Nitrogen fixation (acetylene reduction) associated with roots of winter wheat and sorghum in Nebraska

Abstract

Root segments and root-soil cores (6.5-cm diameter) from fields and nurseries of winter wheat and sorghum were tested for N2 fixation by using the acetylene reduction assay. Wheat samples (-1,200) from 109 sites generally had low or no activity (0 to 3.1 nmol of C2H4 produced per h per g [dry weight] of root segments), even after 24 h of incubation. However, a commercial field of Scout 66, located in western Nebraska, exhibited appreciable activity (290 nmol of C2H4 produced per h per g [dry weight] of root segments). Of 400 sorghum lines and crosses, grain sorghums (i.e., CK-60A, Wheatland A, B517, and NP-16) generally exhibited higher nitrogenase activity than forage sorghums or winter wheats. CK-60A, a male sterile grain sorghum, was sampled at four locations and had the most consistent activity of 24 to 1,100 nmol of C2H4 produced per h per core. The maximum rate extrapolated to 2.5 g of N per hectare per day. Numerous N2-fixing bacterial isolates were obtained from wheat and sorghum roots that exhibited high nitrogenase activity. Most isolates were members of the Enterobacteriacae, i.e., Klebsiella pneumoniae, Enterobacter cloacae, and Erwinia herbicola.

Nitrogen-Fixing (Acetylene Redution) Activity and Population of Aerobic Heterotrophic Nitrogen-Fixing Bacteria Associated with Wetland Rice

“…Comparison with ARA assayed by intact core methods and associated with corn (3,17), wheat and sorghum (16), Agrostis tenuis (13), and Digitaria (2) leads us to conclude that N2 fixation associated with wetland rice is higher than that associated with dryland plants. Tjepkema and Evans (18) pointed out that the wetland plant Juncus balticus also has a higher N2 fixation rate, and they suggested that high rates may be associated with wetland plants.…”

Nitrogen‐fixing Bacteria Associated with Graminaceous Roots with Special Reference to Spirillum lipoferum Beijerinck

“…Lower, presumably more realistic data were obtained with grass roots in undisturbed soil cores from tropical (Balandreau andDommergues 1973, Balandreau 1976) and temperate grasslands (Paul et al 1971, Vlassaket al 1973, Vaughn and Jones 1976, Tjepkema and Burris 1976, Kaputska and Rice 1976, Lockyer and Cowling 1977. Similarly significant, but still lower field activities were observed with soil cores containing roots of maize (Zea mays), winter wheat (Triticum aestivum) and Sorghum (Sorghum vulgare) varieties (Tjepkema and van Berkum 1977, Pedersen et al 1978). It is difficult to extrapolate even from numerous short-term acetylene reduction measurements with root systems in undisturbed soil cores to an annual fixation rate per hectare, because of their high seasonal and spatial variability.…”

Nitrogenase (C2H2) Activity in Roots of Non‐Cultivated and Cereal Plants: Influence of Nitrogen Fertilizer on Populations and Activity of Nitrogen‐Fixing Bacteria

“…The discrepancy between the nitrogenase activity and Azospirillum populations with wheat given organic or mineral N fertilizer (table 3 and 4) may also have been caused by larger differences in the proportions of these groups. With temperate cereal and grass roots, Nt-fixing Enterobacteriaceae were also found to be more numerous ( Pedersen et al 1978 andHaahrela et al, 1981 whereas in roots of tropical cereals and grasses Azospirillum spp. still seem to predominate (v. Eiilow andDobereiner 1975, Koch 1977).…”

“…( Dobereiner and De-Polli, 1980) in temperate climates Klebsiella and Enterobacter spp. have been isolated mainly from grasses ( Haahtela et al 1981) and cereals ( Pedersen et al 1978), but also Bacillus polymyxa was found to be associated with wheat roots ( Larson and Neal, 1978).…”