Abstract：Phosphorus Solubilizing bacteria (PSB) can improve utilization of phosphorus in soil, increase soil fertility, promote plant growth, and alleviate continuous cropping obstacle. In this study, four PSB strains were screened from the rhizosphere soil, and all of them had phosphorus solubilizing ability. By the analysis of comparisons, one of them was screened and classified as Sphingomonas sp., named strain CL01. Further, the efficiency of phosphorus-solubilizing and the secreting level of indole acetic acid (IAA) were determined for the strain CL01, meanwhile, the effects on the root growth of watermelon (Citrullus lanatus) seedling were studied. The results showed that the strain CL01 was the strongest one on the capacity of phosphorus solubilizing than the other strains. Its maximum amount of phosphorus solubilizing was 642.60 mg/L, and the secretion level of IAA was up to 22.87 mg/L, which could promote the development of roots and growth of plants. The watermelon seedlings were treated with the bacterial suspension (in LB medium, OD600=0.5), for 30 d, the underground dry weight, root length, root volume, the number of root tips and the proportion of fibrous roots of watermelon seedlings were increased significantly compared with the controls (CK1, sterilized continuous cropping soil; CK2, unsterilized continuous cropping soil). The underground dry weights of the seedlings were increased by 27.04% and 103.90% compared with CK1 and CK2, respectively, The root length of the seedlings were increased by 83.60% and 63.75% compared with CK1 and CK2, respectively. The root volume of the seedlings were increased by 14.29% and 100% compared with CK1 and CK2, respectively. The number of root tips were increased by 15.16% and 85.45% compared with CK1 and CK2, respectively. The proportion of fibrous roots were increased by 47.81% and 26.80% compared with CK1 and CK2, respectively. Also the average diameter of roots was decreased by 47.89% and 66% compared with CK1 and CK2, respectively. Noticeably, if the concentration of the bacterial suspension was doubled (OD600=1.0), the similar results were obtained, but they were not as good as the lower ones. Based on the results mentioned above, we proposed that strain CL01 had the capacities to dissolve organic phosphorus efficiently and secrete IAA. While the watermelon seedling continuous cropping with the bacterial suspension (OD600=0.5), the growth of root was promoted, root morphology was optimized and the composition of root was improved. The strain CL01 is an excellent candidate for reducing continuous cropping obstacle.
Ahemad M．2014. Phosphate-solubilizing bacteria-assisted phytoremediation of metalliferous soils：a review [J]．3 Biotech, 3, Doi: 10.1007/s13205-014-0206-0de Bolle S, Gebremikael M T, Maervoet V, et al．2013. Performance of phosphate-solubilizing bacteria in soil under high phosphorus conditions [J]. Biology and fertility of soils, 49(6): 705-714．Haling R E, Brown L K, Bengough A G, et al. 2014. Root hair length and rhizosheath mass depend on soil porosity, strength and water content in barley genotypes [J]. Planta, 239(3): 643-651．Hayat R, Ahmed I, Sheirdil R A．An overview of plant growth promoting rhizobacteria (PGPR) for sustainable agriculture [M]//Crop Production for Agricultural Improvement．Springer Netherlands, 2012: 557-579．Kalia V C, Wood T K, Kumar P．2014. Evolution of resistance to quorum-sensing inhibitors[J]．Microbial ecology, 68(1): 13-23．Khan A L, Waqas M, Kang S M, et al. 2014. Bacterial endophyte Sphingomonas sp. LK11 produces gibberellins and IAA and promotes tomato plant growth [J]．Journal of Microbiology, 52(8): 689-695．Landa B B, Montes-Borrego M, Navas-Cortés J A．Use of PGPR for Controlling Soilborne Fungal Pathogens：Assessing the Factors Influencing Its Efficacy [M]//Bacteria in Agrobiology：Disease Management．Springer Berlin Heidelberg, 2013: 259-292．Lee S W, Lee S H, Balaraju K, et al．2014. Growth promotion and induced disease suppression of four vegetable crops by a selected plant growth-promoting rhizobacteria (PGPR) strain Bacillus subtilis 21-1 under two different soil conditions [J]．