the method are filamentous fungi. Three dry stalks include straw, soybean stalk and corn stalk are collected to be pulverized to made stalk powder. Stalk powder added with different matter (NH4NO3, yeast abstract, black soil solution) or not were recruited to made solid culture media to compare the growth of the microorganisms isolated. Results showed that there are little differences between the growths of the same strain on different media but varified differences between the growth of the different strains on the same medium. The simple medium made by stalk powders without any of the adding matters were chosen to determine whether the three stalks were degraded by the 56 strains of fungi. Results showed that all of the 46 strains of filamentous fungi isolated by the method could degrade the three stalks.Twenty-nine strains of bateria and 29 strains of actinomycetes, judging by the colonies differences on the plates, were isolated from the soil (mixture of swine manure,cattle manure,horse manure and black soil) by conventional dilution-plating method, Gaose`s medium and LB medium in which carbon component partly replaced by the three stalk powder(straw,soybean and maize stalks) were used and the cultural time were prolonged to enrich the content of the bacteria and actinomycetes that could degrade stalks. More actinomycetes were discovered on the plates of the soybean stalk enrichment and more bacteria on that of the straw enrichment. The densities of the bacteria and actinomycetes in the suspention of the microorganisms were calculated from the number of the colonies on the plates. Eight strains in the 29 bacteria and 10 strains in the 29 actinomycetes could degrade stalks tested by the determination method from the growth of the microorganisms on the medium made of the mixture powder of the three stalks. Fourteen strains of microorganisms that could degrade the mixture of the three stalks were used to make trials of the growth on the three media (each made of one of the three stalks), results showed that each of the 14 microorganisms could grow on each of the three media, and the colonies` formation of each strains on the three media were different. Stalk powder added with different matter (NH4NO3, yeast abstract, black soil solution) or not were recruited to made solid culture media to compare the growth of the 3 bacteria and 9 actinomycetes that could degrade stalks, results showed that yeast abstract promoted the growth of the 3 bacteria on the stalk powder and the other addings have little effect on them.Cooperativity in the degradation procedure in the core of the maize stalks between each 2 strains among 10 strains of filamentous fungi that could most effectively degrade stalks and colony morphologically different were studied.Results showed that each of the 10 filamentous fungi have the tendency to prevent other fungi penetrating into the space it already occupied. The method of two fungi face to face on the plates was recruited in the study of the effects between each two strains among the 10 strains of fungi on the PDA medium. Results showed that competition and antagonism were seen between most of the 10 fungi, no growth acceleration were showed.The 10 strains of fungi were identified to genus according the morphology of the colonies, the mycelium and the spores. Three (F1,F7,F10) of the 10 strains of fungi form an inhibition cycle,the three fungi taxonomically belong to Mucor,Phytium and Phytophthora. Results showed that the 10 filamentous fungi in the stalks prevent other fungi penetrating.Pot experiments effects of inoculation with each of the 44 filamentous fungi that could degrade stalks on the germination and seedling growth of maize were investigated. The results indicated that germination rate of the maize significantly (P< 0.05) reduced by inoculation of the 8 strains of fungi (F6,F7,F9,F11,F16,F17,F18 and F36) , included two most significantly treatments inoculated with F6 and F36,which 45.0% and 32.5% decreased ; The seedling biomass were also reduced 48.0% by inoculation of the fungus F36; the seedling biomass of maize prominently increased by inoculation of the two strains F5 and F45,which 35.0% and 48.0% increased .The fungi F5 and F45 were identified as Fusarium sp. and Trichoderma sp.. In conclusion, growth of the seedling of maize were significantly promoted by inoculation of the two fungi that could degrade stalks (Fusarium sp.(F5) and Trichoderma sp.(F45)). Theoretically analysis showed that filamentous fungi that could penetrate into the compact stalk all could degrade the stalk to some extent, microorganisms attached on the surface of the stalk may involved in the degradation procedure.Fungi attached on the surface of the stalk could be displayed on the PDA medium, the method is to put the stalk segments on the PDA medium and cultivate for some days,the fungi colonies could be seen on the original surface of the stalks,the fungi could also displayed in the humidity environment. A succession procedure of the microorganisms degrading stalks in soil was analysed based on the following facts and phenomena: competition results of the filamentous fungi in stalks and on PDA, the experimental phenomenon that the appearance of the colorful massive slump on the surface of half decomposed stalks, and the experimental results that only few strains of fungi could isolated from the half decomposed stalk in the soil.