| Most greenhouse crops are susceptible to Fusarium spp., Phytophthora spp. and Meloidogyne spp..Fumigants are regarded as effective pesticides in controlling soil-borne diseases. The objectives, werestudied systematically through methods of selective medium, soil microbial biomass carbon andnitrogen, BIOLOG and phospholipid fatty acid analysis, are:1) the efficacies of chloropicrin (PIC) anddimethyl disulfide (DMDS) used individually or combined in the ratio1:4on Fusarium spp. andPhytophthora spp., as well as their influences on soil microbial community recovery;2) the efficacies ofadding trichoderma harzianum after fumigation with PIC and DMDS on Fusarium spp. andPhytophthora spp., as well as their influences on soil microbial community recovery.Results indicated that PIC40mg/kg showed great efficacies on control of Fusarium spp. andPhytophthora spp., and98days after fumigation, its efficacies against Fusarium spp. and Phytophthoraspp. retained over98%and55%respectively. While applied in the same dosages, PIC+DMDS (8+32)mg/kg could enhance the inhibition ratio and its duration against two soil-borne pathogens especiallyFusarium spp. compared with DMDS.In line with their influences on soil microbial biomass, PIC40mg/kg, PIC+DMDS (8+32) mg/kgand DMDS40mg/kg influenced soil microbial community functional diversity on respective degree.Additionally, all influences of fumigants on soil microbial biomass and soil microbial communityfunctional diversity had recovered to control level in98days after fumigation.PIC40mg/kg and PIC+DMDS (8+32)mg/kg significantly reduced the total soil microbial PLFAs,and their influences did not recovered to control level until77days and28days after fumigation,respectively. In line with their influences on total soil microbial PLFAs, fumigants influenced the fungiPLFAs and bacteria PLFAs in respective degree. PIC40mg/kg and PIC+DMDS (8+32) mg/kgsignificantly reduced the actinonmycete PLFAs and did not recover even in98days after fumigation.For any fumigants, adding trichoderma harzianum after fumigation had little enhancement oncontrol of Fusarium spp. and Phytophthora spp., as well as had little influence on soil microbialbiomass and soil microbial community functional diversity. However, adding trichoderma harzianumafter fumigation would, to some degree, affected the PLFAs of fungi, bacteria and actinonmycete andsoil microbial community structural diversity regardless insingnificantly influence on the ratio ofGN/GP and bacteria/fungi.In summary, fumigants which, had good efficacies in controlling Fusarium spp. and Phytophthoraspp., also significantly reduced the soil microbial biomass (soil microbial biomass carbon and nitrogen,AWCD value and total soil microbial PLFAs) and soil microbial community functional diversity(Shannon index, McIntosh index and Simpson index). However, almost all the fumigants had littleinfluence on soil microbial community structural diversity (Shannon-winner index). All the results(including soil microbial biomass and soil microbial community diversity indicators) analyzed throughsoil microbial biomass carbon and nitrogen, BIOLOG and PLFA methods have significant correlation with each other at the0.01level except the Shannon-winner index analyzed through PLFA method.Therefore, soil microbial community structural diversity would not change in terms of soil microbialbiomass and soil microbial community functional diversity.Studies indicated that, in summary, results from analysis methods such as soil microbial biomasscarbon, soil microbial biomass nitrogen, BIOLOG and PLFA are consistent with each other. What’smore, the best repeatability and reproducibility occurred in BIOLOG method while more detailinformation could be gathered by means of PLFA method. |
