A bradyrhizobial-fungal biofilm (i.e. Bradyrhizobium elkanii SEMIA 5019-Penicillium spp.) developed in vitro was assayed for its nitrogenase activity and was evaluated for N2-fixing symbiosis with soybean under greenhouse conditions. The biofilm showed nitrogenase activity, but the bradyrhizobial strain alone did not. Shoot and root growth, nodulation and N accumulation of soybean increased significantly with an inoculum developed from the biofilm. This study concludes that such biofilmed inoculants can improve N2-fixing symbiosis in legumes, and can also directly contribute to soil N fertility in the long term. Further studies should be conducted to investigate the performance of these inoculants under field conditions. 相似文献
Summary Wheat seedlings were inoculated with rhizosphere nitrogen-fixing bacteria and grown gnotobiotically for 15 days. The growth medium consisted of semisolid agar with or without plant nutrients. The bacteria, isolated from roots of field-grown wheat, were three unidentified Gram-negative rods (A1, A2, E1), one Enterobacter agglomerans (C1) and two Bacillus polymyxa (B1, B2). A strain of Azospirillum brasilense (USA 10) was included for comparison.Nitrogenase activity (acetylene reduction activity, ARA) was tested on intact plants after 8 and 15 days of growth. In semisolid agar without plant nutrients, five isolates showed ARA of 0.01–0.9 nmol C2H4 plant–1 h–1, while the two strains of B. polymyxa had higher ARA of 3.3–10.6 nmol C2H4 plant–1 h–1.Plant development was not affected by inoculation with bacteria, except that inoculation with B. polymyxa resulted in shorter shoots and lower root weight.Transmission electronmicroscopy of roots revealed different degrees of infection. A. brasilense, A1 and A2, occurred mainly in the mucilage on the root surface and between outer epidermal cells (low infectivity). B. polymyxa strains and E1 were found in and between epidermal cells (intermediate infectivity) while E. agglomerans invaded the cortex and was occasionally found within the stele (high infectivity). 相似文献
The placement effects of organic sources (cellulose and rice straw) at different depths on nitrogenase activity (acetylene
reduction assay, ARA) associated with four tropical rice soils were investigated. Results showed that placement of organic
sources in the top profile (1–2 cm) produced a higher nitrogenase activity; while placement in the 2–4 cm and 4–6cm profiles
significantly decreased the activity irrespective of soil type. The effect of organic sources on nitrogenase varied depending
on the soil type. Cellulose and rice straw caused differential stimulation in response to the placement. Evidence was provided
for the creation of favourable redox potential supporting higher nitrogenase activity in series receiving organic amendments
in the top profile. Higher nitrogenase activity in the top profile was associated with greater populations of nitrogen-fixing
Azospirillum sp., anaerobic nitrogen fixers and Azotobacter sp. Moreover, the lower amounts of reducing sugars and higher carbon dioxide evolution gave evidence of higher microbial
activity in the top profile. These results clearly indicate the positive relationship between nitrogenase activity, nitrogen-fixing
populations and redox status in the top layers of flooded tropical rice soils.
Received: 5 June 1996 相似文献
Summary Following co-cultivation of wheat with N2-fixing cyanobacterial isolates capable of forming associations, Nostoc 2S6B, 2S9B or Anabaena C5, for 15 days in the presence or absence of combined N a large stimulation of root length was observed without any increase in root dry weight. Increases in the N concentrations of both roots and shoots occurred following co-cultivation with most cyanobacteria tested. The increase in plant N concentrations appeared to be dependent on the wheat cultivar and the cyanobacterial isolate used. Nostoc isolates had similar nitrogenase activities when associated with roots and when grown in shake-flask cultures. The nitrogenase activity of roots colonized by Anabaena C5 or Nostoc 2S6B was higher following removal of loosely associated cyanobacteria. 相似文献
The perennial legume, Winged Bean (Psophocarpus tetragonolobus (L) DC), has potential as a high protein food crop for the humid, tropical regions of the world. Edible seed pods, oil seed grain, leaves, flowers, and unique high protein tubers provide abundant nutritious components desirable for improved human diets. However, soil characteristics and fertility levels influence plant growth, yields and nitrogen fixation capability of this legume. Objectives of this study were to determine soil‐plant nutrient influences on vigorous regrowth, pod and tuber yields, nitrogenase (C2H2 red.) activity levels, and nodule cytosol components of the perennial Siempre cultivar grown on a Typic Eutrustox during three years, 1978–1980.
Available soil phosphorus was a first limiting plant nutrient during all three years of plant age. Effects of combined 100 mg P with 200 mg K/kg soil were highly significant for every parameter and plant age. Pod and seed yields more than doubled with PK addition compared to the check. Tuber growth, nodule mass and nitrogenase activity levels more than trebled with PK treatments as compared to the check. Both elemental P and K were significantly increased within the nodule cytosol of fertilized plants. Cytosol Na was significantly decreased with soil K additions. The best fit multiple regression was: nitrogenase = 1.99 nodule wt. + 6.34 tuber wt. + 0.39 tuber % N + 5.08 cytosol P + 1.55 cytosol K ‐ 0.45 cytosol Na, R2 = 95.5, C.V. = 11.2%. The dominant nodule cytosol enzymes, aspartate aminotransferase (AST) and glutamine synthetase (GS), significantly increased with soil K additions regardless of P treatments. Glutamate dehydrogenase (GDH) and glutamate synthase (GOGAT) also contributed significantly with multiple regression for nitrogenase = 1.07 GS + 2.1 AST + 1.74 GOGAT ‐ 1.76 GDH + 12.89 Ureide, R2 = .89, C.V. = 17.3%. Highly significant increases in nodule cytosol ureide composition with K soil additions has interest because of the role as a nitrogenous nonprotein component for many legumes. Increases in growth, nodulation and nitrogenase activity levels resulted with increased K levels of 0, 100, 200 and 300 mg K/kg soil when soil P and Ca were not limiting. 相似文献