Abstract: Endophytic diazotrophic bacteria may contribute to the nitrogen nutrition and stress tolerance of host plants. In this paper, endophytic diazotrophtes were isolated from the leaf and root tissues of three typical xerophil gramineae grasses, Cynodon dactylon Agropyron desertorum (Fisch.) Schult., Elytrigria repens (L.) Nevski, and the characteristics of nitrogenase activity, phosphate-solubilizing power and auxin (IAA) producing were investigated to screen strains for developing plant growth-promoting inocula. Results indicated that fifty eight isolates had been obtained using N-free medium and acetylene reduction assays (ARA). Nitrogenase activities differed significantly from different strains, ranging from 464 to 2338 nmol C₂H₄·d^-1·mL^-1. Nitrogenase from the strains of A. desertorum had higher activity than that from C. dactylon and E. repens. Seventeen strains out of all isolated strains showed inorganic phosphate solubilizing capacity varying from 49.93 mg·L^-1 to 225.48 mg·L^-1 based on the measurement of phosphate-solubilizing circle and plasma atomic emission spectrometry. Twenty-four strains had an ability to produce auxin IAA with levels of 0.61~18.54 μg·mL^-1 detected. Thirty-two strains (55.2% of total tested strains), have beneficial effects on plant growth including nitrogen fixation, solubilizing phosphate and indole acetic acid production. XGEB4, XGEB26, XGEB30, XGEB64 and XGEB65 have greater potential as bio-fertilizer inocula.

Key words: Gramineae grass, Endophytic diazotrophic bacteria, Potential for plant growth-promoting, Nitrogenase activity

摘要： 以3种多年生典型旱生禾草新农一号狗牙根(Cynodon dactylon ‘Xinnong No.1’)、沙生冰草(Agropyron desertorum)、偃麦草(Elytrigria repens)为材料,从根、叶组织中分离内生固氮菌株,测定其固氮酶活性、溶磷性及分泌生长素的能力,为禾草多功能促生菌剂的菌种筛选奠定基础。结果表明:通过无氮培养基分离结合乙炔还原法,获得了58个内生固氮菌株,其固氮酶活性在464~2338 nmol C₂H₄·d^-1·mL^-1之间;分离自不同种类禾草的菌株固氮酶活性差异明显,沙生冰草分离菌株固氮酶活性普遍高于从偃麦草和狗牙根中分离的菌株。采用溶磷圈法结合等离子体原子发射光谱法,筛选出17个具有溶解无机磷的能力菌株,溶磷量为49.93~225.48 mg·L^-1。24个菌株具有分泌植物生长素IAA的特性,IAA产生量在0.61~18.54 μg·mL^-1。3种旱生禾草内生固氮菌中有32株兼具2种或3种促生性能,占测定菌株的55.2%,其中菌株XGEB4,XGEB26,XGEB30,XGEB64和XGEB65促生性能较强,具有开发应用的潜力。

关键词: 禾草, 内生固氮菌, 促生潜能, 固氮酶活性