Acta Physiologiae Plantarum, 36(6): 1353-1362．Manickam N, Bajaj A, Saini H S, et al．2012. Surfactant mediated enhanced biodegradation of hexachlorocyclohexane (HCH) isomers by Sphingomonas sp. NM05 [J]. Biodegradation, 23(5): 673-682．Mehta P, Walia A, Chauhan A, et al．2013. Plant growth promoting traits of phosphate-solubilizing rhizobacteria isolated from apple trees in trans Himalayan region of Himachal Pradesh [J]．Archives of microbiology, 195(5): 357-369．Molla A H, Shamsuddin Z H, Halimi M S, et al．2001. Potential for enhancement of root growth and nodulation of soybean co- inoculated with Azospirillum and Bradyrhizobium in laboratory systems [J]．Soil Biology & Biochemistry, 33(4-5): 457-463．Sindhu S S, Phour M, Choudhary S R, et al．Phosphorus Cycling：Prospects of Using Rhizosphere Microorganisms for Improving Phosphorus Nutrition of Plants[M]//Geomicrobiology and Biogeochemistry．Springer Berlin Heidelberg, 2014: 199-237．Wu J, Li L, Du H, et al．2011. Biodegradation of leuco derivatives of triphenylmethane dyes by Sphingomonas sp. CM9 [J]．Biodegradation, 22(5): 897-904．Xu W, Liu D, Wu F, et al. 2015a. Root exudates of wheat are involved in suppression of Fusarium wilt in watermelon in watermelon-wheat companion cropping [J]．European Journal of Plant Pathology, 141: 209 - 216. Xu W, Wang Z, Wu F. 2015b. Companion cropping with wheat increases resistance to Fusarium wilt in watermelon and the roles of root exudates in watermelon root growth [J]．Physiological and Molecular Plant Pathology, 90: 12-20.Zemrany H E, Czarnes S, Hallett P D, et al．2007. Early changes in root characteristics of maize (Zea mays) following seed inoculation with the PGPR Azospirillum lipoferum CRT1 [J]．Plant and Soil, 291(1): 109-118．柯用春, 王爽, 任红, 等．2014. 强化还原处理对海南西瓜连作障碍土壤性质的影响[J]．生态学杂志, 33(4): 880-884．(Ke Y C, Wang S, Ren H, et al. 2014. Effects of intensively reductive treatment on soil properties in a watermelon continuous cropping obstacle field in Hainan Province [J]. Chinese Journal of Ecology, 33(4): 880-884. ) 马玲, 马琨, 汤梦洁, 等. 2013. 间作与接种 AMF 对连作土壤微生物群落结构与功能的影响[J]．生态环境学报, 22(8): 1341-1347．(Ma L, Ma K, Tang M G, et al. 2013. Effects of intercropping and inoculation of AMF on the microbial community structure and function of continuous cropping soil [J]. Ecology and Environmental Sciences, 22(8): 1341-1347. )孙建光, 张燕春, 徐晶, 等. 2010. 玉米根际高效固氮菌Sphingomonas sp. GD542的分离鉴定及接种效果初步研究[J]. 中国生态农业学报, 18(1): 89-93. (Sun J G, Zhang Y C, Xu J, et al. 2010. Isolation, identification and inoculation effect of nitrogen-fixing bacteria Sphingomonas GD542 from maize rhizosphere [J]. Chinese Journal of Eco-Agriculture, 18(1): 89?93.)檀国印, 杨志玲, 袁志林, 等．2013. 植物根际促生菌及其在克服连作障碍中的潜力[J]. 热带作物学报, 34(1): 135-141．(Tan G Y, Yang Z L, Yuan Z L, et al. 2013. Plant growth-promoting rhizobacteria and its potential in overcoming continuous cropping obstacles [J]. Chinese Journal of Tropical Crops, 34(1): 135-141．)王志刚, 徐伟慧, 莫继先, 等. 2012. 东北黑土区大豆根际促生菌群落组成研究[J]. 中国生态农业学报, 20(5): 592-596. (Wang Z G, Xu W H, Mo J X, et al. 2012. Community structure of soybean plant growth-promoting rhizobacteria in the black soil region of Northeast China [J]. Chinese Journal of Eco-Agriculture, 20(5): 592-596. )夏觅真, 马忠友, 曹媛媛, 等．棉花根际固氮菌、解磷菌及解钾菌的相互作用[J]．中国微生态学杂志, 2010, 22(2): 102-105．(Xia M Z, Ma Z Y, Cao Y Y et al. 2010. Interactions between a N-fixation bacterium, a Phosphobacterium and a K-releasing bacterium of cotton rhizosphere [J]. Chinese Journal of Microecology, 22(2): 102-105. ) 徐伟慧, 吴凤芝, 王志刚, 等．2014. 连作西瓜光合特性及抗病性对小麦伴生的响应[J]．中国生态农业学报, 22(6): 655-660．(Xu W H, Wu F Z, Wang Z G, et al. Response of photosynthetic characteristics and disease resistance of watermelon to companion with wheat [J]. Chinese Journal of Eco-Agriculture, 22(6): 655-660. )赵国杰, 牛世全, 达文燕, 等．2014. 四株无机解磷菌处理碱化土壤的理化性质及质量评价[J]．土壤通报, 45(4): 996-1002．(Zhao G J, Niu S Q, Da W Y, et al. 2014. Assessment of soil quality and physicochemical properties of the alkaline soil amended with four inorganic phosphate-dissolving microbial inoculants [J]. Chinese Journal of Soil Science, 45(4): 996-1002. )
