Nitrogen Fixation In Grasses

Immediate Acetylene Reduction by Excised Grass Roots Not Previously Preincubated at Low Oxygen Tensions

“…However, this suggestion is inconsistent with reports that Paspalum notatum roots extracted under N2 gas to prevent contact with 02 in the air also exhibited this long delay before detectable nitrogenase activity (11). All subsequent attempts to eliminate the period of zero acetylene-reducing activity by various treatments failed (1,9,18 Gas Analyses. Gas samples were analyzed with a Varian model 1520 Gas Chromatograph2 equipped with hydrogen flame ionization detectors and separated on a Teflon column (0.71 m x 3 mm) of 100 to 120 mesh Porapak N at 50 C with helium as carrier gas at 15 ml/min.…”

“…The feasibility evaluating nitrogen fixation in grasses in this manner was indicated when low rates of acetylene reduction were reported with excised corn roots within 2 h of collection (23,24). Since assays with excised roots are considered desirable because of ease of use, plant survival, and quantity of analyses possible (8), the objectives of this study were to establish the existence of grass roots, which when excised are able to reduce acetylene without an initial period of zero activity lasting 8 to 18 h.…”

“…Associations between nitrogen-fixing bacteria and the roots of grasses have been indicated (18) and soil cores of grasses were reported to reduce acetylene (11,27,28). Grasses were assumed to fix nitrogen since measurements for nitrogenase activity with component parts of grass-soil systems indicated that acetylene reduction is root-associated (1, 6, 9-12, 21, 29, 30).…”

“…Grasses were assumed to fix nitrogen since measurements for nitrogenase activity with component parts of grass-soil systems indicated that acetylene reduction is root-associated (1, 6, 9-12, 21, 29, 30). Yet, all grass roots, unlike soil cores of plants, failed to reduce acetylene for 8 to 18 h (1,11,18,28), and measurements of acetylene reduction with soil cores of grasses and excised roots from the same cores after the initial inactive period did not correlate (27,28). Neyra and Dobereiner (18) recognized the initial period of zero activity by excised grass roots as a major limitation to the extrapolation of data to quantifying nitrogen fixation in the field.…”

Ocorrência e diversidade de bactérias diazotróficas associadas a gramíneas forrageiras do Pantanal Sul Matogrossense

“…associadas às três espécies de gramíneas forrageiras estudadas (Quadro 1). A presença de bactérias diazotróficas do gênero Azospirillum em braquiária já tinha sido demonstrada por Neyra & Döbereiner, (1977), Souto (1982) e Magalhães et al (1983).…”