Study On The Effect Of Pesticides Such As Triadimefon On Paddy Soil Culturable Fungal Community And SSDs

As an important constituent of soil microorganisms, soil fungi play an important role in the nitrogen and carbon cycle in soils. Extensive applications of pesticides in rice fields in recent yearshave caused serious pollutions in paddy soils. Therefore, effects of pesticides on soil microorganisms have become an important indicator to evaluate their ecological security. At present, there are many reports on the effect of pesticides on soil microbial but less for paddy soil microorganisms, especially paddysoil fungi. Soil microorganisms can influence the ricegrowth through taking part in the material circulation and energy flow in paddy field ecosystem.Study on the effect of rice fungicides on paddy soil indigenous fungi communityis very important for us to understand the ecological effect of fungicides.1. We identified12kinds of paddy soil fungi through the morphological characteristics and sequence of ITS-5.8s rDNA including two species of Trichoderma. Penicillium, Aspergillus and Fusarium, respectively, and one specie of Colletotrichum, Rhizopus, Botrytis. Puccinia, respectively.2. The activity of six kinds of pesticides against the above12kinds of fungi was determined through mycelium growth rate tests and the SSDs curve of four kinds of pesticides was built. Meanwhile, the joint action of carbendazim and prochloraz was assessed. The results showed that prochloraz strongly inhibited the mycelial growth of eight species of fungi with the EC50from0.090to3.063mg/L, while the EC50of carbendazim and triadimefon ranged from0.154to1.837mg/L, and from0.571to8.479mg/L, respectively. However, all fungi showed low sensitivity to validamycin. with EC50from12.116to93.956mg/L. SSDs curve-based analysis indicated that significant differences of sensitivity were attributed to species-variation. When the complex ratios of carbendazim with prochloraz was3:2,1:1and7:3. co-toxicity coefficients were161.616.103.485and104.529, respectively.3. The effects of different concentrations of carbendazim and triadimefon on soil fungal populations and their residual dynamics were further studied in asimulativesoil ecosystem. The results showed that both carbendazim and triadimefon inhibited soil fungal populationsat different dose treatments. And, this inhibition increased as the fungicide dose rised. However, this inhibitory effect tended to decrease, and gradually returned to normal leve as the timeprolonged. Moreover, soil fungi might promote the degradation of these two fungicides.4. Compared with the non-sterilized, the half-life of triadimefon and carbendazim in sterilized soil is significantly longer. The degradation half-life of sterilization is three to five times of non-sterilized. Under the same conditions, the carbendazim degradation rate of high concentration group is higher than the low concentration group. Some soil fungus (Penicillium and Aspergillus) may play a certain role on the degradation of these two kinds of pesticides.