Effect of adding wheat straw carbon source to root knot nematode diseased soil on soil microorganism community

【Objectives】Microbial biomass and the microbial structure are very sensitive to the agricultural practices. The population of microbial biomass and its diversity in structure are important index for soil fertility, the straw returned to field affects species and quantity of soil microorganisms.Severe root-knot nematode disease often arises due to unreasonable agricultural practices, especially in the continuous cropping fields of tomato. The effect of adding straws into soil on the microbial structure and diversity and the ratio of fungus to bacteria (F/B)of mutual relations and change rule were studied to provide a way of biological remediation for the soils suffered with root knot nematode disease. 【Methods】A pot experiment using soils from successive planting of tomato and suffering from serious root knot nematode disease was conducted with a root knot nematode sensitive tomato cultivar as a tested crop. Four gradient amounts of wheat straw were designed: 0 (S0), 2.08 g/kg (S1), 4.16 g/kg (S2) and 8.32 g/kg (S3) in the experiment. The fungal biomass, bacterial biomass and microbial biomass were detected with the method of phospholipid fatty acid (PLFA).【Results】Compared with control, adding wheat straw significantly increases the amounts of total soil microbial biomass (MTB), bacterial biomass (MB) and fungal biomass (FB); increases the ratios of fungal biomass to total soil microbial biomass (FB/MTB), the ratio of fungus to bacteria (F/B). The MTB, MB, FB of S3, S2 and S1 are 30.17, 28.42 and 22.72 nmol/g, 24.27, 23.12 and 22.97 nmol/g, 5.90, 5.30 and 4.93 nmol/g, respectively. There is no significant difference in MTB and MB among the three adding treatments, but the FB of S3 is significantly higher than those of S1 and S2.The proportions of MB in soil MTB are also reduced significantly under the straw addition, and the MB possess is an overwhelming proportion in soil MTB.The average proportions of MTB are 83.10%, 82.22%, 81.35% and 80.44%, and F/B ratios are 20.30%, 21.68%, 22.94% and 24.34% in the S0, S1, S2 and S3 treatments, respectively. 【Conclusions】Adding wheat straw can improve the total microbial biomass, the bacteria biomass and the fugal biomass. the ratio of fungi population to the total microbial and to the bacteria are all increased significantly. Therefore, adding wheat straw is an effective way of remediate the biological diversity and ressistance to the root knot nematode disease. When the adding amount of the straw is 4.16 and 8.32 g/kg, the effect is more signifiant.