Evaluation Of Physiological Activities And Growth-promoting Effects Of Κ-releasing Bacteria On Cotton

Traditionally, the liquid or solid biological products containing live microorganisms, are designated the microbial fertilizer. Using microbial agent as a fertilizer additive, to reduce the use of chemical fertilizer and pesticide and reduce the environmental pollution, microbial fertilizer has a vital role in the sustainable development of agriculture. Currently, the plant growth-promoting rhizobacteria are extensively studied, especially for the azotobacteria, K-releasing bacteria and P-releasing bacteria. In this paper, the high active K-releasing bacteria, which were isolated from cotton rhizosphere, were used as experimental materials. Then, a number of potential K-releasing strains of cotton growth promotion rhizobacteria were evaluated for their growth promotion effects on cotton.Selecting the physiological activities of indole-3-acetic acid (IAA), siderophore production and P-releasing as test indexes, the potassium bacteria were preliminary screened. From the determination of IAA produced capacity, the results showed that most of the cotton rhizosphere bacteria could produce IAA. The siderophore production of strains were tested by semi-quantitative method, using the current international standards to assess its strengths and weaknesses, five strains synthesized extreme high concentration siderophore were screened out and named strain K1111, K1114, K2115,K3105and K3205. The five strains had very strong abilities to release phosphorous in P-releasing tests. Potassium feldspar powder was used as the only source of potassium in K-releasing test, the results showed that the strains, with the exception of strain K3205, had the abilities to release Potassium and the content of Potassium was significantly high than those of the treatments without K-releasing bacteria, especially the strain K3105.From the root-box test, the number of roots of cotton seedlings inoculated with the five strains was significantly high than those of the treatments without inoculating bacteria. In the test of root activity, the results showed that the root activities of cotton seedlings inoculated with the strains were significantly high than control tests, improved24.36%than the treatments with K fertilizer. The cotton roots treated with strain K1111and K1114had the highest root activities. And the potassium content of cotton seedlings inoculated with strain Kl114was equal to those of the treatments with K fertilizer.The heights and dry weights of cotton seedlings inoculated with the five strains respectively were significantly high than those of the treatments without K fertilizer, and higher than or nearly equal to those of the treatments with K fertilizer. The heights and dry weights of cotton seedlings inoculated with strain K3105, significantly high than those of control tests and other strains. Although the strain K3205had low activity to release potassium, it had very strong abilities to release Siderophore and IAA. The root activities and biomass of cotton seedlings inoculated with strain K3205were weaker than those of the other bacteria. It revealed that the activity of potassium releasing positively correlated with the growth of the cotton.In conclusion, all the K-releasing bacteria had the unique role in the early stage of cotton growth, this may be related to the colonization of the strains on the root surface and in cotton rhizosphere.