Nitrogen fixation associated with maize plants (zea mays l.) in a temperate and a tropical soil

Abstract

In the temperate soil, low rates of acetylene reduction activity were detected in excised roots of field grown maize without preincubation. A higher acetylene reduction activity (20 nmol C2H4/ g d.wt./ 24 h) was recorded under an atmosphere containing 5% oxygen than when the roots were incubated under 0% and 20% oxygen. Most probable number (MPN) counts of N2- fixing bacteria associated with field grown maize in the temperate soil were estimated at 7.0 x 106 cells/ g d:wt. roots. The acetylene reduction activity rhizosphere soil was very low (1.7 - 5.8 nmol C2H4/ 10 g d.wt. soil/ 24h) but higner than that recorded in soil sampled between the-maize., plarlt rows (0.8 - 2.8 nmol C2H~/ 10 g d.wt. soil/ 24 h). Soil amendment with glucose stimulated the nitrogenase activity threer hundred fold or more over a 72 h period. The reduction of acetylene to ethylene by intact maize plants grown in the temperate soil was immediate without significant lag periods. Higher rates of nitrogenase activity were observed in intact maize plants incubated under aerobic than under anaerobic conditions.