Effects Of The Casing Soil Properties On Mycelium Biomass Of Agaricus Mushroom And Its Microbial Diversity

Casing soil layer is important for the development of the cultivated mushroom, Agaricus bisporus, especially for the sporophore initiation. The dissertation was focused on: a) searching medium of casing spawn for improvement of mycelia cloning in casing soil layer; b) analyzing the cultured bacterial population, PLFA and DGGE map of casing soil in different cropping stages together with the soil's characteristic and c) application and establishment of a system for evaluative the casing soil based on physical and chemical properties, the structure of microbial community and PCR-DGGE map. The major results are summarized as follows:1 Effect of properties of different casing soils on the mushroom growthIn the tested material used as the casing soil, peat is the best for the development of mycelium and fruit. And the other three industrial or agricultural wastes are better the normal casing soil used in China.Air-filled porosity was an important chemical factor affecting the development of mushroom; but not a promotive key. Electrical conductivity and C value of pH could reflect the increment and activity of mushroom growth, which indicated the mushroom fruit increment and productivity.Mushroom productivity was positively correlated with water retention of the casing soil. Taken the cost into a commercial account, soil with 50% peat was the most suitable in agricultural manufacture.2 Mediam selection of casing spawnThe best components as casing spawn material were determined. At 18℃～20℃, A. bisporus has 10 days for post maturation; while Agaricus bitorquis has 15 days. Different spawning methods were applied in the different cases with different casing materials. Mixture spawning with a spawning rate of 2.5 kg/m~3 was suitable if peat or soil (with rice husk) was used; and surface spawning with a spawning rate of 1.5 kg/m~3 was suitable if river silt was used. Moreover, in the former case, the mushroom productivity was increased by 15%～20%; and in the latter case, the productivity was increased by over 12%.3 The growth and decline regularity of cultured bacteria in different casing soil of Agaricus mushroomThe growth and decline regularity of bacteria in 5 different casing soils were investigated by using plate culture techniques, the soil samples were collected during different growth periods of Agaricus mushroom. Results revealed that bacterial populations increased with mushroom mycelial growth in casing soil, the bacterial populations in different casing soils were in direct proportion to the quantity of mushroom mycelia in casing soil. Of all casing soils, the bacterial populations increased to a peak point when primordium formation, and then decreased to a valley point before harvest, but the bacterial populations increased again rapidly after harvest when mushroom mycelia return to growth, it indicted that the growth and decline regularity of bacteria in casing soil was in direct proportion to the activity of mushroom mycelial growth and metabolism.4 Microbial community structure of casing soil during A. bisporus growthThe phospholipid fatty acid (PLFA) profiles of the casing soil at different mushroom cropping stages were investigated. The change in soil bacterial PLFAs was always accompanied by a change in the soil fungal PLFAs. There was a significant increase in the ratio of fungal to bacterial PLFAs during mushroom growth. Multivariate analysis of PLFA data demonstrated that the mushroom cropping stage could considerably affect the microbial community structure of the casing soil. The bacterial population increased significantly from the casing soil application to the primordia formation stage of the first flush. Casing soil application resulted in an increase in the ratio of gram-negative bacterial PLFAs to gram-positive bacterial PLFAs, which may suggest that some gram-negative bacteria play an important role in mushroom sporophore initiation.5 Molecular characteristics of microbiology diversity in different casing soilThe bands in the bacterial DGGE maps of the different casing soil in the distinct mushroom growing-phases differed in numbers and lighteness, which indicated that the diverseities of the bacterial communities in the different testing soil were different. As the mushroom was growing, the amount of bands in the DGGE map was increased and the lighteness was.enhanced, which suggested that the diverseity of the bacterial community was affected by the mushroom; and these were consistent with the results obtained from the PLFA assays. Based on the observation from the DGGE map of the casing soil, on which the mushroom had high output, the propagation of some bacterial communities which were represented by three special bands were initiated; and the result probably signified a choice symbiotic interaction between the mushroom and these bacteria.6 Application and establishment of evaluative system for mushroom casing soilAccording to the above results, an evaluative system was established for mushroom casing soil based on its properties, population of microbial community and even the molecular character of the population in the casing soil. Considering the nowaday situation in China, casing soil of high quality should be: a) under a applied tensions of 0～-17.28 kPa, water release curve is highly soaring and water retention is higher than 50%; b) soil aggregates is uniform and AFP(l) is ranged in 6%～10%; c) about 9 days after casing soil application, the C value of electrical conductivity is higher than 9, and the cultured bacterium should increase to more than 100 folds; d) the lightness of the three special bands in casing soil bacterial DGGE map should be enhanced during the mushroom mycelial growth in casing soil. It was proved that applying peat or the mixture (peat:soil =1:1) which is up to the standards above as casing soil could significantly increase the mushroom productivity.