Study On The Diazotroph Resoures In The Paddy Field In Northern China

The nitrogen fixing activity and ability of the 18diazotrophs isolated from s northern China have been confirmdwith ¹⁵N isotope tracer technique and DNA hybridization.For All the tested diazotrophs the ¹⁵Nï¼…a.e. Were 0.03-0.32ï¼…,The nitrogen ability for Azotobacter armeniacus, Azotobacternigricans and Bacillus spheaticus were much higher than others.All the DNA hibridization both with pSA30 (carried nifHDKEgene.) and pHU8 (carried nifH gene) showed positive reactions.There have been no evidences for Bacillus azotoformans,bacillus sphaericus, Enterobacter intermedium and Pseudomonasazotofotmans as diazotrophs reported with LD search exceptEnterobacter cloacae. There have been no reports about theisolation for the other 17 dizotrophs in China.The nitrogen activities were remarkably enhanced when thediazotrophs were mixing cultured with different species. Thenitrogen fixing activities (for mixed cluture were 2-5 timeshigher than the pure ones) The mixed culture were moretolerant for the stress of temperature, pH value varition NH₄⁺concentration, herbicides and the alterations of C, N nutrtions.All the seventeen diazotroph pure cultures and some of theirmixed cultures have been inoculted to the rice seedling roots,The diazotroph colonzations were oberserved with the scaningelectron microscope. And the amount of the colonizeeddiazotrophs for the mixed culture were higher than theproduction pure ones. The rice grain for pot exp,eriment andmini plot experiment were enhanced by 25-29ï¼…and 21-37ï¼…compared with uninoculation respectively.